JPS63254857A - Laser beam printer - Google Patents

Abstract

PURPOSE:To finely adjust an image writing position by delaying a photo detecting signal for a prescribed time only and using it as a new photo detecting signal. CONSTITUTION:When plural photo detecting devices corresponding to respective color beams are provided by a laser color printer and when scanning is executed on plural photosensitive bodies by respective beams, the little difference in the providing accuracy and the optical system of the photo detecting device occurs. When the error is in one clock of a basic clock, by adjusting the set value of a counter, the image writing position cannot be made into the same position. Then, a photo detecting device 501 detects a scanning beam, the output is delayed by a delaying circuit 503 only for the delaying time set in a delaying time setting circuit 504 in accordance with the providing misregistration quantity of the photo detecting device and made into a new photo detecting signal. Thus, the image writing position of plural beams can be finely adjusted and the color dislocation can be suppressed with good accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to control of the image writing position of a laser beam printer.

(Prior Art) In a laser beam printer that performs writing by scanning a beam, it is important from the viewpoint of image quality that the image writing position by the beam be accurately and at the same position.

Conventionally, a photodetector is provided at the start of the beam scanning onto the photoconductor and outside the image area, and a counter is generated based on the output signal from the photodetector that is generated when the laser beam passes over the photodetector. There is a known method of controlling the image writing position by starting a basic clock counting operation and starting image writing when the counter value reaches a set value.

However, when multiple photodetectors are provided for each beam, or when multiple photoreceptors are scanned with each beam, slight differences may occur in the placement accuracy of the photodetectors or in the optical system. be. If the difference due to this is an integer multiple of the basic clock mentioned above, it is possible to set the image writing position of each beam to the same position by adjusting the counter setting value, but the above If the error is within one clock of the basic clock, the image writing start position cannot be made to be at the same position by adjusting the set value of the counter.

The above adjustment is not impossible if the printer divides the aforementioned basic clock to obtain a timing clock (image clock) for writing an image. However, in high-speed printers, etc., the image clock is about 5 MHz, and if you try to obtain an image writing position with an accuracy of 1/10 dot of the image using the method described above, a basic clock of about 50 MHz is required, making it impractical for practical use. It had the disadvantage of not being accurate.

(Purpose) The present invention was made based on this background,
It is an object of the present invention to enable adjustment of the image writing position so that the image writing position is precisely the same.

(Structure) For this purpose, the present invention provides a laser beam printer in which the image writing position can be adjusted by delaying the output signal from the photodetector described above using a delay circuit whose delay time can be arbitrarily adjusted. It is something to do.

As an embodiment of the present invention, a laser color printer that scans a plurality of photoreceptors with a plurality of beams and superimposes images on a transfer paper will be described.

A laser color printer will be explained according to FIGS. 1 and 2.

Generally, a color printer capable of outputting full-color images separates the image to be output into yellow (abbreviated as Y), magenta (abbreviated as M), and cyan (abbreviated as C).
Each image signal is received via an appropriate interface, Y, M, and C monochrome images are generated based on the signals, and these are superimposed to obtain a full-color image.

In addition to Y, M, and C, black (abbreviated as Bk) may be used. This is to perform black output corresponding to the corner plate used in the printing industry.

A color expressed using the three colors Y, M, and C is an equal amount of Y,
Since it includes Bk corresponding to M and C, the same color is Bk.
It can be expressed using any two colors of Y, M, or C. Removing equal amounts of Y, M, and C corresponding to Bk is called undercolor removal (
1,, J CR), and the replaced Bk is the corner version. In laser color printers, in addition to color reproduction, performing u cr < has the advantage that toner consumption remains, the thickness of the output image is reduced, and the fixing load is also reduced. Therefore, generally a toner image is formed four times and transferred four times.

