JP5393636B2 - Image forming apparatus and speed control method - Google Patents

Description

  The present invention relates to an image forming apparatus and a speed control method.

  In an electrophotographic process type image forming apparatus, a beam (light beam) is incident on the surface of a photosensitive drum by an exposure device to form an electrostatic latent image, and a toner is attached to the electrostatic latent image by a developing device. Development is performed, the generated toner image is transferred to an intermediate transfer member, the toner image is transferred from the intermediate transfer member to a sheet, and the toner image is fixed on the sheet.

  In the exposure apparatus, the beam from the light source is scanned in the main scanning direction by the polygon mirror, and is incident in the direction perpendicular to the rotation direction of the photosensitive drum. For each surface of the polygon mirror, the beam is scanned once in the main scanning direction, and when the incident surface of the beam from the light source switches from one surface of the polygon mirror to the next adjacent surface, The incident position of the beam on the photosensitive drum moves. Then, an electrostatic latent image is formed by scanning the beam, the electrostatic latent image is developed with toner, and the toner image is transferred to an intermediate transfer member that rotates (circulates) at substantially the same linear velocity as the photosensitive drum. The

  The exposure apparatus includes a single beam type that scans one beam per color and a multi-beam type that scans a plurality of beams arranged at equal intervals in the sub-scanning direction for each color. (For example, refer to Patent Document 1).

  As another technique, there is a method of measuring a linear velocity of an intermediate transfer belt and controlling a motor that drives a driving roller for operating the intermediate transfer belt (see, for example, Patent Document 2).

  As another technique, in a certain image forming apparatus, a sensor for detecting toner density has a plurality of light emitting elements and a plurality of light receiving elements, and these light emitting elements and the light receiving elements advance the intermediate transfer belt. The positions of the toner marks in the direction perpendicular to the traveling direction of the intermediate transfer belt are detected based on the outputs of the light receiving elements (see, for example, Patent Document 3).

JP 2007-232909 A Japanese Patent Laid-Open No. 11-24498 JP 2009-258601 A

  In the case of the single beam system, the line interval in the sub-scanning direction in the toner image is controlled by the rotational speed of the polygon mirror and the linear speed of the intermediate transfer member. Therefore, in the case of the single beam method, even if the rotational speed of the photosensitive drum fluctuates, the line spacing in the sub-scanning direction in the toner image is uniform by controlling the rotational speed of the polygon mirror and the linear speed of the intermediate transfer member. However, in the case of the N multi-beam method, even if the rotational speed of the polygon mirror and the linear speed of the intermediate transfer member are controlled, the rotational speed of the photosensitive drum and the incident position of the beam vary for each apparatus. As a result, the distance between the line of the Nth beam in one scan and the line of the first beam in the next scan is the distance between the lines of the i-th and (i + 1) th beams in the scan (i = 1). ,..., N-1).

  The present invention has been made in view of the above problems, and it is an object of the present invention to obtain an image forming apparatus and a speed control method that make all line intervals in a toner image uniform even when a multi-beam exposure apparatus is used. Objective.

  In order to solve the above problems, the present invention is configured as follows.

  An image forming apparatus according to the present invention includes a photosensitive drum, a multi-beam type exposure apparatus that forms an electrostatic latent image on the photosensitive drum using N (N> 1) beams, and a photosensitive drum. A developing unit for developing the electrostatic latent image on the toner, an intermediate transfer member to which the toner image on the photosensitive drum is transferred, and a toner patch image on the intermediate transfer member by detecting reflected light from a predetermined detection position A sensor for detecting the passage of the light, a linear velocity calculation unit for calculating the linear velocity of the intermediate transfer member based on the detection result by the sensor, and controlling the exposure apparatus to set the leading line with one of the N beams. Forming a first toner patch image, forming a leading line with the other one of the N beams to form a second toner patch image, and forming a first toner patch image at a predetermined detection position. Difference in the passage time of the two toner patch images, And based on the linear velocity of the intermediate transfer member, and a control unit for controlling the rotational speed of the photosensitive drum as line spacing in the sub-scanning direction in the toner image becomes uniform.

  Thus, the interval between the line of the Nth beam and the line of the next first beam is specified based on the difference between the passage times of the two toner patch images at the predetermined detection position and the linear velocity of the intermediate transfer member. The rotational speed of the photosensitive drum is controlled so that the line interval is the same as the other line intervals. Therefore, even if a multi-beam exposure apparatus is used, the line intervals in the toner image are all uniform.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the sensor detects passage of one of the first and second toner patch images at a plurality of detection positions, and the linear velocity calculation unit passes the toner patch image by the sensor at the plurality of detection positions. Is detected, and the linear velocity of the intermediate transfer member is calculated from the passage times of the toner patch images at a plurality of detection positions.

  As a result, the linear velocity is calculated from the time at which one toner patch image passes through a plurality of detection positions. Therefore, the linear velocity is calculated from the time interval when a plurality of toner patch images are detected at one detection position. In comparison, it is less susceptible to changes in the environment of the intermediate transfer belt or the like and changes over time, and the linear velocity of the intermediate transfer belt or the like can be accurately measured.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the sensor causes measurement light to enter the plurality of detection positions, detects reflected light from each of the plurality of detection positions, and outputs an output signal corresponding to the detected reflected light. Based on the output signal, the passage times of the toner patch images at a plurality of detection positions are specified.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the sensor has a pair of a light emitting element that emits measurement light and a light receiving element that receives reflected light, corresponding to each of a plurality of detection positions.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the light emitting element and the light receiving element are each arranged along the traveling direction of the intermediate transfer member.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the linear velocity calculation unit calculates the linear velocity from the passage times at the plurality of detection positions and the intervals between the light emitting elements and / or the light receiving elements corresponding to the plurality of detection positions.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the remaining detection positions of the plurality of detection positions during the period in which the light emitting element corresponding to one detection position of the plurality of detection positions emits measurement light and the toner patch image is detected at the detection position. The light emitting element corresponding to (2) stops emission of measurement light.

  As a result, light from the light emitting element at another detection position in the vicinity of the detection position being measured does not enter the light receiving element at the detection position being measured, and the reflected light can be accurately measured. it can.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, when the value of the output signal of the light receiving element corresponding to one detection position among the plurality of detection positions decreases below the predetermined threshold or increases above the predetermined threshold, the light emitting element corresponding to the detection position Stops emitting measurement light, and the light emitting element corresponding to the next detection position among the plurality of detection positions starts emitting measurement light.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the image forming apparatus causes the measurement light from the light emitting element to enter the detection position corresponding to the light emitting element as parallel light, and the reflected light from the detection position to the light receiving element that makes a pair with the light emitting element. An optical lens for condensing and entering is further provided.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the control unit forms the first toner patch image with the Nth beam of the N beams to form the first toner patch image, and sets the first line with the first beam of the N beams. Then, a second toner patch image is formed.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the control unit controls the rotation speed of the photosensitive drum so that all the line intervals are the line intervals specified from the difference between the passage times of the first and second toner patch images at the predetermined detection position. To do.

  As a result, even when the reference line interval varies due to variations in the linear speed of the intermediate transfer member and the rotation speed of the polygon mirror in the exposure apparatus, the line intervals in the toner image are all uniform.

  The image forming apparatus according to the present invention may be configured as follows in addition to any of the image forming apparatuses described above. In this case, the control unit forms the last line of the first toner patch image and the second toner patch image with the same beam among the N beams, and the first line at the predetermined detection position. The rotational speed of the photosensitive drum is controlled so that the line interval is determined from the difference between the passage times of the rear edges of the first and second toner patch images.

  The speed control method according to the present invention includes (a) a step of forming an electrostatic latent image on a photosensitive drum by a multi-beam method using N (N> 1) beams, and (b) a photosensitive drum. A step of developing the electrostatic latent image on the toner, (c) a step of transferring the toner image on the photosensitive drum onto the intermediate transfer member, and (d) detecting reflected light from a predetermined detection position, Detecting the passage of the toner patch image on the transfer body with a sensor, (e) calculating the linear velocity of the intermediate transfer body based on the detection result of the sensor, and (f) controlling the exposure apparatus to A first toner patch image is formed by forming a leading line with one of the beams, and a leading toner patch image is formed by forming the leading line with the other one of the N beams. A step of forming, and (g) a predetermined detection position The rotational speed of the photosensitive drum is adjusted so that the line spacing in the sub-scanning direction in the toner image is uniform based on the difference between the passage times of the first and second toner patch images and the linear velocity of the intermediate transfer member. Controlling.

  Thus, the interval between the line of the Nth beam and the line of the next first beam is specified based on the difference between the passage times of the two toner patch images at the predetermined detection position and the linear velocity of the intermediate transfer member. The rotational speed of the photosensitive drum is controlled so that the line interval is the same as the other line intervals. Therefore, even if a multi-beam exposure apparatus is used, the line intervals in the toner image are all uniform.

  In addition to the speed control method described above, the speed control method according to the present invention may be as follows. In this case, in this speed control method, the rotational speed of the photosensitive drum is such that all the line intervals are the line intervals specified from the difference between the passage times of the first and second toner patch images at the predetermined detection position. To control.

  As a result, even when the reference line interval varies due to variations in the linear speed of the intermediate transfer member and the rotation speed of the polygon mirror in the exposure apparatus, the line intervals in the toner image are all uniform.

  According to the present invention, even when a multi-beam type exposure apparatus is used in an image forming apparatus, the line intervals in the toner image are all uniform.

FIG. 1 is a side view showing a mechanical internal configuration of the image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a view showing a configuration example of the exposure apparatus in FIGS. 1 and 2. FIG. 4 is a diagram showing an example of a toner line formed on the intermediate transfer belt by four (N = 4) beams in the image forming apparatus shown in FIG. FIG. 5 is a diagram illustrating an example of a toner patch image formed on the intermediate transfer belt in the image forming apparatus shown in FIG. FIG. 6 is a front view showing the configuration of the sensor in FIGS. 1 and 2. 7 is a perspective view and a side view of the sensor shown in FIG. 6 with an optical lens attached. FIG. 8 is a diagram illustrating an example of a plurality of detection positions for detecting a toner patch image in the image forming apparatus illustrated in FIGS. 1 and 2. FIG. 9 is a diagram showing an example of the waveform of the output signal of the light receiving element of the sensor in FIG. FIG. 10 is a diagram illustrating an example of waveforms of output signals of a plurality of light receiving elements of the sensor in FIG. FIG. 11 is a diagram illustrating an example of waveforms of output signals of a plurality of light receiving elements of the sensor in FIG. 12 shows the polygon surface of the polygon mirror, the lines constituting the beam and the patch image, and the patch image interval and the line interval in the sub-scanning direction when adjusting the rotational speed of the photosensitive drum in the image forming apparatus shown in FIG. FIG. FIG. 13 is a diagram illustrating an example of waveforms of output signals of a plurality of light receiving elements of the sensor according to the second embodiment. FIG. 14 shows the polygon surface of the polygon mirror, the lines constituting the beam and the patch image, and the intervals and lines of the patch image in the sub-scanning direction when adjusting the rotational speed of the photosensitive drum in the image forming apparatus according to the second embodiment. It is a figure explaining the space | interval of. FIG. 15 is a diagram showing another arrangement method of the light emitting elements and the light receiving elements of the sensor in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.

  FIG. 1 is a side view showing a mechanical internal configuration of the image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus is an apparatus having a printing function, such as a printer, a copier, a facsimile machine, or a multifunction machine.

  The image forming apparatus of this embodiment has a tandem color developing device. The color developing device includes photosensitive drums 1a to 1d, an exposure device 2, and developing units 3a to 3d. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black.

  The photosensitive drums 1a to 1d have a cylindrical shape, rotate about an axis by a driving force from a driving motor (not shown), and are charged to emit an electrostatic latent image when a beam is irradiated onto the peripheral surface. The toner is attached to the electrostatic latent image to form a toner image and transferred to the intermediate transfer belt 4.

  The exposure device 2 is a multi-beam exposure device that irradiates each of the photosensitive drums 1a to 1d with laser light to form an electrostatic latent image. Each exposure apparatus 2 is a laser scanner unit. The exposure apparatus 2 includes a laser diode that is a light source of laser light and optical elements (lens, mirror, polygon mirror, etc.) that guide the laser light to the photosensitive drums 1a to 1d. There is one exposure apparatus 2 for each color, and the exposure apparatus 2 is attached to a structure such as a housing inside the apparatus.

  The developing units 3a to 3d form toner images by attaching the toner in the toner cartridges to the electrostatic latent images on the photosensitive drums 1a to 1d.

  The photosensitive drum 1d and the developing unit 3d develop magenta, the photosensitive drum 1c and the developing unit 3c develop cyan, and the photosensitive drum 1b and the developing unit 3b develop yellow. Then, black development is performed by the photosensitive drum 1a and the developing unit 3a.

  The intermediate transfer belt 4 is an intermediate transfer body, and is an annular image carrier that contacts the photosensitive drums 1a to 1d and transfers the toner images on the photosensitive drums 1a to 1d. The intermediate transfer belt 4 is stretched around the driving roller 5 and circulates in the direction from the contact position with the photosensitive drum 1d to the contact position with the photosensitive drum 1a by the driving force from the driving roller 5. The intermediate transfer belt 4 carries a toner patch image used for adjusting the rotational speed of the photosensitive drums 1a to 1d.

  The transfer roller 6 brings the conveyed paper into contact with the transfer belt 4 and transfers the toner image on the transfer belt 4 to the paper. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 is in contact with the intermediate transfer belt 4 and removes the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The sensor 8 irradiates the intermediate transfer belt 4 with a beam and detects the reflected light. During the registration process, the sensor 8 irradiates the toner patch image on the intermediate transfer belt 4 with a beam, detects reflected light of the beam, and detects the passage of the toner patch image.

  FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus according to Embodiment 1 of the present invention. In FIG. 2, the print engine 11 controls a driving source (not shown) that drives the above-described roller and the exposure device 2 to execute development, transfer, and fixing of a toner image, and paper feeding, printing, and paper ejection. It is a processing circuit.

  The print engine 11 includes a linear velocity calculation unit 11a and a drum control unit 11b.

  The linear velocity calculation unit 11a identifies the time when the sensor 8 detects the passage of one toner patch image at a plurality of detection positions, and calculates the linear velocity of the intermediate transfer belt 4 from the passage times at the plurality of detection positions. Is a processing unit.

  The drum controller 11b has a uniform line interval in the sub-scanning direction in the toner image based on the difference between the passage times of the two toner patch images at a predetermined detection position and the linear velocity calculated by the linear velocity calculator 11a. The processing unit controls the rotational speed of the photosensitive drums 1a to 1d so that The drum control unit 11b adjusts the rotation speed by controlling a drive motor that drives the photosensitive drums 1a to 1d via a driver circuit (not shown).

  Here, details of the exposure apparatus 2 will be described.

  FIG. 3 is a view showing a configuration example of the exposure apparatus 2 in FIGS. 1 and 2. The exposure apparatus 2 shown in FIG. 3 is an exposure apparatus 2 for the photosensitive drum 1a, and the exposure apparatus 2 for the photosensitive drums 1b to 1d has the same configuration.

  In FIG. 3, a plurality of laser diodes 21 are light emitting elements that emit a plurality of laser beams.

  The optical system 22 is a group of various lenses arranged between the laser diode 21 and the photosensitive drum 1a and the BD sensor 26.

  The polygon mirror 23 is an element having a polygonal cross section perpendicular to the axis perpendicular to the axis of the photosensitive drum 1a, and a side surface of the polygon mirror 23 as a mirror. The polygon mirror 23 rotates about its axis, and scans the beam emitted from the laser diode 21 along the axial direction (main scanning direction) of the photosensitive drum 1a.

  The driver circuit 24 is a circuit that drives the laser diode 21. The driver circuit 24 is supplied with a drive signal for image formation. The driver circuit 24 emits a laser beam based on the drive signal.

  The DA converter 25 is a circuit that DA converts the digital control signal and supplies a drive signal to the driver circuit 24.

  The BD sensor 26 is a sensor that induces an output voltage corresponding to the beam intensity when a beam is incident. The BD sensor 26 is disposed at a predetermined position on the line to which the beam is scanned, and is used to detect the timing at which the beam spot passes through the position.

  The print engine 11 supplies a drive signal to the driver circuit 24 via the DA converter 25.

  FIG. 4 is a diagram showing an example of a toner line formed on the intermediate transfer belt 4 by four (N = 4) beams in the image forming apparatus shown in FIG. FIG. 4A shows an example of a toner line when the rotation speed of the photosensitive drum 1a is a specified value. FIG. 4B is an example of a toner line when the rotational speed of the photosensitive drum 1a is shifted.

  As shown in FIG. 4B, when there is a deviation in the rotational speed of the photosensitive drum 1a, the interval between the line by the first beam and the line by the next first beam remains at a specified value. The distance between the fourth beam and the line of the first beam in the next scan is the distance between the first beam and the second beam, the distance between the second beam and the third beam, and the distance between the third beam and the fourth beam. It is different from the interval. The interval between the first beam and the second beam, the interval between the second beam and the third beam, and the interval between the third beam and the fourth beam are the same.

  FIG. 5 is a diagram illustrating an example of a toner patch image formed on the intermediate transfer belt 4 in the image forming apparatus illustrated in FIG. As shown in FIG. 5, in this embodiment, a plurality of toner patch images 41a and 41b are formed on the intermediate transfer belt 4 when adjusting the rotational speed of the photosensitive drums 1a to 1d.

  Details of the toner patch images 41 a to 41 b will be described later with reference to FIG. 12, but the leading line in the sub-scanning direction of the toner patch image 41 a is the p-th beam (N beams of the exposure apparatus 2). Here, the final line in the sub-scanning direction of the toner patch image 41a is formed with the (p-1) th beam (Nth beam when p = 1). The other lines are repeated in the order from the first beam to the Nth beam, and are formed by any one of the first to Nth beams. Further, the head line in the sub-scanning direction of the toner patch image 41b is formed by the q-th beam (p ≠ q, here, the first beam) of the N beams, and the toner patch image 41b is sub-scanned. The last line in the direction is formed by the (q-1) th beam (Nth beam if q = 1). The other lines are repeated in the order from the first beam to the Nth beam, and are formed by any one of the first to Nth beams. That is, here, the leading edge of the toner patch image 41a in the traveling direction of the intermediate transfer belt 4 is a line by the Nth beam, and the leading edge of the toner patch image 41b is a line by the first beam.

