JP2023173149A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can accurately correct color shift regardless of an image difference.SOLUTION: An image forming apparatus 100 comprises: an image forming unit 10 that forms images on photoconductor drums 1; an intermediate transfer belt 21 to which the images are transferred from the photoconductor drums 1; primary transfer units N1 that transfer the images carried on the photoconductor drums 1 to the intermediate transfer belt 21; a secondary transfer unit N2 that transfers the images carried on the intermediate transfer belt 21 to a recording material; an intermediate transfer belt driving unit (113) that rotates the intermediate transfer belt 21; and a control unit (150). The control unit (150) calculates a correction amount for correcting positions when the images are transferred from the photoconductor drums 1 to the intermediate transfer belt 21 based on the torque of the intermediate transfer belt driving unit (113).SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus such as a printer, a copying machine, or a multifunctional device.

2. Description of the Related Art Some image forming apparatuses, such as those using an electrophotographic method, include an endless belt as an image carrier that carries a toner image. Such a belt is, for example, a second image carrier (intermediate) used to transfer a toner image formed on a first image carrier (photoconductor) having a photosensitive layer to a sheet-like recording material such as paper. transfer belt). The toner image formed on the photoreceptor is primarily transferred to an intermediate transfer belt, and then secondarily transferred to a recording material. In particular, when forming a color image, toner images of different colors are formed on a plurality of photoreceptors, and the toner images of each color are sequentially primarily transferred from each photoreceptor onto the surface of a rotating intermediate transfer belt. As a result, the intermediate transfer belt carries a full-color toner image. The full-color toner image on the intermediate transfer belt is secondarily transferred to a recording material.

The intermediate transfer belt and A secondary transfer portion (secondary transfer nip) that is a contact portion with an external material is formed. A secondary transfer inner roller, which is one of a plurality of tension rollers that tension the intermediate transfer belt, is used as the inner member. As the external member, an outer secondary transfer roller is used, which is disposed opposite to the inner secondary transfer roller with the intermediate transfer belt in between, and is biased toward the inner secondary transfer roller. By applying a voltage with the opposite polarity to the toner charging polarity to the secondary transfer outer roller (or applying a voltage with the same polarity as the toner charging polarity to the secondary transfer inner roller), intermediate transfer is performed in the secondary transfer nip. The toner image on the belt is secondarily transferred onto the recording material.

While the recording material is being conveyed through the secondary transfer nip, the intermediate transfer belt is subjected to load fluctuations in the rotational direction. For example, the load applied to the intermediate transfer belt varies depending on the timing at which the leading edge of the recording material contacts the nip of a conveyance roller for conveying the recording material or a curved guide path on the conveyance path. When images are formed continuously, the intermediate transfer belt is subjected to such load fluctuations at the timing when toner images of each color are primarily transferred. For this reason, the positions where the toner images of each color are primarily transferred are shifted on the intermediate transfer belt for each color. Such a transfer position shift causes color shift.

In order to suppress load fluctuations that occur on the intermediate transfer belt, there is a technique that compares the driving torque of the intermediate transfer belt with an ideal torque value and suppresses the cause of the torque fluctuation at an appropriate timing according to the difference. For example, in the image forming apparatus disclosed in Patent Document 1, based on a drive torque waveform representing fluctuations in the drive torque of the intermediate transfer belt obtained in advance, the intermediate transfer belt is suppresses fluctuations in drive torque. Suppression of fluctuations in the driving torque is performed by adjusting the pressure of the secondary transfer nip, adjusting the position of the outer secondary transfer roller, and controlling the assist drive for conveyance of the recording material. The image forming apparatus disclosed in Patent Document 2 records the rotational speed of the intermediate transfer belt in advance and performs constant speed control against fluctuations in the rotational speed to suppress color shift. At this time, the image forming device can reduce color shift regardless of the paper type by appropriately adjusting the amount of rotational speed control depending on the type of recording material (stiffness, basis weight, etc.) .

Japanese Patent Application Publication No. 2015-22151 Japanese Patent Application Publication No. 2010-8805

In this manner, conventionally, in order to suppress load fluctuations on the intermediate transfer belt caused by conveyance of the recording material, disturbance factors are appropriately suppressed based on load fluctuations obtained in advance. Furthermore, by controlling the rotational speed of the intermediate transfer belt to a constant speed according to the type of recording material, it is possible to suppress color shift caused by load fluctuations on the intermediate transfer belt, regardless of the type of recording material.

However, load fluctuations on the intermediate transfer belt that occur during a print job are also caused by image differences (differences in image size and image density). Generally, the larger the amount of toner that has been primarily transferred onto the intermediate transfer belt, the lower the frictional resistance at the primary transfer portion that performs the primary transfer. In this case, the amount of load fluctuation tends to become smaller. In other words, the load fluctuation (driving torque waveform) of the intermediate transfer belt, which is obtained in advance by the conventional color misregistration reduction method, changes not only depending on the type of recording material but also depending on the image difference.

Image differences are difficult to control because they are determined by images formed according to print jobs, and they become disturbance noise when detecting load fluctuations. On the other hand, load fluctuations due to conveyance of recording materials occur stably when the same recording material is used, and have a large effect on load fluctuations. Therefore, it is important to have a mechanism that separates and removes the component due to the image difference among the load fluctuations on the intermediate transfer belt and corrects only the component due to the conveyance of the recording material.

In view of the above-mentioned problems, the main object of the present invention is to provide an image forming apparatus that can correct color shift with high precision regardless of image differences.

The image forming apparatus of the present invention includes: an image forming means for forming an image on a first image carrier; a second image carrier, which is an endless belt to which the image is transferred from the first image carrier; a first transfer device that transfers the image carried by the first image carrier to the second image carrier; a second transfer device that transfers the image carried by the second image carrier to a recording material; a driving means for rotating a second image bearing member; and a driving means for causing the image forming means to form the image, and transferring the first image bearing member to the second image bearing member rotationally driven by the driving means. control means for transferring the image from the second image carrier to the recording material by the second transfer means, the control means based on the torque of the drive means, The present invention is characterized in that a correction amount for correcting a position when transferring the image from the first image carrier to the second image carrier is calculated.

According to the present invention, color shift can be corrected with high precision regardless of image differences.

FIG. 1 is a configuration diagram of an image forming apparatus. (a) and (b) are explanatory views of an exposure device. An explanatory diagram of a control section. FIG. 4 is an explanatory diagram of torque fluctuations generated by the primary transfer section. FIG. 6 is an explanatory diagram of the occurrence of torque fluctuations due to the secondary transfer section. FIG. 6 is an explanatory diagram of torque fluctuations generated by the secondary transfer section. 5 is a flowchart showing a process for obtaining a color shift correction amount. (a) and (b) are flowcharts showing the acquisition process of the amount of fluctuation in torque. An explanatory diagram of a separation mechanism. 5 is a flowchart showing a process for obtaining a color shift correction amount. 5 is a flowchart showing a process for acquiring torque fluctuation amount.

Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings.

(First embodiment)
FIG. 1 is a configuration diagram of an image forming apparatus according to this embodiment. The image forming apparatus 100 of this embodiment is realized by a tandem copying machine, a printer, a facsimile machine, a multifunction device, etc. that employs an intermediate transfer method. The image forming apparatus 100 forms a full-color image on a sheet-like recording material (transfer material, sheet material, recording medium, media) P such as paper using an electrophotographic method, for example, based on an image signal acquired from an external device. be able to.

Image forming apparatus 100 includes a plurality of image forming sections (stations). In this embodiment, four image forming units 10Y, 10M, 10C, and 10K are provided to form images in four colors: yellow (Y), magenta (M), cyan (C), and black (K). . The image forming units 10Y, 10M, 10C, and 10K are arranged in series along the rotation direction (movement direction) of an image transfer surface of an intermediate transfer belt 21, which will be described later, which is arranged substantially horizontally. In the following, for elements having the same or corresponding functions or configurations of each image forming unit 10Y, 10M, 10C, 10K, the suffix Y, M, C, K indicates which color the element is for. It may be omitted to give a comprehensive explanation. The image forming section 10 includes a photosensitive drum 1, a charger 2, an exposure device 3, a developing device 4, a primary transfer roller 23, a drum cleaner 5, and the like.

The photosensitive drum 1 is a first image carrier that carries a toner image, and is a drum-shaped photosensitive member (electrophotographic photosensitive member) having a photosensitive layer on its surface. The photosensitive drum 1 is rotatable around a drum shaft. The photosensitive drum 1 is rotationally driven in the direction of the arrow (clockwise) in FIG. 1 by a driving force transmitted from a photosensitive drum driving section including a drum driving motor, which will be described later, as a driving source. The charger 2 uniformly charges the surface of the rotating photosensitive drum 1 to a predetermined potential of a predetermined polarity (negative polarity in this embodiment). The charger 2 is, for example, a charging roller. A predetermined charging voltage is applied to the charger 2 by a charging power source (not shown) during charging processing.

The exposure unit 3 forms an electrostatic image (electrostatic latent image) on the surface of the photosensitive drum 1 by exposing the charged surface of the photosensitive drum 1 to light according to an image signal. FIG. 2 is an explanatory diagram of the exposure device 3. The exposure device 3 of this embodiment includes a substrate 302 on which a plurality of light emitting chips 639 are mounted, a lens array 303, and an optical print head 304. The light emitting chip 639 has a plurality of light emitting elements that emit light according to image signals. The lens array 303 focuses the light output from the light emitting chip 639 onto the surface of the photosensitive drum 1. The optical print head 304 is a housing that holds a substrate 302 and a lens array 303.

As shown in FIG. 2A, a plurality of light emitting chips 639 mounted on the substrate 302 are arranged in the direction of the rotation axis of the photosensitive drum 1. The plurality of light emitting chips 639 are arranged alternately in two rows. As shown in FIG. 2(b), in this embodiment, 29 light emitting chips 639 (639-1 to 639-29) are arranged. Each of the light emitting chips 639-1 to 639-29 includes 516 LED (Light Emitting Diode) elements, which are light emitting elements, arranged in a row in the direction of the rotation axis. The distance between adjacent LED elements in the direction of the rotation axis of the photosensitive drum 1 corresponds to the resolution of the image formed by the image forming apparatus 100. In this embodiment, the resolution of the image forming apparatus 100 is 1200 [dpi], and the distance between adjacent LED elements is 21.16 [μm]. The direction of the rotation axis of the photosensitive drum 1 in which the light emitting chips 639 are arranged is the main scanning direction in which the exposure device 3 exposes the photosensitive drum 1 . The sub-scanning direction perpendicular to the main-scanning direction is the same direction as the rotation direction of the photosensitive drum 1.

The substrate 302 has a light emitting chip 639 mounted on one side, and a cable (not shown) having a connector on the other side. A substrate (not shown) including a connector joint is provided on the main body side of the image forming apparatus 100. The connector on the board 302 is connected to the connector joint on the main body side. Thereby, the main body of the image forming apparatus 100 and the exposure device 3 are electrically connected via the cable. When the light emitting chip 639 emits light based on a signal from the main body of the image forming apparatus 100, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 1.

The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by being supplied with toner, which is a developer, by a developing device 4 . By developing the electrostatic latent image, a toner image (developer image) is formed on the photosensitive drum 1. In this embodiment, the exposed portion (electrostatic latent image) on the photosensitive drum 1 whose absolute value has decreased by being exposed to light after being uniformly charged is given the same polarity as the charged polarity of the photosensitive drum 1 (electrostatic latent image). In this embodiment, reversal development is performed in which negatively charged toner is attached.

The developing device 4 includes a developing roller 40 that is a rotatable developer carrier in order to carry the developer and convey it to a developing position, which is a portion facing the photosensitive drum 1 . The developing roller 40 is rotationally driven by a driving force transmitted from, for example, a drive system of the photosensitive drum 1. Further, a predetermined developing voltage is applied to the developing roller 40 during development by a developing power source (not shown).

The intermediate transfer belt 21 is a second image carrier configured as an endless belt, and is an intermediate transfer member that can rotate in the direction of arrow A. Along the image transfer surface of the intermediate transfer belt 21, photosensitive drums 1Y, 1M, 1C, and 1K are arranged. The intermediate transfer belt 21 is wound around a plurality of tension rollers (support rollers), such as a tension roller 24, a pre-secondary transfer roller 29, an upstream auxiliary roller 25, and an inner secondary transfer roller 22, and is rotated with a predetermined tension. It is strung up.

The tension roller 24 is located upstream of the primary transfer nip (primary transfer portion N1) where the toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 21 in the rotating direction (conveying direction, moving direction, running direction) of the intermediate transfer belt 21. placed on the side. Tension roller 24 applies a predetermined tension to intermediate transfer belt 21 . A belt cleaner 28 is provided at a position facing the tension roller 24 with the intermediate transfer belt 21 in between. The pre-secondary transfer roller 29 is disposed upstream of a secondary transfer nip (secondary transfer portion N2) where the toner image is transferred from the intermediate transfer belt 21 to the recording material P in the rotational direction of the intermediate transfer belt 21. The pre-secondary transfer roller 29 forms the surface of the intermediate transfer belt 21 near the secondary transfer portion N2. The upstream auxiliary roller 25 and the pre-secondary transfer roller 29 form an image transfer surface of the intermediate transfer belt 21 arranged substantially horizontally.

