JP4645481B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus such as a color copying machine, a printer, an MFP, a facsimile, or a complex machine of these.

  2. Description of the Related Art Conventionally, color printers and the like use C, M, Y, and K color developing devices, and a toner image developed by each developing device is combined to form a full color image ( Patent Document 1). In addition to the developing devices, there are also electrophotographic process units for each color that are arranged in a row in a tandem format (Patent Document 2). In any case, the toner image of each color is often transferred to a sheet after being transferred to an intermediate transfer belt.

  For example, in the image forming apparatus disclosed in Patent Document 2, the electrophotographic process units of C, M, Y, and K are arranged substantially in a straight line along the intermediate transfer belt, and each of the electrophotographic process units is arranged in a straight line. An intermediate transfer belt that runs in the vicinity of the photosensitive drum is provided, and each primary transfer roller is movably disposed so as to face each photosensitive drum across the intermediate transfer belt. That is, the primary transfer roller is provided so as to be driven to move between a pressure contact position where the intermediate transfer belt is pressed against the photosensitive drum and a separation position (separation position) where the intermediate transfer belt is separated from the photosensitive drum.

  By the way, in a color printer, there are three print modes: a color mode in which an image is formed with C, M, Y, and K colors, a monochrome mode in which an image is formed with K colors, and a save mode in which no image is formed. A mode may be provided. In that case, there is a problem of how to perform switching control of those modes. For this, for example, by detecting the pressure contact position and the separation position of a plurality of primary transfer rollers with one sensor, and controlling the number of pulses given to a pulse motor for moving between them, the monochrome mode and color Management of mode positions has been done.

Further, in the image forming apparatus described in Patent Document 1, a mark on a belt is read by a sensor, an image forming process is started after a certain timing from the time of reading of the sensor, and primary transfer is repeated for each color and intermediate. A color image is superimposed on the transfer body. The ON timing of the next transfer nip contact / separation mechanism is set before the mark detection timing, and the OFF timing is set after the end of the primary transfer. It is disclosed that image quality is maintained by releasing the cohesive force due to Coulomb force.
JP 10-1111589 A JP 2005-241844

  As described above, in the prior art, the positions of the four primary transfer rollers are managed by one sensor, so when moving by changing the print mode, the position is temporarily returned to the home position detected by the sensor. After that, it was necessary to move to the next print mode position. The time required for the movement is a time loss when the print mode is changed.

  Further, only the home position detected by one sensor is used as the reference position, and the moving distance to the position corresponding to each printing mode is long, so that it is advantageous in terms of the stability of the position accuracy of the primary transfer roller and the like. I could not say it.

  The present invention has been made in view of the above-described problems, and is intended to shorten the movement time of the transfer roller when changing the printing mode, to increase the speed of changing the printing mode and to stabilize the position accuracy. Objective.

The apparatus according to the present invention includes a color switching member that switches the pressure contact / separation of the C, M, and Y color transfer rollers, and a black switching member that switches the pressure contact / separation of the K color transfer roller. A color mode for forming an image with each color of C, M, Y, and K as a printing mode, and a cam for moving the color switching member and the black switching member by the rotation. A monochrome mode in which image formation is performed with K color and a retraction mode in which image formation is not performed are provided, and the cam can be rotated in either the forward or reverse direction over 360 degrees. By moving each of the switching member for black and the switching member for black, the color mode, the monochrome mode, or the retreat Switched over de, the is configured to be switched in during one rotation of the cam, the color mode, the monochrome mode, and the mode of the save mode, every third division position during one rotation of the cam The cam is rotationally driven by a stepping motor, and the stepping motor is controlled to rotate the cam approximately one third when instructed to switch the printing mode. Black in which the detection state is switched between a range including the range corresponding to the evacuation mode and wider than the range and a range including the range corresponding to the monochrome mode and the color mode and wider than the range. Including a range corresponding to the retraction mode and the monochrome mode on the cam. And a color sensor that includes a range corresponding to the color mode and a range wider than the range, and the detection state is switched between. The detection by the color sensor and the black sensor It is configured to detect which of the print modes is switched according to a combination of states, and when the stepping motor is instructed to switch the print mode, the detection state of the color sensor or the black sensor is detected. It is controlled so that the print mode is switched by further rotating a predetermined angle from when there is a change.

  In addition, the detection is performed by the actuator provided in the color switching member operating the color sensor, and the actuator provided in the black switching member operating the black sensor. Is done.

  The cam includes a color cam for moving the color switching member and a black cam for moving the black switching member, and the color cam and the black cam. And rotate together on the same axis.

  Note that the color sensor and the black sensor detect that the switching member has been switched to the separated side, but this can be considered equivalent to detecting a side that is not the separated side, that is, the pressure contact side.

  FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention, FIG. 2 is a perspective view illustrating an appearance of an intermediate transfer body TT of the image forming apparatus 1, and FIG. 4 is an enlarged view showing a part of the intermediate transfer member TT shown in FIG. 3, FIG. 5 is an enlarged view showing another part of the intermediate transfer member TT shown in FIG. Is a perspective view showing the appearance of the cams 71 and 72, FIG. 7 is a perspective view showing the shape of the cams 71 and 72, FIG. 8 is a plan view showing a part of the intermediate transfer member TT, and FIG. 9 is a slide of the intermediate transfer member TT. FIG. 10 is a front view showing the shapes of the members 55 and 56, FIG. 10 is a view showing the relationship between the outer shape of the cams 71 and 72, and the printing mode, and FIG. 11 is the relationship between the detection signals S1 and S2 of the sensors SE1 and SE2. FIG.

  In FIG. 1, an image forming apparatus 1 is a digital multi-function peripheral or printer using an electrophotographic system, and has a built-in tandem print engine.

  That is, the image output device 1 has Y (yellow), M (magenta), C (cyan), and K (black) image forming units 24Y, M, C, and K arranged in a row in a tandem format. Yes. Each of the image forming units 24Y, 24M, 24C, 24K exposes the surface of the photosensitive drum 41 in accordance with the photosensitive drum 41, the charging charger 42 for uniformly charging the surface of the photosensitive drum 41, and the image data of each color. Thus, the exposure unit 43 that forms an electrostatic latent image, the developing unit 44 that develops the electrostatic latent image with toner of each color to form a toner image, and the photosensitive drum 41 across the intermediate transfer belt 23. The transfer roller 22 for primarily transferring the toner image formed on the surface of the photosensitive drum 41 provided in contact with the inside of the intermediate transfer belt 23 at the position, and the surface of the photosensitive drum 41 And a cleaner 45 for collecting and cleaning the toner remaining in the toner.

  In the present specification and drawings, the symbols corresponding to the colors Y, M, C, and K may be suffixed with the symbols Y, M, C, and K, respectively.

  The intermediate transfer belt 23 is stretched between the rollers 25 and 26 so as to be along the upper portions of the photosensitive drums 42Y, 42M, 42C, 42K, and travels in the direction of the arrow M1 in FIG. To do. Each of the transfer rollers 22Y, 22M, 22C, and 22K is in contact with the respective photosensitive drums 42Y, 42M, 42C, 42K, and the intermediate transfer belt 23, and the intermediate positions from the respective photosensitive drums 42Y, 42M, 42C, 42K. The transfer belt 23 is movable between a separation position (also referred to as separation or retraction) and a separation position (also referred to as retraction position). The intermediate transfer belt 23 is pressed against the photoconductive drums 42Y, 42M, 42C, and 42K, whereby the toner image on the photoconductive drum 42 is transferred to the intermediate transfer belt 23. The mechanism will be described later.

  The toner image primarily transferred to the intermediate transfer belt 23 is secondarily transferred to the paper PA fed from the paper feed cassette 27 by the secondary transfer roller 28. Thereafter, the paper PA is fixed by the fixing unit 29 and discharged to the paper discharge tray 30. The secondary transfer roller 28 can be retracted to a position where it is not in contact with the intermediate transfer belt 23 by a retracting mechanism (not shown). Further, a belt cleaner 31 and a waste toner box 32 are provided in the vicinity of the roller 26.

  The control unit 21 includes a CPU 211, a memory 212, a control circuit 213, a communication interface 214, a magnetic storage device 215, and the like. The control unit 21 performs image processing on image data and controls each unit of the image forming apparatus 1. In the present embodiment, in particular, the control unit 21 controls the motor 74 based on detection signals S1 and S2 from sensors SE1 and SE2 described later. Details will be described later.

  Note that the image forming means and method in the image forming apparatus 1 are not limited to the examples described above. Further, the image forming apparatus 1 may be a monochrome / color copying machine, a printer, a facsimile, or a complex machine thereof.

  Next, the intermediate transfer member TT will be described with reference to FIGS.

  FIG. 2 shows a view of the intermediate transfer member TT in FIG. 1 as viewed from the upper right side toward the left front side. Further, FIG. 3 shows a frame on the back side when the intermediate transfer body TT in FIG. 1 is viewed from the upper center side toward the back side. This is a state in which the front side of the left hand is viewed from the upper right side of the intermediate transfer member TT in FIG. Further, FIG. 8 shows a view of the intermediate transfer member TT in FIG. 3 as viewed from above. FIG. 9 shows a view of the intermediate transfer member TT shown in FIG. 8 as viewed from below. In these figures, some members may not be shown because of the necessity of showing the internal structure.

  In FIG. 3, a frame 51 for rotatably supporting four transfer rollers 22Y, 22M, 22C, and 22K is shown. The transfer roller control mechanism TK is configured by attaching a large number of components to the frame 51. The transfer roller control mechanisms TK are provided at both ends of the transfer roller 22, respectively, and the two transfer roller control mechanisms TK often have a common structure. Therefore, in the following, only one transfer roller control mechanism TK will be mainly described. In FIG. 3, only one transfer roller control mechanism TK is shown. Further, FIG. 2 shows a state in which each frame 51 is removed in each transfer roller control mechanism TK.

  As shown mainly in FIG. 2, the intermediate transfer member TT includes four transfer rollers 22, rollers 25 and 26, a transfer roller control mechanism TK provided at both ends of these rotors, an intermediate transfer belt 23 (see FIG. 1), and the like. Are integrated.

  As shown in FIG. 3, the transfer roller control mechanism TK includes bearing devices 52Y, 52M, 52C, 53K, compression coil springs 53Y, 53C, 53K, color levers 54Y, 54M, 54C, and black lever 54K. , A color slide member 55, a black slide member 65, a color cam 71, a black cam 72, a guide 76, and the like.

  The bearing devices 52Y, 52M, 52C, and 52K support the shafts of the transfer rollers 22Y, 22M, 22C, and 22K so as to be rotatable, and are provided so as to be vertically movable with respect to the frame 51.

  The compression coil springs 53Y, 53M, 53C, and 53K are mounted in a compressed state between the projections provided on the bearing devices 52Y, 52M, 52C, and 52K, respectively, and the frame 51. The bearing devices 52Y, 52M, 52C, and 53K are biased downward by the compression coil springs 53Y, 53M, 53C, and 53K, respectively. Therefore, in the free state, the transfer roller 22Y, M, C, K is pressed against the surface of the photosensitive drum 41Y, M, C, K with the intermediate transfer belt 23 sandwiched by the bias of the compression coil spring 53, respectively. It is done.

  The lever 54 is formed in a substantially L shape by a hard synthetic resin or the like, and a central portion thereof is rotatably supported by the frame 51. One end portion of the lever 54 engages with a protrusion provided on the bearing device 52 from below to above, and the other end portion of the lever 54 includes claw portions 56Y, 56M, 56M provided on the slide member 55. C or the claw portions 66K provided on the slide member 65 are respectively pushed in the right direction in FIG.

  That is, the slide member 55 is made of a metal material such as a steel plate, and is slid by a predetermined stroke with respect to the frame 51 by the pins 60 that are fitted in the long holes 59 provided at two locations and fixed to the frame 51. It is provided as possible. The slide member 55 is provided with the claw portions 56Y, M, and C described above at three locations, and the claw portion 58 is provided at one location. Cuboid buffer members 57Y, M, and C are respectively provided on the surfaces of the three claw portions 56Y, 56M, and C, and the buffer members 57Y, 57M, and C are in contact with the other tip portion of the lever 54, respectively. The outer peripheral surface of the collar cam 71 is in contact with the claw portion 58. The buffer member 57 can be made of urethane rubber, urethane foam, other synthetic resins, or the like.

  The slide member 55 is biased by a tension coil spring 61 so as to be pulled leftward in FIG. Therefore, the claw portion 58 is always in contact with the cam 71, and the slide member 55 moves to the left and right according to the outer peripheral shape of the cam 71 as the cam 71 rotates.

  When the slide member 55 moves to the right, the three claw portions 56Y, M, C move the three levers 54Y, M, C via the buffer member 57 to rotate rightward in FIG. By rotating the lever 54 in the right direction, the three bearing devices 52Y, 52M, 52C are pushed upward, and the three transfer rollers 22Y, 22M, 22C are lifted upward to be separated from each other. When the three transfer rollers 22Y, 22M, 22C are separated from each other, the intermediate transfer belt 23 that has been pressed against the surfaces of the three photoconductor drums 41Y, 41M, 41C is transferred to the three photoconductor drums 41Y, 41M, 41C. Get away from.

  On the contrary, when the slide member 55 moves to the left, the three claw portions 56Y, 56M, and 56C do not press the levers 54Y, 54M, and 53C, so that the 3 is applied by the urging force of the compression coil springs 53Y, 53M, and 53C. The two bearing devices 52Y, 52M, 52C are pushed downward. As a result, the levers 54Y, 54M, and 54C rotate to the left in FIG. When the three bearing devices 52Y, 52M, 52C are pushed down, the three transfer rollers 22Y, 22M, 22C are pushed down to the pressure contact position. When the transfer rollers 22Y, M, and C are in the pressure contact position, the intermediate transfer belt 23 that has been separated from the surfaces of the three photosensitive drums 41Y, 41, and 41 is pressed against the surfaces of the photosensitive drums 41Y, 41, and 41C. Primary transfer is performed for each of the colors Y, M, and C.

  As described above, the color slide member 55 acts on the three transfer rollers 22Y, 22M, 22C, and moves them between the press contact position and the separation position.

  Similarly to the color slide member 55 described above, the black slide member 65 moves to the left and right according to the rotation of the black cam 72, and moves one transfer roller 22K up and down. It is driven to move between the pressure contact position and the separation position.

  In other words, the slide member 65 is made of a metal material such as a steel plate, and is inserted into long holes provided at two locations and fixed to the frame 51 by a pin 69 (see FIG. 2). It is provided so that sliding movement is possible only by the stroke. The slide member 65 is provided with the claw portion 66K described above at one location, and the claw portion 68 is provided at one location. A rectangular parallelepiped buffer member 67K is provided on the surface of the claw portion 66K, and the buffer member 67K contacts the other tip portion of the lever 54K. The outer peripheral surface of the black cam 72 is in contact with the claw portion 68K.

  The slide member 65 is biased by the tension coil spring 70 so as to be pulled leftward in FIG. Accordingly, the claw portion 68 is always in contact with the cam 72 (see FIG. 9), and the slide member 65 moves to the left and right according to the outer peripheral shape of the cam 72 as the cam 72 rotates.

  When the slide member 65 moves to the right, the claw portion 66K moves the lever 54K via the buffer member 67K to rotate rightward in FIG. By rotating the lever 54K in the right direction, the bearing device 52K is pushed up, and the transfer roller 22K is pulled up to be in the separated position. When the transfer roller 22K reaches the separation position, the intermediate transfer belt 23 that has been pressed against the surface of the photosensitive drum 41K until then moves away from the photosensitive drum 41K.

  On the contrary, when the slide member 55 moves to the left, the claw portion 66K does not press the lever 54K, so that the bearing device 52K is pushed downward by the urging force of the compression coil spring 53K. As a result, the lever 54K rotates in the left direction in FIG. When the bearing device 52K is pushed down, the transfer roller 22K is pushed down to the pressure contact position. When the transfer roller 22K reaches the pressure contact position, the intermediate transfer belt 23 that has been separated from the surface of the photosensitive drum 41K until then is pressed against the surface of the photosensitive drum 41K, and primary transfer with respect to K is performed.

  Cams 71 and 72 provided in the two right and left transfer roller control mechanisms TK are fixed to a shaft 73, and these four cams 71, 71, 72 and 72 are simultaneously the same while maintaining the same relative angular position. Rotate by an angle. The cams 71 and 72 are manufactured by molding with a hard synthetic resin. The cams 71 and 72 can also be manufactured by casting, punching a sheet metal, electric discharge machining, machining, or the like.

  As well shown in FIG. 3, a stepping motor (stepping motor) 74 is fixed to the frame 51 in order to rotationally drive the cams 71 and 72. That is, the rotational force of the motor 74 is decelerated through the plurality of gears 75 and finally rotates the shaft 73 and the cams 71 and 72. The cams 71 and 72 can rotate in both forward and reverse directions over a rotation angle of 360 degrees, and can be driven to rotate by the motor 74 as such. The rotation angles and directions of the cams 71 and 72 are determined by the number of pulses applied to the motor 74 and the phase of the pulse. That is, by controlling the rotation speed (rotation speed) and rotation direction of the motor 74, the rotation angle positions of the cams 71 and 72 can be accurately controlled. Such control is performed by the control unit 21.

  Instead of the gear 75, various known power transmission devices such as pulleys and belts can be used. As the motor 74, a stepping motor, a pulse motor, and other various named motors as described above can be used.

  As described above, the color slide member 55 is moved by the rotation of the color cam 71, and the transfer rollers 22Y, 22M, and 22C are switched between the press contact position and the separation position. The black slide member 65 is moved by the rotation of the black cam 72, and the transfer roller 22K is switched between the press contact position and the separation position. The print mode is set by these combinations.

  That is, the print mode includes a color mode in which image formation is performed with each color of C, M, Y, and K, a monochrome mode in which image formation is performed with K color, and a save mode in which image formation is not performed (all save mode). is there. In the color mode, all the transfer rollers 22Y, M, C, and K are in the pressure contact position. In the monochrome mode, only the transfer roller 22K is in the pressure contact position, and the transfer rollers 22Y, M, and C are in the separated positions. In the retreat mode, all the transfer rollers 22Y, M, C, and K are in the separated positions.

  These three printing modes are switched within one rotation of the cams 71 and 72. That is, the color slide member 55 and the levers 54Y, M, and C are moved by the cam 71, and the black slide member 65 and the lever 54K are moved by the cam 72, so that the color mode, the monochrome mode, or the retract mode is set. The cams 71 and 72 are configured to be switched during one rotation.

  The slide member 55 and the levers 54Y, 54M, 54C correspond to the switching member for color in the present invention, and the slide member 65 and the lever 54K correspond to the switching member for black in the present invention.

  In order to control these printing modes, two sensors SE1 and SE2 for detecting the position state of the slide members 55 and 65 are provided. One is a color sensor SE1, and the other is a black sensor SE2. These sensors SE1 and SE2 are photoelectric light-shielding sensors, and output a detection signal when a light-shielding object is inserted between the projector and the light receiver.

  As actuators for operating these sensors SE1 and SE2 with light shielding, the slide member 55 is provided with a light shielding piece 77 and the slide member 65 is provided with a light shielding piece 78, respectively. These light shielding pieces 77 and 78 can be integrally provided by sheet metal processing of the slide members 55 and 65. Then, by combining the detection signals of these two sensors SE1 and SE2, the motor 74 is controlled so that the setting corresponds to the instructed print mode. Details will be described later.

  Next, the relationship between the rotation angle positions of the cams 71 and 72 and the printing mode will be described with reference to FIGS.

  The two cams 71 and 72 are attached in a rotational angular position relationship shown in FIGS. Here, in FIGS. 10A and 10B, it is assumed that the centers of the cams 71 and 72 (the center of the shaft 73) are at the origin of the XY coordinates, the positive direction of the X axis is the rotation angle of 0 degree, and the counterclockwise rotation direction. Is the angle of the brass. In the figure, the cam 71 shows an example of a detailed shape when manufactured by resin molding, and the cam 72 shows only the outer shape. Although the cam 72 is accompanied by another small cam, it is not related here, so the description is omitted.

  In FIG. 10A, the outer shape of the cam 71 is a circumferential surface with a large radius (distance from the center to the outer periphery) centered on the shaft 73 in the left half of the figure, and the right center has the smallest radius. , And has a smooth arc surface between them. That is, the radius is the smallest at the rotation angle of 0 degrees of the cam 71, and the radius is the largest around the rotation angle of 90 to 270 degrees.

  Accordingly, the transfer rollers 22Y, M, and C are pushed downward by the compression coil springs 53Y, 53, and 53 C to a pressure contact position in a range of about 30 degrees, which is about ± 15 degrees of the rotation angle of 0 degrees, and its periphery. In addition, the slide member 55 is moved by the cam 71 and the transfer rollers 22Y, M, and C are pushed up by the levers 54Y, M, and C in the rotation angle range of 90 to 270 degrees and the periphery thereof to be in the separated positions.

  In the range of the rotation angle of the cam 71 from 70 to 290 degrees, the light shielding piece 77 shields the sensor SE1 by the movement of the slide member 55, and the detection signal S1 is output.

  In FIG. 10B, the outer shape of the cam 72 is a circumferential surface with a small radius in the range of about 150 degrees of the rotation angle of the cam 72 of about 15 to 135 degrees, and about 30 degrees of the rotation angle of 225 to 255 degrees. In this range, the circumferential surface has a large radius, and a smooth circular arc surface is formed between them.

  Accordingly, the transfer roller 22K is pushed downward by the compression coil spring 53K to the pressure contact position in the range of about 150 degrees of the rotation angle of -15 to 135 degrees and its periphery. Further, in the range of about 30 degrees of the rotation angle of 225 to 255 degrees, the slide member 65 is moved by the cam 72 and the transfer roller 22K is pushed up by the lever 54K in the range of 195 to 285 degrees and its periphery. It becomes.

  In the range of the rotation angle of the cam 72 of 195 to 285 degrees, the light shielding piece 78 shields the sensor SE2 by the movement of the slide member 65, and the detection signal S2 is output.

  Referring to FIGS. 10 and 11, eventually, detection signal S1 is output (turned on) in the range of a rotation angle of 70 to 290 degrees. The detection signal S2 is output (turned on) in a rotation angle range of 195 to 285 degrees. In the range of about 30 degrees with a rotation angle of 0 degrees ± 15 degrees, all the transfer rollers 22Y, 22M, 22C, 22C, 22C, 22K, 22K, 22K, 22K In a range of about 30 degrees with a rotation angle of 120 degrees ± 15 degrees, only the transfer roller 22K is in the pressure contact position and the monochrome mode is set. In a range of about 30 degrees with a rotation angle of 240 degrees ± 15 degrees, all the transfer rollers 22Y, M, C, and K are in the separated positions, and the retreat mode is set.

  As described above, the print mode is switched to the color mode, the monochrome mode, and the retreat mode at every rotation angle of 120 degrees of the cams 71 and 72. That is, the color mode, the monochrome mode, and the retreat mode are switched at every third equally divided position during one rotation of the cams 71 and 72. Therefore, when an instruction for switching the print mode is given, the motor 74 controls the cams 71 and 72 to rotate in the forward or reverse direction by approximately one third of the minimum rotation angle, that is, 120 degrees. do it.

  Therefore, in order to switch the print mode, no matter what print mode is switched to any print mode, the time required for the switch is short and the switch is performed in the same time, and the print mode is changed. High speed is achieved.

  Incidentally, the time required for switching the printing mode can be shortened to about one third as compared with the method described in the section of the prior art.

  Further, the print mode setting state is detected by the two sensors SE1 and SE2. That is, none of the detection signals S1 and S2 is output in the color mode. In the monochrome mode, the detection signal S1 is output, but the detection signal S2 is not output. In the evacuation mode, both detection signals S1 and S2 are output. As described above, in the image forming apparatus 1, the state of the print mode is managed by the two sensors SE1 and SE2.

  Therefore, the print mode setting state can be easily and reliably detected by the states of the detection signals S1 and S2, and the print mode control is stabilized.

  In addition, since the combinations of the detection signals S1 and S2 are different from each other among the color mode, the monochrome mode, and the save mode, any one of the detection signals S1 and S2 always changes when the print mode is changed. Arise. Accordingly, the cams 71 and 72 are rotated by the rotational drive of the motor 74, and the motor 74 is controlled so as to rotate by a predetermined angle from the timing at which any one of the detection signals S1 and 2 is changed. Positioning with good characteristics can be performed.

  For example, when switching from the color mode to the monochrome mode, since the detection signal S1 is output at a rotation angle of 70 degrees, the motor 74 may be controlled to rotate 50 degrees thereafter (B1 shown in FIG. 11). When switching from the monochrome mode to the retreat mode, the detection signal S2 is output at a rotation angle of 195 degrees, and thereafter, the motor 74 may be controlled to rotate 45 degrees (B2 shown in FIG. 11). When switching from the evacuation mode to the color mode, the detection signal S1 is not output at a rotation angle of 295 degrees, so that the motor 74 may be controlled to rotate 70 degrees thereafter (B3 shown in FIG. 11). The same control can be performed when the switching is reversed (B4 to 6 shown in FIG. 11).

  In order to control the motor 74 so as to rotate by a predetermined rotation angle, for example, the number of pulses output to the motor 74 may be controlled.

  In the above description, the allowable range of the rotation angle of the cams 71 and 72 in each printing mode is 30 degrees. This is because the backlash of the gear 75 or the like is generated when the cams 71 and 72 are rotated forward and backward, so that the influence of the shift does not occur. The allowable range may be wider than 30 degrees or narrowed. As described above, by controlling the motor 74 to rotate by a predetermined angle based on the change of the detection signals S1 and S2, it is possible to reduce the influence of backlash and stop at an accurate position. .

  In the above embodiment, the two separate cams 71 and 72 are used for the color and the black, but the two cams 71 and 72 are configured by forming different cam shapes on one cam. It is also possible to fulfill the same function. Various sensors other than those described above can be used as the sensors SE1 and SE2 for detecting the position states of the transfer rollers 22Y, 22M, 22C, and 22K. Further, the light shielding pieces 77 and 78 as actuators are provided on the slide members 55 and 65, but the actuators may be provided on other members.