  Next, details of the sensor 8 will be described.

  The sensor 8 is fixed to face the intermediate transfer belt 4 and detects the passage of the toner patch images 41a and 41b on the intermediate transfer belt 4 at a plurality of predetermined detection positions. The sensor 8 causes measurement light to enter the plurality of detection positions, detects reflected light from each of the detection positions, and outputs an output signal corresponding to the detected reflected light. The output signal is supplied to the print engine 11 through an amplifier circuit, a filter circuit, and the like as necessary. The output signal is sampled and treated as digital data.

  The linear velocity calculation unit 11a specifies the passage times of the toner patch images 41a at a plurality of detection positions based on the output signal. Also, the drum control unit 11b specifies the passage time of the leading edge of the toner patch image 41a and the passage time of the leading edge of the toner patch image 41b at one detection position based on the output signal.

  FIG. 6 is a front view showing the configuration of the sensor 8 in FIGS. 1 and 2. 7 is a perspective view and a side view of the sensor 8 shown in FIG. 6 with the optical lens 31 attached. FIG. 8 is a diagram showing an example of a plurality of detection positions for detecting the toner patch image 41a in the image forming apparatus shown in FIGS.

  As illustrated in FIG. 6, the sensor 8 includes a plurality of light emitting elements 51-1 to 51-10 and a plurality of light receiving elements 52-1 to 52-10. In this embodiment, the light emitting element 51-i and the light receiving element 52-i (i = 1,..., 10) are paired, and the measurement light emitted from the light emitting element 51-i is the intermediate transfer belt. 4 and the reflected light enters the light receiving element 52-i.

  The light emitting elements 51-i (i = 1,..., 10) emit measurement light toward the detection positions 61-i. The light emitting elements 51-1 to 51-10 are elements having the same characteristics. As the light emitting element 51-i, for example, a light emitting diode is used. Further, the light receiving element 52-i (i = 1,..., 10) receives the reflected light from the detection position 61-i and outputs an electrical signal corresponding to the intensity of the received light. The light receiving elements 52-1 to 52-10 are elements having the same characteristics. For example, a photodiode is used as the light receiving element 52-i.

  The light emitting elements 51-1 to 51-10 and the light receiving elements 52-1 to 52-10 are arranged along the traveling direction of the intermediate transfer belt 4, respectively. In particular, in this embodiment, the light emitting elements 51-1 to 51-10 and the light receiving elements 52-1 to 52-10 are arranged in parallel to the traveling direction of the intermediate transfer belt 4, respectively.

  In the sensor 8 shown in FIG. 6, the positions of the light emitting elements 51-1 to 51-10 in the direction perpendicular to the traveling direction of the intermediate transfer belt 4 are constant, but along the traveling direction of the intermediate transfer belt 4. If arranged, the positions of the light emitting elements 51-1 to 51-10 in the direction perpendicular to the traveling direction of the intermediate transfer belt 4 may not be constant. The same applies to the light receiving elements 52-1 to 52-10.

  The optical lens 31 is installed between the light emitting elements 51-1 to 51-10 and the light receiving elements 52-1 to 52-10 of the sensor 8 and the intermediate transfer belt 4 as shown in FIG. In this embodiment, the optical lens 31 is a plano-convex cylindrical lens. As shown in FIG. 7B, the optical lens 31 causes the measurement light from the light emitting element 51-i to enter the detection position 61-i corresponding to the light emitting element 51-i as parallel light, and the detection position. The reflected light from the light is condensed and incident on the light receiving element 52-i paired with the light emitting element 51-i.

  Thereby, as shown in FIG. 8, a spot is formed at the detection position 61-i on the intermediate transfer belt 4 by the measurement light from the light emitting element 51-i. That is, in the case of the sensor 8 shown in FIGS. 6 and 7, as shown in FIG. 8, the sensor 8 detects the passage of one toner patch image 41a at the ten detection positions 61-1 to 61-10. The Similarly, the passage of the toner patch image 41b is also detected.

  Next, the operation of the image forming apparatus when adjusting the rotation speed of the photosensitive drums 1a to 1d will be described.

  In adjusting the rotational speed of the photosensitive drums 1 a to 1 d, first, the print engine 11 forms toner patch images 41 a and 41 b on the intermediate transfer belt 4, and the linear speed of the intermediate transfer belt 4 is determined from the output signal of the sensor 8. And the difference between the passage times of the predetermined detection positions of the two toner patch images 41a and 41b, and the corrected rotational speed is determined by the linear velocity and the difference of the passage times of the two toner patch images 41a and 41b. Identify.

  First, the linear velocity measurement of the intermediate transfer belt 4 using the patch image 41a will be described.

  In the measurement of the linear velocity, the print engine 11 or an analog drive circuit (not shown) controls the light emission period of the light emitting elements 51-1 to 51-10.

  FIG. 9 is a diagram illustrating an example of a waveform of an output signal of the light receiving element 52-i of the sensor 8 in FIG. When the toner patch image 41a passes through the detection position 61-i, the reflectance of the surface of the intermediate transfer belt 4 at the detection position 61-i changes, so that the voltage of the output signal increases as shown in FIG. FIG. 10 is a diagram illustrating an example of waveforms of output signals of the plurality of light receiving elements 52-i of the sensor 8 in FIG.

  As shown by the solid line in FIG. 10, when the linear velocity measurement is started, the print engine 11 or an analog drive circuit (not shown) first turns on the light emitting element 51-1, and outputs the output voltage of the light receiving element 52-1. After monitoring, the time T1 when the output voltage exceeds the predetermined threshold is detected, and the light emitting element 51-1 is turned off at the time T1, and the output signal of the light receiving element 52-1 is detected. Is stopped, the light emitting element 51-2 is turned on, and the output of the output signal of the light receiving element 52-2 is started. At this time, the linear velocity calculation unit 11a of the print engine 11 acquires and holds the time T1. When the analog drive circuit controls the light emitting element 51-i and the light receiving element 52-i, a signal indicating the time T1 is supplied from the analog drive circuit to the print engine 11.

  Then, the print engine 11 or an analog drive circuit (not shown) monitors the output voltage of the light receiving element 52-2, detects a time T2 when the output voltage exceeds a predetermined threshold, and becomes lower than the threshold, At the time T2, the light emitting element 51-2 is turned off, the output of the light receiving element 52-2 is stopped, the light emitting element 51-3 is turned on, and the output signal of the light receiving element 52-3 is output. Let it begin. At this time, the linear velocity calculation unit 11a of the print engine 11 acquires and holds the time T2.

  Thereafter, similarly, as the toner patch image 41a progresses, the light emitting element 51-j (j = 3,..., 9) is turned off, the light emitting element 51- (j + 1) is turned on, and the light receiving element 52-j is turned on. Output stop, output start of the light receiving element 52- (j + 1), and acquisition of time Tj are performed in order. After the light emitting element 51-10 is turned on, the print engine 11 or an analog drive circuit (not shown) detects a time T10 when the output voltage of the light receiving element 52-10 exceeds a predetermined threshold and becomes lower than the threshold. At time T10, the light emitting element 51-10 is turned off and the output of the output signal of the light receiving element 52-10 is stopped. At this time, the linear velocity calculation unit 11a of the print engine 11 acquires and holds the time T10.

  The linear velocity calculation unit 11a calculates the linear velocity of the intermediate transfer belt 4 using at least two of the acquired times T1 to T10.

  For example, when using the time Tk and the time T (k + 1) for the two adjacent detection positions 61-k and 61- (k + 1), the linear velocity calculation unit 11a calculates the linear velocity VL using the following equation.

  VL = Lk / (T (k + 1) -Tk)

  However, Lk is the distance between the center of the detection position 61-k and the center of the detection position 61- (k + 1). The light emitting elements 51-1 to 51-10 are arranged at equal intervals, the light receiving elements 52-1 to 52-10 are arranged at equal intervals, and two adjacent light emitting elements in the light emitting elements 51-1 to 51-10 are arranged. When the interval and the interval between two adjacent light receiving elements in the light receiving elements 52-1 to 52-10 are the same, the detection positions 61-1 to 61-10 are also equally spaced, and the detection positions 61-1 to 61-10 are the same. The interval between two adjacent detection positions in the light is also the same as the interval between the light emitting elements and the interval between the light receiving elements. In this case, for example, if the distance between the light emitting element and the light receiving element is 400 micrometers, Lk is also 400 micrometers.

  Note that the linear velocity calculation unit 11a may calculate the linear velocity VL using the following equation using the time Tp and the time Tq for two non-adjacent detection positions 61-p and 61-q (q> p). Good.

  VL = Lpq / (Tq-Tp)

  Note that Lpq is a distance between the center of the detection position 61-p and the center of the detection position 61-q.

  Further, the linear velocity calculation unit 11a calculates the linear velocity VL for each combination of two detection positions as described above, calculates the average value thereof, and uses the average value as the linear velocity of the intermediate transfer belt 4. Good.

  In this way, the linear velocity VL of the intermediate transfer belt 4 is measured.

  In parallel with the measurement of the linear velocity, the passage time of a predetermined detection position (here, the detection position 61-1) of the two patch images 41a and 41b is measured.

  FIG. 11 is a diagram illustrating an example of waveforms of output signals of the plurality of light receiving elements 52-1 of the sensor 8 in FIG.

  When two patch images 41a and 41b pass through one detection position 61-1, an output waveform as shown in FIG. 11 is obtained. The drum control unit 11b determines the rising timing of the output signal of the light receiving element 52-1, that is, the two patch images 41a, 41b based on whether or not the level of the output signal of the light receiving element 52-1 exceeds a predetermined threshold value. The passage times Ta and Tb of 41b are specified.

  The drum controller 11b adjusts the rotational speeds of the photosensitive drums 1a to 1d as follows based on the measured linear velocity VL and the passage times Ta and Tb of the patch images 41a and 41b.

  First, when the resolution of the toner image is 600 dpi, one dot has a size of 42.3 micrometers, and the prescribed value of the interval between dots is also 42.3 micrometers.

  Assuming that the line interval is 1 dot, the interval Ln between the line of the Nth beam among the N and the line of the first beam in the next scan is derived by the following equation.

  Ln = (Tb−Ta) × VL− (Lp1 + G−1) × 42.3

  Here, Lp1 is the length (length in the sub-scanning direction) of the toner patch image 41a (Lp1 = N × a; a is an integer). G is the length of the gap (the length in the sub-scanning direction) between the toner patch image 41a and the toner patch image 41b (G = N × b + 1; b is an integer).

  The line interval (line interval between the i-th and (i + 1) -th beams) in a certain scan is constant. Therefore, if Ln = 42.3 (that is, the length of one dot), the line interval is uniform, and therefore the adjustment of the rotational speed is unnecessary. Otherwise, the drum controller 11b According to the following equation, the speed of the photosensitive drums 1a to 1d is changed from the current value Vdc to the value Vd.

  Vd = Vdc × (N × 42.3−Ln) / {(N−1) × 42.3}

  FIG. 12 shows the polygon surface of the polygon mirror, the lines constituting the beam and the patch image, and the patch image interval in the sub-scanning direction when adjusting the rotational speed of the photosensitive drums 1a to 1d in the image forming apparatus shown in FIG. It is a figure explaining the space | interval of a line. In this example, the number of side surfaces (mirror surfaces) of the polygon mirror 23 is five.

  In the example shown in FIG. 12, N = 4, a = 2, and b = 2. The interval between the patch images 41a and 41b is set to 4N + Ln dots, and N is the period of a single i-th beam and is constant. . The period of the single i-th beam is kept constant by controlling the rotational speed of the polygon mirror 23 and the linear speed of the intermediate transfer belt 4. Therefore, the actual Ln is obtained by the above formula, and the rotational speeds of the photosensitive drums 1a to 1d are set so that the Ln is an original value (here, 1 dot, that is, 42.3 micrometers). Adjusted. In this example, Ln and Vd are as follows.

  Ln = (Tb−Ta) × VL−16 × 42.3

  Vd = Vdc × (4 × 42.3−Ln) / (3 × 42.3)

  Vd = Vdc × {20 × 42.3− (Tb−Ta) × VL} / (3 × 42.3)

  The print engine 11 adjusts the rotation speed of each of the photosensitive drums 1a to 1d as described above.

