JPH01273068A - Optical scanning device - Google Patents

Abstract

PURPOSE:To switch printing density in an image forming device by modifying the variable characteristic of the frequency of an image scanning clock according to the printing density. CONSTITUTION:A light beam turned on/off in synchronization with the image scanning clock and coming from a light source D is image-formed as a subtle beam spot on a photosensitive body E through a focusing lens A and an optical deflector B. A clock frequency modifying means C continuously changes the frequency of the image scanning clock in response to a change in the scanning speed of the beam spot caused by scanning of the optical deflector B. In addition, the means C modifies the variable characteristic of the frequency of the image scanning clock according to signals that change and indicate the printing density such as 300 dot/inch and 400 dot/inch. In this way, the printing density of the image forming device can be switched.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical scanning device used in a laser beam printer, etc., and in particular, an optical scanning device that electrically corrects fluctuations in optical scanning speed without using an f-theta lens. The present invention relates to an optical scanning device configured as described above.

[Prior Art 1] Conventionally, in a laser beam printer, an optical scanning device that writes image information by scanning a photosensitive drum surface with a light beam is generally known.

This type of optical scanning device uses a polygon mirror scanner that rotates at high speed to scan a light beam deflected at a uniform angular velocity onto the surface of a photosensitive drum using an f-theta lens that has a distortion aberration. is widely used. In other words, since the distance from the polygon mirror to the photosensitive drum surface is not constant, an f-theta lens, which is a special spherical lens, is used to connect the focal point of the same size at every position on the scanning line, and to move the light at a constant speed. It is made scannable.

When such an f-theta lens is used, since the scanning speed of the beam on the photosensitive drum surface is constant, there is an advantage that the clock frequency for writing image data can be fixed.

However, the f-8 lens is a special spherical lens that has a complicated structure and is expensive.

One way to solve this problem is to use an optical scanning device that does not use an f-theta lens and to continuously change the frequency of the image data writing clock to correct the scanning distortion of the image recorded on the photosensitive drum surface. A proposal combining means to do this is disclosed in Japanese Patent Application Laid-Open No. 61-242459.

Next, a conventional example disclosed in Japanese Unexamined Patent Publication No. 61-242459 will be explained.

6 to 8 show this conventional laser beam printer.

First, in FIG. 6 showing the overall configuration, a light beam emitted from a light source 1 consisting of a semiconductor laser is focused by a focusing lens 2 so as to be imaged as a beam spot on a photosensitive tram 3. It is deflected by rotation and moves repeatedly in the X direction (main scanning direction) in the figure, and at the same time, the photosensitive drum 3 rotates to perform sub-scanning. A photodetector 5 is disposed near the photosensitive tram 3 outside the information writing area, and detects the light beam deflected by the polygon mirror 4 to generate a synchronizing signal. The signal processing circuit 6 applies an information signal to the semiconductor laser drive circuit 7, and the timing of the application is controlled by a synchronization signal from the photodetector 5.

The semiconductor laser drive circuit 7 drives the semiconductor laser 1 based on the information signal from the signal processing circuit 6, and a light beam modulated by the information signal is emitted from the semiconductor laser 1 and passes through the focusing lens 2. The photosensitive drum 3 is irradiated through the polygon mirror 4 to form an electrostatic latent image. This electrostatic latent image is developed with toner from a developing device (not shown) to form a toner image, which is transferred onto a sheet of paper by a transfer device (not shown).

The light beam separated from the semiconductor laser 1 and emitted backward enters the photodetector 8 and its light intensity is detected, and in response to the output signal of the photodetector 8, the control circuit 9 controls the semiconductor laser drive circuit. 7 to keep the output light amount of the semiconductor laser 1 constant.

-IIQ, in a laser beam printer, an f-theta lens is arranged on the optical path between the photosensitive drum 3 and the polygon mirror 4 so that the light beam scans the photosensitive drum 3 at a constant speed as described above. In this conventional example, the f-theta lens is removed, and instead of the f-theta lens, the frequency of the image scanning clock that transfers the information signal applied to the semiconductor laser drive circuit 7 by the signal processing circuit 6 is changed. , which is continuously variable in proportion to the scanning speed of the light beam scanning the photosensitive drum 3 to correct distortion in optical scanning.

FIG. 7 shows a detailed configuration of the clock frequency variable portion of the signal processing circuit 6 shown in FIG. As shown in this figure, oscillator 1
The clock of frequency f from 0 is divided into 1/1 by the frequency divider 11.
The frequency is divided into N (where N is an integer) to become the position control clock CLKB, and this clock CLKB is used by the phase comparator 1.
2. Low pass filter 13. PLL (Phase Lock) consisting of a voltage controlled oscillator 14 and a frequency divider 15
ed Loop) circuit, the frequency is multiplied by m times, and the frequency fK
image scanning clock CK. In particular, this signal processing circuit 6 controls the timing of the information writing position (hereinafter referred to as an information writing period) using the position control clock CLKB, and outputs an information signal using the image scanning clock CK within the information writing period. The data are sequentially transferred to the semiconductor laser drive circuit 7.

The image scanning clock CK is divided into 1/m by the frequency divider 15, and the phase comparator 12 converts the image scanning clock CK into a position control clock CLKB.
The phases are compared, and a voltage corresponding to the phase difference is output from the phase comparator 12. This voltage output from the phase comparator 12 is inputted to the voltage controlled oscillator 14 via the low-pass filter 13, and its oscillation frequency is controlled. Therefore, the frequency fK of the image scanning clock CK output from the voltage controlled oscillator 14 is expressed by the following equation (1).

fK =fxl/Nxm...(t) Also, the position control clock CLKB is counted by the counter 16,
The counted value is sequentially applied to the ROM (read only memory) 17 as a read address signal, and timing data corresponding to the counted value is read out from the ROM 17.

The frequency division ratio of the frequency divider 11 is made variable by the output signal of the ROM 17. For example, if the scanning distortion of the polygon mirror 4, which is an optical deflector, with respect to the surface of the photosensitive drum 3 is in a curved state as shown in B in FIG. 8, the frequency is divided in proportion to the scanning speed of the light beam. The frequency division ratio N of the circuit 11 changes from small to small within one horizontal scanning period as shown in C in FIG. The ratio is made continuously variable.

Therefore, the position control clock CLKB output from the frequency divider 11 is frequency-modulated in proportion to the scanning speed according to the frequency division ratio N. Therefore, the image scanning clock CK is frequency-modulated according to the above equation (1), but the frequency f changes continuously and transiently due to the action of the low-pass filter 13. That is, the image scanning clock C
Since the frequency fK of K changes continuously according to changes in the scanning speed, scanning distortion is corrected.

Furthermore, since the counter 16 is initialized by a synchronization signal supplied from the photodetector 5, the image scanning clock CK is corrected for each scan.

Further, the frequency divider 11 is initialized by a synchronization signal from the photodetector 5, and the phase relationship between the position control clock CLKB and the synchronization signal is maintained within an accuracy of one clock of the output of the oscillator IO.

Since the image scanning clock CK is generated by the PLL circuit using the position control clock CLKB, the phase accuracy of the position control clock CLKB and the image scanning clock CK is maintained at a predetermined value at least during the time it takes to print one page. be able to.

Therefore, the phase accuracy of the image scanning clock CK and the synchronization signal is 1 of the output of the oscillator 10 within the printing time of one page.
It can be within the clock.

In this way, in the conventional example described above, the value of the frequency division ratio is RO
It is determined by the output signal of M17, and for example, when the printing density is 300 dots/inch, the frequency fK of the image scanning clock CLK changes as shown in Fig. 2 (A). The data stored in ROM17 is determined in advance, and the printing density is 400 dots/
In the case of inches, the ROM is set so that the frequency fK of the image scanning clock CK changes as shown in FIG. 2 (II).
17 stored data were to be tentatively determined.

[Problem to be solved by the invention] However, in the conventional device as described above, only data corresponding to one print density is stored in the ROM 17, so it is difficult to change the print density in the same printer. That was impossible.

On the other hand, in recent years, with the spread of racer beam printers,
For example, when used for desktop publishing, the same printer can print at a print density of 300 dots/inch when printing mainly text, and at a print density of 400 dots/inch when printing mainly graphics. There is a demand for usage in which printing is performed by changing the printing density. However, it has not been possible to realize such requirements with conventional devices for the reasons mentioned above.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide an optical scanning device that can switch printing density in the same image forming apparatus.

[Means for Solving the Problems] In order to achieve the above object, the present invention focuses a light beam emitted from a light source that is turned on and off in synchronization with an image scanning clock into a minute beam spot on a photoreceptor. A focusing lens that generates an image, an optical deflector that scans the light beam in a fixed direction with respect to the photoreceptor, and a continuous change in the frequency of the image scanning clock according to changes in the scanning speed of the beam spot due to the scanning of the optical deflector. and clock frequency variable means for changing the frequency of the image scanning clock according to an instruction signal indicating switching of recording density.

[Function] According to the present invention, with the above configuration, the change characteristics of the frequency of the image scanning clock are changed in accordance with the instruction signal indicating switching of the recording density (printing density). Density can be switched.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the basic configuration of an embodiment of the present invention. In this figure, A is a focusing lens, which is turned on and off in synchronization with an image scanning clock to image a light beam emitted from a light source onto a photoreceptor E as a minute beam spot. Reference numeral B denotes a light deflector, which scans the photoreceptor E with a light beam in a fixed direction.

C is a clock frequency variable means, which continuously changes the frequency of the image scanning clock in accordance with the change in the scanning speed of the beam spot due to the scanning of the optical deflector B. Further, this clock frequency variable means C changes the frequency change characteristic of the image scanning clock in response to an instruction signal indicating switching of recording density.

FIG. 2 shows the circuit configuration of the first embodiment of the present invention, and the same reference numerals as in FIG. 7 described above indicate the same contents. Further, the other configurations are the same as the conventional example shown in FIG.

As shown in Figure 2, as a ROM that provides a frequency division ratio N,
In this embodiment, there are two ROM(I) 18 and ROM(19). Print dot density switching designation command (
When the CPU 20 receives the command signal (command signal), it performs a selection operation to enable either the ROM 18 or the ROM 19 in response to this command. Here, for example, ROM■1
8 stores data on a frequency division ratio N corresponding to a printing density of 300 dots/inch, and ROM 19 stores data on a frequency division ratio N corresponding to a printing dot density of 400 dots/inch. 3(A) by the switching designation command from the postcomputer.
, (B), it is possible to perform operations corresponding to each printing dot density.

Note that in this embodiment, the number of ROMs is not limited to two as described above, but more ROMs are provided corresponding to the required printing dot density, and each ROM can be switched and specified. Of course, this is a good thing.

FIG. 4 shows a circuit configuration of a second embodiment of the present invention, and the same reference numerals as in FIG. 2 indicate the same contents.

In FIG. 4, 21 is a preset counter, and 22 is a RAM connected between the counter 16 and the preset counter 21.
2, 23 are RAMs 2 connected between the preset counter 21 and the frequency divider 11, and these 21, 22, and 23 are reset by a synchronization signal.

FIG. 5 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 4, and shows the frequency fK of the image scanning clock CK in the main scanning direction.
It is shown in an approximate state. First, Fig. 5 (A) shows an approximation when the printing density is 300 dots/inch, and the change in the frequency fK of the image scanning clock is symmetrical about the main scanning center position (scanning center). . In the clock range of Ml dots from the start of scanning, the frequency f.

changes in nl dot steps. In addition, in the clock range from scanning point M1 to M, +M2 dots,
The frequency fK changes in n2 dot steps. However, +1+ >n
2>n3>rz>n5>n6. Also, the fifth
Figure (B) shows an approximation when the printing density is 400 dots/inch, and the frequency fK of the image scanning clock CK changes as described above, but the values of M and n are 30
This is different from the case of 0 dots/inch.

In FIG. 4, RAM 22 is the above-mentioned M shown in FIG.
RAM (random access memory) 23 is a RAM (random access memory) that provides data values of the frequency division ratio N described above. Further, when the CPU 20 receives a print density switching designation command (command signal) from an external host computer via serial communication, the CPU 20 inputs the data by calculation within the CPU 20 or from the data area of the internal ROM in which the M and N data are stored in advance. Take it out and store it in RAM 22 as the value of M, and store it in RAM as the value of N.
■Set the data in 23 respectively. Incidentally, the above command from the post computer may be the value of the data itself to be loaded into the RAM 22 and the RAM 23.

As a result, if the printing density is, for example, 300 dots/inch, RAM 22 will have M+
, N2, N3... are rotated, and the values of RA
The values of N+, N2, N3, . . . are loaded into M23. Also, the printing density is 400 dots/in 1
In the case of 1, RAM 22 is loaded with the values Mlo, M2°9M3", etc., according to the address, and RAM 23 is loaded with N1°, N2°, N3", etc.
The value of ... is rotated. In addition, N+, N2, N3
- corresponds to nl+n2+13'', and N+'
, N 2', N 3°... are n1°, n2'
, n3°, . . .

[Effects of the Invention] As explained above, according to the present invention, the change characteristic of the frequency of the image scanning clock is changed in accordance with the instruction signal indicating switching of the recording density (print density). The effect of being able to switch the recording density in the image forming apparatus can be obtained.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic configuration of the embodiment of the present invention, Figure 2 is a block diagram showing the circuit configuration of the first embodiment of the invention, and Figures 3 (8) and (B) are the circuit diagrams of the present invention. FIG. 4 is a block diagram showing the circuit configuration of the second embodiment of the present invention, and FIGS. 5(A) and (B) are waveform diagrams showing the operation of the first embodiment of the present invention. Figure 6 is a block diagram showing the overall circuit configuration of the conventional device; Figure 7 is a block diagram showing the main part configuration of the signal processing circuit in Figure 6; Figure 8 is the same as in Figure 6. FIG. 3 is a waveform diagram showing the logic operation of the signal IA. ■...Semiconductor laser, 3...Photosensitive drum, 4...Polygon mirror, 5...Photodetector, 6...Signal processing circuit, 7...Semiconductor laser drive circuit, 8... - Photodetector, 9... Control circuit, 11... Frequency divider, 12... Phase comparator, 13... Low pass filter, 14... Voltage controlled oscillator, 15... Frequency divider , 16...Counter, 17.18.19...ROM. 20...CPU. 21...Preset counter, 22.23...RAM. ni← ni-ichibisharan- promotion ice'

Claims (1)

[Scope of Claims] 1) A focusing lens that is turned on and off in synchronization with an image scanning clock to image a light beam emitted from a light source as a minute beam spot on a photoreceptor; The image scanning clock includes an optical deflector that scans a light beam in a fixed direction, and a clock frequency variable means that continuously changes the frequency of the image scanning clock according to a change in the scanning speed of the beam spot due to scanning of the optical deflector. An optical scanning device, wherein the clock frequency variable means changes the frequency change characteristic of the image scanning clock in response to an instruction signal indicating switching of recording density. 2) The apparatus according to claim 1, wherein the clock frequency variable means includes storage means that stores in advance data on frequency change characteristics of the image scanning clock corresponding to a plurality of recording densities, and a storage means that indicates switching of the recording density. reading means for reading out data corresponding to the recording density indicated by the instruction signal from the storage means in accordance with the instruction signal; An optical scanning device comprising: image scanning clock generating means for continuously changing a frequency; 3) The apparatus according to claim 1, wherein the clock frequency variable means is a control means for calculating and outputting data of a frequency change characteristic of an image scanning clock corresponding to a recording density indicated by the instruction signal in response to the instruction signal. a storage means for storing the data supplied from the control means; and an image scanning clock generating means for continuously changing the frequency of the image scanning clock using the data stored in the storage means. An optical scanning device characterized by comprising: