JPS5997118A - Compensator for scanning speed in reciprocating optical scanner - Google Patents

Abstract

PURPOSE:To provide simplification of a device and a reduction of cost by adding signals generated from a means for generating an average value and a means for generating a speed difference, controlling the oscillation frequency of an oscillator and compensating the scanning speed. CONSTITUTION:A scanning speed in a forward path is designated as S1, the scanning speed in a backward path 10 as S2, and main control information S0 and auxiliary control information s0 are set at S0=(S1+S2)/2, s0=(S1-S2)/2. The voltage function value indicating the information S0 is generated by an FG13 and is inputted to an adder 14. Since the information s0 is extremely small as compared with S0, there is no need for generating the function of high accuracy having an extremely high effective digit. The voltage function value indicating the information s0 with respect to the information S0 is thus generated by an inexpensive FG16 having lower accuracy and said value is similarly inputted to the adder 14. The information on the scanning speed obtd. by the adder 14 is inputted to a VCO15 by which the frequency of a DCLK11 is controlled.

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to a reciprocating optical scanning device, and more particularly, to controlling the oscillation frequency of an oscillator that modulates a light beam at a predetermined frequency to account for the difference in scanning speed between the forward and backward paths. This invention relates to a scanning speed compensator in reciprocating optical scanning that compensates for this.

(Background of the fi+ technology) There are two types of optical scanning devices: one uses a rotating polygon mirror to perform unidirectional scanning, and the other uses an oscillating galvanometer mirror to perform reciprocating scanning.The outer diameter of the rotating polygon mirror is The large size increases the size of the optical system, but with a galvano mirror, the optical system can be made smaller and the scanning speed does not decrease because it scans back and forth.However, when using a galvano mirror to scan back and forth, the scanning direction must be reversed. Therefore, the scanning speeds of the forward and backward paths differ due to the mechanical hysteresis of the reciprocating scanning means.

Therefore, it is necessary to compensate for the difference in scanning speed between the forward and backward paths.

(Q. Prior art and problems) In the conventional scanning speed compensator, when performing analog ζ processing, two day-precision function generators (hereinafter referred to as FG) with large effective digits are used for each of the forward and return journeys. A voltage function value corresponding to the forward scanning speed and a voltage function value corresponding to the backward scanning speed were generated.The voltage function value corresponds to the forward scanning speed during forward scanning, and the voltage function value corresponds to the backward scanning speed during backward scanning. The oscillation frequency of the oscillator was controlled by the voltage function value (performed by a voltage-controlled oscillator).In this way, the forward and backward scanning speeds (hereinafter referred to as DCLK) with corresponding frequencies were generated. was.

In addition, in the case of digital processing, in order to obtain a function value with a large number of effective digits, two large-capacity ROMs are installed, and the forward scanning speed function value and the backward scanning speed function value are time-divided. The reference clock is divided by a frequency divider (hereinafter referred to as DIV) according to this data, and a DCLK having a frequency corresponding to the scanning speed is generated.
was occurring.

However, with these scanning speed compensators, the forward pass.

Since a high-precision FG or ROM is required for each return trip, the device has the drawbacks of being complicated and expensive.

(2) Object of the Invention An object of the present invention is to provide a scanning speed compensation system that can simplify the apparatus and reduce costs in view of the drawbacks of the conventional arrangement.

(2) Structure of the invention and object of the invention is to provide an optical scanning apparatus having a light beam generating means, a light beam modulating means for modulating the light beam according to the oscillation frequency of an oscillator, and a reciprocating scanning means for reciprocating the light beam. an average value generating means for generating an average value of the forward scanning speed and the backward scanning speed; a speed difference generating means for generating a difference between the forward scanning speed and the backward scanning speed; the average value generating means; and the speed. Adding the signals generated from the difference generating means ζ Therefore, an adder is provided to output the scanning speed of the forward path and the scanning speed of the backward path, and the oscillation frequency of the oscillator is controlled by the output of the adder. This is achieved by providing a scanning speed compensator in a reciprocating scanning device, which is characterized in that it compensates the scanning speed in the scanning plane.

3- ■ Embodiment of the Invention Below, an embodiment of the present invention will be described using a laser printer as an example.
The drawings will be described in detail below. In this embodiment, a semiconductor laser is used as a light source, and a galvano mirror is used as a reciprocating scanning means.

FIG. 1 is a perspective view schematically showing a laser printer.

In FIG. 1, the laser beam output from the semiconductor laser 1 is adjusted to a required beam diameter by a collimator 2, and then scanned back and forth by a galvanometer mirror 31, and then is directed onto a photoconductor 7 by an imaging system 4. The beam is focused and scanned with an equal spot diameter. At the same time, the photoconductor 7 rotates in a direction perpendicular to the scanning of the light beam, so that a character pattern consisting of dots ζ can be exposed onto the photoconductor 7, and a character pattern consisting of dots ζ can be formed on plain paper using an electrophotographic process. Can be printed.

When performing reciprocating scanning with the galvano mirror 3, due to mechanical hysteresis in the drive means of the galvano mirror 3,
The scanning speeds in the forward and backward passes differ from each other due to the scanning position. It is necessary to compensate for pixel position shifts during printing due to such variations in scanning speed.

To compensate for this, a method is used in which the frequency of DCLK that rises when the light beam reaches the pixel position is controlled.

Now, this DCLK frequency control operation and configuration will be explained in the analog case using FIGS. 2 to 4.

FIG. 2 shows the characteristics of the scanning speed S1 (slope of the curve) on the outward journey 91 and the return journey 10? Scanning speed S.

It is a graph showing the characteristics of (the slope of the curve).

Here, let the main control information So and the sub control information s0 be S,
” (S+ 10 St)/2s o-(S r
S t )/2 (s o << 80).

On the outward journey 9, the main control information S. By adding minute sub-control information s0 to , the scanning speed S on the outward path 9 can be adjusted.

Reproduce. Also, on the return trip 10, main control information S is provided.

The scanning speed S2 on the return path 10 is re-monme by reducing the very small sub-control information 8° (adding a negative value of so). Scanning speed S
The frequency of DCLK is controlled according to S and i times.

Figure 3 shows how the DCLK frequency is controlled.
explain.

FIG. 3 is a diagram showing the relationship between DCLK and pixel position on scanning. When the scanning speed of the original beam is slow, the frequency of DCLKII is lowered correspondingly to this scanning speed (DCLK
II).

From this, when DCLKII rises, the light beam is located at 121 pixel positions corresponding to DCLKII.

Unfortunately, when the scanning speed of the light beam is high, the frequency of DCLKII is increased in accordance with the scanning speed of the light beam (DCLK
II). This is L DCLKI 1
When stopped, the light beam is located at pixel #12I corresponding to DCLK11.

In this way, characters can be formed by controlling the frequency of DCLKII.

Next, the configuration of this embodiment will be explained with reference to FIG.

FIG. 4 is a block diagram showing the configuration of the scanning speed generating circuit in this embodiment. The main control information S described above by FCl2. A voltage function value representing the voltage is generated and inputted to the adder 14. Sub-control information S. Since S0ζ is very small compared to S0ζ, there is no need to generate a highly accurate function with a large number of significant digits. So cheap FG16 with low accuracy? A voltage function value representing the sub-control information s0 for the main control information S0 is generated and also input to the adder 14.

Inverter 17 is activated by switch A during backward scanning.
By inputting the negative inverse of the voltage function value representing the sub-control information S0 to the adder 14 through
o-s. ), and sub control information S during forward scanning. The pressure function value is directly input to the adder 141 to calculate the forward scanning speed (So+s0). The information on the scanning speed obtained by this adder 14 is input to the VCO 15E, and the DC
Performs frequency control of LKII 7-.

As another embodiment, a configuration for digital guard control is shown in FIG. ROM1 in Figures 4 and 5
9 is connected to FG13f, adder 20 is connected to adder 14φ, complement circuit 23 is connected to inverter 17, and RO is inexpensive and has small capacity.
M22 is FG16? This reference oscillator 18 and Div21 are V
Compatible with CO15i. In this case, the main control information S0 is stored in the large capacity ROM 19, and the sub control information 3° is stored in the small capacity and inexpensive ROM 220. Also, by passing through the complement circuit 23, the backward scanning speed (S, -s,
) is calculated by the adder 20. The operation of other parts is shown in Figure 4 I.
This is the same as the analog control case shown above.

(G) Effects of the Invention As explained in detail above, according to the present invention, the DLCK is controlled based on the average value and the difference between the scanning speeds of the forward and backward paths. Although it is generated by an FG (or a ROM with a large capacity), since the difference has a small number of effective digits, it can be generated by a FG (or a ROM complement circuit or an adder with a small capacity) with low precision. Therefore, there is no need to use two high-precision FGs (or large-capacity ROMs) as in the past, and one of the two can be a low-precision FC (or a small-capacity ROM). This has the effect of simplifying the configuration of the scanning speed compensator and reducing cost.

[Brief explanation of drawings]

Figure 1 is a perspective view showing the outline of a laser printer, Figure 2 is a graph showing the characteristics of the scanning speed in the forward path and the scanning speed in the return path, and Figure 3 is a graph showing the relationship between the data clock and the pixel position on the scan. Figure 1 is a block diagram. In the drawing, 13 is a function generator, 14 is an adder, and
5 is a voltage controlled oscillator, 16 is a low precision function generator, I
7 is an inverter.

Claims (1)

[Claims] In an optical scanning device having a light beam modulating means for modulating the light beam and a reciprocating scanning means for reciprocating the light beam based on the oscillation frequency of the light beam generating means and the oscillator, the scanning speed of the forward path on the scanning surface is determined. An average value generation means for generating an average value of the scanning speed of the road; a speed difference generation means for generating a difference between the scanning speed of the forward path and the scanning speed of the return path; Adding the signals ζ Therefore, an adder is provided to output the scanning speed of the forward path and the scanning speed of the backward path, and the oscillation frequency of the oscillator is controlled by the output of the adder.
1. A scanning speed compensation device for a reciprocating scanning device, characterized in that it compensates for a scanning speed at a reciprocating scanning device.