JP3600024B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a printer that performs recording by scanning a recording medium with a plurality of beams.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image forming apparatus such as a copying machine or a printer that scans a recording medium with a beam to record information, deflects and scans a single beam modulated with an information signal using a rotary polygon mirror or the like, and the rotary polygon mirror. A device that records information by repeatedly scanning in the main scanning direction on a recording medium that moves in the sub-scanning direction by using a scanning beam from the like or the like is used. In this image forming apparatus, a scanning beam from a rotary polygon mirror or the like is detected by a beam detector outside a recording area, and the start of image formation by a beam is controlled by a beam detection signal from the beam detector.
[0003]
In a multi-beam optical system, a plurality of beams modulated by individual information signals are deflected and scanned almost simultaneously by a rotating polygon mirror or the like, and are scanned in the sub-scanning direction by a plurality of scanning beams from the rotating polygon mirror or the like. 2. Description of the Related Art An image forming apparatus has been proposed in which information is recorded by repeatedly scanning a moving recording medium at substantially the same time in parallel with a main scanning direction. In this image forming apparatus, a plurality of scanning beams from a rotary polygon mirror or the like are respectively detected by a plurality of beam detection elements outside a recording area, and image formation by each beam is started by a beam detection signal from the plurality of beam detection elements. Each is controlled.
[0004]
Japanese Patent Application Laid-Open No. 57-8887 discloses a write / write position control method for controlling a write / write position of an image in an image forming apparatus that records information by scanning a recording medium with a plurality of beams. In this writing / writing position control method, a timing signal corresponding to each beam is generated by slicing a beam detection signal from a beam detector at a slice level, and the writing / writing position of an image is controlled by the timing signal. .
[0005]
Japanese Patent Application Laid-Open No. 6-206343 discloses an image forming apparatus that scans a recording medium with a plurality of beams from a semiconductor laser to record information by using a semiconductor having a cycle shorter than the cycle of a pixel clock. It is described that a synchronization signal corresponding to each beam is generated by controlling on / off of a laser, and the start of image formation by each beam is controlled by the synchronization signal.
[0006]
[Problems to be solved by the invention]
2. Description of the Related Art Conventionally, an image forming apparatus that scans a recording medium with a beam to record information, deflects and scans a single beam modulated by an information signal with a rotating polygon mirror or the like, and scans the scanning beam from the rotating polygon mirror or the like. Therefore, since information is recorded by repeatedly scanning in the main scanning direction on the recording medium moving in the sub-scanning direction, when recording information at high speed, or when performing high-density image formation, It is necessary to increase the transfer rate of the information signal for modulating the beam.
[0007]
Further, since the scanning speed in the main scanning direction must be increased, when a rotating polygon mirror is used, the number of revolutions may need to be tens of thousands of rpm. There is naturally a limit in its structure. Therefore, in a multi-beam optical system, a plurality of beams modulated by individual information signals are deflected and scanned almost simultaneously by a rotating polygon mirror or the like, and a plurality of scanning beams from the rotating polygon mirror or the like are used in the sub-scanning direction. 2. Description of the Related Art An image forming apparatus has been proposed in which information is recorded by repeatedly scanning a moving recording medium at substantially the same time in parallel with a main scanning direction.
[0008]
In this image forming apparatus, as shown in FIG. 5, it is necessary to arrange the intervals of the plurality of beams B1 to B4 equal to the intervals of the pixels formed on the recording medium. On the other hand, the light emitting point interval of a semiconductor laser generally used as a beam light source for generating the beams B1 to B4 is generally wider than the pixel interval required for an apparatus having a resolution of 600 dpi which is currently mainstream. . Therefore, as shown in FIG. 5, the arrangement of the light emitting points (beams B1 to B4) is inclined by a predetermined angle θ1 with respect to a straight line LL ′ perpendicular to the main scanning direction SL, so that the light emitting point interval P1 is Even if the interval is wider than the interval Ps, the beam interval on the recording medium can be set to Ps.
