JP2009031700A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress degradation of image quality such as color shift by uniforming the pressing force of each of a plurality of developing units against a photoreceptor drum. <P>SOLUTION: An electrostatic latent image is formed on the surface of the photoreceptor drum 21. A rotary developing device 22 has developing units 221 having their respective developing rollers 224 for supplying toners to the photoreceptor drum 21, and frames 222 supporting the developing units 221 and moving the developing rollers 224 so as to face the photoreceptor drum 21 by rotating. A plurality of driving mechanisms rotate the corresponding developing rollers 224. A first braking member 230 adjusts the pressing force of each developing roller 224 against the photoreceptor drum, generated due to the driving force of the corresponding driving mechanism. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of forming a color image.

  The image forming apparatus includes a photosensitive drum as an electrostatic latent image carrier on which an electrostatic latent image is formed, and a developing device that supplies toner to the photosensitive drum. The image forming apparatus capable of forming a color image has a plurality of developing units, and each developing unit is provided with a container main body that contains toner of different colors. The container body of the developing device has an opening in a part thereof, and a developing roller for supplying toner to the photosensitive drum is provided in a portion where the opening is provided. Some of such image forming apparatuses have a rotary developing device in which a plurality of developing devices are supported by a rotatable frame for miniaturization.

  In an image forming apparatus having a rotary developing device, when an electrostatic latent image is formed on a photosensitive drum, the frame rotates, and a developing roller disposed in a developing unit that stores toner of the first color is electrostatically charged. It is positioned so as to face the latent image carrier. Then, a toner image of the first color is formed from the developing roller. Thereafter, the developing roller disposed in the developing unit for storing the second color toner is positioned so as to face the electrostatic latent image carrier by rotating the frame. In this way, toner of all colors is supplied to the electrostatic latent image carrier, and the toner image is transferred to the intermediate transfer belt to form a color image.

  Here, there is one in which the rotary developing device itself is urged toward the photosensitive drum side by a torsion coil spring and the developing device is pressed toward the photosensitive drum side (see Patent Document 1).

In this image forming apparatus, the developing unit is pressed against the photosensitive drum with an appropriate pressure, and the photosensitive drum and the developing roller are accurately positioned when the toner is supplied from the developing roller to the photosensitive drum. Yes.
JP 2003-15381 A

  In the color image forming apparatus having the rotary developing device as described above, a gear train for rotationally driving each developing roller is disposed at one end of the developing device. The driving force of the motor is transmitted to the developing roller through the gear train so that the developing roller and the stirring member are rotated.

  In the apparatus having such a structure, when power is transmitted from the motor to the developing roller or the like, the meshing force acts on the meshing portion of the gear of the gear train. By this meshing force, the side end portion where the gear train of the developing device is arranged is pressed to the photosensitive drum side.

  However, in general, in an image forming apparatus, a specific structure is often different for each developing device, and for this reason, a load when driving each developing device is different. Thus, when the load is different, the driving torque of the motor is different, so that the aforementioned meshing force is different, and as a result, the pressing force of the developing device against the photosensitive drum is different. As described above, if the pressing force acting on one end side of the photosensitive drum is different for each developing device, the position of the photosensitive drum is slightly different each time each toner image is formed. The writing position is shifted, and image defects such as color misalignment and oblique images occur.

  The above-described deterioration in image quality cannot be prevented even when the rotary developing device is urged toward the photosensitive drum by a spring as described in Patent Document 1.

  SUMMARY OF THE INVENTION An object of the present invention is to uniformize the pressing force of a plurality of developing devices against a photosensitive drum, and suppress deterioration in image quality such as color misregistration.

  An image forming apparatus according to a first aspect includes an electrostatic latent image carrier, a rotary developing device, a drive mechanism, and a pressing force adjusting unit. An electrostatic latent image is formed on the surface of the electrostatic latent image carrier. The rotary developing device has a plurality of developing units each having a developing roller for supplying toner to the electrostatic latent image carrier, and supports and rotates the plurality of developing units to respectively rotate the developing rollers. And a frame facing the latent image carrier. The plurality of driving mechanisms are mechanisms for rotating and driving each of the developing rollers. The pressing force adjusting means adjusts the pressing force of the developing roller against the electrostatic latent image carrier generated due to the driving force of the driving mechanism.

  In this image forming apparatus, when an electrostatic latent image is formed on the electrostatic latent image carrier, the developing unit that stores the first color toner is opposed to the electrostatic latent image carrier by rotating the frame. Toner is supplied from the developing device to the electrostatic latent image carrier in a state where the electrostatic latent image carrier and the developing device face each other. Thereafter, the frame rotates and the developing device for storing the second color toner faces the electrostatic latent image carrier. In this way, all the developing devices sequentially face the electrostatic latent image carrier, and toner of each color is supplied onto the electrostatic latent image carrier.

  Here, each of the developing rollers is driven by a corresponding driving mechanism. At this time, due to the driving force for driving the developing roller, the pressing force of the developing roller against the electrostatic latent image carrier acts. The pressing force is often different for each of the plurality of developing devices. Therefore, in the present invention, a pressing force adjusting means for adjusting the pressing force of the developing roller against the electrostatic latent image carrier is provided.

  An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the pressing force adjusting means is disposed between at least one of the plurality of developing devices and the frame, and the developing device is stationary. A first brake member is provided that brakes the movement toward the electrostatic latent image carrier to reduce the pressing force.

  Here, by providing the first brake member between the frame and the developing device having a relatively strong pressing force against the electrostatic latent image carrier among the plurality of developing devices, the pressing force of the developing roller having a strong pressing force can be reduced. It can be lowered by the first brake member, and can be made equal to the pressing force of the other developing roller.

  An image forming apparatus according to claim 3 is the image forming apparatus according to claim 1 or 2, wherein each of the plurality of developing devices has a gear train for rotationally driving the developing roller, The adjusting means includes a torque increasing member that increases the pressing force by increasing the torque of the gear train.

  For example, when the rotational load of the developing roller in the developing device is increased, it is necessary to increase the torque for rotating the developing roller and thus the gear train, and the output torque of the motor increases. For this reason, the meshing force of the gear train increases, and as a result, the pressing force of the developing roller against the electrostatic latent image carrier increases. Therefore, in a developing device having a developing roller with a small pressing force against the electrostatic latent image carrier, by providing a torque increasing member that increases the torque of the gear train, the pressing force of the other developing rollers can be made equal. it can.

  An image forming apparatus according to a fourth aspect is the image forming apparatus according to any one of the first to third aspects, wherein the torque increasing member is a second brake member that brakes rotation of the gear train.

  In this case, by braking the rotation of the gear train, the torque for rotating the gear train is increased as described above, and the pressing force of the developing roller against the electrostatic latent image carrier can be increased.

  An image forming apparatus according to a fifth aspect is the image forming apparatus according to the fourth aspect, wherein the developing device includes a developing device frame that supports the developing roller, and the second brake member forms a gear train. Between the developing gear and the developing device frame.

  In this case, the pressing force of the developing roller of the developing device having this gear train can be increased by mounting the second brake member between the gear constituting the gear train and the developing device frame.

  An image forming apparatus according to a sixth aspect is the image forming apparatus according to the fifth aspect, wherein the second brake member has an elastic member that can be elastically deformed.

  In this case, the torque of the gear train can be easily increased and the pressing force can be increased by elastically deforming and mounting the second brake member between the gear constituting the gear train and the developing device frame. be able to.

  An image forming apparatus according to a seventh aspect is the image forming apparatus according to the sixth aspect, wherein the second brake member is provided on a side surface of the elastic member on the gear side, and protects the elastic member for suppressing wear. It further has a sheet.

  Here, when the second brake member is mounted between the gear and the developing device frame, relative rotation occurs between the second brake member and the gear. In this case, it is conceivable that the side surface of the second brake member on the gear side wears out early. Therefore, in the present invention, a protective sheet is provided on the side surface of the second brake member on the gear side, thereby suppressing wear of the elastic member.

  In the present invention, since the means for adjusting the pressing force of the developing roller against the electrostatic latent image carrier is provided, the pressing force of the developing rollers of all the developing devices against the electrostatic latent image carrier can be made uniform. As a result, it is possible to suppress deterioration in image quality such as color misregistration.

[First Embodiment]
1. Overall Configuration FIG. 1 shows a color printer 1 which is an image forming apparatus in which an embodiment of the present invention is adopted. FIG. 1 is a schematic diagram for showing the arrangement of each component, and details of each part are omitted.

  The color printer 1 is connected to a computer (not shown) or the like, and is a device that can print a color image on paper based on image information sent from an external computer or the like. The color printer 1 includes an image forming unit 2 that forms an image on a sheet based on image information, a sheet conveying unit 3 that conveys the sheet, and a fixing unit 4 that fixes an image formed by the image forming unit 2 to the sheet. A paper storage unit 5 for storing paper, a discharge unit 6 for discharging the paper to the outside of the color printer 1, and a toner supply unit 7.

  The image forming unit 2 includes a photosensitive drum 21, a rotary developing device 22, a charging device 23, a laser unit 24, a cleaning device 25, a drive mechanism 26 (see FIG. 2), and a rotation stop mechanism 27 (FIG. 2). And a pressing force adjusting member 230 (see FIG. 3). The rotation developing device 22, the drive mechanism 26, the rotation stop mechanism 27, and the pressing force adjusting member 230 will be described in detail later. Here, FIG. 2 is a diagram showing the rotary developing device 22, the drive mechanism 26, and the like.

  The photosensitive drum 21 is a member on which an electrostatic latent image is formed, and is disposed at the approximate center of the color printer 1. The photosensitive drum 21 is a drum-shaped member, and a rotation shaft is provided in a direction orthogonal to the paper surface of FIG. An intermediate transfer belt 211 for transferring a toner image on the photosensitive drum 21 to a sheet is disposed below the photosensitive drum 21 in the vicinity of the photosensitive drum 21. The charging device 23 is a device for charging the surface of the photosensitive drum 21, and is disposed on the upper side of the photosensitive drum 21. The laser unit 24 is a member disposed on the upper side of the rotary developing device 22 and is a member for irradiating a laser beam to form an electrostatic latent image based on image data on the photosensitive drum 21. It is. The cleaning device 25 is a device for removing deposits such as residual toner remaining on the photosensitive drum 21. In the color printer 1, the cleaning is performed on the entire axial direction of the photosensitive drum 21 above the photosensitive drum 21. A blade is provided.

  The paper transport unit 3 has a transport path that continues from the paper storage unit 5 through the image forming unit 2 and the fixing unit 4 to the discharge unit 6.

  The fixing unit 4 is disposed below the rotary developing device 22 and has a heating roller 41 and a pressure roller 42. The heating roller 41 is a member for melting toner that forms an image formed on a sheet by heat, and is disposed on the upper side of the pressure roller 42.

  The paper storage unit 5 is a part disposed at the lower part of the color printer 1 and has a paper feed cassette 51.

  The discharge unit 6 is disposed on the upper surface of the color printer 1 and places a sheet on which an image is formed.

  The toner replenishing portion 7 is a portion for replenishing toner into the developing device 221 and is disposed on the upper side of the photosensitive drum 21. The toner supply unit 7 includes four toner containers 71 and four toner supply pipes 72 provided corresponding to the toner containers 71. Each of the four toner containers 71 is a box-like member that stores toner to be replenished in the developing device 221, and is arranged in a direction perpendicular to the paper surface of FIG. The toner replenishment pipe 72 is a member that replenishes the toner in the toner container 71 into the developing device 221 and is a pipe-shaped member that extends in one direction. The toner replenishment pipe 72 has an upper retracted position (a position indicated by a solid line in FIG. 1) and a supply position (a dashed line in FIG. 1) where the tip of the toner replenishment pipe 72 enters the inside of the developing device 221 at a lower position. Position). Further, the toner supply pipe 72 has an opening at the tip, and the tip is inserted into the developing device 221 to supply toner into the developing device 221.

2. Rotating developing device 22, brake member 230 as a pressing force adjusting member, driving mechanism 26, rotation stopping mechanism 27
The rotary developing device 22 is a member disposed adjacent to the photosensitive drum 21 and is a cylindrical device as a whole. The rotary developing device 22 includes four developing units 221 and a frame 222 that supports the four developing units 221.

  The developing device 221 includes a container body 223 and a developing roller 224. The container body 223 has a shape in which a cylinder is divided into four in the circumferential direction, and has an opening extending in the longitudinal direction. Further, a support shaft 221a for rotatably supporting the container body 223, that is, the developing device 221 with respect to the frame 222, is provided at the axial end portion of the container body 223 so as to protrude in the axial direction of the developing roller. . Further, the support shaft 221 a is supported by the disk-like member 222 a of the frame 222. When supplying the developer to the photosensitive drum 21, the developing device 221 swings around the support shaft 221 a and presses the developing roller 224 against the photosensitive drum 21. As shown in FIGS. 3 and 4, a first gear train 227 (gear train) and a cover member 228 provided so as to cover the first gear train 227 are disposed on one end side of the container body 223. ing. Here, FIG. 3 is a diagram showing the positions of the container main body 223, the pressing force adjusting member 230, and the first gear train 227, and FIG. 4 shows the side of the developing device 223 on which the first gear train 227 is arranged. It is a figure which shows an edge part. The first gear train 227 includes a first gear 227a, a second gear 227b, and an input gear 227c. The first gear 227a is a gear that meshes with a developing roller gear 224a described later, and is attached to a rotation shaft of a toner supply roller (not shown) that is disposed in the container body 223 and supplies toner to the developing roller 224. The second gear 227b is a gear that meshes with the first gear 227a, and is attached to a rotation shaft of a toner stirring member (not shown) in the container main body 223. The input gear 227 c is a gear that meshes with the second gear 227 b and extends in the rotation axis direction of the rotary developing device 22. The input gear 227c is rotatably attached to the support shaft 221a, and meshes with a gear 229 (see FIG. 2) to which power from a motor (not shown) provided in the main body is input at the developing position. Has been placed. Further, a bearing such as a bush (not shown) is disposed on the inner peripheral side of the input gear 227c. For this reason, when the power of the motor is input to the input gear 227c, the input gear 227c rotates relative to the support shaft 221a. Here, toners of yellow, cyan, magenta, and black are respectively stored in the four container main bodies 223.

  The developing roller 224 extends in the rotation axis direction of the rotary developing device 22 and is disposed in the opening of the container main body 223. The developing roller 224 is a member for supplying toner to the surface of the photosensitive drum 21. A developing roller gear 224a is disposed at the end of the developing roller 224, and the developing roller 224 rotates as the developing roller gear 224a rotates. Further, a spring (not shown) for biasing the developing roller 224 toward the photosensitive drum 21 is disposed. Further, as shown in FIGS. 2 and 3, distance regulating rollers 225 for keeping the distance between the photosensitive drum 21 and the developing roller 224 are disposed at both ends of the developing roller 224. The distance regulating roller 225 is a member on a disk having a larger radius than the developing roller 224.

  The frame 222 is a member in which four plate-like members 226 (see FIG. 1) extending in the same direction as the rotation axis of the photosensitive drum 21 are arranged at equal intervals. Four spaces are formed. Developers 221 are arranged in these four spaces, respectively. In addition, disk-like members 222a (see FIG. 2) are disposed at both ends of the frame 222. The disk-like member 222a is provided with an annular portion 22b, and the annular portion 22b is provided with gear teeth (not shown) on the outer peripheral side.

  A brake member (second brake member) 230 serving as a pressing force adjusting member is an annular member, and in this embodiment, the brake member (second brake member) 230 is attached to a support shaft 221a provided in a container body 223 that stores black toner. It has been. The brake member 230 is disposed in an elastically deformed state between the input gear 227c and the side wall of the container body 223, and is a photoconductor of the developing roller 224 supported by the container body 223 that stores black toner. It is a member for increasing the pressing force toward the drum 21 side. The brake member 230 is formed by laminating elastically deformable poron 230a and PET (polyethylene terephthalate) 230b (protective sheet). The PET 230b is disposed on one surface of the poron 230a, specifically, on the input gear 227c side, and has a smaller coefficient of friction than the poron 230a. For this reason, wear due to the rotation of the brake member 230 relative to the input gear 227c is suppressed.

  2 and 3, the drive mechanism 26 is a mechanism for rotating the rotary developing device 22, and is a second gear train that rotates the drive mechanism side input gear 261 and the drive mechanism side input gear 261. 262 and a motor (drive source) (not shown) to which the second gear train 262 is connected. The drive mechanism side input gear 261 is a member that transmits power from the gear train and transmits the transmitted power to the frame 222, and connects the pair of disk-shaped members 26a and the pair of disk-shaped members 26a. And a shaft member 26b. The pair of disk-shaped members 26 a are formed with gear teeth on the outer periphery that mesh with the gear teeth of the annular portion 22 b of the frame 222. The shaft member 26 b is provided in parallel with the rotation shaft of the rotary developing device 22. The second gear train 262 is a portion for transmitting power from the motor and transmitting the power transmitted from the motor to the drive mechanism side input gear 261, and is configured by a plurality of gears. A motor shaft is fixed to one of the plurality of gears.

  As shown in FIG. 2, the rotation stopping mechanism 27 includes an input cam 271 that is coaxially connected to the drive mechanism side input gear 261, and a locking member 273 that has a protruding portion 272 that locks the input cam 271. Have. The input cam 271 is a member attached to one end of the shaft member 26b of the drive mechanism side input gear 261, and is disposed outside one of the disk-shaped members 26a (see FIG. 2). The input cam 271 is a disk-shaped member, and has two locking portions that are locked to the protruding portion 272 of the locking member 273. The locking member 273 is connected to a support portion 277 supported by the outer frame of the color printer 1, a protruding portion 272 that locks the locking portion of the input cam 271, and a solenoid (not shown). The connecting portion 278 is a flat plate-like member. Further, the protruding portion 272 is biased toward the input cam 271 by an elastic member (not shown).

3. Operation First, the operation of the image forming operation will be briefly described.

  When image data is transmitted from an external computer, the surface of the photosensitive drum 21 is charged by the charging device 23. Then, a laser beam is emitted from the laser unit 24 to the charged surface of the photosensitive drum 21 based on the image data. When the electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 21 in this manner, the developing units 221 are sequentially positioned at positions facing the photosensitive drum 21 while the frame 222 rotates. Here, the input gear 227c meshes with a gear (not shown) to which power is transmitted from the motor, and the input gear 227c is rotated. When the developing unit 221 that stores black toner is located at a position facing the photosensitive drum 21, the brake member 230 is disposed between the input gear 227 c and the container main body 223, so that the input gear 227 c is It is difficult to rotate. That is, in order to rotate the input gear 227c, a large torque (a larger torque than when the brake member 230 is not disposed) is input to the input gear 227c. Then, torque is transmitted from the input gear 227c to the developing roller gear 224a through the second gear 227b and the first gear 227a. When the power is transmitted from the gear to which the power is transmitted from the motor to the input gear 227c, the developing roller 224 is placed between the gear teeth of the gear to which the power is transmitted from the motor and the gear teeth of the input gear 227c. A pressing force acts on the 21 side. By this force, the end of the developing roller 224 on the side where the developing roller gear 224a is disposed is urged toward the photosensitive drum 21 side.

  Here, for example, the developing device torque of the developing device 221 storing black toner in the state where the brake member 230 is not present (force to rotate the developing device 221 around the support shaft 221a) is 1 To 1.2 (kgf · m), and the developing device torque of a developing device 221 (developing device containing yellow, cyan, and magenta toner) that stores color toner is 2.5 (kgf · m). is there. That is, the black developing unit 221 has a smaller pressing force on the photosensitive drum 21 than the other developing units 221. Therefore, as described above, the brake member 230 is attached to the black developing unit 221 so that the developing unit torque is 2 to 2.5 (kgf · m), so that all the developing rollers 224 with respect to the photosensitive drum 21 are used. The pressing force is made uniform. Note that the developer torque differs between the developer containing black toner and other developers. The black image is a magnetic one-component development method, while the color image is a non-magnetic one-component development method. This is because. That is, since the developing system is different between black and color, the developer torque is different.

  As described above, when each color toner is supplied from the developing units 221 to the photosensitive drum 21 to form a color image, the color image is transferred to the sheet conveyed from the sheet storage unit 5 on the intermediate transfer belt 211. Is transcribed through. The sheet on which the color image has been transferred is conveyed to the fixing unit 4 where the color image is fixed on the sheet. When the color image is fixed by the fixing unit 4, the paper on which the color image is fixed is discharged from the discharge unit 6.

  Here, the brake member 230 is disposed between the input gear 227c and the container body 223 of the developing device 221 storing black toner whose developing device torque is smaller than that of the developing device 221 storing other color toner. For this reason, the developing device torque can be made substantially equal to the developing device 221 storing other color toners. For this reason, the pressing force applied by the developing roller 224 to the photosensitive drum 21 is substantially the same for all the developing rollers 224, and the image on the photosensitive drum 21 is difficult to shift for each color. Therefore, the image can be transferred without shifting only black when transferring the image. For this reason, it is possible to prevent deterioration in image quality.

[Second Embodiment]
FIG. 5 shows the rotary developing device 22 provided in the color printer according to the second embodiment. Here, the configuration of the color printer according to the second embodiment is the same as that of the first embodiment except for the rotary developing device 22, and thus the description thereof is omitted. The rotary developing device 22 has substantially the same configuration as that of the first embodiment, but the arrangement of the pressing force adjusting members is different. For this reason, only the pressing force adjusting member will be described.

  A brake member (first brake member) 430 as a second pressing force adjusting member is a rectangular member and is disposed between the cover member 228 of the developing device 221 that stores color toner and the frame 222. . More specifically, the brake member 430 is a cover member corresponding to the outside of the wall surface forming the opening of the container body 223 where the developing roller 224 is supported, specifically, the portion where the developing roller 224 is supported. It arrange | positions between the wall surface of 228, and the disk shaped part 222a of the frame 222 (part shown with the oblique line of FIG. 5). Further, the brake member 430 is formed of poron and brakes the movement of the container main body 223 toward the photosensitive drum 21 by the developing device torque.

  Here, in order to brake the movement of the end portion of the developing roller 224 of the developing unit 221 storing the color toner to the photosensitive drum 21 side, the end side of the developing roller 224 of all the developing units is the photosensitive drum. The force which presses 21 becomes substantially the same. Therefore, the image can be transferred without shifting only black when transferring the image. For this reason, it is possible to prevent deterioration in image quality.

[Other Embodiments]
(A) In the above embodiment, the color printer 1 has been described. However, the present invention is not limited to this, and may be a multifunction machine, a copier, or the like.

  (B) In the above embodiment, the pressing force adjusting member 230 is disposed between the input gear 227c and the wall surface of the container body. However, the present invention is not limited to this, and another gear, such as the first gear 227a or the first gear 227a. The pressing force adjusting member 230 may be disposed between the two gears 227b and the container body 223.

  (C) Further, it is not necessary to use the pressing force adjusting member 230 as the pressing force adjusting means, and it is difficult to rotate the rotating shafts of the developing roller 224 and the toner stirring member, for example, using a heavier material as the developing roller 224 It may be difficult to rotate by the method of.

1 is an overall schematic diagram of a color printer 1. FIG. FIG. 3 is a diagram illustrating a positional relationship among a rotary developing device 22, a photosensitive drum 21, a driving mechanism 26, and the like. The figure showing the edge part by the side of which the 1st gear row | line | column 227 of the developing device 221 is arrange | positioned. The figure which shows the 1st gear train 227. FIG. 10 is a diagram of a rotary developing device 321 according to a second embodiment.

Explanation of symbols

1 Color printer (image forming device)
21 Photosensitive drum (electrostatic latent image carrier)
22 Rotating developer 221 Developer (Developer)
222 Frame 223 Container body 224 Developing roller 224a Developing roller gear 230b PET (protective sheet)
26 Drive mechanism 27 First gear train (gear train)
230 1st brake member (torque increasing member (pressing force adjusting means))
430 Second brake member (pressing force adjusting means)

Claims (7)

An electrostatic latent image carrier on which an electrostatic latent image is formed;
A plurality of developing units each having a developing roller for supplying toner to the electrostatic latent image carrier, and a plurality of the developing rollers supported by the plurality of developing units and rotated to form the electrostatic latent image carrier. A rotary developing device having a frame to be opposed;
A plurality of drive mechanisms for rotationally driving each of the developing rollers;
A pressing force adjusting means for adjusting a pressing force of the developing roller against the electrostatic latent image carrier generated due to a driving force of the driving mechanism;
An image forming apparatus.   The pressing force adjusting means is disposed between at least one of the plurality of developing devices and the frame, and brakes the moving of the developing device toward the electrostatic latent image carrier to reduce the pressing force. The image forming apparatus according to claim 1, further comprising a first brake member. Each of the plurality of developing devices has a gear train for rotationally driving the developing roller,
The pressing force adjusting means includes a torque increasing member that increases the pressing force by increasing the torque of the gear train.
The image forming apparatus according to claim 1.   The image forming apparatus according to claim 3, wherein the torque increasing member is a second brake member that brakes rotation of the gear train. The developing device has a developing device frame for supporting the developing roller;
The second brake member is disposed between a gear constituting the gear train and the developing device frame.
The image forming apparatus according to claim 4.   The image forming apparatus according to claim 5, wherein the second brake member includes an elastic member that is elastically deformable. The image forming apparatus according to claim 6, wherein the second brake member further includes a protective sheet provided on a side surface of the elastic member on the gear side for suppressing wear of the elastic member.

Images