JP2015118350A - Image forming apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing a possibility of positional shift.SOLUTION: Control is executed in accordance with the number of image carriers in contact with a belt member. An image forming apparatus includes a control part for performing the steps of: S102 for determining whether the number of photoreceptor drums in contact with an intermediate transfer belt is two or more for an image forming indicated by an acquired instruction (step S101); S103 for controlling a drive motor in accordance with a measurement value of an encoder if determined that the number of photoreceptor drums in contact with the intermediate transfer belt is two or more (Yes for step S102); S104 for determining whether a medium is inverted by a transport part if determined that the number of photoreceptor drums in contact with the intermediate transfer belt is less than two (No for step S102); and S105 for controlling the drive motor in accordance with a measurement value of an FG sensor if determined that the medium is not inverted (No for step S104).

Description

  The present invention relates to an image forming apparatus and a program.

Patent Document 1 is provided with an endless belt-shaped intermediate transfer body having a scale attached to the entire inner peripheral surface thereof, and a scale reading sensor for reading the scale. Based on the reading information of the scale reading sensor. An image forming apparatus that controls the rotational drive of the intermediate transfer member is described.
Japanese Patent Laid-Open No. 2004-260688 selects and implements one of motor constant speed control and belt constant speed control according to the content of a user's instruction command, and performs the first print job under the user. Prior to performing the writing position correction process in a state where the belt member is moved endlessly by either one of the belt constant speed control and the motor constant speed control, the belt member is controlled by the other control. Is driven in motor constant speed control based on the result of detecting the amount of misregistration of the toner images by forming a color misregistration detection image including toner images of at least two of the colors. An image forming apparatus that corrects one of a target rotational speed of a motor and a target belt speed in belt constant speed control is described.
In Patent Document 3, when image formation is performed by driving a belt member by a constant speed drive control unit, if the temperature difference between the temperature detected by the temperature detection unit and the reference temperature exceeds a specified temperature difference, An image forming apparatus is described in which the target constant speed is changed so that the deviation between the surface moving speed of the belt member caused by thermal expansion and the target speed becomes small.

JP 2004-198925 A Patent No. 5240579 JP 2011-248003 A

  An object of the present invention is to perform control according to the number of image carriers that are in contact with a belt member.

  An image processing apparatus according to claim 1 of the present invention includes an endless belt member spanned between a plurality of rolls, and a drive motor that rotates at least one of the plurality of rolls to rotate the belt member. A plurality of image holders each holding an image, the image holders contacting the belt member at different positions and transferring the images, respectively, and the images on the plurality of image holders. Image forming means for forming each, transfer means for transferring the image transferred from the plurality of image holders to the belt member to a medium, first measuring means for measuring a rotating speed of the belt member, A second measuring means for measuring the rotational speed of the drive motor; and a plurality of the image holding bodies, wherein a predetermined number or more of the image holding bodies contact the belt member to transfer the image, 1st total The drive motor is controlled to rotate the belt member at a first speed according to the speed measured by the means, and less than the determined number of the image carriers among the plurality of image carriers. Control for controlling the drive motor so that the rotation speed of the drive motor is rotated at the second speed according to the speed measured by the second measuring means when the image is transferred in contact with the belt member. Means.

An image processing apparatus according to a second aspect of the present invention is the image processing apparatus according to the first aspect, wherein the control means does not include an image carrier that forms a colorless image in the plurality of image carriers. And
The image processing apparatus according to a third aspect of the present invention is the image processing apparatus according to the first or second aspect, wherein the control unit is configured to transfer the first image after the transfer unit has transferred the image onto the first surface of the medium. When transferring the image to the second surface, which is the opposite surface, regardless of the number of the image holders in contact with the belt member, according to the speed measured by the first measuring means, A drive motor is controlled.
An image processing apparatus according to a fourth aspect of the present invention is the image processing apparatus according to any one of the first to third aspects, further comprising a detection unit that detects a weight per unit area of the medium transferred by the transfer unit. And the control means rotates the belt member at the first speed according to the speed measured by the first measurement means when the weight detected by the detection means is equal to or greater than a threshold value. When the weight detected by the detection means is less than a threshold value, the rotation speed of the drive motor is set to the second speed according to the speed measured by the second measurement means. The drive motor is controlled to rotate.
A program according to claim 5 of the present invention includes: an endless belt member that spans a plurality of rolls; a drive motor that rotates at least one of the plurality of rolls to rotate the belt member; Is a plurality of image holding bodies that hold images, and a plurality of image holding bodies that contact the belt member at different positions to transfer the images, respectively, and the images are formed on the plurality of image holding bodies, respectively. Image forming means, transfer means for transferring the image transferred from the plurality of image holders to the belt member to a medium, first measurement means for measuring the rotating speed of the belt member, and the drive motor A computer of an image forming apparatus having a second measuring means for measuring the rotation speed of the plurality of image holding bodies, wherein a predetermined number or more of the image holding bodies are in contact with the belt member. When transferring the recorded image, the drive motor is controlled to rotate the belt member at the first speed according to the speed measured by the first measuring means, and among the plurality of image holding bodies, When the number of image carriers less than the determined number contacts the belt member and transfers the image, the rotational speed of the drive motor is set to a second speed according to the speed measured by the second measuring means. This is a program for functioning as a control means for controlling the drive motor so as to rotate the motor.

According to the first and fifth aspects of the invention, the possibility that the control becomes unstable when the number of image carriers that contact the belt member is small is suppressed, and the number of image carriers that contact the belt member is large. The possibility that the position of the image formed sometimes shifts can be suppressed.
According to the second aspect of the present invention, it is possible to suppress the possibility that the control becomes unstable by excluding an image carrier that forms a colorless image in which positional deviation does not become a problem.
According to the third aspect of the present invention, it is possible to suppress the possibility that the positions of the images formed on the first surface and the second surface are shifted.
According to the fourth aspect of the present invention, it is possible to suppress the possibility that the position of the image formed on the belt member is shifted due to an impact received by the belt member from a medium whose weight per unit area is equal to or greater than a threshold value.

1 is a diagram illustrating an overall configuration of an image forming apparatus. FIG. 3 is a diagram illustrating a configuration of a control system of the image forming apparatus. FIG. 3 is a flowchart showing a flow of operations when the image forming apparatus controls a drive motor.

1. Embodiment 1-1. Overall Configuration FIG. 1 is a diagram showing an overall configuration of an image forming apparatus 1 according to the present embodiment. FIG. 2 is a diagram illustrating a configuration of a control system of the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 shown in FIGS. 1 and 2 includes a container 11, a supply unit 12, developing units 13Y, 13M, 13C, and 13K, a transfer unit 14, a fixing unit 15, a transport unit 16, and an encoder 17. A drive motor 18 and a control unit 19.

  Note that the symbols Y, M, C, and K indicate configurations corresponding to yellow, magenta, cyan, and black toners, respectively. Each of the developing units 13Y, 13M, 13C, and 13K has no significant difference in configuration except that the toner to be used is different and the position with respect to the transfer unit 14 is changed according to the mode. Hereinafter, when it is not necessary to particularly distinguish each of the developing units 13Y, 13M, 13C, and 13K, the alphabet at the end of the code indicating the color of the toner is omitted and referred to as “developing unit 13”. In FIG. 1, the encoder 17 and the drive motor 18 are omitted. In FIG. 2, the container 11, the supply unit 12, the developing unit 13, the transfer unit 14, the fixing unit 15, and the transport unit 16 are omitted.

  The control unit 19 is a unit that controls the operation of each unit of the image forming apparatus 1. The control unit 19 includes an arithmetic processing device such as a CPU (Central Processing Unit) and a storage device such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and executes a program stored in these storage devices.

  The container 11 accommodates a sheet P as a medium that has been cut into a predetermined size, and the supply unit 12 presses the stored sheet P against a supply roll included in the supply unit 12, for example. Assist in supplying P. The medium is not limited to paper, and may be a resin sheet, for example. In short, the medium may be any medium that can record an image on the surface.