[0009]
However, in a general multi-beam optical system in which the above-described beams B1 to B4 must be arranged close to each other and scanned, for example, when the resolution is 600 dpi, the interval Ps between the beams B1 to B4 is Since it must be adjusted to about 42.3 μm, it is difficult to arrange a plurality of synchronous detection elements for detecting each beam on the scanning optical path. Therefore, a plurality of beams scan on the same synchronous detection element, and the beam detection signal from one synchronous detection element is as shown in FIG.
[0010]
In order to accurately align the exposure start position (image formation start position) of the recording medium with each beam, a plurality of beam detection signals corresponding to a plurality of beams from one synchronous detection element are accurately separated, and each beam is separated. It is necessary to determine the exposure start position (image formation start position) by the beam modulated by the information signal based on the detection signal.
[0011]
In the write / write position control method disclosed in Japanese Patent Application Laid-Open No. 57-8887, a timing signal corresponding to each beam is generated by slicing a beam detection signal from a beam detector at a slice level. Although the image writing / writing position is controlled by the timing signal, since the slice level is determined in an analog manner, it is easily affected by fluctuations in the power supply and the like. Does not go up.
[0012]
In the image forming apparatus described in JP-A-6-206343, on / off of the semiconductor laser is controlled using a clock having a cycle shorter than the cycle of the pixel clock, so that a synchronization corresponding to each beam is controlled. Since a signal is created and the start of image formation by each beam is individually controlled by this synchronization signal, a high-frequency oscillator is required as an oscillator for generating a basic clock, and a high-frequency compatible control circuit such as a flip-flop or counter is selected. There must be. For this reason, there is a problem that the cost increases and the radio wave radiation increases.
[0013]
According to the first aspect of the present invention, the image writing position can be accurately controlled at a low cost, a good output image can be obtained, and the mixing of external noise can be prevented, and the image writing position can be accurately controlled. It is an object of the present invention to provide an image forming apparatus capable of performing the above operation and stably obtaining a good output image.
According to the second aspect of the present invention, it is possible to accurately separate a plurality of beam detection signals even when the number of rotations of a rotating polygon mirror is changed in accordance with a change in setting of resolution or the like, and to perform optimal image writing position control. It is an object of the present invention to provide an image forming apparatus capable of performing the following.
A third object of the present invention is to provide an image forming apparatus capable of accurately separating a plurality of beam detection signals.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is an image forming apparatus which performs recording by scanning a recording medium with a plurality of beams modulated by individual information signals, wherein each of the plurality of beams is a predetermined beam. Beam detecting means for detecting arrival at a position and generating a plurality of beam detecting signals corresponding to the respective beams; and beam detecting signal separating means for separating the plurality of beam detecting signals, respectively. In an image forming apparatus that controls the start of image formation by the plurality of beams based on each signal separated by the signal separation unit, the beam detection signal separation unit delays a beam detection signal from the beam detection unit Delay means for generating a plurality of masking signals corresponding to the plurality of beam detection signals based on signals from the delay means; Means for separating a plurality of beam detection signals corresponding to the plurality of beams by masking the beam detection signals from the beam detection means with a plurality of masking signals, respectively, and a delay for setting and varying a delay time of the delay means And time setting means.
[0015]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes: a rotary polygon mirror for scanning the plurality of beams; The time setting means sets and varies the delay time of the delay means according to the number of rotations of the rotary polygon mirror set by the setting means.
[0016]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the plurality of beams sequentially enter the beam detecting unit and are detected, the beams incident on the beam detecting unit are turned off immediately. And control means for turning on a beam next to the turned-off beam of the plurality of beams.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 3 shows an embodiment of the present invention. The light source unit 1 includes, for example, an array laser in which light sources including a plurality of semiconductor lasers are arranged in a line, and emits a plurality of light beams, for example, four light beams. The plurality of divergent lights from the light source unit 1 are converted into parallel light beams by the condenser lens 2. A plurality of light beams from the condenser lens 2 are deflected and scanned by a rotary polygon mirror 3 as a deflection scanner so that the light beams are repeatedly scanned on a photoreceptor 4 as a recording medium at substantially the same time in parallel with the main scanning direction. .