  As described above, according to the first embodiment, the print engine 11 controls the exposure apparatus 2 to start with one of the N beams (the fourth beam in the example shown in FIG. 12). A toner patch image 41a is formed by forming a line, and the leading line is formed by another one of the N beams (the first beam in the example shown in FIG. 12) to form the toner patch image 41b. Based on the difference between the passage times of the two patch images 41a and 41b at the predetermined detection position 61-1, and the linear velocity of the intermediate transfer belt 4, the line interval in the sub-scanning direction in the toner image is made uniform. The rotational speed of the photosensitive drums 1a to 1d is controlled.

  Thereby, the interval between the line of the Nth beam and the line of the next first beam is specified based on the difference between the passage times of the two patch images at the predetermined detection position 61-1 and the linear velocity of the intermediate transfer belt 4. The rotational speed of the photosensitive drums 1a to 1d is controlled so that the line interval is the same as the other line intervals. Therefore, even if the multi-beam exposure apparatus 2 is used, the line intervals in the toner image are all uniform. As a result, unevenness caused by non-uniform line spacing can be suppressed, and the output image can be of high quality.

  Further, according to the first embodiment, the sensor 8 detects the passage of the toner patch image 41a on the intermediate transfer belt 4 at a plurality of predetermined detection positions 61-1 to 61-10, and the linear velocity calculation unit 21 Specifies the time at which the passage of the toner patch image 41a is detected by the sensor 8, and the linear velocity of the intermediate transfer belt 4 from the passage times T1 to T10 of the toner patch image 41a at the plurality of detection positions 61-1 to 61-10. Calculate

  As a result, the linear velocity is calculated from the time at which one toner patch image 41a passes through the plurality of detection positions 61-1 to 61-10, so that it is not easily affected by environmental changes or changes with time of the intermediate transfer belt 4. The linear velocity of the transfer belt 4 can be accurately measured, and consequently the rotational speed of the photosensitive drums 1a to 1d can be accurately adjusted.

Embodiment 2. FIG.

  In the first embodiment of the present invention, it is assumed that the rotational speed of the polygon mirror 23 and the linear speed of the intermediate transfer belt 4 are the prescribed values, and the photosensitive member is so exposed that the line interval is the prescribed value (42.3 micrometers). The rotational speed of the body drums 1a to 1d is controlled. For this reason, when the rotational speed of the polygon mirror 23 and the linear speed of the intermediate transfer belt 4 are accurately controlled, no particular problem occurs.

  On the other hand, if the rotational speed of the polygon mirror 23 and the linear speed of the intermediate transfer belt 4 fluctuate, the line interval deviates from the specified value. For this reason, in the image forming apparatus according to Embodiment 2 of the present invention, all the line intervals are the reference line intervals obtained from the rotational speed of the polygon mirror 23 and the linear speed of the intermediate transfer belt 4 at each time point. In this manner, the rotational speed of the photosensitive drums 1a to 1d is controlled. The basic configuration of the image forming apparatus according to the second embodiment is the same as that of the first embodiment. However, the print engine 11 operates as described below.

  The toner patch image 41a in the second embodiment is the same as that in the first embodiment. Therefore, the leading line in the sub-scanning direction of the toner patch image 41a is formed by the p-th beam (here, the N-th beam) of the N beams of the exposure apparatus 2, and the toner patch image 41a is in the sub-scanning direction. The last line at is formed with the (p−1) th beam (Nth beam when p = 1). The other lines are repeated in the order from the first beam to the Nth beam, and are formed by any one of the first to Nth beams.

  On the other hand, for the toner patch image 41b in the second embodiment, the leading line in the sub-scanning direction of the toner patch image 41b is the q-th beam (p ≠ q, here the first beam) of the N beams. ), And the final line in the sub-scanning direction of the toner patch image 41b is formed with the same beam ((p−1) th beam) as the final line of the toner patch image 41a. The other lines are repeated in the order from the first beam to the Nth beam, and are formed by any one of the first to Nth beams.

  In the second embodiment, such toner patch images 41a and 41b are formed.

  Next, the rotational speed control of the photosensitive drums 1a to 1d in the second embodiment will be described.

  FIG. 13 is a diagram illustrating an example of waveforms of output signals of the plurality of light receiving elements 52-1 of the sensor 8 according to the second embodiment.

  When the two patch images 41a and 41b pass through one detection position 61-1, an output waveform as shown in FIG. 13 is obtained. The drum control unit 11b determines the rising timing of the output signal of the light receiving element 52-1, that is, the two patch images 41a, 41b based on whether or not the level of the output signal of the light receiving element 52-1 exceeds a predetermined threshold value. The passage times Ta and Tb of the front edge of 41b are specified, and the falling timing, that is, the passage times Ta 'and Tb' of the rear edges of the two patch images 41a and 41b are specified.

  The drum controller 11b then adjusts the rotational speed of the photosensitive drums 1a to 1d based on the measured linear velocity VL and the passage times Ta, Tb, Ta ′, and Tb ′ of the patch images 41a and 41b. Do as follows.

  First, when the resolution of the toner image is 600 dpi, one dot has a size of 42.3 micrometers, and the prescribed value of the dot interval is also 42.3 micrometers, but the belt linear velocity and / or polygon mirror rotation When the speed deviates from the specified value, the dot interval deviates from the specified value. Therefore, in the second embodiment, the line interval Ldot is calculated from the passage times Ta ′, Tb ′ and the like. The line interval Ldot is in dot units. When the line interval is 1 dot, the line interval is the same as the dot interval.

  Assuming that the line interval is 1 dot, the interval Ln between the line of the Nth beam among the N and the line of the first beam in the next scan is derived by the following equation. The line interval Ldot is derived by the following equation.

  Ln = (Tb−Ta) × VL− (Lp1 + G−1) × Ldot

Ldot = (Tb′−Ta ′) × VL / (Lp2 + G)
Ldot = (Tb′−Ta ′) × VL / (N × (b + c))

  Here, Lp1 is the length (length in the sub-scanning direction) of the toner patch image 41a (Lp1 = N × a; a is an integer). G is the length of the gap (the length in the sub-scanning direction) between the toner patch image 41a and the toner patch image 41b (G = N × b + 1; b is an integer). Lp2 is the length (length in the sub-scanning direction) of the toner patch image 41b (Lp2 = N × c−1; c is an integer).

  The line interval (line interval between the i-th and (i + 1) -th beams) in a certain scan is constant. Therefore, if Ln = Ldot (that is, the length of one dot), the line interval is uniform, and therefore the adjustment of the rotation speed is unnecessary. Otherwise, the drum controller 11b According to the equation, the speed of the photosensitive drums 1a to 1d is changed from the current value Vdc to the value Vd.

  Vd = Vdc × (N × Ldot−Ln) / {(N−1) × Ldot}

  FIG. 14 shows the polygon surface of the polygon mirror, the lines constituting the beam and the patch image, and the patch image in the sub-scanning direction when adjusting the rotation speed of the photosensitive drums 1a to 1d in the image forming apparatus according to the second embodiment. It is a figure explaining the space | interval and the space | interval of a line. In this example, the number of side surfaces (mirror surfaces) of the polygon mirror 23 is five.

  In the example shown in FIG. 14, N = 4, a = 2, b = 2, and c = 2. The interval between the patch images 41a and 41b is set to 4N + Ln dots, and N is the period of a single i-th beam and is constant. . The period of the single i-th beam is kept constant by controlling the rotational speed of the polygon mirror 23 and the linear speed of the intermediate transfer belt 4. For this reason, the actual Ln is obtained by the above formula, and the rotational speeds of the photosensitive drums 1a to 1d are adjusted so that the Ln is an original value (here, 1 dot = Ldot). In this example, Ln, Ldot, and Vd are as follows.

Ln = (Tb−Ta) × VL−16 × Ldot,
Ldot = (Tb′−Ta ′) × VL / 16,
Vd = Vdc × (4 × Ldot−Ln) / (3 × Ldot)

  From these equations, Vd considering the line interval Ldot at the time of measurement is calculated from the current value Vdc and the passage times Ta, Tb, Ta ′, Tb ′ as follows.

  Vd = Vdc × {20 × Ldot− (Tb−Ta) × VL} / (3 × Ldot)

  Vd = Vdc × [20 / 3− {16 × (Tb−Ta)} / {3 × (Tb′−Ta ′)}]

  The print engine 11 adjusts the rotation speed of each of the photosensitive drums 1a to 1d as described above.

  As described above, according to the second embodiment, in the print engine 11, all the line intervals are the dot intervals Ldot specified from the difference between the passage times of the toner patch images 41a and 41b at the predetermined detection positions. In this manner, the rotational speed of the photosensitive drums 1a to 1d is controlled.

  As a result, even when the reference line interval Ldot varies due to variations in the linear speed of the intermediate transfer belt 4 and the rotational speed of the polygon mirror 23, the line intervals in the toner image are all uniform.

  Each embodiment described above is a preferred example of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. It is.

  For example, in the first and second embodiments described above, in order to increase the measurement accuracy, Ln is calculated from the output signals of the plurality of light receiving elements 52-i, and the average value is used as the measured value of Ln. May be.

  In the first and second embodiments described above, the rotational speed is adjusted based on the interval (difference in passage time) between the two patch images 41a and 41b. Are formed with the same size and interval as those described above, the passage times of three or more patch images at a predetermined detection position are detected, and a plurality of intervals (differences in passage times) of the patch images are determined. You may make it identify and use the average value as a difference (Tb-Ta) of passage time.

  In the first and second embodiments, the falling of the output waveform is detected as shown in FIGS. 9 and 10 for the linear velocity measurement. Instead, the rising of the output waveform is detected. You may make it detect.

  In the first and second embodiments, the first line of the first toner patch image 41a is formed with the Nth beam, and the first line of the next toner patch image 41b is formed with the first beam. Instead, the first line of the first toner patch image 41a is formed by the first beam, and the first line of the next toner patch image 41b is formed by the (N-1) th beam. Good. Thereby, since the measured value of Li is obtained, Ln can be specified from the value of Li. Similarly, for the first toner patch image 41a and the next toner patch image 41b, the first line is formed with different combinations of beams different from each other, and the measured value of Li is obtained. Ln may be specified.

  In the first and second embodiments, the interval between the two patch images 41a and 41b is such that the beam from one of the light emitting elements of the detection position of the patch image 41a and the detection position of the patch image 41b and the reflected light thereof. Is a length that does not enter the other light receiving element. Note that monitoring of the passage of the patch image 41b by the sensor 8 is started at a predetermined timing (for example, after a predetermined time has elapsed) after the patch image 41a has passed.

  In the first and second embodiments, the light emitting element arrangement and the light receiving element arrangement method in the sensor 8 are not limited to those described above, and the traveling direction of the intermediate transfer belt 4 (that is, the toner patch image 41a). A light emitting element corresponding to the detection position is disposed at a position where the measurement light is incident on a plurality of predetermined detection positions designated along the movement direction), and the detection light is positioned at the position where the reflected light is incident. Other arrangement methods may be used as long as the corresponding light receiving elements are arranged. Further, the two light receiving elements may be arranged at the same distance from the light emitting element, and the light emitting elements may be used at the two detection positions.

  FIG. 15 is a diagram showing another arrangement method of the light emitting elements and the light receiving elements of the sensor 8 in FIG.

  In the arrangement shown in FIG. 6, the pair of light emitting elements 51-i and light receiving elements 52-i are arranged perpendicular to the traveling direction of the intermediate transfer belt 4, but in FIG. Are lined up. Even in this case, it is possible to form a spot of measurement light at the detection positions 61-1 to 61-10 shown in FIG.

  Further, as shown in FIG. 15B, the light emitting elements 51-i and the light receiving elements 52-i may be alternately arranged in a line. In this case, as shown in FIG. 15B, the light emitting element 51-10 may be omitted, and the light emitting element 51-9 may be used as the light receiving elements 52-9 and 52-10.

  Further, as shown in FIG. 15C, each of all the light emitting elements 51-i may be shared by two light receiving elements.

  In the above embodiment, one optical lens 31 is provided for each sensor 8. However, one optical lens may be provided for each pair of the light emitting element 51-i and the light receiving element 52-i. Alternatively, one optical lens may be provided for each of the light emitting element 51-i and the light receiving element 52-i.

  In the above embodiment, a toner image for registration processing or a toner image for toner density correction may be used as the toner patch images 41a and 41b.

  In the above embodiment, the linear speed of the intermediate transfer belt 4 is measured in the color image forming apparatus. However, the linear speed of the intermediate transfer belt 4 can be measured in the monochrome image forming apparatus. is there.

