JPH1130894A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the useless consumption of a photoreceptor drum in a tandem image forming device. SOLUTION: This image forming device has structure where the motive power of a motor 54 is transmitted by worms 42K to 42C attached to a worm shaft 50 and worm wheels 43K to 43C meshed with the worms 42K to 42C, and the photoreceptor drums 41K to 41C provided coaxially with the worm wheels 43K to U3C are driven to be rotated. In the device, the photoreceptor drum 41K for forming a black image is arranged to be positioned nearest to the motor 54, and a clutch 53 is made to intervene in the worm shaft 50 part between the photoreceptor drum 41K and the adjacent photoreceptor drum 41Y, then the clutch 53 is disengaged in a monochrome mode and it is connected in a color mode, so that the motor 54 is controlled to be driven.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving apparatus for an image forming apparatus, and more particularly to a so-called tandem type image forming apparatus in which a plurality of image carriers such as photosensitive drums are arranged along a recording sheet conveying direction. It relates to the improvement of the structure.

[0002]

2. Description of the Related Art Tandem-type image forming apparatuses have attracted attention in recent years as being capable of high-speed color printing. As an image forming apparatus of this type, for example, in a color copying machine, a recording sheet is conveyed by a conveying belt stretched by a plurality of rollers, and four sheets arranged for each color along a conveying path while conveying the recording sheet. The toner image composed of cyan, magenta, yellow, and black is sequentially transferred onto a recording sheet by the photosensitive drums, and a color image is formed by superimposing the respective colors.

As a driving structure of these photosensitive drums, a structure using a meshing structure of a worm and a worm wheel has been devised. That is, a worm wheel is provided on one end side of the rotating shaft of each photosensitive drum, and a worm is attached to a drive shaft installed along the recording sheet conveyance path at a position where the worm wheel meshes with each worm wheel. By rotating the drive shaft, each photosensitive drum is driven to rotate simultaneously. As a result, all the photosensitive drums can be driven by one motor, a large reduction ratio can be obtained with a small number of parts, and vibration is reduced compared to a case where a reduction mechanism using other types of gears is employed. The occurrence of vibration is extremely small, and the adverse effect of vibration on image formation can be eliminated as much as possible.

[0004]

However, in the above-described photoconductor drum driving structure, all four photoconductor drums are always rotated, so that they are not used for image formation even during monochrome copying. Even the photosensitive drums for cyan, magenta, and yellow rotate, and the photosensitive drums and cleaning blades provided in contact with the photosensitive drums are worn out.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention can prevent unnecessary wear of a photosensitive drum and the like in an image forming apparatus having a drive structure for driving an image carrier by a meshing structure of a worm and a worm wheel. It is an object to provide a simple image forming apparatus.

[0006]

In order to achieve the above object, an image forming apparatus according to the present invention comprises a worm shaft having a plurality of worms formed on a shaft and one end of which is connected to a driving source. A worm wheel is attached to a plurality of image carriers arranged along the recording sheet transport path, and each worm wheel is meshed with each worm on the worm shaft. In the image forming apparatus having an image carrier driving structure, the plurality of image carriers are arranged such that an image carrier for forming a black image is located closest to a driving source, and the black A clutch is inserted in a worm shaft portion between the forming image carrier and an adjacent image carrier, and the clutch is turned on and off in synchronization with switching between the monochrome mode and the color mode. I do.

Further, the image forming apparatus according to the present invention has a rotation position detecting means for detecting a rotation position of a worm wheel attached to the black image forming image carrier, and a detection when the clutch is disengaged. Storage means for storing a rotation position, wherein the clutch is engaged in a state where the rotation position detected by the rotation position detection means matches the rotation position of the worm wheel stored by the storage means. .

Further, the image forming apparatus according to the present invention further comprises a conveying means for driving the conveying belt by a driving roller to convey the recording sheet placed on the conveying belt along the conveying path. The distance between the corresponding image carriers in the direction of the transport path is set to an integral multiple of the distance traveled by the transport belt when the drive roller makes one rotation.

[0009] In this specification, "worm wheel"
The term is used in the concept including all gears that transmit power by meshing with a worm, for example, helical gears and the like. Hereinafter, a pair of the worm and the worm wheel is referred to as a “worm gear”.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described by taking as an example a case where the present invention is applied to a digital full-color copying machine. FIG. 1 shows a front view of the digital full-color copying machine (hereinafter, simply referred to as "copying machine").

