JPH04245263A - Image recording device - Google Patents

Abstract

PURPOSE:To obtain a high-quality color image with no color drift. CONSTITUTION:A laser beam from a light writing unit is once folded by a folding mirror 9 and radiated to a photoreceptor 10. The folding mirror 9 is fitted to a mirror holder 5, a rotary shaft is located nearly at the center of the mirror holder 5, and it is swayably fitted in the auxiliary scanning direction. A PZT 7 is kept in contact with one end of the mirror holder 5, and the other end is energized clockwise by a compression spring 6. When the PZT 7 is excited by a driver 8, the electrostrictive effect occurs, and the folding mirror 9 is rotated counterclockwise.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus, and more particularly to an image recording apparatus for digital color copying machines and printers.

0002

2. Description of the Related Art In electrophotographic recording apparatuses, apparatuses for sequentially forming toner images of a plurality of colors on a recording medium such as a photoreceptor drum, and transferring the toner images in a superimposed manner onto recording paper are conventionally known. However, when toner images of multiple colors are sequentially formed on a single photoreceptor drum and each toner image is transferred to recording paper each time, a transfer technology that allows highly accurate positioning of the recording paper is required. Ta. Further, since the charging of the paper by the transfer device becomes unstable, there are problems in that the transferred image is likely to be blurred or missing in transfer, and the electrostatic adsorption force is reduced, resulting in easy color shift. Furthermore, although the recording paper is attracted to the photosensitive drum before and after the transfer area, this state of attraction is not always constant, resulting in the problem of color misregistration.

[0003] In order to solve these problems, for example, Japanese Patent Laid-Open No. 2-108072 discloses a "color recording device".
is proposed. What is stated in this bulletin is
Toner images of multiple colors are superimposed and electrostatically transferred onto an intermediate transfer body that is driven in synchronization with the recording medium, and then transferred and fixed from the intermediate transfer body to the recording paper using heat and pressure to prevent color misregistration. The objective is to obtain high-quality images without blur or transfer defects. However, in this method, since the image is transferred to an intermediate transfer body and then transferred to a recording paper, there is a drawback that color misregistration is likely to occur due to two transfers.

In other words, conventionally, there is no correlation between the drive linear speed of the photoreceptor (the number of rotations of the drive motor) and the number of rotations of the polygon scanner of the optical writing unit, and since they are individually controlled, they rotate asynchronously. . Therefore, when overlapping colors in a color image, the timing from the photoconductor's home position (write start signal) to the optical write detector (PD) pulse varies each time for each color. , a problem occurred in that the photoreceptor surface was displaced by the amount of movement while one surface of the polygon mirror rotated. This has caused problems such as variation in toner color overlay accuracy and deterioration of color reproduction.

[0005]

[Object] The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide an image recording apparatus capable of obtaining high-quality color images without color shift.

[0006]

[Structure] In order to achieve the above objects, the present invention provides (1)
In an image recording apparatus equipped with an electrophotographic process, which has a plurality of color developing units, one photosensitive drum, and an optical writing unit, and a transfer drum method using a dielectric film is adopted as a transfer method, the optical writing A bending mirror is provided for bending the beam from the unit to expose the photoreceptor, and the bending mirror is made swingable using a piezoelectric element; A control circuit is provided that compares the timing of the home position pulse and the detector pulse of the optical writing unit and controls the drive voltage of the piezoelectric element according to the difference, or (3)
In an image recording apparatus equipped with an electrophotographic process comprising a plurality of color developing units, one photoconductor drum, a laser light source, and an optical writing unit provided with an electro-optic lens on which the laser light source enters, the photoconductor drum It is characterized by comprising a control circuit that compares the timing of the home position pulse from the encoder attached to the drum and the detector pulse of the optical writing unit, and controls the voltage applied to the electro-optic lens according to the difference. This is what I did. below,
An explanation will be given based on an example of the present invention.

FIG. 1 is a configuration diagram for explaining an embodiment of an image recording apparatus according to the present invention. In the figure, 1 is a semiconductor laser (LD), 2 is a cylinder lens, 3 is a polygon mirror, and 4 is a crystal. Image lens (fθ lens), 5 is a mirror holder,
6 is a spring, 7 is a piezoelectric element (PZT: lead titanium zirconate), 8 is a driver, 9 is a bending mirror, 10 is a photosensitive drum, 11 is a developer (BK: black), 12 is a developer (Y: yellow), 13 is the developer (M: magenta), 1
4 is a developing device (C: cyan), 15 is a charger, 16 is a cleaner, 17 is a transfer drum, 18 is a transfer charger,
19 is a separation charger, 20 is a separation melon, 21 is a DC static eliminator, 22 is an AC static eliminator, 23 is a fixing device, and 24 is a recording paper.

The laser beam from the optical writing unit is bent once by a bending mirror 9 and then irradiated onto a photoreceptor 10 . The bending mirror 9 is attached to the mirror holder 5, has a rotation axis approximately at the center of the mirror holder 5, and is attached to be swingable in the sub-scanning direction. A piezoelectric element (PZT) 7 is brought into contact with one end of the mirror holder 5, and the other end is biased clockwise by a compression spring 6. When the PZT 7 is energized by the driver 8, an electrostrictive effect occurs and the PZT 7 rotates counterclockwise. The amount of distortion obtained is approximately proportional to the additional voltage.

FIG. 2 is a block diagram of the optical writing unit. In the figure, 25 is a detector (photodiode: PD), and other parts having the same functions as in FIG. 1 are given the same reference numerals. Deflection scanning is performed by rotating the polygon mirror 3, and fθ
The beam is narrowed down to a predetermined diameter by the lens 3, and scans the photoreceptor at a constant speed. A detector (PD) 25 is placed immediately before the effective image area, generates a pulse signal for each surface of the polygon mirror, performs phase synchronization using the pulse as a reference, and writes image information at a constant timing.

FIGS. 3(a) and 3(b) show a control circuit and its timing chart used in the image recording apparatus according to the present invention. Although not shown, an encoder is attached to the photoreceptor and generates a home position pulse (HP pulse) that serves as a reference for writing. When HP pulse enters, P
The driver 8 of the ZT7 starts energizing, the PZT7 is distorted, and the bending mirror 9 begins to swing. Next, when a detector pulse (PD pulse) for optical writing is input, the voltage of PZT 7 is held and the bending mirror 9 is fixed at a fixed position. In other words, the drive voltage of PZT7 is controlled according to the time difference between the HP pulse of the photoconductor and the PD pulse of the optical writing unit.
You can change the swing angle of the beam.

In an embodiment of the present invention, the HP pulse to PD
The longer the time until the pulse, the more the beam position swings in the direction in which the photoreceptor travels. If the PZT drive voltage is set in advance so that it can be varied by a maximum of one line, writing will always start from a constant position on the photoreceptor, and no misalignment of dots will occur.

FIG. 4 is a diagram showing another embodiment of the image recording apparatus according to the present invention, in which 26 is an electro-optical lens, 27
1 is a driver DC power supply, and other parts having the same functions as in FIG. 1 are given the same reference numerals. A laser beam from a semiconductor laser (LD) unit is incident on an electro-optic lens 26, then a line image is formed on a polygon surface by a cylinder lens 2, deflected and scanned by a polygon scanner 3, and f
The beam is narrowed to a predetermined diameter by the θ lens 4, and the beam is focused onto the photoreceptor 1.
Scan the zero plane at a constant speed.

The electro-optic lens 26 will now be explained. An electro-optic lens is one in which electrode films are formed on opposing surfaces of an electro-optic medium, and a power source for applying voltage is provided. A PLZT electro-optic crystal is used as the optical medium. The incident and exit surfaces are optically polished, and an electrode film is formed along the optical path on a surface perpendicular to these surfaces. FIG. 7 illustrates an electro-optic lens according to an embodiment of the present invention.

When no voltage is applied to the electro-optic lens, the incident laser beam exits without undergoing any change. At this time, if a voltage that does not have a lens effect is applied, an electric field distribution corresponding to the electrodes is generated, and a refractive index distribution is generated within the crystal. In the embodiment of the present invention, deflection occurs in the sub-scanning direction. Furthermore, since the refractive index changes in proportion to the square of the electric field strength, the scanning position in the sub-scanning direction can be corrected by controlling the electric field strength.

FIG. 5 is a block diagram of the optical writing unit. A detector (PD) 25 is placed immediately before the effective image area and generates a pulse signal for each surface of the polygon mirror 3. A position cycle is performed using this pulse as a reference, and image information is written at a constant pixel clock timing.

FIGS. 6(a) and 6(b) show a control circuit and its timing chart used in the image recording apparatus according to the present invention. Although not shown, an encoder is attached to the photoreceptor and generates a home position pulse (HP pulse) that serves as a reference for starting writing. When the HP pulse is input, the driver of the electro-optic lens 26 starts energizing, and the electro-optic effect starts to deflect the lens in the sub-scanning direction. Next, when a detector pulse (PD pulse) for optical writing is input, the voltage to the electro-optic lens 26 is held, and writing for one page is completed at a fixed scanning position. In other words, the H of the photoreceptor
By controlling the voltage applied to the electro-optic lens 26 according to the time difference between the P pulse and the PD pulse of the optical writing unit, the color overlay accuracy of each color can be controlled.

In an embodiment of the present invention, the HP pulse to PD
The electrode shape of the electro-optic lens is determined so that the longer the timing until the pulse, the more the beam position swings in the direction of rotation of the photoreceptor. If the driving voltage of the electro-optical lens is set in advance so that it can vary by one line at most, writing will always start from a fixed position on the photoreceptor, and the dots of each color will not be positioned correctly. Therefore, stable color reproduction can be improved.

[0018]

[Effects] As is clear from the above description, the present invention has the following effects. (1) The swing angle of the bending mirror is controlled by controlling the PZT drive voltage in response to the time difference between the HP pulse of the photoconductor and the PD pulse of the optical writing unit, so the photoconductor always remains constant. It is possible to write in the correct position, prevent color misregistration, and improve the color overlapping accuracy of each color in the sub-scanning direction. (2) By controlling the voltage to the electro-optic lens according to the time difference between the HP pulse of the photoreceptor and the PD pulse of the optical writing unit, the color overlay accuracy of each color can be controlled. Furthermore, by setting the driving voltage of the electro-optical lens in advance so as to be able to vary by a maximum of one line, writing is always started from a fixed position on the photoreceptor, and the dots of each color are not positioned. Therefore, stable color reproduction can be improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining an embodiment of an image recording apparatus according to the present invention.

FIG. 2 is a configuration diagram of an optical writing unit.

FIG. 3 is a diagram showing a control circuit and its timing chart.

FIG. 4 is a diagram showing another embodiment of the image recording device according to the present invention.

FIG. 5 is a configuration diagram showing another example of the optical writing unit.

FIG. 6 is a diagram showing another example of a control circuit and its timing chart.

FIG. 7 is a diagram for explaining an electro-optic lens.

[Explanation of symbols]

1... Semiconductor laser (LD), 2... Cylinder lens, 3...
Polygon mirror, 4...imaging lens (fθ lens), 5...
Mirror holder, 6... Spring, 7... Piezoelectric element (PZT: lead titanium zirconate), 8... Driver, 9... Bending mirror,
10...Photosensitive drum, 11...Developer (BK: black)
, 12... Developing device (Y: yellow), 13... Developing device (M:
magenta), 14...Developer (C: cyan), 15...charger, 16...cleaner, 17...transfer drum, 18...transfer charger, 19...separation charger, 20...separation melon,
21...DC static eliminator, 22...AC static eliminator, 23...fusing device,
24...Recording paper

Claims (3)

[Claims] Claim 1: An image recording apparatus equipped with an electrophotographic process, which has a plurality of color developing devices, one photosensitive drum, and an optical writing unit, and uses a transfer drum method using a dielectric film as a transfer method. , an image recording apparatus characterized in that a bending mirror is provided for bending the beam from the optical writing unit to expose the photoreceptor, and the bending mirror is made swingable using a piezoelectric element. . 2. A control circuit that compares the timing of the home position pulse of the photosensitive drum and the detector pulse of the optical writing unit and controls the drive voltage of the piezoelectric element according to the difference. Claim 1
The image recording device described. 3. An image recording device equipped with an electrophotographic process comprising a plurality of color developing units, one photosensitive drum, a laser light source, and an optical writing unit provided with an electro-optic lens through which the laser light source enters. , further comprising a control circuit that compares the timing of a home position pulse from an encoder attached to the photosensitive drum and a detector pulse of the optical writing unit, and controls the voltage applied to the electro-optic lens according to the difference. An image recording device characterized by: