JPH0720391A - Optical scanner - Google Patents

Abstract

PURPOSE:To improve universal applicability by using pulse width data for ftheta error correction in accordance with selected resolution in a device which performs the correction of an ftheta error electrically. CONSTITUTION:The pulse width data for ftheta error correction which decides driving pulse width in accordance with each dot in one scan is stored in two- kind memory 33 of 300dpi and 400dpi to correct the fgamma error generated by the change of scanning speed during one scan of a laser ray, and the pulse width data for ftheta error correction in accordance with the designation of resolution are read out from the memory 33 by switching the address of the memory 33 designated by an address counter 32 by a resolution switching signal inputted to the address counter 32. The output timing of image data inputted by a programmable counter 35 which counts a reference clock to the laser diode driver 37 can be decided based on read out pulse width data for ftheta error correction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used for laser printers, laser fax machines, digital copying machines and the like.

[0002]

2. Description of the Related Art An optical scanning device used in a laser printer, for example, deflects and scans a laser beam and irradiates it on a photosensitive surface. However, in such an optical scanning device, main scanning / sub-scanning field curvature, It is general to perform optical correction of optical aberrations such as scanning line curvature, fθ correction, and surface tilt, and a structure in which a plurality of fθ lenses and a surface tilt correction cylindrical lens are combined is known. Also, to simplify the optical system,
It is also known to perform optical aberration correction by using a combination of an elliptic cylinder polygon mirror and a double-sided aspherical correction lens without using the fθ lens.

Of the optical aberrations, an fθ error (an error that the interval between pixels is not constant because the scanning speed of the laser light on the scanning surface changes depending on the scanning position when the laser light is scanned at a constant angular velocity) With respect to (1), it is also known to perform electrical correction and optically correct other aberrations.

For example, in Japanese Patent Laid-Open No. 2-131212, as shown in FIG. 11, a divergent laser beam from a semiconductor laser 1 is converged by a collimator lens 2 or corrected into a parallel light beam, and the corrected laser beam is cylindrical. Lens 3
The polygon mirror 4 is irradiated with the polarized light through the toroidal deflector, and the deflected light is reflected by the folding mirrors 6 and 7 via the toroidal lens 5 to form an image on the photosensitive drum 8, and the main scanning line 9 is scanned. In this case, the main scanning line 9 has a difference in scanning speed from the central portion to the end portion, that is, the scanning speed at the end portion is higher than that at the central portion, so that exposure may be performed at isochronous timing. The dot pitch varies.

Therefore, the entire area of the main scanning line 9 is divided into two parts at the center, and half of each area is divided by a to a as shown in FIG.
It is divided into 7 blocks of g, and in each of the blocks a to g, 1 is obtained by 10 pulses of the reference clock which is 10 times the print clock.
By changing the ratio between the part that forms the dot and the part that forms one dot for 9 pulses, the dot print timing is advanced toward the end, and the print interval is macroscopically uniform from the center to the end. Therefore, the fθ error is electrically corrected.

Then, the fθ error correction pulse width data for determining such dot printing timing is stored in the ROM, and the fθ error correction pulse width data is read from the ROM for each scanning to control the laser light on / off. It has become.

[0007]

However, in this publication, no measures are taken against the resolution.
It was not applicable to a device that can select and use multiple resolutions.

In view of this, the present invention provides an optical scanning device for electrically correcting an fθ error, in which the pulse width data for fθ error correction to be used can be switched according to the selected resolution and the versatility can be improved. To do.

[0009]

SUMMARY OF THE INVENTION The present invention is an optical scanning device for deflecting and scanning laser light that is turned on and off based on recording information, and imaging the laser light on a photosensitive surface to record information in dot units. , Fθ which determines the drive pulse width corresponding to each dot in one scan in order to correct the fθ error caused by the change in the scanning speed of the laser beam during one scan
A storage unit that stores a plurality of patterns of error correction pulse width data corresponding to various resolutions and a laser that reads out fθ error correction pulse width data corresponding to the resolution selected from the storage unit for each scanning according to resolution selection The control means for controlling the light on / off is provided.

[0010]

According to the present invention, the pulse width data for f.theta. Error correction corresponding to the resolution selected from the storage means is read out for each scanning in response to the selection of the resolution, and the laser light is turned on and off.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, a laser beam from a semiconductor laser oscillator 11 is converted into a diverging light beam by a converging lens 12 and then shaped into a circular beam by a slit 13, and the beam is reflected by a reflecting mirror. After changing the optical path at a right angle by reflecting the light onto the rotor 14, the rotor 15a of the scanner motor 15
The two 45 ° reflecting surfaces of the right-angle prism 16 arranged on the rotating shaft 15b are irradiated. That is, the right-angled prism 16 has two surfaces that are orthogonal to each other as reflection surfaces. Then, the center of the rectangular surface sandwiched between these two reflecting surfaces is arranged in alignment with the rotating shaft 15b of the scanner motor 15, and the reflected light from the reflecting mirror 14 is separated from the rotating shaft 15b of the scanner motor 15 by several mm. The light is incident on the position parallel to the rotation axis 15b.

The scanner motor 15 has a magnet 15c integrally attached to a rotor 15a. The rotating shaft 1
5b is rotatably attached to a stator member 15d via a ball bearing 15e. The stator member 15
A circuit board 15g is fixed to d via a spacer 15f, and a coil 15h is attached to the back surface side of the portion of the circuit board 15g facing the magnet 15c.

The reflected light from the reflecting mirror 14 is reflected by the reflecting surface of the rectangular prism 16 which is rotationally driven by the scanner motor 15, and is converted into deflected light which is deflected and scanned in a plane direction perpendicular to the rotation axis 15b of the scanner motor 15. After that, the radius of curvature of the exit surface is smaller than that of the entrance surface, and the light enters the meniscus lens 17 that is convex toward the outside, and as shown in FIG. 3, it is a position separated by a distance L from the deflection point, that is, the reflection point of the rectangular prism 16. An image is formed on the photosensitive surface 40 of the photosensitive drum located at. The maximum deflection angle from the center of this deflected light is θ.

The semiconductor laser oscillator 11, the converging lens 12 and the slit 13 are integrated as a light emitting unit 18. The meniscus lens 17 is incorporated in a case 19. Then, the light emitting unit 18 is fitted into the upper rear part of a housing 20 surrounding the entire device made of, for example, a synthetic resin, the reflection mirror 14 is embedded in an upper front inclined part of the housing 20, and the case 19 is housed in the housing. It is fitted in the front opening of 20.

The stator member 1 of the scanner motor 15
The flange portion of the housing 20 is screwed to the peripheral portion of 5d.

The deflected light from the reflecting surface of the rectangular prism 16 forms an image on the photosensitive surface 40 of the photosensitive drum, and the scanning speed on the photosensitive surface goes from the central portion to the end portion as shown in FIG. As you get faster.

Therefore, when the clock is determined so that the maximum angle of view is obtained at a position 110 mm away from the center, the scanning position is 65 mm.
The speed in the vicinity becomes the average (reference) scanning speed, and when the print clock is determined based on this, the central dot shrinks from the regular dot position to the central portion, and the edge gradually approaches the regular position 1
It comes to overlap with the regular position at the position of 10 mm. That is, the relationship between the scanning position and the maximum position error is as shown in the graph (a) of FIG.

Therefore, in order to digitally correct such an f.theta. Error, the scanning distance 110 mm from the center to the end is divided into five blocks b1 to b5 as shown in FIG. And b1 block is 40mm, b2 block is 1
8mm, b3 block is 16mm, b4 block is 18mm,
Set the b5 block to 18 mm.

For example, if one scanning width is 220 mm, the resolution is 2598 dots at 300 dpi, and 3 dpi at 400 dpi.
It becomes 464 dots. And at 300dpi, b1 block is 473 dots, b2 block is 212 dots, b
3 blocks have 189 dots, b4 blocks have 213 dots, and b5 blocks have 212 dots. Also, 400
In dpi, the b1 block has 630 dots, the b2 block has 283 dots, the b3 block has 252 dots, the b4 block has 284 dots, and the b5 block has 283 dots.

Therefore, if a clock 16 times as fast as the print clock is used as the reference clock, at 300 dpi, the b1 block constitutes one dot with 16 reference clocks, the ratio of 1/18, and 1 with 15 reference clocks. The dots make up a ratio of 17/18.
In the b2 block, one reference dot with 15 reference clocks makes up one half, and one reference dot with 14 reference clocks gives one half. Also b
Three blocks form one dot with 14 reference clocks. In the b4 block, one dot is composed of 14 reference clocks, and the ratio is 1/3.
The ratio of one dot to one dot is 2/3. Further, the b5 block has a ratio of 1/3 when one dot is composed of 13 reference clocks and a ratio of 2/3 when one dot is composed of 12 reference clocks.

At 400 dpi, the b1 block has a ratio of 4/19 when 12 reference clocks make up 1 dot and a ratio of 15/19 when 11 dots make up 1 reference clock. For the b2 block, the one that forms one dot with 11 reference clocks is 17/20.
The ratio of 10 dots forming one dot with 10 reference clocks is 3/20. In the b3 block, the ratio of 11 dots forming one dot with 11 reference clocks and one dot forming one dot with 10 reference clocks is 1/2. Also, the b4 block is 1 with 10 reference clocks.
The ratio of dots forming dots is 39/40, and the ratio of dots forming one dot with nine reference clocks is 1/40. Furthermore, the b5 block is 1 with 10 reference clocks.
The ratio of dots forming the dot is 2/9, and the ratio of dots forming one dot with nine reference clocks is 7/9.

By defining the print pulse width in accordance with the above rules, it is possible to digitally correct the fθ error when the resolution is 300 dpi and 400 dpi.

FIG. 7 is a block diagram showing the circuit configuration.
Is a line counter that starts counting by a write position detection signal. The count output of the line counter 31 is input to the address counter 32.

A memory 33 stores fθ error correction pulse width data for digitally correcting the above-mentioned fθ error. That is, as shown in FIG. 8, f of 300 dpi resolution is assigned to addresses "0000" to "0FFF".
Stores the pulse width data for θ error correction, and
The pulse width data for fθ error correction having a resolution of 400 dpi is stored in “0” to “1FFF”. Fθ of resolution 300dpi
The error correction pulse width data consists of data of 2598 pixels + n pixels, and the fθ error correction pulse width data of resolution 400 dpi consists of data of 3464 pixels + m pixels. (N, m ≧ 1 integer). In this embodiment, n =
It is assumed that m = 1.

The reason for increasing the pixel data for one line is to make the dot period constant in each line by shifting the fθ error correction pulse width data of the pixels used between adjacent main scans. This prevents vertical line moire from occurring.

Switching of fθ error correction pulse width data of 300 dpi and 400 dpi is performed by a resolution switching signal. When the resolution switching signal is "0", fdpi of 300 dpi is selected.
Error correction pulse width data is selected. When the resolution switching signal is "1", 400 dpi f.theta. Error correction pulse width data is selected.

The fθ error correction pulse width data read from the memory 33 according to the count data from the address counter 32 is latched by the latch circuit 34, and the output of the latch circuit 34 is programmable counter 35.
Are typing in.

Reference numeral 36 is a reference clock oscillator which generates a reference clock 16 times as high as the print clock. The reference clock from the oscillator 36 is counted by the programmable counter 35.

The programmable counter 35 compares the data from the latch circuit 34 with the count value of the reference clock, and outputs the input image data to the laser diode driver 37 at the timing when the count value reaches the data.

The laser diode driver 37 drives the above-mentioned semiconductor laser oscillator 11 based on the input image data.

In the embodiment having such a configuration, the laser light from the semiconductor laser oscillator 11 is converted into a diverging light beam by the converging lens 12 and then becomes a circular beam by the slit 13. The laser beam that has become a circular beam is reflected by the reflection mirror 14 and the optical path is changed at a right angle to change the scanner motor 15
It irradiates the reflecting surface of the rectangular prism 16 arranged on the rotating shaft 15b. Then, the laser light becomes deflection scanning light that scans in a plane direction perpendicular to the rotation axis by the rotating right-angle prism 16. This scanning light forms an image on the photosensitive surface 40 via the meniscus lens 17.

The line counter 31 starts the counting operation in response to the writing position detection signal S shown in FIG. 6 (a). When the line counter 31 reaches a predetermined value, the address counter 32 addresses the memory 33.

For example, if the resolution switching signal input to the address counter 32 is a "0" signal designating a resolution of 300 dpi, the memory 33 outputs f of 300 dpi.
The θ error correction pulse width data is output to the latch circuit 34.
To enter. The programmable counter 35 outputs the data from the latch circuit 34 and the reference clock oscillator 36.
The image data is supplied to the laser diode driver 37 with a length according to the result of counting the reference clock from the laser diode driver 37 to control the oscillation of the semiconductor laser oscillator 11.

Thus, as shown in FIG. 6B, b5, b4, b3, b2, b1, b1, b2, b in one scan.
The output control of each block of 3, b4, and b5 is performed, and a total of 2,598 dots are printed.

When the resolution is 300 dpi, the 1st to 2598th data are read from the memory 33 and latched in the latch circuit 34 as shown in FIG. As shown in FIG. 9B, the 2nd to 2599th data are read from the memory 33 and latched in the latch circuit 34.

That is, in the scanning of even lines, in the b5 block, 13 dots of the reference clock output 1 dot once, then 12 dots of the reference clock output twice to form 1 dot. Repeat output control.

In the b4 block, 14 reference clocks output 1 dot forming one dot, and then 13 reference clocks output 1 dot forming twice.
Thereafter, this output control is repeated.

In the block b3, only the output control for forming one dot with 14 reference clocks is performed.

Further, in the block b2, output control is performed in which an output forming one dot with 15 reference clocks and an output forming one dot with 14 reference clocks are alternately repeated.

Further, in the b1 block, 16 reference clocks output 1 dot forming once, then 15 reference clocks output 1 dot forming 17 times, and this output control is repeated thereafter.

As a result, the output control of one half of one scanning is completed, and the output control of the other half is performed in the order of b1, b2, b3, b4 and b5 blocks.

When the scanning of the even lines is completed in this way, the scanning of the odd lines is performed next. At this time, the beginning of the b5 block starts from the second data. That is, in the odd-numbered b5 block, first, 12 reference clocks output 1 dot to form one dot, then 13 reference clocks output 1 dot to output once, and then 12 reference clocks output. The output that forms one dot is performed twice,
After that, the output forming one dot with 13 reference clocks once and the output forming one dot with 12 reference clocks twice are repeated.

Thus, fθ is even between the even line and the odd line.
Since the pattern of the error correction pulse width data is shifted, the same pulse width does not occur at the same position in the main scanning direction between the lines, and it is possible to prevent vertical line moire from occurring as much as possible.

If the resolution switching signal input to the address counter 32 is a signal of "1" designating a resolution of 400 dpi, then the memory 33 outputs fθ of 400 dpi.
The error correction pulse width data is output and input to the latch circuit 34. Then, the programmable counter 35 supplies image data to the laser diode driver 37 with a length according to the result of counting the data from the latch circuit 34 and the reference clock from the reference clock oscillator 36,
The oscillation of the semiconductor laser oscillator 11 is controlled.

Thus, in one scan, b5, b4, b3
, B2, b1, b1, b2, b3, b4, b5, output control of each block is performed, and a total of 3464 dots are printed.

Then, when the resolution is 400 dpi, 4096 to 7 as shown in FIG.
The 560th data is read out from the memory 33 and latched in the latch circuit 34.
As shown in (4), the 4097th to 7561th data are read from the memory 33 and latched in the latch circuit 34.

That is, in the scanning of even lines, in the b5 block, the output of forming one dot with 10 reference clocks is first performed once, and the output of forming one dot with 9 reference clocks is then performed three times, and then, The output of forming one dot with 10 reference clocks is performed once, the output of forming one dot with 10 reference clocks is performed four times, and this output control is repeated thereafter.

In the b4 block, 10 reference clocks output 1 dot forming 39 dots, and then 9 reference clocks output 1 dot forming 1 time.
Thereafter, this output control is repeated.

Further, in the block b3, the output forming one dot with 11 reference clocks and the output forming one dot with 10 reference clocks are alternately performed.

In the b2 block, 11 reference clocks output 1 dot forming 17 dots, 10 reference clocks output 1 dot forming 3 times, and this output control is repeated thereafter.

In the b1 block, 12 reference clocks output 1 dot forming 4 times, 11 reference clocks output 1 dot forming 15 times, and this output control is repeated thereafter.

As a result, the output control of half of one scan is completed, and the output control of the remaining half is performed in the order of b1, b2, b3, b4 and b5 blocks.

When the scanning of the even lines is completed in this way, the scanning of the odd lines is performed next. At this time, the beginning of the b5 block starts from the 4097th data. That is, in the odd-numbered line b5 block, first, the output that forms one dot with nine reference clocks is performed, this output is performed three times, and then the output that forms one dot with ten reference clocks is performed once, To output 1 dot with 9 reference clocks four times, then 1 with 10 reference clocks
The output forming the dot is performed once, and thereafter the output control is repeated.

In this way, even when the resolution is 400 dpi, the patterns of the fθ error correction pulse width data are shifted between the even lines and the odd lines, so that it is possible to prevent the occurrence of moire on the vertical lines as much as possible.

As described above, f of 300 dpi is stored in the memory 33.
The pulse width data for θ error correction and the pulse width data for fθ error correction of 400 dpi are stored, and each data is selectively read by the resolution switching signal to control the output timing of the image data. The resolution switching can be dealt with easily and the versatility can be improved.

In the above embodiment, the memory 33 has 300
The pulse width data for fθ error correction of two kinds of resolutions of dpi and 400 dpi are stored, and the corresponding data is selectively read by switching the resolution, but the present invention is not limited to this, for example, 300 dpi, 400 dpi, 6
Data with a resolution of 00 dpi may be stored, and data with a resolution of three or more types may be selected by selectively reading the corresponding data by switching the resolution.

Further, in the above embodiment, f at each resolution
The length of the pulse width data for θ error correction is 2599 dots,
As for 3465 dots, the reading range of the data of 1 scan is 3
For 00dpi, there are two types, 0-2598 and 1-2599, and for 400dpi, 4096-7560 and 4097.
The occurrence of moire was prevented as two types of ˜7561. However, the present invention is not limited to this, and the data length is further increased to set three or more read patterns at the same resolution. Moire may be prevented from occurring by selectively reading.

[0059]

As described above, according to the present invention, in the case of electrically correcting the fθ error, the pulse width data for fθ error correction to be used can be switched according to the selected resolution, and the versatility can be improved. .

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention with a housing omitted.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a diagram showing a scanning range on a photosensitive surface in the embodiment.

FIG. 4 is a diagram showing a relationship between a change in scanning speed and a maximum position error in the embodiment.

FIG. 5 is a diagram showing a relationship between a scanning position, a divided block, and a maximum position error in the embodiment.

FIG. 6 is a diagram showing a write start position detection signal and a print scanning range in the embodiment.

FIG. 7 is a block diagram showing a control circuit configuration of the embodiment.

FIG. 8 is a diagram showing an address relationship of a memory unit in the embodiment.

FIG. 9 is a view showing a pulse width data pattern for fθ error correction with a resolution of 300 dpi in the embodiment.

FIG. 10 is a view showing a pulse width data pattern for fθ error correction with a resolution of 400 dpi in the embodiment.

FIG. 11 is a perspective view showing a conventional example.

FIG. 12 is a diagram showing a cycle of a laser control signal with respect to a scanning position in the conventional example.

[Explanation of symbols]

 11 ... Semiconductor laser oscillator 15 ... Scanner motor 16 ... Right angle prism 31 ... Line counter 32 ... Address counter 33 ... Memory 35 ... Programmable counter 37 ... Laser diode driver

Claims (1)

[Claims] 1. An optical scanning device for deflecting and scanning a laser beam that is turned on and off based on recording information, forming an image of the laser beam on a photosensitive surface, and recording information in dot units, during one scanning of the laser beam. In order to correct the fθ error caused by the change in the scanning speed, a storage unit that stores a plurality of fθ error correction pulse width data that determines the drive pulse width corresponding to each dot in one scan, corresponding to various resolutions, and a resolution. An optical scanning device comprising: a control means for reading out fθ error correction pulse width data corresponding to the resolution selected from the storage means for each scanning in response to selection and for controlling on / off of laser light.