JP6368120B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus.

  2. Description of the Related Art Conventionally, there is known an image forming apparatus that forms an electrostatic latent image on a photosensitive member by deflecting a light beam emitted from a light source with a rotating polygon mirror and scanning the photosensitive member with the deflected light beam. . Such an image forming apparatus includes an optical sensor (beam detection (BD) sensor) for detecting a light beam deflected by a rotating polygon mirror, and the optical sensor generates a synchronization signal when the light beam is detected. Generate. The image forming apparatus emits a light beam from a light source at a timing determined with reference to a synchronization signal generated by an optical sensor, so that an electrostatic latent image in a direction in which the light beam scans on the photoconductor (main scanning direction). The writing start position of the image (image) is constant.

  In addition, in order to increase the image forming speed and increase the resolution of the image, a multi-beam including a plurality of light emitting elements that emit a plurality of light beams that scan different lines in parallel on the photoconductor as a light source. A type of image forming apparatus is known. In such a multi-beam type image forming apparatus, a plurality of lines are scanned in parallel with a plurality of light beams to increase the image forming speed and adjust the spacing between the lines in the sub-scanning direction. As a result, higher resolution of the image is realized.

  Patent Document 1 discloses an image forming apparatus that includes a plurality of light emitting elements as light sources, and that can adjust the resolution in the sub-scanning direction by rotating and adjusting the light sources within a plane in which the plurality of light emitting elements are arranged. ing. Such resolution adjustment is performed in the assembly process of the image forming apparatus. Patent Document 1 discloses a technique for suppressing a shift in the writing position of an electrostatic latent image in the main scanning direction, which is caused by a light source mounting error in an assembly process. Specifically, the image forming apparatus detects a light beam emitted from each of the first light emitting element and the second light emitting element with a BD sensor, and generates a plurality of BD signals. Further, the image forming apparatus sets the relative emission timing of the light beam of the second light emitting element with respect to the emission timing of the light beam of the first light emitting element, based on the generation timing difference between the generated BD signals. To do. This compensates for the light source mounting error in the assembly process and suppresses the deviation of the electrostatic latent image writing position between the light emitting elements.

  Further, the image forming apparatus shortens the time (FCOT: First Copy Output Time) from when the start of image formation (printing) is instructed to when the recording paper on which the image is printed is discharged as much as possible. However, techniques for quickly obtaining print output are known. Patent Document 2 discloses an image forming apparatus having a function of shortening FCOT (flying start function) by starting a drive motor that rotates a polygon mirror (rotating polygon mirror) before instructing to start printing. Is disclosed. In this image forming apparatus, for example, when a copy original is set, the drive motor is started without turning on the light emitting element (laser diode (LD)) and output from the hall element provided in the drive motor. The rotational speed of the drive motor is controlled based on the signal. When a print start instruction is subsequently issued, the image forming apparatus turns on the LD and controls the drive motor based on the BD signal output from the BD sensor in order to control the rotation speed of the drive motor with higher accuracy. Control the rotation speed. As described above, by performing rotation control of the drive motor based on the BD signal as necessary, it is possible to shorten the FCOT and extend the life of the LD.

JP 2008-89695 A JP 2009-299717 A

  However, the multi-beam method is applied to the image forming apparatus described in Patent Document 2, and as described above, the generation timing difference (time interval) of the BD signal generated by the BD sensor is measured, and the laser of each light emitting element is measured. When controlling the emission timing, there are the following problems. Specifically, in order to prevent deterioration in measurement accuracy in measuring the time interval of the BD signal (BD interval measurement), the light emitting element is turned on according to the print start instruction, and the polygon mirror is rotated by rotation control based on the BD signal. The measurement needs to be performed after the speed has stabilized at a constant speed. However, in this case, it takes some time until the rotational speed of the polygon mirror is stabilized after the print start instruction is issued. Furthermore, more time is required until the BD interval measurement is completed after the rotational speed of the polygon mirror is stabilized. Therefore, when performing the BD interval measurement, there is a problem that the time (ie, FCOT) from when the print start instruction is issued until the image is actually printed on the recording paper is increased.

  The present invention has been made in view of the above-described problems. The present invention is an image forming apparatus using a plurality of light emitting elements, and performs rotation control of a rotary polygon mirror based on a detection signal of a light beam without waiting for an instruction to start image formation, thereby measuring a time interval of the detection signal. The purpose is to provide a technology that accelerates execution timing.

The present invention can be realized as an image forming apparatus, for example. An image forming apparatus according to one embodiment of the present invention includes a light source including a plurality of light emitting elements that respectively emit light beams for exposing a photosensitive member, and the plurality of light beams emitted from the plurality of light emitting elements are photosensitive members. A rotating polygon mirror for deflecting the plurality of light beams, a drive motor for rotating the rotating polygon mirror, and a scanning path for the light beam deflected by the rotating polygon mirror. An optical sensor that outputs a detection signal indicating that the light beam deflected by the light beam is detected, and a signal that is provided in the drive motor and that has a period corresponding to the rotational speed of the drive motor is output. A rotation detection sensor that controls the rotation speed of the drive motor based on a period of a signal output from the rotation detection sensor, and a light beam. Rotation control means for controlling the rotational speed of the rotary polygon mirror by one of the second rotational controls for controlling the rotational speed of the drive motor based on the period of the detection signal output from the optical sensor by light. The first rotation control is performed until the rotation speed of the drive motor reaches a target speed, and when the rotation speed of the drive motor reaches the target speed, the first rotation control to the second rotation control are performed. The rotation control means that switches to the rotation control of the light beam, and the light beam from each of the first and second light emitting elements among the plurality of light emitting elements while the rotation control means is executing the second rotation control. Measuring means for controlling the light source to sequentially enter the optical sensor and measuring the time intervals of the first and second detection signals output in order from the optical sensor; and When the image formation is started after the measurement of the time interval, the relative light beams based on the image data of each of the plurality of light emitting elements are based on the time interval measured by the measurement unit. Control means for controlling the emission timing, and when the start of image formation is not instructed before completion of the measurement of the time interval by the measurement means, the rotation control means is configured to measure the time interval. After the end, the rotation speed control is switched from the second rotation control to the first rotation control, and when the start instruction is issued, the rotation speed control is changed from the first rotation control to the second rotation control. It switches to rotation control again, It is characterized by the above-mentioned.

  According to the present invention, an image forming apparatus using a plurality of light emitting elements performs rotation control of a rotating polygon mirror based on a detection signal of a light beam without waiting for an instruction to start image formation, thereby reducing the time interval of the detection signal. It is possible to provide a technique for advancing the execution timing of measurement (BD interval measurement). As a result, it is possible to avoid an increase in the FCOT due to the execution of the BD interval measurement.

1 is a cross-sectional view illustrating a schematic configuration example of an image forming apparatus. The figure which shows the schematic structural example of an optical scanning part. The figure which shows the schematic structural example of a light source, and an example of the scanning position on the photosensitive drum and BD sensor by the laser beam radiate | emitted from the light source. FIG. 3 is a block diagram illustrating a control configuration example of the image forming apparatus. The block diagram which shows the structural example of a scanner unit control part. The figure which shows an example of the change of the scanning position on the photosensitive drum by the laser beam radiate | emitted from the light source. 6 is a timing chart showing the operation timing of each light emitting element and the generation timing of a BD signal by a BD sensor during one scanning period of laser light during BD interval measurement and image formation. The figure which shows the relationship between BD interval measurement and a CLK signal. 9 is a timing chart (comparative example) showing an example of the relationship between the rotation control timing of the polygon mirror and the execution timing of the BD interval measurement. 6 is a timing chart showing an example of the relationship between the rotation control timing of the polygon mirror and the execution timing of the BD interval measurement. 6 is a flowchart showing an execution procedure of image forming processing. 10 is a flowchart showing an execution procedure of print preparation (mode 1) in S104. 10 is a flowchart showing an execution procedure of print preparation (mode 2) in S102. The figure which shows an example of the relationship between the measurement temperature of a thermistor, and the execution time (predetermined time) of FG control until it switches to BD control.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

  Hereinafter, as an embodiment of the present invention, a case where the present invention is applied to an image forming apparatus that forms a multicolor (full color) image using a plurality of color toners (developers) will be described as an example. However, the present invention can also be applied to an image forming apparatus that forms a monocolor image using only a single color (for example, black) toner.

<Hardware configuration of color MFP>
First, a configuration of a color multifunction peripheral according to an embodiment will be described with reference to FIG. As shown in FIG. 1, the color multifunction peripheral includes an image reading apparatus 150 and an image forming apparatus 100.

  The image reading apparatus 150 forms an image of the document 152 on the color sensor 156 via the illumination lamp 153, the mirror groups 154A, 154B and 154C, and the lens 155. As a result, the image reading device 150 reads an image of a document for each color separation light of blue (B), green (G), and red (R), for example, and converts the image into an electrical image signal. The image is converted and transmitted to the central image processing unit 130 on the image forming apparatus 100 side.

  The central image processing unit 130 performs color conversion processing based on the intensity levels of the R, G, and B color components included in the image signal obtained by the image reading device 150. Thereby, image data including color components of yellow (Y), magenta (M), cyan (C), and black (K) is obtained. In addition to the image reading device 150, the central image processing unit 130 is connected to an external device on a network such as a telephone line or a LAN via an external interface (I / F) 413 (FIG. 4) provided in the color multifunction peripheral. Input data can be received. In this case, if the data received from the external device is in PDL (Page Description Language) format, the central image processing unit 130 develops the received external input data into image information by the PDL processing unit 412 (FIG. 4). It is possible to obtain image data.

  The image forming apparatus 100 includes four image forming units that form images (toner images) using Y, M, C, and K toners, respectively. The image forming unit corresponding to each color includes photosensitive drums (photosensitive members) 102Y, 102M, 102C, and 102K. Around the photosensitive drums 102Y, 102M, 102C, and 102K, there are charging units 103Y, 103M, 103C, and 103K, optical scanning units (optical scanning devices) 104Y, 104M, 104C, and 104K, and developing units 105Y, 105M, 105C, and 105K. Are arranged respectively. A drum cleaning unit (not shown) is further disposed around the photosensitive drums 102Y, 102M, 102C, and 102K.

  An endless belt-like intermediate transfer belt (intermediate transfer member) 107 is disposed below the photosensitive drums 102Y, 102M, 102C, and 102K. The intermediate transfer belt 107 is stretched around a driving roller 108 and driven rollers 109 and 110. During image formation, as the drive roller 108 rotates, the peripheral surface of the intermediate transfer belt 107 moves in the direction of the arrow shown in FIG. Primary transfer bias blades 111Y, 111M, 111C, and 111K are disposed at positions that face the photosensitive drums 102Y, 102M, 102C, and 102K with the intermediate transfer belt 107 interposed therebetween. The image forming apparatus 100 includes a secondary transfer bias roller 112 for transferring a toner image formed on the intermediate transfer belt 107 onto a recording paper (recording medium), and the toner image transferred onto the recording paper. And a fixing unit 113 for fixing the image to the camera.

  Next, an image forming process from the charging process to the developing process in the image forming apparatus 100 having the above-described configuration will be described. The image forming process executed in each of the image forming units corresponding to each color is the same. Therefore, hereinafter, an image forming process in the image forming unit corresponding to the Y color will be described as an example, and description of the image forming process in the image forming unit corresponding to the M, C, and K colors will be omitted.

  First, the charging unit 103Y of the image forming unit corresponding to the Y color charges the surface of the rotationally driven photosensitive drum 102Y. The optical scanning unit 104Y emits a plurality of laser beams (light beams) and scans the surface of the charged photosensitive drum 102Y with the plurality of laser beams, thereby exposing the surface of the photosensitive drum 102Y. Thereby, an electrostatic latent image is formed on the rotating photosensitive drum 102Y. The electrostatic latent image formed on the photosensitive drum 102Y is developed with Y-color toner by the developing unit 105Y. As a result, a Y-color toner image is formed on the photosensitive drum 102Y. In the image forming units corresponding to M, C, and K colors, the M, C, and K colors are formed on the photosensitive drums 102M, 102C, and 102K in the same process as the image forming unit corresponding to the Y color, respectively. Color toner images are respectively formed.

  Hereinafter, an image forming process after the transfer process will be described. In the transfer process, first, the primary transfer bias blades 111Y, 111M, 111C, and 111K apply a transfer bias to the intermediate transfer belt 107, respectively. As a result, the four color (Y, M, C, and K) toner images formed on the photosensitive drums 102Y, 102M, 102C, and 102K are transferred onto the intermediate transfer belt 107 in a superimposed manner.

  A toner image composed of four colors of toner formed on the intermediate transfer belt 107 is overlapped between the secondary transfer bias roller 112 and the intermediate transfer belt 107 as the peripheral surface of the intermediate transfer belt 107 moves. To the secondary transfer nip. In accordance with the timing at which the toner image formed on the intermediate transfer belt 107 is conveyed to the secondary transfer nip portion, the recording paper is conveyed from the paper feed cassette 718 to the secondary transfer nip portion. In the secondary transfer nip portion, the toner image formed on the intermediate transfer belt 107 is transferred onto the recording paper by the action of the transfer bias applied by the secondary transfer bias roller 112 (secondary transfer).

  Thereafter, the toner image formed on the recording paper is fixed on the recording paper by being heated by the fixing unit 113. The recording paper on which the multi-color (full color) image is formed in this manner is discharged to the paper discharge unit 725.

  Note that after the transfer of the toner image to the intermediate transfer belt 107 is completed, the toner remaining on the photosensitive drums 102Y, 102M, 102C, and 102K is removed by the drum cleaning unit (not shown). When a series of image forming processes is completed in this way, the image forming process for the next recording sheet is started.

<Hardware configuration of optical scanning unit>
Next, the configuration of the optical scanning units 104Y, 104M, 104C, and 104K will be described with reference to FIGS. Since the optical scanning units 104Y, 104M, 104C, and 104K (image forming units corresponding to Y, M, C, and K colors) have the same configuration, the subscripts Y, M, C, and In some cases, K is omitted. For example, the expression “photosensitive drum 102” represents each of the photosensitive drums 102Y, 102M, 102C, and 102K, and the expression “optical scanning unit 104” represents each of the optical scanning units 104Y, 104M, 104C, and 104K. .

