JPH0263847A - Optical scanner - Google Patents

Abstract

PURPOSE:To make respective main scanning lines uniform in length by a method wherein correction clocks for respective reflecting surfaces obtained by measuring a laser light main scanning time for every reflecting surface of a polygon mirror are randomly dispersed in a printing clock using a random circuit. CONSTITUTION:Based on a detection signal from a mirror sensor part 35 detecting the rotation of a polygon mirror 6, respective reflecting surfaces 71-76 are discriminated. Counters 341-344 count a time difference between a detection signal outputted from a start sensor part 12 and that from an end sensor part 16 by the pulse of a reference clock A, whereby a main scanning time is measured for each of the reflecting surfaces 71-76. Then, in a printing clock B corresponding to the reflecting surface 7 conducting a short main scanning, count enable signals are inserted by the predetermined number by a count enable signal generator 36 and, furthermore, inserting timings are made random by a random circuit 37 and a shift circuit 38, and a correction printing clock D is formed. In this manner, a laser spot scanning and traveling on a photosensitive body can be made uniform in main scanning speed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical scanning device that performs printing using a dot matrix method.

BACKGROUND OF THE INVENTION A first conventional example of an optical scanning device will be described with reference to FIGS. 4 to 6. In this optical scanning device 1, an irradiation optical system 5 is formed from a laser diode 2, a cylindrical lens 31, a convergent lens 32, a reflection mirror 4, etc., and a polygon mirror 6 has its reflection surfaces 71 to 7B sequentially connected to the irradiation optical system. It is directly connected to a scanner motor (not shown) so as to be on the optical axis of the system 5. Here, the laser diode 2 is connected to a print data circuit section (not shown) that operates in synchronization with a print clock B, which will be described later. Further, a correction lens 8 and a photosensitive drum 9, which is a photosensitive member, are arranged on the optical axis of the laser light that is reflected by the reflective surfaces 71 to 76 of the polygon mirror 6 and performs main scanning. In addition, at the start position of the main scanning range of the laser beam, there is a reflection mirror 1 in this case.
A start sensor section 12 formed from a start sensor 11 and a start sensor 11 is provided. Further, in this optical scanning device 1, a reference clock composed of a crystal oscillator or the like and a print clock (both not shown) used for dot irradiation timing, which is obtained by dividing the reference clock by an integer, are set.

In this configuration, the optical scanning device 1 is provided with a print clock B whose frequency is divided every 8 pulses of the reference clock A, and one dot 14 of the image 13 is printed every 8 pulses of the reference clock A. It will be output. Therefore, in synchronization with such printing clock B, the irradiation optical system 5
Laser light corresponding to the image information is emitted from the This laser beam is then reflected by the rotating polygon mirror 6.

The converging lens 32 and the correction lens 8 form an image on the photosensitive drum 9 as a laser spot. At this time, the laser spot moving in the main scanning direction is relatively moved in the sub-scanning direction by the rotation of the photosensitive drum 9. In this way, the image 13 is scanned on the photosensitive drum 9 using the dot matrix method to form a latent image, which is transferred onto paper using an electrophotographic printing method or the like to complete printing of the image 13. Here, in this optical scanning device 1, control is not performed so that the main scanning of the image 13 and the rotation of the polygon mirror 6 are synchronized. Therefore.

In order to accurately arrange the dots 14 of the image 13, the main scanning laser beam is detected by the start sensor section 12,
Based on the synchronization of the start signal SL+82... generated from the start sensor section 12 and the reference clock A,
A print clock B for each main scan is started. Therefore,
As illustrated in FIG. 6, a certain start signal S1+82
Due to the slight deviation present in the reference clock A, the dot 14 is printed with a delay of one pulse of the reference clock A. Dot 1 at the start position of such a main scanning line
The deviation of 4 can be reduced by forming the print clock B by finely dividing the high-frequency reference clock A. However, there is a limit to this because it is necessary to detect synchronization between the reference clock A and the start signal S. Further, since the width of such a shift is about 1/8 of one dot, it is not considered a problem in normal image formation. In other words, the above frequency division ratio is set based on the allowable range of dot deviation.1For example,
If a deviation of about 1/4 dot is acceptable, the frequency division ratio can be set to 1/4.

