JPH01257980A - Exposure system - Google Patents

Abstract

PURPOSE:To obtain an excellent image which is reduced in color shifting through easy operation by adjusting the irradiation position of one of a couple of exposure beams. CONSTITUTION:The position shift at the time of the movement of a photosensitive body 38 has a specific period, which is considered to set the gap X between the two light beams 33 and 34 projected on the photosensitive body 28 according to the variation period interval (x). This relation satisfies an expression I when (m) is an integer. Namely, the irradiation interval between the couple of light beams 33 and 44 is set to a distance which is almost an integral multiple of the periodic position shift in the moving direction of the photosensitive body 38. The interval X of one light beam to the other light beam which is to be adjusted is ideally mx in the expression I, but an excellent result is obtained actually within the range shown by the inequality. Consequently, the speed variation of the photosensitive body 38 itself is permitted and color shifting is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an exposure device used in a recording device that forms an image using light, such as a radar printer.

"Prior art" When two beams, such as a laser beam, are irradiated onto different positions on a photoconductor to form electrostatic latent images, and these are developed in different colors, two colors appear on the photoconductor. A rendered toner image can be obtained.

Therefore, when this is transferred onto recording paper and fixed, a two-color recorded image is obtained.

In such an apparatus, normally, the exposure position of a photoreceptor such as a photoreceptor drum is moved in a direction perpendicular to the scanning direction of the beam. Although the photoreceptor is moved by a drive system such as a motor, there is usually some variation in its moving speed due to, for example, load fluctuations caused by eccentricity of the photoreceptor drum. Therefore, the exposure position of the photoreceptor varies slightly between scanning for the first color and scanning for the second color.

FIG. 5 shows the color shift of the image caused by this, and shows an example of a printed ladder chart in which black and red lines are arranged at equal pitches. In this figure, the solid line 11 is a line developed in black, and the broken line 1
2 is a line developed in red. As shown in this figure, the two types of lines move toward and away from each other due to variations in the moving speed of the photoreceptor. This causes color shift.

FIG. 6 shows an example of a conventionally proposed device for preventing fluctuations in the moving speed of a photoreceptor. In this device, a disk 15 whose center coincides with the rotation axis of the photoreceptor 14 is attached to one end of the photoreceptor 14. Marks consisting of a large number of lines extending radially at a predetermined pitch are printed on the circumferential portion of this circle [15. 1 that makes up this mark
Each line is configured to be detected by an optical encoder 16 fixedly mounted opposite the mark-printed portion of the disc 15. A pulsed detection signal 17 obtained from the optical encoder 16 is input to the phase detector 21 together with a reference clock signal 19 output from the reference clock circuit 18 .

Assume now that the detection signal 17 is a pulse signal generated at irregular intervals as shown in FIG. 7a. The reference clock signal 19 is a pulse signal output at regular intervals as shown in FIG. The phase detector 21 detects both signals 17
．． 19 is detected, and a pulse signal 22 corresponding to the phase lead or lag is output as shown in FIG. 7C. This pulse signal 22 is manually inputted to a low-pass filter 23,
A position fluctuation signal 24 as shown in FIG. 7d is output.

In Figure 8, the horizontal axis shows time t, and the vertical axis shows position fluctuation ΔX.
This figure shows an example of how the positional fluctuation signal 24 changes when .

In this way, variations in the moving speed of the photoreceptor 14 are detected by the position variation signal 24. Therefore, in this conventionally proposed device, the driving force of the drive system is increased when it is detected that the moving speed has decreased, and this driving force is braked when the moving speed exceeds the allowable moving speed. Control is being carried out to keep it within range.

``Problems to be Solved by the Invention'' However, to perform such control, as described above, parts such as the highly accurate disk 15 and the optical encoder 16 are required, which is expensive.

In response to this, efforts have been made to prevent fluctuations in the moving speed of the photoreceptor from occurring as much as possible. However, in order to do this, it is necessary to adopt a mechanism that minimizes load fluctuations caused by the photoreceptor, the drive device, the developing device for developing the electrostatic latent image, the cleaning device for removing the toner image, etc. However, there was a drawback that these mechanisms were complicated. Furthermore, since a complicated mechanism is employed, there is a problem in that the manufacturing cost increases.

Furthermore, a device has been proposed in which the drive system of the photoreceptor is separated from the drive systems of other devices and driven directly, thereby avoiding the influence of load fluctuations of other devices. However, since this proposal requires a plurality of drive systems, there is still a problem that the device becomes complicated and expensive.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an exposure apparatus that can tolerate speed fluctuations of a photoreceptor and can reduce the occurrence of color misregistration.

"Means for Solving the Problem" In the present invention, attention is paid to the fact that there is a predetermined period in the positional fluctuation when the photoreceptor moves, and the irradiation on the photoreceptor is The interval X between the two rays can now be set. This relationship is expressed as follows (when m is an integer)
1) It becomes like the formula.

That is, in the present invention, the above-mentioned object is achieved by setting the irradiation interval of the pair of light beams to a distance that is approximately an integral multiple of the periodic position fluctuation in the moving direction of the photoreceptor.

In this case, the distance X to be adjusted between one ray and the other ray is ideally expressed by the above equation (1), where X=mx
However, in reality, a good result can be achieved within the range shown by the inequality.

"Example" The present invention will be described in detail with reference to Examples below.

FIG. 1 shows the main parts of a two-color recording apparatus to which an exposure apparatus according to an embodiment of the present invention is applied.

This recording device includes a rotating polygon mirror 32 rotated by a drive motor 31, which scans a laser beam output from a laser oscillator (not shown). That is, the first laser beam 33 reflected by the rotating polygon mirror 32 passes through the scanning lens 34 and is then sequentially incident on the first and second mirrors 35 and 36 and is reflected. The first incident position P on the circumferential surface is reached.

Assuming that the photosensitive drum 38 rotates clockwise as shown by an arrow 39, a charge corotron 4 is provided upstream of the first incident position P to uniformly charge the drum surface.
1 is placed. Further, a first developing device 42 is arranged near the first incident position P and on the downstream side thereof.

The first developing device 42 develops the first electrostatic latent image formed on the photoreceptor drum 38 by the exposure operation at the first incident position, and creates a toner image in the first recording color. belongs to.

On the other hand, the second laser beam 44 reflected by the rotating polygon mirror 32 passes through the scanning lens 34 and is then reflected by the third mirror 45 to expose the second incident position on the circumferential surface of the photoreceptor drum 38. Reach position Q. The third mirror 45 is a fixed mirror like the first and second mirrors 35 and 36, but its angle can be adjusted, and the adjusted reflected light irradiation position is shown by the broken line. Thus, the second incident position exposure position Q can be slightly changed.

The second incident position Q is located near the first developing device 42 and on the downstream side thereof. The second electrostatic latent image formed on the photoreceptor drum 38 is developed by the exposure operation at the second incident position Q, creating a toner image in a second recorded color different from the first recorded color. It is for. The two-color toner image created on the photoreceptor drum 38 in this way is transferred to the recording paper 51 by the transfer corotron 49 and fixed by a fixing device (not shown). The paper will be ejected to the output tray. After the transfer, the photosensitive drum 38 is cleaned by a cleaning device 52.
to remove residual toner. This makes the surface of the photoreceptor drum 38 usable again.

FIG. 2 shows the relationship between periodic positional fluctuations of the photosensitive drum and the interval between the two laser beams in this two-color recording apparatus. If the disk 15 as described above in FIG. 6 is attached and positional fluctuations are measured, the characteristics shown in FIG. 2 can be obtained. Position variation Δ with respect to time t
The characteristics of X are caused by the combination of various parts and are unique to each recording device. That is, if the time interval from the peak value of the positional fluctuation ΔX to the next peak value is r, then this time interval r will be a substantially constant value if the devices are the same.

Now, as shown in FIG. 3, the angle between the first incident position P of the first laser beam 33 and the second incident position Q of the second laser beam 44 with the center of the photoreceptor drum 38 is determined. Let it be α. Further, the average rotational angular velocity of the photoreceptor drum 38 is assumed to be ω.

The interval between the first and second incident positions P and Q is X, and the travel time for the circumferential surface of the photoreceptor drum 380 to move through this interval X is t.
o. The travel time t0 can be expressed by the following equation (2).

α If the moving time t0 is set to be an integer multiple of the time interval r shown in FIG.

The above is an explanation of the case where correction is performed based on time, but when expressed in terms of the interval X between the incident positions P and Q, the following equation (3) is obtained.

Here, the symbol R is the radius of the photosensitive drum 38.

X = RX ω

)(=Rxωxr (4) Therefore, it is sufficient to set the incident position interval X of the two laser beams 33, 44 to be an integral multiple of the position fluctuation period interval X.

The above will be explained more specifically.

In the apparatus shown in FIG. 1, the second laser beam 44 is irradiated with the first
The travel time t of the photoreceptor drum 38 is compared with the irradiation of the corresponding portion of the Rade beam 33 with the irradiation time t. I'm way behind. If the positional variation of the first laser beam 33 is expressed as ΔX (t), then the irradiation of the second laser beam 44 at the incident position Q must be delayed by a travel time 1o.

Therefore, the positional fluctuation of the second laser beam 44 is Δx(t
+to). At this time, both laser beams 3
The positional fluctuation difference δX of 3.44 is expressed by the following equation (5).

δX=Δx (t)−Δx(to)・・・・・・(
5) In order to keep this positional fluctuation difference δX as small as possible, the moving time t0 should be made to match the positional fluctuation period τ, as seen in FIG.

Further, from the same viewpoint, the moving time t0 may be an integral multiple of the position fluctuation period r. Therefore, m is an integer (=1.2.3
...), the interval X may be set so as to satisfy the relationship expressed by the following equation (6).

jo”mr (6) This allows the interval between the first incident position P and the second incident position Q to be selected from a wide range, and is suitable for the mounting design of the first developing machine 42, etc. You can obtain the degree of freedom in (6)
Although the equation is an ideal case, in reality, even if there is an error of about ±176 in the position fluctuation period τ, the recording position can be corrected sufficiently effectively.

FIG. 4 shows an example of two-color recording using the apparatus of this embodiment, and corresponds to FIG. 5.

Recording is performed without interference between the black line indicated by the solid line 11 and the red line indicated by the broken line 12. If you look closely, the interval between the black lines shown by solid line 11 is
Due to overall speed fluctuations of the photoreceptor drum 38, recording is not necessarily performed at equal pitches. It can be seen that even in such a case, the red line indicated by the broken line 12 is recorded while maintaining approximately the middle position of the solid line 11. This effectively prevents color misregistration.

Although a two-color recording device using a laser beam has been described above, it is not limited to a device using a light beam scanning method.
A similar effect can be obtained using a non-scanning one-dimensional image exposure device using an array or a liquid crystal display. Further, in the embodiment, an example using two beams has been described, but the present invention can be similarly applied to an apparatus using three or more beams. Furthermore, although a photoreceptor drum was used as the photoreceptor in this embodiment, the present invention can also be applied to an apparatus using a belt-shaped photoreceptor.

"Effects of the Invention" As described above, according to the present invention, a good image with reduced color shift can be obtained by a simple operation of adjusting the irradiation position of one of a pair of exposure beams.

[Brief explanation of the drawing]

1 to 4 are for explaining one embodiment of the present invention. Of these, FIG. 1 is a schematic configuration diagram of a two-color recording apparatus using the exposure device of the present invention, and FIG. A characteristic diagram showing an example of the positional fluctuation characteristics of a photosensitive drum of a color recording device, FIG. 3 is a principle diagram for explaining the principle for correcting fluctuations in recording position, and FIG. 4 is a two-color ladder chart. FIG. 5 is a plan view showing a state in which a two-color ladder chart is recorded using a conventional device; FIG. 6 is a schematic configuration diagram showing the principle of measuring the position variation characteristics of a photoreceptor drum. , 7th
The figure shows various waveform diagrams showing the waveforms of each part of the device shown in Fig. 6, and Fig. 8 shows the change in the position fluctuation signal when time t is plotted on the horizontal axis and position variation ΔX is plotted on the vertical axis. FIG. 3 is a characteristic diagram showing an example of the situation. 38... Photosensitive drum, 33... First laser beam, 44...
- Second laser beam, 45...Third mirror, P...First incidence position, Q...Second incidence position. Map 2, Map 3, Map 4, Map 5

Claims (1)

[Claims] In an apparatus that exposes a photoreceptor that moves in a direction perpendicular to the scanning direction of a light beam, a periodic interval of positional fluctuation of the photoreceptor is defined as a positional fluctuation periodic interval x, and a pair of photoreceptors are arranged on the photoreceptor. 1. An exposure apparatus characterized in that an interval X between irradiated light beams is set to satisfy the following relationship with respect to an integer m and a position fluctuation period interval x. mx-X/6≦X≦mx+x/6