JPH0797244B2 - Laser color printer - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrophotographic laser color printer.

2. Description of the Related Art In recent years, laser printers have become more important as output devices in OA equipment. In addition, such a laser printer is also attempting colorization.

FIG. 6 shows an example of such a laser color printer. First, four photoconductors 1a, 1b, 1c, 1d are juxtaposed in a horizontal state at predetermined intervals. These photoconductors 1a, 1
In accordance with a well-known electrophotographic process around b, 1c, 1d, charging chargers 2a, 2b, 2c, 2d, laser beam optical systems 3a, 3b, 3c,
3d, developing devices 4a, 4b, 4c, 4d for different color toners (black, yellow, magenta, cyan in order), transfer chargers 5a, 5b, 5c, 5d, cleaning devices 6a, 6b, 6c, 6d, etc. are arranged. ing.

Here, the laser beam optical system will be described taking the laser beam optical system 3a as an example. For example, a laser beam 7a modulated by a predetermined color image signal is emitted from a laser light source 8a (including a collimating lens etc.) to the photoconductor 1a, and is rotated and driven by a drive motor 9a (a polygon mirror). ) A single reflecting surface of 10a is illuminated and scanned with its rotation. The laser beam 7a scanned by the rotary polygon mirror 10a passes through the fθ lens 11a, is then reflected by the first and second mirrors 12a and 13a, and is further irradiated onto the photoconductor 1a via the cylinder lens 14a and the dustproof glass 15a. It Since the photoconductor 1a is already charged by the charging charger 2a, an electrostatic latent image is formed by irradiating the laser beam 7a. Then, this electrostatic latent image is developed with a color toner (for example, black) dedicated to the developing device 4a to be visualized. Such image formation is similarly performed in the laser beam optical systems 3b, 3c, 3d for the other photoconductors 1b, 1c, 1d, and the same parts are denoted by the same reference numerals and distinguished by the subscripts b, c, d. It shall be.

Then, a conveyor belt 16 is provided across the transfer positions of these photoconductors 1a, 1b, 1c, 1d, and the transfer paper 18 fed by the paper feeding device 17 is conveyed by the conveyor belts 16 to the photoconductors 1a, 1b, 1c. , 1d
Are sequentially conveyed to the transfer paper 18, and the visible images of the respective colors on the photoconductors 1a, 1b, 1c, 1d are sequentially transferred to the transfer paper 18 by the action of the transfer chargers 5a, 5b, 5c, 5d. A color image will be obtained. Then, the transfer paper 18 is fixed to the fixing device 19
And is discharged by the paper discharge roller 20.

In such a laser color printer, even if the irradiation positions of the laser beams 7a, 7b, 7c, 7d with respect to the respective photoconductors 1a, 1b, 1c, 1d in the sub-scanning direction are set to be normal, If there is a change with time in the main scanning direction, it adversely affects the sub-scanning direction of the superimposed images. here,
To simplify the explanation, consider a case where two images (line images) formed on the two photoconductors 1a and 1b are superposed on the transfer paper 18, for example. In this case, first, as shown in FIG. 7A, a line image 21a on the photoconductor 1a by the laser beam 7a is formed on the transfer paper 18. Next, the line image 21b on the photoconductor 1b by the laser beam 7b is superposed on the line image 21a on the transfer paper 18. However, at this time, after the recording signal of the laser beam 7a is output (distance between the photoconductors 1a and 1b) / the time corresponding to the linear velocity, the recording signal of the laser beam 7b is output at an ideal timing. Even if the recording signal of the beam 7b is output, it is unstable whether or not the laser beam 7b itself is positioned at the ideal position in the main scanning direction, and it is easy to shift the position particularly with time. Will be things. For example, there are causes such as a rotation error between the rotary polygon mirrors 10a and 10b. That is, generally, the writing position in the main scanning direction is regulated by counting the reference clock number after detecting the laser beam by the synchronization detector provided at the start portion in the main scanning direction. As described above, if the laser beam is located at a position advanced from the synchronization detector in the main scanning direction at the time when the recording signal is output, it is detected by the synchronization detector one line after the recording signal is output. Therefore, when this is considered in the sub-scanning direction, it appears as a shift of about 1 dot, and in the case of the above-mentioned line images 21a and 21b, the transfer is performed with a shift as shown in FIG. 7 (b). It will be transferred to paper 18.

In a color printer, such misregistration of image dots appears as a change in image color tone or color bleeding, resulting in poor quality color printing.

The present invention has been made in view of such a point, and minimizes the positional deviation of printing dots when irradiating a plurality of laser beams on each photoconductor to form an image and transferring the image to the same transfer paper. An object of the present invention is to obtain a laser color printer capable of obtaining high-quality color printing without color misregistration and the like.

In order to achieve the above object, the present invention irradiates a laser beam for each color modulated by a color image signal onto a corresponding photoconductor by a laser beam optical system to form an electrostatic latent image. The electrostatic latent image on each photoconductor is developed with toner of different color for each photoconductor, and the same transfer paper is sequentially conveyed to these photoconductors to transfer the visible image on each photoconductor. In a laser color printer for sequentially superposing and transferring on paper to obtain one color image, the irradiation position of the laser beam in the sub-scanning direction on each photoconductor is adjusted and changed with respect to any optical component in each of the laser beam optical systems. And a laser beam detecting means for detecting irradiation of the laser beam for each color to a specific position on the photoconductor, and issuing an image recording signal to each laser beam optical system. Provided is time detection means for detecting the time from when the laser beam is detected to when the laser beam detection means detects the laser beam, and a control drive means for operating the state changing means in accordance with the time detected by the time detection means. It is characterized by being provided.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. The basic configuration of the laser color printer shown in FIG. 6 is the same, the same parts are denoted by the same reference numerals, and the description thereof will be omitted. First, the structure of this embodiment will be described by taking the laser beam optical system 3a as an example. In this embodiment, first, as shown in FIGS. 1 and 2, a laser beam 7a is irradiated to a specific position on the scanning start side on the scanning line with respect to the photoconductor 1a at each scanning start of each scanning line, A synchronous detector 22a is provided as a laser beam detecting means for detecting the laser beam 7a. Such a sync detector 22a
It is also provided in a normal laser color printer, and the writing positions of the laser beam 7a in the main scanning direction are all counting reference clocks from the time when the synchronous detector 22a detects the laser beam 7a, It is regulated by the number of clocks.

Further, in the laser beam optical system 3a, the second mirror 13a, which is one of the optical components in the optical system, serves as state changing means for the mirror support 23a having an opening as shown in FIG. It is supported by the piezoelectric element 24a and the fulcrum member 25a. The piezoelectric element 24a has a length that electrically expands and contracts according to the applied voltage.
The angle of "a" can be changed and finely adjusted by using the fulcrum member 25a as a fulcrum of rotation. By changing the angle of the second mirror 13a in this manner, the irradiation position of the laser beam 7a on the photoconductor 1a changes in the sub-scanning direction.

The control system for the piezoelectric element 24a is constructed as shown in the block diagram of FIG. First, from the time when an image recording signal for instructing the start of optical writing to the photoconductor 1a is output, the synchronization detector 22a
A counter 26a is provided as time detection means for detecting the time until the laser beam 7a is detected by counting the clock signal. Then, the time detected by the counter 26a is compared with a reference value and arithmetic processing is performed to calculate an applied voltage, and the piezoelectric element 24a is expanded or compressed by a minute predetermined amount via the drive circuit 27a as a control driving means. An arithmetic processing circuit 28a is provided.

In such a configuration, basically, after the image recording signal is output, the laser beam 7a is detected by the synchronous detector 22a, so that the actual image data is given and the photoconductor 1a by the laser beam 7a is given. Optical writing is performed on the top. Therefore, the writing position in the main scanning direction on the photoconductor 1a is determined by the reference clock number after the synchronization detector 22a detects the laser beam 7a.

Here, for example, when the image recording signal is output at a normal timing, the laser beam 7a emits A in the main scanning direction.
If it is located at a point (see FIG. 2), the laser beam 7a scans in the main scanning direction as it is, and the laser beam 7a scans the synchronous detector 22 during the main scanning of the next line.
detected by a, the main scan on the next line
Optical writing according to the actual image data will be performed on a. As a result, in this case, the image formation is shifted from the ideal line by about one dot in the sub-scanning direction. That is, even if the irradiation position of the laser beam 7a on the photoconductor 1a is an accurate position in the sub-scanning direction, the timing of the laser beam 7a varies in the main scanning direction due to the rotation error of the rotary polygon mirror 10a and the like. This is because it will end up.

Therefore, in the present embodiment, even in such a case, optical writing can be performed without causing a shift in the sub-scanning direction. First, the counter 26a detects the time from when the image recording signal is output to when the synchronization detector 22a detects the laser beam 7a. That is, it is the time corresponding to the time T in the timing chart shown in FIG. Then, the detected time T is compared with a predetermined reference value (initial setting value), the applied voltage value is calculated by the arithmetic processing circuit 28a, and a predetermined voltage is applied to the piezoelectric element 24a to expand and contract, 2 By changing the angle of the mirror 13a, the photoconductor 1
The irradiation position of the laser beam 7a with respect to a is slightly changed. In other words, if the laser beam is irradiated at a position delayed by one dot as described above, the laser beam
7a is positively shifted so that it is irradiated to a position one dot ahead of the normal position in the sub-scanning direction. As a result, the laser beam 7a is irradiated onto the photoconductor 1a without a delay of one dot. When the detection time T is longer than the initial set value, the piezoelectric element 24a is expanded to rotationally displace the second mirror 13a in the direction of arrow C in FIG. 3, and conversely the detection time T is shortened. Sometimes piezoelectric element 24a
The second mirror 13 is rotated and displaced in the direction of the arrow D by the compression of
The irradiation position of the laser beam 7a may be changed by finely adjusting the angle of a.

Such a configuration is the same in the laser beam optical systems 3b, 3c, 3d for the other photoconductors 1b, 1c, 1d, and the laser beams 7b, 7c, 7d are output by the synchronous detector from the output time point of each image recording signal. The time until it is detected is detected by the counter,
The angles of the second mirrors 13b, 13c, and 13d are adjusted according to the time, and the second mirrors 13b, 13c, and 13d are corrected so that the second mirrors 13b, 13c, and 13d are irradiated at positions appropriately deviated from the reference irradiation position in the sub scanning direction.

Therefore, when the images on the photoconductors 1a, 1b, 1c, 1d are transferred onto the transfer paper 18 in an overlapping manner, they are transferred to the same position without any displacement in the sub-scanning direction. Therefore, high-quality color printing can be performed without misalignment of each color.

Although the synchronous detector is used as the laser beam detecting means in this embodiment, the beam detector may be provided separately from the synchronous detector.

In this embodiment, the piezoelectric element 24 is provided for the second mirrors 13a, 13b, 13c, 13d, which are the optical components in the laser beam optical system, so that the angle can be changed. A state changing means may be provided for. For example, the optical paths may be corrected by holding the cylinder lenses 14a, 14b, 14c, 14d by a piezoelectric element and slightly inclining the cylinder lenses 14a, 14b, 14c, 14d.

Advantageous Effects of Invention The present invention detects the irradiation of a specific position of the laser beam for each color by the laser beam detection means as described above, and the time from the output of the image recording signal to the time when the laser beam is detected by the laser beam detection means. Is detected by the time detecting means, and the state changing means provided for any optical component of the laser beam optical system is driven by the control driving means according to the time to irradiate the laser beam on the photoconductor in the sub-scanning direction. Since the position is forcibly changed slightly, even if the main scanning state of the laser beam fluctuates due to the rotational speed difference of the rotating polygon mirror of the laser beam optical system, the timing due to the change of the irradiation position in the sub-scanning direction It can be corrected by the slow speed, so that when the image formed on each photoconductor is transferred to the same transfer paper, It is possible to perform high-quality color printing without color misregistration or the like by overlapping and transferring at the same position without causing misregistration.

[Brief description of drawings]

1 to 5 show an embodiment of the present invention.
1 is a schematic front view, FIG. 2 is a perspective view showing the arrangement of an optical position detector, and FIG. 3 is a schematic front view near the second mirror.
FIG. 5 is a block diagram showing a control system, FIG. 5 is a timing chart, FIG. 6 is a schematic front view showing the configuration of a general laser color printer, and FIG. 7 is a schematic plan view showing a position shift state. 1a, 1b, 1c, 1d …… photoreceptor, 3a, 3b, 3c, 3d …… laser beam optical system, 7a, 7b, 7c, 7d …… laser beam, 13a, 13b, 13c, 1
3d …… Second mirror (optical component), 18 …… Transfer paper, 22a…
... Synchronous detector (laser beam detection means), 24a ... Piezoelectric element (state changing means), 27a ... Arithmetic processing circuit (control drive means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location G02B 26/10 AB H04N 1/04 B41J 3/00 D (56) Reference JP-A-52- 67337 (JP, A) JP 60-4951 (JP, A) JP 61-17162 (JP, A) JP 61-87468 (JP, A) JP 63-43172 (JP, A) 61-160454 (JP, U)

Claims (1)

[Claims] 1. A laser beam for each color modulated by a color image signal is irradiated by a laser beam optical system onto a corresponding photoconductor to form an electrostatic latent image, and an electrostatic latent image on these photoconductors is formed. The latent image is developed with toner of different color for each photoconductor, the same transfer paper is sequentially conveyed to these photoconductors, and the visible image on each photoconductor is sequentially transferred and transferred onto the transfer paper. In a laser color printer for obtaining one color image, state changing means for adjusting and changing the irradiation position of the laser beam in the sub-scanning direction with respect to each photoconductor with respect to any optical component in each laser beam optical system is provided. Laser beam detecting means for detecting irradiation of the laser beam for each color to a specific position on the photoconductor is provided, and each laser beam is detected from the time when an image recording signal is generated for each laser beam optical system. A time detection means for detecting the time until the emitting means detects the laser beam, and a control drive means for operating the state changing means according to the time detected by the time detection means. Laser color printer to do.