  Further, in the above embodiment, when the value of the output signal of the light receiving element 52-i corresponding to one detection position 61-i decreases below a predetermined threshold, the next detection position 61- (i + 1) is reached. When the corresponding light emitting element 51- (i + 1) is turned on, and the value of the output signal of the light receiving element 52 increases after the center of the toner patch image 41a passes through the center of the detection position 61-i, When the value of the output signal of the light receiving element 52-i corresponding to one detection position 61-i increases to a predetermined threshold value or more, the light emitting element 51-i is turned off, and the next detection position 61- (i + 1) is reached. The corresponding light emitting element 51- (i + 1) is turned on.

  Moreover, in the said embodiment, although the number of detection positions is 10, as long as the number of detection positions is two or more, any number may be sufficient.

  Further, in the above embodiment, the case where the number of beams by one exposure apparatus 2 is set as an example, but the number of beams is not limited to four.

  The present invention is applicable to an image forming apparatus such as a printer, a copier, a facsimile machine, and a multifunction machine.

1a to 1d Photosensitive drum 2 Exposure device 3a to 3d Development unit 4 Intermediate transfer belt (an example of an intermediate transfer member)
8 Sensor 11 Print engine (an example of a control unit)
21 Linear velocity calculation unit 22 Drum control unit (an example of a part of the control unit)
31 Optical lens 41a, 41b Toner patch image 51-1 to 51-10 Light emitting element 52-1 to 52-10 Light receiving element 61-1 to 61-10 Detection position

Claims (14)

A photosensitive drum;
A multi-beam exposure apparatus that forms an electrostatic latent image on the photosensitive drum using N (N> 1) beams;
A developing unit for developing the electrostatic latent image on the photosensitive drum with toner;
An intermediate transfer member to which a toner image on the photosensitive drum is transferred;
A sensor that detects reflected light from a predetermined detection position and detects the passage of a toner patch image on the intermediate transfer member;
A linear velocity calculation unit for calculating a linear velocity of the intermediate transfer member based on a detection result by the sensor;
The exposure apparatus is controlled to form a first toner patch image by forming a first line with one of the N beams, and to form a first toner patch image with the other one of the N beams. To form a second toner patch image, and based on the difference between the passage times of the first and second toner patch images at the predetermined detection position and the linear velocity, the sub-scanning direction in the toner image A control unit for controlling the rotational speed of the photosensitive drum so that the line interval at
An image forming apparatus comprising: The sensor detects passage of one of the first and second toner patch images at a plurality of detection positions;
The linear velocity calculation unit identifies a time at which the passage of the toner patch image is detected by the sensor at the plurality of detection positions, and determines the intermediate transfer body from the passage time of the toner patch image at the plurality of detection positions. Calculating the linear velocity,
The image forming apparatus according to claim 1. The sensor causes measurement light to enter the plurality of detection positions, detects reflected light from each of the plurality of detection positions, and outputs an output signal corresponding to the detected reflected light,
The linear velocity calculation unit specifies a passing time of the toner patch image at the plurality of detection positions based on the output signal;
The image forming apparatus according to claim 2.   The image forming apparatus according to claim 3, wherein the sensor includes a pair of a light emitting element that emits the measurement light and a light receiving element that receives the reflected light corresponding to each of the plurality of detection positions. apparatus.   The image forming apparatus according to claim 4, wherein the light emitting element and the light receiving element are each arranged along a traveling direction of the intermediate transfer member.   The linear velocity calculation unit calculates the linear velocity from the passage times at the plurality of detection positions and the intervals between the light emitting elements and / or the light receiving elements corresponding to the plurality of detection positions. The image forming apparatus according to claim 5.   During the period in which the light emitting element corresponding to one of the plurality of detection positions emits the measurement light and the toner patch image is detected at the detection position, the remaining of the plurality of detection positions The image forming apparatus according to claim 4, wherein the light emitting element corresponding to the detection position stops emission of the measurement light.   The light emitting element corresponding to the detection position when the value of the output signal of the light receiving element corresponding to one detection position of the plurality of detection positions decreases below a predetermined threshold or increases above a predetermined threshold 8. The image forming apparatus according to claim 7, wherein the emission of the measurement light is stopped, and the light emitting element corresponding to the next detection position among the plurality of detection positions starts emission of the measurement light. .   The measurement light from the light emitting element is incident on the detection position corresponding to the light emitting element as parallel light, and the reflected light from the detection position is condensed on the light receiving element paired with the light emitting element. The image forming apparatus according to claim 4, further comprising an incident optical lens.   The control unit forms a first toner patch image by forming a first line with the Nth beam of the N beams, and forms a first line with the first beam of the N beams. The image forming apparatus according to claim 1, wherein the second toner patch image is formed.   The control unit adjusts the rotational speed of the photosensitive drum so that all line intervals become a line interval specified from a difference between passage times of the first and second toner patch images at the predetermined detection position. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled.   The control unit forms a final line of the first toner patch image and the second toner patch image with the same beam among the N beams, and the predetermined detection position. 12. The image according to claim 11, wherein the rotational speed of the photosensitive drum is controlled so as to be a line interval specified from a difference between passage times of rear edges of the first and second toner patch images. Forming equipment. Forming an electrostatic latent image on the photosensitive drum by a multi-beam method using N (N> 1) beams;
Developing an electrostatic latent image on the photosensitive drum with toner;
Transferring the toner image on the photosensitive drum onto an intermediate transfer member;
Detecting reflected light from a predetermined detection position and detecting the passage of the toner patch image on the intermediate transfer member by a sensor;
Calculating a linear velocity of the intermediate transfer member based on a detection result by the sensor;
The exposure apparatus is controlled to form a first toner patch image by forming a first line with one of the N beams, and to form a first toner patch image with the other one of the N beams. Forming a second toner patch image, and
Based on the difference between the passage times of the first and second toner patch images at the predetermined detection position and the linear velocity, the photosensitive drum has a uniform line interval in the sub-scanning direction in the toner image. Controlling the rotational speed;
A speed control method comprising:   The rotational speed of the photosensitive drum is controlled so that all the line intervals are the line intervals specified from the difference between the passage times of the first and second toner patch images at the predetermined detection position. The speed control method according to claim 13.

Images