In the figure, a laser beam modulated by an image signal is emitted by a laser beam fi178, and is deflected by a rotating polygon mirror 188 that is rotated by a rotating motor IBk. The deflected laser beam 10Bk starts the imaging lens 208k and scans a predetermined position on the photosensitive drum 8Bk. This beam scanning is called main scanning, and its direction is called the main scanning direction. By the rotation of the rotating polygon mirror 188, the laser beam is repeatedly scanned in a straight line on the photosensitive drum 8Bk in the same direction. As the photosensitive drum 8bk rotates in the direction of the arrow, the laser beam is also scanned in the circumferential direction on the photosensitive drum 8Bk (this scanning is called sub-scanning and this direction is called the sub-scanning direction), and the laser beam is Scan the photosensitive drum 8Bk. When the photosensitive drum 88, which is initially charged by the corona discharger 78k, is scanned with laser light according to the image signal, the charge in the portion that has received a predetermined exposure energy is removed, and an electrostatic surface is formed on the drum 8Bk. be done. The latent toner is made to adhere to the electrostatic latent image portion on the photosensitive drum 8Bk by the developing device 28k, and the electrostatic latent image is developed. This visible image is 8Y, 8M transferred to transfer paper.
, 8C are also subjected to similar steps.

On the other hand, the transfer paper fed from the tray 5 by the paper feed roller 4 is transported by the transport belt 13 in the direction of the arrow. The conveyor belt 13 is made of Mylar, for example, and is rotationally driven by several rollers. The contact point between the photosensitive drum 8 and the conveyor belt 13 is the transfer position, and the transfer discharger 9 (
Bk, Y, M.

By C), each color toner is attracted onto the transfer paper.

The transfer paper on which the toner images of each color have been transferred is separated from the conveyor belt 13 by a separating claw 20, and is passed through a fixing unit 1) using a heat roll, whereby the overlapping color toner images are fixed, and the paper is ejected. The paper is discharged onto a tray 16 by rollers 12 .

In the figure, 3 is a registration roller, 6 is a cleaning unit, 14 is a belt static elimination charger, 15 is a toner powder receiver, and 19 is a laser detector.

In addition to the above-described configuration, a plurality of laser beams may be scanned using one or two deflectors as shown in FIG. 3.

Using FIGS. 4 and 5, it will be explained that the above-mentioned problem occurs when the photodetectors of each color are misaligned. FIG. 4 schematically shows a C beam scanning line and an M beam scanning line.

The C beam scanning line passes through a photodetector 401 (corresponding to 19 in FIG. 2) and passes through a C photosensitive drum 403 (corresponding to 19 in FIG.
(corresponding to 8 in the figure).

The same applies to the M beam scanning line. When the C beam passes over the photodetector 401, it generates a photodetection signal C3PD shown in the timing cheat of FIG. The basic clock of C (in this case, the image clock CCLK is shared) is C5P.
Occurs at the same time as D rises. The counter that determines the image writing timing counts the CCLK pulse signal, and here, at the fourth count, generates the image writing permission signal CLGATE. In synchronization with this, C data CDATA is generated, and an image is written on the photoreceptor in the same manner for the 0M scanning line for writing an image on the photoreceptor.

Now, for simplicity, the C beam and M beam have the same speed (V)
Consider the case of parallel scanning. Also, if the photodetectors of C and M are placed shifted by △X (△x / v <
When l/f; where f is the CLK frequency), C3
The time interval between PD and MSPD is △t=△x/v, and even if you change the setting value of the counter mentioned above, the image writing positions of both cannot be made to match. Therefore, CL
An adjustment mechanism within one clock of K is required.

The present invention provides a device that delays the SPD by Δt and uses it as a new SPD to match the image writing positions of both.

FIG. 6 shows a block diagram of the present invention.

A photodetector 501 detects the scanning beam, and a photodetector circuit 50
Amplify with 2. The output is delayed by the delay time set in the delay time setting circuit according to the amount of deviation by the delay circuit 5.
It is delayed at 03 and becomes SPD.

FIG. 7 shows a circuit example of the photodetector 501 and the photodetection circuit 502. As the photodetector 501, a high-speed photodiode 601 such as a PIN photodiode is often used, and this generates a current output according to the amount of incident light. This signal is converted into a voltage signal by an amplifier 602, and further compared with a reference voltage Vref by a comparator 603.
A waveform-shaped signal can be obtained.

FIG. 8 shows an embodiment of the delay circuit 503 and the delay time setting circuit 504.

Figure 8 (al is an example configured with CR, and by making the resistor VR variable and the capacitor C, the input signal can be delayed for an arbitrary amount of time. On the output side, a Schmitt trigger inverter is used to remove minute noise. are doing.

8) is a configuration including a delay line 701 and a data selector 702. A large number of delay times are prepared in advance, and the data selector 702 selects and outputs a signal having an arbitrary delay time.

FIG. 8(C) shows a configuration in which gates G are connected in multiple stages.The present invention can be implemented with zero or more configurations.

In the explanation so far, we have used laser color printers as shown in Figures 1 to 3 as an example, but the same adjustment can be made not only in printers that scan the same photoreceptor with multiple beams (color Not exclusively).

For example, the present invention can also be implemented in a laser beam printer that uses an array of semi-quartet lasers as a light source. This is as shown in FIG.

In this example, only a specific beam among the plurality of beams passes over photodetector 501 and generates a signal similar to the previous example. Based on this one generated signal, the image writing position of each beam is determined.

An example is shown in FIG. The beam detected by the photodetector 501 generates a first synchronization signal. On the other hand, the first synchronization signal is input to n-] delay means for generating synchronization signals for other beams (when the number of beams is n), and the time set by each setting means is inputted to the first synchronization signal. 18, which determines the start of image writing. Furthermore, it is also conceivable that the first synchronization signal is also passed through a delay means, instead of as shown in FIG.

In the above example, only a specific beam among the plurality of beams passes over the photodetector, but if the photodetector 33 is provided for each beam, the method explained in FIG. 4 can be used. Alternatively, a plurality of beams may be received by one photodetector, and the signals from each beam may be branched and then passed through delay means.

Note that the purpose of the present invention is to correct the recording start position of the image signal, and that there are multiple beams.
The position of the delay circuit and the delay circuit are not particularly limited.

(Effects) As described above, according to the present invention, it is possible to minutely adjust the image writing position of a plurality of beams, and color shift can be suppressed with high precision, so that high-quality images can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a laser color printer that is the premise of the present invention, Fig. 2 is an external view showing the optical scanning system, and Fig. 3
The figure is an external view showing the optical scanning system with different mechanisms, and Figure 4 is 2
FIG. 5 is a timing chart thereof, FIG. 6 is a block diagram according to the present invention, FIG. 7 is a circuit diagram showing an example of the light detection section, and FIG.
), (bl, (c) is a circuit diagram showing different embodiments of the same delay circuit section, FIG. 9 is a diagram showing how the same photoreceptor is scanned with multiple beams, and FIG. 10 is a diagram showing one example of the mechanism. It is a diagram showing an example. 501... Photodetector, 503... Delay circuit, 504
...Delay time setting circuit. Agent Patent Attorney Kenji Take (Exterior 1'33) Figure 1 Figure 2 Figure 5 Figure 6 Figure 7 (0) Figure 8

Claims (3)

[Claims] (1) A laser beam printer characterized by comprising a photodetector, a clock pulse generating means that generates a clock pulse synchronized with an image signal by inputting a trigger signal, and a signal delay circuit that corrects the image recording start position. (2) The laser beam printer according to claim 1, wherein the signal delay circuit receives a signal from a photodetector as an input signal and outputs a trigger signal. (3) The signal delay circuit uses an output signal from a photodetector as a trigger signal, uses an output clock pulse as an input signal, and outputs a clock pulse. laser beam printer.