The primary transfer rollers 23Y, 23M, 23C, and 23K are roller-shaped primary transfer members arranged on the inner circumferential surface side of the intermediate transfer belt 21 in correspondence with the respective photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 23 is urged toward the photosensitive drum 1 and forms a primary transfer portion N1 (primary transfer nip) that is a contact portion between the photosensitive drum 1 and the intermediate transfer belt 21. The toner image formed on the photosensitive drum 1 is primarily transferred onto the rotating intermediate transfer belt 21 by the action of the primary transfer roller 23 in the primary transfer portion N1. During primary transfer, a primary transfer voltage is applied to the primary transfer roller 23 by a primary transfer power source (not shown), which is a DC voltage having a polarity opposite to the normal charging polarity of the toner (the charging polarity of the toner during development). . When forming a full-color image, the yellow, magenta, cyan, and black toner images formed on each photosensitive drum 1 are superimposed on the same image forming area on the intermediate transfer belt 21, and transferred to the primary transfer roller. 23, the primary transfer is performed sequentially.

The inner secondary transfer roller 22 (secondary transfer opposing roller, internal member) is an opposing member (opposing electrode) that faces an outer secondary transfer roller 41, which will be described later, with the intermediate transfer belt 21 in between. Further, the secondary transfer inner roller 22 of this embodiment also has the function of a driving roller. The secondary transfer inner roller 22 is rotationally driven in the direction of the arrow (counterclockwise) in FIG. 1 by transmission of a driving force from an intermediate transfer belt driving section, which will be described later. As a result, the intermediate transfer belt 21 is driven and rotates (circularly moves) in the direction of arrow A. The tension rollers other than the secondary transfer inner roller 22 rotate as the intermediate transfer belt 21 rotates.

The secondary transfer outer roller (secondary transfer roller, external material) 41 is a roller-shaped two roller-shaped roller disposed at a position facing the secondary transfer inner roller 22 on the outer peripheral surface side (image transfer surface) of the intermediate transfer belt 21. This is the next transfer member (transfer rotating body). The secondary transfer outer roller 41 is biased toward the secondary transfer inner roller 22 and forms a secondary transfer portion N2 (secondary transfer nip), which is a contact area between the intermediate transfer belt 21 and the secondary transfer outer roller 41. Form. The toner image formed on the intermediate transfer belt 21 is conveyed while being sandwiched between the intermediate transfer belt 21 and the secondary transfer outer roller 41 due to the action of the secondary transfer outer roller 41 in the secondary transfer portion N2. Secondary transfer is performed onto the recording material P. In this embodiment, the secondary transfer outer roller 41 is applied with a secondary transfer voltage, which is a DC voltage having a polarity opposite to the normal charging polarity of the toner, by a secondary transfer power source (not shown) during secondary transfer. Ru. The secondary transfer inner roller 22 of this embodiment is electrically grounded (connected to the ground). Note that the inner secondary transfer roller 22 may be used as a secondary transfer member and a secondary transfer voltage having the same polarity as the normal charging polarity of the toner may be applied thereto, and the outer secondary transfer roller 41 may be used as a counter electrode. . In this case, the secondary transfer outer roller 41 is electrically grounded.

The recording material P to be transported to the secondary transfer section N2 is stored in advance in the recording material storage 11 (cassette). The recording materials P are fed one by one to the pre-registration roller 14 by a feeding unit such as a feeding roller 18 provided in the recording material storage 11 . The pre-registration roller 14 is driven by a pre-registration roller driving section (not shown) and conveys the recording material P to the registration adjustment section 12. After adjusting the posture of the recording material P, the registration adjustment section 12 transports the recording material P to the secondary transfer section N2 at a predetermined timing.

The registration adjustment section 12 includes a pair of registration rollers (registration roller pair 13) that are roller-shaped conveying members, and a registration drive section (not shown) that drives the registration roller pair 13. The pair of registration rollers 13 is rotationally driven by a registration drive unit, and thus conveys the recording material P at a contact portion (nip portion) between the pair of registration rollers 13 . The registration drive section drives at least one of the registration roller pair 13. The registration roller pair 13 is stopped at the timing when the recording material P is conveyed, and the leading edge of the recording material P collides with the nip portion. The pre-registration roller 14 continues to convey the recording material P even after the leading edge of the recording material P collides with the nip portion. To this end, the recording material P forms a roll at the leading edge to adjust its posture. Thereafter, the registration roller pair 13 starts rotating at a predetermined timing and conveys the recording material P to the secondary transfer section N2.

A toner image is secondarily transferred to the recording material P at a secondary transfer portion N2, and the recording material P is conveyed to the fixing device 15. The fixing device 15 fixes (melts, fixes) the toner image on the surface of the recording material P by heating and pressurizing the recording material P carrying the unfixed toner image. The recording material P with the toner image fixed thereon is discharged (output) by a paper discharge roller 16 or the like to a paper discharge tray 17 provided outside (outside the machine) of the image forming apparatus 100 .

Note that toner remaining on the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 1 by the drum cleaner 5 and collected. The deposits on the intermediate transfer belt 21, such as toner remaining on the intermediate transfer belt 21 after the secondary transfer (secondary transfer residual toner) and paper dust attached from the recording material P, are removed from the intermediate transfer belt 21 by the belt cleaner 28. removed from and collected.

In this embodiment, an intermediate transfer belt unit is configured by the intermediate transfer belt 21, each of the above-mentioned tension rollers, a frame that supports them, and the like. The intermediate transfer belt unit can be removed from the image forming apparatus 100 for maintenance or replacement work.

(control unit)
FIG. 3 is an explanatory diagram of a control unit that controls the operation of image forming apparatus 100 having such a configuration. The control unit 150 is an information processing device that includes a CPU (Central Processing Unit) 151, a memory 152, and an interface (I/F) unit 153. The CPU 151 is an arithmetic control device that is a central semiconductor element that performs arithmetic processing. The memory 152 includes storage media such as ROM (Read Only Memory) and RAM (Random Access Memory). Information input to the control unit 150, detected information, calculation results, etc. are stored in the RAM. The ROM stores control programs, various data tables, and the like. The CPU 151 and the memory 152 are capable of data communication with each other. The I/F unit 153 controls communication between the control unit 150 and devices connected to the control unit 150.

The control section 150 is connected to each section of the image forming apparatus 100 (the image forming section 10, the intermediate transfer belt 21, drive sections for members related to conveyance of the recording material P, various power supplies, etc.). In FIG. 3, the control section 150 is connected to the photosensitive drum drive section 111, the exposure device 3, the intermediate transfer belt drive section 113, the operation section 160 (operation panel), and the external device 200. In addition, the control unit 150 is connected to various high-voltage power supplies (not shown) (charging voltage, developing voltage, primary transfer voltage, secondary transfer voltage), and the like.

The photosensitive drum drive unit 111 includes a drum drive motor 111a that serves as a drive source for the photosensitive drum 1. The photosensitive drum drive unit 111 controls the rotational drive of the photosensitive drum 1 by driving the drum drive motor 111a according to a control signal obtained from the control unit 150.

The control unit 150 acquires a signal (output value) indicating a detection result such as a current value of each drive motor and stores it in the memory 152. The intermediate transfer belt drive unit 113 includes an intermediate transfer belt drive motor 113a that is a drive source for the intermediate transfer belt 21, and a torque detection unit that can continuously detect the drive load (torque) of the intermediate transfer belt 21 at predetermined time intervals. It has a section 113b. The intermediate transfer belt drive unit 113 controls the rotational drive of the intermediate transfer belt 21 by driving the intermediate transfer belt drive motor 113a according to a control signal obtained from the control unit 150. The torque detection unit 113b detects the current of the intermediate transfer belt drive motor 113a. The control unit 150 stores the current value of the intermediate transfer belt drive unit 113a detected by the torque detection unit 113b in the memory 152 as torque fluctuation data.

The operation unit 160 is a user interface provided on the main body of the image forming apparatus 100. The operation unit 160 includes a display unit that displays information under the control of the control unit 150 and an input unit that inputs information to the control unit 150 through an operation by an operator such as a user or a service person. For example, the operation unit 160 is configured with a touch panel having the functions of a display unit and an input unit. The external device 200 is an image reading device such as a scanner, a personal computer, or the like.

The control unit 150 controls the operation of each unit of the image forming apparatus 100 based on job information input from the operation unit 160 and the external device 200 to form an image. The job information includes information (command signal) regarding the printing operation, such as the type of recording material P, in addition to a start instruction (start signal) and an image signal. Information regarding the type of recording material P (also simply referred to as "information regarding recording material P") includes information that allows the recording materials P to be distinguished. The information that can distinguish the recording material P is, for example, information such as an attribute based on general characteristics (paper type category), a numerical value or a numerical range, or a brand (including manufacturer, product number, etc.). Attributes (paper type categories) based on general characteristics include plain paper, high-quality paper, glossy paper, coated paper, embossed paper, thick paper, and thin paper. The numerical value or numerical range is the basis weight, thickness, size, etc. of the recording material P. In this embodiment, the information regarding the type of recording material P includes information related to the stiffness of the recording material P, in particular, information regarding the basis weight of the recording material P.

When information regarding printing operations is input from the operation unit 160, the operation unit 160 functions as an input unit that inputs information regarding the type of recording material P to the control unit 150. When information regarding the printing operation is input from the external device 200, the I/F unit 153 functions as an input unit that inputs information regarding the type of recording material P to the control unit 150.

In response to one start instruction, the image forming apparatus 100 starts executing a job (print job), which is a series of operations for forming and outputting an image on a single or multiple sheets of recording material P. The operation according to the job generally includes an image forming process (printing operation, printing operation, image forming operation), a pre-rotation process, a paper-interval process when forming images on a plurality of recording materials P, and a post-rotation process. The image forming process is a process from forming an electrostatic latent image to secondary transfer. The period of the image forming process is the time of image formation (image forming period). The pre-rotation process is a process of performing preparatory operations before the image forming process, from when a start instruction is input until actually starting image formation. The inter-sheet process is a process corresponding to between one recording material P and the next recording material P during continuous image formation in which images are continuously formed on a plurality of recording materials P. The post-rotation process is a process of performing a tidying operation (preparation operation) after the image forming process. The non-image forming period (non-image forming period) is a period other than the image forming period. During non-image formation, the above-described pre-rotation process, inter-sheet process, post-rotation process, and pre-multi-rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or returned from a sleep state, are performed. The sleep state (hibernation state) is, for example, a state in which the supply of power to each part of the image forming apparatus 100 other than the control unit 150 (or a part thereof) is stopped, and power consumption is suppressed compared to the standby state. .

In this embodiment, the current value of the intermediate transfer belt drive motor 113a is always detected during the image forming period. The detected current value is stored in the memory 152 as a torque (hereinafter also referred to as “Tq”) representing fluctuations in the torque acting on the intermediate transfer belt 21.

As described above, the substrate 302 of the exposure device 3 is electrically connected to the control section 150 via the connector. The control unit 150 inputs a control signal based on the image signal to the substrate 302 of the exposure device 3. The exposure device 3 forms an electrostatic latent image on the photosensitive drum 1 by individually emitting light from a plurality of light emitting elements included in a plurality of light emitting chips 639 based on the input control signal. The image signal includes image position information (writing start position) in the rotation direction (sub-scanning direction) of the photosensitive drum 1. The starting position of the image is determined by the timing at which the exposure device 3 starts exposure. In the image forming apparatus 100 of this embodiment, the image signal includes information on the time at which the light emitting element should emit light during a job (timing information from the job start time). The image signal is recorded in the memory 152 simultaneously with the input of the control signal.

(Torque fluctuation in the primary transfer section)
In the image forming apparatus 100, torque fluctuations occur in the intermediate transfer belt drive section 113 due to the primary transfer section N1. FIG. 4 is an explanatory diagram of torque fluctuations generated by the primary transfer portion N1. FIG. 4 shows a time axis waveform (torque waveform) of torque fluctuation (Tq1) of the intermediate transfer belt drive unit 113 that occurs in the primary transfer portion N1 during primary transfer. The graph in FIG. 4 shows a time-axis waveform of the intermediate transfer belt driving torque Tq1, with the horizontal axis representing the time axis and the vertical axis representing the driving torque. The graph and time axis indicate the timing at which the drive input signal to the intermediate transfer belt drive motor 113a is turned on, the timing at which the input signal for the primary transfer voltage is turned on, and the timing at which toner enters the primary transfer portion N1. .

When the primary transfer voltage input signal is turned on, adsorption force is generated from the primary transfer roller 23 toward the intermediate transfer belt 21, so that the intermediate transfer belt driving torque Tq1 increases. Here, the steady torque value from when the drive input signal to the intermediate transfer belt drive motor 113a is turned on until the primary transfer voltage input signal is turned on is defined as the reference torque Tq1_ST.

When the toner carried on the photosensitive drum 1 reaches the primary transfer portion N1, the toner is present in the nip between the photosensitive drum 1 and the intermediate transfer belt 21, so that the surface μ changes. When toner is present in the primary transfer portion N1, the surface μ becomes low, so that the load applied to the intermediate transfer belt drive unit 113 by the primary transfer portion N1 is reduced. In this embodiment, the load applied to the intermediate transfer belt driving section 113 by the photosensitive drum 1 rotationally driven by the photosensitive drum driving section 111 is reduced. Therefore, a decrease in the intermediate transfer belt driving torque Tq1 can be confirmed at the timing when the toner reaches the primary transfer portion N1.

Furthermore, the waveforms of the intermediate transfer belt driving torque Tq1 are shown under the condition that the amount of toner entering the primary transfer portion N1 is "large" (solid line) and the condition that the amount of toner is "small" (broken line). It can be seen from each waveform that the drop in the intermediate transfer belt drive torque Tq1 is greater under the condition where the amount of toner is large than under the condition where the amount of toner is small. Note that if duty [%], which is a value indicating image density, is used to replace the value representing the amount of toner, the condition with a large amount of toner = duty 40%, and the condition with a small amount of toner = duty 3%. As described above, the amount of variation in the intermediate transfer belt driving torque Tq1 at the primary transfer portion N1 varies depending on the difference in the amount of toner entering the primary transfer portion N1, that is, the image difference.

(Torque fluctuation in the secondary transfer section)
In the image forming apparatus 100, torque fluctuations occur in the intermediate transfer belt drive section 113 even in the secondary transfer section N2. FIG. 5 is an explanatory diagram of the occurrence of torque fluctuations due to the secondary transfer portion N2. FIG. 5 shows the vicinity of the secondary transfer portion N2. The recording material P is conveyed along the conveyance path in the direction of the arrow. The recording material P has a conveyance path including a pre-registration roller nip N14 formed by the pre-registration roller 14, a registration roller nip N13 formed by the registration roller pair 13, a bending path 50 before secondary transfer, a secondary transfer section N2, and a fixing nip N15 formed by the fixing device 15. They are transported in order.

Intermediate transfer belt drive section 113 receives load variation in the conveyance direction (rotation direction) due to recording material P passing through secondary transfer section N2, and torque variation occurs. This torque fluctuation changes depending on which section on the conveyance path the recording material P is passing through. For example, in this embodiment, the following two sections are listed as sections where the amount of torque fluctuation is particularly large. The first is a section (section A) from when the leading edge of the recording material P enters the secondary transfer section N2 until it enters the fixing nip N15. The second is a section (section B) after section A in which the rear end of the recording material P passes through the pre-registration roller nip N14 until it passes through the secondary transfer section N2.

FIG. 6 is an explanatory diagram of torque fluctuations generated by the secondary transfer portion N2. FIG. 6 shows a time axis waveform (torque waveform) of torque fluctuation (Tq2) of the intermediate transfer belt drive unit 113 that occurs in the secondary transfer portion N2 during secondary transfer. The graph in FIG. 6 shows a time axis waveform of the intermediate transfer belt drive torque Tq2, with the horizontal axis representing time and the vertical axis representing torque. A steady torque value before entering the secondary transfer portion N2 is defined as a reference torque Tq2_ST.

As shown in FIG. 6, in section A, the intermediate transfer belt drive torque Tq2 remains at a value lower than the reference torque Tq2_ST. This is because, in section A, as the recording material P is conveyed to the secondary transfer section N2, the conveyance force from the registration roller nip N13 is added as torque for driving the intermediate transfer belt 21, and the intermediate This is because the transfer belt drive torque Tq2 is reduced. After that, the leading edge of the recording material P enters the fixing nip N15, and the conveyance resistance of the recording material P increases, so that the intermediate transfer belt driving torque Tq2 increases.

In section B, at the timing when the rear end of the recording material P passes through the pre-registration roller nip N14, the conveying force of the pre-registration roller 14 that was used to convey the recording material P is lost. Therefore, the intermediate transfer belt driving torque Tq2 increases by that amount. Thereafter, the recording material P passes through the pre-secondary transfer bending path 50 and the registration roller nip N13, so that the intermediate transfer belt driving torque Tq2 continues to increase. Finally, at the timing when the trailing edge of the recording material P passes the secondary transfer portion N2, the intermediate transfer belt driving torque Tq2 becomes a steady torque Tq2_ST.

As described above, fluctuations in the intermediate transfer belt drive torque Tq2 due to the secondary transfer portion N2 occur due to the leading edge of the recording material P entering each roller nip and the trailing edge passing through each roller nip. In this embodiment, the amount of variation is particularly large in section A and section B. Further, the intermediate transfer belt drive torque Tq2 also differs depending on the type of recording material P to be conveyed (basis weight, stiffness, etc.).

(Color shift correction)
In this embodiment, color misregistration caused by the recording material P is corrected by exposure correction. A method for calculating the amount of color misregistration caused by the recording material P will be explained.

Intermediate transfer belt drive torque Tq fluctuates (increases or decreases) at specific timing during a job. Therefore, at this timing, a positional shift of the image (toner image) transferred by the primary transfer portion N1 on the intermediate transfer belt 21 occurs. Color misregistration occurs because the timing of this positional misalignment differs depending on the color of the transferred image.

The variation amount of the intermediate transfer belt drive torque Tq and the positional deviation amount P (Py, Pm, Pc, There is a proportional relationship with Pk). The relationship between the amount of variation Tq(t) [N・m] in the intermediate transfer belt drive torque Tq at time t(s) from the job start time and the amount of positional deviation P(t) [μm] is expressed by the following formula. be done.
Py(t) = αy×Tq(t)…(Formula 1)
Pm(t) = αm×Tq(t)...(Formula 2)
Pc(t) = αc×Tq(t)...(Formula 3)
Pk(t) = αk×Tq(t)…(Formula 4)
αy, αm, αc, and αk are proportionality constants calculated experimentally.

