JP3158222B2 - Image forming device - Google Patents

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 for performing development by pressing a developer carrier against a latent image carrier.

[0002] Electrophotographic printer (electrophotographic apparatus)
Is widely used because high-quality printing can be performed at high speed. Recently, a small and inexpensive printer of this type has been demanded. To meet this demand, a developer (toner) is applied to a developer carrier, and the developer carrier is charged with a latent image. An apparatus using so-called contact development in which development is performed by pressing against a body has been proposed.

[0003]

2. Description of the Related Art FIG. 7 schematically shows the structure of a conventional electrophotographic printer using contact development. In the figure, 1 is a latent image carrier and 2 is a developing device. The latent image carrier 1 is configured by applying a photoreceptor such as an organic photoreceptor to the surface of a metal tube made of aluminum or the like. The developing device 2 includes a developer carrier 21, a blade 22, a reset roller 23, a paddle roller 24, and a case 25.

The toner contained in the case 25 of the developing device 2 is rubbed against the developer carrier 21 by a reset roller 23. The toner on the developer carrier 21 is charged while being regulated to a predetermined thickness by the blade 22.
The charged toner is conveyed to the surface of the latent image carrier 1 by the rotation of the developer carrier 21 pressed against the latent image carrier 1, and the latent image on the latent image carrier 1 is developed. Although not shown, the developing device 2 is pressed against the latent image carrier 1 by an urging means in order to press the developer carrier 21 against the latent image carrier 1.

By the way, when the developing device is made smaller in order to reduce the size of the apparatus, the diameter of the developer carrying member needs to be reduced. If the axis of the developer carrying member is made thinner as the diameter of the developer carrying member becomes smaller, the developer carrying member may bend and the print density may change between the end portion and the center portion of the sheet. Further, when the developer carrying member is bent, the pressing force is stronger at the end portion than at the center portion, so that the end portion of the latent image carrying member may be more worn.

As a countermeasure, the shaft of the developer carrying member is made thick to prevent the developer carrying member from bending. Also,
The developer carrier is subjected to crown processing so that the distribution of the pressing force on the latent image carrier becomes uniform even if the developer carrier is bent.

[0007]

However, since the developer carrier needs to have some elasticity, the thickness of the elastic body formed on the outer periphery of the shaft cannot be reduced. Therefore, there is a limit in increasing the thickness of the shaft of the developer carrying member, and in some cases, the amount of flexure cannot be suppressed to the extent that no problem occurs in print quality. In addition, crown processing is troublesome and increases the production cost, and the price cannot be reduced even if the apparatus is downsized.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a low-cost image forming apparatus capable of realizing miniaturization without causing uneven printing of the photosensitive member or uneven wear of the photosensitive member due to bending of the developer carrying member.

[0009]

FIG. 1 (FIG. 1 (A) is a schematic diagram of the configuration, FIG. 1 (B) is an explanatory diagram of the operation) and FIG. 1 is a diagram illustrating the principle of the present invention, in which 101 denotes a latent image carrier. And 102, a developer carrying member. Each of these carriers forms a main part of the image forming apparatus. The developer carrier 102 is directly
It has a cylindrical shape with a substantially constant diameter and is supplied to the surface.
The latent image on the latent image bearing member 101 intended to developing <br/> by carrying the developer, is driven by a drive member 65 which receives the transmission of the driving force is fixed in said developer carrying member 102 coaxially.

[0010] central axis 1 ₂ and the center axis 1 ₁ of the image bearing member 101 of the developer carrying member 102 is set to be mutually twisted position. This twist position is determined by the positions of the two carriers 10.
1 and 102 absorb at least one of the deflections when they are pressed against each other, so that each of the carriers 101 and 102 extends along the axial direction.
Substantially as uniform pressing force can be obtained, and the amount of deflection due to the pressing force of the developer carrying member 1 0 2 latent image carrier was 1 0 1 or measured in advance, the latent image bearing at the central portion by twisting positions me and spacing of the body 1 0 1 and the developer carrying member 1 0 2, the difference in distance between the latent image bearing member 1 0 1 at both the end portions and the developer carrying member 1 0 2 is set to be substantially equal I have.

