JP2009029045A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of appropriately setting a plotting start timing by means of respective light sources. <P>SOLUTION: A controller scans only a laser beam L1 to obtain BD signals BD1-BD3 from a BD sensor 37 (#1, #2), with time differences t1, t2 determined between the output timing of the BD signal BD1 and the output timing of the BD signals BD2, BD3 (#3). When an image forming instruction performed (YES in #4), the controller controls lighting of light sources LD1-LD3 in a manner that laser beams L1-L3 are reflected only by corresponding reflection mirrors (#6), with time differences T1, T2 determined between the output timing of the BD signal BD4 and the output timing of the BD signals BD5, BD6 (#7). The plotting start timing of light sources LD2, LD3 is set at a timing delayed by the time (T1-t1), (T2-t2) from the plotting start timing of the light source LD1 (#8). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention belongs to the technical field of image forming apparatuses, and particularly relates to a laser irradiation technique for performing exposure by irradiating a surface of a photosensitive drum with a laser.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, laser light emitted from a laser irradiation unit is reflected by each reflecting surface of a rotary polygon mirror to expose the surface of the photosensitive drum, and electrostatically adhere to the surface of the photosensitive drum. What forms a latent image is widely known. In addition, in this type of apparatus, a technology is also known in which a BD (Beam Detect) sensor that receives laser light at a predetermined position is installed, and the light scanning start timing (start position) is set using an output signal of the BD sensor. It has been.

  Further, for example, the following Patent Documents 1 to 4 are related to this type of technical field. The following Patent Document 1 discloses an image forming apparatus that simultaneously scans a plurality of laser beams whose positions are shifted in the main scanning direction, and the following Patent Document 2 discloses a light beam array of a plurality of light sources. An image forming apparatus that generates a multiplexed horizontal synchronizing signal by tilting with respect to a scanning direction, simultaneously scanning the plurality of light beams, turning on all light sources simultaneously, and scanning one photosensor is disclosed. Has been.

  Patent Document 3 below discloses a multi-beam light source that can emit two light beams simultaneously, and if the shift amount Δx in the main scanning direction on the synchronous detection sensor of the two light beams is larger than 0, It is described that two beams can be detected by the same synchronous detection sensor.

In Patent Document 4 below, in an image forming apparatus in which writing to a plurality of lines is performed by a single scan by a laser array device having a plurality of light emitting elements, the light reception timing of the first passing laser beam and the optical system A technique for adjusting the drawing start timing of another laser beam based on the delay value determined by the magnification, the interval between the light emitting elements and the resolution is disclosed.
JP 2002-29086 A JP 2004-249620 A JP 2002-139690 A JP 2003-305886 A

  In an image forming apparatus in which each light beam output from a plurality of light sources is irradiated to different positions in the main scanning direction, and each light source scans a plurality of light beams on a plurality of lines in one scan, Since the light rays enter the BD sensor at different timings, it is necessary to set the start timing of the lighting operation (drawing operation) by each light source for image formation based on each incident timing.

  However, when the positional deviation amount of each light source in the main scanning direction is small, a state occurs in which the next light beam enters the BD sensor before the previous light beam passes through the BD sensor. In this case, since all the light beams are always incident on the BD sensor until all the light beams have passed through the BD sensor, a constant signal is output from the BD sensor. It is impossible to detect the passage timing of the light beam.

  Therefore, conventionally, further techniques such as changing the frequency and power of each laser beam and causing a voltage difference in the output of the BD sensor to separate the BD signal by each laser beam have been required. However, such a technique causes a decrease in the detection accuracy of the laser beam.

  Although the drawing start timing by each light source can be set by using the technique of the cited document 4, the optical installed on the optical path due to environmental changes (temperature changes and humidity changes) in the image forming apparatus. When the state of the system or the like changes and the distance between the irradiation positions of the laser beams changes, the delay value does not reflect the distance after the change. It is not possible to deal with such cases.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can appropriately set the drawing start timing of each light source.

  According to the first aspect of the present invention, the first and second light sources that irradiate light at different positions in at least the sub-scanning direction, and the light output from each of the light sources is subjected to main scanning within a predetermined fixed region. A light source unit including a scanning unit for repeatedly scanning in a direction, a first optical path changing surface associated with the first light source, and a second optical path changing surface associated with the second light source. And an optical path changing unit that changes the optical path of the light beam output from the light source unit by the first and second optical path changing surfaces, A BD signal generating unit that receives a light beam whose optical path has been changed by the optical path changing unit and performs a photoelectric conversion operation, and generates a BD signal based on an output signal of the light receiving unit; Light for controlling lighting operation by the second light source When the lighting operation based on the image data by the light source is referred to as a drawing operation, the drawing operation start timing in each drawing line by the light source based on the output timing of the BD signal generated by the light beam output from the light source A drawing start timing setting unit for setting the drawing start timing as the drawing start timing, and the light beams output from the first and second light sources are in the order of the first optical path changing surface and the second optical path changing surface. When the light from each light source is scanned by the scanning unit with the first and second light sources turned on while being incident on the change surface, the light beams output from the first light source are the second light sources. Incident on the first optical path changing surface at the same time as or earlier than the light beam output from the light source, and the drawing start timing setting unit includes the first light source and the second light source. The first and second BD signals are obtained by scanning only the light beam output from one of the deviations using the scanning unit, and the output timing of the first BD signal and the output of the second BD signal are obtained. A time difference from the timing is calculated as a first time difference, and light beams output from the first and second light sources are scanned only on the optical path changing surface corresponding to the light source among the optical path changing surfaces. As described above, the third and fourth BD signals are obtained by causing the scanning unit to perform an operation while controlling the lighting operation of the first and second light sources, and the output timing of the third BD signal and the 4 is calculated as a second time difference, and the drawing start timing by the first light source is calculated based on the third BD signal obtained from the light beam output from the light source. When set In addition, the drawing start timing by the second light source is set based on the difference between the first time difference and the second time difference and the drawing start timing by the first light source, and the light emission control unit The image forming apparatus causes each light source to start a drawing operation according to a drawing start timing set by the drawing start timing setting unit.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the drawing start timing setting unit changes the drawing start timing by the second light source from the drawing start timing by the first light source. It is set at a timing delayed by the difference.

  According to these inventions, the first and second BD signals are obtained by scanning only the light beam output from any one of the first and second light sources using the scanning unit, A time difference between the output timing of the first BD signal and the output timing of the second BD signal is calculated as the first time difference.

  Further, the light beams respectively output from the first and second light sources are scanned only on the optical path changing surface corresponding to the light source among the optical path changing surfaces. The scanning unit is operated while controlling the lighting operation, and the time difference between the output timing of the third BD signal and the output timing of the fourth BD signal obtained thereby is calculated as the second time difference.

  Here, the first time difference is a time difference caused by a positional deviation between the first and second optical path changing surfaces, and the second time difference is a difference between the first and second optical path changing surfaces. Since the time difference caused by the positional deviation and the time difference caused by the positional deviation of the irradiation positions of the light beams respectively output from the first and second light sources are included, the first time difference and the second time difference are included. By calculating the difference from the time difference, the time difference caused by the displacement of the irradiation position of the light beam output from each of the first and second light sources is calculated.

  The drawing start timing by the second light source is set based on the difference between the first time difference and the second time difference and the drawing start timing by the first light source. In the present invention, the drawing start timing setting unit sets the drawing start timing by the second light source to a timing delayed by the difference from the drawing start timing by the first light source). The drawing start timing by the second light source is set with reference to the drawing start timing by the light source.

  As described above, in the present invention, since the first and second optical path changing surfaces are provided and the first and second times are merely calculated, the detection accuracy of the laser beam is reduced. The drawing start timing by each light source can be set by a relatively simple configuration and calculation.

  Further, when the state of the optical system or the like installed on the optical path changes due to environmental changes (temperature change or humidity change) in the image forming apparatus and the distance between the irradiation positions of the respective laser beams changes, the change is Since the difference is reflected, even when the environment in the image forming apparatus changes, an appropriate drawing start timing can be set according to the change.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the drawing start timing setting unit calculates and stores the first time difference in advance, and the second light source For each drawing line corresponding to, the second time difference is calculated, and the drawing start timing in the drawing line is set using the second time difference and the first time difference stored in advance. .

  According to the present invention, the drawing start timing by the second light source is appropriately set for each drawing line.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the first and second light sources correspond to the arrangement positions of the first and second light sources. Light beams are emitted to different positions in the main scanning direction and the sub-scanning direction, and when the first and second light sources are turned on and scanned by the scanning unit, the optical path is changed on the same optical path changing surface. The first and second light sources are arranged close to each other so that output periods of the BD signals obtained by the light beams of the light sources to be changed partially overlap.

  According to the present invention, the first and second light sources irradiate light beams at different positions in the main scanning direction and the sub-scanning direction according to the arrangement positions of the first and second light sources. When the first and second light sources are turned on and scanned by the scanning unit, the output period of each BD signal obtained by the light beam of each light source whose optical path is changed on the same optical path changing surface is partial. Since the first and second light sources are arranged close to each other so as to overlap each other, it is easy to integrate the first and second light sources into a single element and reduce the size. Become.

  According to the present invention, it is possible to appropriately set the drawing start timing by the second light source by a relatively simple calculation without causing a decrease in the detection accuracy of the laser beam.

  Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a side view schematically showing an internal configuration of a multifunction peripheral as an example of an image forming apparatus according to an embodiment of the present disclosure.

  The multifunction device 1 has functions such as a copy function, a printer function, a scanner function, and a facsimile function. The multifunction device 1 has a main body 2, a stack tray 3 disposed on the left side of the main body 2, and a main body 2. The document reading unit 5 is disposed above the document reading unit 5 and the document feeding unit 6 is disposed above the document reading unit 5.

  An operation unit 7 is provided at an appropriate front surface of the multifunction machine 1. The operation unit 7 displays a start key 8 for a user to input a print execution instruction, a numeric keypad 9 for inputting the number of copies to be printed, operation guide information for various copying operations, and the like. A display unit 10 including a liquid crystal display having a touch panel function, a reset key 11 for resetting setting contents set on the display unit 10, and a stop key 12 for stopping a printing (image forming) operation being performed. And a function switching key 13 for switching between a copy function, a printer function, a scanner function, and a facsimile function.

  The document reading unit 5 includes a scanner unit 14 including a CCD (Charge Coupled Device) sensor and an exposure lamp, and a document table 15 and a document reading slit 16 made of a transparent member such as glass. The scanner unit 14 is configured to be movable by a drive unit (not shown). When reading a document placed on the document table 15, the scanner unit 14 is moved along the document surface at a position facing the document table 15, and reads the document image. Image data acquired while scanning is output to an unillustrated image processing unit. Further, when reading a document fed by the document feeding unit 6, the document is moved to a position facing the document reading slit 16 and synchronized with the document feeding operation by the document feeding unit 6 via the document reading slit 16. The image of the original is acquired, and the image data is output to an image processing unit (not shown).

  The document feeding unit 6 includes a document placing unit 17 for placing a document, a document ejecting unit 18 for ejecting an image-read document, and a document placed on the document placing unit 17. A document transport mechanism 19 including a paper feed roller, a transport roller, and the like for feeding the paper one by one to a position facing the document reading slit 16 and discharging it to the document discharge section 18 is provided. The document transport mechanism 19 further includes a paper reversing mechanism (not shown) that reverses the document and transports it again to a position facing the document reading slit 16, and scans both sides of the document via the document reading slit 16. 14 is readable.

  The document feeding unit 6 is provided so as to be rotatable with respect to the main body unit 2 so that the front side thereof can move upward. By moving the front side of the document feeder 6 upward to open the top surface of the document table 15, the operator can place a read document, such as a book in a spread state, on the top surface of the document table 15. It has become.

  The main body 2 includes a plurality of paper feed cassettes 20, a paper feed roller 21 that feeds paper one by one from the paper feed cassette 20 and transports the paper to a recording unit 22 described later, and paper fed from the paper feed cassette 20. And a recording unit 22 for forming an image.

  The recording unit 22 outputs a laser or the like based on the image data acquired by the scanner unit 14 or the like and exposes the photosensitive drum 23, and a developing unit 25 that forms a toner image on the photosensitive drum 23. A transfer unit 26 that transfers the toner image on the photosensitive drum 23 to a sheet, a fixing unit 27 that fixes the toner image to the sheet by heating the sheet to which the toner image has been transferred, and a sheet conveyance in the recording unit 22. Conveying rollers 29, 30 and the like that are provided in the path and convey sheets to the stack tray 3 or the discharge tray 28.

  When images are formed on both sides of a sheet, the recording unit 22 forms an image on one side of the sheet, and the sheet is nipped by a conveyance roller 29 on the discharge tray 28 side. In this state, the conveyance roller 29 is reversed to switch back the paper, and the paper is sent to the paper conveyance path L to be conveyed again to the upstream area of the recording unit 22. After the recording unit 22 forms an image on the other surface, The paper is discharged to the stack tray 3 or the discharge tray 28.

  FIG. 2 is a configuration diagram of the optical scanning device 24. As shown in FIG. 2, the optical scanning device 24 includes a laser irradiation unit 31, a collimator lens 32, a prism 33, a polygon mirror (rotating polygonal mirror) 34, an f-θ lens 35, a reflection unit 36, and a beam detector sensor (hereinafter referred to as “beam detector”). 37) (referred to as a BD sensor).

  The laser irradiation unit 31 irradiates light on the surface of the photosensitive drum 23 having a cylindrical surface configured to be rotatable while being supported by a support shaft (not shown) according to image data. . The rotation axis (support axis) direction is referred to as a main scanning direction. As shown in FIG. 3, the laser irradiation unit 31 is formed by unitizing a plurality of laser light sources LD <b> 1 to LD <b> 3 arranged in a line at a constant interval on the tip surface Y, and the center of the normal lines to the tip surface Y It is configured to be rotatable in the direction of arrow A with the normal G passing through the laser light source LD2 positioned at the center as the rotation axis.

  The laser irradiation unit 31 is configured using, for example, a monolithic multi-laser diode. The optical adjustment of the pitch (beam pitch) of the laser beams L1 to L4 output from the laser light sources LD1 to LD3 is performed in the semiconductor generation process.

  When the optical scanning device 24 turns on all the laser light sources LD1 to LD3 and irradiates the surface of the photosensitive drum 23 with the laser beams L1 to L3, the arrangement direction of the irradiation positions (imaging positions) is: The laser irradiation unit 31 is set in a rotated state so as to have an inclination angle with respect to each of the main scanning direction and the sub-scanning direction (a direction orthogonal to the main scanning direction when the surface of the photosensitive drum 23 is developed). Thus, the image can be written to the plurality of drawing lines by one scan, and the resolution in the sub-scanning direction can be adjusted by adjusting the tilt angle.

  Returning to FIG. 2, the collimator lens 32 is for condensing the laser beams output from the laser light sources LD1 to LD3. The prism 33 converts the light transmitted through the collimator lens 32 into parallel light and emits it toward the polygon mirror 34. The polygon mirror 34 has a plurality of reflection surfaces that reflect incident light toward the photosensitive drum 23 and a reflection unit 36 described later. For example, the polygon mirror 34 rotates at a constant speed so that each laser beam is reflected by the reflection surface on the photosensitive drum. 23 and the reflecting portion 36 while scanning in the main scanning direction. The f-θ lens 35 forms an image of the laser beam reflected by the polygon mirror 34 in a spot shape having a predetermined diameter on the surface of the photosensitive drum 23 and on the reflection portion 36.

  The reflection unit 36 is an example of the optical path changing unit. As shown in FIG. 4A, the laser beam scanned in the main scanning direction is incident on the reflection unit 36 before entering the photosensitive drum 23. The plurality of reflecting mirrors 38 to 40 are provided. FIG. 4A is a diagram showing the configuration of the reflecting section 36 and the positional relationship between the photosensitive drum 23, the polygon mirror 34, the reflecting mirrors 38 to 40, and the BD sensor 37.

  The reflecting mirrors 38 to 40 are different from each other in a state in which the orientation (attitude) of each reflecting surface (an example of an optical path changing surface) is set so as to reflect the reflected light from the polygon mirror 34 toward the BD sensor 37. In place. In this case, the direction (posture) of the reflecting surface of the reflecting mirrors 38 to 40 is also included in the concept of the position of the reflecting mirrors 38 to 40.

  The laser light scanned in the main scanning direction by the polygon mirror 34 passes through the surface of the photosensitive drum 23 after passing through the reflecting surfaces of the reflecting mirrors 38 to 40 of the reflecting portion 36. Moreover, the incident angle of the laser beam which injects into the reflective surface of the reflective mirrors 38-40 is within a certain incident angle range in the period which has passed on the reflective surface of each reflective mirror 38-40 of the reflective part 36 ( The laser beam reflected by the reflecting surface is incident on the light receiving surface of the BD sensor 37. The incident position (arrival position) of the laser beam on the light receiving surface of the BD sensor 37 changes in a certain direction (main scanning direction) with the change in the incident angle. When the polygon mirror 34 is rotated in a state where all the laser light sources LD1 to LD3 are turned on, a laser light source is formed on the reflection surface of each reflection mirror 38 to 40 of the reflection unit 36 and the surface of the photosensitive drum 23. Assume that the laser beam L1 output from the LD1 enters first, and the laser beam L3 output from the laser light source LD3 enters last.

  As shown in FIG. 5, the BD (Beam Detect) sensor 37 includes a light receiving surface having a predetermined width w in the fixed direction (main scanning direction), and is configured using, for example, a photodiode. Since the laser light sources LD1 to LD3 are arranged as described above, the irradiation positions of the laser beams L1 to L3 on the light receiving surface of the BD sensor 37 and the surface of the photosensitive drum 23 are main scanning. This is an aspect in which each of the direction and the sub-scanning direction is arranged with a certain interval in one direction inclined at a certain inclination angle. Therefore, when scanning by the polygon mirror 34 is performed with all the laser light sources LD1 to LD3 turned on, the laser beams L1 to L3 have a certain time difference on the light receiving surface of the BD sensor 37, respectively. Will pass.

  When receiving the laser beam, the BD sensor 37 outputs a light reception signal to the BD signal conversion unit 41. Based on this light reception signal, the optical scanning device 24 sets a timing for starting a lighting operation (charge removal operation by laser light irradiation; hereinafter referred to as a drawing operation) based on image data by the laser irradiation unit 31.

  With the above configuration, the laser beam is repeatedly scanned on the surface of the photosensitive drum 23 at a constant speed in the main scanning direction. When the surface of the charged photoconductive drum 23 is irradiated with laser light, the charge of the irradiated portion is removed. The multi-function device 1 irradiates the surface of the photosensitive drum 23 with laser light in accordance with the image data, and selectively attenuates the potential of the surface of the photosensitive drum 23 to form an electrostatic latent image. The electrostatic latent image formed on the surface of the photosensitive drum 23 is developed with toner, and the toner image is transferred to a sheet.

The BD signal conversion unit 41 shapes the light reception signal output from the BD sensor 37 into a rectangular wave BD signal and outputs the BD signal to the drawing start timing setting unit 46. For example, as shown in FIG. 6, the BD signal converter 41 includes a photodiode 42, an amplifier 43, and a Schmitt trigger 44. In the BD signal conversion unit 41, when the laser beam is irradiated onto the photodiode 42, a light reception signal is output from the photodiode 42 to the amplifier 43. The amplifier 43 amplifies the light reception signal, and then amplifies the light reception signal. A signal is input to the inverting input terminal of the Schmitt trigger 44. Furthermore, the Schmitt trigger 44, the amplified signal of the voltage values for two different thresholds V _SHL, has a V _SHH, thresholds are input to the voltage value and the non-inverting input terminal of the amplifier signal input to the inverting input terminal Output signals corresponding to the magnitudes of V _SHL and V _SHH are output.

That is, when the positional relationship (interval) between the irradiation positions of the laser beams is as shown in FIG. 7A, for example, the light reception signal output from the photodiode 42 is the arrow P1 in FIG. 7B. It is assumed that the waveform is as shown in. At this time, when the voltage value of the amplified signal increases and becomes larger than the threshold value V _SHH , the output signal of the Schmitt trigger 44 becomes L (low), and from this state, the voltage value of the amplified signal decreases and the threshold value V SH _When smaller than _SHL, the output signal of the Schmitt trigger 44 becomes H (high). In the following description, of the L (low) output signal and the H (high) output signal output from the Schmitt trigger 44, the L (low) output signal is referred to as a BD signal.

  A period indicated by an arrow W in FIG. 7B is a period in which each laser beam is received by the photodiode 42 (a period in which each laser beam passes through the photodiode 42). In this way, strictly speaking, the period in which each laser beam passes through the photodiode 42 and the output period of the BD signal corresponding to each laser beam are slightly shifted, but the following description will be made assuming that the two periods coincide with each other. I decided to. FIG. 7A shows the positional relationship between the BD sensor 37 and the irradiation position of each laser beam at the time indicated by the arrow Tx in FIG.

  Returning to FIG. 2, the control unit 45 includes a ROM that stores each control program, a RAM that temporarily stores data, and a central processing unit that reads and executes the control program from the ROM. A setting unit 46, a drawing unit 47, and an LD driving unit 48 are provided.

  The drawing start timing setting unit 46 sets a timing for starting a drawing operation based on the BD signal input from the BD signal conversion unit 41 (hereinafter referred to as a drawing start timing), and sets information indicating the drawing start timing to the drawing unit. 47 is output.

  By the way, when the laser light sources LD1 to LD3 are close to each other as in the configuration in which an image is drawn by the monolithic multi-laser diode, it is necessary to obtain drawing start timings by the laser light sources LD1 to LD3. Here, as described above, the laser beams L1 to L3 output from the laser light sources LD1 to LD3 pass through the light receiving surface of the BD sensor 37 and the surface of the photosensitive drum 23 with a certain time difference. When attention is paid to the irradiation positions of the laser beams L1 to L3 on the light receiving surface of the BD sensor 37 by the light sources LD1 to LD3, the pitches in the main scanning direction of the irradiation positions on the light receiving surface of the BD sensor 37 are compared. When the signal is large, BD signals are individually obtained corresponding to the laser beams L1 to L3. Therefore, the laser beams L1 to L3 have passed through the light receiving surface of the BD sensor 37 using the output timing of the BD signals. The timing can be detected, and consequently the drawing start timing by each of the laser light sources LD1 to LD3 can be set.

  However, when the pitch is small, a situation occurs in which the next laser light passes through the light receiving surface before the laser light passing through the light receiving surface of the BD sensor 37 finishes passing through the light receiving surface at the previous timing. As a result, some laser beam is always incident on the BD sensor 37.

  That is, when the laser beams L1 to L3 are scanned with all the laser light sources LD1 to LD3 turned on, for example, when the laser light sources LD1 to LD3 are close to each other as in the case of using a monolithic multi-laser diode, The light L1 to L3 partially overlaps the laser light existing next to the laser light source and the irradiation position on the light receiving surface of the BD sensor 37. Therefore, the BD signal obtained at this time is a constant signal until all the laser beams have passed through the light receiving surface of the BD sensor 37, and the laser beams L1 to L3 are based on the obtained BD signals. The timing of passing through the light receiving surface cannot be detected.

  Further, due to the configuration of the BD signal conversion unit 41, even if the irradiation positions of the laser beams L1 to L3 do not overlap in the main scanning direction, all the laser beams L1 to L3 are on the light receiving surface of the BD sensor 37. There is a case where it becomes a constant signal until it passes and the timing at which each of the laser beams L1 to L3 passes through the light receiving surface cannot be detected.

  That is, the BD sensor 37 detects the light emission start timing of the laser light when performing the drawing operation in nanosecond order. However, since the monolithic multi-laser diode is mounted on the semiconductor silicon wafer, the individual laser light sources are attached. The optical axes of L1 to L3 are aligned, and generally, the irradiation positions of the beam lights L1 to L3 on the light receiving surface of the BD sensor 37 are separated by only about several hundred nm. When the interval between the irradiation positions is set to 200 μm and this interval is replaced with the scanning time, if the beam lighting time of one pixel is 600 ns and 20 ns, (200 μm / 42.333 μm) × 20 ns = 94.5 ns, and BD As will be described later, the sensor 37 is generally used and has a reaction delay of several hundred ns. Therefore, the light reception signal of the BD sensor by the laser beams L1 to L3 cannot be separated for each of the laser beams L1 to L3. As a result, it is not possible to set the drawing start timing other than for the laser light source LD1.

  FIG. 8 is a diagram illustrating an example where the irradiation positions of the laser beams L1 to L3 do not overlap in the main scanning direction, but BD signals cannot be obtained individually corresponding to the laser beams L1 to L3. .

As shown in FIG. 8A, when a certain laser beam finishes passing through the light receiving surface of the BD sensor 37, the signal value of the light receiving signal of the BD sensor 37 decreases with a certain time. as shown by the arrow Q in FIG. 8 (b), when the next laser beam before the signal value is below the threshold V _SHL is incident on the light receiving surface of the BD sensor 37, the signal value to be less than the threshold value V _SHL Will increase again. Even when the positional relationship of the irradiation positions of the laser beams L1 to L3 on the light receiving surface is such a pattern, L (low) is constant until all the laser beams have passed through the light receiving surface of the BD sensor 37. Are output from the BD signal converter 41. FIG. 8A shows the positional relationship between the BD sensor 37 and the irradiation position of each laser beam at the time indicated by the arrow Tx in FIG.

As described above, the laser light L <b> 1 to the laser light L <b> 1 due to the reaction delay due to the time difference between the rising period and the falling period of the output signal of the photodiode 42 and the presence of the hysteresis voltage that is the difference between the threshold values V _SHL and V _SHH. In some cases, a BD signal cannot be obtained every L3.

  As a result, although the passage timing of the laser beam L1 that first passes through the light receiving surface can be detected from the obtained BD signal, the other passage timings of the laser beams L2 and L3 are detected from the obtained BD signal. As a result, the drawing start timing of the drawing line corresponding to the laser light source that outputs the laser beam cannot be set.

