JP4003429B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, and in particular, scans a light beam emitted from a light source on a photoconductor, and modulates the light beam based on the timing at which the light beam is detected by a light beam detector. The present invention relates to an image forming apparatus.
[0002]
[Prior art]
Conventionally, in an image forming apparatus that forms an image according to an electrophotographic process (for example, a copying machine, a printer, a facsimile machine, or a complex machine thereof), a charged photoconductor is exposed according to an image to be formed on the photoconductor. As an exposure apparatus for forming an electrostatic latent image on a light source, a light beam emitted from a light source such as a laser diode (LD) is modulated according to an image to be formed, and the modulated light beam is deflected by a polygon mirror or the like. 2. Description of the Related Art Optical scanning devices that are configured to be deflected by means and scan on a photoreceptor are widely used.
[0003]
In this type of optical scanning device, in order to modulate the light beam at a timing synchronized with the scanning of the light beam, the end of the scanning range of the light beam (for example, the end of the scanning start side (SOS: Start Of Scan) or A light beam detector disposed so that the light beam is incident when the light beam is deflected in a direction corresponding to an end portion (EOS: End Of Scan) on the scanning end side; This light beam detector outputs a synchronizing signal that causes a pulse-like change in signal level (detection pulse) each time a light beam is received. The modulation of the light beam in each scan of the light beam is started at a timing synchronized with the synchronization signal (specifically, after a predetermined time has elapsed since the detection pulse was generated in the synchronization signal).
[0004]
Conventionally, the light beam detector is generally constituted by a single photoelectric conversion element. In this type of light beam detector, the signal level of the synchronization signal is switched when the signal level of the output signal of the photoelectric conversion element that changes according to the amount of received light exceeds a predetermined threshold. When the light amount of the light beam itself changes, the timing at which the signal level of the synchronization signal switches with respect to the actual position of the light beam is shifted (for example, FIG. 9 shows the switching of the signal level as the light amount of the light beam decreases. An example in which a delay of Δt occurs is shown), and the modulation start timing is shifted accordingly, so that the image writing position is the distance corresponding to the product of the time corresponding to the shift of the modulation start timing and the scanning speed. It will shift.
[0005]
For this reason, Japanese Patent Laid-Open No. 2000-321834 discloses a technique for correcting image registration in accordance with a change in the intensity of a light beam. However, image registration correction is generally realized by forming a toner image for registration correction, measuring the position of the formed toner image, and calculating a correction amount for correcting the registration. Is done. Accordingly, if the above processing is performed every time the intensity of the light beam is changed, there is a problem in that the processing capability of the image forming apparatus is significantly reduced.
[0006]
Japanese Patent Laid-Open No. 7-177306 uses a light beam detector having a configuration in which two photoelectric conversion elements are arranged along the scanning direction of a light beam (see FIG. 10B as an example). A signal that switches the signal level at a substantially constant timing regardless of changes in the intensity (light quantity) of the light beam by taking the difference between the two output signals by utilizing the phase shift of the output signal of the photoelectric conversion element Techniques for generating are described. Further, JP-A-4-247761 discloses a technique for preventing malfunction caused by noise that does not reach the clamp level by forcibly clamping one of the two sensor outputs to a predetermined level. .
[0007]
In an optical beam detector having a configuration in which two photoelectric conversion elements are arranged, as shown in FIG. 10A as an example, the switching timing of the signal level of the synchronization signal does not change to the extent that the amount of light beam varies slightly. At present, the majority of image forming apparatuses employ a configuration in which two photoelectric conversion elements are arranged as a light beam detector.
[0008]
[Problems to be solved by the invention]
However, even when using a light beam detector with a configuration in which two photoelectric conversion elements are arranged, in the end, the synchronization signal is generated by comparing the amplitude of the output signal (analog signal) of the photoelectric conversion element with a predetermined threshold value. Therefore, when the light amount of the light beam itself is clearly larger than the appropriate value, the output signal of the photoelectric conversion element is shown as “light amount: excessive” in FIG. 11D as an example. Is saturated with respect to the amplitude corresponding to the amount of received light (denoted as “ideal voltage” in FIG. 11D), thereby causing a shift in the switching timing of the signal level of the synchronization signal (in many cases, the switching timing). There was a problem that delay) occurred. Further, even when the light amount of the light beam itself is clearly small with respect to the appropriate value, the waveform of the output signal of the photoelectric conversion element is, as shown in FIG. A difference in timing of switching the signal level of the synchronization signal occurs due to the difference between the light amount and the appropriate value.
[0009]
In recent years, an image forming apparatus that forms a color image, such as a color printer or a color copying machine, has a plurality of photoconductors, and simultaneously scans and exposes each photoconductor with a plurality of light beams emitted from a plurality of light sources. As a result, so-called tandem systems, in which images of different colors are formed on the respective photoconductors and color images are formed by superimposing the images of the respective colors on the same transfer medium, are becoming mainstream. The tandem image forming apparatus forms each color image at the same time, so it has the advantage that the time required to form a color image can be greatly shortened. And modulating the light beam at a timing synchronized with the generated synchronization signal must be performed independently for each of the plurality of light beams, and the signal level switching timing of the synchronization signal corresponding to each light beam There is a problem that the shift is easily visually recognized as a color shift on the image.
[0010]
In particular, among the tandem color image forming apparatuses, a configuration in which a light beam scanning device that deflects and scans a light beam deflects each of a plurality of light beams by a single deflecting unit (for example, a polygon mirror) (so-called spray method: In the case of Japanese Patent Laid-Open No. 3-142212, etc., since the scanning directions of the individual light beams on the photosensitive member are not constant, image formation when the switching timing of the signal level of the synchronization signal occurs is generated. Since the moving direction of the position differs depending on each light beam, that is, each color, there is a problem that the color shift is visually recognized more remarkably.
[0011]
The present invention has been made in consideration of the above facts, and an object of the present invention is to obtain an image forming apparatus capable of suppressing fluctuations in the image forming position due to a change in the amount of light beams with a simple configuration.
[0012]
[Means for Solving the Problems]
  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention includes a light source that emits a light beam, and deflects the light beam so that the light beam emitted from the light source scans on a photoconductor. And a light beam detector for detecting the light beam deflected by the deflection means at a specific position within a scanning range of the light beam, and a timing at which the light beam is detected by the light beam detector as a reference. Modulation means for modulating the light beam emitted from the light source, light amount setting means for setting the light amount of the light beam emitted from the light source, and the light amount of the light beam emitted from the light source. A light amount adjusting means for adjusting to match the light amount set by the light amount setting means;A position detecting means for detecting a position of an image formed by scanning the photosensitive member with the light beam; and a first control value for adjusting a modulation start timing of the light beam by the modulating means, An image position adjusting unit that is set based on the position of the image detected by the position detecting unit, and a second control value for adjusting the modulation start timing of the light beam by the modulating unit are set as the light amount by the light amount setting unit. When the value is within a predetermined range, the correction amount of the modulation start timing by the second control value is 0, and the light amount setting value is larger than the upper limit value of the predetermined range or lower than the lower limit value of the predetermined range When the value is small, the correction amount of the modulation start timing by the second control value increases as the difference between the light amount setting value and the upper limit value or the lower limit value increases. The light beam by the modulation means is set at a timing delayed by a time corresponding to a value obtained by adding the first control value and the second control value to the timing at which the light beam is detected by the light beam detector. Control means for starting the modulation ofIt is comprised including.
[0013]
According to the first aspect of the present invention, the light beam emitted from the light source is deflected so as to scan on the photosensitive member by the deflecting means. Further, the deflected light beam is detected by the light beam detector at a specific position within the scanning range, and the modulation means is supplied from the light source at a predetermined timing based on the timing at which the light beam is detected by the light beam detector. Modulates the emitted light beam. An image (for example, an electrostatic latent image) is formed on the photosensitive member by scanning the photosensitive member with the light beam modulated by the modulating unit. As the light beam detector, various known configurations (for example, a configuration including a single photoelectric conversion element or a configuration in which a plurality of photoelectric conversion elements are arranged in the light beam scanning direction) are employed. Can do.
[0014]
According to the first aspect of the present invention, the light amount setting means for setting the light amount of the light beam emitted from the light source is provided, and the light amount adjusting means is configured such that the light amount of the light beam emitted from the light source is changed by the light amount setting means. Adjust to match the set light intensity. For example, the sensitivity of the photoconductor with respect to the amount of light beam changes according to the temperature of the photoconductor. For example, when the sensitivity of the photoconductor changes, the light amount of the light beam is set so that the change in the sensitivity of the photoconductor is compensated. By configuring the light amount setting means so as to change the value, the density of the formed image can be kept constant regardless of the change in the sensitivity of the photoconductor.
[0015]
  Note that the configuration of the light amount setting means as described above specifically includes, for example, claims.3As described above, the density of the image formed by scanning the light beam on the photosensitive member (for example, the potential of the electrostatic latent image formed by scanning the light beam may be used, or the electrostatic latent image may be Density detection means for detecting the density of the toner image obtained by development) is provided, and the light quantity setting means is configured to optimize the light quantity of the light beam emitted from the light source based on the density detected by the density detection means. This can be realized by calculating the value and setting the calculated optimum value.
[0016]
  According to a first aspect of the present invention, there is provided a position detecting means for detecting a position of an image formed by scanning a light beam on a photosensitive member, and a first means for adjusting a modulation start timing of the light beam by the modulating means. Image position adjustment means for setting the control value of 1 based on the position of the image detected by the position detection means is provided, and the control means adjusts the light beam modulation start timing by the modulation means. If the light quantity setting value by the light quantity setting means is within a predetermined range, the correction amount of the modulation start timing by the second control value is 0 and the light quantity setting value is larger than the upper limit value of the predetermined range, or When the value is smaller than the lower limit value of the predetermined range, the correction amount of the modulation start timing by the second control value increases as the difference between the light amount setting value and the upper limit value or the lower limit value increases. And the timing at which the light beam is detected by the modulation means at a timing delayed by a time corresponding to a value obtained by adding the first control value and the second control value to the timing at which the light beam is detected by the light beam detector. Start modulation.
[0017]
  In the first aspect of the invention, the light amount setting value is changed and set by the light amount setting means, so that the light amount of the light beam changes. With the change in the light amount of the light beam, the actual light beam position is changed. There is a shift in the timing at which the light beam detector detects the light beam, and the shift in the timing also shifts the position at which the image is formed. On the other hand, the control means according to the first aspect of the invention uses the fact that the light quantity of the light beam is adjusted by the light quantity adjusting means so as to coincide with the light quantity set by the light quantity setting means. Since the modulation timing by the modulation means is changed by setting the second control value for adjusting the modulation start timing of the light beam according to the light quantity setting value by the light quantity setting means, the light quantity change of the light beam The resulting variation in the image forming position can be suppressed. Further, by using the light amount setting value by the light amount setting means, it is not necessary to add a new sensor for detecting the light amount of the light beam, and the configuration of the image forming apparatus can be simplified.
[0018]
  Further, according to an experiment conducted by the inventor of the present application, if the light amount of the light beam is within a predetermined range, the deviation of the light beam detection timing is negligibly small, and when the light beam amount deviates from the predetermined range, It has been confirmed that the deviation of the light beam detection timing becomes significant according to the amount of deviation of the light amount from the predetermined range. For this reason, in detail, the control means according to the first aspect of the invention provides the second control value for adjusting the modulation start timing of the light beam by the modulation means, and the light quantity setting value by the light quantity setting means is within a predetermined range. In this case, the correction amount of the modulation start timing by the second control value is 0, and when the light amount setting value is larger than the upper limit value of the predetermined range or smaller than the lower limit value of the predetermined range, the light amount setting value and the upper limit The correction amount of the modulation start timing by the second control value is set to increase as the value or the difference from the lower limit value increases. As a result, fluctuations in the image forming position caused by changes in the light amount of the light beam can be accurately suppressed by simple processing. Further, in the aspect in which the relationship between the light beam quantity and the deviation amount of the light beam detection timing is stored as data and used for changing the modulation timing, the amount of data to be stored for use in changing the modulation timing is determined. The effect that it can reduce is also acquired.
[0019]
  In addition, the displacement of the image forming position in the image forming apparatus is actually not only a change in the light amount of the light beam, but also, for example, due to a change in the temperature inside the image forming apparatus, This also occurs when the relative position changes. For this reason, in most image forming apparatuses, the position of the image formed by the light beam scanning on the photosensitive member is detected by the position detecting means, and the modulation by the modulating means is performed based on the detected position of the image. Equipped with a function to adjust the image forming position by setting a control value for changing the timing and changing the modulation timing by the modulation means according to the set control value (hereinafter referred to as “registration adjustment function” for convenience) Has been.
[0020]
  Therefore, in the image forming apparatus equipped with the registration adjustment function, when the modulation timing by the modulation unit is changed according to the light amount setting value by the light amount setting unit as described above, the modulation timing by the modulation unit is changed by the position detection unit. Since each change is made in accordance with the detected position of the image and the light amount setting value by the light amount setting means, there is a possibility that the configuration of the processing unit for realizing the registration adjustment function needs to be significantly changed.
[0021]
  On the other hand, according to the first aspect of the present invention, the position of the image formed by the light beam scanning on the photosensitive member is detected by the position detection means, and the modulation start timing of the light beam by the modulation means is adjusted. The first control value is set by the image position adjusting means based on the position of the detected image, and the control means determines the first control value with respect to the timing when the light beam is detected by the light beam detector. Since the modulation of the light beam by the modulation means is started at a timing delayed by a time corresponding to the value obtained by adding the second control value, the position detection means and the image position adjustment means for realizing the registration adjustment function There is also an effect that the fluctuation of the image forming position due to the change in the light amount of the light beam can be suppressed without affecting the configuration.
[0032]
  Claims1In the claimed invention, the claim2As described above, the light source emits a plurality of light beams for forming a plurality of images of different colors, which are finally superimposed as a color image, and the deflecting means is a plurality of light beams emitted from the light source. A plurality of light beams are deflected so that each light beam scans on the photosensitive member, and the light beam detector identifies the plurality of light beams deflected by the deflecting means within the scanning range of each light beam. Each detecting unit detects the position, and the modulation unit modulates each of the plurality of light beams emitted from the light source at a predetermined timing based on the timing at which the corresponding light beam detector detects the light beam, and sets the light amount. The means sets the light quantity of the plurality of light beams emitted from the light source independently for each light beam, and the light quantity adjustment means sets the light quantity of the plurality of light beams emitted from the light source. It may be adjusted to each match the individual light quantity set in independently each light beam by the step.
[0033]
  In this case, the control unit monitors the change of the light amount setting value by the light amount setting unit, and changes the modulation timing by the modulation unit only for the light beam whose light amount setting value has been changed.FurtherCan be configured to do. As a result, different color images respectively formed by a plurality of light beams are formed at fixed positions, so that a change in the light amount of the light beam causes a final color image to be formed. Color misregistration can be prevented.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
[0035]
  [ActualForm]
  FIG. 1 shows a color image forming apparatus 10 as an image forming apparatus according to the present invention. The color image forming apparatus 10 includes three transport rollers 12A to 12C, an endless transfer belt 14 wound around the transport rollers 12A to 12C, and a transfer roller disposed to face the transport roller 12C with the transfer belt 14 interposed therebetween. 16.
[0036]
Above the transfer belt 14, along the moving direction of the transfer belt 14 when the transfer belt 14 is rotationally driven (the direction of arrow A in FIG. 1), a photosensitive drum 18K for forming a black (K) image, cyan ( C) Photosensitive drum 18C for image formation, photosensitive drum 18M for magenta (M) image formation, and photosensitive drum 18Y for yellow (Y) image formation are arranged at substantially equal intervals. Each photosensitive drum 18 is arranged so that the axis thereof is orthogonal to the moving direction of the transfer belt 14. In the following, portions provided for each color of K, C, M, and Y are distinguished from each other by adding a symbol of K / C / M / Y to each portion.
[0037]
Around each photosensitive drum 18, a charger 20 for charging the photosensitive drum 18 is disposed. Above each photosensitive drum 18, a laser beam is applied to each charged photosensitive drum 18. Are arranged, and a plurality of beam scanning devices 30 (details will be described later) for forming an electrostatic latent image on each photosensitive drum 18 are disposed.
[0038]
Further, around each photosensitive drum 18, an electrostatic latent image formed on the photosensitive drum 18 is arranged in a predetermined color (K) on the downstream side of the laser beam irradiation position along the rotation direction of the photosensitive drum 18. Or a developing device 22 that forms a toner image by developing with toner of C, M, or Y), a transfer device 24 that transfers the toner image formed on the photosensitive drum 18 to the transfer belt 14, and the photosensitive drum 18. A cleaner 26 is disposed in order to remove the toner.
[0039]
The toner images of different colors formed on the respective photosensitive drums 18 are respectively transferred to the transfer belt 14 so as to overlap each other on the belt surface of the transfer belt 14. As a result, a color toner image is formed on the transfer belt 14, and the formed color toner image is transferred to the transfer material 28 fed between the transport roller 12 </ b> C and the transfer roller 16. Then, the transfer material 28 is sent to a fixing device (not shown), and the transferred toner image is fixed. As a result, a color image (full color image) is formed on the transfer material 28.
[0040]
A density sensor 74 and a position sensor 76 are provided on the downstream side of the circumferential direction of the transfer belt 14 with respect to the photosensitive drum 18Y along the peripheral circuit of the transfer belt 14, respectively. In the color image forming apparatus 10 according to the present embodiment, a predetermined light amount control pattern is periodically formed on the transfer belt 14 (for example, when the image forming apparatus 10 is turned on or at predetermined time intervals, the image forming apparatus 10 Each time the internal temperature of the recording medium changes by a predetermined value or more, the integrated value of the number of transfer materials 28 onto which the image is transferred / formed by the image forming apparatus 10 reaches a predetermined value). When the light quantity control pattern is formed on the transfer belt 14, the density sensor 74 detects the density of the light quantity control pattern.
[0041]
Further, in this embodiment, although the frequency is lower than that of the light amount control pattern, a predetermined image position detection pattern is also periodically formed on the transfer belt 14 (for example, when the image forming apparatus 10 is turned on or The integrated value of the number of transfer materials 28 onto which an image has been transferred / formed by the image forming apparatus 10 reaches a predetermined value). When the image position detection pattern is formed on the transfer belt 14, the position sensor 76 detects the formation position of the image position detection pattern. The density sensor 74 and the position sensor 76 are connected to a control unit 78 configured to include a microcomputer or the like, and output a detection result to the control unit 78.
[0042]
Next, the multiple beam scanning device 30 will be described with reference to FIG. The multi-beam scanning device 30 includes a casing 32 having a substantially rectangular bottom surface. A rotating polygon mirror 34 (corresponding to the deflecting means of the present invention) that is rotated at high speed by a motor (not shown) is provided at a substantially central portion of the casing 32. A laser diode (corresponding to the light source of the present invention: hereinafter referred to as LD) that emits laser light for irradiating the photosensitive drum from one end of the casing 32 to the other end is disposed on the side in the casing 32. 36M, 36K, 36Y, and 36C are arranged in this order.
[0043]
A collimator lens 38K and a plane mirror 40 are arranged in this order on the laser light emission side of the LD 36K. The laser beam K emitted from the LD 36K is collimated by the collimator lens 38K and is incident on the plane mirror 40. Further, a collimator lens 38C and a plane mirror 42 are arranged in this order on the laser light emission side of the LD 36C, and the laser beam C emitted from the LD 36C is reflected by the plane mirror 42 after being collimated by the collimator lens 38C. And is incident on the plane mirror 40.
[0044]
An fθ lens 44 is disposed between the plane mirror 40 and the rotary polygon mirror 34, and the laser beam K and the laser beam C reflected by the plane mirror 40 pass through the fθ lens 44 and enter the rotary polygon mirror 34. After being incident, reflected and deflected by the rotary polygonal mirror 34, it is configured to pass through the fθ lens 44 again (so-called double path configuration).
[0045]
The positions of the LD 36K and LD 36C are different along the axial direction (corresponding to the sub-scanning direction) of the rotary polygon mirror 34, and the laser beam K and the laser beam Y have different incident angles along the sub-scanning direction. 34, the laser beams K and C transmitted twice through the fθ lens 44 are incident on separate plane mirrors 46K and 46C.
[0046]
Then, as shown in FIG. 1, the laser beam K reflected by the plane mirror 46K is reflected by the plane mirror 47K, then enters the cylindrical mirror 48K, and is emitted from the cylindrical mirror 48K toward the photosensitive drum 18K. Then, the surface of the photosensitive drum 18K is scanned. The laser beam C reflected by the flat mirror 46C is reflected by the flat mirror 47C, then enters the cylindrical mirror 48C, is emitted from the cylindrical mirror 48C toward the photosensitive drum 18C, and the circumferential surface of the photosensitive drum 18C. Scanned up.
[0047]
On the other hand, a collimator lens 38Y and a plane mirror 52 are sequentially arranged on the laser beam emission side of the LD 36Y, and the laser beam C emitted from the LD 36Y is made into a parallel light beam by the collimator lens 38Y and is incident on the plane mirror 52. . Further, a collimator lens 38M and a plane mirror 54 are sequentially arranged on the laser light emission side of the LD 36M, and the laser beam M emitted from the LD 36M is converted into a parallel light beam by the collimator lens 38M and then reflected by the plane mirror 54. The light enters the plane mirror 52.
[0048]
An fθ lens 56 is disposed between the plane mirror 52 and the rotary polygon mirror 34, and the laser beam Y and the laser beam M reflected by the plane mirror 52 pass through the fθ lens 56 and enter the rotary polygon mirror 34. After being incident, reflected and deflected by the rotary polygonal mirror 34, the light passes through the fθ lens 56 again.
[0049]
LD36Y and LD36M have different positions along the axial direction (corresponding to the sub-scanning direction) of the rotary polygon mirror 34, and the laser beam Y and the laser beam M have different angles of incidence along the sub-scanning direction. Therefore, the laser beams C and M that have been transmitted twice through the fθ lens 56 are incident on separate plane mirrors 46Y and 46M.
[0050]
The laser beam Y reflected by the flat mirror 46Y is reflected by the reflecting mirror 47Y, then enters the cylindrical mirror 48Y, is emitted from the cylindrical mirror 48Y toward the photosensitive drum 18Y, and the circumferential surface of the photosensitive drum 18Y. Scanned up. The laser beam M reflected by the flat mirror 46M is reflected by the reflecting mirror 47M, then enters the cylindrical mirror 48M, is emitted from the cylindrical mirror 48M toward the photosensitive drum 18M, and the circumferential surface of the photosensitive drum 18M. Scanned up. As apparent from the above, since the laser beams K and C and the laser beams Y and M are incident on the opposing surfaces of the rotary polygon mirror 34, the laser beams K and Y and the laser beams C and M scan in the opposite directions. Is done.
[0051]
Further, on the laser beam K emission side of the flat mirror 46K, a folding mirror 56K is disposed at a position corresponding to a scanning start side end (SOS: Start Of Scan) in the scanning range of the laser beam K. A lens 58K and a beam position detection sensor 60K are sequentially arranged on the laser beam K emission side of 56K. When the laser beam K emitted from the LD 36K reflects the incident beam in a direction corresponding to the SOS, the reflecting surface reflecting the laser beam K among the reflecting surfaces of the rotary polygon mirror 34 is in the direction corresponding to the SOS. The light is reflected by the folding mirror 56K and is incident on the beam position detection sensor 60K.
[0052]
Similarly, on the laser beam C emission side of the flat mirror 46C, a folding mirror 56C is disposed at a position corresponding to the SOS in the scanning range of the laser beam C, and on the laser beam K emission side of the folding mirror 56C. A lens 58C and a beam position detection sensor 60C are arranged in this order. Further, a folding mirror 56M is arranged on the laser beam M emission side of the flat mirror 46M at a position corresponding to the SOS in the scanning range of the laser beam M, and a lens is arranged on the laser beam M emission side of the folding mirror 56M. 58M and beam position detection sensor 60M are arranged in order. Further, a folding mirror 56Y is arranged on the laser beam Y emission side of the flat mirror 46Y at a position corresponding to the SOS in the scanning range of the laser beam Y, and a lens is arranged on the laser beam Y emission side of the folding mirror 56Y. 58Y and the beam position detection sensor 60Y are arranged in order.
[0053]
Next, the beam position detector 62 configured to include the beam position detection sensor 60 will be described. The beam position detector 62 is provided corresponding to each of the laser beams K, C, M, and Y. Since each has the same configuration, the beam position detector 62 will be described below without distinction. .
[0054]
As shown in FIG. 3B, the beam position detection sensor 60 is composed of a cathode common type two-divided photodiode composed of a pair of photodiodes 64A and 64B whose cathodes are connected to each other. As shown in FIG. 3A, each of the light receiving surfaces of the photodiodes 64A and 64B is a laser so that the laser beam incident on the beam position detection sensor 60 sequentially passes through the light receiving surfaces of the photodiodes 64A and 64B. They are arranged with a predetermined gap along the beam scanning direction.
[0055]
  The cathodes of the photodiodes 64A and 64B are connected to a DC power source (not shown), and a constant voltage V is supplied by the DC power source._CCIs applied. The anode of the photodiode 64A is connected to the input end of the amplifier 68A, and the anode of the photodiode 64B is connected to the input end of the amplifier 68B. The output ends of the amplifiers 68A and 68B are respectively connected to the input ends of the signal processing circuit 72, and the signals output from the photodiodes 64A and 64B are given a predetermined gain (by the amplifiers 68A and 68B).RealIn the embodiment, the gains of the amplifiers 68A and 68B are always constant) and are then input to the signal processing circuit 72. The signal processing circuit 72 includes a clamp circuit and a comparator. The signal output from the amplifier 68A is input to the comparator after being clamped by the clamp circuit, and the signal output from the amplifier 68B is input to the comparator. Directly entered.
[0056]
As a result, when the laser beam sequentially passes through the light receiving surfaces of the photodiodes 64A and 64B, the photodiode 64A passes through the amplifier 68A and the clamp circuit, and is expressed as “element A” in FIGS. A signal having a waveform as shown below (hereinafter referred to as sensor output A) is input to the comparator, and is shown as “element B” in FIGS. 10 and 11 through the amplifier 68B from the photodiode 64B. Thus, a signal (hereinafter referred to as sensor output B) having the same waveform as sensor output A and slightly delayed in phase is output. The signal levels of the sensor outputs A and B are slightly different due to the action of the clamp circuit.
[0057]
The comparator of the signal processing circuit 72 compares the signal level of the signal (signal A) input from the amplifier 68A through the clamp circuit and the signal (signal B) input from the amplifier 68B. The output signal (synchronization signal) is set to the high level if it is equal to or lower than the signal level of the signal B, and the output signal (synchronization signal) is set to the low level if the signal level of the signal A is higher than the signal level of the signal B.
[0058]
As a result, the synchronization signal output from the comparator 54 is always at a high level during a period in which the light beam is not incident on the beam position detection sensor 60, as shown in FIGS. Further, during the period when the light beam is incident on the beam position detection sensor 60, the sensor gradually increases the area of the light beam irradiation region on the light receiving surface of the photodiode 64A with the movement of the light beam irradiation position. When the signal level of the output A gradually increases and the signal level of the sensor output A becomes larger than the signal level of the sensor output B, the synchronization signal is switched from the high level to the low level.
[0059]
Further, as the area of the light beam irradiation region on the light receiving surface of the photodiode 64A is gradually reduced along with the movement of the light beam irradiation position, the signal level of the sensor output A also gradually decreases. As the area of the light beam irradiation region on the light receiving surface of the diode 64B gradually increases, the signal level of the sensor output B also gradually increases. Then, at the timing when the center of the light beam irradiation region passes through a predetermined position in the gap between the light receiving surface of the photodiode 64A and the light receiving surface of the photodiode 64B, the signal level of the sensor output A becomes equal to or lower than the signal level of the sensor output B. The synchronization signal returns from the low level to the high level.
[0060]
Next, the control unit 78 will be described with reference to FIG. The control unit 78 is provided with image processing units 80K, 80C, 80M, and 80Y corresponding to the laser beams K, C, M, and Y, respectively. Since the individual image processing units 80 have the same configuration, they will be described below without distinction.
[0061]
As shown in FIG. 4, the image processing unit 80 is provided with a main scanning direction registration deviation correction value calculation unit 82, and a position sensor 76 is connected to the main scanning direction registration deviation correction value calculation unit 82. The main scanning direction registration deviation correction value calculation unit 82 forms an image position detection pattern on the transfer belt 14, and the position of the image position detection pattern is detected by the position sensor 76. When a signal representing the formation position of the pattern along the direction is input from the position sensor 76, a displacement amount (registration displacement amount) of the pattern formation position along the main scanning direction is recognized based on the input signal. Then, a registration correction amount for correcting the registration deviation along the main scanning direction is calculated.
[0062]
The above registration correction amount indicates the timing at which the modulation of the laser beam should be started in order to correct the registration error in each main scanning of the laser beam, and the synchronization signal output from the beam position detector 62 from the high level to the low level. This data is defined by the elapsed time from the timing of switching to the level (reference timing). The main scanning direction registration deviation correction value calculation unit 82 uses the registration correction amount obtained by the calculation as a period corresponding to one period of a pixel clock (a signal representing a modulation period for each pixel of an image in one main scanning). The registration correction amount is divided into a main scanning direction registration deviation coarse correction value (a quotient of division), which is a registration correction value in units of one period of the pixel clock, and a time shorter than one period of the pixel clock. This is broken down into main-scanning direction registration deviation fine correction values (remainder of division) for correcting the corresponding registration deviation.
[0063]
A main scanning direction registration correction value calculation unit 84 is connected to the main scanning direction registration deviation correction value calculation unit 82, and the main scanning direction registration deviation correction value calculation unit 82 includes a main scanning direction registration deviation correction value and a main scanning direction. The direction registration misalignment fine correction value is output to the main scanning direction registration correction value calculation unit 84, and a signal indicating the formation position of the image position detection pattern along the main scanning direction is newly input from the position sensor 76. During the interval, the main scanning direction registration deviation coarse correction value and the main scanning direction registration deviation fine correction value are held in a memory or the like.
[0064]
  As is clear from the above, the position sensor 76 is1The main-scanning-direction registration deviation correction value calculation unit 82 corresponds to the position detection means described in the above.1This corresponds to the image position adjusting means described in (1). Further, the registration correction amounts (scanning direction registration deviation coarse correction value and main scanning direction registration deviation fine correction value) are claimed in claims.1This corresponds to the first control value described in (1).
[0065]
On the other hand, the density sensor 74 is connected to the light amount set value calculation unit 86. The light amount set value calculation unit 86 forms a light amount control pattern on the transfer belt 14, and the concentration sensor 74 detects the concentration of the light amount control pattern, so that a signal indicating the concentration of the light amount control pattern is received by the concentration sensor. When input from 74, the light amount control value of the laser beam for calculating the image density to the desired density is calculated based on the input signal. The light amount set value calculation unit 86 is connected to the LD drive control unit 92 and the main scanning direction registration correction value calculation unit 84, and the calculated light amount control value is sent to the LD drive control unit 92 and the main scanning direction registration correction value calculation unit 84. In addition to the output, the light quantity control value is held in a memory or the like until a signal indicating the density of the light quantity control pattern is newly input from the density sensor 74.
[0066]
  The light quantity set value calculation unit 86 is a light quantity setting means according to the present invention (specifically, claims).3And the density sensor 74 is claimed in the claims.3It corresponds to the concentration detection means described in 1.
[0067]
A clock generator 88 and a write timing setting unit 90 are connected to the main scanning direction registration correction value calculation unit 84. The main-scanning direction registration correction value calculation unit 84 uses the light amount control value input from the light amount setting value calculation unit 86 to generate a reference timing (a synchronization signal output from the beam position detector 62) corresponding to the light amount of the laser beam. An image writing position correction value is calculated in order to eliminate the influence of fluctuations in the timing of switching from the high level to the low level by correcting the image writing position (laser beam modulation start timing) in each main scanning. The calculation of the image writing position correction value will be described later.
[0068]
Subsequently, the main scanning direction registration correction value calculation unit 84 adds the image writing position correction value obtained by the calculation to the main scanning direction registration deviation fine correction value input from the main scanning direction registration deviation correction value calculation unit 82. If this addition causes a carry or a carry (when the main-scanning direction registration misalignment fine correction value is a value of one or more periods of the pixel clock or the sign is negative), the carry is performed. Alternatively, the coarse correction value for the registration error in the main scanning direction is also changed according to the carry-down. Then, the main scanning direction registration correction value calculation unit 84 sets the main scanning direction registration deviation fine correction value to the clock generator 88 after the addition of the image writing position correction value, and sets the main scanning direction registration deviation coarse correction value to the write timing. Output to the unit 90.
[0069]
A beam position detector 62 and a write timing setting unit 90 are connected to the clock generator 88. The clock generator 88 has a function of generating a plurality of pixel clocks having a constant frequency and different phases, and is defined by a synchronization signal input from the beam position detector 62 from among the generated pixel clocks. A pixel clock whose phase is shifted by a time corresponding to the fine correction value in the main scanning direction registration deviation input from the main scanning direction registration correction value calculation unit 84 with respect to the reference timing is selected, and the selected pixel clock is set as a writing timing. Output to the unit 90.
[0070]
A beam position detector 62 and an LD drive control unit 92 are connected to the write timing setting unit 90. The writing timing setting unit 90 counts the pulse of the pixel clock input from the clock generator 88 every time it detects that the reference timing has arrived based on the synchronization signal input from the beam position detector 62, and count value However, when it coincides with the main scanning direction registration deviation rough correction value input from the main scanning direction registration correction value calculation unit 84, by repeating the output of the pixel clock to the LD drive control unit 92, in each main scanning A write synchronization signal that defines the modulation timing for each pixel of the image is supplied to the LD drive controller 92.
[0071]
The LD drive control unit 92 is connected to the light amount set value calculation unit 86 and the LD drive circuit 94, and further represents an image of a specific color component (K / C / M / Y) among images to be recorded. Image data is input. The LD drive control unit 92 writes each pixel of the input image data based on the write synchronization signal input from the write timing setting unit 90 and the light amount setting value input from the light amount setting value calculation unit 86. A drive control signal for recording with a laser beam having a light amount using the input light amount setting value as a reference light amount is generated at a timing synchronized with the embedded synchronization signal, and is output to the LD drive circuit 94.
[0072]
The LD drive circuit 94 is connected to the LD 36, and the LD drive circuit 94 drives the LD 36 based on the drive control signal input from the LD drive control unit 92 and modulates the laser beam emitted from the LD 36. As described above, the write timing setting unit 90, the LD drive control unit 92, and the LD drive circuit 94 correspond to the modulation unit of the present invention, and the LD drive control unit 92 also has a function as the light amount adjustment unit of the present invention. ing.
[0073]
By performing the above-described processing in the image processing units 80K, 80C, 80M, and 80Y, the lasers modulated from the LDs 36K, 36C, 36M, and 36Y according to the corresponding color component image among the images to be formed. Each of the beams is emitted, and each of these laser beams is deflected by a single rotating polygonal mirror 34 and directed toward the corresponding photosensitive drum 18 through optical components such as an fθ lens 44 (or 56) and a cylindrical mirror 48. The circumferential surface of the photosensitive drum 18 that has been ejected and charged by the charger 20 is scanned.
[0074]
The electrostatic latent image formed on the peripheral surface of the photosensitive drum 18 by scanning with the laser beam is developed as a different color toner image by the developing device 22, and the toner image of each color is transferred to the belt surface of the transfer belt 14. The color image formed by superimposing the image is transferred to the transfer material 28. Then, the transfer material 28 onto which the color image has been transferred is discharged out of the image forming apparatus 10 through a fixing process.
[0075]
  next,RealAs an operation of the embodiment, calculation of the writing position correction value in the main scanning direction registration correction value calculation unit 84 will be described. The timing at which the beam position detector 62 detects the laser beam, that is, the timing at which the synchronization signal output from the beam position detector 62 switches from the high level to the low level is the amount of light of the laser beam incident on the beam position detector 62. With respect to the change, it changes as shown in FIG.
[0076]
As is clear from FIG. 5A, the timing at which the beam position detector 62 detects the laser beam is within the predetermined range (the range indicated as “appropriate amount of light” in the drawing) of the incident laser beam. If there is a change in the amount of light, it hardly changes, but if the amount of light is larger than the upper limit value of the predetermined range or smaller than the lower limit value of the predetermined range, the difference in the light amount with respect to the upper limit value or the lower limit value becomes large. Accordingly, it can be understood that the delay of the laser beam detection timing increases.
[0077]
The characteristics shown in FIG. 5A differ depending on the type of photoelectric conversion element (photodiode) used as the beam position detector 62. However, if the photoelectric conversion elements have the same type, the characteristics are almost the same. Indicates. Further, the delay time slightly changes depending on external factors such as temperature, but in an environment where the image forming apparatus 10 is actually used, a value that can be ignored as compared with the change in the delay time accompanying the change in the light amount. This has been confirmed by the present inventors.
[0078]
  In the beam position detector 62 used in this embodiment, the light amount of the laser beam is higher than the upper limit value of the predetermined range.largeSince the delay time in the area and the area where the laser beam light quantity is smaller than the lower limit of the predetermined range shows a characteristic that changes almost linearly with respect to the change in the laser beam light quantity, the writing position correction value The correction amount y can be approximated by the linear expression y = ax + b, where y is the correction amount (time) due to x and x is the amount of laser beam.
[0079]
  Based on the above,RealThe main scanning direction registration correction value calculation unit 84 according to the embodiment corresponds to the light amount setting value input from the light amount setting value calculation unit 86 as the light amount value c corresponding to the upper limit value of the predetermined range and the lower limit value of the predetermined range. Each is compared with the light amount value d (see FIG. 5B), and the following calculation is performed according to the comparison result to obtain the correction amount y based on the writing position correction value.
[0080]
When the light amount setting value ≦ d Correction amount: y = a′x + b ′
When d <light intensity setting value <c Correction amount: y = 0
When the light quantity setting value ≧ c Correction amount: y = ax + b
It should be noted that the coefficients a and a ′ and the constants b and b ′ in the above arithmetic expression are obtained through experiments and stored in advance in the memory of the main scanning direction registration correction value calculation unit 84.
[0081]
The main scanning direction registration correction value calculation unit 84 uses the registration position correction value calculated by the main scanning direction registration error correction value calculation unit 82 (specifically, the main scanning direction registration error) as the write position correction value obtained as described above. The final registration correction amount in the main scanning direction is calculated by adding to (fine correction value). In addition, when the light quantity setting value input from the light quantity setting value calculation unit 86 is monitored and it is detected that the light quantity setting value has been updated, the final registration correction is performed using the updated latest light quantity setting value. The amount is calculated.
[0082]
  Accordingly, the light amount setting value is changed and set by the light amount setting value calculation unit 86, and the light amount of the laser beam incident on the beam position detector 62 is changed accordingly, thereby causing a delay in the laser beam detection timing. Even when the delay time of the laser beam detection timing changes, the time from the reference timing to the start of the modulation of the laser beam is corrected so that the deviation of the image forming position due to this delay is corrected. (See also FIG. 5B). As mentioned above,RealThe main scanning direction registration correction value calculation unit 84 according to the embodiment is a control unit according to claim 1.In stepsIt corresponds.
[0083]
  Further, the calculation of the writing position correction value and the final registration correction amount by the main scanning direction registration correction value calculation unit 84 are performed for the individual image processing units 80K corresponding to the laser beams K, C, M, and Y. , 80C, 80M, and 80Y in the main scanning direction registration correction value calculation unit 84, respectively (accordingly,RealThe main-scanning direction registration correction value calculation unit 84 according to the embodiment includes:2Therefore, even when the light amount setting value is changed only for a part of the laser beams, each color component formed by each laser beam is not affected by this. An image can always be formed at a fixed position, and color misregistration of a color image formed on the transfer belt 14 and transferred to the transfer material 28 can be prevented.
[0084]
  In addition,RealIn the embodiment, in the region where the light amount of the laser beam is smaller than the upper limit value of the predetermined range and the region where the light amount of the laser beam is smaller than the lower limit value of the predetermined range, the delay time of the laser beam detection timing by the beam position detector 62 is By using the characteristic that changes almost linearly with respect to the change in the light amount of the laser beam, the correction amount (time) y based on the writing position correction value is used as a linear expression y = ax + b regarding the light amount x of the laser beam. However, the present invention is not limited to this, and the relationship between the light amount of the laser beam and the delay time of the laser beam detection timing shows a characteristic that is difficult to approximate with an equation, or If approximation is possible but the approximation formula becomes very complex, the relationship between the amount of laser beam light and the delay time of the laser beam detection timing, for example, Stored in a look-up table to fit measured by reading the delay time corresponding to the current amount of the laser beam from the look-up table may be determined writing out position correction value.
[0085]
Even in this aspect, the data corresponding to a predetermined range in which the laser beam detection timing of the beam position detector 62 hardly changes regardless of the change in the light amount of the laser beam is not stored in the look-up table, and the light amount of the laser beam is reduced. If it is within the predetermined range, the writing position correction value may be set to 0 (no correction) to reduce the scale (data amount) of the lookup table.
[0086]
  [First comparative example]
  Next, the present inventionFirst comparative exampleWill be described. In addition, RealThe same parts as those in the embodiment are denoted by the same reference numerals and the description thereof is omitted., RealOnly portions different from the embodiment will be described.
[0087]
  As shown in FIG.First comparative exampleIn the image processing unit 80 according to the above, the main scanning direction registration correction value calculation unit 84 is not connected to the light amount setting value calculation unit,First comparative exampleIn the main scanning direction registration correction value calculation unit 84 related to, RealProcessing such as calculation of the writing position correction value and addition of the writing position correction value to the registration correction value calculated by the main-scanning direction registration deviation correction value calculation unit 82 described in the embodiment is not performed.
[0088]
  On the other hand, bookFirst comparative exampleA gain control unit 96 is connected to the light quantity set value calculation unit 86 related to the above, and the gain control unit 96 is connected to the beam position detector 62. BookFirst comparative exampleThen, as the amplifiers 68A and 68B of the beam position detector 62, an amplifier whose gain can be changed continuously or stepwise by a gain switching signal from the outside is used (see FIG. 3B). When the light intensity setting value input from the light intensity setting value calculation unit 86 is compared with a predetermined value, if the light intensity setting value is less than the predetermined value, the gains of the amplifiers 68A and 68B are increased, and the light intensity setting value is greater than or equal to the predetermined value. Sets the gains of the amplifiers 68A and 68B to a small value.
[0089]
As a result, when the light amount of the laser beam incident on the beam position detector 62 is smaller than the lower limit value of the predetermined range in which the delay of the laser beam detection timing does not occur, the gains of the amplifiers 68A and 68B are increased. Thus, the amplitude of the signal input to the signal processing circuit 72 from the amplifiers 68A and 68B increases. Further, when the light amount of the laser beam is larger than the upper limit value of a predetermined range in which the delay of the laser beam detection timing does not occur, the gains of the amplifiers 68A and 68B are reduced, so that the signal processing circuits from the amplifiers 68A and 68B. The amplitude of the signal input to 72 is reduced.
[0090]
  Therefore, as shown in FIG. 7 as an example, the range in which the delay of the laser beam detection timing does not occur (laser beam light amount range) is greatly expanded, and the image forming position is changed with the change in the light amount of the laser beam. It is possible to suppress the occurrence of deviation over a wide light amount range.. MaSince the gains of the amplifiers 68A and 68B of the beam position detector 62 described above are switched independently by the individual image processing units 80K, 80C, 80M, and 80Y., RealSimilar to the embodiment, the image of each color component formed by each laser beam can always be formed at a fixed position, and the color shift of the color image formed on the transfer belt 14 and transferred to the transfer material 28 can be reduced. Can prevent the occurrenceThe
[0091]
  In addition,First comparative exampleIn the above description, the case where the gains of the amplifiers 68A and 68B are switched to two stages has been described as an example. However, the gains may be switched to a larger number of stages according to the light amount of the laser beam. The gain is continuously changed according to the light amount of the laser beam so that the amplitude of the signal inputted to the laser beam becomes substantially constant regardless of the light amount of the laser beam incident on the beam position detector 62. Good.
[0092]
  [Second comparative example]
  Next, the present inventionSecond comparative exampleWill be described. In addition,First comparative exampleThe same reference numerals are given to the same parts as in FIG.First comparative exampleOnly different parts will be described.
[0093]
  BookSecond comparative exampleThe multi-beam scanning device 30 according to the above has an attenuation factor for the transmitted laser beam K from the outside on the optical path through which the laser beam K passes when the laser beam K is reflected by the rotary polygon mirror 34 in the direction corresponding to SOS. An optical attenuator 100K that can be changed continuously or stepwise is disposed (not shown). The optical attenuator 100K may be disposed between the rotary polygon mirror 34 and the beam position detection sensor 60K, between the rotary polygon mirror 34 and the plane mirror 46K, and between the plane mirror 46K and the folding mirror 56K. It may be arranged at any position between the folding mirror 56K and the lens 58K and between the lens 58K and the beam position detection sensor 60K. As the optical attenuator 100K, for example, an attenuator using twisted nematic liquid crystal can be used. The twisted nematic liquid crystal can change the attenuation rate (light transmittance) to 0 to nearly 100% by controlling the applied voltage.
[0094]
Although not shown, the laser beams C, M, and Y are also connected to the optical attenuator 100K on the optical path through which each laser beam passes when reflected by the rotary polygon mirror 34 in the direction corresponding to the SOS. Optical attenuators 100C, 100M, and 100Y having the same configuration are disposed.
[0095]
  BookSecond comparative exampleIn the image processing unit 80 according toFirst comparative exampleAn optical attenuator control unit 98 is provided in place of the gain control unit 96 described in the section 1. The optical attenuator control unit 98 is connected to the light amount set value calculation unit 86 and to the optical attenuator 100. Has been. The optical attenuator control unit 98 compares the light amount setting value input from the light amount setting value calculation unit 86 with a predetermined value. For example, when the light amount setting value is less than the predetermined value, the attenuation rate of the laser beam by the optical attenuator 100 is increased. When the light amount setting value is equal to or greater than a predetermined value, control is performed so that the attenuation rate of the laser beam by the optical attenuator 100 is increased.
[0096]
  Thus, the light amount of the laser beam incident on the beam position detector 62 is set to a value within a predetermined range in which the delay of the laser beam detection timing does not occur regardless of the light amount setting value calculated by the light amount setting value calculation unit 86. Therefore, it is possible to prevent the image forming position from being shifted due to the change in the light amount of the laser beam emitted from the LD 36.. MaThe above-described control of the attenuation rate of the laser beam by the optical attenuator 100 is performed independently by the individual image processing units 80K, 80C, 80M, and 80Y., RealForm andFirst comparative exampleIn the same manner as described above, the image of each color component formed by each laser beam can always be formed at a fixed position, and the color misregistration of the color image formed on the transfer belt 14 and transferred to the transfer material 28 can be prevented. Can preventThe
[0097]
  In the second comparative example, the case where the attenuation rate of the laser beam by the optical attenuator 100 is switched to two levels has been described as an example. However, the attenuation rate is switched to a larger number of levels according to the light amount setting value of the laser beam. Alternatively, the attenuation rate by the optical attenuator 100 is continuously changed according to the light amount setting value so that the light amount of the laser beam incident on the beam position detector 62 becomes substantially constant regardless of the light amount setting value. You may make it do.
[0098]
In the above description, the laser beam is detected by the beam position detection sensor 60 (light beam detector) including a plurality of photoelectric conversion elements (photodiodes 64A and 64B) arranged along the scanning direction of the laser beam. However, the present invention is not limited to this, and the present invention can also be applied to a case where a laser beam is detected by a single photoelectric conversion element.
[0099]
In the above description, as the image forming apparatus according to the present invention, a light beam scanning device that deflects and scans a light beam deflects a plurality of light beams by a single deflecting unit, and a plurality of photosensitive members have different color components. The tandem type color image forming apparatus that forms a color image by superimposing the images of the respective color components after forming the image is described as an example, but the present invention is not limited to this. Needless to say, the present invention can also be applied to a color image forming apparatus that deflects the light beam, a color image forming apparatus that forms a color image by another method, and an image forming apparatus that forms a monochrome image.
[0100]
【The invention's effect】
  As described above, the invention described in claim 1The position of the image formed by the light beam scanning on the photoconductor is detected, and the first control value for adjusting the modulation start timing of the light beam is set based on the detected image position. The second control value for adjusting the modulation start timing of the light beam, and when the light amount setting value by the light amount setting means is within a predetermined range, the correction amount of the modulation start timing by the second control value is 0, and the light amount When the set value is larger than the upper limit value of the predetermined range or smaller than the lower limit value of the predetermined range, the modulation start timing of the second control value increases as the difference between the light amount set value and the upper limit value or lower limit value increases. A correction amount is set to be large, and a timing delayed by a time corresponding to a value obtained by adding the first control value and the second control value to the timing at which the light beam is detected by the light beam detector. To start modulation of the light beam at timingTherefore, with a simple configuration, fluctuations in the image forming position due to changes in the light amount of the light beam can be reduced.AccurateIt has an excellent effect that it can be suppressed.
[0105]
  Claim2The described invention is claimed.1In the invention described above, a plurality of light beams for forming a plurality of images of different colors that are finally superimposed as a color image are respectively emitted from the light source, and the change of the light amount setting value by the light amount setting means is monitored. Since only the light beam whose light amount setting value has been changed, either the modulation timing change by the modulation means, the gain change of the amplifier of the light beam detector, or the light amount attenuation change by the optical attenuator is performed. In addition to the effect, there is an effect that it is possible to prevent color misregistration from occurring on a color image that is finally formed due to a change in the light amount of the light beam.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a color image forming apparatus (and a multiple beam scanning apparatus) according to an embodiment.
FIG. 2 is a schematic plan view of a multiple beam scanning device.
3A is a plan view showing the arrangement of light receiving surfaces of a pair of photodiodes of a beam position detection sensor, and FIG. 3B is a circuit diagram of the beam position detection sensor.
[Fig. 4]FruitIt is a block diagram which shows schematic structure of the control part which concerns on embodiment.
5A is a diagram showing a change in laser beam detection timing accompanying a change in the amount of laser beam, and FIG. 5B is a line for explaining the calculation of the write position correction value according to the first embodiment. FIG.
[Fig. 6]First comparative exampleIt is a block diagram which shows schematic structure of the control part which concerns on.
FIG. 7 is a diagram showing a change in the relationship between the light amount of a laser beam and the laser beam detection timing in accordance with the gain switching of the amplifier of the beam position detector.
[Fig. 8]Second comparative exampleIt is a block diagram which shows schematic structure of the control part which concerns on.
FIG. 9 is a diagram for explaining a shift in the signal level switching timing of the synchronization signal accompanying a change in the light amount of the light beam in the light beam detector composed of a single photoelectric conversion element;
FIG. 10 is a diagram showing an example of output signals and synchronization signals of individual elements in a light beam detector composed of a plurality of photoelectric conversion elements.
FIG. 11 is a diagram for explaining a shift in the signal level switching timing of the synchronization signal accompanying a change in the light amount of the light beam in the light beam detector including a plurality of photoelectric conversion elements;
[Explanation of symbols]
      10 Color image forming apparatus
      34 Rotating polygon mirror
      60 Beam position detection sensor
      62 Beam position detector
      68 Amplifier
      74 Concentration sensor
      76 Position sensor
      80 Image processing unit
      82 Main scanning direction registration error correction value calculator
      84 Main scanning direction registration correction value calculator
      86 Light intensity set value calculation means
      86 Light intensity setting value calculator
      96 Gain controller
      98 Optical attenuator controller
    100 optical attenuator

Claims (3)

A light source that emits a light beam;
Deflecting means for deflecting the light beam so that the light beam emitted from the light source scans on the photoreceptor;
A light beam detector for detecting the light beam deflected by the deflecting means at a specific position within a scanning range of the light beam;
Modulation means for modulating the light beam emitted from the light source at a predetermined timing based on the timing at which the light beam is detected by the light beam detector;
A light amount setting means for setting a light amount of a light beam emitted from the light source;
A light amount adjusting means for adjusting the light amount of the light beam emitted from the light source so as to coincide with the light amount set by the light amount setting means;
Position detecting means for detecting the position of an image formed by the light beam scanning on the photosensitive member;
Image position adjusting means for setting a first control value for adjusting the modulation start timing of the light beam by the modulating means based on the position of the image detected by the position detecting means;
The second control value for adjusting the modulation start timing of the light beam by the modulation means, and the modulation start timing correction by the second control value when the light quantity setting value by the light quantity setting means is within a predetermined range. When the amount is 0 and the light amount setting value is larger than the upper limit value of the predetermined range or smaller than the lower limit value of the predetermined range, the difference between the light amount setting value and the upper limit value or the lower limit value is large. The amount of correction of the modulation start timing by the second control value is set so as to increase, and the first control value and the second control value with respect to the timing at which the light beam is detected by the light beam detector. Control means for starting modulation of the light beam by the modulation means at a timing delayed by a time corresponding to a value obtained by adding
An image forming apparatus including: The light source respectively emits a plurality of light beams for forming a plurality of images of different colors, which are finally superimposed as a color image,
The deflecting means deflects the plurality of light beams such that the plurality of light beams emitted from the light source respectively scan the photoreceptor.
The light beam detector detects a plurality of light beams deflected by the deflecting means at specific positions within a scanning range of each light beam,
The modulation means modulates each of a plurality of light beams emitted from the light source at a predetermined timing based on a timing at which the light beam is detected by a corresponding light beam detector,
The light amount setting means sets the light amounts of a plurality of light beams emitted from the light source independently for each light beam,
The light amount adjusting means adjusts the light amounts of a plurality of light beams emitted from the light source so as to coincide with the light amounts independently set for each individual light beam by the light amount setting means,
Wherein the control means monitors the change of light quantity set value of the light amount setting device, the light beam light quantity setting value is changed only, claim 1 Symbol which is characterized in that the change of the modulation timing by the modulating means The image forming apparatus. A density detector for detecting a density of an image formed by the light beam scanning on the photoconductor;
The light amount setting means, on the basis of the concentration detected by the concentration detection means calculates the optimum value of the quantity of the light beam emitted from the light source, according to claim 1, characterized in that setting the calculated optimum value serial mounting the image forming apparatus.

Images