JPH1117902A - Laser writing device - Google Patents

Abstract

(57) [Problem] To provide a laser writing device capable of making the magnification equal to one size regardless of the paper size and when the paper transport position in the main scanning direction is different. SOLUTION: A write clock generator 22 generates the write clock by changing the frequency of the write clock in accordance with the paper size and the transport position of the paper in the main scanning direction. For example, in the case of A3 and A4 (horizontal) sizes of the center reference, the frequency is set to f1, and in the case of A4 (vertical) size of the center, the frequency f2 is set.
In the case of A4 (vertical) size based on the end portion, the frequency is set to f3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser writing apparatus which scans a recording medium such as a photoreceptor with a laser beam and writes information on the recording medium, and is suitable for a digital copying machine, a facsimile, a printer, and the like. It relates to a writing device.

[0002]

2. Description of the Related Art Generally, in a laser writing optical system of this kind, the magnification in the main scanning direction has a non-uniform characteristic with respect to a written image due to the characteristics of a lens system as shown in FIG. Conventionally, in this type of laser writing apparatus, in order to correct the uneven magnification, the writing clock is set so that the magnification becomes equal to the maximum width of the writing paper in the main scanning direction on average. FIG. 8 shows a conventional example. In this example, the frequency f of the write clock is set so that the A3 size and the A4 horizontal size are equal to 297 mm on average.
Is set.

[0003]

However, in the above-described method, when the maximum size paper is used, the magnification when viewed over the entire width of the paper is the same size, but the paper other than the maximum size is used. In such a case, there is a problem that the magnification when viewed from the paper width is not always equal, and for example, in the conventional example shown in FIG. 8, the magnification is not equal to the A4 vertical size. Further, as shown in FIG. 7, since the magnification characteristic of the lens system is symmetrical with respect to the optical axis, even if the paper is the same size, the image formation in which the paper is transported from a different position in the main scanning direction is performed. In the apparatus, there is a problem that the magnification varies depending on the transport position.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is a first object of the present invention to provide a laser writing device capable of making the magnification equal to one regardless of the paper size.

It is a second object of the present invention to provide a laser writing apparatus capable of making the magnification equal to one when the transport position of a sheet in the main scanning direction is different.

[0006]

In order to achieve the first object, the first means scans a recording medium such as a photoreceptor with a laser beam synchronized with a write clock to write information on the recording medium. In a laser writing device for writing,
A write clock generating means for variably outputting the frequency of the write clock in accordance with the paper size so that the average magnification in the main scanning direction becomes equal to the average is provided.

In order to achieve the second object, the second means scans a recording medium such as a photosensitive member with a laser beam synchronized with a writing clock to write information on the recording medium. A write clock generating means for variably outputting the frequency of the write clock in accordance with the transport position of the sheet in the main scanning direction so that the magnification in the main scanning direction is equal to the average is provided.

A third means is that, in the second means, the write clock generating means makes the frequency of the write clock variable and outputs the write clock in accordance with the transport position of the paper in the main scanning direction and the paper size. Features.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an optical system of an embodiment of a laser writing apparatus according to the present invention, and FIG.
FIG. 3 is an explanatory diagram showing main scanning synchronization control by a laser writing optical system, FIG. 3 is a block diagram showing a control system of a laser writing device according to the present invention, FIG. 4 is a block diagram showing a write clock generator in FIG. 3 in detail, FIG. 5 is an explanatory diagram showing the relationship between the paper size and the transport position and the frequency of the write clock;
FIG. 6 is a flowchart for explaining the write clock frequency control.

In FIG. 1, a semiconductor laser (LD: laser diode) 1 emits a laser beam modulated in accordance with image data in synchronization with a write clock. This laser beam is collimated by a collimating lens 2 and then an aperture 3 and a cylindrical lens 4
Is deflected by the polygon mirror 5a of the polygon scanner unit 5 in the main scanning direction at an equal angle. The laser beam reflected by the polygon mirror 5a is applied to the fθ lens 6
Is corrected to constant velocity deflection, and then the surface tilt of the polygon mirror 5a is corrected by the surface tilt correction lens 7, and then reflected by the mirror 8 to irradiate the photoconductive belt 9, so that the surface of the photoconductive belt 9 A latent image is formed. The latent image thus formed is developed by an electrophotographic process and transferred to a sheet.

The laser beam passing through the fθ lens 6 is also reflected by a synchronous mirror 10 and then received by a photodetector 12 via a synchronous cylindrical lens 11, thereby obtaining a polygon mirror 5a as shown in FIG.
The main scanning synchronization detection signal is detected for each one side. And
The writing start position in the main scanning direction is determined based on the main scanning synchronization detection signal, and the phase of the laser writing clock coincides with the main scanning synchronization detection signal in order to suppress the displacement in the main scanning direction to one pixel or less. Is performed.

Next, the configuration of the write control system will be described with reference to FIG. The data sent from the write data generator 21 to the write processing unit 23 is not synchronized with the write clock WCLK sent from the write clock generator 22 to the write processing unit 23. Then, the write processing unit 23 transfers the write data to the LDD (laser diode driver) 24 in synchronization with the write clock WCLK, and the LDD 24 thereby drives the LD 1 in synchronization with the write data WCLK.

Next, the write clock generator 22 will be described with reference to FIG. The oscillator 31 has a constant frequency f
A clock CLK of B is generated, and this clock CLK is divided by the frequency divider 32 into 1 / R based on an external command (frequency fB / R). Next, the phase difference between the clock frequency-divided by the frequency divider 32 and the clock from the feedback frequency divider 36 is detected by the phase comparator 33, and this phase difference is converted into a voltage by the filter 34.

A voltage controlled oscillator (VCO) 35 is provided with a write clock WCL having a frequency such that the voltage becomes "0".
K is generated and sent to the write processing unit 23 shown in FIG. 3, and the write clock WCLK is frequency-divided by the feedback frequency divider 36 based on an external command and fed back to the phase comparator 33. Therefore, the frequency of the write clock WCLK can be controlled by controlling the frequency division ratios of the frequency dividers 32 and 36 by an external command, and as a result, the magnification in the main scanning direction can be controlled.

As described above, this type of laser writing optical system has a characteristic that the magnification in the main scanning direction is not uniform with respect to the written image due to the characteristics of the lens system.
FIG. 5 shows the relationship between A3, A4 (horizontal), and A4 (vertical) sizes as an example of the magnification characteristics in the main scanning direction, the paper size, and the transport position. The A3 and A4 (horizontal) sizes are conveyed only with reference to the center, while the A4 (vertical) size is a paper feed port “1” conveyed with reference to the center and a paper feed port conveyed with reference to the ends. Paper is fed from “2”. FIG. 5 also shows
The frequency of the write clock WCLK is A3, A4
In the case of (horizontal) size, the frequency is f1 and the center reference is A4.
In the case of (vertical) size, frequency f2, A4 based on end part
In the case of the (vertical) size, it is shown that the average magnification becomes equal at the frequency f3.

Referring next to FIG. 6, write clock WC
Processing for controlling the frequency of the LK will be described. First, when writing starts (step S1), the paper size is determined (step S2). If the size is A3 or A4 (horizontal), the frequency is set to f1 (step S3),
In the case of A4 (vertical) size, the paper feed port is determined (step S4). In the case of the paper feed port "1", the frequency is set to f2 (step S5), and in the case of the paper feed port "2", the frequency is set to f3 (step S5).
6).

[0017]

As described above, according to the first aspect of the present invention, the frequency of the write clock is made variable in accordance with the paper size so that the magnification in the main scanning direction becomes the same on average. The magnification can be made the same regardless of the paper size.

According to the second aspect of the present invention, the frequency of the write clock is made variable in accordance with the transport position of the sheet in the main scanning direction so that the magnification in the main scanning direction becomes the same magnification on average. When the transport position in the main scanning direction is different, the magnification can be made equal.

According to the third aspect of the present invention, the frequency of the write clock is variably changed according to the transport position of the sheet in the main scanning direction and the sheet size so that the magnification in the main scanning direction becomes the same magnification on average. Therefore, the magnification can be made the same regardless of the paper size and when the transport position of the paper in the main scanning direction is different.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical system of an embodiment of a laser writing device according to the present invention.

FIG. 2 is an explanatory diagram showing main scanning synchronization control by the laser writing optical system of FIG. 1;

FIG. 3 is a block diagram showing a control system of the laser writing device according to the present invention.

FIG. 4 is a block diagram illustrating a write clock generator of FIG. 3 in detail;

FIG. 5 is an explanatory diagram illustrating a relationship between a paper size, a transport position, and a frequency of a write clock.

FIG. 6 is a flowchart for explaining frequency control of a write clock.

FIG. 7 is an explanatory diagram showing magnification characteristics of a lens system of a laser writing optical system.

FIG. 8 is an explanatory diagram showing the frequency of a conventional write clock.

[Explanation of symbols]

 22 Write Clock Generator 31 Oscillator 32 Divider 33 Phase Comparator 34 Filter 35 VCO (Voltage Controlled Oscillation) 36 Feedback Oscillator

Claims (3)

[Claims] 1. A laser writing apparatus for writing information on a recording medium by scanning a recording medium such as a photosensitive member with a laser beam synchronized with a writing clock so that a magnification in a main scanning direction is equal to an average magnification. A writing clock generating means for variably outputting the frequency of the writing clock in accordance with a sheet size. 2. A laser writing apparatus for writing information on a recording medium by scanning a recording medium such as a photosensitive member with a laser beam synchronized with a writing clock so that a magnification in a main scanning direction is equal to an average magnification. A writing clock generating means for variably outputting a frequency of the writing clock in accordance with a transport position of a sheet in a main scanning direction and outputting the writing clock. 3. The laser according to claim 2, wherein said write clock generating means variably outputs a frequency of said write clock in accordance with a transport position of said paper in a main scanning direction and a paper size. Writing device.