This copying machine is a so-called tandem-type copying machine. The copying machine includes a sheet cassette 12 which is set in a right side wall 11 of a housing 10 so as to be freely inserted into and removed from the left side wall 1 of the housing.
3, a conveyor belt 31 is installed horizontally in the lower space of the housing up to the paper discharge tray 14 attached in an outwardly protruding posture. 4) imaging units 40C, 40M,
40Y and 40K are arranged in line, and the toner image of each color component is transferred onto the recording sheet S by each image forming unit while the recording sheet S is transported by the transport belt 31, and a color image is formed by superimposing each color. It is.

An image reader 15 is provided at the upper part of the housing 10.
The original image optically read here is subjected to required image processing in the image processing unit 16 to obtain each color of Y (yellow), M (magenta), C (cyan), and K (black). The image forming unit 40C
The laser diodes 18C to 18K of the optical units 17C to 17K disposed above the light components 40K to 40K are optically modulated based on the respective color component signals. The light-modulated laser light is scanned in the main scanning direction by the polygon mirrors 19C to 19K, and is introduced into the image forming units 40C to 40K for the corresponding color components. The image forming units 40C to 40K include the photosensitive drum 41
An electrostatic charger formed by exposing a photosensitive drum rotating in the direction of arrow c with a laser beam modulated by arranging a charging charger, a developing machine and the like around C-41K. This is a unit structure for forming an image by a so-called electrostatic copying method in which a latent image is visualized as a toner by a developing machine. The developing unit of each unit is an optical unit 17.
C, M, Y, K corresponding to the light modulation color components of C to 17K
Is supplied to the photosensitive drum as a developer.

The transfer charger 2 is located directly below the photosensitive drum of each of the image forming units 40C to 40K via a conveyor belt.
0C to 20K, so that the toner image on the surface of the photosensitive drum is transferred to the recording sheet S on the conveyor belt 31. The transport belt 31 is stretched between a driving roller 32 and a driven roller 33, and the driving roller 32
When the conveyor belt 31 is rotated in the direction of arrow a,
Drive in the direction of.

The intervals between the photosensitive drums 41C to 41K are arranged such that the transfer position of the toner image is an integral multiple of the distance traveled by the conveyor belt 31 when the drive roller 32 makes one rotation. In the present embodiment, the interval between the photosensitive drums 41C to 41K is equal to the travel distance of the transport belt corresponding to one rotation of the drive roller 32 (that is, 1
Times).

Next, referring to FIG.
The driving mechanism of the driving rollers 32 and C to 41K will be described. FIG. 2 is a diagram illustrating a schematic configuration of a driving mechanism of the photosensitive drums 41C to 41K and the driving roller 32. As shown in the figure, worm wheels 43C to 43K and 32 are attached to the front ends of the rotating shafts (not shown) of the photosensitive drums 41C to 41K and the driving roller 32.

A worm shaft 50 is laid in parallel with the direction in which the conveyor belt 31 is stretched (that is, the direction in which the recording sheet is conveyed).
Worms 42C-42 meshing with 3C-43K, 32
K and 35 are provided. The left end of the worm shaft 50 is connected to an output shaft of a stepping motor 54, and a well-known electromagnetic member is attached to the worm shaft 50 between the photosensitive drum 41K for black image formation and the adjacent photosensitive drum 41Y. A micro clutch 53 (hereinafter, simply referred to as “clutch 53”) is interposed. That is, the worm shaft 50 is
The first worm shaft 51 is divided into a first worm shaft 51 and a second worm shaft 52 at an insertion position of the clutch 53.
The transmission of the power of the motor 54 transmitted through the second worm shaft to the second worm shaft is interrupted by the clutch 53.

Each worm gear is set such that when the worm shaft 50 is turned in the direction of arrow d, each worm wheel is turned in the direction of arrow e or f, respectively. In addition, the size of the diameter of each of the photosensitive drums 41C to 41K and the drive roller
2 in consideration of the size of the diameter and the thickness of the conveyor belt 31, etc.
The speed reduction ratio of each worm and worm wheel is determined. In the present embodiment, each of the photosensitive drums 41C to 41K
And the length of the drive roller 32 plus the thickness of the conveyor belt 31 in the stretched state are all set to be the same, and the same parts are used for each worm and each worm wheel. I do. By doing so, the cost can be reduced by sharing the parts.