  Therefore, in the present embodiment, the reflection unit 36 as described above is provided, and the drawing start timing by the laser light sources LD2 and LD3 is set by the method described below.

  The drawing start timing setting unit 46 performs a pre-scan operation before performing an image forming operation. In the pre-scan operation, the polygon mirror 34 is rotated with only one predetermined laser light source (here, the laser light source LD1) among the laser light sources LD1 to LD3 turned on (the laser light L1). This is an operation of obtaining a BD signal from the BD signal converter 41 by performing scanning. In FIG. 4A, the rotation of the polygon mirror 34 is performed with only the laser light source LD1 turned on, so that the laser light L1 is reflected on each reflection surface of the reflection mirrors 38 to 40 and on the peripheral surface of the photosensitive drum 23. A state scanned in the main scanning direction is shown. FIG. 9A is a waveform diagram of the BD signal obtained by the scanning.

  When only the laser light L1 output from the laser light source LD1 is scanned as described above, the BD sensor 37 receives the laser light L1 reflected by the reflection mirror 38 as shown in FIG. The signal BD1 is generated, the laser beam L1 reflected by the reflection mirror 39 is received by the BD sensor 37, the BD signal BD2 is generated, and the laser beam L1 reflected by the reflection mirror 40 is received by the BD sensor 37. As a result, the BD signal BD3 is generated.

  Paying attention to each of the BD signals BD1 to BD3, the time difference t1 between the output timing of the BD signal BD1 and the output timing of the BD2 is caused by the separation of the reflection mirror 38 and the reflection mirror 39, Further, the time difference t2 between the output timing of the BD signal BD1 and the output timing of the BD3 is caused by the separation of the reflection mirror 38 and the reflection mirror 40. The drawing start timing setting unit 46 stores these timing differences t1 and t2.

  Then, the drawing start timing setting unit 46 performs lighting control so that each of the laser light sources LD1 to LD3 is reflected only by the reflection surfaces of the corresponding reflection mirrors 38 to 40 during image formation (during the drawing operation). That is, here, the laser light source LD1 and the reflection mirror 38 are associated with each other, the laser light source LD2 and the reflection mirror 39 are associated with each other, and the laser light source LD3 and the reflection mirror 40 are associated with each other. Then, the drawing start timing setting unit 46 turns on the laser light source LD1 so that the laser light L1 of the laser light source LD1 is reflected only by the reflecting surface of the reflecting mirror 38 while rotating the polygon mirror 34, and the laser light source LD2 The laser light source LD2 is turned on so that the laser light L2 is reflected only on the reflection surface of the reflection mirror 39, and the laser light source LD3 is turned on so that the laser light L3 of the laser light source LD3 is reflected only on the reflection surface of the reflection mirror 40 To do.

  4B, only the laser beam L1 indicated by the one-dot chain line among the laser beams L1 to L3 is reflected by the reflecting surface of the reflecting mirror 38, and only the laser beam L2 indicated by the dotted line is reflected by the reflecting surface of the reflecting mirror 39. Only the laser beam L3 indicated by a solid line is reflected by the reflecting surface of the reflecting mirror 40.

  Thereby, the waveform of the BD signal as shown in FIG. 9B is obtained. As shown in FIG. 9B, the laser beam L1 reflected by the reflecting mirror 38 is received by the BD sensor 37 to generate a BD signal BD4, and the laser beam L2 reflected by the reflecting mirror 39 is converted to the BD sensor. The BD signal BD5 is generated by being received by the light 37, and the BD signal BD6 is generated by receiving the laser light L3 reflected by the reflection mirror 40 by the BD sensor 37.

  Paying attention to the BD signals BD4 to BD6, the time difference T1 between the output timing of the BD signal BD4 and the output timing of the BD signal BD5 is that the reflection mirror 38 and the reflection mirror 39 are separated from each other, and the light reception of the BD sensor 37. This is because the irradiation position of the laser beam L1 and the irradiation position of the laser beam L2 on the surface are different in the main scanning direction.

  Similarly, the time difference T2 between the output timing of the BD signal BD4 and the output timing of the BD signal BD6 is that the reflection mirror 38 and the reflection mirror 40 are separated from each other and that the laser beam L1 on the light receiving surface of the BD sensor 37 is separated. This is caused by the difference between the irradiation position and the irradiation position of the laser beam L3 in the main scanning direction.

  Here, considering the drawing start timing by the laser light sources LD1 to LD3, the drawing start timing by the laser light source LD1 can be set based on the output timing of the BD signal BD4. The drawing start timing by the laser light source LD2 is caused by the difference between the irradiation position of the laser beam L1 and the irradiation positions of the laser beams L2 and L3 in the main scanning direction with the drawing start timing by the laser light source LD1 as a reference timing. It is only necessary to delay from the reference timing by the time generated.

  As described above, the time differences T1 and T2 are caused by the fact that the two reflecting mirrors are separated from each other and the irradiation positions of the two laser beams on the light receiving surface of the BD sensor 37 are different in the main scanning direction. Of these, the time difference caused by the separation of the two reflecting mirrors is the time difference t1 and t2 stored in advance in the drawing start timing setting unit 46. The amount of time generated due to the difference between the irradiation position and the irradiation position of the laser beam L2 in the main scanning direction is a time (T1−t1) obtained by subtracting the time difference t1 from the time difference T1. The amount of time caused by the difference between the irradiation position and the irradiation position of the laser beam L3 in the main scanning direction is a time (T2−t2) obtained by subtracting the time difference t2 from the time difference T2.

  Accordingly, when the drawing start timing setting unit 46 sets the drawing start timing by the laser light source LD1 based on the BD signal BD4, the drawing start timing is set as a reference timing, and the drawing start timing by the laser light source LD2 is set as the reference timing. And the drawing start timing by the laser light source LD3 is set to a timing delayed by the time (T2-t2) from the reference timing.

  The drawing start timing setting unit 46 outputs a signal indicating the drawing start timing by the laser light sources LD1 to LD3 set in this way to the drawing unit 47. That is, the drawing start timing setting unit 46 outputs a drawing start signal for the laser light source LD1 to the drawing unit 47 after a predetermined reference clock count from the output timing of the BD signal BD4 generated by the laser light L1 of each laser light source LD1. After a lapse of time (T1-t1) from the output timing, a drawing start signal for the laser light source LD2 is output to the drawing unit 47, and a time (T2-t2) from the output timing of the drawing start signal for the laser light source LD1. After the elapse, a drawing start signal for the laser light source LD3 is output to the drawing unit 47. The predetermined reference clock count number is determined for each machine at the time of adjustment at the time of machine manufacture.

  The drawing unit 47 performs LD driving based on the image signal of the image to be written output from the image memory M that temporarily stores the image data obtained by the reading operation of the document reading unit 5 based on the drawing start signal. The drive of the part 48 is started. The LD driving unit 48 drives and controls the laser irradiation unit 31 based on an instruction from the drawing unit 47.

  FIG. 10 is a flowchart showing a drawing start timing setting process by the control unit 45. In this case as well, the laser irradiation unit 31 has three laser light sources LD1 to LD3, which will be described with reference to FIG.

  As shown in FIG. 10, the control unit 45 rotates the polygon mirror 34 (scanning only the laser beam L1) with only the laser light source LD1 turned on (step # 1), and the BD sensor 37 performs BD. Signals BD1 to BD3 are acquired (step # 2). Then, control unit 45 calculates and stores time differences t1 and t2 between the output timing of BD signal BD1 and the output timing of BD signals BD2 and BD3 (step # 3).

  When an image formation instruction is issued by the user (YES in step # 4), the control unit 45 causes the laser beam L1 of the laser light source LD1 to be reflected only on the reflection surface of the reflection mirror 38 while rotating the polygon mirror 34. The laser light source LD1 is turned on and off, the laser light source LD2 is turned on and off so that the laser light L2 of the laser light source LD2 is reflected only by the reflection surface of the reflection mirror 39, and the laser light L3 of the laser light source LD3 is reflected by the reflection surface of the reflection mirror 40. The laser light source LD3 is turned on / off so as to be reflected only by the laser beam (step # 5), and the BD signals BD4 to BD6 are obtained from the BD sensor 37 (step # 6).

  Next, the control unit 45 calculates time differences T1 and T2 between the output timing of the BD signal BD4 obtained from the laser light L1 and the output timing of the BD signals BD5 and BD6 obtained from the laser lights L2 and L3 (step). # 7).

  Then, the control unit 45 sets the drawing start timing by the laser light source LD1 based on the output timing of the BD signal BD4 (step # 7), and then each time difference t1, t2, T1, calculated in steps # 3, # 7. Using T2, the drawing start timings by the laser light sources LD2 and LD3 are set based on the drawing start timing by the laser light source LD1 (step # 9). That is, the control unit 45 sets the drawing start timing by the laser light source LD2 to a timing delayed by a time (T1-t1) from the drawing start timing by the laser light source LD1, and also sets the drawing start timing by the laser light source LD3. The timing is set to be delayed by a time (T2-t2) from the drawing start timing by the laser light source LD1.

  Then, the control unit 45 causes the laser light sources LD1 to LD3 to start a drawing operation based on the drawing start timing set in step # 9 (step # 10).

  As described above, the laser light sources LD1 to LD3 are turned on so that the BD signals (BD4 to BD6) by the laser beams L1 to L3 of the laser light sources LD1 to LD3 are individually obtained using the plurality of reflection mirrors 38 to 40. Each of the lasers by subtracting the time differences t1 and t2 caused by the positional deviation of the reflecting mirrors 38 to 40 from the time differences T1 and T2 between the output timing of the BD signal BD4 and the output timing of the BD signals BD5 and BD6. The time difference caused by the positional deviation of the irradiation position of the light L1 to L3 on the light receiving surface of the BD sensor 37 is calculated, and the drawing start timing by the laser light sources LD2 and LD3 is set based on this time difference. Therefore, the drawing start timing of the laser light sources LD2 and LD3 can be derived relatively easily.

  In addition, a change in the position of the reflection mirrors 38 to 40, a change in the positional relationship between the reflection mirrors 38 to 40 and the BD sensor 37, or a change in the position of the BD sensor 37 due to an environmental change (temperature change, humidity change, etc.) When the positional relationship between the irradiation positions of the laser beams L1 to L3 on the light receiving surface changes, the output timing of the BD signals BD1 to BD6 reflects those changes. Even when an environmental change occurs, an appropriate drawing start timing can be set according to the change.

  This case includes the following modes in place of or in addition to the above embodiments.

  (1) The pre-scan operation may be performed when the multifunction device 1 is activated, or may be performed every time an image is formed on one sheet.

  (2) In the above-described embodiment, the number of the reflection mirrors 38 to 40 is the same as the number of the laser light sources. However, the present invention is not limited to this configuration. Any structure may be used as long as at least the number of reflection surfaces is equal to the number of laser light sources, such as forming a surface.

  (3) This case is not limited to the number of laser light sources provided in the laser irradiation unit 31, but may be any number, for example, including two or eight laser light sources.

  (4) In the above embodiment, a reflective surface is provided as an example of the optical path changing surface. However, a refractive surface of an optical element such as a prism is adopted instead of the reflective surface, and the light receiving surface of the BD sensor 37 is formed by the refractive surface. It is also possible to adopt a form in which the light beam is guided to.

1 is a side view schematically showing an internal configuration of a multifunction peripheral as an example of an image forming apparatus according to an embodiment of the present disclosure. It is a block diagram of an optical scanning device. It is a figure which shows the arrangement | sequence state of a laser light source. It is a figure which shows the structure of a reflection part, the positional relationship of a photosensitive drum, a polygon mirror, a reflection mirror, and a BD sensor, and the scanning mode of a laser beam. It is a figure which shows the state in which each laser beam output from each said laser light source forms an image in a different position in a main scanning direction and a subscanning direction on the light-receiving surface of a BD sensor. It is a figure which shows the electrical structure of a BD signal conversion part. It is a figure which shows the positional relationship of the irradiation position of each laser beam, the light reception signal obtained from a photodiode in the case of this positional relationship, and the BD signal obtained from a Schmitt trigger. It is a figure which shows the positional relationship of the irradiation position of each laser beam, the light reception signal obtained from a photodiode in the case of this positional relationship, and the BD signal obtained from a Schmitt trigger. (A) is a waveform diagram of the BD signal obtained by the pre-scan operation, and (b) is a waveform diagram of the BD signal obtained by scanning at the time of image formation. It is a flowchart which shows the setting process of the drawing start timing by a control part.

Explanation of symbols

24 Optical scanning device 46 Drawing start timing setting unit 47 Drawing unit 48 LD driving unit 31 Laser irradiation unit 34 Polygon mirror 36 Reflecting unit 37 BD sensors 38 to 40 Reflecting mirror 41 BD signal converting unit

Claims (4)

First and second light sources that irradiate light beams at least in different positions in the sub-scanning direction, and a scanning unit that repeatedly scans the light beams output from the light sources in the main scanning direction within a predetermined fixed area. A light source unit comprising:
The first optical path changing surface associated with the first light source and the second optical path changing surface associated with the second light source are installed at different positions in the main scanning direction within the fixed region. An optical path changing unit that changes the optical path of the light beam output from the light source unit by the first and second optical path changing surfaces;
A BD signal generating unit that receives a light beam whose optical path has been changed by the optical path changing unit and performs a photoelectric conversion operation, and generates a BD signal based on an output signal of the light receiving unit;
A light source control unit for controlling a lighting operation by the first and second light sources;
When the lighting operation based on the image data by the light source is referred to as a drawing operation, the drawing start timing of each drawing line by the light source is based on the output timing of the BD signal generated by the light beam output from the light source. A drawing start timing setting unit that is set as
Light rays output from the first and second light sources are incident on the respective optical path changing surfaces in the order of the first optical path changing surface and the second optical path changing surface, and the first and second light sources are used. When the light from each light source is scanned by the scanning unit in a state where each light is turned on, the light beam output from the first light source is the same as or earlier than the light beam output from the second light source. Incident on the optical path changing surface,
The drawing start timing setting unit
The first and second BD signals are obtained by scanning only the light beam output from any one of the first and second light sources using the scanning unit, and the first BD signal Calculating the time difference between the output timing and the output timing of the second BD signal as the first time difference;
Lighting operation of the first light source and the second light source so that light beams respectively output from the first light source and the second light source are scanned only on the light path changing surface corresponding to the light source among the light path changing surfaces. The third and fourth BD signals are obtained by causing the scanning unit to perform an operation while controlling the time difference between the output timing of the third BD signal and the output timing of the fourth BD signal. Calculated as the time difference between
The drawing start timing by the first light source is set based on the third BD signal obtained by the light beam output from the light source, and the drawing start timing by the second light source is set by the first light source. Set based on the difference between the time difference and the second time difference and the drawing start timing by the first light source,
The light emission control unit
An image forming apparatus that causes each light source to start a drawing operation according to a drawing start timing set by the drawing start timing setting unit.   The image forming apparatus according to claim 1, wherein the drawing start timing setting unit sets the drawing start timing by the second light source to a timing delayed by the difference from the drawing start timing by the first light source.   The drawing start timing setting unit calculates and stores the first time difference in advance, calculates the second time difference for each drawing line corresponding to the second light source, and the second time difference. The image forming apparatus according to claim 1, wherein a drawing start timing in the drawing line is set using the first time difference stored in advance.   The first and second light sources irradiate light at different positions in the main scanning direction and the sub-scanning direction according to the arrangement positions of the first and second light sources, respectively. When the two light sources are turned on and scanned by the scanning unit, the output periods of the BD signals obtained by the light beams of the light sources whose optical paths are changed on the same optical path changing surface are partially overlapped. The image forming apparatus according to claim 1, wherein the first and second light sources are arranged close to each other.

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