JPS6068358A - Generating device of beam control signal for exposure of laser beam printer - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an image and grasp the scanning period of a laser beam properly when necessary by detecting and controlling variation in the shape of the laser beam. CONSTITUTION:A generating means for a beam control signal for exposure consists of a photodetection part 9 which has a cylinder lens 8 for convergence and plural photodetecting elements on the optical path of the laser beam and a decision part 10 (provided that the decision part 10 is included in a control part 7) which inputs a shape signal from the photodetection part 9 and decides on the shape of the beam and the scanning period. Then, a laser beam printer is provided with a semiconductor laser oscillator 1, rotary polygon mirror 4, ftheta lens 6, and further a charging corotron, developing device, etc., arranged at the circumference of a photosensitive drum 5 which rotates, and the control part 7 consisting of the ROM 7b, CPU 7c, RAM 7d, and output interface 7e of an input interface is provided.

Description

[Detailed Description of the Invention] [Technical Field] The present invention provides a laser beam VC' modulated by an image signal, ↓
A laser beam printer that scans a recording drum to form an electrostatic latent image and visualizes that latent image to obtain an image.The laser beam printer detects the shape of the exposure beam and controls it appropriately. The present invention relates to an exposure beam control signal generating device.

[Background technology]

As a conventional laser beam printer, there is one shown in FIG. 1, for example. This laser beam printer
Semiconductor laser oscillator l.

A rotating polygon mirror 4 that polarizes the laser beam, and an fθ lens 6 that moves the polarized laser beam onto the recording drum 5 at a constant speed and keeps the beam diameter constant on the recording drum surface 5.
ft. Around the rotating recording drum 5, there are a charged corotron (not shown), a developing device (not shown), and a transfer device (not shown).
(not shown), fuser (not shown), static eliminator (not shown)
However, a control section 7 is provided inside the printer. The control unit 7 includes sensor signals from various sensors in the printer (not shown), an input interface 71 that inputs operation command signals from the console, and a ROM that stores programs necessary for arithmetic processing of the input signals.
7 b, and a CP that performs predetermined calculations based on the program.
U 7 e, RAM 7 d for temporarily storing calculation results and data storage, and control to various control objects of the printer (not shown) or the display part of the console (not shown) based on the calculation results. It has an output interface 7ei for outputting a signal.

In the above configuration, the operation will be explained as follows. The laser beam output from the laser beam oscillator 1 is polarized by the rotating polyhedron 4, and the beam diameter is made constant by the fθ lens 6, and the laser beam is scanned at a constant speed over the recording drum surface 5. The recording drum 5 is charged in advance by a charged corotron, and a latent image is formed by scanning with a laser beam.

The latent image is developed by a developing device and transferred onto plain paper by a transfer device. The plain paper enters the fixing device and is fixed thereon, and the recording drum 5 is treated with a static eliminator and a cleaning device to remove residual developer from the transfer device. The above operation instructions are input to the input interface 7a of the control section 7 together with various sensor signals or operation instructions from the console, and predetermined calculations are performed based on the program by outputs from the output interface 7e.

However, in conventional laser beam printers,
For example, even if the shape of the beam changes due to deformation of a plastic lens due to temperature changes, resulting in image deterioration, the system did not have a function to detect and control the problem. I wasn't able to handle it.

[Object and structure of the invention]

The present invention has been developed in view of the above, and detects and controls changes in the shape of a laser beam to prevent image deterioration and accurately determine the scanning timing of the beam as necessary. Therefore, a plurality of light receiving elements are provided in arbitrary homK symmetry passing perpendicularly to the beam axis of the laser beam, and the shape of the laser beam is completely determined based on the light reception signal, and,
The present invention provides an exposure beam control signal generating device for a laser beam printer that determines the timing of starting scanning.

〔Example〕

The exposure beam control signal generating means of the laser beam printer according to the present invention will be explained in detail below. FIG. 12 shows an embodiment of the present invention.

The laser beam printer consists of a semiconductor laser oscillator 1, a rotating polygon mirror 4 that polarizes the laser beam, a laser beam whose polarization is distorted, and a laser beam that moves at a constant speed onto the recording drum 5, and whose beam diameter is constant on the surface of the recording drum 5. to make fθ
Surrounding the lens 6 and the rotating recording drum 5 are a charging corotron, a developing device, a transfer device, a fixing device, a static eliminator, etc. (none of which are shown), and an input interface 7 *%ROM
7 b, CPU 7 c% RAM 7 d, output interface 7, and a mechanical control unit 7 are the same as the device shown in Fig. 1, but a converging cylinder lens 8 and a plurality of a light receiving section 9 having a light receiving element and outputting a shape signal according to the shape of the laser beam;
A determination unit io (however,
The determination unit 1O can also be included in the control unit 7).

In the above configuration, the operation of the laser beam printer will be explained. The laser beam from the semiconductor laser oscillator 1 is polarized by the rotating polyhedron 4, and then the beam diameter is kept constant by the fθ lens 6, and the beam is scanned at a constant speed on the recording drum 5. do.

The recording drum 5 is charged in advance by a charged corotron), and a latent image is formed on the recording drum 5 by scanning with a laser beam.
The image is printed by developing this latent image, transferring it to plain paper, and fixing it.

In addition to the above printing operation, just before the laser beam scans the entire image area on the recording drum 5, the beam is focused by the cylinder lens 8 and sent to a plurality of light receiving elements.
For example, when entering the light receiving section 9 having a photodiode, the light reception signal from the light receiving section 9 enters the determining section IO. FIG. 3 is an explanatory diagram of the light receiving section 9 and the determining section IO. In FIG. 3, the light-receiving elements of the light-receiving section 9 include, for example, four photodiodes 9m, 9b, 9c, which are arranged symmetrically with two lines x and yK passing perpendicularly to the beam axis (perpendicular to the paper surface). Although the example in which photodiodes 9d are used is shown, the number of photodiodes is not limited to four (two linear sensors may be arranged orthogonally). In FIG. 3, the four photodiodes are arranged in a square, and after adjustment, the shape of the beam passing through the cylinder lens 8 becomes circular as shown in FIG. 4. In this case, the outputs of the four photodiodes 9m, 9b, 9e, and 9d are equal. Since the output of the photodiode is a minute current, it is amplified by the amplifiers 11a, llb, lla, and lld of the determination section 10. Photodiode 9 by adder 12aK
When the outputs of a and 9d are added together and the sum of the outputs of photodiodes 9b and 90 is subtracted by an adder 12b from the skin value by a subtracter 13, the value becomes 0 if the beam shape is circular. As shown in Figure 5, if the conditions change and the shape of the beam changes and deviates from a circular shape and becomes an elliptical shape, 9a and 9
If the value obtained by adding the outputs of 9c and 9b is subtracted by the subtracter 13 from the value obtained by adding the outputs of d, it becomes positive.] In the case where the shape of the ellipse in Fig. 5 is reversed by 906 (not shown) are 9a and 9d
If the subtracter 13 subtracts the sum of the outputs of 96 and 9b from the value, a negative value is obtained. In other words, a change in the beam shape can be detected by the output of the light reception signal from the light receiving section 9.

Also, the signals of the photodiodes 9a and 9b are added to an adder 12a.
The summed output is used as a scanning timing signal (for example, scanning is started when a predetermined minute time has elapsed from the output of the adder 12o).

As described above, the laser beam that has passed through the cylinder lens 8 provided on the beam optical path can be shaped into a beam by arranging a beam detector consisting of a plurality of photodiodes and adding circuits of an amplifier, an adder, and a subtracter. and scan timing signals can be obtained. These signals are input to the input interface 7a of the control section 7, and predetermined calculations are performed along with other signals as necessary for the copying machine.

On the output interface 7e, temperature control is performed on the fθ1/7 lens, collimator lens, etc. to obtain a normal beam shape, and the scanning timing signal is used to control the temperature of the recording drum 5.
It is possible to accurately determine the starting point for soil scanning.

〔Effect of the invention〕

As explained above, according to the exposure beam control signal generator for a laser beam printer of the present invention, a plurality of light receiving elements are provided symmetrically to an arbitrary line passing perpendicularly to the beam axis of the laser beam, and the light receiving signal is The shape of the laser beam is determined based on the received light signal, and the scanning start timing is determined as necessary based on the received light signal. , it is possible to accurately determine the timing for starting beam scanning.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional laser beam printer, FIG. 2 is an explanatory diagram showing an embodiment of the present invention, FIG. 3 is an explanatory diagram of an embodiment of the light receiving section and determination section of the present invention, and FIG. The figure is a cross-sectional view of the beam shape when the beam is adjusted and normal.
The figure is a cross-sectional view of an example of the shape of the beam when it is deformed. Explanation of symbols 1... Laser beam oscillator, 4... Rotating polygon mirror,
5... Recording drum, 6... fθ lens, 7... Control unit, 7a... Input interface, 7 b ''-
ROM, 7 o”-CPU, 7 d”-RAM
. 7... Output interface, 8... Cylinder lens, 9... Light receiving section, 9m, 9b, 9e. 9d... Photodiode, lO... Judgment unit, eye,
a, llb, lla, 1ld-...amplifier, 12&. 12bs12a...Adder, 13...Subtractor. Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] A laser printer that forms an electrostatic latent image on a photoreceptor based on a laser beam modulated with an image signal, develops the electrostatic latent image, and then transfers and fixes it to print an image, Based on a plurality of receiving f elements and a light receiving signal outputted when the plurality of light receiving elements receive the laser beam, A determining means for determining the shape of the laser beam; and a control means for outputting a control signal for controlling the shape of the laser beam based on the determination result of the determining means. Beam control signal generator for printer exposure.