  FIG. 2 is a diagram illustrating a configuration of the optical scanning unit 104. The optical scanning unit 104 includes a laser driver 200, a laser light source 201, and various optical members 202 to 206 (collimator lens 202, cylindrical lens 203, polygon mirror (rotating polygonal mirror) 204, fθ lenses 205 and 206). . The laser driver 200 controls driving of the laser light source 201 by a driving current supplied to the laser light source 201. A laser light source (hereinafter simply referred to as “light source”) 201 generates and outputs (emits) laser light (light beam) having a light amount corresponding to a drive current. The collimator lens 202 shapes the laser light emitted from the light source 201 into parallel light. The cylindrical lens 203 condenses the laser light that has passed through the collimator lens 202 in the sub-scanning direction (direction corresponding to the rotation direction of the photosensitive drum 102).

  The laser light that has passed through the cylindrical lens 203 is incident on one of the plurality of reflecting surfaces provided in the polygon mirror 204. The polygon mirror 204 reflects the laser beam on each reflecting surface while rotating in the direction of the arrow shown in FIG. 2 so that the incident laser beam is deflected at a continuous angle. The laser light deflected by the polygon mirror 204 enters the fθ lenses 205 and 206 in order. By passing through the fθ lenses (scanning lenses) 205 and 206, the laser light becomes scanning light that scans the surface of the photosensitive drum 102 at a constant speed.

  The optical scanning unit 104 includes a reflection mirror (synchronization detection mirror) 208 at a position on the scanning start side of the laser light in the scanning path of the laser light that has passed through the fθ lens 205. Laser light that has passed through the end of the fθ lens is incident on the reflection mirror 208. The optical scanning unit 104 further includes a beam detection (BD) sensor 207 as an optical sensor for detecting the laser light in the reflection direction of the laser light from the reflection mirror 208. As described above, the BD sensor 207 is arranged on the scanning path of the laser light deflected by the polygon mirror 204. That is, the BD sensor 207 is provided on a scanning path when a plurality of laser beams emitted from the light source 201 scan the surface of the photosensitive drum 102.

When the laser beam deflected by the polygon mirror 204 is incident, the BD sensor 207 outputs a detection signal (BD signal) indicating that the laser beam has been detected as a (horizontal) synchronization signal. The BD signal output from the BD sensor 207 is input to the scanner unit control unit 210. As will be described later, the scanner unit control unit 210 controls the lighting timing of each light emitting element (LD _{1 to} LD _N ) based on the image data based on the BD signal output from the BD sensor 207.

Next, the configuration of the light source 201 and the scanning positions on the photosensitive drum 102 and the BD sensor 207 by the laser light emitted from the light source 201 will be described with reference to FIG.
First, FIG. 3A is an enlarged view of the light source 201, and FIG. 3B is a diagram showing a scanning position on the photosensitive drum 102 by the laser light emitted from the light source 201. The light source 201 includes N light emitting elements (LD _{1 to} LD _N ) each emitting (outputting) laser light. N-th light source 201 (n is an integer of 1 to N) light-emitting element of n (LD _n) emits the laser beam L _n. The X-axis direction in FIG. 3A corresponds to a direction (main scanning direction) in which each laser beam deflected by the polygon mirror 204 scans on the photosensitive drum 102. The Y-axis direction is a direction orthogonal to the main scanning direction, and corresponds to the rotation direction (sub-scanning direction) of the photosensitive drum 102.

As shown in FIG. 3B, the laser beams L _{1 to} L _N emitted from the light emitting elements 1 to _N are spotted on the photosensitive drum 102 at different positions S _{1 to} S _N in the sub scanning direction. Form an image. Thus, the laser beams L _{1 to} L _N scan a plurality of main scanning lines adjacent in the sub scanning direction in parallel on the photosensitive drum 102. Further, since the light emitting elements 1 to N are arranged in an array as shown in FIG. 3A in the light source 201, the laser beams L _{1 to} L _N are shown in FIG. As shown, images are formed on the photosensitive drum 102 at different positions in the main scanning direction. In FIG. 3A, the N light emitting elements (LD _{1 to} LD _N ) are linearly (in one dimension) arranged in a line in the light source 201, but may be arranged in two dimensions. Good.

D1 shown in FIG. 3A represents an interval (distance) between the light emitting element 1 (LD ₁ ) and the light emitting element N (LD _N ) in the X-axis direction. In the present embodiment, the light emitting elements 1 and N are light emitting elements arranged at both ends among a plurality of light emitting elements arranged in a line in the light source 201. The light emitting element N is farthest from the light emitting element 1 in the X-axis direction. For this reason, as shown in FIG. 3B, the imaging position S _N of the laser beam L _N among the plurality of laser beams is changed from the imaging position S ₁ of the laser beam L ₁ on the photosensitive drum 102. It is the farthest position in the main scanning direction.

D2 shown in FIG. 3A represents an interval (distance) between the light emitting element 1 (LD ₁ ) and the light emitting element N (LD _N ) in the Y-axis direction. Among the plurality of light emitting elements, the light emitting element N is farthest from the light emitting element 1 in the Y-axis direction. For this reason, as shown in FIG. 3B, the imaging position S _N of the laser beam L _N among the plurality of laser beams is changed from the imaging position S ₁ of the laser beam L ₁ on the photosensitive drum 102. It is the farthest position in the sub-scanning direction.

The light emitting element interval Ps = D2 / N−1 in the Y-axis direction (sub-scanning direction) is an interval corresponding to the resolution of the image formed by the image forming apparatus 100. Ps, the interval of imaging position S _n neighboring in the sub scanning direction on the photosensitive drum 102, so that the interval corresponding to the predetermined resolution, the light source 201 in the assembly process of the image forming apparatus 100 (color MFP) This value is set by adjusting the rotation. As shown in FIG. 3A, the light source 201 is rotationally adjusted in the direction of the arrow within a plane (XY plane) including the X axis and the Y axis. When the light source 201 is rotated, the interval between the light emitting elements in the Y-axis direction changes, and the interval between the light emitting elements in the X-axis direction also changes. The light emitting element interval Pm = D1 / N−1 in the X axis direction (main scanning direction) is a value uniquely determined depending on the light emitting element interval Ps in the Y axis direction.

The timing at which laser light is emitted from each light emitting element (LD _n ) based on the timing at which the BD sensor 207 generates and outputs the BD signal is set for each light emitting element using a predetermined jig in the assembly process. Is done. The set timing for each light emitting element is stored in the memory 406 (FIG. 5) as an initial value when the image forming apparatus 100 (color multifunction peripheral) is shipped from the factory. A value corresponding to Pm is set as the initial value of the timing at which the laser light is emitted from each light emitting element (LD _n ) set in this way.

Next, FIG. 3C is a diagram showing a schematic configuration of the BD sensor 207 and a scanning position on the BD sensor 207 by the laser light emitted from the light source 201. The BD sensor 207 includes a light receiving surface 207a on which photoelectric conversion elements are arranged in a planar shape. When the laser light is incident on the light receiving surface 207a, the BD sensor 207 generates and outputs a BD signal indicating that the laser light has been detected. The optical scanning unit 104 causes laser beams L ₁ and L _N emitted from the light emitting elements 1 and N (LD ₁ and LD _N ) to sequentially enter the BD sensor 207 in the BD interval measurement described later. Thereby, the optical scanning unit 104 sequentially outputs two BD signals corresponding to the respective laser beams from the BD sensor 207. In the present embodiment, the light emitting elements 1 and N (LD ₁ and LD _N ) are examples of a first light emitting element and a second light emitting element, respectively.

In FIG. 3C, the width of the light receiving surface 207a in the main scanning direction and the width in the direction corresponding to the sub scanning direction are represented as D3 and D4, respectively. In this embodiment, the laser beams L ₁ and L _N emitted from the light emitting elements 1 and N (LD ₁ and LD _N ) respectively scan the light receiving surface 207a of the BD sensor 207 as shown in FIG. . Therefore, the width D4 is set to a value satisfying D4> D2 × α so that both the laser beams L ₁ and L _N can enter the light receiving surface 207a. Here, α is a variation rate in the sub-scanning direction with respect to the interval between the laser beams L ₁ and L _N that have passed through various lenses. Further, even when the light emitting elements 1 and N (LD ₁ and LD _N ) are turned on at the same time, the width D3 is D3 <D1 × so that the laser beams L ₁ and L _N do not enter the light receiving surface 207a at the same time. It is set to a value that satisfies β. Here, β is a fluctuation rate in the main scanning direction with respect to the interval between the laser beams L ₁ and L _N that have passed through the various lenses.

<Control Configuration of Image Forming Apparatus>
Next, the control configuration of the image forming apparatus 100 will be described with reference to FIG. As shown in FIG. 4, the image forming apparatus 100 includes a central image processing unit 130, a reading system image processing unit 411, a PDL processing unit 412, an external I / F 413, an image memory 414, an external control configuration related to image formation. A memory 415 and scanner unit controllers 210Y, 210M, 210C, and 210K are provided.

  The central image processing unit 130 temporarily stores in the image memory 414 the image data that has undergone the PDL processing by the PDL processing unit 412. The scanner unit control unit 210 requests image data from the central image processing unit 130 at a timing described later. In response to the request, the central image processing unit 130 reads out image data from the image memory 414, performs image processing using the external memory 415 and the like, and then transmits image data corresponding to each color to the scanner unit control unit 210. To do.

  The BD signal generated and output by the BD sensor 207 is input to the scanner unit control unit 210. The scanner unit control unit 210 converts the image data received from the central image processing unit 130 into a laser drive pulse signal for controlling the light source 201. Further, the scanner unit controller 210 outputs a laser drive pulse signal to the laser driver 200 with reference to the timing when the BD signal is generated by the BD sensor 207.

<Control configuration of optical scanning unit>
Next, the control configuration of the optical scanning unit 104 will be described with reference to FIG. FIG. 5 is a block diagram illustrating a configuration of the scanner unit control unit 210. The scanner unit control unit 210 includes a CPU 401, a clock (CLK) signal generation unit 404, an image output control unit 405, a memory (storage unit) 406, a drive motor control unit 408, a motor driver 409, and a thermistor (temperature sensor) 410. .

  The CPU 401 controls the entire optical scanning unit 104 by executing a control program stored in the memory 406. The CLK signal generation unit 404 generates a clock signal (CLK signal) having a predetermined frequency, and outputs the generated CLK signal to the CPU 401. The CPU 401 counts the pulses of the CLK signal input from the CLK signal generation unit 404 and transmits a control signal to the drive motor control unit 408, the image output control unit 405, and the laser driver 200 in synchronization with the CLK signal. . The CPU 401 controls the drive motor control unit 408, the image output control unit 405, and the laser driver 200 using the control signal.

  The drive motor control unit 408 controls the rotation speed of the polygon mirror 204 by outputting an acceleration signal or a deceleration signal to the motor driver 409 in accordance with an instruction from the CPU 401. The drive motor 407 is a motor that rotationally drives the polygon mirror 204. The motor driver 409 accelerates or decelerates the rotation of the drive motor 407 according to the acceleration signal or the deceleration signal output from the drive motor control unit 408.

  The drive motor 407 includes a speed sensor (rotation detection sensor) 420 that employs a frequency generator (FG) system that generates a frequency signal proportional to the rotation speed of the drive motor itself. The speed sensor 420 outputs a signal (FG signal) having a period corresponding to the rotational speed of the polygon mirror 204. The speed sensor 420 is, for example, a Hall element that outputs a signal having a frequency corresponding to the rotation of the drive motor 407. The drive motor 407 generates an FG signal having a frequency (cycle) corresponding to the rotation speed of the polygon mirror 204 by the speed sensor 420 and outputs the FG signal to the drive motor control unit 408. The drive motor control unit 408 measures the generation period of the FG signal input from the drive motor 407, and when the measured generation period of the FG signal reaches a predetermined target period, the rotation speed of the polygon mirror 204 is changed to the predetermined target speed. It is determined that it has reached. As described above, the drive motor control unit 408 controls the rotation speed of the polygon mirror 204 by feedback control in accordance with an instruction from the CPU 401. The CPU 401 can also determine the rotational speed of the polygon mirror 204 by receiving the FG signal output from the drive motor 407 via the drive motor control unit 408.

  The FG signal is a signal generated by using the permanent magnet of the motor, and the period of the FG signal is easily affected by the magnetization accuracy of the permanent magnet at the time of manufacturing the motor. Therefore, it can be said that the period of the BD signal is a parameter reflecting the rotational speed of the polygon mirror more than the period of the FG signal. For the above reasons, at least during electrostatic latent image formation, feedback control of the drive motor using the BD signal is executed.

In the present embodiment, the CPU 401 (drive motor control unit 408) selectively uses one of the following two methods as a method for controlling the rotation speed (rotation control) of the drive motor 407 (polygon mirror 204). . In the first method, as described above, rotation control that controls the rotation speed of the drive motor 407 based on the period of the signal (FG signal) output from the speed sensor 420 (hereinafter also referred to as “FG control”). It is. The second method is a rotation control (hereinafter referred to as “rotation control”) that controls the rotational speed of the drive motor 407 based on the period of a detection signal (BD signal) output from the sensor by receiving a light beam (laser light). , Also referred to as “BD control”). One of the light emitting elements 1 to N (LD _{1 to} LD _N ) is used for the BD control. Note that the CPU 401 (or the drive motor control unit 408) of this embodiment functions as an example of a rotation control unit that controls the rotation speed of the rotary polygon mirror (polygon mirror 204). The FG control and the BD control are examples of the first rotation control and the second rotation control, respectively.

