JP2002341279A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device by which scanning with all light beams is always performed at an ideal position by correcting the scanning magnification of at least one part while correcting the offsetting of each beam in a main scanning direction in an optical scanner having several light beam sources. SOLUTION: A VCK signal is generated based on an SOS signal and a clock signal by a clock phase synchronizing circuit 22, and a main scanning position signal based on the SOS signal and the VCK signal is generated by a counter circuit 20. Then, writing start timing by a video signal outputted from video memories 14A, 14B and 14C by a writing permission signal generating unit 18 is corrected for each beam based on the main scanning start signal, and also frequency sweeping start timing by VCK controllers 16A, 16B and 16C is corrected for each beam based on the main scanning start signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by scanning a photosensitive member with a light beam.

[0002]

2. Description of the Related Art A laser diode (hereinafter, referred to as an LD) is used as a light source as an optical scanning device of a general image forming apparatus. In order to further improve the image forming speed,
For example, an optical scanning device using an LD array including a plurality of LDs as a light source has been devised as disclosed in Japanese Patent Application Laid-Open No. 5-294005.

According to the technique described in Japanese Patent Application Laid-Open No. 5-294005, as shown in FIG.
The plurality of laser beams emitted from the plurality of light emitting units are collimated (parallelized) into a laser beam having a predetermined beam diameter by the collimator lens 52. This laser beam enters a rotary polygon mirror 56 via a cylindrical lens 54, and is deflected by the rotation. The deflected laser beam is transmitted to the toroidal lens 58 and the scanning lens 6.
The laser beam passing through the scanning lens 60 and passing through the scanning lens 60 forms a spot image on the image carrier 62 placed on the surface to be scanned.

[0004] A reflection mirror 64 is provided within the deflection range of the laser beam and at a position not involved in scanning the surface to be scanned, and the laser beam reflected by the reflection mirror 64 is incident on a photodetector 66. In order for the laser beam to be detected by the photodetector 66, the laser is turned on immediately before the laser beam is deflected by the photodetector 66 during the scanning period, and the laser beam is turned off just before the scanning range necessary for the original scanning. Is performed. The start of laser modulation according to image data is controlled by the horizontal synchronization signal output from the photodetector 66.

Further, as a color image forming apparatus, there is an apparatus provided with a plurality of photosensitive members as disclosed in Japanese Patent Application Laid-Open No. 11-198435. In this color image forming apparatus, as shown in FIG. 14, an image reading device 68 which separates an optical signal obtained by scanning an original into a signal of each color by a filter and performs photoelectric conversion to form an image signal of each color.
And a control unit 7 for controlling the operation of the entire color image forming apparatus
0, three transport rollers 72A to 72C, and an endless transfer belt 74 wound around the transport rollers 72A to 72C.
And four transport rollers 76A to 76D disposed below the transfer belt 74; an endless transport belt 78 wound around the transport rollers 76A to 76D;
And a rotation driving unit 80 that rotationally drives the transport belt 78;
Above the transfer belt 74, an image forming section 82K for forming a black (K) image, and a yellow (Y)
The image forming unit 82 </ b> Y for forming an image, the image forming unit 82 </ b> M for forming a magenta (M) image, and the image forming unit 82 </ b> C for forming a cyan (C) image include the rotation driving unit 80 and the transfer belt 7.
4 are arranged at substantially equal intervals along the moving direction of the transfer belt 74 when the transfer belt 4 is driven to rotate. Image forming units 82K, 82
Y, 82M, and 82C have the same mechanism and each include a photosensitive drum 84 as an irradiation target.

[0006] The photosensitive drum 84 has an axis that is parallel to the transfer belt 7.
4, a charger 86 for charging the photosensitive drum 84 is provided around each photosensitive drum 84, and a laser beam is irradiated on the charged photosensitive drum 84. An optical scanning device 88 for forming an electrostatic latent image by supplying toner of a predetermined color to a portion of the photosensitive drum 84 on which the electrostatic latent image has been formed, thereby developing the electrostatic latent image. A developing unit 90 for supplying a predetermined toner to a portion where the electrostatic latent image is formed to develop the electrostatic latent image and form a toner image on the photosensitive drum 84;
A cleaning device 92 for removing the toner remaining on 4 is disposed. Image forming units 82K, 82Y, 82M, 8
The toner images formed on the 2C photoconductor drum 84 are respectively transferred onto the belt surface of the transfer belt 74.

The image forming units 82K, 82Y, 82
A registration detection sensor 94 is disposed downstream of the transfer belt 74 in the moving direction of the transfer belt 74 from the M and 82C. The registration detection sensor 94 includes three registration detection sensors 94A to 94C each including a pair of a light emitting element such as an LED and a light receiving element such as a CCD sensor.
As shown in FIG. 15, they are respectively disposed above the center and three sides (positions corresponding to the center and both ends of the image area along the width direction of the transfer belt 74) along the width direction of the transfer belt 74, respectively. The light emitted from the light emitting element is applied to a predetermined position on the transfer belt 74, and the light reflected by the transfer belt 74 is received by the light receiving element, so that the light is formed at a corresponding position on the transfer belt 74. The registered marks are read by the registration detection sensors 94A to 94C, respectively. The registration detection sensor 94 is connected to the control unit 70.

The transport belt 78 located below the transfer belt 74 is arranged so that its outer peripheral surface is in contact with the outer peripheral surface of the transfer belt 74, and is rotated in synchronization with the rotation of the transfer belt 74. The section 80 is driven to rotate so as to move in the direction of movement of the belt indicated by the arrow shown in FIG. On the other hand, a large number of sheet-like transfer materials P are stored in an unillustrated sheet feed tray in an accumulated state. The transfer material P pulled out from the paper feed tray is placed on the upper surface of the transport belt 78 and transported to a position where the transfer belt 74 and the transport belt 78 are in contact with each other.
8, the toner image formed on the outer peripheral surface of the transfer belt 74 is transferred. The toner image is fixed on the transfer material P on which the toner image has been transferred by a fixing device (not shown). Thus, a color image is formed on the transfer material P.