Further, as the driving member 65, a helical gear can be used. In this case, the direction of the helical teeth is a direction in which the thrust force generated by disposing the two carriers 101 and 102 at the twist position is canceled. Note that a pulley driven by a belt may be used as the driving member.

[0012]

[Action] l_ThreeDenotes a latent image passing through the center of the developer carrier 102
Center line l of body 101₁Is a line parallel to. Conventionally supported on both sides
The centers of the bodies 101, 102 were parallel. That is, l
_TwoAnd l_ThreeWas consistent. In contrast, in the present invention,
The amount of deflection generated by pressing the carriers 101 and 102
The central axes of both carriers 101 and 102 are adjusted
Have been placed.

Therefore, as shown in FIG. 1B, the contact portion 103 of the developing carrier 102 on the latent image carrier 101 becomes convex, and the two carriers 101 and 102 come into substantially uniform contact. . That is, a substantially uniform contact pressure can be obtained without increasing the width of the shaft of the developer carrying member or performing crown processing on the developer carrying member. 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.

Further, if the above-mentioned helical gear is used as the driving member, the thrust force generated by the twist position can be canceled.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 is a side view of the electrophotographic printer (image forming apparatus) of the present embodiment. In the figure, reference numeral 31 denotes a photosensitive drum (latent image carrier), and 32 denotes a developing device. The photosensitive drum 31 is formed by applying a photosensitive member such as an OPC to an aluminum tube, and has a precharger 33, a laser optical system 34, a developing device 32, a transfer device 35, a static eliminator 36, and a cleaner 37 around the photosensitive drum. Is arranged. Reference numeral 38 denotes a sheet storage unit, 39 denotes a pick roller, 40 denotes a fixing device, and 41 denotes a stacker.

The pre-charger 33 is for uniformly charging the surface of the photoreceptor, and uses a corotron, a scorotron, or the like. The laser optical system 34 is for forming an electrostatic latent image by laser-scanning the photoreceptor with a print signal. The developing device 32 is for developing the electrostatic latent image by attaching toner to the electrostatic latent image formed on the photosensitive drum 31. The transfer device 35 includes the photosensitive drum 3
A corotron is used to transfer the toner image formed on the sheet 1 to a sheet.

The fixing device 40 is for fixing a toner image on paper, and uses a heat roller. Static eliminator 36
Is for irradiating the photosensitive drum 1 with light to remove a latent image, and an LED array or the like is used. Cleaner 37
Is for removing the toner remaining on the photosensitive drum 31 after the transfer, and a cleaning blade, a fur brush or the like is used.

The developing device 32 comprises a developing roller (developer carrier) 42, a charging blade 43, a reset roller 44, a paddle roller 45, and a case 46 as in the prior art. It is being rushed. As a result, the developing roller 42 is in pressure contact with the photosensitive drum 31. The developing roller 42 is formed by lining a conductive shaft 42a of stainless steel, aluminum or the like with a conductive rubber or foam (such as a sponge).
A conductive rubber 42b having a rubber hardness of 30 ° is lined with a stainless steel shaft having a diameter of 8 mm so as to have an outer diameter of 20 mm.

The charging blade 43 is made of a stainless steel plate.
It is pressed against the developing roller 42 at 0 gf / cm. Further, the developing device 32 presses the photosensitive drum 3
1 is pressed so that the pressure contact force of the developing roller 42 with respect to 1 is 30 gf / cm. Further, by changing the height of the front and back of the developing device table 48 that supports the developing device 32,
The central axis of the photosensitive drum 31 and the central axis of the developing roller 42 are mutually twisted. Next, three examples of the deflection correction will be described.

(1) Example 1 of Deflection Correction The height difference between the front and the back of the developing unit table 48 for correcting the deflection is determined as follows. First, as shown in FIG. 3, the amount of deflection when the developing roller 42 is uniformly loaded is measured by the developing roller deflection measuring device 51. The developing roller deflection measuring device 51 includes a measuring device fixing procedure (not shown), a plurality of developing roller pressing means 52, and a developing roller displacement measuring means (not shown). The developing roller pressing means 52 is a spring only, and in this example, six are used, but ideally,
Since it is better to load the developing roller evenly, the number of springs is better.

Further, as a developing roller displacement measuring means,
Using a laser displacement meter, three points P ₁ and P at the center and both ends
Make measurements at _2, P _3.

In measuring the amount of deflection, the developing device is fixed, and the position of the developing roller is measured by a laser displacement meter.
Next, the developing roller is pressed. In this case, the developing roller pressing means 52 is adjusted so that a uniform load is applied over the entire length of the developing roller. The pressing force at this time is made equal to the force with which the developing device is pressed by the device. In this example, 30 gf / cm
The developing roller pressing means 52 was adjusted such that

After the adjustment of the developing roller pressing means 52 is completed, the displacement of the developing roller is measured again. The displacement at this time is the deflection δ when the developing roller is evenly loaded. As a result of measurement, P ₂ and P ₃ were 250 mm, and δ = 36 μm. The height difference between the front and the back of the developing unit table 48 can be determined from this δ. The procedure will be described with reference to FIG.

First, a horizontal line passing through the center O of the photosensitive drum 31 is drawn, and a perpendicular line is drawn from the center by δ from the intersection P of the drum surface and the horizontal line. The height from the horizontal line at the center of the developing roller 42 in contact with the drum surface at the intersection Q between the perpendicular and the drum surface is defined as h. As a result, the developing roller 42 moves the displacement measurement positions (P ₂ , P ₃ ) at both ends of the photosensitive roller 31
It can be understood that the arrangement should be made such that the center line is shifted by ± h up and down from the center line. In this example, the diameter of the photosensitive drum 31 is 80 mm
And h = 2.0.

Accordingly, the developing unit table 48 is moved to the position P ₂ at 2.
Becomes the 0 mm, it will be arranged to be under 2.0mm at P ₃ position. By doing so, the pressure contact force between the photosensitive drum 31 and the developing roller 42 can be made substantially uniform, and good printing without uneven printing density can be obtained.

(2) Deflection Correction Example 2 Even when the shaft of the developing roller is thick and almost no deflection occurs, the photosensitive drum may be bent when the thickness of the photosensitive drum is small. In this case, the deflection amount of the photosensitive drum may be measured instead of the developing roller of the first correction example, and the height difference ± h may be determined from the cross section of the developing roller.

Specifically, the diameter of the photosensitive drum 31 is 40
The device having a diameter of 1 mm and a wall thickness of 1 mm was mounted on the apparatus, the developing device was removed from the apparatus, and the amount of deflection δ was determined by pressing the device at the developing roller contact position by pressing means. The result was 53 μm. As a result, h was 2.1 mm, and uniform printing without uneven print density was obtained by raising the front side of the developing unit table by 2.1 mm and lowering the rear side by 2.1 mm.

[0029] (3) Deflection Correction Example 3 Further, when the photosensitive drum, the deflection in both the developing roller occurs, the sum of both the [delta] by measuring the amount of deflection [delta] _d of deflection amount [delta] _p and the developing roller of the photosensitive drum Then, h for correcting the deflection is obtained from the cross-sectional shape of the photosensitive drum.

Specifically, the developing roller of the first correction example and the photosensitive drum of the second correction example were used. Developing roller deflection δ _d
Is 36 μm and the amount of deflection δ _p of the photosensitive drum is 53 μm, so that δ is 89 μm. The photosensitive drum diameter is 40
mm, h is 2.8 mm. By raising the front of the developing unit base by 2.8 mm and lowering the back side by 2.8 mm, uniform printing without uneven printing density was obtained and uneven wear of the drum was also eliminated.

In the above example of the deflection correction, h is set so that the deflection amount of the developing roller or the photosensitive drum matches the deflection correction amount. However, in the case of the developing roller used in the deflection correction example, h is actually set. And uniform printing can be obtained even if there is a deflection of about ± 20 μm. That is, the deflection correction amount is: deflection amount δ−20 μm ≦ deflection correction amount ≦ deflection amount δ + 2
Within the range of 0 μm, uniform printing is obtained, and in the case of the deflection correction example (1); h = 1.4 to 2.6 mm; in the case of the deflection correction example (2); h = 1.7 to 2. 5 mm, in the case of the deflection correction example (3); h = 2.5 to 3.1 mm, uniform printing can be obtained.

By the way, in the present invention, since the shaft of the photosensitive drum and the shaft of the developing roller are mounted at the twisted positions, it is sometimes necessary to consider driving. Normally, the backlash between the gears absorbs the inclination, and smooth driving is performed. However, care must be taken when the inclination is large. Specific examples for that purpose are shown in FIGS. In the case of FIG. 5, the developing roller 42 is driven by a motor (drive source) 61 provided in the developing device via a belt 62 and a pulley 63 (drive member). In this case, the developing roller 4
Even if 2 is installed at the twist position, smooth driving is performed. As the belt 62, a round belt, a flat belt,
A V-belt can be used, and in the case of a flat belt, a crowned pulley is used.

In the case of FIG. 6, the developing roller is provided with a helical gear (drive member) 65 coaxially.
Helical gear 64 for connecting the
It rotates by driving.

If the inclination of the mounting of the developing roller driven by such a driving system is large, thrust is generated in the direction indicated by the arrow in FIG. In such a case, the problem is solved by using a helical gear for the drive system as shown in FIG. 7 and setting the direction of the helical gear of the helical gear to the direction in which the force in the thrust direction is canceled. can do.

[0035]

As described above, according to the present invention, by disposing the central axis of the latent image carrier and the central axis of the developer carrier at the twisted position, the developer carrier of the latent image carrier is provided. The contact position of the developer carrier or the contact position of the developer carrier with the latent image carrier has a convex shape. Therefore, even if the developer carrier or the latent image carrier is bent, a substantially uniform load distribution can be obtained, and an inexpensive and compact image forming apparatus free from uneven printing and uneven wear of the photoconductor can be obtained. Further, the developer carrier is driven by a helical gear and the direction of the helical teeth is appropriately set, thereby canceling out the thrust force generated by the twist position.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams illustrating the principle of the present invention, in which FIG. 1A is a schematic configuration diagram and FIG.

FIG. 2 is a side view of the electrophotographic printer according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a developing roller deflection measuring procedure according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a procedure for setting a developing roller position from a cross section of a photosensitive drum according to the embodiment of the present invention.

FIG. 5 is a side view showing a developing roller driving mechanism according to the embodiment of the present invention.

FIG. 6 is a perspective view illustrating a developing roller driving mechanism according to the embodiment of the present invention.

FIG. 7 is a side view showing an outline of the structure of a conventional electrophotographic printer.

[Explanation of symbols]

 31, 101 Photosensitive drum (latent image carrier) 32 Developing device 42, 102 Developing roller (developer carrier) 63 Pulley (drive member) 65 Helical gear (drive member)

Claims (3)

(57) [Claims] 1. A latent image carrier (101), which is disposed so as to be in pressure contact with the latent image carrier (101);
By the developer applied to the surface, the latent image carrier (10
With even a developer carrying member for developing a latent image on 1) and (102) small <br/> without the developer carrier (102), said developing agent carrier (10
While being driven by 2) and is fixed coaxially receiving the transmission of the driving force driving member (63), the central axis of the developer carrier (102), the central axis of the latent image bearing member (101) is In an image forming apparatus located at a mutually twisted position
The developer carrier (102) has a columnar shape with a substantially constant diameter.
And the latent image carrier (101) measured in advance
Alternatively, bending due to the pressing force of the developer carrying member (102) is performed.
The latent image holding at the center by the amount of twist and the twist position
The distance between the body (101) and the developer carrier (102);
The latent image carrier (101) at the end and the developer carrier (1)
02), the torsional position that makes the difference between
Image forming apparatus being characterized in that disposed. 2. The image forming apparatus according to claim 1, wherein the twist position is at least one of the respective carriers (101, 102) when the developer carrier (102) is pressed against the latent image carrier (101). One of the supports (101, 101) absorbs one of the deflections .
102) An image forming apparatus which is set so as to obtain a substantially uniform pressing force along the axial direction . 3. The image forming apparatus according to claim 1, wherein a helical gear is used for the driving member (65), and the direction of the helical gear of the helical gear is set to be equal to that of the latent image carrier (101). An image forming apparatus, wherein a direction in a thrust direction generated by disposing the developer carrier (102) at a twist position is canceled.