JPH06171157A - Device for forming color image - Google Patents

Abstract

PURPOSE:To provide a small-sized laser printer capable of high speed printing at low prices by subjecting a scanner to a plurality of laser polarization of light. CONSTITUTION:Lasers of each color are collectively provided in a laser unit 20 and lasers and a projected collimated beams from the laser unit 20 comprising collimeter lenses 15-18 are reflected and defected by rotary polygonal mirrors 23, 24 wherein two polygonal mirrors are disposed coaxially in two stages and the mirrors are rotated by one motor at high speeds, and the lasers and collimated beams are projected respectively into ftheta lenses 65-68 and reflected by reflection mirrors 45-48 so that images are then formed on photosensitive drums 55-58. In this case, the location of the center of rotation of the mirrors 23, 24 is disposed at the middle point between the drums 56, 57 so that the optical path of the drums 55, 58 is equal to the optical path of the drums 56, 57 and focal lengths of the lenses 65-68 are made equal to one another.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus.

[0002]

2. Description of the Related Art In a conventional laser printer using electrophotography, a prism or a reflecting mirror (hereinafter referred to as "scanner") in which a laser beam modulated by an image signal is rotated.
Image is formed by scanning on the electrophotographic photosensitive member. The photoconductor in this case is mainly a drum type. When this method is applied to a color printer, it is necessary to superimpose a plurality of images of different colors on recording paper. The main configuration for achieving this superposition technique is as follows.

As one configuration, a first color image signal is scanned on a photosensitive drum to form a latent image, a developer is attached to the latent image for visualization, and this is transferred to a recording paper, after which the photosensitive drum is cleaned. Then, the second color image signal is again scanned on the same photosensitive drum to form a latent image, and the same step as the first step is performed. However, the developer of the second color is used. The same process is repeated for the third color image signal and the fourth color image signal. In this way, one image is recorded by superposing the developed images on the same recording paper a plurality of times.

In another configuration, the same number of photosensitive drums are provided for a plurality of image signals, and latent images are formed on the photosensitive drums corresponding to each color image signal in a one-to-one manner. Visual development is carried out with a color developer, and then sequentially transferred to a recording paper. In this case, it is general to prepare one laser, one scanner, and one photosensitive drum for one image signal. Therefore, when there are a plurality of image signals to be superimposed, the same number of lasers as the image signals and the same number of lasers are used. You need as many photosensitive drums as there are scanners.

[0005]

In the above-mentioned first structure, a series of electrophotographic processes of charging-exposure-developing-transfer-cleaning are performed on a first color image signal and then a second color image signal. The same process has to be performed again for the image signal, and for the third color image signal and the fourth color image signal, they must be performed in time series. Therefore 1
It has the drawback that the printing time of one sheet is very long.

Further, the above-mentioned second structure is characterized in that printing can be performed in a shorter time than the first structure. However, as described above, the laser, the scanner and the drum are supplied with respective color image signals. It is necessary to prepare the same number as the number of, and there is a drawback that the device becomes large and expensive. Usually, the reduction of the printing time of the laser printer is performed by increasing the rotation speed of the scanner. The conventional scanner rotation speed of the laser printer is 200 rpm to 2000.
High speed rotation of 0 rpm is common. Further, the prism or mirror used in the scanner is a polygonal mirror (usually an octahedron), and an error in the deflection angle causes a positional change on the photosensitive drum depending on the optical path length of the laser beam. For this reason, the scanner needs to have a very small tilt error on each surface, specifically within several seconds, and it is also necessary that vibration due to high-speed rotation be as small as possible. Therefore, in order to obtain a stable high-speed rotation of the polygon mirror, the motor becomes large, and it is necessary to limit the tilt error of each surface of the mirror. Therefore, a precision processing technique is required in the scanner manufacturing process. For this reason, the manufacturing yield is low and the cost is very high.

An apparatus having a plurality of scanners having the above drawbacks becomes large and expensive.

[0008]

The present invention is proposed under the disadvantages and technical background of the conventional color image forming apparatus as described above, and its main purpose is to provide a simple structure. Therefore, a color image forming apparatus capable of low-cost and high-speed printing is provided. For example, the following configuration is provided as one means for achieving the above object.

That is, the first to fourth laser beam generating means for generating the first to fourth laser beams corresponding to the respective color components and the first and third laser beams are the first in the rotation axis direction of the rotary polygon mirror. Of the polygon mirror, which deflects in the opposite directions at the positions of 1 and 2, and deflects the second and fourth laser beams in the opposite directions at the second positions different from the first positions in the rotation axis direction. Deflection means and first to fourth imaging lenses for forming images of the first to fourth laser beams deflected by the deflection means on the first to fourth photoconductors juxtaposed in the recording medium conveyance direction, respectively. And the first to fourth laser beams from the first to fourth imaging lenses, respectively.
First to fourth reflecting mirrors for reflecting the light toward the photoconductor, respectively.

[0010]

With the above structure, it is possible to provide a color image forming apparatus capable of high-speed printing at low cost with a simple structure.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a diagram showing an embodiment according to the present invention. In FIG. 1, 20 is a laser unit including a laser and its drive circuit, and 15 is a collimator lens for making the laser parallel light.

The laser light emitted from the first laser in the laser unit 20 and modulated by the image signal is
It becomes a parallel laser beam through the collimator lens 15,
Scanning is performed by the rotary polygon mirror 24 which is rotated by a high speed rotation motor (not shown). The scanned laser light is reflected by the reflecting mirror 45.
Is reflected on the photosensitive drum 55 and is irradiated onto the photosensitive drum 55. Around the photosensitive drum 55, there are provided a charging device, a developing device, a transfer device for recording paper, a cleaning device, etc., which are necessary for the electrophotographic method, and these components are obvious to those skilled in the art. Therefore,
In order to prevent complication of the drawings, these are omitted in the drawings.

The photosensitive drum 55 rotates at a low speed in the direction of the arrow in the figure, and the recording paper (not shown) advances from the photosensitive drum 55 to the photosensitive drum 58. Reference numeral 65 denotes an fθ lens, which has an optical path length of the deflected laser beam
It is configured such that different focus fluctuations are corrected because they are different between the central portion and both end portions of 5 and the optimum focus is obtained at all positions in the longitudinal direction on the photosensitive drum 55.

In the optical system for the second to fourth photosensitive drums 56 to 58, the laser beams emitted from the second to fourth lasers in the laser unit 20 pass through the collimator lenses 16 to 18 similarly to the above. The parallel laser light passes through, is scanned by the rotary polygon mirrors 23 and 24, is reflected by the reflecting mirrors 46 to 48 through the fθ lenses 66 to 68, and is guided to the photosensitive drums 56 to 58.

In this case, the collimator lenses 16 and 17
The spacing between the collimator lenses 15 and 18 (or the collimator lenses 15 and 18) is set so that the respective laser beams are applied to different surfaces of the rotary polygon mirror 23 (or the rotary polygon mirror 24) as shown in FIG. For example, the rotary polygon mirror 23 shown in FIG. 1 is an octahedron,
In this case, it is usually arranged such that every other surface is irradiated, and in the case of a tetrahedron, it is common that the adjacent surfaces are irradiated.

However, this embodiment is not necessarily applied only to the above case, and needless to say, each surface may be independently irradiated with each laser beam. Although FIG. 1 illustrates the case where there are four photosensitive drums, in this case, for example, the photosensitive drum 55 is for cyan, the photosensitive drum 56 is for magenta, the photosensitive drum 57 is for yellow, and the photosensitive drum 58 is for black. The laser unit 20 is provided with four lasers corresponding to the respective drums. These four color image signals drive each of the four lasers through the drive circuit.

Further, as can be understood from the drawing, since the scanning directions of the photosensitive drums 55 and 58, 56 and 57 are opposite, one line to several lines of electricity are applied to the photosensitive drums 57 and 58. The color image signals are input to the laser drive circuit (not shown) of the laser unit 20 through the memory so that the output order of the color image signals for each line is reversed.

FIG. 2 is a block diagram for explaining the structure of an electric memory for reading data in the reverse order of output. Serial data for one line in the forward direction is transferred via the input line 101 to the L line.
It is stored in the IFO buffer memory 100. At the time of output, the direction opposite to that at the time of input, that is, "LAST IN FAST OU
Is output to "T". Therefore, the image information for one line on the output line 102 is reversed.

The image information is preferably stored in the memory 100 during the non-recording time (blanking period). When the non-recording time is short and the memory transfer time cannot be obtained, a double buffer method having two memories 100, 100 (two or more are possible) is used as shown in FIG. Store the data in the other memory. Reference numerals 103A and 103B are switches that operate in reverse to connect the input / output line to either of the two memories. A FIFO buffer memory is used for the electric memory that does not need to reverse the output order.

If necessary, a shift register for correcting the color shift for the four colors is added to the laser drive circuit. As described above, the collimated beam emitted from the laser unit 20 including the semiconductor laser (not shown) and the collimator lenses 15, 16, 17, and 18 is reflected by the rotating polygon mirrors 23 and 24 having a two-stage structure, After being deflected, they are incident on the fθ lenses 65, 66, 67 and 68, respectively, and after being reflected by the reflection mirrors 45, 46, 47 and 48, images are formed on the photosensitive drums 55, 56, 57 and 58.

That is, four lasers are connected to the laser unit 2
0, and the polygon mirrors 23 and 24 are coaxially arranged,
Rotate at high speed with one motor. In this embodiment,
The rotation center position of the rotary polygon mirrors 23 and 24 is the photosensitive drum 56.
And 57 are arranged at the central positions, and the optical path lengths of the photosensitive drums 55 and 58 are equal to the optical path lengths of the photosensitive drums 56 and 57. Therefore, the focal lengths of the fθ lenses 65 to 68 are equal.

When the fθ lenses 68 to 68 are implemented with the same focal length as in this embodiment, the distance between the two rotary polygon mirrors may be set to be approximately the same as the distance between the drums. Therefore, it is preferable to dispose the rotary polygon mirror on both sides of the rotary polygon mirror drive motor. With this arrangement, electrical processing such as pixel clock correction for preventing the scanning speed from changing due to the difference in the focal length of the fθ lens becomes unnecessary.

The arrangement of the lasers corresponding to the image signal may be assembled as a hybrid, and in the case of a semiconductor laser, an array laser may be used. Furthermore, the number of lasers is one, and different image signals may be temporally separated and guided to a plurality of drums by a beam splitter or the like, or laser beams may be separated by a beam splitter or the like and then different image signals may be generated. It may be modulated and each may be directed to multiple drums.

According to this embodiment having the above construction, the scanner can be integrated and the polygon mirror driving motor (not shown) can be made one. The present invention may be applied to a system including a plurality of devices or an apparatus including a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0025]

As described above, according to the present invention, since the scanner can be used for deflecting a plurality of lasers, it is possible to contribute to miniaturization and to provide a laser printer capable of high-speed printing at a low price.

[Brief description of drawings]

FIG. 1 is a perspective view for explaining the principle of an embodiment according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of an electric memory for reading by reversing the output order in the present embodiment.

FIG. 3 is a diagram showing a configuration in a case where an electric memory of this embodiment is a double buffer system.

[Explanation of symbols]

 20 Laser unit 15, 16, 17, 18 Collimator lens 23, 24 Rotating polygon mirror 45-48 Reflecting mirror 55-58 Photosensitive drum 65, 66, 67, 68 fθ lens 100 LIFO buffer memory 103A, 103B switch

Claims (1)

[Claims] 1. A first to a fourth laser beam generating means for generating a first to a fourth laser beam corresponding to each color component, and a first to a third laser beam in a rotation axis direction of a rotary polygon mirror. Deflection means for deflecting the second and fourth laser beams in opposite directions at different positions, and for deflecting the second and fourth laser beams in opposite directions at a second position different from the first position in the rotation axis direction, First to fourth image forming lenses for forming images of the first to fourth laser beams deflected by the deflecting means on first to fourth photoconductors juxtaposed in the transport direction of the recording medium, respectively, and the first to fourth image forming lenses. A color image comprising: first to fourth reflecting mirrors for reflecting the first to fourth laser beams from the fourth imaging lens toward the first to fourth photoconductors, respectively. Forming equipment.