[0018]
The plurality of scanning light beams from the rotating polygon mirror 3 are imaged on the photoconductor 4 by the fθ lens 5. The photoconductor 4 is, for example, a photoconductor drum, and is rotationally driven by a driving unit including a motor. The reflecting mirror 6 is arranged at the tip of the scanning line (outside the image writing area) to guide the plurality of light beams from the rotary polygon mirror 3 to the beam detecting means 7 including a beam detector as a synchronous detecting means, and has an fθ lens. When scanned with the light beam from 5, the light beam is reflected toward the beam detector 7.
[0019]
When the light beam from the reflecting mirror 6 is incident on the edge of the beam detector 7, the beam detector 7 starts detecting the light beam and generates a beam detection signal. The beam detection signal from the beam detector 7 is input to a synchronization detection signal generation circuit 8, and the synchronization detection signal generation circuit 8 separates a plurality of beam detection signals corresponding to a plurality of light beams from the beam detector 7 into a plurality of beams. (Also referred to as a synchronization detection signal).
[0020]
An image data control circuit 9 as a control unit converts image data as an information signal for modulating a plurality of beams into a light source based on a plurality of synchronization signals corresponding to the plurality of light beams from the synchronization detection signal generation circuit 8, respectively. By outputting to the laser driver circuit 10 as a driving means, the start of image formation by a plurality of beams is respectively controlled based on a plurality of synchronization signals corresponding to a plurality of light beams, and the photoconductor 4 is controlled by the plurality of light beams. Despite the scanning, the image writing position by each light beam is accurately aligned.
[0021]
The laser driver circuit 10 drives a plurality of semiconductor lasers in the light source unit 1 with each image data for modulating a plurality of beams from the image data control circuit 9, and the plurality of semiconductor lasers modulate the plurality of beams. A light beam individually modulated with image data to be emitted is emitted. The rotary polygon mirror 3 is rotationally driven by a drive unit composed of a motor (not shown). The motor has a rotational speed set and variable by a rotary polygon mirror rotational speed setting circuit 11 as setting means for setting and changing the rotational speed of the rotary polygon mirror 3. To rotate the rotating polygon mirror 3.
[0022]
FIG. 4 shows the configuration of the synchronization detection signal generation circuit 8. The beam detection signal from the beam detector 7 is binarized by a binarization circuit 12 as binarization means and shaped into a pulsed beam detection signal as shown in FIG. The beam detection signal from the binarization circuit 12 is a pulse signal that is continuous by the number of light beams emitted from the light source unit 1 and is generated every time the rotary polygon mirror 3 scans a line. The synchronization signal separation circuit 13 separates the beam detection signal from the binarization circuit 12 to generate a synchronization signal.
[0023]
FIG. 1 shows the configuration of the synchronization signal separation circuit 13, and FIG. 2 shows the operation timing of the synchronization signal separation circuit 13. The set (SET) signal is generated by the image data control circuit 9 based on the synchronization detection signal generated from the synchronization detection signal generation circuit 8 in the previous line scanning and outside the image output (except when writing the image). It is generated by measuring the timing immediately before the synchronization detection (light beam detection) by the beam detector 7.
