JPH02221975A - Image output device - Google Patents

Abstract

PURPOSE:To eliminate the start misregistration of recording color by positioning a horizontal scanning start position detector ahead of the electrostatic latent image forming area of a photosensitive body, and making a laser beam incident at the same angle as that of the laser beam incident on the photosensitive body. CONSTITUTION:The inclination of the detection plane of the first scanning position detector 25 is adjusted, the angle piP of beam 13 incident on the photosensitive drum 11 is equal to the angle thetaS of the beam incident on the detector 25. The detector 25 generates a horizontal scanning start signal 28 when the top edge of the electrostatic latent image forming area of the drum 11 is irradiated with the laser beam to set an FF 52. A second scanning position detector 26 generates a horizontal scanning terminating signal 31 to reset the FF 52. A synchronizing pulse 53 is given to a closed loop circuit constituted of a phase comparator 37, LPF 41, VCO 35 and a counter 38 from the FF 52. The frequency of a clock 17 is controlled in the direction which the phase of a count termination pulse 39 coincides with. In this constitution, the start misregistration of recording color does not occur so that high quality image can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an image output device such as a laser printer, and more particularly to an image output device in which the writing position of an image on a rotating polygon mirror is stabilized.

"Prior Art" In an image output device such as a laser printer, a laser beam is sequentially scanned line by line on a photoreceptor such as a photoreceptor drum to form an electrostatic latent image. Then, this electrostatic latent image is developed to obtain a toner image using the same principle as a normal electrophotographic copying machine, and this toner image is transferred and fixed onto paper to obtain a recorded image.

FIG. 4 shows an outline of the configuration of the image output device. This image output device includes a photosensitive drum 11 for forming an electrostatic latent image. Around the photosensitive drum 11, various corotrons, developing devices, and cleaning devices (not shown) are arranged. The surface of the photosensitive drum 11 is first uniformly charged with a charge corotron (not shown), and then exposed to a laser beam 13 that passes through an imaging lens 12. At this time, the charge disappears at the portion of the photoreceptor drum 11 that is irradiated with the laser beam I3. In this way, the photoreceptor drum
An electrostatic latent image is formed thereon, represented by the presence or absence of charge. This electrostatic latent image is developed into a toner image by the above-mentioned developing device, and this is transferred onto a recording sheet (not shown) by a transfer corotron. The toner image on the recording paper is fixed by a fixing device (not shown) by heating or pressure, and recording is completed. The recorded recording paper is discharged onto a discharge tray (not shown).

Further, toner particles remaining on the photoreceptor drum II during transfer of the toner image to the recording paper are removed from the drum surface by a cleaning device, and this surface is charged again by the charge corotron and used for the next recording operation. It turns out.

Image information recorded by such a radar printer is output from an image information signal generator 15.

The image information signal generator 15 may be a reading device using a reading element such as a one-dimensional image sensor, or a communication control device that outputs image information received from a host computer that creates image information. It may be something like a department. The output image information is temporarily stored in the buffer memory 16. The stored image information is sequentially read out pixel by pixel by the timing clock 17 and supplied to the semiconductor laser driving device 18 . The timing clock 17 is set using the PL, which will be explained later.
This is done using an L circuit.

The semiconductor laser driving device 18 has a timing clock 17.
The semiconductor laser 19 is driven for each pixel supplied in synchronization with, and the output laser beam 13 is controlled on/off. Laser beam 1 output from semiconductor laser 19
3 is condensed by a collimating lens 21 and incident on one surface of a polygon mirror (rotating polygon mirror) 22. The polygon mirror 22 is rotated at high speed by a drive motor z3, and the reflected light of the incident laser beam 13 is deflected by the rotation of the mirror surface, and the beam that has passed through the imaging lens 12 hits the surface of the photoreceptor drum 11. It will now scan in the direction of the drum axis.

By the way, on the extension of the scanning line of the photosensitive drum 11, near both ends of the drum, there are a first scanning position detector 25 and a second scanning position detector 25.
A scanning position detector 26 is arranged. The first of these
The scanning position detector 25 detects the beam immediately before the laser beam 13 starts scanning the electrostatic latent image forming area of the photoreceptor drum 11, and detects the horizontal scanning start timing indicating the scanning start timing of the electrostatic latent image forming area. A signal 28 is output. On the other hand, the second scanning position detector 26 detects the beam immediately after the laser beam 13 finishes scanning the electrostatic latent image forming area of the photoreceptor drum 11, and detects the beam immediately after the laser beam 13 finishes scanning the electrostatic latent image forming area. A horizontal scanning end signal 31 representing the timing is output.

The horizontal scanning start signal 28 is a voltage controlled oscillator (VCO) 3
5 input. Further, the horizontal scanning end signal 31 serves as a manual input to one side of the phase comparator 37.

Now, the voltage controlled oscillator 35 starts oscillating a signal from its output side in response to the horizontal scanning start signal 28, and the signal is sent to the buffer memory 11 as the timing clock 17.
In addition to being supplied to the counter 6, the counter 38 is also supplied. The counter 38 is configured to output a count end (EOC> signal 39) after counting the timing clock 17 by N.

This count end signal 39 is sent to another phase comparator 37.
In addition to the two inputs, the voltage controlled oscillator 35 also receives other human power. When the voltage controlled oscillator 35 receives the input signal 39, the voltage controlled oscillator 35 stops oscillating, and thereby also stops outputting the timing clock 17. In this way,
The timing clock 17 performs readout of all pixels for one line and transfer control to the semiconductor laser driving device 18.

The phase comparator 37 compares the timing of the end of one line as seen from the timing clock 17 side and the end of scanning of the horizontal scanning end signal 31 and the laser beam 13. The error signal corresponding to the phase difference output from the phase comparator 37 passes through a low-pass filter (LPF) 41 and is applied to the voltage controlled oscillator 35, and its oscillation frequency is controlled in a direction that makes the phase difference zero. It will be done.

FIG. 5 shows the optical path of reflected light from a polygon mirror in such a conventional image output device.

As shown in FIG. 5, the laser beam 13 reflected from one surface of the polygon mirror 22 passes through the imaging lens 12 and is irradiated onto the photosensitive drum 11, as shown by the solid line. Since the photoreceptor drum 11 has a cylindrical shape, when the laser beam 13 travels in a direction deviated from the central axis of the drum, the incident angle θP with respect to the photoreceptor drum 11 is not zero. It is a finite value. On the other hand, the first scanning position detector 25 and the second scanning position detector 26 (hereinafter, the explanation of the second scanning position detector 26 and (not shown), the incident angle of the laser beam 13 was set to approximately 0 degrees.

"Problem to be Solved by the Invention" In this way, the laser beam 1 directed toward the photoreceptor drum 11
The incident angle of the laser beam on the first scanning position detector 25 was different from the incident angle of the laser beam on the first scanning position detector 25.

For this reason, vibrations and shocks of the device may cause the laser beam to
3 changes to the position shown by a broken line 43 in the figure, for example, the optical path length to the first scanning position detector 25 relative to the optical path length to the photosensitive drum 11 changes. As a result, the first scanning position detector 25
This has the drawback that the timing of detecting the image information is relatively shifted, and the position at which image information starts to be written to the photosensitive drum 11 changes. For example, in an image output device that performs multicolor recording using a plurality of laser beams, this means that the recording start position of each recording color is shifted, and there is a problem in that image quality deteriorates due to color shift.

Furthermore, an image output device using a PLL circuit as shown in FIG. 4 has a problem in that the magnification of the output image in the main scanning direction fluctuates.

