JPH0720395A - Laser beam scanning optical device - Google Patents

Abstract

PURPOSE:To perform focusing (adjusting the diameter of a beam) with simple constitution even when the focal distance of an optical system is changed by the change of temperature, etc. CONSTITUTION:Photosensors 21 and 22 are provided at positions optically equivalent to points PI and P2 on a photoreceptor drum, and the focusing of a laser beam (adjusting the diameter of the beam) is performed by using the photosensors 21 and 22. The photosensors 21 and 22 incorporate a photoelectric conversion element, and the beam passing through a slit is made incident on the element. A slit orthogonally crossed with a main scanning direction and an inclined slit thereto are provided as the slit. By detecting the beam passing through the slit orthogonally crossed, the diameter of the beam in the main scanning direction is adjusted. By detecting the beam passing through the inclined slit, the diameter of the beam in a subscanning direction is adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam scanning optical device, and more particularly to a laser beam scanning optical device for forming an image by scanning a surface to be scanned with a laser beam modulated based on image data.

[0002]

2. Description of the Related Art In recent years, in electrophotographic copying machines, digitization of image processing has been adopted in order to promote multifunctional and full-color image editing. In such digitization, a print head used in a laser printer is used as an image printing means on a photoconductor.
This print head modulates and controls a laser diode on the basis of image data, deflects a laser beam emitted from the laser diode by a polygon mirror, and moves the laser beam on the photosensitive member to 1
Scan line by line. This is called main scanning, and an image is two-dimensionally printed on the photoconductor by the main scanning and the sub-scanning by the rotation of the photoconductor. This print head (laser beam scanning optical device) can be easily modulated for each dot, has less image unevenness in the main scanning direction, is relatively easy to narrow the beam diameter, and can be constructed at a low cost.

On the other hand, the print head of a digital copying machine is required to have higher performance than that of a laser printer.
One is the accuracy of the print position. In a digital copying machine, since an error of an original image reading device (image scanner unit) is added, the main scanning magnification, the skew, and the equal pitch property in the main scanning direction are required to have a higher level than the laser printer. Further, it is required that the accuracy of the fluctuation of the printing position in the sub-scanning direction is severe. The fluctuation of the print position in the sub-scanning direction appears as periodic density unevenness (pitch unevenness). This fluctuation is a phenomenon that occurs because the printing position in the sub-scanning direction periodically moves due to the surface tilt error of the polygon mirror, vibration, and the like. The permissible width of fluctuation in the printing position in the sub-scanning direction in a digital copying machine is smaller than that in a laser printer.

By the way, there are an area gradation method, a density gradation method, and a multi-valued dither method which is an intermediate method for expressing the halftone. The area gradation method expresses gradation by changing the printing area by changing the number of dots to be printed with several dots as one unit. The density gradation expresses gradation by changing the density of one dot in units of one dot. As a halftone expression, the density gradation method is superior.
In addition, this method is sensitive to fluctuations in the print position in the sub-scanning direction, and has a narrow fluctuation range. In the area gradation method, if the surface tilt correction rate is about 1 / several tens, the fluctuation of the printing position in the sub-scanning direction becomes about several μm, and there is no problem. However, the density gradation method requires an accuracy of 1 μm or less. For this reason, it is necessary to improve the surface tilt accuracy of the polygon scanner or employ an optical system having a high correction effect.

Increasing the precision of the polygon scanner will increase the manufacturing cost of the polygon scanner itself.
Not preferable. Therefore, it is necessary to adopt an optical system having a high effect of correcting the surface tilt. In the surface tilt correction optical system, the vicinity of the deflection point and the surface to be scanned (photoconductor) have a conjugate relationship in the sub-scanning direction, and the smaller the magnification, the higher the surface tilt correction effect. That is, it is necessary to adopt an optical system having a small magnification in the sub-scanning direction. If the focal length of the fθ lens is constant, in order to reduce the magnification in the sub-scanning direction, it is inevitable to increase the diameter of the lens close to the surface to be scanned.

On the other hand, it is preferable that the print head of a digital copying machine has a small beam diameter in order to improve gradation expression. Also, aberrations such as field curvature and distortion need to be small, which increases the number of lenses,
It was a factor of cost increase. As a solution to this,
It is conceivable to change the material from glass to plastic by reducing the number of lenses with aspherical surfaces. But,
Plastic has the disadvantage that its refractive index and shape change with changes in temperature and the focal length changes. Such a change in focal length actually appears as defocus (change in beam diameter).

The above-mentioned defocus caused by the change in the focal length is
It is conceivable that the laser beam passes through the slit and is received by a photoelectric conversion element at a position optically equivalent to the photoconductor to be detected and adjusted. However, if the slit extends parallel to the main scanning direction, the photoelectric conversion element cannot detect the beam diameter in the main scanning direction, and further, the incident beam is slightly deviated in the sub scanning direction. Detection becomes impossible. Focusing is performed separately in the main scanning direction and the sub-scanning direction, but if the focus in the main scanning direction is adjusted, the focus in the sub-scanning direction may shift.

[0008]

Therefore, an object of the present invention is to perform focusing (adjustment of beam diameter) with a simple structure even if the focal length of the optical system changes due to changes in temperature and the like. Another object of the present invention is to provide a laser beam scanning optical device capable of performing the above. In order to achieve the above object, a laser beam scanning optical device according to the present invention includes a light source that generates a laser beam that is modulated based on image data; and a deflector that deflects the laser beam emitted from this light source. Firstly, the laser beam immediately after being emitted from the light source is converted into parallel light.
A second optical element for linearly focusing the laser beam emitted from the first optical element in the vicinity of the deflection surface of the deflector; and a laser beam deflected by the deflector. A third optical element for forming an image on the scanning surface; a slit orthogonal to the main scanning direction and a slit inclined,
And a focusing sensor means which is composed of a photoelectric conversion element for receiving a laser beam that has passed through these slits, the photoelectric conversion element being installed at a position optically equivalent to the surface to be scanned.

In the above structure, the slit through which the laser beam incident on the photoelectric conversion element passes has an angle with respect to the main scanning direction. Therefore, the beam diameter is detected in both the main scanning direction and the sub-scanning direction, and the focusing is performed so that the beam diameter is minimized. In particular, if the focus in the main scanning direction is adjusted with the laser beam that has passed through the slits that are orthogonal to each other, the rise of the output signal of the photoelectric conversion element becomes steep, which is preferable. Moreover, this output signal is used for the print start position for each line. It can also be used as a reference signal of.

Further, the laser beam scanning optical apparatus according to the present invention comprises a focus adjusting means in the main scanning direction, a means for adjusting the focus in the sub scanning direction independently of the main scanning direction, and a focus in the main scanning direction. And a control unit for adjusting the focus in the sub-scanning direction after the adjustment. As described above, by adjusting the focus in the sub-scanning direction after adjusting the focus in the main-scanning direction, it becomes unnecessary to readjust the focus in the sub-scanning direction, and the focusing can be performed quickly.

[0011]

Embodiments of the laser beam scanning optical device according to the present invention will be described below with reference to the accompanying drawings. The following description will be given of a full-color digital copying machine having a laser beam scanning unit according to an embodiment of the present invention. As shown in FIG. 1, this copying machine includes an image reader unit 1 and a laser beam scanning unit 10 on the upper stage.
The full-color image forming unit 30 is arranged in the middle section, and the sheet feeding section 60 is arranged in the lower section.

The image reader unit 1 is a scanner 2 which reads an image of an original set on the platen glass 9 by moving in the direction of an arrow a, and an image signal which converts the read image data into printing data. And a processing unit 6. The scanner 2 includes a lamp 3 for illuminating a document, a rod lens array 4 for collecting reflected light from the document, and a contact color image sensor (CCD) 5 for converting the collected light into an analog electric signal. . The scanner 2 is driven by the pulse motor M1,
The image sensor 5 reads an original image line by line as color signals of three primary colors of R (red), G (green), and B (blue). The image signal processing unit 6 converts the R, G, and B color signals photoelectrically converted by the image sensor 5 into C (cyan) and M
(Magenta), Y (yellow), Bk (black) 4
The digital image data corresponding to the color is generated, subjected to the necessary edit processing, and then transferred to the laser beam scanning unit controller 7.

The laser beam scanning unit 10 includes a controller 7
A laser beam is irradiated onto the photosensitive drum 31 rotating in the direction of the arrow b based on the image data transferred to the electrostatic latent image on the photosensitive drum 31. The configuration and operation of the unit 10 and the image signal processing unit 6 will be described later in detail. The full-color image forming unit 30 mainly includes the photosensitive drum 31 and the transfer drum 34. Around the photosensitive drum 31, the charging charger 3
2, a developing unit 33, a transfer drum 34, a residual toner cleaner 35, and an residual charge eraser lamp 36 are arranged. The developing unit 33 has developing units 33M, 33C, 33Y, and 33Bk that contain developer containing magenta, cyan, yellow, and black toners in order from the top, and are vertically movable integrally by a motor M2. , Each time an electrostatic latent image of each color is formed on the photosensitive drum 31, the corresponding developing device is set to the developing position,
Develop.

The transfer drum 34 is rotatably driven in the direction of arrow c in synchronism with the photosensitive drum 31, and a claw member (not shown) for chucking the leading edge of the sheet is provided inside and outside thereof. Adsorption charger 41 for adsorbing a sheet on the surface of transfer drum 34, sheet pressing roller 42 that can be brought into contact with and separated from transfer drum 34, transfer charger 43 for transferring toner onto a sheet, charge removing chargers 44, 45, sheets A separation claw 46 for separating the transfer drum 34 from the transfer drum 34, a cleaner 47 for residual toner, a sensor 48 for detecting the reference position of the transfer drum 34, and an operating plate 49 of the sensor 48 are arranged.

When forming a full-color image, M, C, Y, and Bk toner images are sequentially formed on the photosensitive drum 31, and the respective toner images are sequentially transferred onto the sheet wound around the transfer drum 34. Are synthesized.
When the four images are combined on the sheet, the separation claw 46 operates to separate the sheet from the transfer drum 34. Further, the cleaner 47 operates to remove the residual toner on the transfer drum 34.

The paper feed unit 60 has a specific size (for example, A4 size).
It is composed of three-stage paper feed trays 61, 62, 63 for accommodating sheets of landscape, A4 portrait, B4 portrait). The sheet is one of the paper feed trays 6 selected by the operator.
Sheets are fed one by one from 1, 62, and 63, and are conveyed to a suction portion of the transfer drum 34 by a conveying roller. on the other hand,
The sheet separated from the transfer drum 34 is conveyed by the conveyor belt 5
1, the toner is sent to the fixing device 52, where the toner is fixed, and then the toner is discharged onto the tray 53.

Further, this copying machine incorporates an intermediate accommodating unit 55 for temporarily accommodating a sheet. In the composite copy mode in which two images are combined and copied on one side of the sheet, the sheet on which the first image is transferred is the branch claw 56.
And is guided downward by another branch claw 57 and is guided leftward by another branch claw 57 to be accommodated in the intermediate accommodating unit 55. Further, in the double-sided copy mode in which images are formed on both sides of the sheet, the sheet having the image transferred on the first side is once conveyed to the switchback passage 58, and the intermediate storage unit 55 is turned upside down and front and back. To be housed in. The stored sheets are stored in the intermediate storage unit 5 based on the refeed signal.
Sheets are fed one by one from 5 and conveyed to the suction portion of the transfer drum 34.

Next, the laser beam scanning unit 10 will be described. As shown in FIG. 2, this unit 10
Includes a laser diode 11, a collimator lens 12, a cylindrical lens 13, a plane mirror 14, a polygon mirror 15, fθ lenses 16 and 17, a cylindrical mirror 18, plane mirrors 19 and 20, and optical sensors 21 and 22. It is integrally attached to the casing.

The laser diode 11 is an LD drive circuit 24.
4 (see FIG. 13), intensity modulation (on / off) is performed, and a divergent light flux carrying image information is emitted. This divergent light beam is corrected to parallel light by the collimator lens 12,
The light passes through the cylindrical lens 13, is returned by the plane mirror 14, and illuminates the deflection surface of the polygon mirror 15.
The cylindrical lens 13 has power in the sub-scanning direction, and focuses the light beam emitted from the collimator lens 12 in the sub-scanning direction near the deflection surface of the polygon mirror 15.

The polygon mirror 15 is rotationally driven at a constant speed in the direction of arrow d around the support shaft 15a by a motor (not shown). Therefore, the light beam returned by the plane mirror 14 is continuously reflected by the deflecting surface of the polygon mirror 15,
It is deflected at a constant angular velocity. The deflected light beam passes through the fθ lenses 16 and 17, is reflected by the cylindrical mirror 18, and forms an image on the photosensitive drum 31 with a small beam diameter. The light beam is generated by the lenses 13, 16, 17 and the mirror 1
By the action of 8, the surface tilt of each deflecting surface of the polygon mirror 15 is corrected. Further, by the action of the fθ lenses 16 and 17, (distortion aberration) is corrected so that the scanning speed on the photoconductor drum 31 becomes uniform from the center of the image region to both end portions, and on the photoconductor drum 31, The field curvature in the main scanning direction and the sub-scanning direction is corrected.

Of the light beams deflected by the polygon mirror 15, the light beams outside the image region and on the start end side and the end side in the main scanning direction are the cylindrical mirror 1.
After being reflected by 8, it is reflected by the plane mirrors 19 and 20,
It is incident on the optical sensors 21 and 22. The optical sensors 21 and 22 are used to detect the focus position of the optical system and the magnification in the main scanning direction, and in particular, the optical sensor 21 is also used to detect the print start position for each line.

As shown in FIGS. 3 and 4, the optical sensors 21 and 22 house a photoelectric conversion element 24 inside the holder 23, and a light diffusion / transmission plate 25 and a slit plate 26 are provided in front of the holder 23. It is a thing. The slit plate 26 is made of a light shielding material, and has a slit 26a perpendicular to the main scanning direction A and a slit 26b inclined. The inner surface of the holder 23 is painted white to reflect light. The photoelectric conversion elements 24 of the optical sensors 21 and 22 are arranged at positions equivalent to the points P1 and P2 of the photosensitive drum 31, respectively. Therefore, the detection signal of the light beam incident on the photoelectric conversion element 24 when passing through the slit 26a of the optical sensor 21 is used as a reference signal of the print start position.

In FIG. 2, the plane mirror 14 is used to fold the optical path so that the optical path of the beam emitted from the laser diode 11 and the optical path of the beam deflected by the polygon mirror 15 are orthogonal to each other. This is to make it compact. By the way, the collimator lens 12, the cylindrical lens 13, the fθ lenses 16 and 1
7 and the cylindrical mirror 18 are molded products made of plastic, aspherical surfaces are frequently used, and aberrations are well corrected. The reason why plastic is used is that the aspherical surface is relatively easy to form and is suitable for mass production. However, when plastic is used as a lens, there is a disadvantage in that the refractive index and the shape change due to a change in ambient temperature, and the focal length changes to a level that cannot be ignored. Therefore, the image forming position shifts on the optical axis and the beam diameter increases.

FIG. 5 shows current signals Ia, I of the photosensors 21, 22 (photoelectric conversion element 24) with respect to the beam spot shape.
b is shown. The current signal Ia is a signal when the beam passes through the slit 26a, and the current signal Ib is the beam when the beam is in the slit 26a.
This is the signal when passing through 6b. Let Bc be the ideal beam spot shape (when in focus),
The current signals Ia and Ib are both large. When the beam spot shape is large in the main scanning direction A and the sub scanning direction B like Ba, both the current signals Ia and Ib are small. When the beam spot shape is large only in the sub-scanning direction B like Bb, the current signal Ia is large and the current signal Ib is small.
In this way, the shape of the beam spot incident on the optical sensors 21 and 22 can be determined by the current signals Ia and Ib, and the collimator lens 12 and the cylindrical lens 13 on the optical axis can be determined based on the current signals Ia and Ib. Image formation plane (photosensitive drum 31) by adjusting the position
You can focus on the above.

By the way, the photoelectric conversion element 24 used in this embodiment converts the beam intensity per unit time of the beam and per unit area into a current signal and outputs it.
Therefore, considering that the beam intensity when radiated from the laser diode 11 is constant when the beam spot shape spreads widely, the beam intensity per unit area becomes small, and the current signal output from the photoelectric conversion element 24 is reduced. Becomes smaller. On the contrary, when the current signal is maximum, the beam spot has an ideal shape without defocus, that is,
You can think that it is in focus. In the embodiment, the beam spot shape is adjusted so that the current signal becomes maximum.

More specifically, as shown in FIG. 6, a holder 71 for holding the laser diode 11 and a holder 73 for holding a lens barrel 72 of the collimator lens 12 are connected to each other, and a space between the lens barrel 72 and the holder 73 is connected. A cylindrical piezoelectric element 74 was interposed between the two. The piezoelectric element 74 is distorted by the applied voltage, and the amount of distortion is proportional to the voltage value. Therefore, by changing the voltage value, the collimator lens 12 moves along with the lens barrel 72 on the optical axis. By moving the collimator lens 12, the beam diameter in the main scanning direction can be adjusted. vice versa,
The moving distance of the collimator lens 12 can be detected by the voltage value.

On the other hand, as shown in FIG. 7, the cylindrical lens 13 is held by a bracket 77 via a holder 76, and the bracket 77 is mounted on a linear motor 78. By driving the linear motor 78, the cylindrical lens 13 moves on the optical axis together with the bracket 77. By moving the cylindrical lens 13, it is possible to adjust the beam diameter in the sub-scanning direction. On the contrary, the moving distance of the cylindrical lens 13 can be detected by the driving amount of the linear motor 78.

As an adjusting method, first, the collimator lens 12 is moved so that the corresponding current signal Ia becomes maximum when the beam passes through the slit 26a of the optical sensor 21, and the moving distance at this time is stored in the storage means. Remember.
Similarly, when the beam passes through the slit 26a of the optical sensor 22, the corresponding current signal Ia becomes maximum,
The collimator lens 12 is moved, and the average value of the moving distance at this time and the moving distance detected by the optical sensor 21 and stored in the storage means is obtained. The collimator lens 12 is moved according to this average value. As a result, the beam diameter in the main scanning direction is adjusted.

On the other hand, regarding the beam diameter in the sub-scanning direction,
The cylindrical lens 13 is moved so that the corresponding current signal Ib becomes maximum when the beam passes through the slit 26b of the optical sensor 21, and the moving distance at this time is stored in the storage means. Similarly, the slit 2 of the optical sensor 22
The cylindrical lens 13 is driven so that the corresponding current signal Ib becomes maximum when the beam passes through 6b, and the moving distance at this time and the moving distance detected by the optical sensor 21 and stored in the storage means are stored. Calculate the average value. The cylindrical lens 13 is moved according to this average value. As a result, the beam diameter in the sub-scanning direction is adjusted.

As described above, according to this embodiment, the adjustment of the beam spot shape (focal position of the optical system) is performed by the optical sensor 2.
1 and 22 are used. The adjustment can be performed by using only one of the optical sensors 21 and 22. However, when the image plane in the main scanning direction or the sub scanning direction is tilted or curved due to a processing error, an assembly error, or the like, the optical sensor 2
By averaging the detection results of 1 and 22, the influence of this type of error can be reduced.

The collimator lens 12 has power in the main scanning direction and the sub-scanning direction, and the cylindrical lens 13 has power only in the sub-scanning direction. If the cylindrical lens 13 is moved first to adjust the beam diameter in the sub-scanning direction and then the collimator lens 12 is moved to adjust the beam diameter in the main-scanning direction, the beam diameter in the sub-scanning direction may change. There is. As in this example,
By moving the collimator lens 12 first to adjust the beam diameter in the main scanning direction and then moving the cylindrical lens 13 to adjust the beam diameter in the sub-scanning direction, the cylindrical lens 13 has power in the main scanning direction. Since it does not exist, there is no risk that the beam diameter in the main scanning direction that was previously adjusted will change.

Next, the extending direction of the slits 26a and 26b will be described. When the slit extends in the main scanning direction, the output of the photoelectric conversion element is the same even if the beam diameter in the main scanning direction changes, and the change cannot be detected. Moreover, if the beam is slightly displaced in the sub-scanning direction, detection will be impossible. On the other hand, when the slit extends in the sub scanning direction, the output of the photoelectric conversion element is the same even if the beam diameter in the sub scanning direction changes, and the change cannot be detected. Therefore, in the present embodiment, the slit is made to have an angle with respect to the main scanning direction. The slit 26b for adjusting the beam diameter in the sub-scanning direction is inclined by 45 ° with respect to the main scanning direction. The slit 26a for adjusting the beam diameter in the main scanning direction may be inclined by 45 ° with respect to the main scanning direction. However, in this embodiment, the slit 26a is also used to obtain the reference signal of the print start position for each line, so that the rising of the current signal Ia is made steep, so 90 ° with respect to the main scanning direction. Made it orthogonal.

The adjustment of the beam spot shape (focal point position) described above is prohibited while the image for one sheet is printed on the photosensitive drum 31. If this adjustment is performed in real time and the lenses 12 and 13 are continuously moved, there is no problem. However, it is practically difficult to carry out in real time, and when the lenses 12 and 13 move stepwise, the image density changes stepwise and image deterioration occurs. Specifically, this adjustment is preferably performed immediately before printing one original image.

FIG. 8 shows a control circuit for controlling the full-color image forming section 30 and the sheet feeding section 60 of the copying machine. Control is C
The current signal of the optical sensors 21 and 22 is input to the CPU 100 via the signal processing circuit 101, with the PU 100 as the center. The signal processing circuit 101 includes a memory 102. The CPU 100 also outputs a control signal to the drive circuit 104 of the piezoelectric element 74 that is the drive source of the collimator lens 12, and the drive circuit 105 of the linear motor 78 that is the drive source of the cylindrical lens 13.

Next, the main scanning magnification correction will be described. When the focal lengths of the fθ lenses 16 and 17 change with a change in temperature, the main scanning magnification changes, which appears as an expansion or contraction of the print width in the main scanning direction on the image. As a method for correcting such a change in the main scanning magnification, there are a method using the optical sensors 21 and 22 and a method using a temperature sensor 28 provided in the laser beam scanning unit 10 as shown in FIG. .

When using the optical sensors 21 and 22, first, the detection of the beam by the optical sensor 21 to the detection of the optical sensor 22 are performed.
Measure the time until the beam is detected by. Specifically, the system clock SYNCK is counted. ROM1
Reference numeral 03 (the time from the beam detection of the optical sensor 21 to the beam detection of the optical sensor 22) corresponding to all copy magnifications that can be set by the operator is stored in advance in 03. Therefore, the reference time corresponding to the currently set copy magnification is compared with the measurement time. If the measurement time is x and the reference time is 1, the change in the main scanning magnification due to the change in the focal length of the fθ lenses 16 and 17 is 1 / x.
Therefore, if the current set magnification is multiplied by x, printing is performed at the set magnification. Note that the reference time, the measurement time, and the correction value data may be stored in the ROM 103 in advance, and the correction magnification may be obtained by the data reference format.

On the other hand, when the temperature sensor 28 is used, f
The temperature near the θ lenses 16 and 17 is measured by the temperature sensor 28. This measured value is input to the CPU 100 and the correction magnification corresponding to the measured value is calculated. F due to temperature change
The change rates of the focal lengths of the θ lenses 16 and 17 are obtained in advance, and this data is stored in the ROM 103. Therefore, the calculation is performed based on this data, or the correction magnification is obtained by the data reference format, and the obtained correction magnification is transferred to the image signal processing unit 6. When the copy magnification set by the operator is α and the correction magnification based on the measurement value of the temperature sensor 28 is β, the magnification in the main scanning direction is α ×.
It will be reset to β.

If the main scanning magnification is corrected by using the humidity sensor in addition to the temperature sensor 28, the correction effect is further improved. By the magnification correction in the main scanning direction as described above,
The set magnification can be correctly maintained despite the change in the focal length of the fθ lenses 16 and 17. A specific method of magnification correction in the main scanning direction in the image signal processing unit 6 will be described in detail later.

The magnification correction in the main scanning direction described above is 1
It is prohibited while printing the image for one sheet on the photosensitive drum 31. If this correction is performed continuously, there will be no problem. However, in reality, since the image signal processing unit 6 digitally corrects, a step is generated in the image before and after the correction. Therefore, it is preferable to execute this correction immediately before printing one original image.

Next, the image signal processing section 6 provided in the image reader unit 1 will be described. In FIG. 9, the image signal processing unit 6 is controlled by the CPU 210, and the CPU 210 appropriately communicates with the CPU 100 shown in FIG. 8 to exchange necessary information. The image signal processing unit 6 is composed of the following blocks.

Analog amplifier / S / H (sample hold) block 201: Amplifies the analog signal of the original image photoelectrically converted by the color image sensor (CCD) 5 in the scanner 2. A / D conversion block 202: Converts the analog signal amplified in the block 201 into a numerical (digital) signal.

Shading correction block 203: corrects the unevenness of the light amount of the exposure lamp 3 and the variation in the sensitivity of each pixel of the image sensor 5. An image signal whose density is corrected for each pixel is obtained. Reflectance / density conversion block 204: The image signal processed up to this point is a signal proportional to the amount of light reflected from the document. Here, the reflectance is converted into the density in order to facilitate the processing in the subsequent block. Furthermore, this block 2
At 04, tone reproduction processing for emphasizing the highlight portion and the shadow portion is also performed at the same time. Incidentally, each of the blocks 201, 202, 203, 204
Then, the read three primary colors (R, G, B) are processed in parallel.

Color correction / UCR / BP block 205: 3
The image signals of the primary colors are combined to generate Y, M, C, Bk print signals. The color of the print signal to be generated depends on C
PU 210 directs this block 205.

Editing block 206: Various editing is performed on the print signal. For example, in trimming editing, the image outside the designated area is erased. MTF correction block 207: Performs edge enhancement processing and smoothing processing. Scale / move block 208: Performs pixel density conversion (magnification change) in the main scanning direction, image shift, and repeated output of the same area (image repeat). γ-curve correction block 209: corrects image quality, color tone and the like.

Each of the above blocks includes an operation parameter directly given by the CPU 210 and a control signal generator 22.
It operates according to a signal (drive pulse signal or the like) given from 0. The print signal generated by the above processing is transferred to the laser beam scanning unit controller 7 and used for modulation control of the laser diode 11.

FIG. 10 shows the structure of the scaling / moving block 208. The image signal supplied from the MTF correction block 207 in the preceding stage is first line by line in the line memory 2
It is stored in 31a. At this time, the write address counter 233 controls the address written in the line memory 231a. The write address counter 233 generates address data by counting the clock signal output from the selector 235.

The clock signal that can be selected by the selector 235 is SYNC which is a transfer clock of the input image signal.
It is a thinning clock R_SYNCK generated by thinning K or its SYNCK. The thinning clock R_SYNCK is given to the write address counter 233 at the time of reduction. When enlarged, SYNCK is given. The operation of the selector 235 follows the enlargement / reduction signal RE given from the CPU 210. Thinning rate (magnification)
Is given as MAG_DATA from the CPU 210 to the thinning clock generation unit 232.

The line memories 231a and 231b receive the horizontal sync signal Hsync based on the print start position detection signal as CP.
Write address counter 2 every time it is input to U210
The relationship between 33 and the read address counter 234 is exchanged. That is, when the image signal of a certain one line is stored in the line memory 231a and the image signal of the next one line is input to the scaling / move block 208, the line memory 231a storing the previous image signal is the line memory 231a. 231
It is b. The read address counter 234 performs a read process on the line memory 231b. The read address counter 234 also receives the clock SYNCK or the thinned clock or R_SYNC and counts the clock. However, contrary to the write address counter 233, SYNCK is given at the time of reduction and R_SYNCK is given at the time of enlargement. Further, the read address counter 234 receives a repeat position signal REP_POS and a read start position signal FST from the CPU 210.
_POS and the count signal UD are given. These signals are used for the functions of image repeat, image shift, and mirror image, and the description will proceed assuming that all these control signals are in the standard state.

The decimation clock generator 232 is the CPU 2
Thinning rate (magnification) data MAG_D given by 10
According to the ATA, a clock R_SYNCK is generated by thinning out pulses at a target ratio from a clock pulse train of SYNCK. For example, in FIG. 11, R_SYN is obtained by subtracting a pulse of SYNCK for half a minute in order to realize a reduction ratio of 1/2.
The state in which CK is generated and the operation state in each part are shown. FIG. 12 shows a state of operation in each part for realizing a double magnification. The above-described magnification correction in the main scanning direction is fed back to the control in the scaling / movement block 208 as thinning rate data MAG_DATA.

FIG. 13 shows the configuration of the laser beam scanning unit controller 7 and the signal generation state. This control unit 7 is CP
It is controlled by U100. The print data transferred from the image signal processing unit 6 is first stored in the write buffer memory 241a. The address stored at this time is controlled by the write address counter 242 counting the clock SYNCK while the HD signal is active. The address is reset to 0 every time the horizontal synchronizing signal Hsync is input.

The print data for one line stored in the write buffer memory 241a is next read by the horizontal synchronizing signal Hsy.
When nc is input, it is treated as the read buffer memory 241b. The read of the print data is performed based on the address obtained by the read address counter 243 counting the synchronous clock DOTCK for causing the laser diode 11 to emit light. This read is HI
This is performed while the A signal is active. HIA signal is L
The D light emission permission area generator 247 outputs the horizontal synchronization signal Hsync.
It is generated by counting the synchronous clock DOTCK with reference to the input of.

The synchronous clock DOTCK for causing the laser diode 11 to emit light is generated by the generator 245, and the horizontal cycle signal Hsync is generated by the generator 246 based on the laser beam detection signal from the photosensor 21. The print data read from the read buffer memory 241b is input to the LD drive circuit 244. The LD drive circuit 244 converts print data into LD light emission data that matches the light emission characteristics of the laser diode 11, and drives the laser diode 11 for modulation.

FIG. 13B shows the write / read timing of print data. As is apparent from this, the write timing to the buffer memory 241a and the read timing from the buffer memory 241b are asynchronous operations. The read timing can be arbitrarily selected by the CPU 100 based on the horizontal synchronizing signal Hsync. This means that the printing position on the photosensitive drum 31 by the laser beam can be arbitrarily moved in the main scanning direction. That is, the image transfer position in the main scanning direction can be moved with respect to the sheet on which the image is transferred.

Next, the control procedure of the CPU 210 will be described with reference to the flow charts of FIGS. However, the control procedure is shown only for the portion related to the present invention. FIG. 14 shows a control procedure by the CPU 100 after the print switch is turned on. First, in step S1, the adjustment of the beam diameter is automatically processed, and in step S2, the correction of the main scanning magnification is automatically processed. Next, when it is determined in step S3 that the adjustment and correction are completed, printing of one page is processed in step S4. Next, when it is determined in step S5 that the printing of one page is completed, it is determined in step S6 whether or not the copy operation number Pn is equal to or more than the copy number Ps set by the operator, and the copy operation number Pn is calculated from the copy number Ps. If it is smaller, the process returns to step S1 and P
When n becomes equal to Ps, this subroutine is finished.

FIG. 15 shows a subroutine for adjusting the beam diameter, which is executed in step S1. First, the beam diameter in the main scanning direction is adjusted in step S11, and when the completion is confirmed in step S12, the beam diameter in the sub scanning direction is adjusted in step S13. And step S
When the completion is confirmed at 14, the subroutine is finished.

FIG. 16 shows a subroutine of the beam diameter adjusting process in the main scanning direction and the sub scanning direction which is executed in steps S11 and S13. Here, first, the piezoelectric element 74 or the linear motor 78 is driven to return the collimator lens 12 or the cylindrical lens 13 to the initial position. Here, the laser diode is forcibly emitted and the polygon mirror 15 is rotated, and the signal S _n from the sensor 21 is stored in step S22. The signal S _n means the value of the n-th current signal Ia or Ib, and the initial value is S ₀ .

Next, in step S23, the current signal S _n and the previous signal S _n-1 are compared. If S _n > S _n-1 , the lens 12 or 13 is moved by +1 step in step S24. And returns to step S22. The +1 step movement means that the lens 12 or 13 is moved by a predetermined amount in the direction toward the laser diode 11. On the other hand, if S _n > S _{n-1 is} not satisfied, the lens 12 or 13 is moved by -1 step in step S25, and this subroutine is ended. -1 step movement means to move the lens 12 or 13 to the laser diode 1
It means moving a predetermined amount in the direction away from 1. Through the above processing, the lens 12 or 13 is set so that the beam spot on the photosensitive drum 31 is focused with the minimum shape.

In the subroutine shown in FIG. 16, a method of automatically adjusting the beam diameter using only the optical sensor 21 is shown. As described with reference to FIGS. 5, 6 and 7, the optical sensors 21 and 22 may be used to move the lens 12 or 13 to the average value.

FIG. 17 shows a subroutine of the first example of main scanning magnification correction executed in step S2. This first
An example is a method using the optical sensors 21 and 22. First, the beams passing through the slit 26a are detected by the optical sensors 21 and 22 in steps S31 and S32. Based on the time from the detection of the optical sensor 21 to the detection of the optical sensor 22, the current main scanning magnification a is calculated in step S33. Next, in step S34, the copy magnification b set by the operator is changed to b / a.

FIG. 18 shows a subroutine of the second example of the main scanning magnification correction executed in step S2. This second
An example is a method using the temperature sensor 28. First, in step S41, the temperature inside the laser beam scanning unit 10 is measured by the temperature sensor 28, and in step S42, the correction magnification a ′ corresponding to the measured value is read from the ROM 103.
Next, in step S43, the copy magnification b set by the operator is changed to b × a ′.

The laser beam scanning optical device according to the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the scope of the gist.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show a full-color copying machine equipped with a laser beam scanning unit according to an embodiment of the present invention.

FIG. 1 is an elevation view showing the internal configuration of a full-color copying machine.

FIG. 2 is a perspective view showing a schematic configuration of a laser beam scanning unit.

FIG. 3 is a perspective view showing an optical sensor.

FIG. 4 is a cross-sectional view showing an optical sensor.

FIG. 5 is a chart showing a current signal of an optical sensor corresponding to a beam spot shape.

FIG. 6 is a sectional view showing a driving unit of a collimator lens.

FIG. 7 is a cross-sectional view showing a driving unit of a cylindrical lens.

FIG. 8 is a block diagram showing a control circuit of the copying machine main body.

FIG. 9 is a block diagram showing an image signal processing unit.

FIG. 10 is a block diagram showing a scaling / moving block.

FIG. 11 is an explanatory diagram for realizing a reduction ratio of 1/2,
(A) is a chart showing the operation, and (B) is a conceptual view of the operation.

FIG. 12 is an explanatory diagram for realizing a magnifying power of 2 times,
(A) is a chart showing the operation, and (B) is a conceptual view of the operation.

FIG. 13 is a block diagram showing a laser beam scanning unit controller.

FIG. 14 is a flowchart showing a subroutine relating to print processing of CPU 100.

FIG. 15 is a flowchart showing a beam diameter adjustment subroutine executed in step S1 of FIG.

16 is a flowchart showing a subroutine of beam diameter adjustment processing executed in steps S11 and S13 of FIG.

FIG. 17 is a flowchart showing a subroutine of a first example of main scanning magnification correction executed in step S2 of FIG.

FIG. 18 is a flowchart showing a subroutine of a second example of main scanning magnification correction executed in step S2 of FIG.

[Explanation of symbols]

 10 ... Laser beam scanning unit 11 ... Laser diode 12 ... Collimator lens 13 ... Cylindrical lens 15 ... Polygon mirror 16, 17, ... f.theta. Lens 18 ... Cylindrical mirror 21, 22 ... Photosensor 24 ... Photoelectric conversion element 26a, 26b ... Piezoelectric element 78 ... Linear motor 100 ... CPU

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Takeshita 2-33 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Camera Co., Ltd.

Claims (4)

[Claims] 1. A light source for generating a laser beam modulated based on image data, a deflector for deflecting the laser beam emitted from the light source, and a laser beam immediately after being emitted from the light source into parallel light. A first optical element for correction; a second optical element for linearly focusing the laser beam emitted from the first optical element in the vicinity of the deflection surface of the deflector; and a deflector deflected by the deflector. A third optical element for forming an image of the laser beam on the photoconductor, a slit orthogonal to the main scanning direction and a slit inclined, and a photoelectric conversion element for receiving the laser beam passing through these slits, A laser beam scanning optical device, comprising: a focus sensor unit in which a photoelectric conversion element is installed at a position optically equivalent to the surface to be scanned. 2. A light source for generating a laser beam modulated based on image data, a deflector for deflecting the laser beam emitted from the light source, and a laser beam immediately after emitted from the light source into parallel light. A first optical element for correction; a second optical element for linearly focusing the laser beam emitted from the first optical element in the vicinity of the deflection surface of the deflector; and a deflector deflected by the deflector. A third optical element for forming an image of the laser beam on the photoconductor, a slit orthogonal to the main scanning direction and a slit inclined, and a photoelectric conversion element for receiving the laser beam passing through these slits, A focusing sensor means in which a photoelectric conversion element is installed at a position optically equivalent to the surface to be scanned, a focus adjusting means in the main scanning direction, and a focus in the sub scanning direction independently of the main scanning direction. The laser beam scanning optical apparatus comprising: the stage, and a control means for adjusting the focus of the sub-scanning direction after adjusting the focus in the main scanning direction. 3. A laser beam passing through orthogonal slits is detected to adjust the focus in the main scanning direction, and a laser beam passing through an inclined slit is detected to adjust the focus in the sub-scanning direction. The laser beam scanning optical device according to claim 1 or 2. 4. The focus adjusting means in the main scanning direction includes a moving member for moving the first optical element on the optical axis, and the focus adjusting means in the sub scanning direction moves the second optical element on the optical axis. The laser beam scanning optical device according to claim 2, further comprising moving means for moving.