JPS6364063A - Laser beam printer - Google Patents

Abstract

PURPOSE:To fix the length of an image scanned on a photosensitive body by a laser printer by individually varying the frequency of a deflection speed control reference signal in control means which deflect plural laser beams. CONSTITUTION:Laser beams are emitted from plural laser units different in color and are deflected by plural polygonal mirrors 12C-12BK as deflecting means. With respect to deflection control, a reference frequency signal f0 is inputted from an oscillator 5c to a driver circuit 5. A feedback signal FG from a scanner motor 11C is inputted to a PLL circuit 13C and is compared with the signal f0, and a driving signal 14C obtained as the result is sent to the motor 11C to fix the rotation speed of the polygonal mirror 12C. The reference frequency signal f0 is individually varied to control the optical path length of laser beams from polygonal mirrors 12C-12BK, and the photosensitive drum is scanned by these laser beams. Since the optical path length of the laser beam is fixed, the length of the image scanned on the photosensitive drum is fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser beam printer having a scanning system that scans a plurality of photoreceptors, respectively, with laser light emitted from a plurality of laser units.

[Conventional technology]

Conventionally, in this type of device, the number of rotations of a plurality of rotary multi-facets that scan a photoreceptor with laser beams emitted from a plurality of laser units is made to match, and at the same time, the number of rotations of a plurality of rotary multi-facets and the photoreceptor are simultaneously scanned. Images were created by setting the optical path length to a predetermined distance, and the sizes of the images were matched.

FIG. 5 is a cross-sectional view illustrating the configuration of a conventional laser beam printer. Reference numeral 31 denotes a main body of the apparatus, and numeral 32 denotes a paper feed system, which is composed of a paper feed cassette 32a, a paper feed roller 32b, and the like. A laser unit 33C forms a latent image on a cyan photosensitive drum 34C according to color image data. 3
3M is a laser unit that forms a latent image on a magenta photosensitive drum 34M according to color image data. 33Y
A laser unit forms a latent image on the yellow photosensitive drum 34Y according to the color image data. 33BK
is a laser unit that forms a latent image on the black photosensitive drum 34BK according to color image data. 35C,
35M, 35Y, and 35BK are toner hoppers filled with cyan, mazanta, yellow, and black toners.

36C, 36M, 36Y, 36BK are transfer chargers,
The toner image is transferred onto the conveyed recording paper 37F. A conveyance belt 38 conveys the recording paper 37 in the direction of the arrow. In addition, each laser unit) 33C, 33M, 33Y, 33BK
has a polygon mirror (polygon mirror) shown in FIG. 4, and horizontally scans the laser beam in the main scanning direction.

Uniformly charged photosensitive drums 34C and 34M.

34Y, 34BK with laser unit 33Y, 33M
, 33Y, and 33BK are irradiated with laser light that turns on and off according to the color image signal, and the photosensitive drums 34G,
Latent images are formed on 34M, 34Y, and 348K, and are developed and visualized by cyan, magenta, yellow, and black toners filled in each toner hopper 35C, 35M, 35Y, and 35BK. Transfer chargers 36C and 36M are placed on the recording paper 37 on which the toner image is conveyed.
36Y and 36BK are transferred respectively.

FIG. 6 is a perspective view illustrating the laser irradiation operation by the laser unit shown in FIG. 5, and the same reference numerals as those in FIG. 5 are given below.

In this figure, a polygon mirror 41 has a plurality of mirror surfaces and is rotated by a scanner motor 42 at a constant speed in the direction of the arrow. 43 is an imaging lens, and polygon mirror 4
The laser beam deflected in step 1 is horizontally scanned, for example, on the photosensitive drum 34C via the scanning mirror 45.

[Problem that the invention seeks to solve]

In the conventional laser beam printer configured as described above, since the deflection angle θ of the beam is determined in advance, the length L of the image formed on the photosensitive drum 34C changes depending on the optical path length. For example, when the polygon mirror 41 shown in FIG. 6 shifts forward in the direction of the arrow, the length L of the image becomes shorter, and when it shifts backward as the polygon mirror 41 wears, the length L of the image becomes longer. Therefore, accuracy is an important factor when attaching the polygon mirror 41.For example, if the resolution is 16 pixels/■, one pixel has 62.5 pixels, so in a printer with multiple polygon mirrors 41, each A positional accuracy of 62.5 μm is required, but in reality this level of positional accuracy cannot be achieved, and the quality of the output image will be significantly lower in laser beam printers that have multiple laser units and multiple scanning systems. There were problems such as the

This invention was made in order to solve the problem of L, and while the frequency of the image data transport lock signal is held constant, the rotation speed of each rotation multi-face is controlled by PLL.
An object of the present invention is to obtain a laser beam printer that can make the length of an image scanned on each photoreceptor constant by independently varying the frequency of a reference frequency signal for control.

[Means for solving problems]

A laser beam printer according to the present invention includes: a plurality of deflection means for deflecting each of the laser beams emitted from a plurality of laser units; a plurality of control means for controlling the deflection speed of the plurality of deflection means; A variable means for independently varying the frequency of a reference signal for deflection speed control supplied to each of the control means is provided.

[Effect]

In this invention, the variable means independently varies the frequency of the reference signal that is used as a reference when the respective control means control the deflection speeds of the plurality of deflection means.

〔Example〕

FIG. 1 is a diagram for explaining the invention in detail.
Stators a to 1d rotate the rotor 2 in the direction of the arrow by applying current. Reference numeral 3 denotes a Hall element, which generates an electromotive force such that when the north pole of the rotor 2 approaches, the (-) side becomes "0" and the (+) side becomes "1". 4a is a Hall element, and when the S pole of rotor 2 approaches, the (-) side is rQJ, and the (+) side is
An electromotive force is generated so that the voltage becomes 1. 4b is a Hall IC that detects the rotational speed of the rotor 2 and sends a generated pulse to the scanner driver 50 and the PLL circuit 5a. 5b is a current amplifier that flows a driving current to each driver D1 to D4;
5C is a reference oscillator (◯SC) which supplies a reference frequency signal fO to the PLL circuit 5a. Note that depending on the current direction and the winding direction of the coils of the stators 1a to 1d, the stator 1a
, 1b, the magnetic field facing the rotor 2 becomes the south pole, and when the current flows through the stators 1c, 1d, Tf, the magnetic field faces the north pole. Further, there are as many scanner drivers 5 as there are colors to be developed, but for convenience of explanation, only one is shown.

Next, the operation shown in FIG. 1 will be explained with reference to FIG.

FIG. 2 is a diagram for explaining the operation of the scanner driver 5 shown in FIG. 1, and the same reference numerals as in FIG. 1 are given.

In this figure, 11C, 11M, 11Y.

11BK is a scanner motor, polygon mirror 12C,
12M, 12Y, 12BK (deflection means) are PLL circuits 13C, 13M of the driver circuit 5.

Drive signals 14C and 14 sent from 13Y and 13BK
Rotate at a constant speed according to M, 14Y, and 14BK.

As can be seen from this figure, the reference frequency signal fo sent out from one substrate oscillator 5C and the scanner motor II
By comparing the feedback signals FG from C, 11M, 11Y, and 11BK, each polygon mirror 12C
, 12M, 12Y.

Drive signal 14C to keep the rotation speed of 12BK constant
, 14M, 14Y, 14BK are PLL circuits 13C, 13
It is sent out from M, 13Y, and 13BK, and the rotational speed of each is kept constant. Therefore, polygon mirror 12C
, 12M, 12Y.

The rotation speed of 128 can be maintained constant. Therefore, if the frequency of the image data transport lock signal is controlled to be constant, and the frequency of the reference frequency signal fO supplied to the PLL circuits 13C, 13M, 13Y, and 13BK is independently controlled, the photosensitive drums 34C, 34M , 34Y,
The laser optical path lengths scanned by 34 B and K can be adjusted respectively.

FIG. 3 is a PLL control block diagram of a laser beam printer showing an embodiment of the present invention, and the same parts as in FIG. 2 are given the same reference numerals.

In this figure, 21 to 24 are oscillators constituting the variable means of the present invention, which generate reference frequency signals F1 to F4. 21a to 24a are variable resistors, and reference frequency signal F
Vary the frequencies of 1 to F4.

FIG. 4 shows the oscillators 21 to 24 and the PL shown in FIG.
It is a circuit diagram explaining the structure of L circuits 13C, 13M, 13Y, and 13BK. Components that are the same as those in FIG. 3 are given the same reference numerals. For purposes of explanation, the oscillator 21 and the PLL
One circuit 13C will be explained.

In this figure, 25 is a PL which constitutes the control means of this invention.
The LIC is composed of, for example, Toshiba TC9142P,
For example, feedback signal FG is input to pin 6,
This shows a state in which the reference frequency signal F1 is input to the CP terminal of pin 14. CT is a capacitor (capacitance Ct) and generates a reference frequency signal F1 based on the following equation (1) determined by a variable resistor 21a (resistance value VR).

As can be seen from this figure, the resistance value V of the variable resistor 21a
By finely adjusting R, the frequency of the reference frequency signal F1 can be finely adjusted, so that the optical path length of the laser beam that scans the photosensitive drum 34C can be finely controlled.

Since the oscillators 22 to 24 having such a configuration are independently arranged in the PLL circuits 13Y, 13M, and 138K, each of the photosensitive drums 34C, 34M, 34Y, and 34B
All laser optical path lengths scanning K can be kept the same.

〔Effect of the invention〕

As explained above, the present invention includes a plurality of deflection means for deflecting each of the laser beams emitted from a plurality of laser units, a plurality of control means for controlling the deflection speed of the plurality of deflection means, and a plurality of control means for controlling the deflection speed of the plurality of deflection means. Since variable means for independently varying the frequency of the j5 quasi-signal for deflection speed control supplied to each of the control means is provided, the length of the laser optical path applied to each photoreceptor can be made constant; The positional accuracy of the optical path length between the photoreceptor and the optical scanning system can be greatly reduced. Further, since the positional accuracy requirement does not need to be increased so much, the assembly process of the optical scanning system is simplified and the cost of the equipment can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the details of the present invention, FIG. 2 is a diagram for explaining the operation of the scanner driver shown in FIG. 1, and FIG. 3 is a diagram for explaining the operation of the scanner driver shown in FIG. 1. A PLL control block diagram of a beam printer, FIG. 4 is a circuit diagram explaining the configuration of the oscillator and PLL circuit shown in FIG. FIG. 6 is a perspective view illustrating the laser irradiation operation by the laser unit shown in FIG. 5. In the figure, 21 to 23 are oscillators, 21a to 23a are oscillation elements 21a to 23a, 24 is a multiplexer, 24'C, 2
4M, 24Y, 24BK are switches, 25C, 25M
, 25Y, and 25BK are image data memories. 1st stage, 2nd figure, 3rd figure, 21-24: Explosive device, figure 4 and

Claims (1)

[Claims] A laser beam printer that scans each of a plurality of photoreceptors with laser light emitted from a plurality of laser units, a plurality of deflecting means for deflecting each of the laser light emitted from the plurality of laser units; It is characterized by comprising a plurality of control means for controlling the deflection speed of the deflection means, and a variable means for independently varying the frequency of a reference signal for deflection speed control supplied to each of the plurality of control means. laser beam printer.