[0024]
First, in the operation relating to the first light beam B1, an RS-flip-flop (hereinafter referred to as F / F) 20 as a control means for turning on / off the first light beam is set by a SET signal from the image data control circuit 9. As a result, the output signal a becomes high level, and the output signal a of the F / F 20 is output to the image data control circuit 9 as an ON / OFF signal for turning on / off the first light beam B1. The image data control circuit 9 outputs an ON / OFF signal a from the F / F 20 to the laser diode circuit 10 as a first light beam synchronization detection modulation signal, and the laser diode circuit 10 receives the ON / OFF signal a from the image data control circuit 9. The first light beam B1 is turned on by driving the first semiconductor laser of the light source unit 1 by the first light beam synchronization detection modulation signal a to turn on the first semiconductor laser.
[0025]
When the first light beam B1 passes through the beam detector 7, a beam detection signal b is output from the binarization circuit 11. The beam detection signal b from the binarization circuit 11 is converted to an extremely small time (a time shorter than the time until the next light beam B2 passes through the beam detector 7) by a delay (Delay) circuit 21 as delay means. ), And is delayed to become signal c. The one-shot multivibrator 22 is triggered by the rising edge of the first pulse signal of the output signal c of the delay circuit 21 so that the output signal becomes low level. Only maintain the low level state and then go to the high level.
[0026]
Here, the time set for the one-shot multivibrator 22 is sufficiently longer than the time when all of the plurality of light beams B1 to B4 pass over the beam detector 7 in a state where the rotary polygon mirror 3 is constantly rotating. Set the time. Further, the one-shot multivibrator 22 and the inverter 23 constitute a masking signal generating means.
[0027]
Gate means 24 composed of an AND circuit as a masking means receives the output signal of the one-shot multivibrator 22 as a gate signal (masking signal) and responds to the light beams B1 to B4 from the binarization circuit 11 by the gate signal. By gating (masking) the detected beam detection signal b, the beam detection signal corresponding to the first light beam B1 is separated, and the F / F 20 and the image data are output as a synchronization signal e corresponding to the first light beam B1. Output to the control circuit 9. The F / F 20 is reset by the output signal e of the AND circuit 24, and the first light beam B1 is turned off.
[0028]
The image data control circuit 9 outputs the image data as the first light beam modulation information signal to the laser diode circuit 10 in synchronization with the synchronization signal e from the AND circuit 24 (with a certain time delay from the synchronization signal e). Thus, the start of image formation (start of exposure) by the first light beam B1 is controlled based on the synchronization signal e. The laser diode circuit 10 drives the first semiconductor laser of the light source unit 1 with the image data as the first light beam modulation information signal from the image data control circuit 9, so that the first semiconductor laser modulated by the image data Out of the light beam B1.
[0029]
Next, in the operation relating to the second light beam B2, the F / F 25 serving as control means for turning on / off the second light beam is set by the output signal e of the AND circuit 24, and the output signal f of the F / F 25 is It is output to the image data control circuit 9 as an ON / OFF signal for turning on / off the second light beam B2. The image data control circuit 9 outputs the ON / OFF signal f from the F / F 25 to the laser diode circuit 10 as a second light beam synchronization detection modulation signal, and the laser diode circuit 10 outputs the ON / OFF signal f from the image data control circuit 9. The second semiconductor laser of the light source unit 1 is driven by the synchronization detection modulation signal f for the second light beam to turn on the second semiconductor laser, thereby turning on the second light beam B2.
[0030]
When the second light beam B2 passes through the beam detector 7, the binarization circuit 11 outputs a beam detection signal b. The gate means 26 composed of an AND circuit as a masking means receives the output signal d of the one-shot multivibrator 22 after being inverted by an inverter 23 as an inverting means and inputs the inverted signal d. The beam detection signal b corresponding to the light beams B1 to B4 is gated to separate the beam detection signal g corresponding to the light beams B2 to B4.
[0031]
The beam detection signal g corresponding to the light beams B2 to B4 from the AND circuit 26 is processed by a delay (Delay) circuit 27 as a delay means for a very short time (until the next light beam B3 passes through the beam detector 7). (Time shorter than the time), the signal h is delayed. The one-shot multivibrator 28 is triggered by the rising edge of the first pulse signal of the output signal h of the delay circuit 27, the output signal becomes low level, and thereafter, the output signal is set to the one-shot multivibrator 28 for a period of time. Only maintain the low level state and then go to the high level.
[0032]
Here, the time set in the one-shot multivibrator 28 is sufficiently longer than the time when all of the plurality of light beams B2 to B4 pass on the beam detector 7 in a state where the rotary polygon mirror 3 is constantly rotating. Set the time. Further, the one-shot multivibrator 28 and the inverter 29 constitute a masking signal generating means.
[0033]
The gate means 30 composed of an AND circuit as a masking means receives the output signal i of the one-shot multivibrator 28 as a gate signal (masking signal). The gate signal corresponds to the light beams B2 to B4 from the AND circuit 26. By gating (masking) the beam detection signal g, the beam detection signal corresponding to the second light beam B2 is separated and the F / F 25 and the image data control are performed as the synchronization signal j corresponding to the second light beam B2. Output to the circuit 9. The F / F 25 is reset by the output signal j of the AND circuit 30, and the second light beam B2 is turned off.
[0034]
The image data control circuit 9 outputs image data as a second light beam modulation information signal to the laser diode circuit 10 in synchronization with the synchronization signal j from the AND circuit 30 (with a certain time delay from the synchronization signal j). Thus, the start of image formation (start of exposure) by the second light beam B2 is controlled based on the synchronization signal j. The laser diode circuit 10 drives the second semiconductor laser of the light source unit 1 with the image data as the second light beam modulation information signal from the image data control circuit 9, and the second semiconductor laser modulated by the image data Out of the light beam B2.
[0035]
Similarly, in the operation relating to the third light beam B3, the F / F 31 serving as control means for turning on / off the third light beam is set by the output signal j of the AND circuit 30, and the output signal k of the F / F 31 Is output to the image data control circuit 9 as an ON / OFF signal for turning on / off the third light beam B3. The image data control circuit 9 outputs the ON / OFF signal k from the F / F 31 to the laser diode circuit 10 as a third light beam synchronization detection modulation signal, and the laser diode circuit 10 receives the ON / OFF signal k from the image data control circuit 9. The third semiconductor laser of the light source unit 1 is driven by the synchronization detection modulation signal k for the third light beam to turn on the third semiconductor laser, thereby turning on the third light beam B3.
[0036]
When the third light beam B3 passes through the beam detector 7, the binarization circuit 11 outputs a beam detection signal b. The gate means 32 composed of an AND circuit as a masking means is inputted with the output signal i of the one-shot multivibrator 28 inverted by an inverter 29 as an inverting means, and the output signal of the inverter 29 outputs the light beam from the AND circuit 26. The beam detection signals g corresponding to B2 to B4 are gated to extract the beam detection signals corresponding to the light beams B3 and B4.
[0037]
The beam detection signals corresponding to the light beams B3 and B4 from the AND circuit 32 are processed by a delay (Delay) circuit 33 as a delay means for a very short time (the time until the next light beam B4 passes through the beam detector 7). Less time). The one-shot multivibrator 34 is triggered by the rising edge of the first pulse signal of the output signal of the delay circuit 33, and the output signal becomes low level. Maintain a low level and then go to a high level.
[0038]
Here, the time set in the one-shot multivibrator 34 is sufficiently longer than the time when all of the plurality of light beams B3 and B4 pass on the beam detector 7 in a state where the rotary polygon mirror 3 is constantly rotating. Set the time. The one-shot multivibrator 34 and the inverter 35 constitute a masking signal generating means.
[0039]
The gate means 36 composed of an AND circuit as a masking means receives the output signal of the one-shot multivibrator 34 as a gate signal (masking signal), and outputs the beam corresponding to the light beams B3 and B4 from the AND circuit 32 by the gate signal. By gating (masking) the detection signal, a beam detection signal corresponding to the third light beam B3 is separated and sent to the F / F 31 and the image data control circuit 9 as a synchronization signal corresponding to the third light beam B3. Output. The F / F 31 is reset by the output signal of the AND circuit 36, and the third light beam B3 is turned off.
[0040]
The image data control circuit 9 outputs image data as a third light beam modulation information signal to the laser diode circuit 10 in synchronization with the synchronization signal from the AND circuit 36 (after a certain time delay from the synchronization signal). Controls the start of image formation (start of exposure) using the third light beam B3 based on the synchronization signal. The laser diode circuit 10 drives the third semiconductor laser of the light source unit 1 with the image data as the third light beam modulation information signal from the image data control circuit 9, and the third semiconductor laser modulated by the image data Out of the light beam B3.
[0041]
Next, in the operation relating to the fourth light beam B4, the F / F 37 serving as control means for turning on / off the fourth light beam is set by the output signal of the AND circuit 36, and the output signal of the F / F 37 is the fourth signal. The signal is output to the image data control circuit 9 as an ON / OFF signal for turning on / off the light beam B4. The image data control circuit 9 outputs the ON / OFF signal from the F / F 37 to the laser diode circuit 10 as a fourth light beam synchronization detection modulation signal, and the laser diode circuit 10 outputs the ON / OFF signal from the image data control circuit 9. The fourth light beam B4 is turned on by driving the fourth semiconductor laser of the light source unit 1 with the fourth light beam synchronization detection modulation signal to turn on the fourth semiconductor laser.
[0042]
When the fourth light beam B4 passes through the beam detector 7, the binarization circuit 11 outputs a beam detection signal b. The gate means 38 comprising an AND circuit as a masking means is inputted with the output signal of the one-shot multivibrator 34 inverted by an inverter 35 as an inverting means, and the output signal of the inverter 35 outputs the light beam B3 from the AND circuit 32. , B4 are gated to separate the beam detection signal corresponding to the light beam B4.
[0043]
The beam detection signal corresponding to the light beam B4 from the AND circuit 38 is processed by a delay (Delay) circuit 39 as a delay means for a very short time (from the time until image writing by the next light beams B1 to B4 is started). Also a short time), will be delayed. The one-shot multivibrator 40 is triggered by the rising edge of the output signal of the delay circuit 39, the output signal becomes low level, and thereafter, the output signal maintains the low level state for the time set in the one-shot multivibrator 40. And then to a higher level.
[0044]
Here, the time set for the one-shot multivibrator 40 is set to a time sufficiently longer than the time when the light beam B4 passes over the beam detector 7 in a state where the rotary polygon mirror 3 is constantly rotating. deep. The one-shot multivibrator 40 constitutes a masking signal generating means.
[0045]
An output signal of the one-shot multivibrator 40 is input as a gate signal (masking signal) to a gate means 41 composed of an AND circuit as a masking means, and a beam detection signal corresponding to the light beam B4 from the AND circuit 38 is input by the gate signal. Is gated (masked) to separate only the beam detection signal corresponding to the fourth light beam B4 and output it to the F / F 37 and the image data control circuit 9 as a synchronization signal corresponding to the fourth light beam B4. I do. The F / F 37 is reset by the output signal of the AND circuit 41, and the fourth light beam B3 is turned off.
[0046]
The image data control circuit 9 outputs image data as a fourth light beam modulation information signal to the laser diode circuit 10 in synchronization with the synchronization signal from the AND circuit 41 (with a certain time delay from the synchronization signal). Controls the start of image formation (exposure start) by the fourth light beam B4 based on the synchronization signal. The laser diode circuit 10 drives the fourth semiconductor laser of the light source unit 1 with the image data as the fourth light beam modulation information signal from the image data control circuit 9, so that the fourth semiconductor laser modulated by the image data is output. Out of the light beam B3.
By a series of operations as described above, a plurality of beam detection signals generated by a plurality of light beams can be separated with high accuracy, a writing position of an image can be accurately controlled, and a good output image can be obtained. .
[0047]
In this embodiment, the beam detection signal generated by each light beam is separated as described above, and the image writing position is determined based on the signal. Conversely, if noise is mixed in this signal, the image writing position is changed. As a result, the image is deteriorated.
Therefore, in order to prevent external noise from being mixed as much as possible, it is necessary to make the masking area for masking the beam detection signal as narrow as possible. Further, in an image forming apparatus such as a printer that changes the resolution by changing the rotation number of the rotating polygon mirror, the masking time for masking the beam detection signal must be changed according to the rotation number of the rotating polygon mirror.
[0048]
This point will be described with reference to FIG. 2. The synchronization signal separating circuit 13 receives the beam detection signal b from the binarizing circuit 12 as a train of a plurality of pulses. The width A and the signal interval B of the beam detection signal b from the binarization circuit 12 are both reduced. Here, assuming that the delay times of the delay circuits 21, 27, 33, and 39 are constant, the masking of the beam detection signal b is released for a while after the falling of the beam detection signal b having a reduced pulse width. In addition, at the same time as the danger of mixing external noise increases, the signal interval B of the beam detection signal b is shortened, so that there is a risk that the input of the rising edge of the next beam detection signal is permitted.
[0049]
Therefore, the delay time setting means 42 to 45 change the delay times of the delay circuits 21, 27, 33, 39 according to the rotation speed of the rotary polygon mirror 3 based on the rotation speed setting information from the rotation polygon mirror rotation speed setting circuit 11. That is, the delay times of the delay circuits 21, 27, 33, and 39 are changed such that the higher the rotation speed of the rotary polygon mirror 3, the shorter the delay times of the delay circuits 21, 27, 33, and 39. Thereby, optimal beam detection signal separation can be performed according to the number of rotations of the rotary polygon mirror 3.
[0050]
As described above, this embodiment is an image forming apparatus that performs recording by scanning the photosensitive member 4 as a recording medium with a plurality of beams B1 to B4 modulated by individual information signals. Each of B1 to B4 detects that it has arrived at a predetermined position, and separates the plurality of beam detection signals from a beam detector 7 as a beam detection unit that generates a plurality of beam detection signals corresponding to each beam. An image forming apparatus comprising: a synchronization detection signal generating circuit 8 as a beam detection signal separating unit; and controlling the start of image formation by the plurality of beams based on each signal separated by the beam detection signal separating unit 8. The beam detection signal separating means 8 includes a delay circuit 21 as a delay means for delaying the beam detection signal from the beam detection means 7. 27, 33, 39 and a plurality of masking signals corresponding to the plurality of beam detection signals are generated based on the signals from the delay means 21, 27, 33, 39, and the plurality of masking signals are used to generate the respective beam detection signals. AND circuits 24, 26, 30, 32, 36, 38, and 41 as means for separating a plurality of beam detection signals corresponding to the plurality of beams by masking the beam detection signals from the means 7; Since it has the vibrators 22, 28, 34, and 40, the inverters 23, 29, and 35, and the delay time setting means 42 to 45 for setting and varying the delay time of the delay means, it is inexpensive, and even if only one beam detecting means is used, the image is reduced. It is possible to control the writing position with high accuracy, obtain a good output image, and set the masking time optimally Rukoto makes it possible to prevent mixing of external noise, the image writing position stably able to precisely control it is possible to obtain a satisfactory output image.
[0051]
Further, this embodiment has a rotating polygon mirror 3 for scanning the plurality of beams, and a rotating polygon mirror rotation number setting circuit 11 as setting means for setting and changing the number of rotations of the rotating polygon mirror 3; The delay time setting means 42 to 45 change the delay time of the delay means 21, 27, 33, 39 in accordance with the number of rotations of the rotary polygon mirror 3 set by the setting means 11, so that setting changes such as resolution are changed. , The delay time of the delay means 21, 27, 33, 39 can be set to an appropriate time according to the number of rotations of the rotating polygonal mirror even if the number of rotations of the rotating polygonal mirror is changed in accordance with the above. A plurality of beam detection signals can be separated well, and optimal image writing position control can be performed.
[0052]
Further, in this embodiment, as soon as the plurality of beams sequentially enter the beam detection means 7 and are detected, the beams incident on the beam detection means 7 are turned off, and the lights of the plurality of beams are turned off. Since the F / Fs 20, 25, 31, and 37 are provided as control means for lighting the next beam after the beam, the plurality of beams are not turned on at the same time, and the plurality of beam detection signals can be accurately separated.
In the above embodiment, the number of light beams is four, but the present invention can be similarly applied to a case where the number of light beams is other than four.
[0053]
【The invention's effect】
As described above, according to the first aspect of the present invention, with the above configuration, it is possible to accurately control the image writing position at low cost, obtain a good output image, and prevent external noise and the like from being mixed. As a result, the image writing position can be accurately controlled, and a good output image can be stably obtained.
According to the second aspect of the present invention, with the above configuration, it is possible to accurately separate a plurality of beam detection signals even when the number of rotations of the rotary polygon mirror is changed in accordance with a change in setting of resolution or the like. The writing position control can be performed.
According to the third aspect of the present invention, a plurality of beam detection signals can be accurately separated by the above configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a synchronization signal separation circuit according to an embodiment of the present invention.
FIG. 2 is a timing chart illustrating operation timings of the synchronization signal separation circuit according to the first embodiment.
FIG. 3 is a schematic diagram showing the same embodiment.
FIG. 4 is a block diagram illustrating a configuration of a synchronization detection signal generation circuit according to the first embodiment.
FIG. 5 is a diagram for explaining a multi-beam optical system.
FIG. 6 is a waveform chart showing a signal obtained from a synchronous detector in the multi-beam optical system.
[Explanation of symbols]
7 Beam detector
8 Synchronization detection signal generation circuit
20, 25, 31, 37 F / F
21, 27, 33, 39 delay circuit
22, 28, 34, 40 One-shot multivibrator
23, 29, 35 Inverter
24, 26, 30, 32, 36, 38, 41 AND circuit
42-45 delay time setting means

Claims (3)

An image forming apparatus for performing recording by scanning a recording medium with a plurality of beams modulated by individual information signals, wherein the image forming apparatus detects that the plurality of beams have reached predetermined positions, and corresponds to each of the beams. Beam detecting means for generating a plurality of beam detecting signals, and beam detecting signal separating means for separating the plurality of beam detecting signals, respectively, wherein the plurality of beam detecting signals are separated based on the signals separated by the beam detecting signal separating means. In the image forming apparatus, each of which controls the start of image formation by using the beam, the beam detection signal separating unit includes: a delay unit that delays a beam detection signal from the beam detection unit; A plurality of masking signals corresponding to the beam detection signals are generated, and the plurality of masking signals are used to generate the beam detection signals. Means for separating a plurality of beam detection signals corresponding to the plurality of beams by masking a beam detection signal from a stage, and a delay time setting means for setting and varying a delay time of the delay means. Image forming apparatus. 2. The image forming apparatus according to claim 1, further comprising: a rotary polygon mirror that scans the plurality of beams; and a setting unit configured to set and change the number of revolutions of the rotary polygon mirror. An image forming apparatus, wherein a delay time of the delay unit is set and variable according to a set rotation speed of the rotary polygon mirror. 3. The image forming apparatus according to claim 1, wherein, when the plurality of beams sequentially enter the beam detection unit and are detected, the beam incident on the beam detection unit is turned off immediately, and among the plurality of beams, An image forming apparatus, comprising: a control unit that turns on a beam next to the beam that has been turned off.

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