The optical scanning device 1 as described above can perform printing quickly and quietly. Here, the polygon mirror 6 that deflects light inevitably has eccentricity of its axis, angular errors of each of the reflecting surfaces 71 to 76, and the like. Therefore, as illustrated in FIG. 5, the printed image 13 has a portion 1 corresponding to the main scanning start position.
31, the dots 14 are generally beautifully aligned, but in a portion 132 corresponding to the end position of the main scan, the dots 14 are periodically shifted and unsightly. The width of such a shift is proportional to the length of the main scanning line, and may be as much as 2 to 6 dots, for example. Here, such a shift is due to the manufacturing error of the polygon mirror 6 and the scanner motor described above, and here, the polygon mirror 6 has six reflecting surfaces 71.
76, the deviation of the main scanning line occurs periodically with each person as one cycle. Due to this misalignment, the image 13 printed by the optical scanning device 1 has a low quality and is unsightly. Therefore, as a solution to the above-mentioned problems, Japanese Patent Application Laid-Open No. 133009/1983 has proposed a method that solves the above problems. There is a disclosed scanning light control clock correction device. Therefore, an optical scanning device using this scanning light control clock correction device will be described as a second conventional example with reference to FIGS. 7 to 9. In addition, the fourth
The same parts as the optical scanning bag M1 illustrated in the figure are given the same names and symbols, and descriptions thereof will be omitted. The optical configuration of this optical scanning device 15 is such that an end sensor section 16 is also provided at the end position of the main scanning range of the laser beam. Therefore, the scanning light control clock correction device 17 of the irradiation optical system of the optical scanning device 15 will be explained with reference to FIG. 7.

The start sensor section 12, the lower engine sensor section 16, and the reference clock generator 18 are connected to a memory 21 via a clock gate 19 and a first counter 20. Further, a second counter 22 for counting the number of main scans from the output of the start sensor section 12 is also connected to the memory 2.
1 is connected to a variable branching unit 24 and an up/down counter 25 via a ROM 23. And this up/down counter 25 is.

It is connected via a delay circuit 26 to a data selector 27 to which the clock gate 19 is connected.

In such a configuration, the first counter 20 counts the main scanning time from the output of each sensor unit 12, 16, and the main scanning time for each reflective surface 71 to 7e is stored in the memory 21 based on this and the output of the second counter 22. Time is recorded. Therefore, when the same reflective surfaces 71 to 76 perform main scanning again, the ROM
From 23, an operating pulse is outputted to the variable frequency divider 24 using each of the above-mentioned main scanning times as an address, and a correction direction for increasing or decreasing the main scanning time is outputted to the up/down counter 25. Further, as illustrated in FIG. 8, the delay circuit 26 allows the data selector 27 to output the reference clock generator 18.
Pulse trains φ0 to φ7 are formed by sequentially shifting the pulse train emitted by At(see) corresponding to one pulse. Therefore, the data selector 27 selects one of the desired pulse trains φ0 to φ7 as the corrected print clock C according to the count of the up/down counter 25. On the other hand, this corrected print clock C is counted by the variable division divider 24, and the up/down counter 25 is counted again according to this counted value. Then, the up/down counter 25 sequentially changes the pulse train φ0 to φ7 outputted via the data selector 27 as the count increases. Note that the frequency of these pulse trains φ0 to φ7 is the same as that of the reference clock A.

Only the phase is shifted.

An image 28 printed according to such a scanning light control clock correction device 17 has gaps 29 periodically formed in a predetermined main scanning line, as illustrated in FIG. The portion corresponding to the starting position of 30. Similarly, the dots are beautifully aligned in a portion 302 corresponding to the end position of the main scan. Note that this gap 29 corresponds to, for example, one pulse of the reference clock A, and here has a width of about 178 dots.

Problems to be Solved by the Invention In the image 28 printed by the optical scanning device 15 using the scanning light control clock correction device 17 as described above, the dots 14 are beautifully aligned even in the portion 302 corresponding to the end position of the main scan. It is effective.

However, since the gap 29 formed in the main scanning line exists at the same position in the main scanning line due to the same reflecting surfaces 71 to 76, one image 28 does not have a moire pattern like a stripe running in the sub-scanning direction. This tends to cause unevenness. Therefore, the printing quality of the optical scanning device 15 is low.