In such an image forming apparatus, when the position of each optical scanning device deviates from a predetermined value, the scanning width in the main scanning direction changes, and as a result, the image width in the main scanning direction changes. Therefore, according to the technique described in Japanese Patent Application Laid-Open No. H11-198435, a registration mark formed by each optical scanning device is detected, and the control unit 70 shown in FIG. The image width is adjusted by adjusting the scanning magnification and the partial scanning magnification of the scanning device. At this time, the relationship between the registration mark and the video clock is as follows.

When each registration mark is detected at a standard position as shown in FIG. 16A, a standard video clock is used, and as shown in FIG. If the video clock is detected to be shifted uniformly in the scanning direction, the phase of the video clock is shifted so as to correct the shift amount, and as shown in FIG. 16C, the interval between the adjacent registration marks is longer than the interval at the standard position. If it is detected widely, the scanning width per video clock is reduced, that is, the frequency of the video clock is increased in order to reduce the overall scanning magnification, and as shown in FIG. If only the side is detected wider than the interval at the standard position, the scanning width per video clock is gradually reduced from the main scanning start side to the scanning end side, that is, the partial magnification is gradually reduced. The frequency of the video clock is gradually or stepwise increased from the scanning start side to the scanning end side (hereinafter referred to as a positive frequency sweep), and only the scanning start side of the adjacent registration mark is provided as shown in FIG. If the interval is detected wider than the standard position, the scanning width per video clock is gradually increased from the scanning start side to the scanning end side, that is, the frequency of the video clock is gradually increased to gradually increase the partial magnification. , And gradually or stepwisely decrease to the scanning end side (hereinafter referred to as a negative frequency sweep). The positive frequency sweep and the negative frequency sweep are collectively referred to as a frequency sweep.

Here, although not shown, when the whole is reduced, the correction can be made by lowering the video clock frequency. When only the scanning start side or only the scanning end side is reduced, the reduced video clock is used. Sweep the video clock frequency to lower the frequency. It is also possible to shift the phase while changing the video clock frequency. Further, the registration mark can be detected at the corresponding registration detection sensor at any point other than the three points of the scanning start, the center, and the scanning end described above, and the scanning magnification and the partial scanning magnification can be corrected.

Although an image forming apparatus having a plurality of photosensitive members has been described above, a high quality image can be obtained by correcting the scanning magnification and the partial scanning magnification even in an image forming apparatus having one photosensitive member. Can be.

In the above-described optical scanning apparatus using a plurality of laser light sources, when an image is to be formed when a plurality of beams are offset in the main scanning direction, the position of the light beam on the photosensitive member is also changed in the main scanning direction. Offset to
Therefore, in the technique described in Japanese Patent Application Laid-Open No. 5-294005, in order to expose a predetermined position, the offset is corrected by performing a delay corresponding to the beam offset amount on the image signal.

As shown in FIG. 17, when the time for scanning the offset of a plurality of beams is an integral multiple of the video clock, both beams A and B are synchronously modulated by the same video clock, and correspond to the offset. By delaying the output timing of the beam B video signal by the number of video clocks (two clocks in FIG. 17), it becomes possible to expose a plurality of beams offset in the main scanning direction at the same position in the main scanning direction.

As shown in FIG. 18, when the scanning time of the offset of a plurality of beams does not become an integral multiple of the video clock, the video clock of the beam A is shifted by one time or less from the video clock. B, the output timing of the video signal of the beam B is delayed by an integer of the video clock corresponding to the offset (two clocks in FIG. 18), so that the plurality of beams offset in the main scanning direction are located at the same position in the main scanning direction. It is possible to expose.

In the technique described in Japanese Patent Application Laid-Open No. 6-227037, offset correction between beams is performed by making it possible to adjust the phase of a video clock for modulating a light source independently of each light source. The overall magnification is corrected by means capable of changing the frequency.

Further, in the techniques described in JP-A-8-258329 and JP-A-11-198435,
The partial magnification is corrected by sweeping the video clock by means for varying the video clock frequency using a scanning start signal (SOS signal) or the like.

[0018]

However, according to the technique described in Japanese Patent Application Laid-Open No. 5-294005, as shown in FIG. 19, when the time for scanning the offset of a plurality of beams does not become an integral multiple of the video clock, A video clock obtained by shifting the phase of the video clock of the beam A by one cycle or less is used for the beam B, and the video clock is an integer of the video clock corresponding to the offset (two clocks in FIG. 19).
Even if the output timing of the video signal of the beam B is delayed, the video clock cycle changes, so that there is a problem that a plurality of beams offset in the main scanning direction cannot be exposed at the same position in the main scanning direction.

In the technique described in Japanese Patent Application Laid-Open No. 5-294005, in order to cope with a multi-beam light source offset in the main scanning direction, a scan start signal (Hsync signal) is delayed by an offset to a predetermined position. Although an image is formed, it cannot be corrected if the scanning width fluctuates due to variations in the optical scanning device. That is, no consideration is given to sweeping the frequency of the video clock and correcting the partial magnification.

In the technique described in JP-A-6-227037, the partial magnification is corrected by independently adjusting the phase of each light source. No consideration is given to sweeping the clock frequency and correcting the partial magnification.

Further, in the techniques described in JP-A-8-258329 and JP-A-11-198435,
No consideration is given to a multi-beam light source using a plurality of beams having an offset in the main scanning direction.

The present invention has been made in view of the above facts, and in an optical scanning device having a plurality of light sources, at least one portion of the scanning magnification is corrected while correcting the main scanning direction offset of each beam. It is an object of the present invention to provide an image forming apparatus which can perform all the light beams at an ideal position.

[0023]

According to one aspect of the present invention, there is provided a light source for emitting a plurality of beams, and a scanning device for scanning the plurality of beams so as to form an image on a medium to be scanned. Means, based on a modulation signal corresponding to each of the plurality of beams, corresponding to each of the plurality of beams, and synchronizing with a plurality of clock signals capable of changing at least one partial oscillation frequency during one scanning period by the scanning means, Modulating means for modulating a plurality of beams, clock generating means for outputting the plurality of clock signals, and outputting a frequency change timing control signal to the clock generating means to control timing for changing the oscillation frequency of the plurality of clock signals Frequency change timing control means, the frequency change timing control means comprising: The oscillation frequency change timing of the clock signal corresponding to the offset beam of the plurality of clock signals is offset so that the frequency change timing is offset by substantially the same time as the time required for scanning the scanning direction offset distance on the medium to be scanned. It is characterized by controlling.

According to the first aspect of the present invention, the plurality of beams generated by the light source are scanned by the scanning means so as to form an image on the medium to be scanned, thereby forming an image on the medium to be scanned. Becomes possible.

In the modulating means, a modulating signal corresponding to each of the plurality of beams is converted into a plurality of clocks output from a clock generating means capable of changing at least one partial oscillation frequency during one scanning period by the scanning means corresponding to each of the plurality of beams. Multiple beams are modulated in synchronization with the signal. That is, the oscillating frequency is swept during one scan, and an image is formed by a plurality of beams modulated in synchronization with a plurality of clock signals output from the clock generating unit, whereby the magnification of the scanning width by the scanning unit can be corrected. .

For example, the correction of the magnification of the scanning width can be realized by using the technique described in Japanese Patent Application Laid-Open No. 11-198435 proposed by the present applicant.

The frequency change timing control means outputs a frequency change timing control signal to the clock generation means to control the timing of changing the oscillation frequency of the plurality of clock signals output from the clock generation means. At this time, the frequency change timing control means controls the offset beam of the plurality of clock signals so that the frequency change timing is offset by substantially the same time as the time required for scanning the scanning direction offset distance generated between the plurality of beams. The oscillation frequency change timing of the corresponding clock signal is controlled. That is, it is possible to start the frequency sweep of the beam offset in the scanning direction from the same position in the scanning direction. Further, if the modulation timing of the beam by the modulating means is modulated in accordance with the offset distance, it is possible to form a plurality of beams having the offset at the same position in the scanning direction on the medium to be scanned. Thus, even if the frequency sweep is performed, it becomes possible to form an image of a plurality of offset beams at the same position in the scanning direction on the medium to be scanned.

Therefore, in an optical scanning device having a plurality of light sources, it is possible to correct the scanning magnification of at least one portion while correcting the offset in the main scanning direction of each beam. Can scan by position.

As the light source, a light source composed of a plurality of beam groups including a group composed of a plurality of beams having substantially the same position in the scanning direction by the scanning means is used. In this case, the frequency change timing control means controls the oscillation frequency change timing for each beam group. , And at least one portion of the scanning magnification can be corrected, so that all light beams can always be scanned at ideal positions.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the frequency change timing control means includes a signal synchronized with the start of each scan by the beam that generates the scan direction offset distance. And calculating the oscillation frequency offset timing in accordance with the calculation result, and controlling the oscillation frequency change timing according to the calculation result.

According to the invention described in claim 3, according to claim 1
Alternatively, in the invention according to claim 2, the frequency change timing control means calculates the offset distance based on a signal synchronized with the start of each scan by the beam that generates the scan direction offset distance. For example, it is possible to calculate the offset distance from a signal synchronized with the start of scanning and a predetermined scanning speed.

Further, the frequency change timing control means controls the oscillation frequency change timing according to the calculation result. That is, the oscillation frequency change timing is controlled according to the calculated offset distance.
The frequency sweep can be started from the same scanning direction position for the beam or the beam group offset in the scanning direction. Therefore, even if the frequency is swept, it is possible to form an image of a plurality of offset beams at the same position in the scanning direction, and it is possible to correct the offset in the scanning direction on the medium to be scanned, which occurs between the plurality of beams.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the measuring means for measuring the scanning direction offset distance at a predetermined timing, Update setting means for updating and setting the scanning direction offset distance in accordance with the measurement result.

According to the invention described in claim 4, claim 1 is
The invention according to any one of claims 3 to 3, wherein the offset distance is measured at a predetermined timing by measuring means, and the offset distance used by the correction means is updated and set by the update setting means, so that all of the offset distances are always set. The light beam can be scanned at an ideal position.

That is, although the offset amount is a fixed value as it is as a design value or a measured value during manufacture, the offset amount may fluctuate for some reason. The position of the beam in the scanning direction is shifted, and the image quality is reduced. Factors that cause the offset amount to fluctuate include the positional shift of each component due to strong impact, thermal deformation of the component due to temperature fluctuation in the device, etc., at a predetermined timing, that is, periodically,
The oscillation frequency change timing is updated by measuring the offset distance and updating and setting the offset distance of each beam. Therefore, it is possible to always scan all light beams at ideal positions, and it is possible to prevent the image quality from being lowered.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. [First Embodiment] In the present embodiment, the present invention is applied to the optical scanning device shown in FIG. 13 and the image forming apparatus shown in FIG. 14 described in the related art.
The three beams arranged as shown in FIG.
→ It is assumed that scanning is performed at an earlier timing in the order of beam 3. Note that the rotary polygon mirror 56 and the scanning lens 60 shown in FIG. 13 correspond to the scanning unit of the present invention.

FIG. 1 shows a configuration of a control unit, a laser array, and a driving circuit of the image forming apparatus according to the first embodiment. As shown in FIG. 1, an SOS signal detecting photodetector 24 that detects the start of scanning and outputs an SOS signal, and an oscillator 26 that outputs a clock signal include a clock phase synchronization circuit 22.
It is connected to the.

A counter circuit 20 and VCK controllers 16A, 16B, 16C are connected to the clock phase synchronizing circuit 22, and a VCK signal which synchronizes a clock signal output from the oscillator 26 with the falling edge of the SOS signal is provided. Counter circuit 20 and VCK controllers 16A, 16B, 16
C.