FIG. 6 is for explaining this latter problem. In the figure, a solid line 45 indicates the laser beam on the photoconductor drum 11 that has reached the normal position, and a broken line 46 indicates the laser beam on the photoconductor drum 11 that has reached the predetermined position where the incident angle θ is further reduced. It is a laser beam. In the PLL circuit, a counter 38 starts counting each pixel constituting one line in response to a horizontal scanning start signal 28 caused by the detection of the laser beam 45 or 46 by the first scanning position detector 25. Then, the timing at which the count end signal 39 is output is determined by the horizontal scanning end signal 31.
Phase control is performed to match the timing at which the signal is output. As a result, the optical path length to the first scanning position detector 25 or the optical path length to the second scanning position detector 26 becomes relative to the optical path length to the photoreceptor drum 11 due to the deviation in the traveling direction of the laser beam. If it shifts to , counter 3
The oscillation frequency of the voltage controlled oscillator 35 for counting 8 to N changes. This means that the modulated time width of each pixel changes, and as shown in Figure 6, the length of the pixel row for N counts, that is, the length of one line in the main scanning direction, expands and contracts. It means that. This is a major cause of deterioration of image quality, similar to the problem described above.

SUMMARY OF THE INVENTION A first object of the present invention is to provide an image output device that can reduce fluctuations in the starting position of image formation on a photoreceptor even if the irradiation direction of a laser beam is changed.

A second object of the present invention is to provide an image output device that can reduce expansion and contraction of an image on a photoreceptor in the main scanning direction even if the irradiation direction of the laser beam is changed. .

"Means for Solving the Problem" The invention according to claim 1 includes (i) laser beam output means such as a semiconductor radar that outputs a laser beam; (ii)
a laser beam modulation means for modulating the laser beam;
(iii) a photoreceptor such as a photoreceptor drum that forms an electrostatic latent image; (iv) a scanning means such as a polygon mirror that scans a modulated laser beam on the photoreceptor; (v)
This photoreceptor is placed just in front of the electrostatic latent image forming area, and the inclination of its surface is adjusted so that the laser beam is incident on the photoreceptor at almost the same angle of incidence as the laser beam. The image processing device is equipped with a horizontal scan start position detector that supplies a horizontal scan start signal based on the detection output to the laser beam modulation means to start modulating the laser beam on the recording line.

By making the incident angle of the laser beam on the horizontal scanning start position detector approximately equal to that on the photoreceptor, the timing at which the horizontal scanning start signal is output is kept almost constant even when the optical path of the laser beam is shifted, and the Reduces fluctuations in the starting position of image formation on the body.

Further, in the invention according to claim 2, (i>laser beam output means such as a semiconductor laser that outputs a laser beam;
(1i) a laser beam modulator that modulates this laser beam; (iii) a photoreceptor such as a photoreceptor drum that forms an electrostatic latent image; and (iv) scanning the modulated laser beam onto the photoreceptor. scanning means such as a polygon mirror,
(■) is placed immediately in front of the electrostatic latent image forming area of this photoconductor, and the inclination of its surface is adjusted so that the laser beam is incident on the photoconductor at almost the same incident angle as the laser beam incident angle; (vi) forming an electrostatic latent image on a photoreceptor; The inclination of the surface is adjusted so that the laser beam enters the photoreceptor at almost the same angle of incidence as that of the laser beam, and the horizontal scanning end signal is generated based on the detection output of the laser beam. (vii) a horizontal scan end position detector that supplies the signal to the laser beam modulation means to stop the modulation of the laser beam in the recording line; and (vii) divides the time interval between the horizontal scan start signal and the horizontal scan end signal by a predetermined integer. The image output device is provided with clock generation means for generating a clock for modulating the image signal pixel by pixel by the laser beam modulation means.

Even if the optical path of the laser beam shifts, by keeping the time interval between the horizontal scanning start signal and the horizontal scanning end signal constant, the frequency of the clock for modulating the image signal for each pixel remains unchanged, and the laser beam Prevents image expansion/contraction in the main scanning direction.

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

FIG. 1 shows the main parts of an image output device according to an embodiment of the present invention. The same parts as in FIGS. 4 and 5 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

In the image output device of this embodiment, the normal incident angle of the laser beam 13 with respect to the photosensitive drum 11 is θP as in FIG. This angle of incidence θ is usually set to, for example, 5° or more. The inclination of the detection surface of the first scanning position detector 25, which is a type of photoelectric converter, is adjusted so as to coincide with the circumferential direction at the irradiation point of the laser beam 13 on the photoreceptor drum 11.

Therefore, when the laser beam 13 is irradiated to a regular position as shown by the solid line in the figure, the incident angle θ of the laser beam 13 with respect to the first scanning position detector 25 is expressed by the following equation. .

θs”θp ・・・・・・(1,) As a result,
Even if the laser beam 13 enters the photoreceptor drum 11 along an optical path as shown by a broken line 43 in the figure, the optical path length with respect to the photoreceptor drum 11 and the first scanning position detector 2
5 will be kept in a constant relationship and no relative error will occur. Therefore, the first scanning position detector 25 generates a horizontal scanning start signal 28 based on the detection of the laser beam 13, thereby causing the laser beam 1
When starting the modulation of 3, the image formation start position of each line will be constant regardless of the variation of the incident angle θ.

FIG. 2 shows a timing clock generator for image signal modulation in an image output device that detects both the scanning start point and the scanning end point of the photosensitive drum and controls the modulation period of the image signal.

It is assumed that a laser beam is main-scanned on the photosensitive drum 11 in the direction of an arrow 51 to form an electrostatic latent image. In this case, a first scanning position detector 25 is placed on the scanning start side of the photosensitive drum 11, and a second scanning position detector 2 is placed on the scanning ending side of the photosensitive drum 11.
6 are arranged respectively. First scanning position detector 2
5 generates a horizontal scanning start signal 28 at the timing when the laser beam is irradiated to the starting end of the electrostatic latent image forming area of the photosensitive drum 11. This horizontal scanning start signal 28 is supplied to the set terminal of the flip-flop circuit 52 to set it.

On the other hand, the second scanning position detector 26 generates a horizontal scanning end signal 31 at the timing when the laser beam is irradiated to the end of the electrostatic latent image forming area of the photosensitive drum 11. This horizontal scanning end signal 31 is supplied to the reset terminal of the flip-flop circuit 52 to reset it.

In this way, the flip-flop circuit 52 outputs a line synchronization pulse 53 that is set at the start timing of image signal modulation of each line and reset at the end timing of modulation. The line synchronization pulse 53 serves as one input for the phase comparator 37.

The phase comparator 37, the low-pass filter 41, the voltage controlled oscillator 35, and the counter 38 collectively constitute a closed loop circuit. Here, the voltage controlled oscillator 35 is a circuit for generating a timing clock 17 for modulating the image signal. This timing clock 17 is the fourth
In addition to being input to the buffer memory 16 shown in the figure and used for reading and transferring image signals in pixel units, the input is also input to the counter 38. The counter 38 outputs a count end signal 39 after counting this timing clock 17 by N times. The phase comparator 37 receives this count end signal 3.
9 and line synchronization pulse 53.

If these two pulses 39.53 are in phase, the timing clock 17 output from the voltage controlled oscillator 35
Line synchronization pulses 53 are output at time intervals corresponding to the number of pixels for one line.

At this time, the error signal output from the phase comparator 37 becomes zero, and no change occurs in the timing clock 17 output from the voltage controlled oscillator 35. On the other hand, if the phases of the two pulses 39.53 are different, an error signal corresponding to this deviation is generated, and eventually both pulses 39.53
The frequency of the timing clock 17 is controlled in a direction in which the phases of the timing clocks 17 and 17 match.

In this way, in an image output device using a PLL circuit, the frequency of the timing clock 17 varies depending on the interval between occurrences of the horizontal scanning start signal 28 and the horizontal scanning end signal 31. However, as shown in FIG.
1 that θ.

and the second scanning position detector 26
Also, the incident angle θ is that of the photoreceptor drum 11 θ
If it is set to be equal to P, - as shown in FIG.
8 and the interval between occurrences of the horizontal scanning end signal 31 do not change. Therefore, the counter 38 in both laser beams 45,46
The length of N counts does not change, and the image does not expand or contract in the main scanning direction.

In the embodiments described above, an example was shown in which a photoreceptor drum was used as the photoreceptor, but it is needless to say that the present invention is not limited to this as long as an electrostatic latent image is formed using a laser beam.

"Effects of the Invention" As described above, in the invention as claimed in claim 1, the angle of incidence of the laser beam on the horizontal scanning start position detector is adjusted so as to be almost the same as that on the photoreceptor, so that vibrations of the device etc. This has the advantage that even if a shift occurs in the optical path, the position at which image recording is started is less likely to change, making it easier to design the apparatus.

Further, in the invention as claimed in claim 2, even when a clock is created using a PLL circuit, the possibility that the reference time interval will be deviated due to a deviation in the optical path of the laser beam is reduced, so that the linear magnification in the main scanning direction is increased. It has a stabilizing effect.

[Brief explanation of the drawing]

Figures 1 to 3 are for explaining one embodiment of the present invention, of which Figure 1 is a side view showing the laser beam scanning mechanism and the beam receiving portion, and Figure 2 is a side view showing the photoreceptor. A schematic configuration diagram showing the circuit configuration of the drum and the part that creates the timing clock for image signal modulation. Figure 3 is an explanatory diagram for explaining the influence of the image due to the deviation of the laser beam. Figure 4
The figure is a schematic configuration diagram showing an example of an image output device using a PLL circuit, FIG. 5 is a side view showing a conventional laser beam scanning mechanism and a beam receiving part, and FIG. 6 is a diagram of a conventional image output device. FIG. 3 is an explanatory diagram for explaining the influence of a laser beam shift on an image. 11...Photosensitive drum, 13...Laser beam, 17...Timing clock, 19...
- Semiconductor radar, 22... Polygon mirror, 25... First scanning position detector, 26...
...Second scanning position detector, 28...Horizontal scanning start signal, 31...Horizontal scanning end signal, 35...Voltage controlled oscillator, 37... ... Phase comparator, 38 ... Counter, 39 ... Count end signal, 41 ... Low pass filter, 53 ... Line synchronization Hals, θ ,...Incidence angle (with respect to the photoreceptor drum), θ
S: Incident angle (with respect to the detector). Applicant: Fuji Xerox Co., Ltd. Representative: Patent Attorney Ume Yamanouchi Figure 1 Figure 3 Atsushi Figure 4

Claims (1)

[Claims] 1. Laser beam output means for outputting a laser beam; laser beam modulation means for modulating the laser beam; a photoreceptor for forming an electrostatic latent image; and a photoreceptor for forming an electrostatic latent image on the photoreceptor after modulation a scanning means for scanning a laser beam; and a scanning means located immediately in front of the electrostatic latent image forming area of the photoconductor so as to make the laser beam incident on the photoconductor at an incident angle substantially the same as the incident angle at which the laser beam is incident on the photoconductor. 1. An image output device comprising: a horizontal scanning start position detector which is arranged and supplies a horizontal scanning start signal based on a detection output of a laser beam to the laser beam modulating means to start modulating the laser beam. 2. Laser beam output means for outputting a laser beam, laser beam modulation means for modulating this laser beam, a photoreceptor for forming an electrostatic latent image, and scanning the modulated laser beam on the photoreceptor. a scanning means, located immediately in front of the electrostatic latent image forming area of the photoconductor, positioned so that the laser beam is incident on the photoconductor at an incident angle substantially the same as the incident angle at which the laser beam is incident on the photoconductor; a horizontal scanning start position detector that supplies a horizontal scanning start signal based on a detection output to the laser beam modulating means to start modulating the laser beam; It is arranged so that the laser beam is incident on the photoconductor at an incident angle that is approximately the same as the incident angle at which the laser beam is incident, and a horizontal scanning end signal based on the detection output of the laser beam is supplied to the laser beam modulating means to modulate the laser beam. a horizontal scanning end position detector for stopping modulation; and a laser beam modulating means that divides the time interval between the horizontal scanning start signal and the horizontal scanning end signal by a predetermined integer and transmits the result to the laser beam modulation means.
1. An image output device comprising: clock generation means for generating a clock for modulating an image signal on a pixel-by-pixel basis.