  The image forming apparatus 1 may include a plurality of containers 11. Specifically, as shown in FIG. 1, the image forming apparatus 1 includes four containers 11, containers 11 a, 11 b, 11 c, and 11 d, and a supply unit 12 a corresponding to a position facing each upper surface thereof. , 12b, 12c, 12d are arranged. In addition, the left side surface of the image forming apparatus 1 shown in FIG. 1 is provided with a container 11e that rotates in a counterclockwise direction about the axis SFT and is configured to accommodate the paper P on the upper surface. A corresponding supply unit 12e is disposed on the leading end side in the supply direction of the paper P accommodated in the container 11e.

  Each supply unit 12 has a plurality of supply rolls, and takes out the paper P from the corresponding container 11 by these supply rolls and supplies it to the registration roll 61 of the transport unit 16. The position of the edge on the leading end side is adjusted so that the paper P supplied to the registration roll 61 is stopped there and has a straight posture in the transport direction.

  The conveyance unit 16 includes a registration roll 61, an exit roll 62, a discharge roll 63, and retransmission rolls 64a, 64b, and 64c (hereinafter, collectively referred to as “retransmission roll 64” unless there is a particular need for distinction). Is provided. The registration roll 61 rotates at a predetermined timing and conveys the stopped paper P to the transfer unit 14. The exit roll 62 is disposed on the downstream side (upward in FIG. 1) of the fixing unit 15 and conveys the paper P that has passed through the transfer unit 14 and the fixing unit 15 to the discharge roll 63 through the path r1.

  The discharge roll 63 conveys the paper P conveyed from the outlet roll 62 to a paper discharge place STO outside the image forming apparatus 1. Further, the discharge roll 63 is rotated in the reverse direction after the path through which the sheet P passes is switched from the path r1 to the path r2 by a switching gate (not shown) while the rear end portion of the sheet P is sandwiched, and rotates in the reverse direction. Is conveyed to the retransmission roll 64a. The paper P is transported in this order by the retransmission rolls 64a → 64b → 64c, and is transported to the registration roll 61 again. The paper P that has been transported to the registration roll 61 again is reversed from the front and the back when it is first transported to the registration roll 61, and the leading edge and the trailing edge are reversed.

  Each developing unit 13 includes a photosensitive drum 31, a charger 32, an exposure device 33, a developing device 34, a primary transfer roll 35, a drum cleaner 36, and a toner cartridge 39. The toner cartridges 39Y, 39M, 39C, and 39K as developer containers have storage spaces for storing toners of colors of yellow, magenta, cyan, and black, and developing units 13Y and 13M corresponding to these toners. , 13C, and 13K.

  The photosensitive drum 31 is an image carrier having a charge generation layer and a charge transport layer, and is rotated by a driving unit (not shown). The charger 32 charges the surface of the photosensitive drum 31. The exposure device 33 includes a laser emission source, a polygon mirror, and the like (both not shown). The exposure device 33 is controlled by the control unit 19 and is charged with laser light corresponding to image data representing an image by the charger 32. Irradiation toward the photosensitive drum 31. Thereby, a latent image is held on each photosensitive drum 31.

  Note that the image data may be acquired from the external device by the control unit 19 via a communication unit (not shown). The external device is, for example, a storage device that stores image data or a reading device that reads an image from a document and generates image data indicating the image.

  The developing device 34 stores a two-component developer containing toner of any one of Y, M, C, and K supplied from the toner cartridge 39 and a magnetic carrier such as ferrite powder. The tip of the magnetic brush formed on the developing unit 34 comes into contact with the surface of the photosensitive drum 31 so that the toner is exposed on the surface of the photosensitive drum 31 by the exposure device 33, that is, the image line of the electrostatic latent image. A toner image corresponding to the above image is formed (developed) on the photosensitive drum 31. That is, the charger 32, the exposure device 33, and the developing device 34 are an example of an image forming unit that forms an image on an image holding member.

  The primary transfer roll 35 generates a predetermined potential difference at a position where the intermediate transfer belt 41 of the transfer unit 14 faces the photosensitive drum 31, and transfers the toner image to the intermediate transfer belt 41 by this potential difference. Of the developing unit 13, each of the photosensitive drums 31 provided in the developing units 13Y, 13M, and 13C is configured to be movable between a position in contact with the intermediate transfer belt 41 of the transfer unit 14 and a position not in contact with the mode. Has been. Each photosensitive drum 31 of the developing unit 13 contacts the intermediate transfer belt 41 at a different position to transfer an image. That is, each of the four photosensitive drums 31 shown in FIG. 1 is an image holding body that holds an image, and is an example of an image holding body that contacts the belt member at different positions and transfers the image.

  The drum cleaner 36 removes untransferred toner remaining on the surface of the photosensitive drum 31 after the transfer of the toner image, and neutralizes the surface of the photosensitive drum 31. That is, the drum cleaner 36 removes unnecessary toner and charges from the photosensitive drum 31 in preparation for the next toner image formation.

  The transfer unit 14 includes an intermediate transfer belt 41, a secondary transfer roll 42, a belt transport roll 43, a backup roll 44, and a belt cleaner 49. The toner image formed by the developing unit 13 is transferred to the user. Is transferred to the paper P of the paper type determined according to the operation. The intermediate transfer belt 41 is an endless belt member, and the belt conveyance roll 43 and the backup roll 44 bridge the intermediate transfer belt 41. That is, the intermediate transfer belt 41 shown in FIG. 1 is an example of an endless belt member that is stretched around a plurality of rolls.

  At least one of the belt conveying roll 43 and the backup roll 44 is provided with the drive motor 18 shown in FIG. 2, and moves the intermediate transfer belt 41 in the direction of arrow D14 in the drawing. That is, the drive motor 18 shown in FIG. 2 is an example of a drive motor that rotates at least one of the plurality of rolls to rotate the belt member.

  Note that the belt conveyance roll 43 or the backup roll 44 that does not have a driving unit rotates as the intermediate transfer belt 41 moves. As the intermediate transfer belt 41 moves and rotates in the direction of arrow D14 in the drawing, the toner image on the intermediate transfer belt 41 is moved to a region sandwiched between the secondary transfer roll 42 and the backup roll 44.

  The drive motor 18 is a DC brushless motor provided with an FG sensor 181. The FG sensor 181 includes a Hall element in the configuration, and measures the rotation speed of the drive motor 18 by detecting the rotation of the magnetic pole of the drive motor 18. That is, the FG sensor 181 shown in FIG. 2 is an example of a second measuring unit that measures the rotational speed of the drive motor.

The secondary transfer roll 42 transfers the toner image on the intermediate transfer belt 41 onto the paper P conveyed from the conveyance unit 16 by the potential difference with the intermediate transfer belt 41. As a result, a toner image is formed on the surface of the sheet P facing the intermediate transfer belt 41. That is, the secondary transfer roll 42 shown in FIG. 1 is an example of a transfer unit that transfers an image transferred from a plurality of image carriers to a belt member onto a medium.
The belt cleaner 49 removes untransferred toner remaining on the surface of the intermediate transfer belt 41. Then, the transfer unit 14 or the conveyance unit 16 conveys the paper P on which the toner image is transferred to the fixing unit 15.

  The fixing unit 15 includes, for example, a magnetic field generation circuit that generates a magnetic field, a heating belt that generates heat by electromagnetic guidance generated by the action of the generated magnetic field, and a pressure roll that conveys the paper P with the heating belt interposed therebetween. The fixing unit 15 heats the paper P and fixes the toner image transferred to the paper P. The paper P on which the toner image has been fixed through the fixing unit 15 is conveyed to the outside of the image forming apparatus 1 by the conveyance unit 16 or is reversed and conveyed to the transfer unit 14 again.

  The encoder 17 shown in FIG. 2 is provided in at least one of the belt conveyance roll 43 and the backup roll 44, and measures the rotational speed of the roll. Specifically, the encoder 17 includes, for example, a light emitting diode, a slit disk provided with a plurality of slits, and a phototransistor. The slit disk is attached to the measurement object, and the measurement object is rotated. Rotate. Then, the encoder 17 measures the rotation speed of the measurement target by outputting the number of times per unit time detected by the phototransistor through the slit of the slit disk where the light emitted from the light emitting diode rotates. . The encoder 17 measures the number of rotations of the attached roll as the speed of the intermediate transfer belt 41 (circulation speed). That is, the encoder 17 shown in FIG. 2 is an example of a first measuring unit that measures the speed at which the belt member rotates.

1-2. Operation FIG. 3 is a flowchart showing a flow of operation when the image forming apparatus 1 according to the present embodiment controls the drive motor 18.
When the control unit 19 of the image forming apparatus 1 acquires an image formation instruction from a user who operates an operation panel (not shown) (step S101), the image formation indicated by the instruction is a photosensitive drum 31 that contacts the intermediate transfer belt 41. It is determined whether or not the number is equal to or greater than a predetermined number “2” (step S102). This determination may be performed, for example, by determining whether the image formation mode indicated by the user instruction is the color mode or the monochrome mode. Further, the control unit 19 may detect the number of the photosensitive drums 31 that actually contact the intermediate transfer belt 41 by a sensor that detects contact or proximity.

  When it is determined that the number of the photosensitive drums 31 in contact with the intermediate transfer belt 41 is 2 or more (step S102; YES), the control unit 19 controls the drive motor 18 according to the measurement value of the encoder 17. 1 control "is executed (step S103), and the process ends. Specifically, as the first control, the control unit 19 rotates the intermediate transfer belt 41 at a predetermined speed (first speed) according to the rotation speed of the intermediate transfer belt 41 measured by the encoder 17. The drive motor 18 is controlled.

  On the other hand, when it is determined that the number of the photosensitive drums 31 in contact with the intermediate transfer belt 41 is not 2 or more, that is, the number is less than 2 (step S102; NO), the control unit 19 indicates the above instruction. In image formation, it is determined whether or not the paper P, which is a medium, is reversed by the transport unit 16 (step S104). When it is determined that the medium is reversed (step S104; YES), the control unit 19 proceeds to the process of step S103. When it is determined that the medium cannot be reversed (step S104; NO), the control unit 19 executes “second control” for controlling the drive motor 18 in accordance with the measurement value of the FG sensor 181 (step S105). The process ends. Specifically, as the second control, the control unit 19 drives the drive motor 18 to rotate at a predetermined speed (second speed) according to the rotation speed of the drive motor 18 measured by the FG sensor 181. The motor 18 is controlled.

  That is, the control unit 19 responds to the speed measured by the first measuring unit when a predetermined number or more of the plurality of image holding members contact the belt member to transfer the image. When the drive motor is controlled so as to rotate the belt member at the first speed, and when less than a predetermined number of the image holders contact the belt member and transfer the image among the plurality of image holders, It is an example of the control means which controls a drive motor so that the rotational speed of a drive motor may be rotated at a 2nd speed according to the speed measured by the 2nd measurement means.

  Further, when the paper P is reversed by the transport unit 16, the secondary transfer roll 42 transfers the toner image to the first surface of the paper P, and then the toner is applied to the second surface that is the opposite surface of the first surface. Transfer the image. That is, the control unit 19 transfers the image onto the first surface of the medium and then transfers the image onto the second surface, which is the opposite surface of the first surface, and then the image holding member that contacts the belt member. It is an example of the control means which controls a drive motor according to the speed measured by the 1st measurement means irrespective of the number.

  Through the operation described above, the control unit 19 of the image forming apparatus 1 determines the stability of the belt member according to whether or not a predetermined number or more of image holding members are in contact with the belt member. Since 18 is controlled, possibility that control will become unstable is suppressed. Further, for example, in the case of a color mode in which all four photosensitive drums 31 are in contact with the intermediate transfer belt 41, when the possibility of unstable control is relatively low, the measured value of the encoder 17 is used. Since the drive motor 18 is controlled, the response to the fluctuation of the intermediate transfer belt 41 is improved as compared with the case where the drive motor 18 is controlled according to the measured value of the FG sensor 181. Thereby, for example, the position of the image formed on the intermediate transfer belt 41 may be shifted due to an impact received by the intermediate transfer belt 41 from a medium having a relatively large weight per unit area (called basis weight) such as so-called thick paper. Is suppressed.

2. Modification The above is the description of the embodiment, but the contents of this embodiment can be modified as follows. Further, the following modifications may be combined.

2-1. Modification 1
In the above-described embodiment, when the paper P is reversed by the transport unit 16, the control unit 19 determines the speed measured by the first measurement unit regardless of the number of image carriers that contact the belt member. Although the drive motor is controlled, the transport unit 16 may not have a mechanism for inverting the medium. In this case, the control part 19 should just perform 2nd control shown to step S105, without performing judgment of step S104 shown in FIG.

2-2. Modification 2
In the above-described embodiment, the four developing units 13 respectively use yellow, magenta, cyan, and black toners. However, the number of toners used by the developing unit 13 is not limited to four as long as the number is two or more. . Further, the developing unit 13 may use colorless toner under visible light. In this case, the control unit 19 of the image forming apparatus 1 determines whether or not the number of the photosensitive drums 31 in contact with the intermediate transfer belt 41 is equal to or larger than the predetermined number in step S102 shown in FIG. The photosensitive drum 31 that holds an image formed of colorless toner may not be included in the number. That is, the control unit 19 in this modified example is an example of a control unit that does not include an image carrier that forms a colorless image in a plurality of image carriers. Accordingly, when the accuracy of the position where the colorless toner image is formed is not required, the control is not affected by the photosensitive drum 31 that forms the colorless toner image.

2-3. Modification 3
In the above-described embodiment, the control unit 19 controls the drive motor 18 regardless of the basis weight of the paper P. However, the control unit 19 may perform control according to the basis weight of the paper P. For example, the image forming apparatus 1 may have a basis weight sensor 10 as indicated by a broken line in FIG. The basis weight sensor 10 is an example of a detection unit that detects the basis weight of the paper P onto which the secondary transfer roll 42 transfers a toner image, that is, the weight per unit area.

  When the basis weight detected by the basis weight sensor 10 is equal to or greater than the threshold value, the control unit 19 rotates the intermediate transfer belt 41 at a speed (first speed) determined according to the speed measured by the encoder 17. The drive motor 18 is controlled so that Thereby, the response to the fluctuation of the intermediate transfer belt 41 is improved, and the possibility that the position of the image formed on the intermediate transfer belt 41 is shifted due to the impact received by the intermediate transfer belt 41 from a medium having a relatively large basis weight is suppressed. The

  On the other hand, when the basis weight detected by the basis weight sensor 10 is less than the threshold value, the control unit 19 determines the rotational speed of the drive motor 18 according to the speed measured by the FG sensor 181 (first speed). The drive motor is controlled to rotate at a second speed. This suppresses the possibility of unstable control.

2-4. Modification 4
In the above-described embodiment, when the control unit 19 determines that the number of the photosensitive drums 31 in contact with the intermediate transfer belt 41 is equal to or more than a predetermined number, the drive motor 18 is set according to the measurement value of the encoder 17. However, when it is determined that the number is equal to or greater than a predetermined number, the pressing force received from each photosensitive drum 31 in contact with the intermediate transfer belt 41 is further measured to determine each pressing force. When the above conditions are satisfied, the above control according to the measurement value of the encoder 17 may be performed. Here, the conditions include, for example, that the lowest value of each pressing force is equal to or greater than a threshold value, or that the total pressing force is equal to or greater than the threshold value. According to this configuration, when the force for supporting the intermediate transfer belt 41 is large, for example, so as not to make the control unstable, the control is performed so that the accuracy of the position where the toner image is formed is improved.

2-5. Modification 5
A program executed by the control unit 19 is stored in a computer-readable recording medium such as a magnetic recording medium such as a magnetic tape or a magnetic disk, an optical recording medium such as an optical disk, a magneto-optical recording medium, or a semiconductor memory. Can be provided in state. It is also possible to download this program via a communication line such as the Internet. Note that various devices other than the CPU may be applied as the control means exemplified by the control unit 19. For example, a dedicated processor is used.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Container, 12 ... Supply part, 13 ... Developing part, 14 ... Transfer part, 15 ... Fixing part, 16 ... Conveying part, 17 ... Encoder, 18 ... Drive motor, 181 ... FG sensor, 19 Control unit 31 Photoconductor drum 32 Charger 33 Exposure device 34 Developer 35 35 Primary transfer roll 36 Drum cleaner 39 Toner cartridge 41 Intermediate transfer belt 42 Next transfer roll, 43 ... belt transport roll, 44 ... backup roll, 49 ... belt cleaner, 61 ... registration roll, 62 ... exit roll, 63 ... discharge roll, 64a ... retransmission roll, P ... paper, r1 ... path, r2 ... Path, SFT ... axis, STO ... paper discharge place.

Claims (5)

An endless belt member spanned across a plurality of rolls;
A drive motor for rotating the belt member by rotating at least one of the plurality of rolls;
A plurality of image holders each holding an image, wherein the plurality of image holders contact the belt member at different positions and transfer the images respectively;
Image forming means for forming the images on the plurality of image carriers,
Transfer means for transferring the image transferred from the plurality of image carriers to the belt member to a medium;
First measuring means for measuring a speed at which the belt member circulates;
Second measuring means for measuring the rotational speed of the drive motor;
According to the speed measured by the first measuring means, when a plurality of the image holding bodies, among the plurality of image holding bodies, transfer the image in contact with the belt member, respectively, Controlling the drive motor to rotate the belt member at the first speed;
According to the speed measured by the second measuring unit, when the image holders of the plurality of image holders contact the belt member to transfer the image when the number of image holders is less than the determined number, An image forming apparatus comprising: control means for controlling the drive motor so as to rotate the rotation speed of the drive motor at a second speed. The control means includes
The image forming apparatus according to claim 1, wherein an image carrier that forms a colorless image is not included in the plurality of image carriers. The control means includes
The image carrier that contacts the belt member when the image is transferred to a second surface opposite to the first surface after the transfer means transfers the image to the first surface of the medium. 3. The image forming apparatus according to claim 1, wherein the drive motor is controlled according to a speed measured by the first measuring unit regardless of the number of the image forming apparatuses. Detecting means for detecting the weight per unit area of the medium to be transferred by the transfer means;
The control means includes
When the weight detected by the detection means is greater than or equal to a threshold, the drive motor is controlled to rotate the belt member at the first speed according to the speed measured by the first measurement means;
When the weight detected by the detection means is less than a threshold value, the drive motor is rotated so that the rotation speed of the drive motor is rotated at the second speed according to the speed measured by the second measurement means. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled. An endless belt member spanned between a plurality of rolls, a drive motor that rotates at least one of the plurality of rolls to rotate the belt member, and a plurality of image carriers each holding an image A plurality of image holders that contact the belt member at different positions to transfer the images, an image forming unit that forms the images on the plurality of image holders, and the plurality of image holders. Transfer means for transferring the image transferred from the body to the belt member to a medium; first measurement means for measuring the rotating speed of the belt member; and second measurement means for measuring the rotational speed of the drive motor; A computer of an image forming apparatus having
According to the speed measured by the first measuring means, when a plurality of the image holding bodies, among the plurality of image holding bodies, transfer the image in contact with the belt member, respectively, Controlling the drive motor to rotate the belt member at the first speed;
According to the speed measured by the second measuring unit, when the image holders of the plurality of image holders contact the belt member to transfer the image when the number of image holders is less than the determined number, A program for functioning as a control means for controlling the drive motor so as to rotate the rotation speed of the drive motor at a second speed.

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