A resin molded product is used for the worm wheel. By using a resin molded product, it is possible to further reduce the cost by mass production and reduce the occurrence of vibration during power transmission. However, while the resin molded article has the above advantages, it is slightly deformed due to the manufacturing method. When power is transmitted by the deformed worm wheel to drive the photosensitive drum, the peripheral speed of the photosensitive drum varies with one rotation of the worm wheel as one cycle. If the fluctuation phases do not match between the photosensitive drums, a color shift occurs in the finished image. However, since the deformation appears uniformly on each molded product, markings such as recesses (hereinafter simply referred to as "markings") 44C to 44K are provided near the outer periphery as a part of the shape of the worm wheel, and each marking is performed. The worm gears are assembled such that are aligned in one direction (upward in FIG. 2). By doing so, the fluctuation phases of the peripheral speed between the respective photosensitive drums match, and color shift can be prevented.

A rotary encoder 44 is provided between the photosensitive drum 41K for forming a black image and the worm wheel 43K. The rotary encoder 44 includes a slit plate 45 attached to the drive shaft of the photosensitive drum 41K, and a photocoupler 46 having a light-emitting element and a light-receiving element opposed to each other with the slit plate 45 interposed therebetween. Slit plate 4 rotated by coupler 46
5 (not shown), and a CPU 6 described later.
2 (FIG. 3), a pulse signal (encoder pulse) is output. In addition, N slits are provided in a line at equal intervals along the outer periphery of the slit plate.

An operation panel 61 (FIG. 3) is provided at a position on the front of the copying machine where it can be easily operated. The operation panel is
In addition to various input keys such as a copy start key for instructing the start of copying, a numeric keypad for setting the number of copies, and a mode switching key for switching between monochrome mode and color mode, a display unit for displaying the set contents is provided. Have. Here, the monochrome mode is a mode in which an image is formed using only the photosensitive drum 41K for forming a black image, and the color mode is a state in which all of the four photosensitive drums 41C to 41K can be used. Refers to a mode in which an image is formed.

Next, the drive control section 60 for controlling the drive of the photosensitive drums 41C to 41K and the drive roller 32 will be described with reference to the block diagram shown in FIG. As shown in the figure, the drive control unit 60 includes a main control unit 71 that controls the entire copying machine with the CPU 62 at the center.
Operation panel 61, photo coupler 45, RAM 63, RO
An M64, a motor control circuit 65, and a clutch 53 are connected, and the CPU 62 controls according to a program stored in the ROM 64.

The RAM 63 is a work area for executing a program, and has a mode setting flag and a mode instruction flag. The mode setting flag is a flag indicating the current setting mode, and the flag is 0
Indicates that the monochrome mode is set, and 1 indicates that the color mode is set. The mode instruction flag is a flag indicating the mode instructed from the operation panel 61. When the flag is 0, the monochrome mode is indicated, and when the flag is 1, the color mode is indicated. CPU62
Determines the necessity / unnecessity of mode switching by comparing both flag states.

The motor control circuit 65 is a known control circuit for controlling the drive of the stepping motor 54 in accordance with the speed setting signal input from the CPU 62. here,
The speed setting signal is given as a pulse train, and the motor control circuit 6
5 receives a pulse once, the stepping motor 5
4 is rotated by one step angle. Therefore, the CPU 62
Is shorter, the stepping motor 54 is rotated at a higher speed.

The CPU 62 receives an instruction from the main control unit 71 and the operation panel 61 and an encoder pulse from the photocoupler 45, and performs drive control of the motor 54 and release / connection control of the clutch 53. Subsequently, FIGS. 4 and 5
The control contents of the drive control unit 60 will be described based on the flowchart shown in FIG.

FIG. 4 is a flowchart showing a rotational position detecting routine for detecting the rotational position of the worm wheel 43K. This routine is started when the power of the copying machine is turned on, and is independent of other routines. Executed. First, when the power of the copying machine is turned on (step S1).
And Yes), the CPU 62 resets an internal counter (hereinafter simply referred to as “counter”) to 0 (step S).
2) Every time an encoder pulse is input from the photocoupler 46 (Yes in step S3), the counter value is incremented (step S4). When the counter value reaches the number N of slits of the slit plate 45 (Yes in step S5), the counter is reset to 0 again (step S2), and thereafter, steps S2 to S5 are repeated. Therefore, by referring to the counter value, it is possible to know the rotational position such as how much the worm wheel is rotated from the reference position based on the position when the power is turned on.

The flowchart of FIG.
1C to 41K and a drive control routine for controlling the drive of the drive roller 34. The routine is started by an instruction from the main control unit 71. First, with reference to the mode setting flag, it is determined whether or not the monochrome mode is set (step S11). If the monochrome mode is not set (mode setting flag = 1),
Proceeding to step S12, referring to the mode instruction flag,
It is determined whether or not it is necessary to switch from the color mode to the monochrome mode. If it is determined that the mode is necessary (mode instruction flag = 0), the counter value at that time is read (step S).
13) At the same time, the counter value is stored in the RAM 63 (step S14), and at the same time, the clutch 53 is disengaged (step S15), the mode setting is set to the monochrome mode (step S16, the mode setting flag is set to 0), and the motor 54 is started (step S17). Step S12
When it is determined that there is no need to switch from the color mode to the monochrome mode (mode instruction flag = 1), steps S13 to S16 are skipped and the motor 54 is started (step S17).

On the other hand, if it is determined in step S11 that the monochrome mode has been set (mode setting flag =
0), proceeding to step S18, referring to the mode instruction flag, determining whether or not it is necessary to switch from the monochrome mode to the color mode. If it is determined that it is necessary (mode instruction flag = 1), the motor 54 is started (step S18). S1
9) When the counter value matches the counter value stored in the RAM 63 (Yes in step S20), the motor 54 is stopped (step S21), the clutch 53 is engaged (step S22), and the mode setting is changed to color. The mode is set (step S23, the mode setting flag is set to 1), and the motor 54 is started (step S1).
7). If it is determined in step S18 that there is no need to switch from the monochrome mode to the color mode (mode instruction flag = 0), steps S19 to S23 are skipped and the motor 54 is started (step S17).

When the motor 54 is started in step S17, an input of an image forming process end signal from the main control unit 71 is input (Yes in step S24), and the motor 5 is turned on.
4 is stopped (step S25), and the process returns. The image forming process end signal indicates, for example, that the transfer of the toner image onto the recording sheet has been completed, the trailing edge of the conveyed recording sheet has been detected by a detection sensor provided above the drive roller 32, and the conveyance by the conveyance belt 31. Is entered when is no longer needed.

As described above, according to the image forming apparatus of the present embodiment, the image formation in the monochrome mode (Yes in step S11, No in S18 or No in step S11, Yes in S12) Since the transmission is performed with the clutch 53 disconnected, the transmission of the driving force of the motor 54 is disconnected by the clutch 53, and the photosensitive drums 41Y, 41M, and 41C that are not used for image formation are not driven. Unnecessary consumption of the photosensitive drum and the like caused by the rotation can be prevented.

The worm wheels attached to the rotating shafts of the respective photosensitive drums are mounted such that the deformation directions thereof are the same for all the photosensitive drums.
Is connected at the same position as the rotational position of the worm wheel 43K at the time of disengagement. Therefore, even if the clutch is interrupted by switching the mode, when forming an image in the color mode, all the worm wheels are always The deformation directions of the worm wheels coincide with each other, and color misregistration caused by the deformation of the worm wheel can be prevented.

Further, the intervals between the photosensitive drums 41C to 41K are arranged such that the transfer position of the toner image is the same as the distance that the conveyor belt 31 travels when the drive roller 32 makes one rotation. A fluctuation cycle of the traveling speed of the transport belt 31 due to the eccentricity of the drive roller 32,
The time required for the recording sheet on the conveyor belt 31 to move from the transfer position of one photosensitive drum to the transfer position of the next photosensitive drum coincides, so that color misregistration can be prevented. This is true even when the distance between the photosensitive drums 41C to 41K is arranged such that the transfer position of the toner image is an integral multiple of the distance traveled by the conveyor belt 31 when the drive roller 32 makes one rotation. The same is true.

Further, since the driving force is transmitted by the worm gear, when the worm is rotated, the worm wheel is also rotated following the rotation of the worm. Due to the so-called worm gear self-locking action that the worm does not follow, the vibration generated in one photosensitive drum propagates to the other photosensitive drum via the power transmission mechanism (worm gear and their rotating shaft). It will be difficult to
For example, it is possible to avoid as much as possible a situation in which the vibration generated on one photoconductor drum is superimposed on the vibration generated on another photoconductor drum and the finished image is degraded.

In this embodiment, the rotation position of the worm wheel 43K is detected by the rotary encoder 44K.
Is performed by counting encoder pulses output from the photocoupler 46. However, the present invention is not limited to this, and for example, the following may be performed. When the pulse motor 54 rotates by a sharp number of steps (for example, M steps), the gear ratio of the worm 42K and the worm wheel 43K is set so that the worm wheel 43K makes exactly one rotation. Instead of counting the pulses, a pulse of the speed setting signal input from the CPU 62 to the motor control circuit 65 is counted, and when the count value becomes M, the counter is reset. This eliminates the need for a rotary encoder, thereby reducing costs.

[0034]

As described above, according to the image forming apparatus of the present invention, the position between the image carrier for forming a black image and the adjacent image carrier arranged so as to be closest to the driving source. The on / off of the clutch inserted into the worm shaft portion is performed in synchronization with the switching between the monochrome mode and the color mode, so that in the monochrome mode, only the image carrier for forming a black image is driven, and other Since the carrier is not driven, it is possible to prevent unnecessary consumption of the other image carrier and the like.

Further, the rotational position of the worm wheel when the clutch is disengaged is stored, and the clutch is engaged in a state where the rotational position of the worm wheel matches the stored rotational position. If each worm wheel is mounted in advance so that the direction of deformation is the same for all worm wheels, the direction is always the same when a plurality of image carriers are driven simultaneously. The phase of the fluctuation of the peripheral speed of the photoconductor drum caused by the deformation of the wheel is the same between the respective image carriers, so that the color shift can be prevented.

Further, since the interval between adjacent image carriers in the direction of the transport path is set to an integral multiple of the distance traveled by the transport belt when the drive roller of the transport belt makes one rotation, the distance on the transport belt is reduced. Since the time required for the recording sheet to move from one image carrier to the next image carrier is an integral multiple of the fluctuation period of the traveling speed of the conveyor belt caused by the eccentricity of the driving roller, color shift can be prevented. it can.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of a digital full-color copying machine to which an image forming apparatus according to the present invention is applied.

FIG. 2 is a diagram illustrating a configuration of a drive mechanism of a photosensitive drum and a drive roller of the copying machine.

FIG. 3 is a block diagram illustrating a configuration of a drive control unit that performs drive control of a photosensitive drum and a drive roller.

FIG. 4 is a flowchart showing a part of control contents of the drive control unit.

FIG. 5 is a flowchart showing a part of control contents of the drive control unit.

[Explanation of symbols]

 31 Conveying belt 32 Drive rollers 41K, 41Y, 41M, 41C Photoreceptor drums 42K, 42Y, 42M, 42C Worms 43K, 43Y, 43M, 43C Worm wheels 44 Rotary encoder 50 Worm shaft 53 Clutch 54 Stepping motor 60 Drive control unit 62 CPU 63 RAM 64 ROM 65 Motor control circuit

Claims (3)

[Claims] 1. A plurality of worms are formed on a shaft, and one worm shaft having one end connected to a drive source is erected along a recording sheet conveyance path, and the other worm shaft is formed along the recording sheet conveyance path. A worm wheel is attached to a plurality of image carriers, and each worm wheel has an image carrier driving structure in which each worm wheel meshes with each worm on the worm shaft. Are arranged such that the image carrier for black image formation is located closest to the drive source, and a clutch is interposed between a worm shaft portion between the image carrier for black image formation and an adjacent image carrier. An image forming apparatus, wherein the clutch is turned on and off in synchronization with switching between a monochrome mode and a color mode. 2. A rotational position detecting means for detecting a rotational position of a worm wheel attached to an image carrier for forming a black image, and a storing means for storing a rotational position detected when the clutch is disengaged. The clutch is engaged in a state where the rotational position detected by the rotational position detecting means matches the rotational position of the worm wheel stored in the storage means.
The image forming apparatus as described in the above. 3. The transport belt is driven to travel by a drive roller,
A transport unit configured to transport the recording sheet placed on the transport belt along the transport path, wherein the distance between the adjacent image carriers in the transport path direction is changed when the drive roller makes one rotation. 3. The image forming apparatus according to claim 1, wherein the distance is an integral multiple of a distance traveled by the conveyor belt.