JPH04333872A - electrophotographic equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus using a reversal development method.

0002

2. Description of the Related Art In recent years, an electrophotographic apparatus has been developed as one of the apparatuses that electrostatically forms images. This electrophotographic device has a structure in which at least a charger, an exposure device, and a developer are arranged facing each other on a latent image carrier whose surface is located on the conveyance path of the print medium, and the latent image charged by the discharge of the charger is An electrostatic latent image is formed on the surface of the carrier by selective light irradiation from an exposure device, and the electrostatic latent image is developed by supplying toner to which a voltage is applied from a developing device to the surface of the latent image carrier. The toner image on the surface of the latent image carrier developed by this developing device is transferred onto a printing medium by a transfer voltage supplied from a transfer device.

[0003] The electrophotographic method of the above-mentioned electrophotographic apparatus includes reversal development in which the charge-eliminating area exposed to light becomes a toner image, and regular development in which a charged area not irradiated with light becomes a toner image. , are used in laser printers and copying machines, respectively. In the electrophotographic apparatus using reversal development as described above, there is a problem in that the uncharged portion of the latent image carrier is developed when the apparatus starts operating, resulting in wasteful consumption of toner and staining of various parts.

[0004] In other words, normally the charger discharges -500 (
V) The surface of the latent image carrier charged with -20
The toner to which a voltage of 0 (V) is applied does not adhere due to the potential difference, and a toner image is formed by adhering only to the part where the charge has been removed to -70 (V) by light irradiation from the exposure device. It has become. However, as illustrated in FIG. 3, when the surface of the latent image carrier starts moving when the device is started, etc., and at the same time voltage application to the charger and developer begins, the charger initially moves to the developer. Since the surface of the latent image carrier that reaches 0 (V) is not charged, the developing device applies -
Toner to which a voltage of 200 (V) is applied will adhere. In other words, in this electrophotographic apparatus, at the start of operation, a portion where toner is completely adhered is formed on the surface of the latent image carrier, resulting in wasteful consumption of toner and staining of various parts.

[0005] As a conventional example of an electrophotographic apparatus that solves the above-mentioned problems, an apparatus disclosed in Japanese Patent Application Laid-Open No. 61-290455 will be described with reference to FIG. first,
In this electrophotographic apparatus 1, a charging device 3, an exposure device 4, and a developing device 5 are arranged facing each other in sequence on the surface of a photosensitive drum 2, which is a latent image carrier. A pulse generator 8 is directly connected to a drive motor 7 which is connected to the drive motor 2 . A first counter 9 connected to the pulse generator 8 is connected to the drive motor 7 via a switch 10 and is also connected to the high voltage power supply 11 of the charger 3. A second counter 12 connected to the second counter 8 is connected to a changeover switch 15 provided between two high voltage power supplies 13 and 14 having different polarities and the developing roller 6 of the developing device 5.

With such a configuration, in this electrophotographic apparatus 1, the circumferential surface of the rotating photosensitive drum 2 is sequentially heated to -500 (
V), and when exposed to light from an exposure device, it becomes -10
An electrostatic latent image whose charge is removed to 0 (V) is formed. Therefore,
A toner image is formed by supplying toner to which a voltage of -300 (V) is applied to the electrostatic latent image by the developing roller 6 of the developing device 5 to which the regular high-voltage power supply 13 is connected by the changeover switch 15. Image formation is completed by transferring this toner image onto a printing medium such as printing paper.

In the electrophotographic apparatus 1, the developing roller 6 of the developing device 5 is kept at a regular high voltage until the charged portion of the surface of the photosensitive drum 2 reaches the developing device 5, such as when starting up the device. A high voltage power source 14 having a polarity opposite to that of the power source 13 is connected by a changeover switch 15 . By doing so, toner does not adhere to uncharged portions of the photosensitive drum 2 due to potential difference, thereby preventing wasteful consumption of toner and staining of various parts. In addition,
This electrophotographic apparatus 1 is configured to integrate pulses generated by a pulse generator 8 directly connected to a drive motor 7 using counters 9 and 12 to control the operation of the changeover switch 15 as described above.

[0008]

[Problems to be Solved by the Invention] In the above-described electrophotographic apparatus 1, the high-voltage power supply 14 of opposite polarity to the normal one is connected to the developing roller 6 of the developing device 5 until the charged portion of the photosensitive drum 2 reaches the electrophotographic apparatus 1.
This connection prevents toner from adhering to the uncharged portion of the photosensitive drum 2.

However, this electrophotographic apparatus 1 has a structure in which the above-mentioned high voltage power supply 14 of opposite polarity to the regular one is added as a dedicated device, which impedes the reduction in size and weight of the apparatus and productivity. It turns out. Therefore, there is a need to propose a means for applying a high voltage of opposite polarity to the normal one to the developing device with a simpler structure.

0010

[Means for Solving the Problems] A latent image carrier whose surface is located on the conveyance path of a print medium is provided, a charger is provided for discharging the surface of the latent image carrier, and the surface of the latent image carrier is provided with a charger that generates a charge by the discharge of the charger. A developing device that is provided with an exposure device that selectively irradiates the surface of the latent image carrier with light, and supplies toner with a voltage applied to an electrostatic latent image formed on the surface of the latent image carrier by the light irradiation of the exposure device. In an electrophotographic apparatus equipped with a transfer device that supplies a printing medium with a transfer voltage that attracts the toner image formed on the surface of the latent image carrier by the development of the developing device, the surface of the latent image carrier is An unnecessary development prevention mechanism is provided that connects the power source of the transfer device to the developing device until the portion charged by the discharge of the charging device reaches a position facing the developing device.

[0011]

[Operation] The unnecessary development prevention mechanism connects the power supply of the transfer device to the development device until the charged part of the surface of the latent image carrier reaches the position facing the development device, thereby eliminating unnecessary development. While the prevention mechanism connects the power supply of the transfer device to the developing device, toner does not adhere to the uncharged parts of the latent image carrier, which prevents wasteful consumption of toner and staining of various parts. Since the power source for the transfer device is used as a power source of opposite polarity to the power source for the developing device, a dedicated power source is not required.

0012

[Embodiment] An embodiment of the present invention will be explained based on FIGS. 1 and 2. First, in the electrophotographic apparatus 16 of this embodiment, FIG.
As illustrated in FIG. A drum cleaner 22, a drum charger 23, a laser scanner 24 serving as an exposure device, and a developing device 25 are arranged at positions facing the surface of the latent image carrier 21.
etc. are arranged in order. A paper feed roller 26 and a belt charger 27, which is a transfer device, are disposed on one end of the paper transport belt 19 in the tension direction, with a paper feed tray (not shown) being disposed opposite to it. The paper conveyance belt 1
At the other end in the tension direction of 9, there is a fixing device 28 which also serves as a paper ejection device.
are placed facing each other. Further, the paper conveyance belt 19
has a structure in which an insulating layer (not shown) is laminated on a dielectric layer (not shown), and a belt static eliminator 29 and a belt cleaner 30 are sequentially arranged on the surface of the stretched lower part. At the same time, it is grounded via a conductive roller 31 on the back surface.

Here, the drum charger 23 has a needle electrode 32 connected to a positive high voltage power source 33 and a grid 3
4 is grounded via a constant voltage element 35, and the belt charger 27 has a needle electrode 36 connected to a positive high voltage power source 37, and a grid 38 is grounded via constant voltage elements 39, 40. There is. Two input terminals of a changeover switch 42 connected to the developing roller 41 of the developing device 25 are connected to a negative high voltage power supply 43 and between the constant voltage power supplies 39 and 40.
By connecting the control terminal of No. 2 to an encoder (not shown) connected to the drive shaft of the guide roller 17 via a timer circuit 44, an unnecessary development prevention mechanism 45 is formed by the members 42 and 44. ing. Note that the latent image carrier 2
1 is grounded, and an AC power source 47 is connected to the needle electrode 46 of the belt static eliminator 29.

With such a configuration, in this electrophotographic apparatus 16, as illustrated on the right side of FIG. The peripheral surface of 21 is sequentially charged to -500 (V), and an electrostatic latent image whose charge is removed to -70 (V) is formed by light irradiation from the exposure device. Therefore, by using the changeover switch 42 of the unnecessary development prevention mechanism 45, the regular high-voltage power supply 43
-200 from the developing roller 41 of the developing device 25 connected to
A toner image is formed by supplying toner to which a voltage of (V) is applied to an electrostatic latent image of -70 (V). on the other hand,
The printing paper 48, which is a printing medium that is sequentially transported on the paper transport belt 19 in synchronization with the above-described operation, is charged onto the paper transport belt 19 by the discharge of the belt charger 27 connected to the positive high voltage power supply 37. Since it is attracted and a transfer voltage of +1600 (V) is applied, the toner image of -70 (V) is attracted by the potential difference. Then, the printing paper 48 to which this toner image has been transferred is heated under pressure by the fixing device 28 and discharged from the apparatus, thereby completing image formation by the electrophotographic apparatus 16.

Note that the paper conveyance belt 19 from which the printing paper 48 has been peeled off as described above continues to rotate for a predetermined period of time, and the charge on the surface thereof is eliminated by positive and negative voltages applied from the belt static eliminator 29. This electricity-eliminated paper conveyance belt 1
Dust such as toner adhering to the surface of belt cleaner 3
It is removed with a value of 0 and waits for the next printing.

In the electrophotographic apparatus 16, the developing roller 41 of the developing device 25 is not required until the charged portion of the surface of the latent image carrier 21 reaches the developing device 25, such as when starting up the device. Changeover switch 42 of development prevention mechanism 45
A high-voltage power source 37 for the belt charger 27 is connected thereto. By doing this, as illustrated on the left side of FIG.
) is applied, toner does not adhere to uncharged portions of the latent image carrier 21, and wasteful consumption of toner and staining of various parts are prevented.

In this electrophotographic device 16, as described above, the high voltage power source 37 connected to the developing device 25 and having the opposite polarity to the regular one is also used as the high voltage power source 37 for the belt charger 27, so that a dedicated device can be used. Since it is not necessary, it can contribute to making the equipment smaller and lighter and improving productivity. In this electrophotographic apparatus 16, since the set voltages of the constant voltage elements 39 and 40 connected in series are +1300 (V) and +300 (V), respectively, +
A voltage of 1600 (V) is applied, and a voltage of +300 (V) is applied from the high voltage power supply 37 to the developing device 25.

In this electrophotographic apparatus 16, the timer circuit 44 that detects the start of rotation of the guide roller 17 drives the operation of the changeover switch 42 in a time-division manner, thereby realizing the above-mentioned operation. , it is not necessary to calculate and control the rotation amount of the photosensitive drum by the number of pulses as in the electrophotographic apparatus 1 illustrated as a conventional example, so the structure is simple, making the device smaller and lighter, and improving productivity. can contribute to That is, in this electrophotographic apparatus 16, as illustrated in FIG. 2, the time t1 for the latent image carrier 21 that has started rotating until the portion facing the charger 23 reaches the position facing the developer 25; The time t2 at which the portion to which light is irradiated by the laser scanner 24 reaches the position facing the developing device 25 is detected in advance, and the time t at which the high voltage power source 37 is connected to the developing device 25 as described above is t1< t
The operation of the timer circuit 44 is set so that <t2.

[0019]

Effects of the Invention As described above, the present invention provides a latent image carrier whose surface is located on the conveyance path of a printing medium, and a charger for discharging on the surface of the latent image carrier. An exposure device that selectively irradiates the surface of the latent image carrier charged by electric discharge with light is provided, and a voltage is applied to the electrostatic latent image formed on the surface of the latent image carrier by the light irradiation of this exposure device. In an electrophotographic apparatus, an electrophotographic apparatus is provided with a developing device that supplies a toner image, and a transfer device that supplies a printing medium with a transfer voltage that attracts a toner image formed on the surface of a latent image carrier by the development of the developing device,
Unnecessary development is prevented by providing an unnecessary development prevention mechanism that connects the power source of the transfer device to the development device until the charged part of the surface of the latent image carrier reaches the position facing the development device. While the mechanism connects the power source of the transfer device to the developing device, toner does not adhere to the uncharged parts of the latent image carrier, which prevents unnecessary consumption of toner and staining of various parts. Since the power source for the transfer device is used as a power source with the opposite polarity to the power source for the developing device, a dedicated power source is not required.
This has effects such as being able to contribute to reducing the size and weight of equipment and improving productivity.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view showing an embodiment of the present invention.

FIG. 2 is a time chart.

FIG. 3 is a time chart showing a general example.

FIG. 4 is a longitudinal side view showing a conventional example.

[Explanation of symbols]

16 Electrophotographic device 21 Latent image carrier 23 Charger 24 Exposure device 25 Developing device 27 Transfer device 37 Power source 45 Unnecessary development prevention mechanism 48
print media

Claims (1)

[Claims] 1. A latent image carrier whose surface is located on a conveyance path of a printing medium is provided, a charger is provided on the surface of the latent image carrier for discharging electricity, and the latent image carrier is charged by the discharge of the charger. The developing device is provided with an exposure device that selectively irradiates the surface of the body with light, and supplies toner with voltage applied to an electrostatic latent image formed on the surface of the latent image carrier by the light irradiation of the exposure device. An electrophotographic apparatus is provided with a transfer device that supplies the print medium with a transfer voltage that attracts the toner image formed on the surface of the latent image carrier by the development of the development device,
An unnecessary development prevention mechanism is provided that connects the power source of the transfer device to the developing device until a portion of the surface of the latent image carrier that is charged by the discharge of the charging device reaches a position facing the developing device. An electrophotographic device featuring: