JPH09160400A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a cause of deterioration of various kinds of images caused by static electricity in using a contact transfer member for transferring the toner image on a transfer material. SOLUTION: A transferring voltage variable output circuit 211 is, composed so as to apply specified voltage in between a photoreceptor drum and a transfer roller 45 being held in contact with each other, and to make the electric current detecting circuit 211 possible to detect the current made to flow at this time. This detection result is made reference to data stored in a ROM 103 and environments where a printer 241 is located is decided. The transferring voltage variable output circuit 211 and the discharging voltage variable output circuit 112 is respectively allowed to control applying voltage to a desired value, with respect to the transfer roller 45 or a charge removing rod 78A corresponding to temp. and humidity of a first surface or the second surface of the paper sheet, or the device, to eliminate the static discharge in separating the paper sheet, and to prevent the deterioration of the image quality caused by the electric discharge between the potential on the paper sheet and the photoreceptor drum, re-transfer of the toner image on the paper sheet by transferring of the toner image to a thermal fixing device 83 or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer, a copying machine,
The present invention relates to an image forming apparatus that forms an image on an image carrier using an electrophotographic process, such as a facsimile machine. Specifically, the toner image formed on the image carrier is transferred using a contact type transfer unit. The present invention relates to an image forming apparatus that improves the quality of an image by a device that transfers the material.

[0002]

2. Description of the Related Art An image forming apparatus for forming a toner image corresponding to an image on an image bearing member such as a photosensitive drum by using an electrophotographic process and transferring the toner image onto a transfer material such as plain paper is a printer or a copying machine. It is widely applied to machines such as machines and facsimile machines. In such an image forming apparatus, the toner image held on the image carrier is electrostatically attracted to the transfer material and transferred. For this reason, conventionally, a corona discharger called a transfer corotron is arranged at a predetermined distance from the surface of an image carrier, for example, a photosensitive drum. Then, in this example, a sheet as a transfer material is conveyed between the photoconductor drum and the transfer corotron at the same speed as the peripheral speed of the photoconductor drum, and the toner images are sequentially transferred thereto.

In such an image forming apparatus, a paper sheet or a gripper that holds the paper sheet may pass between the transfer corotron and the photosensitive drum. Therefore, the transfer corotron needs to be arranged at a certain distance from the surface of the photoconductor. Therefore, the voltage for causing the discharge wire constituting the transfer corotron to discharge to the surface of the photoconductor becomes relatively high, and a special high voltage generating circuit is required. Further, since the toner image is transferred by utilizing the discharge phenomenon, there is a problem that ozone is generated, and particularly when negative discharge is performed, the amount of ozone generated is large. Therefore, in the conventional image forming apparatus, a special filter is used for the exhaust fan or the like in order to remove the generated ozone, and not only it becomes difficult to reduce the cost of the apparatus by that amount, but also the filter is used. Maintenance was also required. Furthermore, when a transfer corotron is used, if the discharge wire is contaminated with a substance such as toner, the discharge characteristics deteriorate, so periodic cleaning is necessary, and the wire is cut at this time. There was also a problem that it took time to replace it. Many of these problems also occur in other corona chargers or corona chargers such as a charge corotron that charges the surface of the photosensitive drum.

Therefore, recently, an image bearing member such as a photosensitive drum (hereinafter simply referred to as a photosensitive drum or a photosensitive member).
The contact type charger or the discharger has come to be used.

FIG. 26 shows an essential part of an image forming apparatus using such a contact type charger or discharger. The charging roller 1 is provided around the photosensitive drum 11.
2, the developing device 13, the transfer roller 14, and the cleaning device 15 are arranged in this order. A laser beam 17 output from a laser (not shown) and deflected by a polygon mirror (not shown) is applied to the drum surface charged by the charging roller 12 to form an electrostatic latent image corresponding to an image. It is like this. This electrostatic latent image is developed by the toner supplied from the developing roller 18 of the developing device 13 to form a toner image. A transfer roller 14 is in rolling contact with the photosensitive drum 11 on the downstream side of the developing device 13. The sheet 22 conveyed through the conveying path 21 from a supply tray (not shown) passes between the photosensitive drum 11 and the transfer roller 14, and at this time, the toner image is transferred onto the sheet 22. Then, after being fixed by a fixing device (not shown), it is reflected on a discharge tray (not shown).

The toner particles remaining on the drum surface after the transfer by the transfer roller 14 are removed by the cleaning device 15. In the example shown in FIG. 26, the cleaning blade 24 is in contact with the drum surface, and the toner particles are removed by scraping. After that, the surface of the photosensitive drum 11 is uniformly charged again by the charging roller 12, and the photosensitive drum 11 is ready for the next image forming process. A static eliminator 26 having a static elimination needle 25 is arranged on the downstream side adjacent to the transfer roller 14 in order to eliminate static electricity on the charged paper 22 when the toner image is transferred.

FIG. 27 shows how an image is formed by the reversal development method which is often adopted in the image forming apparatus shown in FIG. As shown in FIG. 6A, the surface of the photosensitive drum 11 (FIG. 26) is negatively charged by the charging roller 12. Next, as shown in FIG. 3B, the laser beam 17 irradiates the "black" portion of the image with light. Then, the resistance of the irradiated portion of the drum surface is lowered, the electric charge is discharged, and the potential of this portion approaches 0 V (volt). Here, the developing device 13 (see FIG.
A voltage is applied to 6) to cause the negatively charged toner 31 to be adsorbed to the portion irradiated with light as shown in FIG. Next, as shown in FIG. 3D, when a positive (+) voltage is applied from the back surface of the paper 22 by the transfer roller 14, the negatively charged toner 31 is attracted to the paper 22 side. In this way, the toner image is transferred to the paper 22.

[0008]

Generally, in an image forming apparatus, various sizes of paper are used as the paper 22 as a transfer material. On the other hand, the transfer roller 14
Sets the length on the assumption that the paper has the maximum width. Therefore, when the toner image is transferred onto a sheet having a width shorter than this, there is an area where the transfer roller 14 directly contacts the surface of the photosensitive drum 11 without the sheet 22. . This area will be referred to as a transfer material outside area in the following description.

Taking the image forming apparatus by reversal development described with reference to FIG. 27 as an example, since the photosensitive drum 11 is generally negatively charged, negative toner is used as the toner and the transfer roller is used. A positive voltage having a reverse polarity to this is applied to 14. Since the transfer roller 14 is in direct contact with the area outside the transfer material, the potential of this portion fluctuates to the positive side, and in an extreme case, it is charged to the positive polarity opposite to the negative potential to be originally charged. Will end up.

In an image forming apparatus using a conventional corona charger, discharge is performed in a wide range from a position spaced a predetermined distance from the surface of the photoconductor, so that it is sufficient as compared with the case of using a non-contact type charger. It has a charging ability. Therefore, even if the charging potential changes in this way, it is possible to sufficiently restore the original charging potential in the next charging process. However, in the contact charging device represented by the charging roller 12 shown in FIG. 26, the area to be charged is only a thin strip-shaped area in contact with the roller, and this area is the photosensitive drum 11
The time for the surface to pass is extremely short. For this reason, there is not enough margin in the charging ability, and the toner is adsorbed by the developing device 13 to the area where the original charging potential has not been recovered, and the image is visualized. In this specification, a phenomenon in which a history remains in the transfer process of the image forming process before the image forming process of the image bearing member such as the photosensitive drum 11 is called a transfer memory in this specification.

In an image forming apparatus for printing or recording on both sides of a sheet (hereinafter simply referred to as "printing"), a toner image is once transferred onto the sheet and then heat fixing is performed by a fixing device, and then the remaining surface (second side). ) Is often printed. In such a case, the paper 22 is dried when the transfer of the second surface is performed, and the resistance thereof is significantly increased. At the time of transferring the toner image, the voltage applied to the transfer roller 14 is set slightly higher in the case of the second surface in consideration of such a change in characteristics. Therefore, a transfer memory is more likely to occur when transferring the second surface, and it becomes difficult to obtain a high-quality image.

Further, in an environment of low temperature and low humidity (hereinafter referred to as L / L
The environment. When printing with () or transferring the second surface, the paper 22 has a high resistance and is very easily charged. In such a situation, if the static eliminator 26 does not sufficiently neutralize the paper 22 after the transfer of the toner image, the electric charge on the paper 22 causes abnormal discharge when approaching the paper transport unit. Will be awakened. This abnormal discharge disturbs the toner image before fixing and causes deterioration of image quality.

On the other hand, if the charging ability of the contact charging device represented by the charging roller 12 is insufficient, the paper 2
By separating 2 from the photoconductor drum 11, stains and uneven density occur after one round of the photoconductor drum 11. This will be referred to as a peeling memory in this specification. A charge having a polarity opposite to the transfer potential remains on the photoconductor drum 11 due to the peeling discharge when the paper 22 is peeled from the photoconductor drum 11 serving as an image carrier, and this charge is originally charged by the contact charging device. If the potential cannot be restored to the potential, a history of the transfer step of the previous image forming process remains in the next image forming process as in the transfer memory described above. That is, the inconvenience that the previous history is developed after the photosensitive drum 11 makes one revolution is generated.

In the static eliminator 26 shown in FIG. 26, by increasing the static eliminator voltage, the disadvantages such as the charging due to the reverse polarity of the photosensitive drum 11 by the contact transfer member and the high charging of the paper 22 as described above are caused. It acts in the direction of eliminating it. However, when the charge removing voltage of the charge removing device 26 is increased, the paper 22 is transferred onto the developer (toner).
Will significantly weaken the binding force with. Therefore, if the fixing means such as a heat roll for fixing the toner image after the transfer is charged to the opposite polarity to the toner for some reason, these toners adhere to the fixing means at the time of fixing. If these toners adhere to other parts of the paper 22 again, the image will be disturbed. Such an offset to the fixing unit will be referred to as a fixing offset in this specification.

Further, in an environment of high temperature and high humidity (hereinafter referred to as H / H
The environment. In (), the resistance of the paper 22 is extremely low. Therefore, the static eliminator 2 is used when static electricity is removed from the paper 22 as the transfer material and the photosensitive drum 11 as the image carrier.
When a neutralization voltage having a polarity opposite to that of the transfer voltage is applied to 6, the phenomenon occurs that the neutralization voltage flows into the neutralization device 26 through the paper 22. As a result, there is a problem in that the current required for the transfer roller 14 to perform the original transfer cannot be obtained, and the toner image transferred to the sheet is missing.

In the above description, the reversal development of the image forming apparatus has been described, but the same inconvenience also exists in the image forming apparatuses of other developing systems.

Therefore, an object of the present invention is to provide an image forming apparatus capable of performing stable printing regardless of environmental conditions even if a contact transfer member is used.

Another object of the present invention is to provide an image forming apparatus capable of stably transferring a toner image onto various transfer materials by using a contact transfer member.

Still another object of the present invention is, when a toner image is transferred onto a transfer material by using the contact transfer member, the size of the transfer material is small and the area where the contact transfer member directly contacts the image carrier. With respect to the above, it is to provide an image forming apparatus that does not adversely affect the image.

[0020]

According to a first aspect of the invention, (a) an image bearing member carrying an electrostatic latent image, and (b) forming a toner image corresponding to the latent image on the image bearing member. And (c) contact transfer means for electrostatically transferring the toner image formed by the toner image forming means to the transfer material by making contact with the image carrier through the transfer material. A static eliminator arranged adjacent to the contact transfer means for static erasing the transfer material on which the toner image has been transferred; and (e) a static erasing applied voltage generating means capable of changing the voltage applied to the static erasing means,
(F) The image forming apparatus is provided with a static elimination applied voltage adjusting unit that adjusts the voltage output from the static elimination applied voltage generating unit according to various predetermined conditions.

That is, according to the first aspect of the invention, the voltage applied to the discharging means for discharging the transfer material on which the toner image has been transferred is adjusted in accordance with various conditions such as the transfer material such as paper and the apparatus. I have decided. Then, the electrostatic coupling between the transfer material and the toner and the relationship between the transfer material and the image carrier such as the photosensitive drum are adjusted so that good printing can be performed even when the contact transfer member is used. .

According to the second aspect of the invention, (a) an image bearing member carrying an electrostatic latent image, and (b) a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member. ,
(C) Contact transfer means for contacting the image carrier with the transfer material via the transfer material to electrostatically transfer the toner image formed by the toner image forming means to the transfer material; and (d) Adjacent to the contact transfer means. A static eliminator for removing static electricity from the transfer material onto which the toner image has been transferred; and (e) a transfer material relative moving means for moving the transfer material relative to the contact transfer means in accordance with the transfer of the toner image,
(F) fixing means for fixing the transfer material onto which the toner image has been transferred, and (g) when the toner image is transferred onto both sides of the transfer material,
Transfer fixing control means for double-sided printing, in which the toner image is transferred to the first print surface and fixed by the fixing means, and then the toner image is transferred to the second print surface and fixed again on the transfer material. And (h) the image forming apparatus is provided with a static elimination applied voltage switching means for switching the level of the voltage applied to the static elimination means according to the relative position of the contact transfer means of the transfer material and the printing surface of the transfer material. .

That is, according to the second aspect of the invention, paying attention to the change in the characteristics after the transfer material is fixed by heat, pressure, etc., when performing double-sided printing, the voltage applied to the charge eliminating means by the printing surface of the transfer material. Decided to change the level of.
Further, for example, in order to solve the problem caused by the discharge when the transfer material is peeled from the image carrier, the level of the voltage applied to the charge eliminating means depending on the relative position of the transfer material in the contact transfer means. Decided to change. Depending on the device, it is not necessary to change the applied voltage in a relative positional relationship between both printing surfaces, and the applied voltage may be changed in a relative positional relationship only on one specific printing surface.

According to a third aspect of the present invention, (a) an image bearing member carrying an electrostatic latent image, and (b) a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member. ,
(C) Contact transfer means for contacting the image carrier with the transfer material via the transfer material to electrostatically transfer the toner image formed by the toner image forming means to the transfer material; and (d) Adjacent to the contact transfer means. A static eliminator for removing static electricity from the transfer material on which the toner image has been transferred;
(F) Environment discrimination means for discriminating the environment inside the device, and (g)
The image forming apparatus is provided with a static elimination applied voltage switching unit that switches the level of the voltage applied to the static elimination unit according to the relative position of the transfer material in the contact transfer unit and the environment determined by the environment determination unit.

That is, in the third aspect of the present invention, attention is paid to the relationship between static electricity and changes in the environment in which an image forming apparatus such as a printer, a facsimile machine, and a copying machine is placed, and the humidity, temperature, etc. determined by the environment determining means. It was decided to change the level of the voltage applied to the static elimination means according to the environment. Further, for example, in order to solve the problem caused by the discharge when the transfer material is peeled from the image carrier, the level of the voltage applied to the charge eliminating means depending on the relative position of the transfer material in the contact transfer means. Decided to change.

According to a fourth aspect of the present invention, (a) an image bearing member carrying an electrostatic latent image, and (b) a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member. ,
(C) Contact transfer means for contacting the image carrier with the transfer material via the transfer material to electrostatically transfer the toner image formed by the toner image forming means to the transfer material; and (d) Adjacent to the contact transfer means. A static eliminator for removing static electricity from the transfer material onto which the toner image has been transferred; and (e) a transfer material relative moving means for moving the transfer material relative to the contact transfer means in accordance with the transfer of the toner image,
(F) transfer material characteristic determining means for determining the characteristics of the transfer material,
(G) The image forming apparatus is provided with a static elimination applied voltage switching unit that switches the level of the voltage applied to the static elimination unit according to the relative position of the transfer material in the contact transfer unit and the characteristic determined by the transfer material characteristic determination unit. Prepare.

That is, in the invention according to claim 4, paying attention to the relationship between the characteristics such as water content and resistance of the transfer material such as paper and static electricity, the transfer material characteristic determining means for determining the characteristic of the transfer material is prepared, The level of the voltage applied to the static elimination means is changed according to the characteristics determined by this.
Further, for example, in order to solve the problem caused by the discharge when the transfer material is peeled from the image carrier, the level of the voltage applied to the charge eliminating means depending on the relative position of the transfer material in the contact transfer means. Decided to change.

According to a fifth aspect of the invention, (a) an image bearing member carrying an electrostatic latent image, and (b) a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member. ,
(C) Contact transfer means for contacting the image carrier with the transfer material via the transfer material to electrostatically transfer the toner image formed by the toner image forming means to the transfer material; and (d) Adjacent to the contact transfer means. A static eliminator for removing static electricity from the transfer material onto which the toner image has been transferred; and (e) a transfer material relative moving means for moving the transfer material relative to the contact transfer means in accordance with the transfer of the toner image,
(F) A predetermined voltage is applied to the charge removing means from the time when the leading edge of the transfer material comes into contact with the contact transfer means, and the absolute value of the voltage is increased from the predetermined time when the rear edge of the transfer material faces the charge removing means. The image forming apparatus is provided with an applied voltage switching unit that changes the voltage and stops the application of the voltage after a lapse of a predetermined time after the trailing edge of the transfer material passes through the charge removing unit.

That is, in the fifth aspect of the invention, the absolute value of the voltage applied to the charge eliminating means is made higher at the time of peeling to enhance the effect of the charge eliminating. As a result, discharge is less likely to occur when the electrostatically adsorbed transfer material is peeled off from the image carrier, and the deterioration of the image due to this discharge can be prevented.

According to a sixth aspect of the invention, (a) an image bearing member carrying an electrostatic latent image, and (b) a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member. ,
(C) Contact transfer means for contacting the image carrier with the transfer material via the transfer material to electrostatically transfer the toner image formed by the toner image forming means to the transfer material; and (d) Adjacent to the contact transfer means. A static eliminator for removing static electricity from the transfer material onto which the toner image has been transferred; and (e) a transfer material relative moving means for moving the transfer material relative to the contact transfer means in accordance with the transfer of the toner image,
(F) Current detection means for detecting the current flowing between the contact transfer means and the image carrier without passing through the transfer material, and (g) Environment determination for determining the environment inside the apparatus from the detection result of this current detection means. And (h) applied voltage switching means for switching the level of the applied voltage applied to the static elimination means according to the relative position of the transfer material in the contact transfer means and the environment in the apparatus determined by the environment determination means. It is equipped in the forming device.

That is, in the sixth aspect of the invention, instead of individually detecting the environment such as the temperature and humidity in the apparatus by individual sensors, a voltage is applied between the contact transfer means and the image carrier. The current flowing between them is detected to determine the environment of the device. Then, the level of the applied voltage applied to the charge eliminating means is switched according to the determined environment of the apparatus according to the relative position of the transfer material in the contact transfer means and the environment in the apparatus determined by the environment determination means to obtain a good image. I am trying to reproduce.

According to a seventh aspect of the present invention, (a) an image bearing member carrying an electrostatic latent image, and (b) a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member. ,
(C) Contact transfer means for contacting the image carrier with the transfer material via the transfer material to electrostatically transfer the toner image formed by the toner image forming means to the transfer material; and (d) Adjacent to the contact transfer means. A static eliminator for removing static electricity from the transfer material onto which the toner image has been transferred; and (e) a transfer material relative moving means for moving the transfer material relative to the contact transfer means in accordance with the transfer of the toner image,
(F) a current detecting means for detecting a current flowing between the contact transfer means and the image carrier both in the state without the transfer material and in the state with the transfer material, and (g) from inside the apparatus based on the detection result of the current detecting means. Environment discrimination means for discriminating the environment of the transfer material,
(H) An image of the applied voltage switching means for switching the level of the applied voltage applied to the charge eliminating means in accordance with the relative position of the transfer material in the contact transfer means and the inside of the apparatus judged by the environment judging means and the environment of the transfer material. It is equipped in the forming device.

That is, in the invention described in claim 7, instead of detecting the environment such as the temperature and humidity in the apparatus and the environment such as the water content of the transfer material by the individual sensors, respectively, the contact transfer means and the image carrier may be provided between them. Both the state in which the transfer material is interposed and the state in which the transfer material is not interposed are realized, and the current flowing between them is detected in these states to determine the environment of the apparatus and the transfer material. Then, the level of the applied voltage applied to the charge eliminating unit is switched according to the determined environment, according to the relative position of the transfer material on the contact transfer unit and the environment in the apparatus determined by the environment determining unit, and the image quality is improved. I am trying to reproduce.

In the invention described in claim 8, (a) an image bearing member carrying an electrostatic latent image, and (b) a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member. ,
(C) Contact transfer means for contacting the image carrier with the transfer material via the transfer material to electrostatically transfer the toner image formed by the toner image forming means to the transfer material; and (d) Adjacent to the contact transfer means. A static eliminator for removing static electricity from the transfer material onto which the toner image has been transferred; and (e) a transfer material relative moving means for moving the transfer material relative to the contact transfer means in accordance with the transfer of the toner image,
(F) Environment discriminating means for discriminating the environment inside the device as either high temperature / high humidity, low temperature / low humidity or other
(G) a fixing unit that fixes the transfer material on which the toner image has been transferred; and (H) when the toner image is transferred to both sides of the transfer material,
Transfer fixing control means for double-sided printing, in which the toner image is transferred to the first print surface and fixed by the fixing means, and then the toner image is transferred to the second print surface and fixed again on the transfer material. And (i) an applied voltage switching means for switching the level of the applied voltage applied to the charge removing means in accordance with the relative position of the transfer material on the contact transfer means, the printing surface of the transfer material, and the environment determined by the environment determination means. And the image forming apparatus.

That is, according to the invention of claim 8, the environment in which the image forming apparatus is placed is classified into three of high temperature / high humidity, low temperature / low humidity, or any other in accordance with the relationship between temperature and humidity, and the transfer is performed. The surface for transferring the toner image to the material is divided into two areas, that is, the first surface for the first transfer and the second surface for the second transfer, and is applied to the static eliminator so as to cope with the combination thereof. The level of the applied voltage to be applied is set to a desired value to achieve good reproduction of the image.

According to a ninth aspect of the present invention, (a) an image bearing member carrying an electrostatic latent image, and (b) a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member. ,
(C) Contact transfer means for contacting the image carrier with the transfer material via the transfer material to electrostatically transfer the toner image formed by the toner image forming means to the transfer material; and (d) Adjacent to the contact transfer means. A static eliminator for removing static electricity from the transfer material on which the toner image has been transferred, (e) a transfer applied voltage generator for changing the voltage applied to the contact transfer device, and (f) a change in voltage applied to the static eliminator. And a static elimination applied voltage adjusting means for adjusting the voltage output from the transfer applied voltage generating means and the static elimination applied voltage generating means in accordance with various preset conditions. Are provided in the image forming apparatus.

That is, in the invention described in claim 9, the voltage applied to both the charge eliminating means for eliminating the charge of the transfer material on which the toner image is transferred and the contact transfer means for electrostatically transferring the toner image to the transfer material, It will be adjusted according to various conditions such as paper as a transfer material and the device. Then, the electrostatic coupling between the transfer material and the toner and the relationship between the transfer material and the image carrier such as the photosensitive drum are adjusted so that good printing can be performed even when the contact transfer member is used. .

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

First embodiment

FIG. 1 shows an outline of a printer as an image forming apparatus in one embodiment of the present invention. The printer 41 includes a photoconductor drum 42 as an image carrier for forming an electrostatic latent image. Around the photosensitive drum 42, a charging roller 43 for uniformly charging the surface of the drum, a developing roller 44 for developing an electrostatic latent image, and a toner image formed on the drum surface by the development are provided. Transfer rollers 45 for transferring to a sheet not shown in the figure are in rolling contact with each other. These units except the transfer roller 45 and the toner box 46 containing the toner to be supplied to the developing roller 44 constitute a replaceable cartridge 48 as a whole.

A laser beam 51 modulated by an image signal is emitted from a laser scanning device 49 to a predetermined position on the drum surface between the charging roller 43 and the developing roller 44 of the photosensitive drum 42. The laser scanning device 49 is
In FIG. 1, the semiconductor laser is arranged at a position hidden by the polygon mirror 53. The laser beam 51 modulated according to the image signal emitted from the semiconductor laser enters the mirror surface of the polygon mirror 53, is reflected in the direction according to the rotation angle, passes through the lens 54, and passes through the first reflecting mirror. 5
5 reflected. Then, the second reflection mirror 56
The light is reflected by and is incident on a predetermined position of the photosensitive drum 42. As a result, the surface of the photosensitive drum 42 is repeatedly scanned in the drum axis direction, that is, the main scanning direction, and an electrostatic latent image is formed.

This image forming apparatus is equipped with a supply tray 61 capable of feeding various sizes of paper. The sheet (not shown) stacked on the supply tray 61 is one sheet by the half-moon roller 62 at a predetermined timing synchronized with the movement of the photosensitive drum 42 having a diameter of 30 mm and a peripheral speed of 70 mm / sec in this embodiment. Each of them is sent out at a predetermined interval, and passes between the photosensitive drum 42 and the transfer roller 45 having a diameter of 16 mm through the feed rollers 64 and 65 and the registration roller 66 for controlling the positioning of the leading edge of the paper in order. Only during this passage, a positive DC voltage is applied to the transfer roller 45 to transfer the toner image. In addition, in order to send out the paper from the supply tray 61, various known methods can be adopted instead of the half-moon roller 62. For example, a retard roller can be used.

FIG. 2 specifically shows the periphery of the photosensitive drum. The printer of this embodiment forms an image by the reversal development method. Since the photoconductor drum 42 of this embodiment uses an organic photoconductor, the charging roller 43 gives a negative (−) charge to the photoconductor drum 42. The photoconductor drum 42 rotates clockwise as indicated by an arrow 71, and discharges the electric charge at the position irradiated with the laser beam 51. The negatively charged toner magnetically stands on the surface of the developing roller 44. An AC voltage and a negative DC voltage are applied to the developing roller 44, the toner moves to the surface of the photosensitive drum 42 where the laser beam 51 is irradiated, and the toner moves to the surface of the drum to form a toner image corresponding to the electrostatic latent image. Is created.

On the other hand, the paper (plain paper) 73 is conveyed from the feed roller 66 shown in FIG. 1 in the direction of arrow 74 at the same speed as the peripheral speed of the photosensitive drum 42, and the photosensitive drum 42 and the transfer roller are transferred. Pass between 45. The transfer roller 45 is pressed against the photosensitive drum 42 by a compression spring 76 at a predetermined pressure. A predetermined positive voltage is applied to the transfer roller 45, so that the toner image is transferred onto the paper 73.