The counter circuit 20 is further connected to a photodetector 24 for detecting an SOS signal.
The VCK signal is counted based on the signal, and the count value is used as a main scanning position signal as a write permission signal generator 18.
And VCK control devices 16A, 16B and 16C.

The writing permission signal generator 18 is provided with a memory and a comparator (not shown). The writing position in the main scanning direction shown in FIG. 2 and the main scanning of each beam are determined for each beam in the memory. A set value defined by the count number of the VCK signal determined according to the offset amount in the direction is stored in advance, and when the main scanning position signal output from the counter circuit 20 matches the set value in the comparator. The write permission signals (LS1, LS2, LS3) corresponding to the respective beams are output to the video memories 14A, 14B, 14C. The set value is set in accordance with the writing start position of each beam in the main scanning direction and the offset amount of each beam in the main scanning direction.

VCK controllers 16A, 16B, 16C
Has a function of sweeping a video clock frequency in response to a correction signal for correcting a scanning magnification and a partial scanning magnification (for example, a signal for correcting a magnification obtained from a result of detecting a test pattern). A video clock signal whose frequency is swept as required based on the signal is output. VCK controllers 16A, 16B,
Similarly to the write permission signal generator 18, the memory 16C is provided with a memory and a comparator (not shown), and a frequency sweep start position in the main scanning direction shown in FIG. A setting value defined by the count number of the VCK signal determined according to the offset amount of the beam in the main scanning direction is stored in advance, and the main scanning position signal output from the counter circuit 20 is compared with the setting value by the comparator. When they match, the frequency sweep corresponding to each beam is started.

The VCK controllers 16A, 16B, 1
6C are provided in a number corresponding to the plurality of beams described above. In the present embodiment, three VCK control devices 16A, 16B, and 16C are provided as described above,
A video clock VCK1 signal from the CK controller 16A,
The video clock VCK2 signal from the VCK controller 16B and the video clock VCK3 from the VCK controller 16C.
Each signal is output.

As for the function of sweeping the video clock frequency, the scanning magnification and partial magnification during one scan can be reduced by using the technique described in Japanese Patent Application Laid-Open No. H11-198435 which has already been filed by the present applicant. Can be corrected.

Each VCK controller 16A, 16
B and 16C are video memories 1 in which video signals are stored.
4A, 14B, and 14C, respectively, and the video memories 14A, 14B, and 14C are output from the respective VCK controllers 16A, 16B, and 16C when the write permission signals LS1, LS2, and LS3 are output. Video clock VCK signals VCK1, VCK2, VCK
A video signal corresponding to each beam is output to the laser drive circuit in synchronization with CK3. The laser drive circuit 12 controls the driving current to flow through the corresponding laser only when the video signal corresponding to each laser is on, thereby controlling the beam 1, beam 2, and beam 3 output from the laser array 10. To form an image.

Further, the laser array driving circuit 28 includes the laser driving circuit 12 and the laser array 10.

The laser drive circuit 12 and the video memories 14A, 14B, 14C correspond to the modulating means of the present invention, and include the oscillator 26, the clock phase synchronization circuit 22, and the VCK.
The control devices 16A, 16B and 16C correspond to the clock generation means of the present invention, and the counter circuit 20 and the VCK control devices 16A, 16B and 16C correspond to the frequency change timing control means of the present invention.

Next, the operation of the image forming apparatus configured as described above will be described.

FIG. 3 shows the SOS signal, the write permission signals LS1, LS2, LS3 and the video clock signal VCK.
1, a timing chart of VCK2 and VCK3 is shown.

When a predetermined time elapses from the fall timing of the SOS signal and the beam position of the beam 1 scanned at the earliest timing reaches the image formation start position on the photosensitive member, the write permission signal LS1 is set to ENABLE (this state). In this embodiment, the video signal is "L"), and the video signal is output from the video memory 14A in synchronization with the video clock VCK1. The video clock VCK1 has the same frequency as the VCK signal, but when LS1 becomes ENABLE, a frequency sweep is started based on the correction signal.

Subsequently, when the beam position of the beam 2 reaches the image forming start position on the photosensitive member, the writing permission signal LS2
Becomes ENABLE, and a video signal is output from the video memory 14B in synchronization with the video clock VCK2. The video clock VCK2 has the same frequency as the VCK signal, but when LS2 becomes ENABLE, a frequency sweep is started based on the correction signal.

Finally, when the beam position of the beam 3 reaches the image forming start position on the photosensitive member, the write permission signal LS3
Becomes ENABLE, and a video signal is output from the video memory 14C in synchronization with the video clock VCK3. The video clock VCK3 has the same frequency as the VCK signal, but when LS3 becomes ENABLE, a frequency sweep is started based on the correction signal.

Here, the offset shown in FIG. 3 is a time from the start of the write enable signal LS1 to the start of the enable of the write enable signal LS2. That is, it is time to scan the offset amount between the position of the beam 1 in the main scanning direction and the position of the beam 2 in the main scanning direction on the photoconductor. Similarly, the offset is the write permission signal LS.
2 is the E of the write permission signal LS3 from the start of ENABLE.
This is the time until the start of NABLE, and is the time for scanning the offset amount between the position of the beam 2 in the main scanning direction and the position of the beam 3 in the main scanning direction on the photoconductor. The frequency sweep start points of the video clock signals VCK1, VCK2, and VCK3 are respectively determined by the write permission signals LS1, LS.
2. Equal to the ENABLE start point of LS3, and the frequency change timing from the sweep start point is controlled so that all of the video clock signals VCK1, VCK2, and VCK3 are equal.

That is, the video clock signal VCK1,
VCK2 and VCK3 are offset in frequency change timing, and the amount of the frequency change timing offset is the time required to scan each beam by the offset in the main scanning direction.

Therefore, such a video clock signal V
By using CK1, VCK2 and VCK3, FIG.
As shown in (1), the writing position in the main scanning direction by the beam 1 and the writing position in the main scanning direction by the beam 2 can be matched. Since the frequency sweep start position on the photosensitive member also coincides, it is possible to correct the scanning magnification and the partial scanning magnification while correcting the main scanning direction offset of each beam in the optical scanning device of the multiple beam light source, and always perform the correction. All light beams can be scanned at ideal positions. [Second Embodiment] Next, an image forming apparatus according to a second embodiment of the present invention will be described. In the present embodiment, as in the first embodiment, the present invention is applied to the optical scanning device shown in FIG. 13 described in the related art and the image forming apparatus shown in FIG. As shown in FIG. 6, three beams arranged in a 3 × 3 two-dimensional manner and having substantially the same position in the main scanning direction on the photoconductor are respectively G1 (G1-1, G1-2, G1-2).
G1-3), G2 (G2-1, G2-2, G2-3),
The description will be made assuming that a 9-beam laser array forming three groups G3 (G3-1, G3-2, G3-3) is used.

FIG. 5 shows a configuration of a control unit, a laser array, and a driving circuit of the image forming apparatus according to the second embodiment. Note that the same components as those of the first embodiment will be described with the same reference numerals.

As shown in FIG. 5, similarly to the first embodiment, an SOS signal detecting light detector 24 for detecting the start of scanning and outputting an SOS signal, and an oscillator 2 for outputting a clock signal.
6 is connected to the clock phase synchronization circuit 22.

A counter circuit 20 and VCK controllers 16A, 16B, 16C are connected to the clock phase synchronization circuit 22, and a VCK signal which synchronizes the clock signal output from the oscillator 26 with the falling edge of the SOS signal is provided. Counter circuit 20 and VCK controllers 16A, 16B, 16
C.

The counter circuit 20 is further connected to a photodetector 24 for detecting an SOS signal, counts the VCK signal based on the SOS signal obtained by beam scanning in the beam group, and permits the writing of the VCK signal as a main scanning position signal. Signal generator 18 and VCK controller 16A, 1
6B and 16C.

The writing permission signal generator 18 is provided with a memory and a comparator (not shown). The writing position in the main scanning direction shown in FIG. 6 and the main position of each beam are determined in the memory for each beam group. A set value defined by the count number of the VCK signal determined according to the offset amount in the scanning direction is stored in advance, and the main scanning position signal output from the counter circuit 20 matches the set value in the comparator. Sometimes, the write permission signal (LS1, LS1) corresponding to each beam group
2, LS3) to video memories G1-1 to G1-3, G2
-1 to G2-3 and G3-1 to G3-3. The set values are set according to the writing start position of each beam group in the main scanning direction and the offset amount of each beam group in the main scanning direction.

VCK controllers 16A, 16B, 16C
Has a function of sweeping a video clock frequency in response to a correction signal for correcting a scanning magnification and a partial scanning magnification (for example, a signal for correcting a magnification obtained from a result of detecting a test pattern). A video clock signal whose frequency is swept as required based on the signal is output. VCK controllers 16A, 16B,
Similarly to the write permission signal generator 18, the memory 16C includes a memory and a comparator (not shown), and a frequency sweep start position in the main scanning direction shown in FIG. A preset value defined by the count number of the VCK signal determined according to the offset amount of the beam in the main scanning direction is predetermined, and the main scanning position signal output from the counter circuit 20 is set by the comparator. When the values match, a frequency sweep corresponding to each beam group is started.

The VCK controllers 16A, 16B, 1
6C are provided in a number equal to the number of beam groups whose positions in the main scanning direction are substantially equal to each other. In the present embodiment,
As described above, the three VCK controllers 16A, 16B,
A video clock VCK1 signal is output from the VCK control device 16A, a video clock VCK2 signal is output from the VCK control device 16B, and a video clock VCK3 signal is output from the VCK control device 16C.

As for the function of sweeping the video clock frequency, the technique described in Japanese Patent Application Laid-Open No. 11-198435, which has already been filed by the applicant of the present application, can be used to reduce the scanning magnification and partial magnification during one scan. Can be corrected.

The VCK controller 16A is provided corresponding to the beam group G1 having substantially the same position in the main scanning direction.
Video memories G1-1 and G1- in which video signals are stored
2, G1-3, and the VCK control device 16B similarly controls the beam group G2 having substantially the same position in the main scanning direction.
Are connected to video memories G2-1, G2-2, and G2-3 in which video signals are stored.
Similarly, control device 16C is provided corresponding to beam group G3 having substantially the same position in the main scanning direction, and stores video signals G3-1, G3-2, and G3- in which video signals are stored.
3 is connected.

The video memories G1-1, G1-2, G1-
3 indicates that when the write permission signal LS1 is mainly used, VCK
The video signals (G1-1, G1-2, G1-3) corresponding to each beam are synchronized with the video clock VCK signal VCK1 output from the control device 16A, and the laser drive circuit 1
2 and video memories G2-1, G2-2, G2-
3, when the write permission signal LS2 is output,
Video clock V output from VCK controller 16B
Video signals (G2-1, G2-2, G2-3) corresponding to the respective beams are output to the laser drive circuit 12 in synchronization with the CK signal VCK2, and the video memories G3-1, G3-2,
Similarly, when the write permission signal LS3 is output, the video signals G3-3 are synchronized with the video clock VCK signal VCK3 output from the VCK control device 16C, and the video signals (G3-1, G3-2, G3-3) to the laser drive circuit 12.

The laser drive circuit 12 controls the laser array 1 by controlling the drive current to flow only when the video signal corresponding to each laser is on.
An image is formed by the beams G1-1 to G3-3 output from 1.

Next, the operation of the image forming apparatus configured as described above will be described.

Note that the SOS signal and the write permission signal (L
S1, LS2, LS3) and the video clock signal (VCK)
1, VCK2, and VCK3) are the same as those in the first embodiment shown in FIG. 6, and will be described with reference to FIG.

When a predetermined time elapses from the fall timing of the SOS signal and the plurality of beam positions of the group G1 scanned at the earliest timing reach the image formation start position on the photosensitive member, the write enable signal LS1 is set to ENABLE.
(“L” in this embodiment), and the video clock VC
In synchronization with K1, the video memories G1-1, G1-2, G
1-3 to the video signals (G1-1, G1-2, G1-
3) is output. The video clock VCK1 is VCK
Although the frequency is the same as that of the signal, when LS1 becomes ENABLE, the frequency sweep is started based on the correction signal.

Subsequently, when the plurality of beam positions of the group G2 reach the image forming start position on the photoconductor, the write permission signal LS2 becomes ENABLE and the video clock VC
In synchronization with K2, video memories G2-1, G2-2, G
2-3 to video signals (G2-1, G2-2, G2-
3) is output. The video clock VCK2 is VCK
Although the frequency is the same as that of the signal, when LS2 becomes ENABLE, the frequency sweep is started based on the correction signal.

Finally, when the plurality of beam positions of the group G3 reach the image formation start position on the photosensitive member, the write permission signal LS3 becomes ENABLE, and the video clock VCK is generated.
3, the video memories G3-1, G3-2, G3
-3 to video signal (G3-1, G3-2, G3-3)
Is output. The video clock VCK3 has the same frequency as the VCK signal, but when LS3 becomes ENABLE, a frequency sweep is started based on the correction signal.

Here, the offset shown in FIG. 6 is a time from the start of the write enable signal LS1 to the start of the enable of the write enable signal LS2. That is, it is a time for scanning the offset amount between the main scanning direction beam position of the group G1 and the main scanning direction beam position of the group G2 on the photoconductor. Similarly, the offset is the time when the write enable signal LS2 is written from the start of ENABLE. This is the time until the start of the enable of the enable signal LS3, and the time for scanning the offset amount between the beam position in the main scanning direction of the group G2 and the beam position in the main scanning direction of the group 3 on the photoconductor. The frequency sweep start points of the video clock signals VCK1, VCK2, and VCK3 are respectively determined by the write permission signals LS1, LS2, and LS3.
The frequency change timing from the sweep start point is equal to the frequency sweep start point of the video clock signal VCK.
1, VCK2 and VCK3 are controlled to be equal.

That is, the video clock signals VCK1,
VCK2 and VCK3 are offset in frequency change timing, and the frequency change timing offset amount is the time required for scanning the main scan direction offset amount of each beam group.

Accordingly, by controlling the three beam groups having substantially the same positions in the main scanning direction using the video clocks VCK1, VCK2, and VCK3 controlled as described above, the multi-beam light source can be controlled similarly to the first embodiment. The scanning magnification and the partial scanning magnification can be corrected while correcting the main scanning direction offset of each beam group in the optical scanning device, so that all light beams can always be scanned at ideal positions. .

The image forming apparatus according to the first and second embodiments does not have a plurality of VCK controllers, but a single VCK controller and a plurality of delay circuits as shown in FIG. Video clocks VCK1 and VCK
2. VCK3 may be generated. FIG.
In the description of the first embodiment, the same components as those of the first and second embodiments are denoted by the same reference numerals.

That is, as shown in FIG.
A K control device 16 is provided. The VCK control device 16
As in the embodiment and the second embodiment, it has a function of sweeping the video clock frequency by a correction signal for correcting the scanning magnification and the partial scanning magnification. And VCK
A SWEEP VCK signal whose frequency is swept as necessary based on the signal is output. In addition, the VCK control device 16 is, like the first embodiment and the second embodiment,
The VCK signal output from the clock phase synchronization circuit 22 and the main scanning position signal output from the counter circuit 20 are input.

The delay circuits 30A, 30B and 30C are provided for each beam or beam group. The delay circuit 30A provided corresponding to the beam or beam group to be scanned first is connected to the output side of the VCK controller 16. And a delay circuit 3 provided corresponding to the beam or beam group to be scanned subsequently to the output side of the delay circuit 30A.
0B, and further connected to the output side of the delay circuit 30B is a delay circuit 30C provided corresponding to the beam or beam group to be scanned subsequently. The VCK1 signal is output from the delay circuit 30A and the delay circuit 30B
From the delay circuit 30C to the VCK2 signal.
The K3 signal is output. The video memory of the beam 1 or the beam group G1 is connected to the delay circuit 30A, and the beam 2 or the beam group G is connected to the delay circuit 30B.
2 video memories, and the beam 3 is connected to the delay circuit 30C.
Or connect the video memory of beam group G3,
By setting the delay time of each of the delay circuits 30A, 30B, and 30C in accordance with the beam offset amount, the main scanning of each beam group in the optical scanning device of the multi-beam light source is performed as in the first and second embodiments. It is possible to correct the scanning magnification and the partial scanning magnification while correcting the directional offset.

FIG. 7 shows the same as in the second embodiment.
3 shows a three-dimensional three-dimensional arrangement in which three beams having substantially the same position in the main scanning direction on the photosensitive member are formed using a nine-beam laser array forming three beam groups G1, G2, and G3, respectively. [Third Embodiment] An image forming apparatus according to a third embodiment includes:
The image forming apparatus according to the first embodiment further includes a measuring device for measuring the offset amounts of three beams and a configuration for updating the offset correction.

The same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 8 shows a 3D image offset in the main scanning direction.
3 shows a measuring device for measuring an offset amount of one beam.
As shown in FIG. 8, an optical sensor 32 is disposed at a position corresponding to the scanned medium, and when the optical sensor 32 is exposed with a light amount equal to or more than a predetermined level, the optical sensor 32 outputs a digital signal as an optical detection signal. High level (H) is output. Note that the photosensor 32 may use the SOS signal detection photodetector 24 in the first embodiment and the second embodiment.

As shown in FIG. 9, the output of the optical sensor 32 is input to a count control circuit 34. The counter control circuit 34 has two counters 36,
The count control circuit 34 outputs a count permission signal.
The count of 38 is started. In addition,
The counter 36 counts a time T12A (see FIG. 10) from when the optical sensor 32 detects the beam 1 to when the beam 2 is detected. T to detect
23A (see FIG. 10) is counted.

The outputs of the counters 36 and 38 are connected to a beam offset calculator 40 for generating a timing change signal for updating the write start time and the offset time of the video clock signal. It is connected to the write permission signal generator 18 and the VCK control device 16 (16A, 16B, 16C), outputs a timing change signal to the write permission signal generator 18, and outputs a timing change signal to the VCK control device 16 '. It is output. The timing signals are basically the same signal, but may be different signals.

The VCK controller 16 'and the write permission signal generator 18' are the same as those of the first embodiment.
It corresponds to the control devices 16A, 16B, 16C and the write permission signal generator 18, but the VCK in the first embodiment
The control device and the write permission signal generator 18 are configured to have a function of updating the set values stored respectively in response to a timing change signal.

The optical sensor 32 corresponds to the measuring means of the present invention, and the count control circuit 34, the counters 36 and 38, and the beam offset calculator 40 correspond to the update setting means of the present invention.

Next, measurement of the beam offset amount and updating of the beam offset correction will be described.

FIG. 10 shows a timing chart of a light detection signal obtained by scanning the optical sensor 32 with a beam.

Here, the interval between beam 1 and beam 2 is BP
12 (see FIG. 8), the distance between beam 2 and beam 3 is BP2
3 (see FIG. 8), the difference between the rising timing of the light detection signal corresponding to the beam 1 and the rising timing of the light detection signal corresponding to the beam 2 is T12A, the light detection signal corresponding to the beam 2 and the beam 3
The difference in the rising timing of the light detection signal corresponding to
Assuming that the scanning speed is 23A and the beam scanning speed is VS, the distance between beams can be obtained as BP12 = T12A × VS (1) BP23 = T23A × VS (2)

When the light detection signal is input to the count control circuit 34, the count permission signal is sent to each counter 36,
38. The counter 36 counts T12A, and the counter 38 counts T23A. That is, when the optical sensor 32 detects the beam 1, the count control circuit 34 outputs the count permission signal 1.
Is output to the counter 36, the counting of the counter 36 is started, the beam 2 is detected by the optical sensor 32,
When the count control circuit 34 outputs the count permission signal 1 again to the counter 36, the count of T12A ends. At the same time, when the beam 2 is detected, the count control circuit 34 outputs the count permission signal 2 to the counter 38. When the beam 3 is detected, the count control circuit 34 outputs the count permission signal 2 to the counter 38. The count is performed by the counter 38 until it is output, and T23A is counted. The outputs of the counters 36 and 38 are output to the beam offset calculator 40.

The beam offset calculator 40 calculates the inter-beam distance from the above equations (1) and (2) based on T12A and T23A counted by the respective counters 36 and 38, and calculates the calculated inter-beam distance. The count number of the VCK signal corresponding to the distance is calculated, and a timing change signal for updating a preset value stored in the write permission signal generator 18 'and the VCK control device 16' is output. As a result, the writing time of each beam and the offset time of the video clock signal are updated. Therefore,
Since the writing time of the beam and the offset amount between the beams can be changed based on the actual measurement, the light beam can be scanned at an ideal position, and the deterioration of the image quality can be prevented.

In the above description, the case where the distance between the beams is sufficiently large has been described. However, if the beam interval is small and it is impossible or difficult to detect each beam independently with one optical sensor, FIG. As shown, a plurality of optical sensors 32
This can be realized by using a measuring device having A, 32B, and 32C.

That is, the optical sensor 32 for detecting the beam 1
The distance between A and the optical sensor 32B for detecting the beam 2 is SP1.
2. When the distance between the optical sensor 32B for detecting the beam 2 and the optical sensor 32C for detecting the beam 3 is SP23, all the beams are turned on, and the respective optical sensors 32A, 32B, and 32C are exposed. As shown in (2), the light detection signal is output in close proximity. Therefore, each of the optical sensors 32A, 32B, 3
At a timing prior to the exposure of 2C, only the corresponding beam is turned on, and after exposing the optical sensors 32A, 32B, and 32C, the corresponding beam is turned off.
By exposing 2A, 32B, and 32C, a light detection signal as shown in FIG. 12B can be obtained.

Here, the distance between the beam 1 and the beam 2 is BP
12, the distance between beam 2 and beam 3 is BP23, beam 1
The difference between the rising timing of the light detection signal of the light sensor 32A corresponding to the light beam and the rising timing of the light detection signal of the light sensor 32B corresponding to the beam 2 is represented by T12B.
Assuming that the difference between the rise timing of the light detection signal of B and the rise timing of the light detection signal of the light sensor 32C corresponding to the beam 3 is T23B and the beam scanning speed is VS, BP12 = (T12B × VS) -SP12 (3) BP23 = (T23B × VS) -SP23 (4), the distance between beams can be obtained.

As a configuration for updating the beam offset correction, the count control circuit 34 shown in FIG.
The count permission signal 1 is the time from the rise of the light detection signal of the light sensor 32A to the rise of the light detection signal of the light sensor 32B, and the count permission signal 2 is the light sensor 32B. As described above, the writing start time of each beam and the offset time of the video clock signal can be updated by replacing the time from the rise of the light detection signal to the rise of the light detection signal of the optical sensor 32C. Therefore,
Even when it is impossible or difficult to detect each beam independently, by using the above measuring device, the writing time of the beam and the amount of offset between the beams can be changed based on the actual measurement, so that the light beam is ideal. Scanning at an appropriate position, and it is possible to prevent a decrease in image quality.

Note that the holding position of the optical sensor of the measuring device in the third embodiment does not have to be a position corresponding to the medium to be scanned, and the distance between beams on the optical sensor and the distance between beams on the medium to be scanned. If the relationship is known in advance, it is also possible to calculate the inter-beam distance on the medium to be scanned from the measured inter-beam distance on the optical sensor.

Further, in the third embodiment, the image forming apparatus according to the first embodiment has been described as being added with a measuring device for measuring the offset amount of the beam and a configuration for updating the offset correction. By replacing the beam with the X group of the beam of the image forming apparatus according to the second embodiment, a measuring device for measuring the beam offset amount and a configuration for updating the offset correction may be added.

The write permission signal generator 18 and the VCKs 16A, 16 in the first and second embodiments are also provided.
The set values stored in B and 16C do not need to be set in advance. For example, the count control circuit 34, the counters 36 and 38 and the beam offset calculator 40 in the third embodiment may be used to write the write permission signal generator 18 and VCK. Control device 1
The beam offset amount may be calculated and set by providing each of 6A, 16B, and 16C and detecting each beam with the SOS signal detection photodetector 24.

Further, the plurality of light sources in the optical scanning device according to the embodiment of the present invention are not limited to devices as long as they can perform independent modulation. Can be manufactured relatively easily and inexpensively.

[0097]

As described above, according to the present invention, the frequency change timing control means controls the scanning means, which is generated between a plurality of beams, to scan the offset distance in the scanning direction on the medium to be scanned by substantially the same time. By controlling the oscillation frequency change timing of the clock signal corresponding to the offset beam of the plurality of clock signals output from the clock generation means so as to offset the frequency change timing, the beam offset in the scanning direction can be the same. Since the frequency sweep can be started from the position in the scanning direction, if the modulation timing of the beam by the modulation means is also modulated according to the offset distance, the offset of the main scanning direction of each beam in an optical scanning device having a plurality of light sources can be achieved. While at least one portion of the scanning magnification Correction can be performed, always all light beams can be scanned in an ideal position, there is an effect that.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a control unit, a laser array, and a driving circuit of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a plurality of beams on a photoconductor according to the first embodiment of the present invention.

FIG. 3 is a timing chart showing an SOS signal, a write permission signal, and a video clock signal.

FIG. 4 is a diagram for explaining the operation of the first embodiment of the present invention.

FIG. 5 is a block diagram illustrating a schematic configuration of a control unit, a laser array, and a driving circuit of the image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a plurality of beams on a photoconductor according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a modification of the first embodiment and the second embodiment of the present invention.

FIG. 8 is a diagram illustrating a measurement device that measures an offset amount of three beams offset in a main scanning direction in an image forming apparatus according to a third embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration for updating offset correction in the image forming apparatus according to the embodiment of the present invention.

FIG. 10 is a timing chart showing a light detection signal obtained by scanning the light sensor with a beam.

FIG. 11 is a diagram showing a modification of the measuring device.

FIG. 12 is a timing chart showing a light detection signal obtained by scanning an optical sensor with a beam in a modified example of the measurement apparatus.

FIG. 13 is a perspective view illustrating a schematic configuration of an optical scanning device.

FIG. 14 is a diagram illustrating a schematic configuration of an image forming apparatus.

FIG. 15 is a diagram illustrating registration mark detection by a registration detection sensor.

FIG. 16 is a diagram showing registration mark detection positions.

FIG. 17 is a diagram illustrating a delay of a video clock when a time for scanning an offset of a plurality of beams is an integral multiple of a video clock.

FIG. 18 is a diagram illustrating a delay of a beam clock when a time for scanning an offset of a plurality of beams does not become an integral multiple of a video clock.

FIG. 19 is a diagram illustrating a case where a beam clock is delayed when a time for scanning an offset of a plurality of beams does not become an integral multiple of a video clock.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Laser array 12 Laser drive circuit 14 Video memory 16 VCK control device 18 Write permission signal generator 20 Counter circuit 22 Clock phase synchronization circuit 24 SOS signal detection light detector 26 Oscillator 32 Optical sensor 34 Count control circuit 36, 38 counter 40 Beam offset calculator 56 Rotating polygon mirror 60 Scanning lens

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) H04N 1/113 H04N 1/04 104A 1/23 103 F term (reference) 2C362 BA51 BA68 BA70 BB28 BB29 BB37 BB38 CA18 CA39 CB02 CB07 CB13 2H045 BA22 BA23 BA33 BA34 CA98 CA99 DA26 DA41 2H076 AB05 AB06 AB12 AB32 AB67 AB72 5C072 AA03 BA04 HA06 HA13 HB11 HB13 UA14 XA05 5C074 AA08 BB17 CC26 DD11 DD16 EE02 EE06

Claims (4)

[Claims] A light source that emits a plurality of beams; a scanning unit that scans the plurality of beams so as to form an image on a medium to be scanned; and a light source that emits a plurality of beams based on modulation signals corresponding to the plurality of beams. A modulating means for modulating the plurality of beams in synchronization with a plurality of clock signals capable of changing at least one partial oscillation frequency during one scanning period by the scanning means; and a clock generating means for outputting the plurality of clock signals. A frequency change timing control unit that outputs a frequency change timing control signal to the clock generation unit to control a timing at which the oscillation frequency of the plurality of clock signals is changed. When it is necessary to scan the scanning direction offset distance on the medium to be scanned by the scanning means, which is generated between a plurality of beams. An image forming apparatus, comprising: controlling an oscillation frequency change timing of a clock signal corresponding to an offset beam of the plurality of clock signals so as to offset the frequency change timing by substantially the same time as the interval. 2. The light source according to claim 1, wherein the light source includes a plurality of beam groups, each of which includes a group of a plurality of beams having substantially the same position in a scanning direction by the scanning unit.
The image forming apparatus according to claim 1, wherein the frequency change timing control unit controls the oscillation frequency change timing for each of the beam groups. 3. The frequency change timing control means,
2. The method according to claim 1, wherein the scanning direction offset distance is calculated based on a signal synchronized with the start of each scan by the beam generating the scanning direction offset distance, and the oscillation frequency change timing is controlled according to the calculation result. Or the image forming apparatus according to claim 2. 4. The apparatus further comprises: a measuring unit that measures the scanning direction offset distance at a predetermined timing; and an update setting unit that updates and sets the scanning direction offset distance in accordance with a measurement result of the measuring unit. The image forming apparatus according to claim 1, wherein: