JPH05333675A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to an image forming apparatus which develops by bringing a developer bearing member into pressure contact with a latent image bearing member. It is an object of the present invention to provide an inexpensive contact developing type image forming apparatus that can prevent such a phenomenon. [Structure] The image forming apparatus includes a latent image carrier 1 such as a photosensitive drum.
And a developing device 20 for developing the electrostatic latent image formed on the latent image carrier 1. The developing device 20 includes a developer carrier 21 and a blade 22 for toner thickness regulation and charging.
And a reset roller 23 for rubbing the toner on the developer carrying member. Developer carrier 21
Is pressed against the latent image carrier 1 by the force of Fd, and the blade 22 and the reset roller 23 contact the developer carrier 21 with Fb and Fr.
It is pressed by the force of. In the present invention, the sum of the forces of Fd, Fb and Fr is set to be substantially zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus in which a developer carrying member is pressed against a latent image carrying member for developing.

Electrophotographic printer (image forming apparatus)
Is widely used because high-speed and high-quality printing can be obtained, but recently, there has been a demand for a smaller and cheaper one.
In order to meet this demand, various devices using so-called contact development have been proposed in which a developer (toner) is applied to a developer carrier and the developer carrier is pressed against the latent image carrier to perform development.

[0003]

2. Description of the Related Art FIG. 10 shows a main structure of a conventional electrophotographic printer of this type. In the figure, 1 is a latent image carrier and 2 is a developing device. The latent image carrier 1 is formed by coating a metal tube 1a made of aluminum or the like with a photoconductor 1b such as an organic photoconductor. The developing device 2 includes a developer carrier 3 and a blade 4.
The reset roller 5, the paddle roller 6 and the like are housed in a case 7, and the developer carrying member 3 has a latent image carrying member 1 by means of a spring 8 which biases the case 7 in the arrow direction (to the left). Is pressed against.

The toner contained in the developing device 2 is sent to the developer carrying member 3 side by the paddle roller 6 and rubbed onto the developer carrying member 3 by the reset roller 5. The toner on the developer carrying member 3 is charged while being regulated to a predetermined thickness by the blade 4 pressed against the developer carrying member 3 by the biasing force of the spring 9.

The charged toner is conveyed to the surface of the latent image carrier 1 by the rotation of the developer carrier 3, and the latent image on the latent image carrier 1 is developed by the toner. The latent image is formed on the latent image carrier 1 by charging and exposure by an unillustrated charger and exposure means arranged around the latent image carrier 1.

In such an electrophotographic printer, if the developing device is made small in order to make the apparatus compact, it is necessary to make the diameter of the developer carrier small. If the shaft of the developer carrying member is made thinner as the diameter of the developer carrying member is made smaller, the developer carrying member may bend, and the print density may change between the edge portion and the central portion of the paper. In addition, when the developer carrying member is bent, the end portion of the latent image carrying member wears more than the center portion because the bearing pressure becomes stronger.

As a countermeasure against this, the shaft of the developer carrying member is thickened so that the developer carrying member does not bend. Also,
The developer carrying member is crowned so that the pressing force on the latent image carrying member is evenly distributed even when the developer carrying member is bent.

[0008]

However, since the developer carrier requires elasticity to some extent, the thickness of the elastic body cannot be reduced. Therefore, there is a limit to thickening the shaft of the developer carrying member, and the amount of bending may not be suppressed to the extent that a problem does not occur in print quality. In addition, since crowning requires time and labor, the manufacturing cost is high, and the cost cannot be reduced even if the device is downsized, which is a problem.

It is an object of the present invention to provide an inexpensive image forming apparatus of the contact developing type which can prevent uneven printing due to the deflection of the developer carrying member and uneven wear of the photosensitive member.

[0010]

FIG. 1 is a diagram for explaining the principle of the present invention, in which 1 is a latent image carrier similar to the conventional one, and 20 is a developing device. The developing device 20 includes a developer carrier 21, a blade 22, and a reset roller 23. The developer bearing member 21 is pressed against the latent image bearing member 1 by the biasing force of a spring that biases a case (not shown) accommodating the developer bearing member 21, the blade 22, the reset roller 23, etc. to the left, As a result, the developer carrier 21
Is subjected to the reaction force of Fd on a straight line passing through the centers of both carriers.

Further, the pressing force Fb of the blade 22 and the reset roller 23, which are in pressure contact with the developer carrying member 21, is applied to the developer carrying member 21.
And Fr are working. Here, the direction parallel to the line passing through the centers of both carriers is defined as the x direction, and the direction perpendicular to this is the y direction.
In the direction, when the sum of the components of Fd, Fb, and Fr in the x direction is large, the developer carrying member 21 is bent in the x direction. Therefore, in the present invention, in order to eliminate this deflection, the sum of the components of these forces in the x direction Fx = Fdx + Fbx + F
rx is set to substantially zero.

Further, if the developer carrying member 21 is largely deflected in the y direction, it may cause a problem. Even if this deflection in the y direction occurs, the distance between the developer carrying member 21 and the latent image carrying member 1 does not change much, so the influence is less than in the case of the x direction, but the axis of the developer carrying member 21 is more It becomes a problem when it is thin or long. In such a case, the sum Fy = Fdy + Fby + Fry of the y-direction force components is set to zero. In consideration of the allowable value, the sum of the pressing force is
It suffices that the amount of deflection of the developer carrying member 21 that occurs when the developer carrying member 21 is evenly loaded at a position where the developer carrying member 21 comes into contact with the force is equal to or greater than the allowable value.

[0013]

According to the present invention, since the sum of the forces applied to the developer carrying member 21 is made substantially zero, the developer carrying member can be prevented from sagging, so that the developer carrying member 21 and the latent image carrying member 1 are separated from each other. It comes to contact evenly. That is, a uniform contact pressure can be obtained between the two carrier members without thickening the shaft of the developer carrier or crowning the developer carrier. Therefore,
It is possible to prevent uneven printing due to the deflection of the developer carrying member and uneven wear of the photosensitive member without increasing the cost.

[0014]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 2 is a side view showing the structure of the electrophotographic printer (image forming apparatus) of this embodiment, in which 20 is a developing device and 31 is a developing device.
Is a pre-charger, 32 is a laser optical system, 33 is a transfer device, 34
Is a fixing device, 35 is a static eliminator, and 36 is a cleaner. The developing device 20 is configured by accommodating the developer carrier 21, the blade 22, the reset roller 23, and the paddle roller 24 in a case 25, and by a biasing force of a spring 26 that biases the case 25 to the left, The developer carrier 21 is pressed against the latent image carrier 1.

The pre-charger 31 is for uniformly charging the surface of the latent image carrier 1 (the surface of the photoconductor), and is made of corotron, scorotron, or the like. Laser optical system 3
Reference numeral 1 is for forming an electrostatic latent image by laser scanning on the photoconductor in response to a print signal. The transfer device 33 is for transferring the toner image obtained by developing the electrostatic latent image formed on the photoconductor as described above with the toner conveyed by the developer carrying member 21, to the paper. Corotron is used.

The fixing device 34 is for fixing the toner image on the paper and uses a heat roller. Static eliminator 3
Reference numeral 5 is for erasing (decharging) the latent image by irradiating the photoreceptor with light, and an LED array or the like is used. Cleaner 3
Reference numeral 6 is for removing the toner remaining on the photoconductor, and a cleaning blade, a fur brush or the like is used.

The paper is stored in the paper cassette 37 and is picked up by the pick roller 38 at a predetermined time. The standby roller 39 temporarily stops the fed-out paper, and sends the paper to the transfer position between the latent image carrier 1 and the transfer device 33 at the timing when the toner image is formed on the photoconductor. At the transfer position, the toner image on the photoconductor is transferred to the transfer device 33.
Is transferred onto a sheet by means of a sheet, and then the sheet is sent to a fixing device 34 where the toner image on the sheet is fixed. The sheet on which the fixing is completed is discharged to the stacker 40.

The developer carrying member 21 of the developing unit 20 is made of a conductive shaft made of stainless steel, aluminum or the like, and a conductive rubber or foam (sponge etc.) lined on the shaft. In this example, the diameter is 8 mm. The stainless steel shaft has an outer diameter of 20
A conductive rubber having a rubber hardness of 30 ° was lined so as to have a thickness of mm. The blade 22 is made of a stainless steel plate, and the reset roller 23
Was a conductive shaft lined with a conductive sponge.

The developing device 20 is set on the developing device base 27, and is biased to the left by the spring 26 as described above. As a result, the developer carrier 21 is pressed against the latent image carrier 1 (the latent image carrier 1 presses the developer carrier 21). Further, the blade 22 and the reset roller 23 respectively press the developer carrier 21. In the present invention, in order to eliminate the deflection of the developer carrier due to these pressure contact forces, the x-direction component of each pressure contact force,
The sum of y-direction components is set to be substantially zero. Next, two specific examples for that purpose will be described.

Deflection Prevention Example 1 FIG. 3 is an explanatory view of the configuration of this example. The developing device 20 is pressed against the latent image carrier 1 so that the pressing force of the developer carrier 21 becomes 30 gf / cm. .. Further, the blade 22 and the reset roller 23 are pressed by the force of 26 gf / cm 10 gf / cm at the angles of 30 ° and 45 ° shown in the figure. Here, since the pressing force Fd between the latent image carrier 1 and the developer carrier 21 is 30 gf / cm, in order to make the x component of the sum of the pressing forces zero, the pressing force Fb of the blade 22 is reset. The sum of the components of the pressing force Fr of the roller 23 in the x direction may be set to 30 gf / cm.

Therefore, it is sufficient to set Fb · cos 30 ° + Fr · cos 45 ° = 30. The relationship between Fb and Fr obtained from this equation is shown in FIG. Here, in the case of the present embodiment, the developer carrying member 21
The blade pressing force for forming a uniform developer layer on the top is 20 to 30 gf / cm, and the range within the dotted line can be used. For example, when the blade pressing force Fb is 26 gf / cm, the reset roller pressing force Fr is 10 gf / cm.

The amount of deflection is ideally zero, but there is an allowable range. The allowable range was calculated by the following procedure. First, as shown in FIG. 5, a developer carrying member deflection measuring jig 1
At 00, the amount of bending when the developer carrying member 21 is evenly loaded is measured. The deflection measuring jig 100 includes a developing device fixing means (not shown), a developer carrying member pressing means 101, and a developer carrying member displacement measuring means (not shown).

Although only six springs are used as the pressing means 101, and six springs are used in this example, it is ideal that the developer carrying member is evenly loaded. Therefore, the number of springs should be large. Further, the amount of deflection of the developer carrying member is measured by using displacement measuring means. Therefore, for example, a laser displacement meter is used to measure three points P ₁ , P ₂ , and P _{3 at} the center and both ends.

When measuring the amount of deflection, first, the developing device is fixed and the position of the developer carrying member is measured by a laser displacement meter. Next, the developer bearing member is pressed. At this time,
The pressing means is adjusted so that the load is evenly distributed over the entire length of the developer carrier. After the adjustment of the pressing means is completed, the displacement of the developer carrying member is measured again. The displacement at this time is the deflection δ when the developer carrying member is uniformly loaded. The amount of deflection is measured by changing the pressing force, the developing device is set in the device, and printing is performed.

In this way, the relationship between the flexure amount and the printing is obtained, and the allowable flexure amount is obtained. In the case of this example, the allowable deflection amount was 12 μm. When the relationship between the pressing force and the deflection was obtained only with the developer carrying member, the pressing force at which the deflection amount was 12 μm or less was 10 gf / cm. Therefore, the total force of the pressing force may be 20 to 40 gf / cm, and Fb and Fr may be in the range of the cross hatched lines shown in FIG.

Deflection Prevention Example 2 FIG. 7 is an explanatory diagram of the configuration of this example. This example is different from the above-described deflection prevention example 1 in that not only the deflection in the x direction but also the deflection in the contact surface direction (y direction) between the latent image carrier 1 and the developer carrier 21 is prevented. The pressing force of the developing device was 30 gf / cm, the pressing force of the blade 22 was 22 gf / cm, and the pressing force Fr of the reset roller 23 was 16 gf / cm.
In order to make the sum of the pressing forces zero, it is necessary not only to make the x-direction component of each pressing force sum zero, but also to make the y-direction component zero.

Therefore, it is also necessary to satisfy Fb · sin30 ° −Fr · sin45 ° = 0. FIG. 8 shows the relationship between Fb and Fr in the deflection preventing example 1 to which this condition is added, as shown in FIG. The intersection of the two straight lines in this figure is the condition for Fb and Fr. If this intersection is outside the allowable range of blade pressing, the attachment angle of the blade or the reset roller may be changed to find a point that satisfies the condition.

In the case of this example, there is an allowable range.
The allowable range in the y direction was obtained in the same manner as in the case of the deflection prevention example 1 by changing the blade pressing force Fb and the reset roller pressing force Fr to bend the developing roller. As a result, the allowable pressing force is 10 gf / cm, which is within the cross hatched area shown in FIG.

As described above, according to the present invention, the deflection of the developer carrying member can be prevented by making the sum of the forces applied to the developer carrying member substantially zero, so that the developer carrying member and the latent image can be prevented. The carriers come into even contact with each other. That is, a substantially uniform contact pressure can be obtained between the two carrier members without thickening the shaft of the developer carrier or crowning the developer carrier. Therefore, it is possible to prevent uneven printing due to the deflection of the developer carrier and uneven wear of the latent image carrier without increasing the cost.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a side view showing the structure of the electrophotographic printer of the embodiment of the present invention.

FIG. 3 is a configuration explanatory diagram of a deflection prevention example 1 of the embodiment of the invention.

FIG. 4 shows Fb and Fr of a flexure prevention example 1 according to an embodiment of the present invention.
FIG.

FIG. 5 is an explanatory diagram of a deflection allowable amount setting procedure in deflection prevention example 1 according to the embodiment of the present invention.

FIG. 6 is a diagram for explaining the relationship between Fb and Fr in consideration of the allowable amount of deflection in the deflection prevention example 1 according to the embodiment of the present invention.

FIG. 7 is a configuration explanatory diagram of a second example of deflection prevention according to the embodiment of the present invention.

FIG. 8: Fb and Fr of deflection prevention example 2 of the embodiment of the present invention
FIG.

FIG. 9 is a diagram for explaining the relationship between Fb and Fr in consideration of the allowable amount of flexure in the flexure prevention example 2 of the embodiment of the present invention.

FIG. 10 is a side view showing a main structure of an electrophotographic printer using conventional contact development.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Latent image carrier 20 Developing device 21 Developer carrier 22 Blade 23 Reset roller

Claims (2)

[Claims] 1. A latent image bearing member (1) and a developer bearing member which is brought into pressure contact with the latent image bearing member (1) and develops a latent image on the latent image bearing member (1) with a developer on the surface. (2
1) and a blade (22) which is brought into pressure contact with the developer carrying member (21) to uniformly apply the developer to the developer carrying member (21).
And an image forming apparatus including a reset roller (23) which is brought into pressure contact with the developer carrying member (21) to uniformize unevenness of the developer layer on the developer carrying member (21) caused by development. In the pressure forces of the latent image carrier (1), the blade (22) and the reset roller (23) that press the developer carrier (21), at least the latent image carrier (1) An image forming apparatus, wherein the sum of pressing forces in a direction perpendicular to the pressure contact surface of the developer carrying member (21) is substantially zero. 2. The image forming apparatus according to claim 1, wherein the sum of the pressing forces is generated when the developer carrier (21) is evenly loaded at a position where it contacts the latent image carrier (1). An image forming apparatus characterized in that a deflection amount of a carrier (21) is equal to or less than an allowable force.