A static eliminator 78 is arranged at a predetermined interval below the conveyance path of the sheet 73 on the exit side of the transfer roller 45. The static eliminator 78 is composed of a static eliminator needle 78A made of metal and a static eliminator main body 78B which is bound from both sides of the metal, and is designed to neutralize the paper 73 from behind. The photosensitive drum 42 is not transferred to the paper 73.
The toner remaining on the surface of the is removed by the cleaning blade 79 arranged on the front side of the charging roller 43.

FIG. 3 is a side view of the photosensitive drum and the static eliminator. The static eliminator 78 is equipped with a flat plate-shaped static eliminator needle 78A having the same axial length as the cylindrical photosensitive drum 42. This static eliminator main body 78B is indicated by a chain line.
Is located within. The tip of the static elimination needle 78A is arranged in parallel with the surface of the photoconductor drum 42 at a constant interval, and these tip portions are processed into a sawtooth shape. In this embodiment, there are many teeth having a height of 2 mm and a pitch of 2 mm, and the distance between these teeth and the drum surface of the photosensitive drum 42 is about 5 mm. Static elimination needle 78
A is connected to a high-voltage cable (not shown), and discharge for discharging electricity is performed on the sheet 73 (FIG. 2) from the tooth-shaped tip portion of the saw.

Returning to FIG. 1, the description will be continued. The sheet that has passed through the photosensitive drum 42 and the transfer roller 45 is conveyed along a conveying path 81 indicated by a broken line, and then passes through a heat fixing device 83 including a heat roller and a pressure roller. The heat roller and the pressure roller are in contact with each other in a strip shape with a predetermined width (nip), and the heat applied to the surface of the paper on which the toner image is transferred from the side of the heat roller, which is held at a predetermined high temperature, causes the toner image to form. Fixing takes place. At this time, the pressure roller presses the paper against the pressure roller side to enable efficient heat transfer, and at the same time, the heat transferred from the heat roller side is also applied to the paper from the back side thereof to ensure heat fixing. The paper that has been fixed is fed by the feed roller 84,
The sheet is sequentially conveyed by the 85 and the discharge roller 86, and is discharged onto the discharge tray 88 provided on the upper part of the apparatus main body.
This is a single-sided printing operation in which printing is performed on only one side of the paper.

In double-sided printing in which both sides of the paper 73 (FIG. 2) are printed, the conveyance path is partially different between the printing on the first side and the printing on the second side. When printing on the first side, the leading edge of the paper passes the feed roller 85 and the trailing edge of
At the time of passing the feed roller 84 on the front side, the switching lever 91 rotates from the position indicated by the chain double-dashed line to the position indicated by the solid line.
Then, the rotation of the feed roller 85 is reversed. As a result, the trailing edge, that is, the lower edge, of the paper on which the printing on the first side is completed becomes the leading edge this time and starts moving downward. And
The feed rollers 93 to 95 arranged at a slight distance above the supply tray 61 are sequentially passed, and the conveyance of the sheet for printing the second surface is restarted.

The paper that has passed above the supply tray 61 is
The feed rollers 64 and 65 and the registration roller 6 again
6 in order, and this time with the second surface facing upward, it passes between the photosensitive drum 42 and the transfer roller 45. At this time
The surface is printed. Then, after the toner image is fixed by the thermal fixing device 83, the feed rollers 84, 8 with the switching lever 91 rotated to the position shown by the chain double-dashed line this time.
5 and the discharge roller 86 in order, and a discharge tray 88.
Will be discharged above.

In this image forming apparatus, in addition to single-sided printing or double-sided printing using the supply tray 61 described above, it is also possible to perform printing on manual paper or postcards. Since these are not directly related to the present invention, description thereof will be omitted. Further, in this printer 41, various controls for printing an image are performed by an electronic circuit housed in the control casing 97.

FIG. 4 shows the main part of the circuit configuration of the printer of this embodiment. The printer 41 has a CPU (Central Processing Unit) 101 for performing various controls. The CPU 101 is connected to each unit in the device through a bus 102 such as a data bus. ROM
Reference numeral 103 is a read-only memory that stores a program for controlling each unit of the printer 41.
The RAM 104 is a random access memory for temporarily storing various data. Operation panel 105
Has a switch for turning the power on / off and other operations, and also has a display lamp and a liquid crystal display for displaying necessary information. The communication control circuit 106 is a communication cable 107.
It communicates with an external image processing device such as a host computer via the printer to receive print data and send / receive control signals.

The transfer voltage output circuit 111 includes a transfer roller 45.
It is a circuit for outputting a transfer voltage applied to. The static elimination voltage variable output circuit 112 is a circuit for applying a static elimination voltage to the static elimination needle 78A. The charging voltage output circuit 113 outputs the voltage applied to the charging roller 43. These output circuits 111 to 113 are composed of a switching circuit for turning on / off the output of voltage, a well-known voltage control circuit for controlling the output voltage, and the like.

In the present embodiment, the charging roller 43 is applied with an alternating voltage superimposed with a negative direct voltage. The developing voltage output circuit 114 outputs the voltage applied to the developing device 115. Laser scanning device control circuit 116
Is a circuit for controlling the laser scanning device 49. A page memory for expanding print data is also included in this circuit. The fixing control circuit 117 controls the temperature of the heat roll of the heat fixing device 83. The main drive circuit 118 includes a main motor 119 for rotating the photosensitive drum 42.
It is designed to control the driving of.

FIG. 5 shows how the voltage applied to the transfer roller and the discharging needle in the printer of this embodiment changes. 2A shows the transfer roller 4 shown in FIG.
5 shows how the voltage applied from the transfer voltage output circuit 111 is turned on and off. A section indicated by an arrow A is a section in which the sheet 73 (FIG. 2) is in contact with the transfer roller 45, and a transfer voltage composed of a predetermined positive DC voltage is applied from the start to the end of the section. Applied to.
Such control of the transfer voltage can be performed by measuring the elapsed time of the sheet 73 after passing through the registration rollers 66.

5 (b) and 5 (c) show how the static elimination voltage applied to the static elimination needle 78A shown in FIG. 2 changes. Of these, FIG. 7B shows the charge removal voltage when printing is performed on the first surface of the paper 73. If the tip of the paper 73 reaches a position directly above the static elimination needle 78A,
mm seconds earlier, that is, the paper 7 is transferred to the transfer roller 45.
From the time when the tip of No. 3 arrives, the static elimination voltage of -100V is applied to the static elimination needle 78A. Then, from the time when the rear end of the sheet 73 reaches the transfer roller 45, a voltage of −2000 V is applied to the charge eliminating needle 78A.
The rear end of 3 passes just above the charge elimination needle 78A and is stopped when a short time has passed.

FIG. 5C shows the static elimination voltage when printing is performed on the first surface of the sheet 73. Paper 7 in this case
The static elimination voltage of -2000V is applied to the static elimination needle 78A from a time point 50 mm seconds before the tip of 3 reaches the position directly above the static elimination needle 78A. Then, from the time when the rear end of the sheet 73 reaches the transfer roller 45,
A voltage of 3000 V is applied, and this voltage is applied to the paper 73.
Similarly, when the rear end passes just above the charge elimination needle 78A and a short time has passed, it is similarly stopped. As described above, the static elimination voltage changes on one side and two sides of the sheet 73, but as shown in FIG. 7A, the voltage applied to the transfer roller 45 does not change on any side of the sheet 73.

The voltage applied to the charge elimination needle 78A is changed between the first surface and the second surface of the print because the first voltage is changed when the second surface is printed.
This is because the water content of the paper 73 is lower than that of the surface. That is, since the second surface of the paper sheet 73 has passed through the heat roll of the fixing device 83 once, the water content is low and the insulation resistance is high. Therefore, the degree of charging by the transfer roller 45 is further increased, and it is necessary to more strongly perform the static elimination by the static elimination needle 78A. Further, the absolute value of the voltage applied to the static elimination needle 78A is increased near the rear end of the paper 73 because the peeling discharge at the time when the paper 73 is completely separated from the photosensitive drum 42 is suppressed as much as possible and the peeling memory is removed. This is because. Further, the voltage for static elimination is applied to the static elimination needle 78A until just after the sheet 73 has passed just above the static elimination needle 78A, because the photoconductor drum 42 at the peeled portion is neutralized and the history is removed. This is because

In the first embodiment described above, the paper 73
The toner image can be stably transferred to a sheet as a transfer material by simply performing a simple control such that the voltage applied to the transfer roller 45 is changed depending on the difference in the printing surface of the sheet. It is possible to prevent the deterioration of the image.

Second embodiment

FIG. 6 shows a circuit configuration of a main part of a printer as an image forming apparatus according to the second embodiment of the present invention. 6, the same parts as those of the circuit shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be appropriately omitted. The printer 241 of the present embodiment is configured to enable printing of a higher quality image as compared with the first embodiment. For this reason, the ROM 203 stores a program showing a procedure for determining the environment, a procedure for changing the voltage applied to the transfer roller 45 and the charge eliminating needle 78A according to the determined environment, and the like. Further, a transfer voltage variable output circuit 211 capable of outputting the transfer voltage in a variable state is connected to the transfer roller 45. Further, the transfer roller 45
Is provided with a current detection circuit 221 that detects a current flowing between the photoconductor drum 42 and the photosensitive drum 42, and the environment is determined based on the current detection circuit 221.

Although not shown in FIG. 1, in the printer 241 of the second embodiment, a transmissive optical sensor 222 is arranged on the conveyance path between the transfer roller 45 and the registration roller 66. The transmissive optical sensor 222 detects the leading end and the trailing end of the sheet 73 passing on the conveying path, and sends the detection outputs to the bus 102.

FIG. 7 shows a control flow for determining the printing environment of the printer of this embodiment.
The printer of the present embodiment is the communication control circuit 10 shown in FIG.
6 is connected to an external device via a communication cable 107 connected to the printer 6, and print data is supplied from this. The CPU 101 waits for reception of a print start signal sent before starting printing from the external device (step S101). When the print start signal is received (Y), the CPU 101 sends a drive start signal to the main drive circuit 118 shown in FIG. 4 to start driving the main motor 119 to move the photosensitive drum 42 at a constant speed. Rotate (step S
102). Then, the charging voltage output circuit 113 is controlled to apply a negative voltage of −400 V to the charging roller 43 to uniformly charge the drum surface (step S103).

In this state, the CPU 101 monitors the time when the charged portion of the photosensitive drum 42 reaches the transfer position, that is, the position where the photosensitive drum 42 and the transfer roller 45 are nipped (step S104). Then, when this time is reached (Y), the transfer voltage variable output circuit 211
Is controlled to apply a monitor voltage of +1000 V to the transfer roller 45 (step S105). And the paper 73
In this state where there is no intervening current, the current flowing between the transfer roller 45 and the photosensitive drum 42 is detected (step S1).
06). The current value detected by the current detection circuit 221 is analog-digital converted by the built-in A / D converter. C
The PU 101 stores the digital value of this detected voltage in the ROM 1
The reference value stored in 03 is compared to determine the current printer environment (step S107).

In the apparatus of this embodiment, the printer environment is classified into the following three types. The voltage applied to the transfer roller 45 and the charge eliminating needle 78A is controlled according to the determined environment. L / L environment: low temperature and low humidity environment H / H environment: high temperature and high humidity environment N / N environment: normal temperature and normal humidity environment (environments other than the above L / L and H / H environments) Although there is no unified standard for the two environments, there is no big difference in each standard that is generally applied, so no matter which standard is applied, there is only a slight difference in the applied voltage described below. , No big problem.

FIG. 8 shows how the resistance values of the transfer roller and the photosensitive drum used in this embodiment change depending on these three types of environments. In this figure, the vertical axis represents the resistance values of the transfer roller 45 and the photosensitive drum 42 in logarithm, and the horizontal axis represents three types of environments. Here, the polygonal line 122 in which each measurement point is represented by a black square represents the characteristic of the transfer roller 45, and the polygonal line 123 in which the white square is represented represents the characteristic of the photosensitive drum 42. In the L / L environment, the resistance values of both the transfer roller 45 and the photosensitive drum 42 are high,
/ H becomes lower as it shifts to the environment. For example, the transfer roller 45 has a resistance value of 10 ⁹ Ω or more in the L / L environment, but in the H / H environment, this decreases to about 1/100. As a result of the resistance values of both of them changing depending on the environment in this way, a monitor voltage of +1000 V is applied to the transfer roller 45 in this embodiment, and the current detection circuit 221 shown in FIG.
The current environment can be determined by measuring the current flowing through both.

FIG. 9 shows the relationship between the detected current of the transfer roller and each environment when the monitor voltage is applied to the transfer roller. As shown in FIG. 8, the resistance value of the transfer roller 45 varies depending on the environment, so that it is possible to distinguish three types of environments based on the current detected by the current detection circuit 221. Here, the case where a positive 1000 V is applied as the monitor voltage is shown. Transfer roller 4
If the current flowing in 5 is, for example, 6 μA, the printer 241
Is the H / H environment, 2.0 μA is the N / N environment, and 0.2 μA is the L / L environment. In FIG. 9, the boundaries of the three environments are called by broken lines, but the currents flowing through the transfer roller 45 are about 4 μA and 0.5 μA, respectively. Therefore, step 107 in FIG.
The current detection circuit 221 classifies the current when it is 4 μA or more, when it is 0.5 μA or less, and at other times.

FIG. 10 specifically shows the logic of the environment discrimination shown in step S107 of FIG. When the current flowing through the transfer roller 45 is 4 μA or more (step S201; Y), the H / H environment control mode for determining the voltage under the H / H environment is executed (step S20).
2). If the current is less than 4 μA (step S
201; N), and it is determined whether this is 0.5 μA or less (step S203). As a result, 4μ
If it is less than A and exceeds 0.5 μA (N), the N / N environment control mode for determining the voltage under the N / N environment is executed (step S204). When the current flowing through the transfer roller 45 is 0.5 μA or less, the L / L environment control mode for determining the voltage under the L / L environment is executed (step S205).

FIG. 11 shows the control of the voltage applied to the charge elimination needle of this printer in the H / H environment, as a concrete content of the processing of step S202. The CPU 101 illustrated in FIG. 6 determines whether the printing of the sheet 73 is performed on the first side or the second side (step S301).
This is recognized by the printer 241 side in relation to the switching control of the switching lever 91 shown in FIG. 1, and this information may be used. When printing is performed on the first surface of the sheet 71 (Y), it is determined when the vicinity of the rear end of the sheet 73 reaches the transfer position, that is, the nip position described above (step S (step S302). Such control measures a time shorter by a predetermined time than the time from when the transmissive optical sensor 222 shown in FIG. 6 detects the rear end of the sheet 73 to when the rear end reaches directly above the static elimination needle 78A. It can be determined by that.

When the vicinity of the rear end of the sheet 73 reaches the transfer position (Y), the CPU 101 causes the transfer voltage variable output circuit 211 to operate.
Is controlled to apply −3000 V to the charge elimination needle 78A (step S303). That is, on the first surface in the H / H environment of this embodiment, the paper 73 on which the toner image is transferred is
Is not removed even when the tip of the battery reaches the static elimination needle 78A, and -3000V is reached when the vicinity of the rear end reaches the static elimination needle 78A.
Will be applied. In this way, the reason why the static elimination is not performed up to the vicinity of the rear end of the sheet 73 is that high temperature,
This is because it is considered that the conditions are high. CPU
101 starts the time counting operation from the time when a voltage of -3000V is applied, and stops the application of this voltage after a lapse of a time t until the rear end of the sheet 73 has passed just above the static elimination needle 78A and slightly passed ( Step S304; Y).

On the other hand, when it is determined in step S301 that the printing is on the second side (N), when the leading edge of the sheet 73 reaches the transfer position where the transfer roller 45 and the photosensitive drum 42 are nipped (step S305). ; Y), static elimination needle 78A
-2000V voltage is applied to (step S30
6). This is because even in the H / H environment, since the paper 73 is once heat-fixed, its surface needs to be neutralized. Then, from the time when the vicinity of the trailing edge of the sheet 73 reaches the transfer position (step S307; Y), the same as before, -3
A voltage of 000 V is applied to the charge elimination needle 78A (step S303). The timing at which the application of the voltage of -2000V is started is determined by measuring the time from the time when the transmission optical sensor 222 shown in FIG. 6 detects the leading edge of the sheet 73 to the stop position. be able to.

FIG. 12 shows the control of the voltage applied to the charge elimination needle of this printer in the N / N environment, as a concrete content of the processing of step S204. The CPU 101 illustrated in FIG. 6 determines whether the printing of the sheet 73 is performed on the first side or the second side (step S401).
When printing is performed on the first surface of the paper sheet 71 (Y), when the leading edge of the paper sheet 73 reaches the transfer position (step S402; Y), -100 V is applied to the charge removal needle 78A.
Is applied (step S403). In the H / H environment, the voltage for static elimination was not applied at this point, but N
In the / N environment, the humidity has decreased to the normal value, so we decided to perform a small amount of static elimination. After this, paper 7
3 from the time when the vicinity of the rear end reaches the transfer position (step S404; Y), the time t is the same as in the previous H / H environment.
The voltage of −3000 V is applied to the charge removal needle 78A only during this period (steps S405 and S406).

On the other hand, when it is determined in step S401 that the printing is on the second side (N), when the leading edge of the sheet 73 reaches the transfer position where the transfer roller 45 and the photosensitive drum 42 are nipped ( In step S407; Y), a voltage of -1000V is applied to the charge elimination needle 78A (step S).
408). This is because the paper sheet 73 has been once heat-fixed, so that the surface of the paper sheet 73 needs to be destaticized more strongly. When the vicinity of the rear end of the sheet 73 reaches the transfer position (step S
409; Y), and a voltage of −3000 V is applied to the static elimination needle 78A as before (step S405).

FIG. 13 shows the control of the voltage applied to the charge elimination needle of this printer in the L / L environment, as a specific content of the processing of step S205. The CPU 101 illustrated in FIG. 6 determines whether the printing of the sheet 73 is performed on the first side or the second side (step S501).
When printing is performed on the first surface of the sheet 71 (Y), when the leading edge of the sheet 73 reaches the transfer position (step S502; Y), the static elimination needle 78A has -500V.
Is applied (step S503). In the L / L environment, the humidity is lower than the normal value.
I decided to do the strongest static elimination on the first surface of the. After this, from the time when the vicinity of the trailing edge of the sheet 73 reaches the transfer position (step S504; Y), as in the case of the previous H / H environment and N / N environment, only −300 during the time t.
A voltage of 0V is applied to the charge elimination needle 78A (steps S505 and S506).

On the other hand, when it is determined in step S501 that the printing is on the second side (N), the time when the leading edge of the sheet 73 reaches the transfer position where the transfer roller 45 and the photosensitive drum 42 are nipped ( In step S507; Y), a voltage of −800 V is applied to the charge elimination needle 78A (step S5).
08). This is because the paper sheet 73 has been once heat-fixed, so that the surface of the paper sheet 73 needs to be destaticized more strongly. When the vicinity of the rear end of the sheet 73 reaches the transfer position (step S5
09; Y), the voltage of −3000 V is the same as the above.
8A (step S505).

FIG. 14 is a comparison of the voltages applied to the transfer roller and the discharging needle under each environment of H / H, N / N and L / L, and corresponds to FIG. 5 in the first embodiment. is there. FIG. 14A shows how the voltage applied from the transfer voltage output circuit 211 shown in FIG. 6 to the transfer roller 45 is turned on and off. A section indicated by an arrow A is a section in which the sheet 73 (FIG. 2) is in contact with the transfer roller 45, and a transfer voltage composed of a predetermined positive DC voltage is applied from the start to the end of the section. Applied to. The on / off control of the transfer voltage is realized by measuring the time based on the output of the transmissive optical sensor 222 described above.

14 (b) to 14 (d) respectively show H /
The change of the voltage applied to the transfer roller 45 with respect to the first surface of the H environment, the first surface of the N / N environment, and the first surface of the L / L environment is shown in FIGS. ) Is H / H
The second aspect of the environment, the second aspect of the N / N environment, the second aspect of the L / L environment
The change in the voltage applied to the transfer roller 45 with respect to the surface is shown. These are as described in FIGS. 11 to 13 above.

Unlike the case of the first embodiment, the voltage applied to the transfer roller 45 shown in FIG.
The first surface and the second surface of the printer 241 and the environment in which the printer 241 is placed are different. In this embodiment, the transfer roller 45 has an N / N environment of 22 ° C. and 55% RH.
Under the conditions of 1.0 × 10 ⁸ Ω. As shown in FIG. 8, it is well known that the volume resistance value of the transfer roller 45 and the volume resistance value of the sheet 73 as a transfer material change due to the change of environment. Therefore, the voltage to be applied to the transfer roller 45 varies depending on the environment. Therefore, in the H / H environment of the present embodiment, + 350V is applied to the transfer roller 45 when printing the first surface. After that, the toner passes through the feed rollers 93 to 95 shown in FIG. 1 in order, and + 1000V is applied to the transfer roller 45 when the second surface is printed. In the N / N environment, + 1000V is applied on the first surface and +1 on the second surface.
500V is applied. +15 on the first side in L / L environment
00V is applied and + 3000V is applied on the second surface.

A test was conducted to compare the printer of the second embodiment described above with other printers. In this test, as the H / H environment, 28 ° C, 85% RH, N
The conditions were 22 ° C and 55% RH as the / N environment, and 10 ° C and 15% RH as the L / L environment. Further, it is decided to apply a voltage of -3000V to the charge elimination needle 78A. In this test, the transfer material was a letter size (8.5 × 11) for 4024DP manufactured by Xerox Co., Ltd.
Inch) paper 73 was used.

First test

In the first test, no voltage was applied to the static elimination needle 78A, and the line on the output side of the static elimination voltage variable output circuit 112 shown in FIG. 6 as the power source for the static elimination needle was grounded.

FIG. 15 shows changes in the voltage applied to the transfer roller and the charge elimination needle in this first test. FIG. 6A shows the voltage applied to the transfer roller 45. The transfer voltage is applied at the timing when the leading edge of the paper 73 comes into contact with the transfer roller 45 until the trailing edge of the paper 73 comes into contact. This voltage is continuously applied. The figure (b) has shown the voltage applied to the charge elimination needle 78A, and in this case, it becomes 0V.

FIG. 16 shows the result of the first test in each environment. With regard to the peeling memory, it was not possible to obtain the result of removing it in any environment. This is because the static elimination needle 78A does not specifically eliminate the static electricity on the paper sheet 73, and the discharge phenomenon at the time of peeling adversely affects the image in all environments. Regarding the transfer memory, the occurrence was observed only when the second surface was transferred in the H / H environment. The transfer image omission did not occur in any case. Disturbance of the transferred image was severe on the second side of the H / H environment. No fixing offset (fixing device offset) occurred.

Second test

FIG. 17 shows the result of the second test in each environment. FIG. 6A shows the voltage applied to the transfer roller 45. The transfer voltage is applied at the timing when the leading edge of the paper 73 comes into contact with the transfer roller 45 until the trailing edge of the paper 73 comes into contact. This voltage is continuously applied. (B) of the figure shows the voltage applied to the charge elimination needle 78A, which is −30 from 50 msec before the rear end of the sheet 73 reaches the transfer position to 200 msec.
A voltage of 00V is applied to the charge elimination needle 78A. Static elimination needle 78
The applied voltage to A is the same on the first surface and the second surface of the sheet 73.

FIG. 18 shows the result of the second test in each environment. Charge removing needle 78 when the paper 73 is peeled off
Since the voltage of −3000 V is applied to A, the problem of image quality deterioration caused by the peeling memory for the transfer of the first surface and the second surface is solved. However, even with such improvement, it is not possible to improve the image quality trouble caused by the transfer image disturbance and the transfer memory due to the leakage of the charge of the sheet 73 which occurs at the time of the transfer of the second surface.

Third test

FIG. 19 shows the result of the third test in each environment. The voltage application to the transfer roller 45 shown in FIG. 9A is the same as in the previous test. The figure (b) has shown the voltage applied to the static elimination needle 78A,
-300 from the time when the leading edge of the paper 73 reaches the transfer position
A voltage of 0 V is applied to the charge elimination needle 78A, and this applied state is maintained until 150 msec has elapsed since the rear end of the sheet 73 reached the transfer position. Static elimination needle 78A
The applied voltage to the first surface and the second surface of the paper 73 is the same.

FIG. 20 shows the result of the third test in each environment. Not only when the paper 73 is peeled off, but also when the tip of the paper 73 reaches the angel position
Since the voltage of −3000 V is applied to A, not only the problem of image quality deterioration caused by the peeling memory is solved but also H
Disturbance of the transfer image due to a leak caused by charging of the transfer memory and the sheet 73, which is a problem on the second surface of the / H environment, does not occur. However, when water-containing paper (for example, paper left under conditions of 28 ° C. and 85% RH for 8 hours or more) is used on the first side of the H / H environment, the problem of image loss is severe, and N / N Environment and L / L environment,
Paper 73 due to transfer of toner image to heat roll
There is a new problem that fixing offset occurs in the. This is because the electrostatic attraction of the paper 73 reduces the attraction force of the toner, and as a result, the conditions of the third test cannot satisfy the specifications of the actual printer.

Fourth test

FIG. 21 shows the result of the fourth test in each environment. The voltage application to the transfer roller 45 shown in FIG. 9A is the same as in the previous test. FIG. 7B shows the voltage applied to the charge eliminating needle 78A on the first surface of the sheet 73. In this case, the same voltage control as the voltage application to the charge removal needle 78A of the second test shown in FIG. 17B is performed. FIG. 7C shows the voltage applied to the charge elimination needle 78A on the second surface of the sheet 73. In the latter case, the same voltage control as the voltage application to the charge eliminating needle 78A of the third test shown in FIG. 19B is performed.

FIG. 22 shows the result of the fourth test in each environment. The image quality failure caused by the transfer memory that could not be solved in the second test does not occur, and the transfer failure when using water-containing paper during the first surface transfer in the H / H environment that newly occurred in the third test It was also possible to prevent the occurrence of. However, even under the conditions of the fourth test, the fixing offset state on the second surface was severe under the N / N environment and the L / L environment, and the deterioration of the image quality due to this was not able to be improved. In addition, the disturbance of the transferred image due to the leakage of electrification of the paper, which could be prevented in the third test, occurs again on the first surface of the L / L environment.

Fifth test

The fifth test is shown in FIG. 1 in the previous embodiment.
This is the same as the voltage control shown in FIG. That is, the static elimination needle 7
Control is performed such that the voltage application to 8A is finely switched between the H / H, N / N, and L / L environments and the first surface and the second surface of the sheet 73.

FIG. 23 shows the result of the fourth test in each environment. Image quality problems that cannot be solved by the first to fourth tests are all cleared in each environment and the first and second sides of the sheet 73. Of course, in image forming apparatuses other than such printers, due to differences in conditions such as specifications and types of paper used,
Of course, it may be possible to obtain an acceptable image quality under the conditions before the fifth test.

FIG. 24 shows the occurrence of the fixing offset solved by the fifth test and the voltage applied to the charge elimination needle (charge elimination voltage).
It shows the relationship with. When a voltage indicated by a straight line in the figure or a voltage larger in absolute value than the voltage is applied to the charge eliminating needle 78A, the electrostatic balance between the toner and the paper 73 is lost and a fixing offset occurs. Therefore, if the absolute value is lowered to the voltage in the region where these straight lines are not drawn in this figure, the fixing offset does not occur. For example, L
On the second surface of the / L environment, if a voltage from 0 V to -1000 V is applied to the static elimination needle 78A, the fixing offset does not occur. However, the voltage applied to the charge elimination needle 78A should be determined for each printer 241 or image forming apparatus in consideration of other conditions.

FIG. 25 shows the relationship between the voltage applied to the charge elimination needle and the occurrence of various printing problems in the environment of the printer of this embodiment. In this figure, the area indicated by reference symbol a is the area where the fixing offset occurs, and the area indicated by reference symbol b is the area where the offset generation is unstable, in which the fixing offset occurs or does not occur. Further, the area indicated by the reference sign c is the area where the transfer omission occurs, and the area indicated by the reference sign d is the area where the image disturbance occurs. At a place where a plurality of codes are present in one partitioned area, the quality of the image is degraded due to each cause indicated by these codes.
After all, only the area indicated by the symbol e becomes the image good area in which no problem occurs in the printing of the image. For this reason, in the case of this embodiment, the voltage applied to the static elimination needle 78A is set to each value as shown in FIG.

Deformability of the invention

In the second embodiment described above, a predetermined constant voltage is applied to the transfer roller 45 as the monitor voltage, the flowing current is detected, and each environment is discriminated from this value. It is possible to discriminate each environment by other methods. For example, when the voltage applied to the transfer roller 45 is V _m and the current flowing between the transfer roller 45 and the photosensitive drum 42 at this time is I _m , this is prepared in advance by the following formula (1). Alternatively, the coefficient value Z including the impedance may be obtained by substituting it into another calculation formula. Z = k × V _m / I _m (1)

For example, the applied voltage V _m to the transfer roller 45
Is similarly set to +1000 V, and the current I _m flowing between the photosensitive drum 42 and the photosensitive drum 42 is set to 2.0 μA, these are (1)
Using the coefficient value Z substituted in the equation, the environment in which the printer 241 is placed is discriminated as, for example, the N / N environment, or the voltage applied to the charge eliminating needle 78A or the transfer roller 45 is more finely determined in association with the coefficient value Z. You may do it.

Although the environment of the apparatus is detected by the current flowing through the transfer roller 45 in the embodiment, it is of course possible to directly detect such an environment by using a sensor for detecting temperature and humidity. It is possible. Further, in the embodiment, the applied voltage of the charge elimination needle 78A or the like is determined regardless of the water content of the paper 73 or the transfer material, but the water content and thickness of the transfer material, the type of constituent material, etc. can be determined by a known method. Other characteristics may be measured and the applied voltage may be controlled accordingly.

Further, although the image forming apparatus using the organic photoconductor has been described in the embodiment, the photoconductor may be other than this, and further, other than the drum-shaped one such as a belt-shaped one. Of course, it may be a flat plate. Further, in the embodiment, the image forming apparatus using the laser beam has been described, but the present invention can be applied to other apparatuses such as a copying machine of a type that exposes an optical image of a document. Further, in the embodiment, the case of using the static elimination needle 78A having the serrated teeth has been described, but it goes without saying that the means for static elimination may be another known one.

Further, in the embodiment, the environment in which the device is placed is H
Although there are three types, / H, N / N, and L / L, classifications other than this and types other than this may be used. Further, in the embodiment, these divisions are determined based on the current temperature and humidity, but other data such as the degree of change in temperature and humidity may be used, or such data and the current temperature and humidity may be used. The environment may be set by combination.

[0104]

As described above, according to the first aspect of the invention, the voltage applied to the charge eliminating means for eliminating the charge on the transfer material on which the toner image has been transferred is placed on the paper or the like as the transfer material or on the device. Since it is decided to adjust according to various conditions, it is possible to adjust the electrostatic coupling between the transfer material and the toner and the relationship between the transfer material and the image bearing member such as the photoconductor drum. Even if it is used, there is an effect that good printing can be performed.

According to the second aspect of the present invention, paying attention to the change in the characteristics after the transfer material is fixed by heat, pressure, etc., when performing double-sided printing, the static electricity removing means is selected by the printing surface of the transfer material. In addition to changing the level of the applied voltage, the level of the voltage applied to the charge eliminating means is also changed depending on the relative position of the transfer material in the contact transfer means. In this way, the level of the voltage applied to the charge eliminating means is changed according to the printing surface of the transfer material, so that the characteristics are large between the first surface and the second surface of the transfer material as in a device using a thermal fixing device. Even if there is a change, there is an effect that good image quality can be secured on both sides.

Further, according to the third aspect of the invention, paying attention to the relation between the static electricity and the change of the environment where the image forming apparatus such as a printer, a facsimile machine, and a copying machine is placed, the humidity determined by the environment determining means, Since we decided to change the level of the voltage applied to the static eliminator according to the environment such as temperature, if the applied voltage is adjusted according to these environments,
It is possible to create a device that corresponds to a wide range of environments.
Further, there is also an advantage that the quality of the image can be kept good even if the environment changes.

According to the fourth aspect of the present invention, the transfer material characteristic determining means for determining the characteristics of the transfer material is prepared by paying attention to the relationship between the characteristics such as water content and resistance of the transfer material such as paper and static electricity. Then, since the level of the voltage applied to the charge eliminating means is changed according to the characteristics determined by this, it is possible to obtain an image of stable quality on various transfer materials.

Further, according to the invention of claim 5, the absolute value of the voltage applied to the charge eliminating means is made higher at the time of peeling, so that the effect of the charge eliminating is enhanced. As a result, discharge is less likely to occur when the transfer material is peeled off, and deterioration of the image due to this discharge can be prevented.

Further, according to the invention of claim 6, a method of applying a voltage between the contact transfer means and the image bearing member instead of detecting the environment such as temperature and humidity in the apparatus by individual sensors respectively. Since the current flowing between them is detected to determine the environment of the device, the structure of the device can be simplified and the device can be manufactured at low cost.

According to the invention described in claim 7, instead of individually detecting the environment such as the temperature and humidity in the apparatus and the environment such as the water content of the transfer material, the contact transfer means and the image carrier are provided. Since both the state in which the transfer material is interposed and the state in which the transfer material is not interposed are realized, the current flowing between them is detected in these states, and the environment of the apparatus and the transfer material is determined. The structure of the device can be simplified and the device can be manufactured at low cost. Further, since the level of the applied voltage applied to the charge eliminating means is switched in consideration of not only the environment inside the apparatus but also the environment or characteristics of the transfer material, it is possible to achieve good reproduction of the image.

Further, according to the invention of claim 8, the environment in which the image forming apparatus is placed is divided into three, which are high temperature / high humidity, low temperature / low humidity, or other in accordance with the relationship between temperature and humidity. , The surface when transferring the toner image to the transfer material is divided into the first surface for the first transfer and the second surface for the second transfer, and the charge removing means is provided so as to cope with these combinations. Since the level of the applied voltage applied to each is set to a desired value, it is more stable in various situations than an apparatus considering only the environment or only the first surface or the second surface of the transfer material. The image quality can be secured.

According to the invention described in claim 9, application is made to both the charge eliminating means for eliminating the charge of the transfer material on which the toner image is transferred and the contact transfer means for electrostatically transferring the toner image to the transfer material. Since the voltage is adjusted according to the conditions such as the transfer material such as paper and the device, it is possible to print better in various situations than when changing only the voltage applied to the static eliminator. Can be secured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a printer as an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing the periphery of a photosensitive drum of the printer of the first embodiment.

FIG. 3 is a side view showing an arrangement relationship between a photosensitive drum and a charge eliminating device in the first embodiment.

FIG. 4 is a block diagram showing a main part of a circuit configuration of the printer according to the first embodiment.

FIG. 5 is a waveform diagram showing how the voltage applied to the transfer roller and the discharging needle of the first embodiment changes.

FIG. 6 is a block diagram showing a circuit configuration of a main part of a printer according to a second embodiment of the present invention.

FIG. 7 is a flow chart showing the flow of control for determining the printing environment of the printer of this embodiment.

FIG. 8 is a characteristic diagram showing the relationship between the resistance value of the transfer roller and the photosensitive drum and the environment in the second embodiment.

FIG. 9 is a characteristic diagram showing the relationship between the detected current of the transfer roller and each environment when a monitor voltage is applied to the transfer roller in the second embodiment.

FIG. 10 is a flowchart specifically showing the logic of environment determination shown in step S107 of FIG.

FIG. 11 is a flow chart showing a state of controlling a voltage applied to a charge eliminating needle of a printer in an H / H environment, which is the process of step S202.

FIG. 12 is a flow chart showing a state of controlling the voltage applied to the charge removal needle of the printer in the N / N environment, which is the process of step S204.

FIG. 13 is a flowchart showing a state of controlling the voltage applied to the charge removal needle of the printer in the L / L environment, which is the process of step S205.

FIG. 14 is a waveform diagram comparing the voltages applied to the transfer roller and the discharging needle under each environment of H / H, N / N, and L / L, and shows the contents of the fifth test.

FIG. 15 is a waveform diagram showing changes in the voltage applied to the transfer roller and the charge eliminating needle in the first test.

FIG. 16 is an explanatory diagram showing the result of the first test in each environment.

FIG. 17 is a waveform diagram showing changes in the voltage applied to the transfer roller and the charge elimination needle in the second test.

FIG. 18 is an explanatory diagram showing the results of the second test in each environment.

FIG. 19 is a waveform diagram showing changes in the voltage applied to the transfer roller and the discharging needle in the third test.

FIG. 20 is an explanatory diagram showing the results of a third test in each environment.

FIG. 21 is a waveform diagram showing changes in the voltage applied to the transfer roller and the static elimination needle in the fourth test.

FIG. 22 is an explanatory diagram showing the results of a fourth test in each environment.

FIG. 23 is an explanatory diagram showing the results of a fourth test in each environment.

FIG. 24 is a characteristic diagram showing the relationship between the occurrence of fixing offset and the voltage applied to the charge elimination needle in the environment of the embodiment.

FIG. 25 is a characteristic diagram showing the relationship between the voltage applied to the static elimination needle and the occurrence of various printing faults in the environment of the printer of the second embodiment.

FIG. 26 is a schematic configuration diagram showing a main part of a conventional image forming apparatus using a contact type charger or discharger.

FIG. 27 is an explanatory diagram showing a state of image formation by a reversal development method which is often adopted in the image forming apparatus as shown in FIG. 26.

[Explanation of symbols]

41, 241 ... Printer, 42 ... Photosensitive drum, 43 ...
Charging roller, 44 ... Developing roller, 45 ... Transfer roller, 7
3 ... Paper, 78 ... Static eliminator, 78A ... Static elimination needle, 101 ...
CPU, 103, 203 ... ROM, 104 ... RAM, 1
11 ... Transfer voltage output circuit, 112 ... Static elimination voltage variable output circuit, 113 ... Charging voltage output circuit, 211 ... Transfer voltage variable output circuit, 221 ... Current detection circuit, a ... Fixing offset occurrence area, b ... Offset occurrence unstable area , C ... Transfer drop occurrence area, d ... Image disturbance occurrence area, e ... Image good area

Claims (9)

[Claims] 1. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and an image bearing member in contact with each other via a transfer material. Contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material, charge removing means arranged adjacent to the contact transfer means for removing charge from the transfer material on which the toner image has been transferred, and this charge removing means A static elimination applied voltage generating means capable of changing the voltage applied to the means, and a static elimination applied voltage adjusting means for adjusting the voltage output by the static elimination applied voltage generating means according to various predetermined conditions. An image forming apparatus comprising: 2. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and an image bearing member in contact with each other via a transfer material. Contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material, charge removing means arranged adjacent to the contact transfer means for removing charge from the transfer material on which the toner image is transferred, and transfer material The transfer material relative moving means for moving the toner image relative to the contact transfer means in accordance with the transfer of the toner image, the fixing means for fixing the transfer material on which the toner image is transferred, and the toner image on both surfaces of the transfer material. When the transfer is performed, the toner image is transferred to the first printing surface and is fixed by the fixing unit, and then the toner image is transferred to the second printing surface, and the fixing is performed again on the transfer material. Time transfer fixing control means, and the static elimination means Applying an image forming apparatus characterized by comprising a charge removing the applied voltage switching means for switching in accordance with the level of voltage on the printed surface of the relative position and the transfer material in the contact transfer means of the transfer material to. 3. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and the image bearing member being in contact with each other via a transfer material. Contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material, charge removing means arranged adjacent to the contact transfer means for removing charge from the transfer material on which the toner image is transferred, and transfer material Of the transfer material relative to the contact transfer means in accordance with the transfer of the toner image, an environment determination means for determining the environment in the apparatus, and a voltage level applied to the static elimination means An image forming apparatus comprising: a static elimination applied voltage switching unit that switches depending on a relative position of the transfer material in the contact transfer unit and the environment determined by the environment determination unit. 4. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and the image bearing member being in contact with each other via a transfer material. Contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material, charge removing means arranged adjacent to the contact transfer means for removing charge from the transfer material on which the toner image is transferred, and transfer material Of the transfer material relative to the contact transfer means in accordance with the transfer of the toner image, transfer material characteristic determining means for determining the characteristics of the transfer material, and the level of the voltage applied to the static eliminating means. An image forming apparatus, comprising: a static elimination applied voltage switching unit that switches the transfer material according to the relative position of the transfer material in the contact transfer unit and the characteristics determined by the transfer material characteristic determination unit. 5. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and the image bearing member being in contact with each other via a transfer material. Contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material, static eliminator arranged adjacent to the contact transfer means for neutralizing the transfer material on which the toner image has been transferred, and transfer material Of the transfer material relative to the contact transfer means in accordance with the transfer of the toner image, and a predetermined voltage to the charge removing means from the time when the tip of the transfer material contacts the contact transfer means. The voltage is applied to change the absolute value of the transfer material near the trailing edge of the transfer material so that its absolute value becomes higher from a predetermined point of time, and the voltage is applied after a lapse of a certain period of time after the trailing edge of the transfer material passes through this neutralizing means. Turn off the applied voltage to stop the application of An image forming apparatus characterized by comprising a means. 6. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and the image bearing member being in contact with each other via a transfer material. Contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material, charge removing means arranged adjacent to the contact transfer means for removing charge from the transfer material on which the toner image is transferred, and transfer material And a transfer material relative moving means for moving the toner relative to the contact transfer means in accordance with the transfer of the toner image, and a current for detecting a current flowing between the contact transfer means and the image carrier without the transfer material. A detection unit, an environment determination unit that determines the environment inside the apparatus based on the detection result of the current detection unit, and the level of the applied voltage applied to the charge removal unit to the relative position of the transfer material in the contact transfer unit. Determine the environment determination means An image forming apparatus characterized by comprising the applied voltage switching means for switching in accordance with the environment in the apparatus. 7. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and an image bearing member in contact with each other via a transfer material. Contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material, charge removing means arranged adjacent to the contact transfer means for removing charge from the transfer material on which the toner image is transferred, and transfer material Of the transfer material relative to the contact transfer means according to the transfer of the toner image, and between the contact transfer means and the image carrier both in the state without the transfer material and in the state with the transfer material. A current detection unit that detects a flowing current, an environment determination unit that determines the environment of the inside of the apparatus and the transfer material from the detection result of the current detection unit, and the level of the applied voltage applied to the static elimination unit to the contact of the transfer material. The transfer means An image forming apparatus characterized by comprising the applied voltage switching means for switching in accordance with the relative positions and environments discriminated device and a transfer material environment determination means. 8. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and the image bearing member being in contact with each other via a transfer material. Contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material, charge removing means arranged adjacent to the contact transfer means for removing charge from the transfer material on which the toner image is transferred, and transfer material And a transfer material relative moving means for moving the toner relative to the contact transfer means in accordance with the transfer of the toner image, and an environment for discriminating the environment inside the apparatus as high temperature / high humidity, low temperature / low humidity or any other When the toner image is transferred to both sides of the transfer material, the determination means, the fixing means for fixing the transfer material onto which the toner image has been transferred, and the toner image is transferred to the first printing surface of the transfer material, and the fixing means performs fixing. Toner on the second printed surface after being broken Transfer fixing control means for double-sided printing for transferring an image and fixing the image again on the transfer material, and a level of an applied voltage applied to the charge eliminating means, a relative position of the transfer material in the contact transfer means and a transfer operation. An image forming apparatus comprising: an applied voltage switching unit that switches according to the printing surface of the material and the environment determined by the environment determination unit. 9. An image bearing member carrying an electrostatic latent image, a toner image forming means for forming a toner image corresponding to the latent image on the image bearing member, and the image bearing member being in contact with each other via a transfer material. A contact transfer means for electrostatically transferring the toner image formed by the toner image forming means onto a transfer material; a charge removing means disposed adjacent to the contact transfer means for removing the charge of the transfer material on which the toner image has been transferred; A transfer applied voltage generation means capable of changing the voltage applied to the transfer means, a static elimination applied voltage generation means capable of changing the voltage applied to the static elimination means, and An image forming apparatus comprising: a transfer applied voltage generating means and a charge eliminating applied voltage adjusting means for adjusting a voltage outputted by the charge eliminating applied voltage generating means.