JPH04263566A - Image exposing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an image exposure device,
More specifically, the present invention relates to an image exposure apparatus capable of detecting velocity unevenness of a moving image exposure surface and correcting the intensity of a light beam of a semiconductor laser element to eliminate unevenness in the exposure amount of the image exposure surface.

0002

2. Description of the Related Art As is well known, a semiconductor laser device has a characteristic of starting to generate a laser beam when an applied current exceeds a threshold current. Since oscillation is unstable near the threshold current, and the applied current and light intensity are not linear, generally when performing intensity modulation, a current slightly larger than the threshold current is always applied and the image signal is Modulation was performed by changing the light intensity by superimposing a corresponding current. This relationship is shown in equation (1), where Po is the light intensity and d is the image signal.

[0003]Po=η×K×d+Pt...(1)
Here, η is the quantum differential efficiency which is the current-light conversion efficiency of the semiconductor laser, K is the image signal-current conversion efficiency, and Pt is the light intensity emitted by the threshold current applying means. . As shown in FIG. 2, even if the temperature changes and the magnitude of the threshold current changes, the threshold current applying means changes the applied current to keep Pt constant.

In a conventional image exposure apparatus using a semiconductor laser driven in this manner, the image exposure surface is moved by a moving means, and the intensity of the light beam is changed based on an input image signal to move the image exposure surface. was exposed to light to form an image.

[0005]

However, since the moving means generally moves the image exposure surface by decelerating the rotation of the motor using a gear or the like, speed irregularities ranging from several Hz to several tens of Hz occur. Along with this, there has been a problem in that the amount of exposure on the image exposure surface changes, resulting in uneven exposure and the generation of stripes in the image, deteriorating the quality of the formed image.

The present invention has been made to solve the above-mentioned problems, and its purpose is to eliminate exposure unevenness on the image exposure surface even when the image exposure surface is moved with some speed unevenness. An object of the present invention is to provide an image exposure device that can obtain high-quality images.

[0007]

[Means for Solving the Problems] In order to achieve this object, the image exposure apparatus of the present invention includes an addition circuit that adds a predetermined value to an input image signal, and a detection circuit that detects speed unevenness of a moving image exposure surface. a multiplier circuit that multiplies the speed unevenness measured by the speed unevenness detection means by the output of the adding circuit; and a correction that corrects by applying a current to the semiconductor laser element based on the output of the multiplication circuit. The current applying means is provided.

[0008]

[Operation] A predetermined value is added to the input image signal by an adding circuit. A speed unevenness detection means detects the speed unevenness of the moving image exposure surface, and a multiplication circuit multiplies the output of the adding circuit by the speed unevenness measured by the speed unevenness detection means. Based on the output of the multiplication circuit, the correction current applying means applies a current to the semiconductor laser element for correction.

[0009] Therefore, the image formed is a high quality image free from stripes of light and shade due to speed unevenness.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle operation of the present invention will be explained.

The image exposure surface is moved at a predetermined speed V by the moving means.
The speed unevenness detecting means is configured to be able to detect speed unevenness ±ΔV/V of the movable image exposure surface. (The + sign represents speed increase, and the - sign represents deceleration.) The light intensity Pa by the correction current applying means is calculated by adding the predetermined value D to the input image signal d.
After multiplying by ΔV/V, a current is applied to the semiconductor laser element based on the multiplied value, so that the following equation (2) is obtained.

0012

[Math 1]

The light intensity P exposed to the image exposure surface is based on the current sum of the threshold current and the currents of the image current applying means and the correction current applying means, and its magnitude is determined by equation (1).
Since it is the sum of equation (2),

[0014]

[Math 2]

It is expressed as follows. here,

[0016]

[Math 3]

If the addition value D is chosen so that
is expressed as the following equation.

[0018]

[Math 4]

By the way, the exposure amount E of a pixel on the image exposure surface is expressed as the product of the light intensity of the laser beam received by the pixel (light intensity per unit area) and the exposure time during which the pixel is exposed. S, and the width of the image exposure surface is L, then the light intensity of the laser beam that exposes the pixel is:

002
0]

[Math 5]

[0021]The action time for the pixel to be affected is:

[0022]

[Math 6]

Therefore, the exposure amount E is calculated using equations (6) and (7).
)from

[0024]

[Math 7]

It is expressed as follows.

When the movement of the image exposure surface has speed unevenness ±ΔV, the pixel exposure amount EWF is

[0027]

[Math. 8]

It can be expressed as follows.

In other words, the amount of exposure fluctuates due to the unevenness of the moving speed of the image exposure surface, forming stripes of light and shade in the formed image and deteriorating the image quality.As mentioned above, the light intensity P of the laser beam is corrected according to the speed unevenness ±ΔV,
The exposure amount EADJ when exposed with the laser beam expressed by equation (5) can be expressed as shown in the following equation by substituting equation (5) into equation (9).

[0030]

[Math. 9]

[0031] Here,

[0032]

[Math. 10]

Therefore, equation (10) can be expressed as follows.

[0034]

[Math. 11]

That is, the corrected exposure amount E of the pixels on the image exposure surface is not affected by the speed unevenness ΔV.

[0036] Therefore, the image formed is a high quality image free from stripes of light and shade due to speed unevenness.

An embodiment embodying the present invention will be described below with reference to the drawings.

The overall structure of the image exposure apparatus of this embodiment will be briefly described with reference to FIGS. 1 and 3.

The semiconductor laser 1 emits a laser beam for exposure. The drive circuit 2 applies a drive current proportional to the input image signal to the semiconductor laser 1,
The threshold current circuit 3 applies a current slightly larger than the threshold current of the semiconductor laser 1 to the semiconductor laser 1. The adding circuit 4 adds a predetermined value D to the input image signal. The speed unevenness detection device 5 detects the rotational speed of a rotating drum 10 around which a photosensitive paper 11 is wound and rotates at a circumferential speed V (m/s), and detects a speed unevenness signal. The scanning device 8 consists of a well-known rotating polygon mirror 81 and an f-θ lens 82, and the laser beam emitted by the semiconductor laser 1 is scanned across the photosensitive paper 11 with a width L (
Scan with m). Further, the detected speed unevenness signal and the result of the adder circuit 4 are multiplied by a multiplier circuit 6, and the result is applied to the semiconductor laser 1 as a correction current by a correction circuit 7. That is, as shown in FIG. 4, the sum of currents generated by three circuits, the threshold current circuit 3, the drive circuit 2, and the correction circuit 7, is applied to the semiconductor laser 1 in a superimposed manner.

The drive circuit 2 is a D/A drive circuit as shown in FIG.
Consisting of a converter 21 and a current drive circuit 22, it supplies a drive current proportional to the input image signal to the semiconductor laser 1.
to be applied. The threshold current circuit 3 has the configuration shown in FIG. 6, in which a photocurrent detected by a monitoring photodiode 31 incorporated in the same package as the semiconductor laser 1 is amplified by an amplifier 32, and a photocurrent is amplified by a reference voltage 33 and a comparator. 34, and the count value of the counter 35 is increased or decreased according to the comparison result of the comparator 34, and the count value is changed to D/D so that light is emitted with a predetermined small light intensity slightly exceeding the threshold current.
The A converter 36 converts the signal into an analog signal, and the current drive circuit 37 applies a current to the semiconductor laser 1 based on the analog signal. This control operation to increase or decrease the count value is performed when a control signal (not shown or explained) is input from the outside, and in that case, the drive circuit 2 and the correction circuit 7 stop their operations, and the threshold current circuit The count value of 3 is determined.

Further, the control signal is inputted intermittently between the original exposure operations, and this control operation is performed so as not to disturb the exposure operations. During the exposure operation, a current is applied according to the determined count value, so the intensity of the light emitted by the threshold current circuit 3 remains unchanged even if the threshold current of the semiconductor laser 1 changes due to changes in temperature, etc. It becomes a constant small value Pt. As shown in FIG. 3, the speed unevenness detection device 5 is composed of a speed generator or the like connected to the central axis of the rotating drum 10, and outputs a speed unevenness signal ±ΔV/V with the circumferential speed of the rotating drum being V. The correction circuit 7 includes a D/A converter 71 and a current drive circuit 72, as shown in FIG. 7, and applies a correction current to the semiconductor laser 1.

The spot area of the laser beam on the photosensitive paper 11 is S (m2), and the size of the pixel is also the same S (m2).

Next, the operation of the image exposure apparatus configured as described above will be explained.

When the operation is started, the rotating drum 10 around which the photosensitive paper 11 is wound rotates at a predetermined circumferential speed V (m/s). At this time, the rotating drum 10 has a peripheral speed V±ΔV (m/
s). The speed unevenness detection device 5 is attached to the rotation center axis of the rotating drum 10, and detects the actual speed unevenness signal ±ΔV/of the rotating drum 10 including this rotational unevenness.
Outputs V. Image data d generated by an image data generator (not shown or described) is input to the drive circuit 2 and the correction circuit 7, and the light intensity Pd due to the current applied by the drive circuit 2 to the semiconductor laser 1 is as follows: Pd=η ×K×d (W) (12)
The light intensity Pa due to the current applied to the semiconductor laser 1 by the correction circuit 7 is

[0045]

[Math. 12]

[0046] Here, η is the current-light intensity conversion efficiency (quantum differential efficiency) of the semiconductor laser 1, and K is the signal-current conversion efficiency of the drive circuit 2 and the correction circuit 7.

The addition value D added by the addition circuit 4 is selected so that the following relationship with the light intensity Pt due to the current of the threshold current circuit 3 is established.

[0048]

[Math. 13]

At this time, the light intensity P of the laser beam emitted by the semiconductor laser 1 is expressed by the following equation.

[0050]

[Math. 14]

A laser beam expressed by equation (15) exposes the photosensitive paper 11, which is charged by a charging device which will not be explained, to form an electrostatic latent image.

Since the amount of exposure E received by each pixel of the photosensitive paper 11 at this time is the product of the light intensity of the laser beam and the exposure time, as described above,

[0053]

[Math. 15]

The exposure amount E is not affected by the speed unevenness ±ΔV.

After an electrostatic latent image is formed on the exposed photosensitive paper 11, a visible image is formed by a well-known developing device (not shown or described), and then a visible image is formed by a well-known developing device (not shown or described). The paper is ejected by the paper device.

Note that the present invention is not limited to the embodiments detailed above, and various modifications and improvements can be made. For example, in this embodiment, each current is superimposed and applied to the semiconductor laser, but the count value of the threshold current circuit, the image signal, and the multiplication result are added together, the current is converted, and the current is applied to the semiconductor laser. It is also possible to have a configuration in which

[0057]

[Effect of the invention] As is clear from the detailed description above,
According to the present invention, the light intensity of the laser beam of the semiconductor laser is corrected by the current circuit that corrects the speed unevenness detected by the speed unevenness detection means, so even if there is speed unevenness, a high-quality image without stripes can be obtained. It is possible to provide an image exposure apparatus that can obtain an image.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an image exposure apparatus that is an embodiment of the present invention.

FIG. 2 is a waveform diagram showing how a conventional semiconductor laser is driven.

FIG. 3 is a diagram showing the configuration of an image exposure apparatus that is an embodiment of the present invention.

FIG. 4 is a diagram showing a circuit that drives a semiconductor laser.

FIG. 5 is a diagram showing the configuration of a drive circuit.

FIG. 6 is a diagram showing the configuration of a threshold current circuit.

FIG. 7 is a diagram showing the configuration of a correction circuit.

[Explanation of symbols]

1 Semiconductor laser 2 Drive circuit 3 Threshold current circuit 4 Adder circuit 5　Speed unevenness detection device 6 Multiplication circuit 7 Correction circuit

Claims (1)

[Claims] 1. A semiconductor laser element that generates a laser beam for exposure, an image current applying means that applies a current to the semiconductor laser element according to an input image signal, and a threshold value of the semiconductor laser element. In an image exposure apparatus comprising a threshold current applying means for applying a current slightly larger than the current to the semiconductor laser element, an addition circuit for adding a predetermined value to an input image signal, and a speed unevenness of a moving image exposure surface. a speed unevenness detection means for detecting the speed unevenness detection means; a multiplication circuit for multiplying the output of the adding circuit by the speed unevenness measured by the speed unevenness detection means; and applying a current to the semiconductor laser element based on the output of the multiplication circuit. An image exposure apparatus characterized by comprising a correction current applying means for correction.