JP3165707B2 - Optical scanning type image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning type image forming apparatus having a variable resolution in the sub-scanning direction.

[0002]

2. Description of the Related Art As an optical scanning type image forming apparatus, L
BP (laser beam printer) is well known and used.

In this method, a laser spot is scanned by a polygon mirror (polyhedral mirror) rotating at a high speed, and the laser spot blinks according to an image signal to form an image.

[0004] The image signal is a multi-valued or binary digital signal transmitted from an external device (hereinafter referred to as a host) connected to the LBP.
Alternatively, the light is converted into light emission intensity, and the scanning line is exposed.

[0005] The LBP has an optical sensor for detecting the passage of an optical spot on a scanning line, and based on this, a horizontal synchronizing signal (H).
(sync) is generated, and the host adjusts the timing of image signal transmission by the host to control the writing start position in each scan.

The number of dots that can be printed in a certain area is called a pixel density. In recent years, a single LBP has been required to have a plurality of pixel densities.

Since the pixel density in the main scanning direction is determined by the speed of the image signal transmitted from the host, that is, the frequency of the image clock, the host can set it relatively freely.

In the sub-scanning direction, the distance is determined by the distance the photosensitive member moves during the scanning cycle of the laser spot. Therefore, when the pixel density is changed, it is usually handled by changing the polygon rotation speed on the LBP side. ing.

[0009]

However, if the number of rotations of the polygon is changed, the scanning speed of the laser spot also changes, which affects the pixel density of the main scanning.

That is, even when the pixel density of only the sub-scanning is changed, the image clock must be deflected, and the burden on the host increases.

Also, on the LBP side, it is necessary to keep the polygon rotation stable over a wide range of rotation speeds, and there has been a problem that the cost of the polygon drive unit becomes large.

The present invention has been made in view of the above-described problems, and provides an optical scanning type image forming apparatus capable of forming an image at a desired pixel density without changing the control mode in a complicated manner. The purpose is to:

An optical scanning type image forming apparatus according to the present invention comprises: a light source for generating a light beam modulated by an image signal; a deflecting means for periodically deflecting the light beam; Detecting means for detecting a light beam deflected by a predetermined position and generating a light detection signal; clock counting means for counting a clock signal; and light detection each time the deflecting means deflects the light beam a plurality of times. Control means for controlling the timing of forcibly turning on the light source based on the count value of the clock counting means so that the signal is generated once; and shaping a light detection signal generated by the detection means to perform horizontal synchronization. It has a horizontal synchronizing signal generating means for generating a signal.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. FIGS. 1 to 4 show a first embodiment of the present invention.

FIG. 1 shows a scanning optical system and a control unit of a laser beam printer. 1 is a semiconductor laser element which is a light source, and 2 is a divergent light beam from the semiconductor laser element which is converted into a substantially parallel light beam. The collimator lens 3 is a polygon mirror which is a deflector, and rotates in the direction of arrow A. Reference numerals 4 and 5 denote imaging lens systems, which form a laser beam deflected by a polygon mirror on a photoreceptor described later,
It has a function of scanning at a constant speed.

The light beam from the semiconductor laser 1 is scanned by the polygon mirror 3 and the imaging lens systems 4 and 5 in the direction of arrow B at a constant period.

Reference numeral 6 denotes a photosensitive drum, which is formed by observing a cylindrical photosensitive member from the side. The photoreceptor drum rotates at a constant rotational speed with its center axis L as a rotation axis.
Therefore, the surface of the photosensitive member moves by a fixed amount during the scanning cycle of the laser beam, and the relative position of the scanning line moves perpendicularly to the scanning direction (sub-scanning direction), which is the pixel interval in the sub-scanning direction. .

Reference numeral 7 denotes a light detecting element which is located at a laser beam scanning start position, detects passage of a laser beam, and generates a light detection signal (BD signal).

Reference numeral 10 denotes a control circuit, the configuration of which will be described later.
The control circuit receives a BD signal from the light detection element 7 and is connected to an external host via a signal line.

The input Res is a sub-scanning pixel density instruction signal, for example, 600 DPI at H level and 30 D at L level.
It is assumed that the setting is made to be 0 DPI. Output Hsy
nc is a horizontal synchronizing signal for adjusting the write start position in the scanning direction, and input Video is an image signal from the host.

FIG. 2 is a block diagram of the control circuit.

Reference numeral 21 denotes a horizontal synchronizing signal generation circuit, and reference numeral 22 denotes a down counter, which is reset by an Hsync signal, and loads an initial value corresponding to a sub-scanning pixel density instruction signal Res from a buffer 23.

Reference numeral 25 denotes an unblanking signal generating circuit which keeps the unblanking signal Unb at the H level for a certain period in synchronization with the borrow signal of the counter 22. Here, the unblanking signal Unb is a signal for forcibly turning on the laser to obtain a BD signal.

An OR gate 26 performs an OR operation on the unblanking signal Unb and the Video signal and outputs the OR signal to the laser driver 27.

The laser driver 27 turns on the laser when the input is at the H level and turns off the laser when the input is at the L level.

At the time of a printing operation, the Hsync generation circuit shapes the BD signal from the light detecting element 7 to generate an Hsync signal. The Hsync signal is transmitted to the host, and the host synchronizes with this signal and starts transmitting the image signal Video. The Video signal is input to the laser driver 27 through the OR gate 26, and the laser driver blinks the semiconductor laser device 1 according to the level of the Video signal. H
The sync signal also serves as a reset signal for the counter 22. At the same time as the Hsync, a preset value is read from the buffer 23 to the counter 22 and is counted down by the clock from the clock generation circuit 24.

When the down-counting is completed, a borrow signal is sent to the unblanking generation circuit 25. The unblanking generation circuit receives the borrow signal and generates an unblanking signal Unb. This signal is sent to the laser driver through the OR gate, and the semiconductor laser element is forcibly turned on. At this time, the next Hsync signal is obtained by the laser spot passing over the light detecting element.

A numerical value corresponding to the sub-scanning pixel density is stored in the buffer 23 in advance, and is selected by the sub-scanning pixel density indication signal Res transmitted from the host.
It is used as a preset value of the counter 22.

The setting of the preset value is performed as follows.

When the pixel density is the highest, that is, when the deflection period of the optical axis of the scanning system is equal to the light scanning period, the count value such that the down-counting of the count 22 is completed in a time slightly shorter than the deflection period. Set to. At this time, an Hsync signal is generated each time the optical axis is deflected.

FIG. 3 shows a timing chart at this time.

After the generation of the Hsync signal, the host
The video signal is transmitted, which causes the laser to flash and 1
The laser, which is subjected to the scanning exposure, is turned on by the unblanking signal Unb immediately before the optical axis to be deflected again passes on the light detecting element, and the Hsync signal is generated again by the light detecting signal BD.

When the pixel density is low, for example, when the maximum density is 1 / n (n = 2 in this embodiment), the down-counting is completed in a time slightly shorter than n times the deflection period. Set.

At this time, an Hsync signal is generated once every n times of deflection. FIG. 4 shows the timing chart at the time of 2.

After the generation of the Hsync signal, the V
The video signal is transmitted, which causes the laser to flash and 1
The laser is turned on by the unblanking signal Unb just before the optical axis to be changed passes the second time on the light detecting element, and the Hsync signal is generated again by the light detecting signal BD. As can be seen from FIG. 4, the period of the horizontal synchronization signal Hsync is twice as long as that of FIG.
Due to the double movement, the pixel interval in the sub-scanning direction is extended, so that the pixel density can be reduced to half. At this time, even in the period between the horizontal synchronizing signals Hsync, the light beam is not modulated by the recording signal in the latter half period.

Since the polygon rotation speed is not changed between FIG. 3 and FIG. 4, the relationship between the image clock and the main scanning pixel density does not change. No need to change.

2 and 5 show a control unit according to a second embodiment of the present invention, and the same components as those in FIG. 2 are denoted by the same reference numerals.

Reference numeral 51 denotes a waveform shaping circuit for generating a signal BD2 obtained by shaping a light detection (BD) signal. The down counter 22 is reset by the BD2 signal, and a buffer 53 is provided.
The preset value is loaded from the CPU and the unblanking signal generating circuit is operated at a predetermined timing. There is only one preset value, and the preset value is set so that the unblanking signal is generated every time the optical axis is deflected.

Reference numeral 52 denotes a frequency dividing circuit which divides the BD2 signal to generate an Hsync signal.

The frequency dividing circuit 52 has a sub-scanning pixel density control signal R
The frequency division ratio can be changed according to es.

In this configuration, the BD2 signal is generated for each optical axis deflection, but the Hsync cycle can be changed by changing the setting of the frequency dividing circuit 52 as in the first embodiment.

[0041]

As described above, according to the present invention, a light source for generating a light beam modulated by an image signal, a deflecting means for periodically deflecting the light beam, and a light beam deflected by the deflecting means are provided. Detecting means for detecting the detected light beam at a predetermined position to generate a light detection signal; clock counting means for counting a clock signal; and a light detection signal for each time the deflecting means deflects the light beam a plurality of times. Control means for controlling the timing of forcibly turning on the light source based on the count value of the clock counting means so as to generate a horizontal synchronization signal by shaping a light detection signal generated by the detection means. With such a horizontal synchronizing signal generating means, an image can be formed at a desired pixel density without complicatedly changing the control mode.

[0042]

[Brief description of the drawings]

FIG. 1 shows a scanning optical system and a control circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a control circuit according to the first embodiment of the present invention.

FIG. 3 is a timing chart at the time of the maximum sub-scanning image density in the first embodiment of the present invention.

FIG. 4 is a timing chart when the sub-scanning image density is half in the first embodiment of the present invention.

FIG. 5 is a block diagram of a control circuit according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser element 3 Polygon mirror 7 Photodetector 10 Control part 21 Horizontal synchronizing signal generation circuit 22 Down counter 25 Unblanking signal generation circuit 27 Laser driver

Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) B41J 2/44 G02B 26/10 G03G 15/04 H04N 1/113

Claims (4)

(57) [Claims] A light source for generating a light beam modulated by an image signal; a deflecting means for periodically deflecting the light beam; and a light beam deflected by the deflecting means at a predetermined position.
Detecting means for generating a light detection signal by detecting the light beam ; clock counting means for counting a clock signal; and light detecting means each time the deflecting means deflects the light beam a plurality of times.
The light source is forcibly turned on so that the knowledge signal is generated once.
The timing of the clock counting means.
Control means for performing control based on the position and a light detection signal generated by the detection means , and
An optical scanning type image forming apparatus comprising a horizontal synchronizing signal generating means for generating a synchronizing signal . 2. The image processing apparatus according to claim 1, wherein said control means controls a pixel density of an image to be formed.
Change the timing of forcibly turning on the light source according to the degree
2. The optical scanning image type according to claim 1, wherein
Equipment. 3. The control means for forcibly turning on the light source.
Generating a forced lighting signal for generating
Item 2. An optical scanning type image forming apparatus according to Item 1. 4. The method according to claim 1, wherein the light source is a semiconductor laser device.
The optical scanning type image forming apparatus according to claim 1, wherein: