JPS6031417B2 - optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device used as a means for recording and displaying image information from electronic calculators, facsimile transmitters, etc. at high speed and with high quality.

Prepare line memory that supports multiple scanning lines,
A method in which multiple beams of light are scanned simultaneously and writing of the multiple beams is completed in one light scan, that is, main scan, is known as a multi-beam scanning method. In the multi-beam scanning method, the speed of the scanning surface, that is, the speed of the sub-scanning, is determined according to the number of beams, and this method is effective for printers and the like that require high printing speeds.

As such a multi-beam scanning type light source, a device having a monolithic or hybrid array of semiconductor lasers, that is, a semiconductor laser array can be considered.

Semiconductor lasers have many advantages such as being able to be directly modulated, having a small size, and being inexpensive, and it is easy to form semiconductor lasers into an array based on semiconductor manufacturing technology. However, the pitch between each laser is limited to about 50 peaks. If the pitch is made smaller than this, the electrical
Problems arise, such as poor optical separation, which makes independent modulation of each laser impossible, and concentration of heat, which shortens the life of the element. Here, a secondary optical scanning device using a semiconductor laser as a light source will be explained with reference to FIG.

The light beam 2 emitted from the semiconductor laser 1 usually has a spread angle of 40 degrees or more, and the lens 3 that condenses the light into a parallel beam is made of the brightest possible lens. The parallel beam 2 is deflected in a plane perpendicular to the optical axis by a deflector 4 such as a rotating polygon mirror, passes through a lens 5 with a scanning distortion correction function, and is directed onto a photoreceptor 6. imaged and scanned. In the optical scanning device described above, the light emitting portion of the semiconductor laser 1 is less than a few peaks, and can be regarded as a point light source.

In the optical system, lenses 3 and 5 constitute an imaging system, and the ratio of the focal length f of the lens 3 to the focal length of the lens 5 is the magnification m. That is, m=ra/f. Furthermore, if F,, F2 are F numbers indicating the brightness of lenses 3 and 5, then the relational expression of F = f/D (f is the focal length of the lens, D is the aperture of the lens), and parallel Since the beam is emitted and input, if the apertures of lenses 3 and 5 are made equal, m=f2/
The relational expression f,=F2/F holds true. Practically, the F number of the lens 5 with a scanning distortion correction function suitable for a scanning width of 30 or more is about 20, making it difficult and expensive to manufacture a bright lens.

As mentioned above, lens 3 needs to be a bright lens, so if F2=20 and F,=1, then m=
20, which is an enlargement magnification of 2 tones or higher. On the other hand, the pitch of the semiconductor laser array is 50 as mentioned above.
Since it is more than the size of a Buddha, the pitch of the imaged spot on the photoreceptor 6 by the imaging optical system having a magnification of 2 folds becomes more than 1 Yanagi. The sub-scanning density required for normal printers is about 10 lines/skin, but if a semiconductor laser array is simply used as a light source in an optical scanning device, the sub-scanning density is about 1 line/skin from the above explanation. I can't help but
Not practical. Further, the diameter of the imaged spot is almost determined by the diffraction development by the lens 5, since the semiconductor laser 1 can be regarded as a point light source.

If the image spot diameter of the Fairy disk is d, then d=2
．． 442 (input is the wavelength of light), and if the intrusion is about 0.8 degrees, d will be less than 80 degrees even at F2=4 star power. This relationship holds true for semiconductor laser arrays as well. An object of the present invention is to obtain an optical scanning device that uses a multi-beam scanning method using a semiconductor laser array and can easily change the sub-scanning pitch. It is characterized in that it controls the pitch of sub-scanning and simultaneously controls the delay of main scanning.

One embodiment of the present invention will be described with reference to FIG. 2. Reference numeral 7 denotes a semiconductor laser array, the light emitting surface of which is in a plane perpendicular to the optical axis of the lens 3, and the output from each laser is transmitted by the lens 3. A parallel beam group 8 is formed.

The optical system is constructed in the same manner as that shown in FIG. scanned. Lens 3 is F! 1, and there is almost no light loss in the semiconductor laser array. 9
is a rotation angle damping mechanism using, for example, a gear train, and the semiconductor laser array 7 is attached to the rotation center of the rotation angle transmission side of the rotation angle damping mechanism 9.

1 is a rotary drive device such as a step motor, and the rotary drive device 10 and the rotation angle damping mechanism 9 work together as a minute rotation angle adjustment device, and the semiconductor laser array 7
The array direction of the lens 3 can be rotated and maintained within a plane perpendicular to the optical axis of the lens 3.

FIG. 3 shows a spot image of the semiconductor laser array 7 on the photoreceptor 6, with arrow A indicating the main scanning direction and arrow B indicating the sub-scanning direction.

This is represented by an angle 8 formed by a straight line connecting each spot image and the main scanning direction, and this angle can be adjusted by the minute rotation angle adjustment device. Further, if the imaging magnification of the optical system is m, the pitch of the spot image is m times the pitch p of the semiconductor laser array 7, and the pitch in the sub-scanning direction is m.
sln8, and the pitch in the main scanning direction is mpcos8.
Note that it is assumed here that the main scanning direction and the sub-scanning direction are perpendicular to each other. By adjusting the pitch mpsln8' in the sub-scanning direction and the angle 8, it is possible to freely select the magnification m of the optical system and the pitch p of the semiconductor laser array 7 while keeping them fixed.In extreme cases, 8 can be set to zero degrees. Main scanning can be reduced to one line. Note that the sub-scanning speed will be described later. Next, a synchronization method when spot images aligned on a straight line at a certain angle are scanned with respect to the above-described main scanning will be described.

FIG. 4 shows a control system according to the present invention, in which 11 is a line memory such as a shift register for accommodating video signals and the like corresponding to each line, and the number of line memories 11 is the same as the number of lasers in the semiconductor laser array 7. . 12 is a driver that modulates each laser with a signal from the line memory 1;

Reference numeral 13 denotes a delay control circuit, which is composed of, for example, a monostabilized multipipulator, and controls the timing at which the output of each line memory 11 starts to be sent to each driver 12.

That is, with respect to the main synchronization signal obtained by means such as photoelectric conversion, secondary synchronization signals corresponding to the number of line memories 11 are generated with different delay times. As explained with reference to FIG. 3, if the pitch of the spot images in the main scanning direction is mpCos8 and the scanning speed is constant, then the pitch of the second spot image in the main scanning direction is mpCos8. Since the image is delayed by Δt time, Δt=mpcos8/. The same goes for the third and subsequent ones, and there is a delay of nΔt from the n'th. Therefore, the delay control circuit 13 may set delay times sequentially in multiples of Δt, and of course may set delay times for each beam to obtain synchronization. FIG. 5 is a time chart showing the delay time, and a is the main synchronization signal, which is also the synchronization signal for the first line memory 11.

b, c, and d are slave synchronization signals for the second, third, and nth lasers, respectively. By the control method described above, each beam can be synchronized.

Next, sub-scanning will be explained.

Multi-beam scanning period (scanning period of deflector 4) T vs. sub-scanning speed (rotation speed of photoreceptor 6) = n
-If you set mpsin8/T, it will match the main scanning. Here, n is the number of multi-beams. Normally, when the sub-scanning pitch is changed by adjusting the angle 0, the scanning period T of the deflector 4 is
It is necessary to adjust the rotational speed of the photoreceptor 6 and the rotational speed of the photoreceptor 6 to match the main scanning. However, in the present invention, the pitch of sub-scanning can be changed while the scanning period T of the deflector 4 and the rotational speed of the photoreceptor 6 are fixed. In other words, the video signal is input to the line memory 1 so as to scan with (n-1) multi-beams without using the n-th beam, and the nsm
By adjusting the angle a and the aforementioned delay time Δt up to the angle 6' where the relationship 8=(n-1)sin8' holds true, alignment with the main scanning and synchronization with the main scanning can be achieved. be able to. This also applies to the case of using (n-2) or less multi-beams. In this way, the angle 6 can be adjusted and the number of multi-beams (i.e., the number of driving lasers)
By controlling the sub-scanning speed (rotational speed of the photoreceptor 6), the scanning period T of the deflector 4, the magnification m of the optical system, and the pitch p of the semiconductor laser array can be adjusted without fluctuation.
The pitch of sub-scanning, that is, the sub-scanning density, can be varied, albeit discontinuously.

It is not easy to change the rotation speed of the photoreceptor 6 and the scanning period of the deflector 4 because of the large inertia. Therefore, as described above, it is extremely effective to be able to vary the sub-scanning density by simply controlling the line memory or the like using the minute rotation angle adjusting device combined with the semiconductor laser array. To summarize the effects of the embodiments described above, it is possible to perform imaging scanning without loss of light quantity using a semiconductor laser array as a light source, and also to perform multi-beam scanning, which facilitates high-speed recording.

It is possible to have flexibility in designing the array pitch of the semiconductor laser array and the imaging magnification of the optical system. The sub-scan density can be easily changed without adjusting or changing the sub-scan, main scan, or optical system. To describe a specific configuration example of the present invention, a semiconductor laser array 7 with a pitch p of 50 and a laser number of 5 dots, a lens 3 with L = 10, F, = 1, and a deflector 4 with a rotating polygon mirror. =400,F2=
A scanning device was constructed with 40 lenses 5 having a scanning distortion correction function. In addition, a gear train with a gear ratio of 1/3 is used as the rotation angle damping mechanism 9, and a step motor with a 1.8 degree/step is used as the rotation drive device 10 to configure a minute rotation angle adjustment device. set to 2.4 degrees and 300
A sub-scanning density of books/inch was set. Here, the scanning speed〃
Scanning was performed using a rotating polygon mirror, that is, a deflector 4, at a rate of 1 skin/skin sec.

The main scanning period at this time is 1 sec, and the delay time Δt with respect to the main synchronization signal is 2 sec. next,
The step motor was driven one step to set the angle 8 to 3 degrees, and the semiconductor laser array 7 was used in a 4-dot array to change the sub-scanning density to 240 lines/inch.

The time required for the change is determined by the drive time of the step motor, and is 1 second. Since the angle 8 was small, there was no need to change the delay time Δt. A detailed explanation of the main scanning disassembly is omitted, but it can be easily changed by changing the control clock and the like. As explained above, the present invention uses a semiconductor laser array as a light source,
This is combined with a minute rotation angle adjustment device, a delay control circuit, etc. to enable multi-beam scanning, so it is possible to use a high-speed laser beam printer, and it is also a scanning method that allows the resolution to be easily changed. This allows flexibility in formatting the laser beam printer.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram showing a conventional example, Fig. 2 is a schematic explanatory diagram showing an embodiment of the present invention, Fig. 3 is an explanatory diagram of a spot image in the present invention, and Fig. 4 is a control system in the present invention. 5 is a time chart showing an example of control in the present invention, and FIG. 6 is a diagram showing a spot diagram for explaining sub-scanning in the present invention. 3... Lens, 4... Deflector, 5...
Lens, 6...Photoconductor, 7...Semiconductor laser array, 8...Parallel beam group, 9...
・Rotation angle damping mechanism, 10...Rotation drive device, 1
1...Line memory, 12.・・・． ...Driver, 13...Delay control circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. In an optical scanning device that scans a beam emitted from a light source using an imaging optical system and a deflector, a semiconductor laser array is used as the light source, and the angle formed between the array direction of the semiconductor laser array and the main scanning direction A minute rotation angle adjustment device consisting of a rotation angle damping mechanism and a rotation drive device that adjusts and maintains the rotation angle, and a main synchronization signal for beam scanning in units of delay time corresponding to the rotation angle of the minute rotation angle adjustment device. a delay circuit that sequentially delays the start of modulation of each laser of the semiconductor laser array, and adjusts the angle by the minute rotation angle adjustment device, and adjusts the angle of the laser of the semiconductor laser array according to the changed angle. An optical scanning device characterized in that sub-scanning density can be adjusted by increasing or decreasing the number of driven elements.