Color shift exposure correction for correcting color shift will be explained. As described above, color misregistration caused by the recording material P occurs due to fluctuations in the intermediate transfer belt drive torque Tq that occur at a fixed timing during a job. Therefore, it is recommended to execute the job in advance using an image or recording material P that is equivalent to the content of the print job, record the amount of variation Tq(t) at that time, and calculate the amount of positional deviation P(t) from this. It is possible to derive in advance the amount of color misregistration that occurs when a job is executed. In this embodiment, the color misregistration in the sub-scanning direction is defined as the amount of misregistration of other colors with respect to yellow (Y), which is the reference color. Therefore, the amount of color shift Im(t), Ic(t), Ik(t) [μm] of each color in the sub-scanning direction is expressed by the following formula.
Im(t): Pm(t) - Py(t)...(Formula 5)
Ic(t): Pc(t) - Py(t)...(Formula 6)
Ik(t): Pk(t) - Py(t)...(Formula 7)

Correcting color shift in the sub-scanning direction by shifting the image writing start position from the original position based on the amount of color shift in the sub-scanning direction Im(t), Ic(t), Ik(t) for each color. becomes possible. That is, if Pos(t) is the writing position of the image of each color that the control unit 150 was scheduled to instruct the exposure device 3 based on the image signal, the corrected writing position Pos'(t) is calculated by the following formula. expressed.
Pos'(t)y = Pos(t)y...(Formula 8)
Pos'(t)m = Pos(t)m - Im(t)...(Formula 9)
Pos'(t)c = Pos(t)c - Ic(t)...(Formula 10)
Pos'(t)k = Pos(t)k - Ik(t)...(Formula 11)

Using the variation amounts Tq1(t) and Tq2(t) of the intermediate transfer belt drive torque Tq, the respective color shift amounts I1(t) and I2(t) in the sub-scanning direction are calculated. Further, although details will be described later, in an actual control procedure, the fluctuation amounts Tq1(t) and Tq2(t) cannot be obtained simultaneously (during one job). This is because the operating state of the image forming apparatus 100 when acquiring the variation amount Tq1(t) and the variation amount Tq2(t) is different. Specifically, the load applied to the intermediate transfer belt 21 (the torque of the intermediate transfer belt drive unit 113) is different when obtaining the variation amount Tq1(t) and when obtaining the variation amount Tq2(t). To become. Therefore, the fluctuation amounts Tq1(t) and Tq2(t) are calculated using separate sequences.

In this embodiment, the amount of variation Tq(t) acquired through the print job is described as the amount of variation Tq2(t) for convenience. That is, the amount of variation Tq2(t) includes not only the torque variation in the secondary transfer section N2 but also all the torque variation that the intermediate transfer belt drive section 113 receives during the job. Similarly, the amount of color misregistration I2(t) calculated using the amount of variation Tq2(t) also includes all amounts of color misregistration caused by torque fluctuations of the intermediate transfer belt drive unit 113 that occur during the job.

The correction of color misregistration by exposure in this embodiment corrects color misregistration with higher precision by suppressing the difference in the amount of color misregistration correction due to the image difference (color misregistration at the primary transfer portion N1). It is in. In other words, by subtracting the amount of color shift I1(t) from the amount of color shift I2(t), it is possible to calculate the correction amount without being influenced by the image. Therefore, the color shift correction amount I(t) to be corrected is expressed by the following formula.
I(t) = I2(t) - I1(t)...(Formula 12)

In this embodiment, color misregistration correction is performed when the operator instructs the image forming apparatus 100 to execute a print job from the operation unit 160. Here, the process of correcting color shift by exposure correction will be described, and the description of many other processes that are normally performed to execute a job and output an image will be omitted. FIG. 7 is a flowchart showing the process for obtaining the color shift correction amount I(t). In this embodiment, the color misregistration exposure correction process is performed in advance prior to the print job. The amount of torque fluctuation due to the primary transfer portion N1 of the intermediate transfer belt 21 is determined by the surface properties of the intermediate transfer belt 21 and the frictional force of each belt solid. Therefore, it is appropriate to execute the color misregistration exposure correction process at the same time as the initial installation of the main body of the image forming apparatus 100 or the periodic replacement of the intermediate transfer belt 21. At this time, it may be performed simultaneously with other installation work or replacement work (initialization operation).

When the control unit 150 receives an instruction to execute the correction amount acquisition job from the operation unit 160, the control unit 150 starts the correction amount acquisition job by sending commands to each part of the image forming apparatus 100 based on the instruction. The instruction sent to the control unit 150 includes information regarding the type of recording material P. In this embodiment, the information regarding the type of recording material P includes at least information about the basis weight of recording material P. The information regarding the recording material P may include information such as information on the surface properties of the recording material P and information on the electrical resistance value of the recording material P in addition to information on the basis weight. The control unit 150 can acquire information regarding the type of recording material P that is directly input (including selection from a plurality of options) from the operation unit 160 or the external device 200 through the operation of the operator. . The control unit 150 also acquires information regarding the type of recording material P based on the information of the recording material storage 11 that sends out the recording material P in the job, which is input from the operation unit 160 or the external device 200. You can also do it. When registering information regarding the type of recording material P, the operator may select the applicable type from a list of types of recording material P. The list of types of recording material P is stored in advance in, for example, the memory 152 or a storage device connected to the control unit 150 via a network. When the control unit 150 acquires information regarding the type of recording material P used for a job, it sets the printing operating conditions for the job to predetermined printing operating conditions for each type of recording material P (S1).

The control unit 150 sets an image signal (S2). This image signal may be an image signal used by the operator in an actual print job, or may be a dedicated image signal for a color misregistration correction job. In this embodiment, an image with an image duty of 0% (no image density) is used. In this case, there is an advantage that toner consumption can be reduced compared to cases where other images are used.

After setting the image signal, the control unit 150 performs processing to obtain the above-mentioned torque fluctuation amounts Tq1(t) and Tq2(t) (S3). The color shift exposure correction process is performed by two variation amount acquisition sequences (S10) and (S20). The process in S10 is a sequence for obtaining the torque variation amount Tq1(t). The process of S20 is a sequence for obtaining the torque variation amount Tq2(t). The processing in S10 and the processing in S20 may be executed in random order.

The control unit 150 subtracts the color shift amount I1(t) from the color shift amount I2(t) obtained from the torque fluctuation amounts Tq1(t) and Tq2 based on the above-mentioned (Formula 1) to (Formula 12). The color shift correction amount I(t) is calculated (S4). The control unit 150 stores the color misregistration correction amount I(t) and the conditions of the recording material P in the memory 152 in association with each other (S5). With the above steps, the color misregistration correction amount acquisition process is completed. The color shift correction amount I(t) is calculated for each type of recording material P used for printing, and is stored in the memory 152 in association with the corresponding type of recording material P.

FIG. 8 is a flowchart showing the process of obtaining the torque fluctuation amounts Tq1(t) and Tq2(t) in S3.

The process of acquiring the variation amount Tq1(t) in S10 (referred to as "non-sheet passing job") will be explained with reference to FIG. 8(a). The operator uses the operation unit 160 to set a paper non-passing job. The control unit 150 is notified of the settings for the paper non-passing job. Control unit 150 starts a paper non-passing job by sending commands to each unit of image forming apparatus 100 based on the notification.

The control unit 150 that has started the paper non-passing job starts a printing operation (S101). Upon the start of the printing operation, the control unit 150 starts driving the drum drive unit 111 and the intermediate transfer belt drive unit 113 (S102). At the same time, the control unit 150 starts acquiring the intermediate transfer belt driving torque Tq1 using the torque detection unit 113b (S103).