  In the above embodiment, the sensors SE1 and SE2 have been described as detecting that the transfer roller 22 is in the separated position, but it may be detected that the transfer roller 22 is in the pressure contact position. The logic levels of the detection signals S1 and S2 may be any. That is, either side of the separation position or the pressure contact position may be turned on (H) or off (L). The arrangement of Y, M, C, and K in the image forming apparatus 1 can be variously changed.

  In addition, the structure, shape, dimensions, number, material, operation method, etc. of the whole or each part of the transfer roller control mechanism TK, the intermediate transfer body TT, or the image forming apparatus 1 can be appropriately changed in accordance with the spirit of the present invention. it can.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view illustrating an appearance of an intermediate transfer member of the image forming apparatus. FIG. 3 is a perspective view showing a part of an intermediate transfer member. FIG. 4 is an enlarged view showing a part of the intermediate transfer member in FIG. 3. FIG. 4 is an enlarged view showing another part of the intermediate transfer member in FIG. 3. It is a perspective view which shows the external appearance of a cam. It is a perspective view which shows the shape of a cam. FIG. 3 is a plan view showing a part of an intermediate transfer member. It is a front view showing the structure of the slide member of the intermediate transfer member. It is a figure which shows the relationship between the external shape of a cam, and printing mode. It is a figure which shows the relationship between the detection signal of a sensor, and printing mode.

Explanation of symbols

1 Image forming apparatus 21 Control unit 22Y, M, C, K Transfer roller (transfer roller)
23 Intermediate transfer belt 54Y, M, C lever (color switching member)
54K lever (switching member for black)
55 Slide member (color switching member)
65 Slide member (switching member for black)
71 Cam 72 Cam 74 Motor (Stepping Motor)
77,78 Light-shielding piece (actuator)
TT Intermediate transfer body TK Transfer roller control mechanism SE1 Sensor (color sensor)
SE2 sensor (black sensor)
S1, S2 detection signal

Claims (3)

A color switching member for switching the pressure contact / separation of the transfer rollers for each color of C, M, and Y;
A black switching member for switching the pressure contact and separation of the K color transfer roller;
A cam for moving the switching member for color and the switching member for black by the rotation;
As printing modes, there are provided a color mode for forming an image with each color of C, M, Y, and K, a monochrome mode for forming an image with a color of K, and a retreat mode for not forming an image.
The cam can rotate in either forward or reverse direction over 360 degrees;
The color switching member and the black switching member are moved by the cam so that the color mode, the monochrome mode, or the retraction mode can be switched during one rotation of the cam. Has been
The color mode, the monochrome mode, and the retraction mode are switched every three divided positions during one rotation of the cam,
The cam is rotationally driven by a stepping motor,
The stepping motor is controlled to rotate the cam approximately one third when an instruction to switch the printing mode is given,
The detection state is between a range that includes the range corresponding to the retraction mode on the cam and is wider than the range, and a range that includes the range corresponding to the monochrome mode and the color mode and is wider than the range. A black sensor that switches,
A detection state between a range corresponding to the retraction mode and the monochrome mode on the cam and wider than the range and a range corresponding to the color mode and wider than the range. A color sensor for switching, and
A combination of detection states by the color sensor and the black sensor is configured to detect which of the print modes has been switched,
When the stepping motor is instructed to switch the print mode, the print mode is switched by further rotating by a predetermined angle from the time when the detection state of the color sensor or the black sensor is changed. Controlled to
A color image forming apparatus. The detection is performed by the actuator provided in the color switching member operating the color sensor,
The detection is performed by an actuator provided on the black switching member operating the black sensor.
The color image forming apparatus according to claim 1 . The cam
A collar cam for moving the color switching member;
A black cam for moving the black switching member;
The collar cam and the black cam rotate integrally on the same axis,
The color image forming apparatus according to claim 1 .