JP2007086335A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the constant speed deviation or the like of a light beam on a face to be scanned when a deflecting element is used for deflecting the light beam by a sine wave oscillation. <P>SOLUTION: In a raster output scanner (ROS), on-pulses 90A to 90G are used as a basis, a magnitude correction is performed when equal pitch dots 100A to 100G are formed in a main scanning direction, thus LD is driven by on-pulses 94A to 94G in which the beginning of lighting time is advanced at the beginning side of a main scanning, and the beginning of lighting time is delayed on the ending position side of the main scanning, and dots 96A to 96G which coincide with dots 100A to 100G are formed. Further, the dots 100A to 100G are formed by using on-pulses 97A to 98G corrected as much as to become the both directions of the main scanning for each of the on-pulses 94A to 94G. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that scans a light beam in accordance with image data to form a black and white image or a color image, and more specifically, as a deflection unit that is provided in the image forming apparatus and deflects the light beam. The present invention relates to an optical scanning device using a sinusoidal deflection element.

  In an image forming apparatus such as a digital copying machine or a laser printer to which an electrophotographic process is applied, an optical scanning device (Raster Output Scanner, hereinafter referred to as ROS) is often used as an image writing device. In ROS, when a light beam emitted from a laser light source such as a laser diode is irradiated in a spot shape on a surface to be scanned by an imaging optical system, the light beam is deflected on a surface to be scanned by deflecting by a deflecting unit. The scanning is performed at a constant speed.

  As a deflecting means for scanning a light beam, a rotating polygon mirror (polygon scanner) that rotates at a constant speed is widely used. However, the rotating polygon mirror requires a large device and needs to rotate mechanically at high speed. For this reason, there are problems such as a rise in temperature inside the apparatus, noise, an increase in power consumption, and a decrease in image quality due to banding caused by vibrations.

  In recent years, a deflecting element using a micromirror that performs sinusoidal vibration of a resonance structure using micromachine technology as a deflecting means has been proposed. By using this deflecting element, it is possible to reduce the size of the optical scanning device (ROS), and it is possible to prevent temperature rise, noise generation, and power consumption increase, as well as generation of banding due to vibration and the like. It becomes possible to prevent.

  By the way, since the deflection element using a micromirror has a resonance structure, it is difficult to increase the speed, and it is technically difficult to increase the wide amplitude and the deflection surface. For this reason, the deflection angle of the deflection element is small. In addition, there is a problem in applying to an optical scanning device of an image forming apparatus such as a printer or a digital copying machine that requires a sufficient scanning width and a small spot diameter because the deflection surface is also small.

  Further, since the deflection element swings sinusoidally, a deviation occurs in linearity (constant velocity), which causes a problem in that deviation occurs in the image height and the spot diameter of the main scanning light beam.

  From here, by utilizing the surface width in the main scanning direction of the deflecting element that swings sinusively to the maximum, by defining the conditional expression of the spot diameter and the surface width of the deflecting element, and by using a lens with arc-sin characteristics There have been proposals for improving the linearity (constant velocity) deviation and the spot height deviation of the image height main scanning light beam (see, for example, Patent Document 1).

  In addition, an electrical correction method has been proposed without performing optical correction of an arc-sin lens or an fθ lens (see, for example, Patent Document 2).

This proposal is a method of adding an image information extinguishing period (laser light source extinguishing period) according to the scanning speed of the deflecting element. The lighting period of the laser light source with respect to the pixel at a point where the scanning speed of the deflecting element is fast and slow. And the extinction period ratio are the same, and the linearity (constant velocity) deviation is corrected.
JP 2002-182147 A JP 2003-329952 A

  However, when using a deflecting element that swings sinusoidally as a deflecting means, a lens having an arc-sin characteristic has a characteristic that Fno (F number) in the main scanning direction of the scanning end changes with respect to the scanning center. There is a problem that the spot diameter is non-uniform on the scanning center and the scanning surface at the end.

  The present invention has been made in view of the above facts, and when using a sinusoidal deflection element, by making an electrical correction, the linearity (constant velocity) deviation of the light beam and the image height main scanning light beam are corrected. An object of the present invention is to provide an optical scanning device that eliminates the spot diameter deviation.

  In order to achieve the above object, the present invention provides a light source that emits a light beam, a light source driving unit that controls emission of the light beam by turning on and off the light source based on image data, and an emission from the light source. A scanning optical system capable of forming an image on the scanning range of the irradiated surface, and a light emitting source provided on the reflecting surface that is provided in the scanning optical system and is sine-oscillated by being driven by a driving means. Deflection means for deflecting and scanning the irradiated surface with the light beam emitted from the irradiation surface, and the scanning position on the irradiated surface to which the light beam is irradiated. Correction means for correcting the driving of the light source.