  When performing the BD control, the CPU 401 (drive motor control unit 408) measures the period (generation period) of the BD signal output from the BD sensor 207 by the laser light emitted from the specific light emitting element. When the measured cycle reaches a predetermined target cycle, the CPU 401 determines that the rotational speed of the polygon mirror 204 has reached a predetermined target speed. The BD signal is output from the BD sensor 207 every scan of the photosensitive drum 102 by the laser light emitted from the specific light emitting element. The period at which the BD signal is output from the BD sensor 207 becomes shorter as the rotational speed of the polygon mirror 204 becomes faster (that is, the scanning speed of the laser light becomes faster).

  The BD signal generated and output by the BD sensor 207 is input to the CPU 401, the image output control unit 405, and the laser driver 200. At the time of image formation, the image output control unit 405 requests the central image processing unit 130 for image data for each line when the BD signal output from the BD sensor 207 is input. In response to the request, the image output control unit 405 converts the image data for each line acquired from the central image processing unit 130 into a laser drive pulse signal, and outputs the laser drive pulse signal to the laser driver 200.

  At the time of image formation, the CPU 401 transmits, to the image output control unit 405, a control signal for controlling the relative emission timing of the laser light from the light emitting elements 1 to N based on the image data based on the input BD signal. To do. The emission timings of the laser beams from the light emitting elements 1 to N are controlled so that the writing positions of the electrostatic latent images (images) in the main scanning direction coincide with each other for the light emitting elements 1 to N. The image output control unit 405 transfers a laser driving pulse signal corresponding to one line of image data for each light emitting element to the laser driver 200 at a timing based on the control signal.

At the time of image formation, the laser driver 200 converts a drive current based on image data for image formation input from the image output control unit 405 (that is, modulated according to the image data) to each light emitting element (LD _{1 to} LD _N). ). As a result, the laser driver 200 causes each light emitting element to emit a laser beam having a light amount corresponding to the drive current.

  The thermistor 410 measures the temperature of the scanner unit control unit 210 (the temperature inside the optical scanning unit 104), and outputs the measurement result to the CPU 401. However, the thermistor 410 may be configured to measure the temperature of the light source 201.

<Influence of temperature change of optical scanning unit>
In the image forming apparatus 100, due to the configuration of the light source 201 as shown in FIG. 3A, the laser light emitted from each light emitting element is irradiated on the photosensitive drum 102 as shown in FIG. The images are formed at different positions S _{1 to} S _N in the main scanning direction. In such an image forming apparatus, in order to make the writing position in the main scanning direction of the electrostatic latent image (image) formed by the laser light emitted from each light emitting element constant, the timing of emitting the laser light is emitted. It is necessary to appropriately control each element.

For example, a single BD signal is generated based on the laser light emitted from a specific light emitting element, and the laser light is emitted at a fixed timing preset for each light emitting element with the BD signal as a reference. Each light emitting element is controlled. According to this control, as long as the relative positional relationship between the imaging positions S _{1 to} S _N is always constant during image formation, an electrostatic latent image formed by the laser light emitted from each light emitting element ( It is possible to match the writing position in the main scanning direction of (image).

However, when each light emitting element emits laser light during image formation, the wavelength of the laser light emitted from each light emitting element changes as the temperature of the light emitting element itself increases. Further, due to the heat generated from the drive motor 407 when the polygon mirror 204 is rotated, the temperature of the entire optical scanning unit 104 is increased, and the optical characteristics (refractive index and the like) of the scanning lenses 205 and 206 are changed. Thereby, the optical path of the laser beam emitted from each light emitting element changes. When such a change in the wavelength or optical path of the laser light occurs, the imaging positions S _{1 to} S _{N of} each laser light change from the position shown in FIG. 6A to the position shown in FIG. 6B, for example. . As described above, when the relative positional relationship between the imaging positions S _{1 to} S _N changes, the laser emission timing control based on the single BD signal described above is formed by the laser light emitted from each light emitting element. The writing position of the electrostatic latent image in the main scanning direction cannot be matched.

  Therefore, in the present embodiment, two BD signals are generated in the BD sensor 207 by the laser light emitted from the two light emitting elements (first and second light emitting elements) among the light emitting elements 1 to N, and the two The time interval of the BD signal (also referred to herein as “BD interval”) is measured. When this BD interval measurement is performed in the non-image forming period and image formation is performed after the non-image forming period, the relative light of the laser light based on the image data of each light-emitting element is used with reference to a single BD signal. The emission timing is controlled according to the measurement value obtained by the BD interval measurement. The non-image forming period in which the BD interval measurement is performed is a period before the start of image formation on the recording material, and when image formation is performed on a plurality of recording papers, after image formation on each recording paper, This is a period before the start of image formation. Thereby, even if a temperature change of the light emitting element or the like occurs during image formation, the writing position in the main scanning direction of the electrostatic latent image formed by the laser light emitted from each light emitting element is matched. The laser emission timing can be controlled.

<BD interval measurement and laser emission timing control>
Next, with reference to FIG. 7 and FIG. 8, operations of the optical scanning unit 104 according to the present embodiment at the time of BD interval measurement and image formation will be described.
When measuring the BD interval, the CPU 401 controls the light source 201 via the laser driver 200 so that each of the two light emitting elements emits laser light in order, and each laser light enters the BD sensor 207 in order. That is, the BD interval measurement is performed based on two BD signals output in order from the BD sensor 207 (double BD mode). On the other hand, the CPU 401 controls the light source 201 via the laser driver 200 so that laser light emitted from a specific light emitting element enters the BD sensor 207 during image formation. Further, the CPU 401 controls the relative emission timing of the laser light based on the image data for each light emitting element with reference to a single BD signal output from the BD sensor 207 when the laser light is incident (single BD). mode).

  FIGS. 7A and 7B are timings showing the operation timing of each light emitting element and the generation timing of the BD signal by the BD sensor in one scanning period of the laser beam at the time of BD interval measurement and image formation, respectively. It is a chart. In the following, it is assumed that the light emitting elements 1 and N are used to generate two BD signals in the BD interval measurement, and the light emitting element 1 is used to generate a single BD signal during image formation.

As shown in FIG. 7A, during the BD interval measurement performed in the non-image forming period, the laser beams emitted from the light emitting elements 1 and N (LD ₁ and LD _N ) are incident on the BD sensor 207 in order. In addition, drive signals are supplied from the laser driver 200 to the light emitting elements 1 and N, respectively. As a result, the BD signal generated by the BD sensor 207 by receiving the laser light from the light emitting element 1 and the BD signal generated by the BD sensor 207 by receiving the laser light from the light emitting element N are the BD sensor. 207 is output (double BD mode). The CPU 401 measures the time interval (BD interval measurement) of the generation timing of these two BD signals output in order from the BD sensor 207.

On the other hand, as shown in FIG. 7B, at the time of image formation, first, the laser driver 200 drives the light emitting element 1 so that the laser light emitted from the light emitting element 1 (LD ₁ ) enters the BD sensor 207. A signal is supplied. As a result, a single BD signal generated by the BD sensor 207 by receiving the laser light from the light emitting element 1 is output from the BD sensor 207 (single BD mode). Thereafter, when forming an image on the recording paper, the CPU 401 outputs the single BD signal output from the BD sensor 207 and the light emission start timing values A _{1 to} A _N set for the respective light emitting elements. Based on the above, the laser emission timing of the light emitting elements 1 to N is controlled.

