JP3576745B2 - Image forming apparatus and printer - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that records an image using a plurality of laser beams, and a printer including the same.
[0002]
[Prior art]
In recent years, laser beam printers having features of high-speed printing and high resolution have been widely used. A semiconductor laser array has attracted attention as a light source for image recording of this laser beam printer. The characteristics of the semiconductor laser array are as follows.
[0003]
(1) Since scanning lines by a plurality of laser beams can be simultaneously recorded, high-speed printing is possible, and therefore, the rotation speed of the rotary polygon mirror for scanning the laser beams can be reduced.
[0004]
(2) The modulation frequency of each laser beam can be reduced, and the digital modulation circuit can be easily operated.
[0005]
(3) Since the power of the semiconductor laser can be kept low, the life of the laser is prolonged.
[0006]
When a semiconductor laser array is used for an ultra-high resolution laser beam printer, the pitch of the semiconductor laser array (the interval between adjacent semiconductor arrays) must be very short.
[0007]
However, if the pitch of the laser semiconductor laser array is made very short, there is a problem that thermal interference between adjacent lasers becomes large and the light intensity of each laser becomes unstable.
[0008]
As a method of avoiding the problem of thermal interference between adjacent lasers, there is a method of inclining a semiconductor laser array obliquely with respect to a scanning surface. FIGS. 8 and 9 show the explanatory diagrams.
[0009]
8, reference numeral 101 denotes a semiconductor laser array; 102, a collimator lens for condensing a plurality of laser beams output from the semiconductor laser array 101; 103, a laser beam passing through the collimator lens 102 for scanning the photosensitive drum 105; A rotary polygon mirror 104; a scanning lens 104 for condensing the laser beam reflected by the rotary polygon mirror 103 on the rotating photosensitive drum 105 to equalize the scanning beam speed on the photosensitive drum 105; A reflecting mirror disposed on the scanning surface of the scanning laser beam passing through 104; 108, a beam detector for detecting the laser beam reflected by the reflecting mirror 106; 109, provided between the beam detector 9 and the reflecting mirror 106 The light shielding plate is used to determine the scanning start reference of the scanning laser beam. It was those.
[0010]
The number of laser beams output from the semiconductor laser array 1 in FIG. 8 is four. In FIG. 8, those laser beams are denoted by L1, L2, L3, and L4. The semiconductor laser array 1 is tilted so that the laser beams L1, L2, L3, and L4 are obliquely incident on the rotary polygon mirror 3. At this time, the scanning laser beam on the photosensitive drum 5 is as shown in FIG.
[0011]
As shown in FIG. 9, when the semiconductor laser array 1 is arranged obliquely, the four laser beams output from the semiconductor laser array 1 are shifted on the photosensitive drum 5 along the scanning direction with respect to each other. Is scanned.
[0012]
If a laser modulation circuit that drives the semiconductor laser array 1 is controlled so as to correct the time difference between the beam groups in the scanning direction, a normal laser scanning image with no image shift between beams on the photosensitive drum 5 is formed.
[0013]
By arranging the laser beam group obliquely, the apparent pitch of the laser beam group in the rotation direction of the photosensitive drum 5 becomes shorter.
[0014]
Therefore, depending on the inclination angle of the semiconductor laser array 1, the apparent pitch of the laser beam group becomes shorter, and a high-resolution laser beam printer can be formed. In addition, the pitch of the semiconductor laser array can be widened and the thermal interference can be avoided.
[0015]
[Problems to be solved by the invention]
However, in the technology of tilting the semiconductor laser array obliquely, in order to accurately adjust the apparent pitch on the photosensitive drum 5 to a desired value, a mechanical mechanism for fixing the semiconductor laser array at a highly accurate tilt angle is used. Is required. In particular, if the pitch is to be narrowed on the photosensitive drum 5 in order to achieve ultra-high resolution, it is necessary to increase the inclination angle of the semiconductor laser array. In addition, since it is difficult to accurately adjust the pitch of the semiconductor laser array to a desired value, a shift may occur on the image in the scanning direction of each laser beam and the rotation direction of the photosensitive drum 5. .
[0016]
Further, if an attempt is made to detect a plurality of scanning laser beams with a single beam detector, a plurality of detection pulses are generated by the beam detector 9 for each laser scanning of the laser array 1. When the rotation speed of the rotary polygon mirror 3 is stabilized based on the signal output from the beam detector 9, a plurality of detection pulses are output, so that the rotation speed may be stabilized. It was difficult.
[0017]
[Means for Solving the Problems]
An image forming apparatus according to the present invention includes a modulating unit that modulates each of a plurality of light beams according to an image signal output from an image signal generating unit, and a light beam group including the plurality of light beams. A scanning unit that scans the photoreceptor in such a manner that the beam is obliquely shifted with respect to the main scanning direction and the sub- scanning direction, and detects a light beam group scanned by the scanning unit at a predetermined position and outputs a detection pulse train Beam detection means, shaping means for forming a single pulse defining a reference time from the detection pulse train, measuring a time interval between the detection pulses, and a time from the single pulse to an image signal output based on the measurement result. And a scanning control unit that measures the period of the single pulse and controls the scanning period of the scanning unit based on the measurement result.
[0018]
In the above image forming apparatus, the scanning unit includes a rotation driving unit, and the scanning control unit controls a rotation frequency of the rotation driving unit in accordance with a comparison result between a cycle of the single pulse and a reference cycle. Is also good .
[0019]
The image forming apparatus further includes a developing unit that converts an electrostatic latent image formed on the photoconductor by the light beam into a visible image, and a transfer unit that transfers the visible image to a sheet. It may be .
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment 1]
FIG. 1 is a block diagram showing a first embodiment of the image forming apparatus according to the present invention. Reference numeral 1 denotes a semiconductor laser array in which a plurality of semiconductor lasers are arranged in a row, and the rows formed by these semiconductor lasers are oblique to the rotation direction of a rotating polygon mirror described later. In the present embodiment, the number of beams of the laser array is assumed to be three, where n is three. Reference numeral 2 denotes a collimator lens that converts the light beams L1, L2, and L3 emitted from the semiconductor laser array 1 into parallel beams. The emitted light L1, L2, L3 forms an image on the photosensitive drum 5 by an imaging lens not shown. Reference numeral 3 denotes a rotating polygon mirror for scanning the light beam L1, L2, L3, which has become a parallel beam, on the photosensitive drum 5. Reference numeral 4 denotes a motor control circuit for rotating the rotary polygon mirror 3. Reference numeral 6 denotes a charger for charging the photosensitive material drum 5. Reference numeral 7 denotes a developing unit for developing an electrostatic latent image formed on the photosensitive drum 5 by beam scanning with toner. Reference numeral 8 denotes a transfer unit for transferring the toner image visualized by the developing unit 7 onto the paper. Reference numeral 9 denotes a beam detector which is arranged at a scanning reference position on the scanning surface of the beam and detects the scanning beam. The beam detector is arranged, for example, adjacent to the photosensitive drum 5. Reference numeral 10 amplifies the output from the beam detector 9 and outputs a pulse signal by comparing with a threshold value defined between a level when the beam is not detected and a peak value when the beam is detected. It is a beam detection circuit. Reference numeral 11 denotes a pulse interval measurement circuit for measuring a pulse interval of a beam detection output pulse train from the beam detection circuit 10. Reference numeral 12 denotes a pulse shaping circuit that detects a leading pulse from the output pulse train from the beam detection circuit 10 and shapes the pulse into a single pulse. Reference numeral 13 denotes an A / D conversion circuit that converts a pulse interval measurement result from the pulse interval measurement circuit 11 into digital data. 14 is a CPU. The operation of the CPU 14 will be described later. 15, 16, and 17 receive the pulse output of the pulse shaping circuit 12 and the output of the CPU 14, and control the pulse shaping circuit 12 so that the images corresponding to the respective beams formed on the photosensitive drum 5 do not deviate from each other. Is an image start timing adjustment circuit for adjusting the amount of delay from when the pulse rises to when each image starts to be generated. Reference numerals 18, 19, and 20 input image signals (not shown), and generate image signals in which image start timings of beams for scanning on the photosensitive drum 5 are adjusted by image start timing adjustment circuits 15, 16, and 17. It is a signal generation circuit. Reference numerals 21, 22, and 23 denote optical modulation circuits for modulating a current for driving a semiconductor laser array with each image signal and consequently modulating a laser beam.
[0024]
Note that the pulse shaping circuit 12 may use the output of the pulse interval measuring circuit 11. Further, the pulse shaping circuit 12 only needs to output a single pulse representing the reference time from the output pulse train of the beam detection circuit 10, and the rising edge does not have to coincide with the rising edge of the leading pulse.
[0025]
In the image forming apparatus according to the present embodiment configured as described above, the displacement of the image in the scanning direction due to the mounting angle error and the pitch error of the semiconductor laser array is corrected by the method described below, and there is no pitch shift between beams. Form an image.
[0026]
As shown in FIG. 4, the beam spot 1, the beam spot 2, and the beam spot 3 are arranged obliquely to each other with respect to the rotation direction of the rotary polygon mirror 3, and are adjusted in advance so that the line pitch Lp1 becomes a desired pitch. I have. The pitch between the beams is Bp1, and the angle formed by the line connecting the scanning direction and each beam is θ1. The interval between the beams along the scanning direction is Bp1 '. The interval Bp1 'is, as shown in FIG. 6, a time interval t1 between the output pulse of the first laser and the output pulse of the second laser of the beam detection circuit 10, and the output pulse of the second laser and the output pulse of the third laser. Corresponding to the time interval t1.
[0027]
Next, as shown in FIG. 5, when using a semiconductor laser array in which the pitch between the beams satisfies Bp2 <Bp1, by adjusting the line pitch Lp1 in advance so as to have a desired pitch, the scanning direction and The angle θ2 formed by the lines connecting the beams becomes larger than θ1. The interval between the beams along the scanning direction at this time is defined as Bp2 '. The interval Bp2 'is a time interval t2 between the output pulse of the first laser and the output pulse of the second laser of the beam detection circuit 10 as shown in FIG. 7, and the time interval between the output pulse of the second laser and the output pulse of the third laser. Corresponds to time interval t2. That is, the difference ΔBp12 between the distance Bp1 ′ and the distance Bp2 ′ (shown in FIG. 5) and the difference ΔBp23 between the distance 2 × Bp1 ′ and the distance 2 × Bp2 ′ (shown in FIG. 5) cause the first difference in FIG. A time interval error Δt12 between the output pulse from the laser and the output pulse from the second laser and a time interval error Δt23 between the output pulse from the second laser and the output pulse from the third laser are generated. ΔBp12 and ΔBp23 are shifts in the pitch in the scanning direction, and the images between the beams are shifted. The beam detection output pulse train output from the beam detection circuit 10 is measured by a pulse interval measurement circuit 11, the pulse interval is converted into a voltage, and the A / D conversion circuit 13 converts this voltage into a digital value. The CPU 14 outputs delay data for correcting each image start timing to the image start timing adjustment circuits 15 to 17 so that Δt12 and Δt23 become zero according to the input value from the A / D conversion circuit 13. The image start timing adjustment circuits 15, 16, and 17 delay the single pulse detected by the pulse shaping circuit 12, which detects the leading pulse, by the delay time output by the CPU 14, and the image signal generation circuits 18, 16 corresponding to each semiconductor laser. The image start timing is output to 19 and 20. Then, the signals are modulated by the image signals whose timings have been corrected from the respective semiconductor laser elements of the semiconductor laser array 1 via the image signal generation circuits 18, 19, and 20 and the optical modulation circuits 21, 22, 23 corresponding to the respective semiconductor lasers. Beam is fired. In this way, it is possible to correct the mounting angle error of the semiconductor laser array and the pitch shift in the scanning direction due to the pitch shift of the semiconductor laser array, and to obtain an entire image without any shift in the scanning direction between the beams.
[0028]
In this embodiment, the case where the number of beams is three has been described. However, the present invention is not limited to this, and it goes without saying that any number of beams may be used as long as the number is two or more. The case where the angle formed by the line connecting the scanning direction and each beam is θ2> θ1 has been described, but the same applies to the case where θ2 <θ1.
[0029]
[Embodiment 2]
FIG. 2 is a block diagram showing a second embodiment of the image forming apparatus according to the present invention. This is obtained by adding a pulse interval storage circuit 24 to the image forming apparatus of the first embodiment. The pulse interval data measured by the pulse interval measurement circuit 11 in the first embodiment is taken into the CPU 14 via the A / D conversion circuit 13, but the measurement error in the pulse interval measurement circuit 11 and the quantum error in the A / D conversion circuit 13 The conversion error is also included in the image start timing correction value. Therefore, the average value of the pulse interval data of a plurality of beam scans taken into the CPU 14 is stored in the pulse interval storage circuit 24, and the CPU 14 sends the image start timing adjustment circuits 15, 16, 17 to each of the semiconductor lasers according to the average value. Output the delayed data.
[0030]
[Embodiment 3]
FIG. 3 is a block diagram showing a third embodiment of the image forming apparatus according to the present invention. This is obtained by adding a portion surrounded by a dotted line to the image forming apparatus of the first embodiment. Reference numeral 25 denotes a period measuring circuit that measures the period of a single pulse output from the pulse shaping circuit 12, and reference numeral 26 denotes a clock used by the period measuring circuit 25. Reference numeral 27 denotes a comparison circuit that compares the cycle data from the cycle measurement circuit 25 with the value of a reference value 28 that is theoretically set in advance, and outputs the difference data. Reference numeral 29 denotes a D / A conversion circuit which D / A converts the difference data of the comparison circuit 27 and outputs the data to the motor control circuit 4.
[0031]
The pulse train from the beam detection circuit 10 includes a state where the pulse is dense and a state where the pulse is coarse. This pulse train is shaped into a single pulse in the pulse shaping circuit 12. Therefore, the cycle of the output of the pulse shaping circuit 12 is measured by the cycle measuring circuit 25, and is compared by the comparator 27 with the output of the reference cycle holding circuit 28 which holds the theoretically set reference cycle. As a result, when the period measured by the period measuring circuit 25 is longer than the reference period, a signal for increasing the rotation speed is output to the motor control circuit 4 via the D / A conversion circuit 29, and conversely, the signal is compared with the reference value. When the cycle measured by the cycle measuring circuit 25 is short, a signal for lowering the rotation speed is output to the motor control circuit 4 via the D / A conversion circuit 29, so that the beam scanning cycle always becomes equal to the reference value. The motor can be controlled as described above.
[0032]
As described on the following, measures the pulse interval corresponding to the beam distance output from the bi chromatography beam detector, by changing the image generation start timing according to the measured value, the semiconductor laser array scanning direction By correcting the pitch shift, it is possible to form a high-quality whole image in which the images formed by the respective beams are not shifted in the scanning direction.
In addition, the average value of the pulse intervals of a plurality of beam scans is stored in the storage element, and the image generation start timing is changed according to the data stored in the storage element, so that the measurement error of the pulse interval and the A / D converter are changed. By performing more accurate pitch shift correction without the influence of the quantization error, a higher quality whole image in which the images formed by the respective beams are not shifted in the scanning direction can be formed.
Further, a cycle measuring means for measuring the cycle of the output of the beam detection circuit unitized so as to generate one pulse for each beam group is provided, and the output of the cycle measuring means is compared with the reference cycle. By correcting the motor rotation speed so that it is equal to, even when using a semiconductor laser array, the rotation speed of the rotating polygon mirror is stabilized based on the signal output from the beam detection means, and the beam The scanning speed can be stabilized.
[0033]
【The invention's effect】
According to the present invention, the main scanning position of an image formed by each light beam can be stabilized.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram of an image forming apparatus according to a second embodiment of the present invention.
FIG. 3 is a configuration diagram of an image forming apparatus according to a third embodiment of the present invention.
FIG. 4 is a diagram for explaining the influence of a beam interval along a scanning direction.
FIG. 5 is a second diagram illustrating the effect of a beam interval along a scanning direction.
FIG. 6 is a diagram for explaining timing to a beam detection output pulse in FIG. 4;
FIG. 7 is a diagram illustrating timings to beam detection output pulses in FIGS. 4 and 5;
FIG. 8 is a diagram illustrating an image forming apparatus using a semiconductor laser array in a conventional example.
FIG. 9 is a diagram illustrating scanning of a laser spot in FIG. 8;
[Explanation of symbols]
REFERENCE SIGNS LIST 1 semiconductor laser array 2 collimator lens 3 rotating polygon mirror 4 motor control circuit 5 photosensitive drum 9 beam detector 10 beam detection circuit 11 pulse interval measurement circuit 12 pulse shaping circuit 13 A / D conversion circuit 14 CPU
15-17 Image start timing adjustment circuits 18-20 Image signal generation circuits 21-23 Light modulation circuit 24 Pulse interval storage circuit 25 Period measurement circuit 27 Comparison circuit 28 Reference period holding circuit 29 D / A conversion circuit 104 Scanning lens 106 Reflection mirror 109 Light shielding plates L1 to L4 Laser beam

Claims (3)

Modulating means for modulating each of the plurality of light beams according to the image signal output from the image signal generating means,
Scanning means for scanning a light beam group consisting of the plurality of light beams on the photoconductor in a manner in which the plurality of light beams are obliquely shifted with respect to the main scanning direction and the sub-scanning direction ;
Beam detection means for detecting a light beam group scanned by the scanning means at a predetermined position and outputting a detection pulse train;
Shaping means for forming a single pulse that determines a reference time from the detection pulse train,
Time adjustment means for measuring the time interval of the detection pulse, and adjusting the time from the single pulse to the image signal output based on the measurement result,
An image forming apparatus comprising: a scanning control unit that measures a period of the single pulse and controls a scanning period of the scanning unit based on the measurement result. The scanning unit includes a rotation driving unit,
The image forming apparatus according to claim 1, wherein the scanning control unit controls a rotation frequency of the rotation driving unit according to a comparison result between a cycle of the single pulse and a reference cycle. Developing means for converting the electrostatic latent image formed on the photoconductor by the light beam into a visible image,
2. The image forming apparatus according to claim 1, further comprising a transfer unit configured to transfer the visible image to a sheet.

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