In addition, in the optical scanning device 15 as described above, the laser beam is main scanned at a constant angular velocity around the polygon mirror 6, so the main scanning speed of the laser beam on the photosensitive drum 9 is slow near the center. It becomes faster near the end. Therefore, the laser beam is refracted just before it enters the photosensitive drum 9 using a correction lens 8 having two wave-shaped curves, thereby correcting the main scanning speed to make it uniform, but this is not perfect.

Means for solving the problem In an optical scanning device that performs printing based on image information synchronized with a print clock obtained by dividing the frequency of a reference clock by an integer, a starting point placed at the start side of the main scanning range of the laser beam is used. A main scanning time measuring means is provided for measuring the main scanning time of the laser beam for each reflecting surface of the polygon mirror using a sensor section and an end sensor section disposed on the end side, and based on these measured main scanning times, Calculate the number of reference clocks required for scanning a main scanning line of a certain length for each reflecting surface, and calculate the number of reference clocks counted during scanning of a main scanning line by one reflecting surface and during scanning by another reflecting surface. A correction clock number calculation means is provided to calculate the difference from the reference clock number for each reflecting surface, and a random number circuit is used to randomly calculate the correction clock for each reflection surface during the printing clock. Main scanning line length matching means for distributing the main scanning lines is provided.

In an optical scanning device that performs printing based on image information synchronized with a print clock obtained by dividing the frequency of an operation reference clock by an integer, a start sensor section is installed at the start side of the main scanning range of the laser beam, and a sensor section is installed at the end side of the main scanning range of the laser beam. A main scanning time measuring means is provided which measures the main scanning time of the laser beam for each reflective surface of the polygon mirror using an end sensor unit provided, and a main scanning time of a constant length is provided based on each of the measured main scanning times. Calculate the number of reference clocks required for scanning a line for each reflective surface, and calculate the difference between the number of reference clocks counted during scanning of the main scanning line by one reflective surface and the number of reference clocks counted during scanning by other reflective surfaces. A correction clock number calculation means is provided for calculating the number of correction clocks for each reflecting surface, and a main scanning line length is provided in which the correction clocks for each reflection surface calculated by the correction clock calculation means are randomly distributed among the print clocks using a random number circuit. By providing an alignment means, it is possible to make the length of each main scanning line uniform, and furthermore, to make the scanning speed during one main scanning uniform, the printing clock of each reflective surface can be adjusted to the areas where the scanning speed is high. It is also possible to provide a scanning speed correction means that is set to insert a relatively large number of speed correction clocks, so that the main scanning speed of the laser spot that scans and moves on the photoreceptor can be made uniform.

Embodiment A first embodiment of the present invention will be explained based on FIGS. 1 and 2. First, the configuration of the optical member of the optical scanning device 31 of this embodiment illustrated in FIG. 2 includes an end sensor section 16, similar to the optical scanning device 15 described above. Therefore, the image information output device 3 of this optical scanning device 31
2 will be explained with reference to FIG. This output device 32
Here, the start sensor section 12, end sensor section 16, and reference clock generator 18 are connected to a main counter 33 that also serves as a frequency divider, and four counters that are main scanning time measuring means that count up to four digits with digital values. 341 to 344. Furthermore, these counters 341 to 34
4 and a mirror sensor unit 35 that detects the rotation of the polygon mirror 6 are connected to a count enable signal generator 36. Here, this count enable signal generator 36 calculates a count enable signal that is a correction clock that increases or decreases the number of pulses of the print clock B, and
B. The count enable signal generator 36 is connected to the main counter 33 via a shift circuit 38 to which a random number circuit 37 is connected.
9 is provided. And this main counter 33
is connected to a laser driver 41 that controls the irradiation optical system 5 via a print data circuit section 40 .

In such a configuration, first, the setting operation of the corrected print clock D of this optical scanning device 31 will be explained. For example, if the paper (not shown) used for printing is A4 paper and the dot density is 300 dots/inch, the main scanning line of the optical scanning device a31 will be formed by approximately 2,600 dots. Here, if this optical scanning device 31 divides the frequency of the reference clock A into one dot by dividing it every 8 pulses in the same way as the optical scanning device 1 described above, then - the reference clock A is output during the main scanning line. The number of pulses is 20,800 pulses. Here, the counters 341 to 344 are formed to count up to four digits with digital values, so 65
It is possible to count up to 536 pulses (=16'). Therefore, each of the reflecting surfaces 71 to 76 is determined based on the detection signal of the mirror sensor section 35 that detects the rotation of the polygon mirror 6, and the time difference between the detection signals output from the start sensor section 12 and the end sensor section 16 is set as a reference. The counters 34L to 344 count based on the pulses of the clock A. In this way, the main scanning time, which is proportional to the main scanning line length, is measured for each of the reflecting surfaces 71 to 76. Also,
The optical scanning device 31 is set here to align the other main scanning lines with the longest main scanning line as a reference. Therefore, for example, the optical scanning device 31 operates the polygon mirror 6 and the like at the time of starting up the machine, and calculates the difference in the number of pulses of the reference clock A required for scanning each main scanning line. . Then, during the print clock B corresponding to the reflective surface 7 that has undergone a short main scan, a count enable signal is generated 936.

A predetermined number of count enable signals, which are the results of the calculation described above, are inserted, and the random number circuit 37 and shift circuit 38 randomize the insertion timing of the count enable signals to form a corrected print clock D.

After registering the corrected printing clocks D1 to D6 for each of the predetermined reflective surfaces 71 to 7B in this way, this optical scanning device 31
becomes ready for printing.

Therefore, this optical scanning device t! Printing by No. 31 will be explained. First, a laser beam irradiated from the irradiation optical system 5 is reflected by the rotating polygon mirror 6 and enters the start sensor 11 . Then, a start signal S is issued from the start sensor 11 and one image scanning is started. At this time, the main scanning line length matching means 39 determines the reflecting surface 7 that has reflected the laser beam based on the output of the mirror sensor section 35, and detects the reflection surface 7 via the main counter 33 in synchronization with the counts of the counters 341 to 344. A corrected print clock D is output. Incidentally, the number of print timings present in the corrected print clock D corresponds to one pulse of the reference clock A, and the width of the gap (not shown) between the dots 14 is equal to one pulse.
It is about 1/8 of a dot. And this laser light is
After completing one main scan of the image (not shown), the end sensor unit 1
6.

Then, based on the output of this end sensor section 16.

Counter 34. The count of ~344 is cleared and preparations are made for the next scan by the reflective surface 7.

In this way, the latent image of the image is scanned on the photosensitive drum 9 by the dot matrix method, and printing of the image is completed by the electrophotographic printing method or the like.

Therefore, the image printed based on the corrected print clock D as described above, similar to the image 28 illustrated in FIG.
The portions of the image corresponding to the end positions of the main scan line up beautifully, and since the positions of the gaps are random, moire-like unevenness does not occur.

Further, in the optical scanning device 31 of this embodiment, the corrected printing clock D is set to match the short main scanning line to the longest main scanning line, but the present invention is not limited to this, and the short main scanning line It is also possible to match long main scanning lines to
In that case, a signal is set that reduces the print clock B by a predetermined number of pulses.

In addition, in the optical scanning device 31 of this embodiment, the positions of the gaps in each main scanning line are simply arranged at random.
The present invention is not limited to this, and for example, it is also possible to control so that one or more voids are not arranged in two dots. By doing so, it is expected that the unevenness of the gaps, which tends to occur in random arrangement, will be prevented, and a more beautiful image will be printed.

Next, a second embodiment of the present invention will be explained based on FIG. In this optical scanning device 42, a ROM 43 is connected to the count enable signal generator 36, and the ROM 43 is connected to the count enable signal generator 36.
M43 and count enable signal generator 36. The random number circuit 37 and the shift circuit 38 form a main scanning line length matching means 44 which also serves as a scanning speed correction means. Further, the configuration of the other optical scanning device 42 is similar to that of the optical scanning device 31 described above. Note that the ROM 43 includes:
Based on the pre-measured main scanning speed of the light spot moving on the photosensitive drum 9, a scanning speed correction clock E for inserting gaps so that the dot spacing on the photosensitive drum 9 becomes uniform is registered. There is.

In such a configuration, printing by the optical scanning device 42 produces a beautiful image with randomly arranged gaps similar to the above-mentioned optical scanning device 31, and furthermore, the spacing between each dot on the main scanning line is also simulated. Since the dot density is uniform in the main scanning direction, the dot density is uniform in the main scanning direction.

Note that in the optical scanning device 42 of this embodiment, the gap and the count enable signal generator 3 are controlled by the scanning speed correction clock E.
Although it was assumed that there was no correlation with the voids due to 6, 5
The present invention is not limited to this, and for example, it may be possible to control the two types of voids to prevent them from overlapping or shifting.

Effects of the Invention The present invention provides an optical scanning device that performs printing based on image information synchronized with a print clock obtained by dividing the frequency of a reference clock by an integer as described above. A main scanning time measuring means is provided for measuring the main scanning time of the laser beam for each reflective surface of the polygon mirror using a start sensor section provided at the end sensor section and an end sensor section arranged at the end side. The number of reference clocks required for scanning a main scanning line of a certain length is calculated for each reflecting surface based on the number of reference clocks counted during scanning of a main scanning line by one reflecting surface and the other reflecting surfaces. A correction clock number calculation means is provided for calculating the difference from the reference clock number during scanning for each reflective surface, and a random number circuit is used to calculate the correction clock for each reflective surface calculated by the correction clock calculation means during printing clock. By providing a main scanning line length matching means that randomly distributes the length of each main scanning line, it is possible to make the length of each main scanning line uniform, and at the same time, the arrangement of the gaps formed in each main scanning line is random. that's why,
The print quality is high because moiré-like unevenness does not occur in the printed image.Furthermore, in order to make the scanning speed uniform during one main scan, the printing clock of each reflective surface is set to a higher number of speeds in areas where the scanning speed is higher. It is also possible to provide a scanning speed correction means that is set to insert a correction clock, so that the main scanning speed of the laser spot that scans and moves on the photoreceptor can be made uniform, so that the main scanning direction of the printed image can be made uniform. The dot density of #1 (rL can be equalized,
This has the effect that higher quality printing is expected.

[Brief explanation of the drawing]

FIG. 1 is a circuit explanatory diagram of one embodiment of the present invention, FIG. 2 is a plan view of the optical configuration, FIG. 3 is a circuit explanatory diagram of the second embodiment of the present invention, and FIG. 4 is a circuit diagram of the first embodiment. A plan view of the conventional example, FIG. 5 is an explanatory diagram of the printed image, FIG. 6 is an explanatory diagram of the dot printing timing, FIG. 7 is an explanatory diagram of the circuit, and FIG. 8 is an explanatory diagram of the pulse train.
FIG. 9 is an explanatory diagram of a printed image. 5... Irradiation optical system, 6... Polygon mirror, 71~
76... Reflective surface, 12... Start sensor section, 16
... End sensor section, 31 ... Optical scanning device, 34x
~344... Main scanning time measuring means, 36... Correction clock calculating means, 37... Random number circuit, 39... Main scanning line length matching means, 42... Optical scanning device, 44...・
Scanning speed correction means, main scanning line length matching means''

Claims (1)

[Claims] 1. A print data circuit unit is provided which outputs image information in the form of dots in synchronization with a print clock obtained by dividing the frequency of a reference clock by an integer, and a print data circuit unit is connected to the print data circuit unit and outputs image information in the form of dots. An irradiation optical system that emits a corresponding laser beam is provided, and a polygon mirror having a plurality of reflective surfaces and rotated at a constant speed by a drive source is arranged so that the reflective surface is located on the optical axis of the irradiation optical system. In an optical scanning device that has a convergence optical system that converges laser light reflected by a polygon mirror and scanned on a photoreceptor into a spot, a start sensor part located at the start side of the main scanning range of the laser light and a start sensor part located at the end side of the main scanning range of the laser light are used. Main scanning time measuring means is provided for measuring the main scanning time of the laser beam for each reflective surface of the polygon mirror using an end sensor section provided, and a fixed length is provided based on each of the measured main scanning times. Calculate the number of reference clocks required for scanning the main scanning line of each reflecting surface, and calculate the number of reference clocks counted during scanning of the main scanning line by one reflecting surface and the number of reference clocks counted during scanning by other reflecting surfaces. A correction clock number calculating means is provided for calculating the difference between the two reflecting surfaces for each reflecting surface, and the correction clocks for each reflecting surface calculated by the correction clock calculating means are randomly distributed in the print clock using a random number circuit. An optical scanning device characterized by being provided with line length matching means. 2. A scanning speed correction means is provided which is set to insert a larger number of speed correction clocks into the printing clock of each reflective surface in areas where the scanning speed is higher so that the scanning speed during one main scan is uniform. The optical scanning device according to claim 1.