  According to the present invention, the light beam emitted from the light source driven by the electric signal corresponding to the image data is scanned on the surface to be scanned using the deflection element that deflects by the limited swing. At this time, the correcting means corrects the electric signal for driving the light source in accordance with the scanning position of the light beam.

  As a result, when a deflecting element that deflects the light beam by sine oscillation is used, the light beam constant velocity (linearity) deviation on the scanned surface and the spot height deviation of the image height main scanning light beam are Appearing on the surface to be scanned is prevented.

  In the present invention as described above, the correction unit can prevent the linearity deviation from appearing by correcting the lighting start timing of the light source for each pixel of the image data within one scan. In some cases, the lighting start timing may be corrected so as to be advanced on the scanning start position side and delayed on the scanning end position side.

  In the present invention, the correction unit may include a lighting time correction unit that corrects the lighting time of the light source for each pixel of the image data within one scan. What is necessary is just to correct so that it may become long in both directions.

  In the present invention, the correction means can include lighting intensity correction means for correcting the lighting intensity of the light source for each pixel of the image data within one scan. At this time, the lighting intensity and the scanning direction are included. The light intensity correction unit may include an adjustment unit that adjusts the amount of overshoot when the light source is turned on.

  Thereby, the spot diameter deviation of the image height main scanning light beam can be prevented from appearing on the surface to be scanned.

  As described above, according to the present invention, linearity (constant velocity) deviation and spot height deviation of the image height main scanning light beam when using a sinusoidal deflection element can be suppressed. It is possible to obtain an excellent effect that quality image formation is possible.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an image forming apparatus 10 applied to the present embodiment. The image forming apparatus 10 exposes one photoconductor provided as an image carrier in accordance with image data for four colors of Y (yellow), M (magenta), C (cyan), and K (black). Thus, a so-called four-cycle color laser printer for forming an image is obtained.

  The image forming apparatus 10 is provided with a ROS (Raster Output Scanner) 12 as an optical scanning apparatus to which the present invention is applied. Further, the image forming apparatus 10 is provided with a photosensitive drum 14 facing the ROS 12. In the image forming apparatus 10, after the peripheral surface of the photosensitive drum 14 is uniformly charged, a light beam is scanned from the ROS 12. A latent image (electrostatic latent image) is formed by irradiating the film with irradiation.

  Further, the image forming apparatus 10 is provided with a developing unit 16 and an endless transfer belt 18 serving as an intermediate transfer member, facing the photosensitive drum 14. The developing unit 16 is provided with toner cartridges 20Y, 20M, 20C, and 20K (hereinafter collectively referred to as toner cartridge 20) of each color of Y, M, C, and K. The toner cartridges 20Y, 20M, 20C, and 20K are provided. Are sequentially opposed to the photosensitive drum 14.

  The photosensitive drum 14 is supplied with toner (colored toner) from the toner cartridge 20 facing the photosensitive drum 14, thereby forming a toner image corresponding to the electrostatic latent image.

  The transfer belt 18 is wound around a plurality of rollers 22 and is rotationally driven while being in contact with the peripheral surface of the photosensitive drum 14. Thus, the toner image formed on the photosensitive drum 14 is transferred to the transfer belt 18 when passing through the contact position between the photosensitive drum 14 and the transfer belt 18.

  The image forming apparatus 10 forms a full-color toner image on the transfer belt 18 by transferring toner images of each color of Y, M, C, and K in order from the photosensitive drum 14 while being superimposed on the transfer belt 18.

  The image forming apparatus 10 is provided with a paper feed unit 26 on which recording papers 24 are stacked and loaded, and a paper discharge tray 28 from which the recording papers 24 on which images are formed are discharged. In addition, the image forming apparatus 10 is provided with a conveyance path 32 (conveyance path is indicated by a broken line in FIG. 1) that conveys the recording paper 24 while sandwiching the recording paper 24 by a plurality of roller pairs 30. The recorded recording sheet 24 is taken out from the uppermost layer and conveyed along the conveyance path 32.

  The recording paper 24 conveyed through the conveyance path 32 passes through a transfer position between the transfer belt 18 and the roller 34, and the recording paper 24 is transferred when passing through the transfer position. It is sandwiched between the roller 20 and the roller 34 together with the belt 18.

  The recording paper 24 is fed with the toner image on the transfer belt 18 transferred. The image forming apparatus 10 is provided with a fixing device (not shown), and the recording paper 24 onto which the toner image has been transferred is heated while being pressed by the fixing device, whereby the toner image is fixed. The

  As a result, the image forming apparatus 10 discharges the recording paper 24 on which the color image corresponding to the image data is formed onto the paper discharge tray 28.

  On the other hand, FIG. 2 shows a schematic configuration of the ROS 12 that scans and exposes the photosensitive drum 14. The ROS 12 includes an LD (semiconductor laser) 40 that is a light source (laser light source) that emits a light beam, and a deflection element 42 that is a deflection unit.

  The LD 40 emits a light beam in which the intensity, phase, and amplitude of the light beam are modulated. The light beam emitted from the LD 40 is reflected by the mirror 44 and applied to the reflecting surface of the deflection element 42. Reflected by this reflecting surface. The deflecting element 40 is sine-oscillated in synchronization with the modulation of the light beam, whereby the light beam reflected by the deflecting element 42 is deflected in the main scanning direction.

  An fθ lens 46 is provided on the optical path of the light beam reflected by the deflection element 42. The fθ lens 46 corrects the imaging position of the light beam reflected by the deflection element 42.

  Further, reflection mirrors 48 and 50 are provided on the optical path of the light beam transmitted through the fθ lens 46, and the light beam is reflected toward the reflection mirror 50 by the reflection mirror 48.

  A pickup mirror 52 is arranged in the middle of the optical path from the reflection mirror 48 to the reflection mirror 50, and the light beam directed toward the pickup mirror 52 by the reflection mirror 48 is SOS (Start Of Scan) by the pickup mirror 52. ) Reflected toward the sensor 54. The ROS 12 is provided with an EOS (End Of Scan) sensor 56 (not shown in FIG. 2, see FIG. 3), and the light beam is on the optical path of the light beam from the reflection mirror 48 to the reflection mirror 50. A pickup mirror (not shown) for reflecting the light toward the EOS sensor 56 is provided.

  The light beam applied to the reflection mirror 50 from the reflection mirror 48 is reflected by the reflection mirror 0 toward the irradiation position (exposure position) on the outer peripheral surface of the photosensitive drum 14.

  The photosensitive drum 14 is exposed by being irradiated with the light beam reflected by the reflecting mirror 50. At this time, the light beam is deflected by the deflecting element 42 to be scanned in the axial direction (main scanning direction) of the photosensitive drum 14, whereby an electrostatic latent image is formed on the photosensitive drum 14.

  On the other hand, as shown in FIG. 1, the image forming apparatus 10 is provided with a control unit 60, and the operation is controlled by the control unit 60. FIG. 3 shows a schematic configuration of a main part that executes drive control of the LD 40 and the deflection element 42 in the control unit 60. In addition, the structure of the control part 60 shown in FIG. 3 shows an example, and is not limited to this structure.

  The deflection element 42 applied to the present embodiment includes, for example, a deflection unit provided with a reflection mirror (micromirror) 42A by etching a substrate made of single crystal silicon, and a torsion bar (supporting the reflection mirror 42A). (Twisting shaft) is formed integrally. At this time, the deflecting unit is formed with a reflecting mirror 42A in which a member made of single crystal silicon is coated with a reflecting film, and a support plate that prevents the deflecting unit including the reflecting mirror 42A from bending, and is made of non-magnetic material such as aluminum. It is a general configuration that is supported by a bracket formed by a body so as to be swingable via a torsion bar.

  In the deflection element 42, a driving magnet is fixed to the surface of the support plate opposite to the reflecting mirror 42A, and a driving coil is fixed to the bracket so as to face the driving magnet.

  As a result, when a current is passed through the drive coil, the deflection element 42 generates a magnetic attraction force between the deflection element 42 and the drive magnet, and the deflection unit starts rotating with the torsion bar as the rotation axis. At this time, the current of a frequency that matches the frequency (resonance frequency) determined by the moment of inertia of the deflection unit and the torsion bar is supplied to the drive coil, so that the vibration of the reflection mirror 42A (deflection element 42) becomes a resonance vibration, and is greatly touched. A sinusoidal oscillation can be generated that provides an angle (scanning angle θ in FIG. 3).

  The light beam applied to the deflecting element 42 is deflected when reflected by the reflecting mirror 42A of the deflecting element 42 by the sine oscillation of the deflecting element 42 (reflecting mirror 42A). The driving method of the deflection element 42 is not limited to the electromagnetic method, and a known driving method such as a piezoelectric method or an electrostatic method can be applied.

  The control unit 60 includes a write control unit 62, an LD drive unit 64 that drives the LD 40, a clock pulse generation unit 66 that generates a clock pulse that serves as a synchronization signal when driving the LD 40, and a deflection element drive that drives the deflection element 42. 68, a drive pulse generator 70 for generating a drive pulse for driving the deflection element 42, a phase synchronization unit 72, a magnification calculator 74, and an amplitude calculator 76 are provided.

  The image recording apparatus 10 generates raster data (bitmap data) of each color of Y, M, C, and K based on the image data, and forms a toner image based on the raster data. The writing control unit 62 generates and holds raster data of each color based on the image data, and outputs the raster data of each color to the LD driving unit 64 sequentially, for example, one main scanning line at a timing based on the reference clock. .

  Further, the clock pulse generator 66 outputs a clock pulse based on the reference clock to the LD driver 64.

  Thus, the LD 40 is driven based on the image data and the clock pulse, and a light beam corresponding to the image data is emitted.

  Further, the drive pulse generator 70 outputs a drive pulse having a drive frequency based on the reference pulse to the deflection element driver 68. Thereby, the deflection element 42 is oscillated at the driving frequency to deflect the light beam.

  The SOS sensor 54 and the EOS sensor 56 output an SOS signal (synchronization detection signal) and an EOS signal (termination detection signal) when the light beam deflected by the deflection element 42 is input. The phase synchronization unit 72 outputs a reference clock synchronized with the SOS signal output from the SOS sensor 54 to the write control unit 62 and the clock pulse generation unit 66. As a result, the LD 40 is driven in synchronization with the SOS signal.

  The amplitude calculator 76 calculates and outputs a drive frequency correction signal from the interval of the SOS signals output by the SOS sensor 54. As a result, the deflection angle (scanning angle θ) of the deflection element 42 is maintained within a certain range.

  The magnification calculation unit 74 detects a time difference between the SOS signal output from the SOS sensor 54 and the EOS signal output from the EOS sensor 56, and an image caused by a variation in the deflection speed of the deflection element 42, a shape error of a lens of the scanning optical system, or the like. A control signal for suppressing the change in recording width is output to the clock pulse generator 66.

  Incidentally, the drive pulse generator 70 includes a drive pulse generator 78 and a PLL circuit 80. When the reference clock is input, the drive pulse generator 78 divides the reference clock by a programmable frequency divider, and outputs a drive pulse at a half cycle of the drive frequency fd.

That is, as shown in FIGS. 4A and 4B, when the drive frequency fd is the period T ₀ (T ₀ = 1 / fd), the pulse is generated at the period (1/2) · T ₀ . A drive pulse having a width T is output. The PLL circuit 80 generates a predetermined phase delay δ in this drive pulse.

Further, when the scanning angle θ of the deflection element 42 (reflection mirror 42A) has a maximum value of θ ₀ and a range of θ ₀ <θ <−θ ₀ , the drive pulse is at the maximum amplitude (scanning angle θ = (θ ₀ or −θ ₀ ), the pulse width T is controlled so that the reflection mirror 42A is output in a horizontal range (scanning angle θ = 0). That is, the drive pulse is output with a duty ratio of 50% or less (T <T _0/4 ).

On the other hand, as shown in FIG. 5, the ROS 12 scans within the period (in the forward period) from the scanning angle θ ₀ , which is the maximum value of the scanning angle θ of the deflection element 42, to the scanning angle −θ _0. Image recording is performed in the period from the angle θs to the scanning angle −θs (θ ₀ <θs <0 <−θs <−θ ₀ ), and the period from the scanning angle −θ ₀ to the scanning angle θ ₀ (from the scanning angle −θs). In the period of the scanning angle θs), the image recording is stopped.

  In other words, with the drive frequency fd as one scanning cycle, image recording is performed during scanning in the same direction (here, the forward path) of the light beam.

  In the ROS 12, when the image forming apparatus 10 is turned on or started from a standby state, the drive frequency fd output from the drive pulse generator 78 is increased by continuously changing the frequency division ratio using a programmable frequency divider. The scanning angle is expanded until the deflection element 42 is excited and the light beam is detected by the SOS sensor 54 while changing from the frequency side.

  The ROS 12 determines that the resonance vibration band of the deflection element 42 has been reached by detecting the light beam with the SOS sensor 54. At the same time, in the ROS 12, the SOS signal (synchronization detection signal) output when the SOS sensor 54 detects the light beam, and the EOS sensor 56 detects the light beam, so that the SOS signal and the EOS signal are detected. The scanning angle is calculated from the time difference, and the drive frequency fd is set so that the deflection angle (amplitude) of the reflection mirror 42A of the deflection element 42 becomes a predetermined value.

On the other hand, the synchronization detection is performed in the vicinity where the scanning angle θ becomes the scanning angle θ _0, and the SOS sensor 54 is provided at this position. As shown in FIG. 6A, the light beam that has passed through the SOS sensor 54 is folded when the amplitude reaches the maximum value, and passes through the SOS sensor 54 again.

At this time, as shown in FIG. 6B, the SOS sensor 54 outputs an SOS signal at a signal interval tr corresponding to the scanning angle θ ₀ .

From here, the amplitude calculator 76 shown in FIG. 3 detects the amplitude of the light beam by measuring the signal interval tr of the SOS signal, and adjusts the maximum value of the amplitude to the scanning angle θ ₀ . In the ROS 12, the adjustment of the amplitude of the light beam is performed not only at the time of starting but also at a preset timing such as when the use is continued regularly or for a long time. That is, it is possible to stabilize the sine swing of the deflection element 42.

In the ROS 12 applied to the present embodiment, the EOS sensor 56 is provided in the vicinity of the irradiation position of the light beam whose scanning angle θ is the scanning angle −θ _0, and the light beam on the scanning end side is detected by the EOS sensor 56. is doing.

  From this, by measuring the time difference between the SOS signal and the EOS signal, it is possible to detect changes in the scanning speed of the deflection element 42 and changes in the image recording width due to the shape error of the scanning lens of the scanning optical system. The image recording width is corrected by changing the pixel clock based on the detection result.

  The deflection element 42 is driven by the drive pulse output from the drive pulse generation unit 70, thereby changing the scanning angle θ of the light beam into a sin wave as shown in FIG.

θ = θ ₀ · sin (2π · fd · t)
However, (-1/4) .fd <t <(1/4) .fd
On the other hand, in order to print dots at regular intervals along the main scanning direction on the recording paper 24, spots of light beams are imaged at regular intervals on the peripheral surface of the photosensitive drum 14 which is the surface to be scanned. There is a need.

The scanning lens provided in the scanning optical system has imaging characteristics such that the scanning distance dH / dθ per unit scanning angle is proportional to sin ⁻¹ (θ / θ ₀ ). That is, assuming that the center (scanning angle θ = 0) of the main scanning range of the photoconductor drum 14 is the image center C, the image center C is slow and the periphery (scanning angle θ = θ ₀ or θ = −θ ₀ side). The direction of the light beam must be corrected so that it gets faster as you go. To this end, it is necessary to distribute power from the center to the periphery of the scanning lens so that the imaging point is farther away. There is a limit to widening the scanning angle θs as the effective scanning region with respect to the scanning angle θ ₀ (including −θ ₀ ) at the maximum amplitude.

From here, in the ROS 12, the phase for each pixel (dot) advances from the recording start position (scanning start position) to the recording end position (scanning end position) at the scanning start position (scanning angle θ ₀ side). From there, it is delayed in steps, and further from the image center C to the scanning end position (scanning angle −θ ₀ side) so that there is no phase shift at the image center C (see FIGS. 4 and 5). The pulse width (on time of the LD 40) when forming each pixel (dot) is gradually reduced from the recording start position toward the image center C. The pixel clock fk input to the LD drive unit 64 is corrected so as to spread stepwise from the image center C toward the scanning end position.

  As a result, the ROS 12 suppresses the occurrence of deviation in the pixel position with respect to the change in the scanning speed due to the amplitude on the peripheral surface of the photosensitive drum 14.

  Here, correction (variation) of the pixel clock fk input to the LD driving unit 64 will be described.

  As shown in FIG. 3, the clock pulse generator 66 includes a clock pulse generator 82 and a PLL circuit 84.

When the reference clock f ₀ is input, the clock pulse generation unit 82 divides the reference clock f ₀ by the programmable frequency divider based on the variable data, and counts the divided clocks. A pulse having a length of one minute is generated as the PLL reference signal fa and output to the PLL circuit 84.

The PLL circuit 84 outputs a pixel clock fk based on the PLL reference signal fa according to the variable data and the phase of the reference clock f ₀ . In the clock pulse generator 66, for example, the generation of the pixel clock fk based on the variable data is repeated every several tens of pixels.

The phase synchronization unit 72 normally receives an SOS signal (synchronization detection signal) output from the SOS sensor 54 from a clock obtained by delaying one cycle of the reference clock every 1 / n when a reference clock is input. A phase synchronization process of selecting clocks having the same phase and outputting the selected clock as the reference clock f ₀ is executed for each main scan, that is, every time an SOS signal is input as the main scan start timing. At this time, the phase synchronizer 72 can select clocks having different phases, and the timing for starting clock variability is determined in the horizontal state of the reflecting mirror 42A of the deflecting element 42 (light beam scanning angle θ = 0) is corrected so as to surely match the position of the center C of the image.

Further, the clock pulse generator 82 adjusts the image width in the main scanning direction by changing the frequency division ratio of the reference clock f ₀ . That is, the time difference between the SOS signal output from the SOS sensor 54 and the EOS signal output from the EOS sensor 56 is measured by the magnification calculator 74, and when the measured time difference is shorter than a preset value, the reference clock f ₀ is corrected in the direction of increasing the frequency, and when the time difference is longer than a preset value, the reference clock f ₀ is corrected in the direction of decreasing the frequency.

  Here, the scanning of the light beam by the ROS 12 will be described with reference to FIG.

  FIG. 7A shows an outline of a lighting waveform when the LD 40 is turned on at a constant lighting timing and lighting time regardless of the scanning position (scanning angle θ) in one main scanning range. In FIG. 7A, the on-pulses 90A, 90B, 90C, 90D, 90E, 90F, and 90G of the LD 40 are set in order from the main scanning start side, the on-pulse 90D is the position of the image center C, and the on-pulse 90G ends. On the side. Further, the ON pulses 90A to 90G have the same ON time at equal intervals.

  FIG. 7B shows a surface to be scanned by the scanning optical system provided in the ROS 12 while deflecting the light beam emitted by turning on the LD 40 with the lighting waveform of FIG. 2 shows an outline of a light amount distribution when an image is formed on a peripheral surface of a certain photosensitive drum 14. In the following, the light amount distribution is represented as pulsed dots, and the dots 92A, 92B, 92C, 92D, 92E, 92F, and 92G correspond to the ON pulses 90A, 90B, 90C, 90D, 90E, 90F, and 90G in order. The light beam irradiation position and the light amount (dot diameter) are used.

  Here, the dot 92D with respect to the on-pulse 90D at the image center C is a position corresponding to the image center C, and the dot diameter also corresponds to the on-time of the on-pulse 90D.

  On the other hand, in the dots 90A to 90C and 90E to 90G on the main scanning start side and the main scanning end side, the dot positions (light beam irradiation positions) are biased toward the image center C side. For this reason, the dot interval is narrow. It has become.

  The deviation of the dot position becomes larger toward the main scanning start position side and the main scanning end position side, and as a result, the dot interval becomes narrower toward the main scanning start position side and the main scanning end position side.

  Further, the dots 90A to 90C and 90E to 90G have small dot diameters (spot diameter and light amount of the light beam), and the dot diameters at this time are closer to the main scanning start position side and the main scanning end position side. It becomes smaller (narrower).

  Here, the dot interval becomes a magnification error on the image, and this magnification error is large on the main scanning start side and the main scanning end side.

  From here, the ROS 12 individually sets the lighting start timing of the LD 40 for each pixel in one main scanning line by the magnification correction by the magnification calculator 74. At this time, the lighting start timing of the LD 40 is advanced on the main scanning start position side, the lighting timing is delayed in stages, and the lighting start timing coincides (no correction) in the image center C.

  That is, as shown in FIG. 7C, the on-pulses 94B and 94C along the main scanning direction are changed to the on-pulse 90B, so that the on-pulse 94A corresponding to the on-pulse 90A becomes the earliest and the on-pulse 94D coincides with the on-pulse 90A. It is earlier than each of 90C. On-pulses 94E, 94F, and 94G are delayed from on-pulses 90E, 90F, and 90G, and the amount of delay is the largest in on-pulse 94G.

  By turning on the LD 40 with such on-pulses 94A to 94G, as shown in FIG. 7D, the dots 96A to 96G by the light beam applied to the peripheral surface of the photosensitive drum 14 are aligned in the main scanning direction. The positional deviation along the line is eliminated, and the occurrence of an image magnification error can be prevented.

  On the other hand, in this state (dot diameter shape in FIG. 7D), the width (dot diameter) of the light amount distribution becomes smaller toward the main scanning direction side (periphery side of the image).

The ROS 12 controls the lighting width of the LD 40 for each pixel within one main scanning line using the image clock fk obtained by correcting the main fraction with respect to the reference clock f ₀ by the clock pulse generator 66. At this time, the lighting width is controlled to be longer toward the both ends in the main scanning direction.

  Thereby, the lighting waveform of LD40 shown by FIG.7 (E) is obtained. That is, the on-time of the on-pulse 98D at the center C of the image remains the same, but the on-pulses 98A to 98G corrected in a stepwise manner so that the on-time of the on-pulses 98A and 98G on both sides in the main scanning direction are the longest. .

  In the ROS 12, the LD 40 is turned on using the on pulses 98 </ b> A to 98 </ b> G with respect to the on pulses 90 </ b> A to 90 </ b> G, and the peripheral surface of the photosensitive drum 14 is scanned and exposed.

  Thereby, the light quantity distribution shown in FIG. 7F is obtained. That is, the dots 100A to 100G that coincide with the on pulses 90A to 90G can be formed.

  As described above, in the ROS 12 using the deflecting element 42 that deflects the light beam by sine oscillation, the linearity of the light beam along the main scanning direction is corrected by correcting the electric signal that is a lighting waveform when the LD 40 is turned on. (Constant velocity) Deviation and spot height deviation of image height main scanning light beam are eliminated.

  As a result, the image forming apparatus 10 provided with the ROS 12 can form a high-quality image on the recording paper 24. In other words, when the light beam is deflected using the deflecting element 24, an image in which the linearity deviation of the light beam and the spot diameter deviation of the image height main scanning constraint are prevented can be formed on the recording paper 24. .

  On the other hand, in the scanning optical system, the spot power (light intensity) of the light beam applied to the peripheral surface of the photosensitive drum 14 may be non-uniform due to the influence on the lens characteristics. If the change in the light intensity at this time is large, as shown in FIG. 8B, when the LD 40 is turned on with the lighting waveform in FIG. Will be.

  In such a case, the ON pulses 98A to 98G (see FIG. 8C) in which the ON timings and ON times of the ON pulses 90A to 90G are corrected by error magnification correction are also shown in FIG. 8D. As a result, the dots 104A to 104G whose height changes in the main scanning direction are formed.

  In order to prevent this, as shown in FIG. 9, an LD driving unit 64A including an intensity modulating unit 86 is provided. The intensity modulator 86 corrects the light emission intensity of the LD 40 according to the image position. At this time, the light beam emitted from the LD 40 is strengthened by maximizing the correction amount on both sides in the main scanning direction.

  That is, as shown in FIG. 8E, correction is performed so that the on pulses 106A to 106C and 106E to 106G on both sides in the main scanning direction are higher than the on pulse 106D at the center C of the image. At this time, the correction is performed so that the on-pulses 106A and 106G on both ends become the highest and gradually decrease.

  By using such a lighting waveform of the LD 40, dots 100A to 100G having a uniform light amount distribution can be formed as shown in FIG. That is, it is possible to correct the spot diameter deviation of the image height main scanning light beam along the main scanning direction with higher accuracy.

  On the other hand, when the LD 40 is turned on, overshoot may occur. Since the overshoot when the LD 40 is turned on affects the amount of light when the light beam is irradiated onto the photosensitive drum 14, an adjustment unit (not shown) that suppresses the overshoot of the LD 40 is provided in the LD drive unit 64. May be provided.

  From here, the amount of overshoot may be adjusted by the adjustment unit to correct the amount of light by the light beam irradiated onto the photosensitive drum 14.

  That is, as shown in FIG. 10E, overshoot is not generated for the on-pulse 108D at the center C of the image, but the on-pulses 108A to 108C and the on-pulses 108E to 108G on both sides in the main scanning direction are prevented. In contrast, overshoots 110A to 110C and 110E to 110G are generated in the on pulses 98A to 98C and 98E to 98G. In FIG. 10, FIGS. 8A to 8D are shown as FIGS. 10A to 10D for easy comparison.

  The amount of overshoot at this time is adjusted so that it is the largest in the overshoots 110A and 110G on both sides in the main scanning direction and gradually decreases toward the image center C.

  As shown in FIG. 10G, the LD 40 is turned on using the lighting waveforms (on pulses 108A to 108G) that form an amount of overshoot according to the position along the main scanning direction. The dots 100A to 100G having a uniform light amount distribution can be formed.

  Further, the lighting intensity correction of the LD 40 and the overshoot correction may be combined.

  That is, as shown in FIG. 10 (F), for the on-pulse 112D at the center C of the image, the lighting intensity is not corrected and overshoot does not occur, but in the main scanning direction. The on-pulses 108A to 108C and the on-pulses 108E to 108G on both sides are corrected so that the lighting intensity increases stepwise toward both sides in the main scanning direction, and an overshoot (overshoot 114A) that increases stepwise. To 114C and 114E to 114G) are used. On-pulses 112A to 112C and 112E to 112G are used.

  The overshoots 114A to 114C and 114E to 114G at this time can make the amount of overshoot smaller than the overshoots 110A to 110C and 110E to 110G described above, and use the lighting waveforms (on pulses 112A to 112G). By turning on the LD 40, dots 100A to 100G having a uniform light quantity distribution can be formed as shown in FIG. 10G, and the spot height of the image height main scanning light beam along the main scanning direction is formed. The deviation can be corrected with higher accuracy.

  In addition, this Embodiment demonstrated above does not limit the structure of this invention. For example, in this embodiment, the lighting start timing is corrected by correcting the magnification along the main scanning direction of the light beam, and the dot of a desired position and light amount is formed by correcting the on-time. However, for example, if only the dot position is corrected, it is only necessary to adjust the lighting start timing by the magnification correction, and the magnification correction is unnecessary, and only the on-time correction is performed.

  Furthermore, when only the light intensity is corrected, intensity modulation corresponding to the scanning position of the light beam may be performed, or overshoot adjustment, or a combination of intensity modulation and overshoot adjustment may be used.

  In the present embodiment, the four-cycle image forming apparatus 10 has been described as an example. However, the present invention is not limited to this, and a photosensitive member such as four photosensitive drums corresponding to each of four color toners is used. The image forming apparatus may be applied to a so-called tandem image forming apparatus that individually scans and exposes each photoconductor. In this case, the ROS 12 may be provided for each photoconductor.

1 is a schematic configuration diagram of an image forming apparatus applied to the present embodiment. 1 is a schematic configuration diagram of a ROS provided in an image forming apparatus. It is a functional block diagram which shows the principal part of a control part. (A) is a diagram showing the sine oscillation of the reflecting mirror of the deflection element, and (B) is a timing chart showing the drive timing of the deflection element. It is a diagram which shows the sine rocking | fluctuation of the deflection | deviation element for 1 main scanning. (A) is a schematic diagram showing the scanning of the light beam to the SOS sensor, (B) is a schematic diagram showing the SOS signal output by the scanning of (A). (A) is a schematic diagram showing an LD lighting waveform that is the basis for forming constant dots at regular intervals, and (B) is a light amount distribution on the peripheral surface of the photosensitive drum formed by the lighting waveform of (A). (C) is a schematic diagram showing the lighting waveform of the LD obtained by the magnification correction of (A), (D) is a light amount distribution on the peripheral surface of the photosensitive drum formed by the lighting waveform of (C). (E) is a schematic diagram showing a lighting waveform of an LD obtained by the lighting time correction of (A), and (F) is a light amount of the peripheral surface of the photosensitive drum formed by the lighting waveform of (E). It is the schematic which shows distribution. (A) is a schematic diagram showing an LD lighting waveform that is the basis for forming constant dots at equal intervals, and (B) is a photosensitivity formed by the lighting waveform of (A) when a change occurs in light intensity. Schematic showing the light amount distribution on the peripheral surface of the body drum, (C) is a schematic diagram showing the lighting waveform of the LD obtained by the magnification correction and on-time correction of (A), and (D) is when the light intensity changes (C) is a schematic diagram showing the light amount distribution on the peripheral surface of the photosensitive drum formed by the lighting waveform of (C), (E) is a schematic diagram showing the lighting waveform of the LD obtained by the intensity correction of (C), (F). FIG. 6 is a schematic diagram showing a light amount distribution on the peripheral surface of the photosensitive drum formed by the lighting waveform of (E) when a change occurs in the light intensity. It is a functional block diagram which shows another example of the principal part of a control part. (A) is a schematic diagram showing an LD lighting waveform that is the basis for forming constant dots at equal intervals, and (B) is a photosensitivity formed by the lighting waveform of (A) when a change occurs in light intensity. Schematic showing the light amount distribution on the peripheral surface of the body drum, (C) is a schematic diagram showing the lighting waveform of the LD obtained by the magnification correction and on-time correction of (A), and (D) is when the light intensity changes (C) is a schematic diagram showing the light amount distribution on the peripheral surface of the photosensitive drum formed by the lighting waveform of (C), (E) is a schematic diagram showing the lighting waveform of the LD obtained by the overshoot correction of (C), ) Is a schematic diagram showing the lighting waveform of the LD obtained by the overshoot correction and intensity correction of (C), and (G) is formed by the lighting waveform of (E) or (F) when a change occurs in the light intensity. The light intensity distribution on the peripheral surface of the photosensitive drum A to schematic diagrams.

Explanation of symbols

10 Image forming device 12 ROS (Optical scanning device)
14 Photosensitive drum (image carrier)
24 Recording paper 40 LD (light source)
42 Deflection element 42A Reflection mirror 46 fθ lens (scanning optical system)
54 SOS sensor 60 Control unit (correction means)
62 Write controller 64, 64A LD driver (light source driver)
66 Clock pulse generator (correction means)
68 Deflection element driver (deflection means)
70 Drive pulse generator 72 Phase synchronizer (correction means)
74 Magnification calculator (correction means)
76 Amplitude calculation section (correction means)
86 Intensity modulation part (correction means)

Claims (8)

A light source that emits a light beam;
Light source driving means for controlling the emission of the light beam by turning on and off the light source based on image data;
A scanning optical system capable of forming an image of the light beam emitted from the light source on a scanning range of an irradiated surface;
The surface to be irradiated is deflected by irradiating a light beam emitted from the light source to a reflecting surface provided in the scanning optical system and sine-oscillated by being driven by driving means. Deflection means for scanning up;
Correction means for correcting the driving of the light source according to a scanning position on the irradiated surface irradiated with the light beam;
An optical scanning device comprising:   The optical scanning device according to claim 1, wherein the correction unit corrects the lighting start timing of the light source for each pixel of the image data within one scan.   3. The optical scanning device according to claim 2, wherein the lighting start timing is corrected so as to be advanced on the scanning start position side and delayed on the scanning end position side.   The said correction | amendment means contains the lighting time correction | amendment means which correct | amends the lighting time of the said light source for every pixel of the said image data within 1 scan, The any one of Claims 1-3 characterized by the above-mentioned. Optical scanning device.   The optical scanning device according to claim 4, wherein the lighting time is corrected so as to be longer on both sides in the scanning direction.   6. The lighting device according to claim 1, wherein the correcting unit includes a lighting intensity correcting unit that corrects a lighting intensity of the light source for each pixel of the image data within one scan. 7. Optical scanning device.   The optical scanning device according to claim 6, wherein the lighting intensity is corrected so as to increase in both sides of the scanning direction.   The optical scanning device according to claim 6, wherein the light intensity correction unit includes an adjustment unit that adjusts an overshoot amount when the light source is turned on.

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