The light emission start timing values A _{1 to} A _N shown in FIG. 7B correspond to the light emission start timings of the light emitting elements 1 to N with reference to the generation timing of a single BD signal by the BD sensor 207. That is, A _{1 to} A _N correspond to the relative delay times of the emission timings of the laser light based on the image data of the light emitting elements 1 to N with respect to the single BD signal output from the BD sensor 207. A _{1 to} A _N are set so that the writing positions in the main scanning direction of the electrostatic latent images (images) formed by the laser beams respectively emitted from the light emitting elements 1 to N match.

A _{1 to} A _N are obtained by correcting the reference timing value Ad _n as shown in the following equation using the correction value As _n for each light emitting element.
A _n = Ad _n + As _n (n = 1, 2,..., N) (1)
The CPU 401 controls the laser emission timing of the light emitting elements 1 to N by setting A _{1 to} A _N in the image output control unit 405. As shown in FIG. 7B, the image output control unit 405 uses the generation timing of a single BD signal as a reference, and the image data corresponding to each light emitting element is lasered at a timing according to A _{1 to} A _N. Output to the driver 200. Accordingly, each light emitting element is driven by the laser driver 200 at a timing according to A _{1 to} A _N, and an electrostatic latent image (image) of each line is formed at a desired main scanning position on the photosensitive drum 102. The

The reference timing values Ad _{1 to} Ad _N are obtained when an electrostatic latent image is formed at a desired main scanning position with respect to the light emitting elements 1 to N under a specific temperature condition at the time of factory adjustment, and in the main scanning direction. This is a value that is determined so that the latent image writing position coincides between a plurality of lines. Ad _{1 to} Ad _N are stored in the memory 406 in advance. At the time of factory adjustment, BD interval measurement is performed under the same temperature condition, and the count value as the measurement result is stored in the memory 406 in advance as the reference count value Cr. As described above, the reference timing values Ad _{1 to} Ad _N are determined in advance corresponding to the reference count value Cr.

  Here, the count value corresponds to a value obtained by the CPU 401 counting pulses of the CLK signal generated by the CLK signal generation unit 404. When the CPU 401 performs the BD interval measurement, as shown in FIG. 8, from the timing when the BD signal 1 corresponding to the light emitting element 1 is generated to the timing when the BD signal 2 corresponding to the light emitting element N is generated. The count value is generated by counting the pulses of the CLK signal. This count value corresponds to the time interval ΔT of the BD signal and is generated as a measurement result of the BD interval measurement.

On the other hand, when the image formation positions S _{1 to} S _N are shifted due to temperature changes of the light emitting elements, the electrostatic latent image writing position in the main scanning direction can be matched between the plurality of lines as described above. Disappear. For this reason, the correction values As _{1 to} As _N are generated by the CPU 401 using the following equation in order to compensate for such a shift in the imaging positions S _{1 to} S _N.
As _n = (Cs−Cr) / (N−1) × k × (n−1) (n = 1, 2,..., N) (2)
Here, n represents the number of the light emitting element. Cs is a count value stored in the memory 406 (in S127 and S147) corresponding to a measurement result in BD interval measurement 1 and 2 described later. Cr is a reference value for BD interval measurement obtained by measurement during factory adjustment. k is a conversion coefficient for converting a count value indicating a time interval between two BD signals into a scanning time interval at an imaging position on the photosensitive drum 102.

As is clear from the equation (2), the correction value As ₁ corresponding to the light emitting element ₁ is always 0. Therefore, equation (2), generates a correction value for correcting the deviation of the imaging position S ₁ to S _N by a temperature change, such as a light emitting element, the imaging position S ₁ corresponding to the light emitting element 1 as a reference To do. As shown in Expression (1) and FIG. 7B, the CPU 401 adds the calculated As ₁ to As _N to Ad ₁ to Ad _N stored in the memory 406, so that the light emitting elements 1 to _N are added. The light emission start timing values A _{1 to} A _N to be set for each of the above can be calculated.

<Polygon mirror rotation control>
As described above, the image forming apparatus 100 according to the present embodiment selectively executes FG control and BD control as rotation control of the polygon mirror 204. The BD control can control the rotation speed of the polygon mirror 204 with higher accuracy than the FG control. This is because the accuracy of the BD sensor BD signal itself is higher than the accuracy of the FG signal itself. On the other hand, in the FG control, although the accuracy of the rotation control is inferior to that of the BD control, the rotation control of the polygon mirror 204 can be performed without causing the light emitting element to emit light. For this reason, in FG control, rotation control can be performed without shortening the lifetime of the light emitting element.

  For example, when a document (for copying) is set on the image reading device 150 or a user operation is performed on an operation unit (not shown), the image forming apparatus 100 performs an image before an instruction to start image formation is performed. It has a function (flying start function) for starting the formation preparation operation. The image forming apparatus 100 shortens the FCOT by starting the drive motor 407 and starting the rotation of the polygon mirror 204 when the image forming preparation operation is started by the flying start function. Hereinafter, rotation control of the polygon mirror 204 when the flying start function is executed will be described with reference to FIGS. 9 and 10.

  FIG. 9 is a timing chart showing an example of the relationship between the polygon mirror rotation control timing and the BD interval measurement execution timing, and shows a comparative example with respect to the present embodiment. FIG. 9 shows the operation (rotation on / off) and rotation state of the polygon mirror, and the execution state of the BD interval measurement. FIG. 9A shows a case where the BD interval measurement is not executed, and FIG. , BD interval measurement is performed.

  In the comparative example shown in FIG. 9A, when rotation of the polygon mirror is started by the flying start function, the polygon mirror is controlled by FG control until an instruction to start (input) image formation (printing) is performed. Rotation control is performed. When the rotation speed of the polygon mirror reaches the target speed by the FG control, the FG control is continued as it is, so that the polygon mirror is stably rotated at the target speed. Thereafter, when a print start instruction is issued, the polygon mirror rotation control is switched from FG control to BD control in order to control the rotation speed of the polygon mirror with higher accuracy. When the rotation speed of the polygon mirror reaches the target speed by the BD control, printing preparation is completed, and printing of the image on the recording paper is started in a state where the polygon mirror is stably rotated at the target speed by the BD control. The As described above, by limiting the execution of the BD control after the print start instruction is performed, the lifetime of the light emitting element can be extended.

  However, in the above comparative example, when the BD interval measurement is executed before the start of printing, as shown in FIG. 9B, the timing at which the BD interval measurement can be executed is stable at the target speed by the BD control. And after it is in a rotating state. In this case, the time from the timing when the print start instruction is given to the timing when the print preparation is completed (printing is actually started) is delayed by the time required for the BD interval measurement. As described above, when the BD interval measurement is performed after the print start instruction is performed and the polygon mirror rotation control is switched from the FG control to the BD control, the image on the recording sheet is actually printed after the print start instruction is performed. The time until printing is completed (that is, FCOT) becomes long.

  In view of this, the image forming apparatus 100 according to the present embodiment switches the rotation control of the polygon mirror 204 from the FG control to the BD control before the print start instruction is issued when the print preparation operation is started by the flying start function. Perform a BD interval measurement. That is, the rotation control of the polygon mirror 204 is performed so that the execution of the BD interval measurement can be started before the print start instruction is issued. Thereby, it can be avoided that the FCOT becomes longer due to the execution of the BD interval measurement.

  Specifically, when the printing preparation operation is started by the flying start function, the image forming apparatus 100 first starts rotation of the polygon mirror 204 and performs FG control. When the rotation speed of the polygon mirror 204 reaches the target speed by the FG control, the image forming apparatus 100 switches the rotation control of the polygon mirror 204 from the FG control to the BD control without waiting for a print start instruction before starting printing. , BD interval measurement is executed during execution of BD control. In this way, the image forming apparatus 100 performs FG control until the rotational speed of the polygon mirror 204 (drive motor 407) reaches the target speed, and when the rotational speed reaches the target speed, the image forming apparatus 100 switches from FG control to BD control. , BD interval measurement is performed during execution of BD control. Note that the BD interval measurement is performed while the rotational speed of the polygon mirror 204 is constant at the target speed by BD control, as in the comparative example described above.

  By performing the BD interval measurement while the polygon mirror 204 is stably rotating at a constant speed, measurement errors in the BD interval measurement can be reduced. In the present embodiment, the state where the rotational speed of the polygon mirror 204 is constant at the target speed refers to a state where the rotational speed fluctuates within ± 0.5% from the target rotational speed. That is, when the target rotation speed of the polygon mirror (rotation speed during electrostatic latent image formation) is set to 40000 rpm, ± 200 rpm is set as an allowable range of fluctuations in the rotation speed. Hereinafter, a specific example of such control executed by the optical scanning unit 104 will be described with reference to FIG.

(First control example)
FIG. 10A shows a case where a print start instruction has not been issued before the end of the BD interval measurement. In this case, the optical scanning unit 104 returns (switches) the rotation control of the polygon mirror 204 from the BD control to the FG control after the BD interval measurement ends. Thereafter, when a print start instruction is issued, the optical scanning unit 104 switches the rotation control of the polygon mirror 204 from FG control to BD control again. When the polygon mirror 204 is stably rotated at the target speed by the BD control, the print preparation is completed, and the image forming apparatus 100 starts printing the image on the recording paper. As described above, by performing FG control during a period from when the BD interval measurement is completed until when a print start instruction is issued, the lifetime of the light emitting element used for BD control is extended as compared with the case where BD control is continued. Can do.

When printing in response to the completion of print preparation after completion of the BD interval measurement is started, the optical scanning unit 104, based on the measured BD intervals BD interval measurement, light emitting element 1~N (LD ₁ ~LD _N The emission timing of the laser beam based on the image data is controlled.

(Second control example)
FIG. 10B shows a case where a print start instruction is given before the end of the BD interval measurement. In this case, the optical scanning unit 104 continues the BD control as the rotation control of the polygon mirror 204 without switching to the FG control as in the case of FIG. Accordingly, simultaneously with the end of the BD interval measurement, the image forming apparatus 100 is ready for printing, and can quickly start printing an image on a recording sheet.

(Third control example)
FIG. 10C shows a case where a print start instruction is not made before the end of the BD interval measurement, and a print start instruction is made after a relatively long time has elapsed after the end of the measurement. In this case, as in the case of FIG. 10A, the optical scanning unit 104 returns (switches) the rotation control of the polygon mirror 204 from the BD control to the FG control after the end of the BD interval measurement. After that, the optical scanning unit 104 returns the rotation control of the polygon mirror 204 to the FG control, and when a predetermined time has elapsed without issuing a print start instruction, the rotation control of the polygon mirror 204 is switched to the BD control, and the BD is performed again. Perform interval measurements. This is because an error occurs in the measurement result obtained by the BD interval measurement as a result of the temperature inside the optical scanning unit 104 increasing with time due to the rotation of the polygon mirror 204. In order to compensate for such an error in the measurement result, in this example, the BD interval measurement is executed every time a predetermined time elapses, and the measurement result is updated. After the BD interval measurement is completed, the rotation control of the polygon mirror 204 is returned (switched) from the BD control to the FG control again.

  The predetermined time for determining the timing for switching from the FG control to the BD control is based on the measurement result of the temperature inside the optical scanning unit 104 or the temperature of the light source 201 by the thermistor 410, for example, as shown in FIG. It may be changed to. Specifically, a longer time may be set as the predetermined time as the temperature measured by the thermistor 410 is higher. That is, as the temperature increases, the change in the measured value of the BD interval measurement decreases, so the execution time interval of the BD interval measurement is lengthened. With such control, the execution time interval of the BD control can be increased with the passage of time, leading to an increase in the lifetime of the light emitting element used for the BD control.

<Image formation processing>
Hereinafter, an execution procedure of image forming processing in the image forming apparatus 100 (optical scanning unit 104) will be described with reference to FIGS. FIG. 11 is a flowchart showing an execution procedure of the image forming process in the image forming apparatus 100 (optical scanning unit 104), and FIGS. 12 and 13 are flowcharts showing an execution procedure of the processes in S104 and S102 of FIG. 11, respectively. is there. Note that the processing of each step shown in FIG. 11 is realized by the CPU 401 reading and executing the control program stored in the memory 406. Control shown in FIGS. 10A to 10C can be realized in the image forming apparatus 100 (optical scanning unit 104) by the processing according to the flowcharts of FIGS.

  First, in step S <b> 101, when a document is set on the image reading apparatus 150 or a user operation on the operation unit is performed, the CPU 401 determines whether to perform the above-described flying start. For example, if the image forming apparatus 100 is set in advance to use the flying start function, the CPU 401 determines to execute the flying start, and advances the process to S102. On the other hand, when determining that the flying start is not to be executed, the CPU 401 advances the process to step S103 and waits until a print start instruction is received. In step S103, if the CPU 401 has not received a print start instruction, the process returns to step S101. If a print start instruction has been received, the process proceeds to step S104.

  In step S <b> 104, the CPU 401 executes the mode 1 print preparation without executing the flying start according to the procedure illustrated in FIG. 12. On the other hand, in step S102, the CPU 401 executes mode 2 print preparation for executing flying start according to the procedure shown in FIG. When the processing of S104 or S102 is completed (that is, when preparation for printing is completed), in S105, the CPU 401 performs control for printing an image on recording paper (that is, rotation control of the polygon mirror 204, light emitting elements 1 to 3). N emission control, etc.). When the printing of the image on the recording paper is completed, the CPU 401 ends the process.

<Preparation for printing (mode 1)>
Next, with reference to FIG. 12, the execution procedure of the print preparation (mode 1) in S104 will be described. First, in step S201, the CPU 401 starts rotation of the polygon mirror 204 and starts rotation control of the polygon mirror 204 by FG control. During execution of the FG control, in S202, the CPU 401 determines whether or not the rotational speed of the polygon mirror 204 is stabilized at the target speed by the FG control, and if it is determined that the rotational speed is stable, the process proceeds to S203. Proceed.

In step S203, the CPU 401 switches the rotation control of the polygon mirror 204 from the FG control to the BD control, thereby performing rotation control with higher accuracy in preparation for the start of printing. In the present embodiment, the BD control is performed using the light emitting element 1 (LD ₁ ) as a specific light emitting element as in the above-described single BD mode. During the execution of the BD control, in S204, the CPU 401 determines whether or not the rotational speed of the polygon mirror 204 is stabilized at the target speed by the BD control, and if it is determined that the rotational speed is stable, the process proceeds to S205. Proceed.

In step S205, the CPU 401 performs BD interval measurement in a state where BD control is continued. Further, in S206, the CPU 401 controls the laser emission timing of the light emitting elements (LD _{1 to} LD _N ) based on the measurement result of the BD interval measurement. Specifically, the CPU 401 generates correction values As _{1 to} As _N from the measurement result of the BD interval measurement, and sets light emission start timing values A _{1 to} A _N to be set for each of the light emitting elements 1 to _N. calculate. As described above, the CPU 401 completes the print preparation and advances the process to S105.

<Preparation for printing (mode 2)>
Next, with reference to FIG. 13, the execution procedure of the print preparation (mode 2) in S102 will be described. First, the process of S301-S306 is the same as that of S201-S206. Following S306, in S307, the CPU 401 determines whether or not a print start instruction has been received before the end of the BD interval measurement (S305). If the CPU 401 determines that the print start instruction has been received, as shown in FIG. 10B, the CPU 401 completes the print preparation and advances the process to S105. On the other hand, if the CPU 401 determines that the print start instruction has not been received, the process proceeds to step S308, and the rotation control of the polygon mirror 204 is controlled from the BD control as shown in FIGS. 10 (a) and 10 (c). Return to FG control.

  During execution of FG control, in step S309, the CPU 401 determines whether a print start instruction has been received. When determining that the print start instruction has not been received, the CPU 401 advances the processing to step S310, and determines whether or not a predetermined time has elapsed since the rotation control of the polygon mirror 204 was returned to the FG control. When determining that the predetermined time has not elapsed, the CPU 401 returns the process to step S309 and determines again whether or not a print start instruction has been received. On the other hand, when the CPU 401 determines that the predetermined time has elapsed, the process returns to S303, and as shown in FIG. 10C, the rotation control of the polygon mirror 204 is returned from the FG control to the BD control, and the BD interval measurement is performed. Is executed again (S305).

  On the other hand, if it is determined in S309 that the print start instruction has been received, the CPU 401 advances the processing to S311 and performs rotation control of the polygon mirror 204 by FG control as shown in FIGS. 10 (a) and 10 (c). Switch to BD control again. In step S312, the CPU 401 determines whether the rotation speed of the polygon mirror 204 is stabilized at the target speed by BD control. If it is determined that the rotation speed is stable, the CPU 401 completes print preparation and performs the process in step S105. Proceed to

  As described above, when the image forming apparatus 100 according to the present embodiment starts the image forming preparation operation by the flying start function, the rotation control of the polygon mirror 204 is controlled from the FG control to the BD control without waiting for the print start instruction. BD interval measurement is performed. As a result, it is possible to advance the execution timing of the BD interval measurement as compared with the case where the BD interval measurement is executed after waiting for the print start instruction, and avoiding an increase in the FCOT due to the execution of the BD interval measurement. Is possible.

100: Image forming apparatus, 102 (Y, M, C , K): a photosensitive drum, 104 (Y, M, C , K): the optical scanning unit, 201: laser light source, LD ₁ to Ld _N: the light emitting element 1 N, 204: Polygon mirror, 207: BD sensor, 401: CPU, 407: Drive motor, 420: Speed sensor (rotation detection sensor)

Claims (9)

A light source comprising a plurality of light emitting elements that respectively emit light beams for exposing the photoreceptor;
A rotary polygon mirror that deflects the plurality of light beams so that the plurality of light beams emitted from the plurality of light emitting elements scan the photoconductor;
A drive motor for rotating the rotary polygon mirror;
An optical sensor provided on a scanning path of the light beam deflected by the rotating polygon mirror, and outputting a detection signal indicating that the light beam is detected by the incidence of the light beam deflected by the rotating polygon mirror;
A rotation detection sensor which is provided in the drive motor and outputs a signal having a period according to the rotation speed of the drive motor;
Based on the first rotation control for controlling the rotation speed of the drive motor based on the period of the signal output from the rotation detection sensor, and the period of the detection signal output from the optical sensor by receiving the light beam. Rotation control means for controlling the rotation speed of the rotary polygon mirror by one of the second rotation controls for controlling the rotation speed of the drive motor until the rotation speed of the drive motor reaches a target speed. The rotation control means for performing the first rotation control and switching the first rotation control to the second rotation control when the rotation speed of the drive motor reaches the target speed;
While the rotation control means is executing the second rotation control, the light source is controlled so that light beams from each of the first and second light emitting elements among the plurality of light emitting elements are sequentially incident on the optical sensor. Measuring means for controlling and measuring a time interval between the first and second detection signals sequentially output from the optical sensor;
When image formation is started after the measurement of the time interval by the measurement unit, the light beam based on the image data of each of the plurality of light emitting elements is based on the time interval measured by the measurement unit. Control means for controlling the relative emission timing ,
If the image forming start instruction has not been given before the measurement of the time interval by the measuring unit, the rotation control unit controls the rotation speed after the measurement of the time interval. Switching from rotation control to the first rotation control, and when the start instruction is issued, the rotation speed control is switched again from the first rotation control to the second rotation control. apparatus.   The image forming apparatus according to claim 1, wherein the measurement unit measures the time interval while the rotation speed is constant at the target speed by the second rotation control. After the rotation control means switches the rotation speed control to the first rotation control, a predetermined time elapses without the start instruction being performed,
The rotation control means switches the rotation speed control from the first rotation control to the second rotation control,
The measuring means measures the time interval during the execution of the second rotation control by the rotation control means,
3. The image formation according to claim 1, wherein the rotation control unit switches the rotation speed control from the second rotation control to the first rotation control after completion of the measurement of the time interval. apparatus. A temperature sensor for measuring a temperature inside the image forming apparatus or a temperature of the light source;
The image forming apparatus according to claim 3 , wherein the predetermined time is set to a longer time as the temperature measured by the temperature sensor is higher. When the image forming start instruction is given before the measurement of the time interval by the measuring unit, the rotation control unit continues the second rotation control after the measurement of the time interval. the image forming apparatus according to claim 1, any one of 4, wherein. Said rotation control means, the image forming apparatus according to any one of claims 1 to 5, characterized in that said second rotation control during execution of the image formation. Said rotation control means, the image forming apparatus according to any one of claims 1 to 6, characterized in that said second rotation control by using a light beam emitted from the first light emitting element . The rotation detecting sensor, the image forming apparatus according to any one of claims 1 to 7, characterized in that a Hall element which outputs a signal corresponding to the rotation of the drive motor. The photoreceptor;
Charging means for charging the photoreceptor;
And developing means for developing an electrostatic latent image formed on the photoconductor by scanning the plurality of light beams to form an image on the photoconductor to be transferred to a recording medium. Item 9. The image forming apparatus according to any one of Items 1 to 8 .

Images