Subsequently, the control unit 150 starts applying the primary transfer voltage and the developing voltage (S104). Thereby, the control unit 150 controls the operation of primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer belt 21 (S105). After that, the control unit 150 stops applying the primary transfer voltage and the development voltage (S106). The control unit 150 also stops acquiring the intermediate transfer belt driving torque Tq1 (S107). Further, the control unit 150 stops driving the drum drive unit 111 and the intermediate transfer belt drive unit 113 (S108). With the above steps, the process for obtaining the torque variation amount Tq1(t) is completed.

The process of acquiring the variation amount Tq2(t) in S20 (referred to as "paper passing job") will be explained with reference to FIG. 8(b). The operator sets a paper passing job using the operation unit 160. The control unit 150 is notified of the paper passing job settings. Control unit 150 starts a paper passing job by sending commands to each unit of image forming apparatus 100 based on the notification.

The control unit 150 that has started the paper passing job starts a printing operation (S201). Upon the start of the printing operation, the control unit 150 starts driving the drum drive unit 111 and the intermediate transfer belt drive unit 113 (S202). At the same time, the control unit 150 starts acquiring the intermediate transfer belt driving torque Tq2 using the torque detection unit 113b (S203).

Subsequently, the control unit 150 starts the feeding operation of the recording material P (S204). Further, the control unit 150 starts applying the primary transfer voltage and the development voltage (S205). Thereby, the control unit 150 controls the operation of primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer belt 21 (S206). The control unit 150 controls the secondary transfer operation of the toner image onto the conveyed recording material P by the secondary transfer unit N2 by applying the secondary transfer voltage (S207).

After that, the control unit 150 stops applying the primary transfer voltage and the development voltage (S208). The control unit 150 also stops acquiring the intermediate transfer belt driving torque Tq2 (S209). Further, the control unit 150 stops driving the drum drive unit 111 and the intermediate transfer belt drive unit 113 (S210). With the above steps, the process for obtaining the torque variation amount Tq2(t) is completed.

The control unit 150 uses the color misregistration correction amount I(t) obtained by the correction amount acquisition job as described above to correct the position at which the exposure device 3 starts writing the image during the print job. As a result, color misregistration in the sub-scanning direction caused by fluctuations in the drive torque of the intermediate transfer belt 21 in response to conveyance of the recording material P can be corrected with high precision without being affected by image differences. Note that the correction amount acquisition job may be performed for each type of recording material P. In this case, the obtained color misregistration correction amount is stored in the memory 152 in association with the information (type) of the recording material P.

(Second embodiment)
The configuration and image forming operation of the image forming apparatus 100 of the second embodiment are the same as those of the image forming apparatus 100 of the first embodiment, and the configuration of the control unit 150 is also the same as that of the first embodiment. Therefore, descriptions of the configuration and operation of the image forming apparatus 100 of the second embodiment and the configuration of the control unit 150 will be omitted.

In the second embodiment, the color misregistration correction amount I(t) is obtained by removing the influence of the torque fluctuation of the intermediate transfer belt drive unit 113 that occurs in the primary transfer portion N1 (color misregistration correction amount I'(t) ). Therefore, if all the primary transfer rollers 23Y, 23M, 23C, and 23K are separated from the intermediate transfer belt 21, the torque fluctuation amount Tq'( t). The amount of torque variation Tq'(t) obtained in this case is data detected without primary transfer, and therefore the load conditions are different from those of the actual job. Therefore, although the second embodiment has lower accuracy than the first embodiment, it has the advantage that the color shift amount acquisition process (S10, S20), which was divided into two processes in the first embodiment, can be performed in one process. Further, since the amount of torque fluctuation Tq'(t) is detected without the primary transfer roller 23 coming into contact with the intermediate transfer belt 21, there is no need to consume the durable life of the primary transfer roller 23.

In order to separate the primary transfer roller 23 from the intermediate transfer belt 21, the image forming apparatus 100 of the second embodiment includes an abutment mechanism for bringing the primary transfer roller 23 into contact with and away from the intermediate transfer belt 21. . FIG. 9 is an explanatory diagram of such a separation mechanism. In FIG. 9, a separation control section 30 as a separation mechanism is connected to each of the primary transfer rollers 23Y, 23M, 23C, and 23K. The separation control section 30 is capable of bringing the primary transfer rollers 23Y, 23M, 23C, and 23K into contact with and separating them from the inner peripheral surface of the intermediate transfer belt 21 under the control of the control section 150. When the primary transfer roller 23 contacts and separates from each other, the intermediate transfer belt 21 and the photosensitive drum 1 contact and separate from each other.

FIG. 10 is a flowchart illustrating the color shift correction amount acquisition process according to the second embodiment. The processes in S11 and S12 are similar to the processes in S1 and S2 in FIG. After setting the image signal, the control unit 150 performs processing to obtain the torque variation amount Tq'(t) (S13). The control unit 150 calculates the color shift correction amount I'(t) from the variation amount Tq'(t) based on the above-mentioned (Equations 1) to (Equations 11) (S14). The control unit 150 associates the color misregistration correction amount I'(t) with the information on the recording material P and stores it in the memory 152 (S15). With the above steps, the color misregistration correction amount acquisition process is completed.

FIG. 11 is a flowchart showing the process of obtaining the torque variation amount Tq'(t) in S13. The operator sets a paper passing job using the operation unit 160. The control unit 150 is notified of the paper passing job settings. Control unit 150 starts a paper passing job by sending commands to each unit of image forming apparatus 100 based on the notification.

The control unit 150 that has started the paper passing job starts a printing operation (S301). The control unit 150 that has started the printing operation separates the primary transfer roller 23 from the inner peripheral surface of the intermediate transfer belt 21 (S302). After that, the control unit 150 starts driving the drum drive unit 111 and the intermediate transfer belt drive unit 113 (S303). At the same time, the control unit 150 starts acquiring the intermediate transfer belt driving torque Tq (S304).

The control unit 150 starts the feeding operation of the recording material P (S305). Furthermore, the control unit 150 starts applying the primary transfer voltage and the development voltage (S306). Thereby, the control unit 150 controls the primary transfer operation of the toner image on the photosensitive drum 1 onto the intermediate transfer belt 21 (S307). The control unit 150 controls the secondary transfer operation of the toner image onto the conveyed recording material P by the secondary transfer unit N2 by applying the secondary transfer voltage (S308).

After that, the control unit 150 stops applying the primary transfer voltage and the development voltage (S309). The control unit 150 also stops acquiring the intermediate transfer belt driving torque Tq (S310). Further, the control unit 150 stops driving the drum drive unit 111 and the intermediate transfer belt drive unit 113 (S311). Finally, the control unit 150 brings the primary transfer roller 23 into contact with the inner peripheral surface of the intermediate transfer belt 21 (S312). With the above steps, the process for obtaining the torque variation amount Tq'(t) is completed.

The control unit 150 uses the color misregistration correction amount I'(t) obtained by the correction amount acquisition job as described above to correct the position at which the exposure device 3 starts writing the image during the print job. As a result, color misregistration in the sub-scanning direction caused by fluctuations in the drive torque of the intermediate transfer belt 21 in response to conveyance of the recording material P can be corrected with high precision without being affected by image differences. Note that the correction amount acquisition job may be performed for each type of recording material P. In this case, the obtained color misregistration correction amount is stored in the memory 152 in association with the information (type) of the recording material P.

(Modified example of exposure device 3)
The exposure device 3 may be of a laser beam scanning exposure type, in addition to the configuration using the light emitting chip 639 made up of a plurality of light emitting elements (LED elements) described in FIG. 2. The laser beam scanning exposure type exposure device 3 scans the irradiation beam of a semiconductor laser with a rotating polygon mirror or the like and exposes the photosensitive drum through an f-θ lens or the like. In this case, the color shift exposure correction is performed by the control unit 150 changing the control signal to the exposure device 3 as needed so that the image writing start position is shifted by the color shift correction amount I(t).

Even if the exposure device 3 uses a laser beam scanning exposure method, as in the first and second embodiments, the color in the sub-scanning direction is caused by fluctuations in the driving torque of the intermediate transfer belt 21 caused by conveyance of the recording material P. Misalignment can be corrected without being affected by image differences. Note that the correction amount acquisition job may be performed for each type of recording material P. In this case, the obtained color misregistration correction amount is stored in the memory 152 in association with the information (type) of the recording material P.

(Modified example)
Although the case of color misregistration correction has been described above, the above-mentioned technique is effective for purposes other than color misregistration correction. For example, the above-mentioned technique can also be used to correct the geometric characteristics of an image, such as the position and shape of the image. This is because the geometric characteristics of the image are affected by load fluctuations (torque fluctuations) of the intermediate transfer belt 21 during primary transfer, similar to color shift. Correction of the geometric characteristics is performed by adjusting the timing of light emission by the exposure device 3, similarly to the color shift correction. Note that color shift correction and geometric characteristic correction may be performed by adjusting the rotational speeds of the photosensitive drum 1 and the intermediate transfer belt 21 if these can be adjusted with high precision. In other words, color shift correction and geometric characteristic correction can be made by adjusting image forming conditions such as the timing of the start of exposure by the exposure device 3, the rotational speed of the photosensitive drum 1, and the rotational speed of the intermediate transfer belt 21. be.

Claims (13)

an image forming means for forming an image on a first image carrier;
a second image carrier, which is an endless belt to which the image is transferred from the first image carrier;
a first transfer means for transferring the image carried by the first image carrier to the second image carrier;
a second transfer means for transferring the image carried by the second image carrier to a recording material;
a driving means for rotating the second image carrier;
causing the image forming means to form the image; causing the first transfer means to transfer the image from the first image bearing member to the second image bearing member rotationally driven by the driving means; control means for transferring the image of the body onto the recording material by the second transfer means,
The control means calculates a correction amount for correcting a position when transferring the image from the first image carrier to the second image carrier based on the torque of the drive means. do,
Image forming device. The image forming means is plural, each forming an image of a different color on the first image carrier,
The control means causes each of the plurality of image forming means to form the image, and transfers the image from each of the first image bearing members by the first transfer means to the second image bearing member rotationally driven by the driving means. transferring the image, causing the second transfer means to transfer the image on the second image carrier to the recording material;
The control means controls the torque of the drive means between a first state in which the image is not transferred from the second image carrier to the recording material and a second state in which the image is transferred from the second image carrier to the recording material. correction for correcting color shift due to the image of each color transferred to the second image carrier by the torque detected in the first state and the torque detected in the second state; characterized by calculating the amount,
The image forming apparatus according to claim 1. The control means calculates the amount of positional deviation of the image of each color to be formed on the first image carrier based on the amount of variation in the torque from the start time of image formation, and based on the amount of positional deviation, Calculating the amount of color shift between an image of a reference color and an image of another color, and calculating the amount of correction based on the amount of color shift,
The image forming apparatus according to claim 2. The control means calculates a first color shift amount from the torque detected in the first state, calculates a second color shift amount from the torque detected in the second state, and calculates a second color shift amount from the torque detected in the second state, and calculates a second color shift amount from the torque detected in the second state. characterized in that the difference between the two-color shift amount is the correction amount;
The image forming apparatus according to claim 3. The control means causes the image forming means to form an image without image density in the first state and the second state, and detects the torque at that time.
The image forming apparatus according to claim 2. further comprising a conveying means for conveying the recording material,
The control means does not cause the conveyance means to convey the recording material to the second transfer means in the first state, and causes the conveyance means to convey the recording material to the second transfer means in the second state. characterized by
The image forming apparatus according to claim 2. The first transfer means has a transfer roller,
The image forming means includes a separation control means that brings the transfer roller into contact with the second image carrier when transferring the image, and separates the transfer roller from the second image carrier when the image is not transferred. and
The control means detects the torque of the drive means in a state where the transfer roller is separated from the image carrier by the separation control means.
The image forming apparatus according to claim 1. The control means calculates a correction amount for correcting color shift when transferring the image from the first image carrier to the second image carrier based on the detected torque. do,
The image forming apparatus according to claim 7. The image forming means is plural, each forming an image of a different color on the first image carrier,
The control means causes each of the plurality of image forming means to form the image, and transfers the image from each of the first image bearing members by the first transfer means to the second image bearing member rotationally driven by the driving means. Transferring the image, and causing the second transfer means to transfer the image on the second image carrier onto the recording material,
The image forming apparatus according to claim 8. The control means adjusts image forming conditions when the image forming means forms the image based on the correction amount, and causes the image forming means to form the image based on the adjusted image forming conditions. Characterized by
The image forming apparatus according to claim 1. The image forming means has an exposure means that exposes the first image carrier to form an electrostatic latent image on the first image carrier,
The image forming apparatus according to claim 10, wherein the control means corrects the timing of starting exposure by the exposure means based on the correction amount. The driving means includes a driving source for driving the second image carrier, and a detecting means capable of continuously detecting the torque of the driving source at predetermined time intervals,
The control means obtains the torque of the drive means from the detection means,
The image forming apparatus according to claim 1. The detection means detects the current of the drive source,
The control means is characterized in that the current value detected by the detection means is acquired as the torque.
The image forming apparatus according to claim 12.

Images