JPH01147419A - Laser image recorder - Google Patents

Abstract

PURPOSE:To prevent the dislocation of a beam spot when an image is written on photosensitive material by beginning to write an image after a prescribed period of time has passed since laser beams crossed a horizontal synchronizing sensor. CONSTITUTION:When red, green and blue laser beams, three in total cross the horizontal synchronizing sensor 1, beam detecting signals can be obtained, and are waveform-shaped in a synchronizing signal generating circuit 2, where scanning synchronizing signals R, G and B are obtained. They are sent to image element clock generating circuits 3-3'', and applied to counting circuits 5-5'' with which image element clock signals correspond. Each counting circuit counts image element clock signals enough to correspond with the scanning distance between the horizontal synchronizing sensor 1 and an image writing start position on the phototsensitive material. At the end of counting, counting completion signals are output, and image write clock generating circuits 6-6'' generate image write clocks are send them to corresponding acoustic optical modulators 7-7''. Thus, the dislocation of spots on which plural laser beams are projected can be corrected readily at high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in positional deviation correction of the recording start position of each laser beam in an image recording apparatus using a plurality of laser beams.

(Prior Art) FIGS. 7 and 8 are diagrams showing the basic configuration of a conventional color laser printer, which is one of the image recording apparatuses that record images using a plurality of laser beams. Figure 7 shows
As a laser light source, a red laser 18 and a green laser I
9. In a method using three lasers: blue laser 20, 3
It is called the tube type.

The system shown in FIG. 8 uses one helium-cadmium (He-Cd) white laser 17 that outputs white laser light containing the three primary colors of red, green, and blue, and is called a single-tube system.

In the three-tube type, each color laser beam output from each laser has a laser beam corresponding to that color, for example, A OM (
Acousto 0ptic modulator) 16, 16' and 16'' are used to modulate each color with a color image signal, and each modulated color laser beam is transmitted to a corresponding dichroic mirror 14, 14' and 14'', and by aligning the optical axes at the time of reflection, the beam is combined into a single beam, which passes through the subsequent optical system and is scanned by a deflector. A color image is photosensitively formed on the surface of 13.

In the single-tube type, one laser outputs laser light of three primary colors, red, green, and blue, as a single beam.

However, the intensity modulation by color image signals of each color is
This must be done separately for each blue laser beam. For this reason, dichroic mirrors 15, 15', and 15" are used to separate the laser beams into red, green, and blue. After separation, the configuration is the same as that of the three-tube type.

In this manner, all conventional image recording apparatuses combine three modulated laser beams into one beam and irradiate the image plane as the same spot.

Horizontal synchronization (H
or 1zontal-5ynchron: H-5
ync, ) signal sensor (beam detection means) is arranged, and the synchronization signal generated from the detection signal output from this is used to determine the timing at which the image of one combined beam starts to be written. is taking.

FIG. 9 is a diagram showing this time relationship.

Figure (a) shows the output waveform of the horizontal synchronization sensor 1, and Figure (b) shows the output waveform of the horizontal synchronization sensor 1.
) is a scanning synchronization signal obtained by shaping the waveform of figure (a), and figure (c) shows that image writing is started after a certain period of time TO has elapsed from the scanning synchronization signal, and image writing continues for a predetermined period of time. It shows.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional technology, it is difficult to completely overlap the three laser beams on the imaging plane. In order to completely overlap the beam spots of the three laser beams on the imaging plane, use the dichroic mirrors 14, 14' and 14 shown in FIGS. 7 and 8 to completely overlap the three laser beams. It is necessary to superimpose them, and very strict accuracy is required. For example, if the spot diameter on the imaging plane is 80 μm%, the focal length of the f-theta lens is 200+ea+, and the allowable positional deviation of the beam spot on the imaging plane is 1/4 dot, then Figures 7 and 8 The setting angle error of the dichroic mirrors 14, 14' and 14'' must be kept to less than approximately 1/180 degree (20 seconds), which requires a high level of machining accuracy of the installation mechanism, and requires a lot of effort in the installation adjustment. There is a problem in that it requires a high degree of skill and man-hours.

In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a laser image recording system capable of correcting positional deviations of beam spots of a plurality of laser beams on an imaging plane with simple means and with high precision. The goal is to provide equipment.

(Means for Solving the Problems) In order to achieve the above object, the present invention has the following means configuration. That is, the laser image recording device of the present invention is an image recording device that records an image on a photosensitive material by simultaneously scanning a plurality of laser beams separated in the scanning direction in the separated state. A plurality of beam detection means are provided corresponding to the plurality of laser beams and:
a synchronization signal generator 8 for receiving a beam detection signal from the beam detection means and outputting a waveform-shaped scanning synchronization signal for each of the plurality of laser beams; predetermined based on the scanning synchronization signal; the plurality of pixel clock generation means for selecting one clock signal substantially synchronized with the scanning synchronization signal from a plurality of clock signals having the same frequency as the pixel clock frequency and having a phase difference, and outputting the selected clock signal as a pixel clock signal; ; the plurality of counting means outputting a coefficient expiry signal when counting for a predetermined number of pixels is completed upon receiving the pixel clock signal from each of the pixel clock generation means; counting from each of the coefficient means; A plurality of image writing clock generating means generates an image writing clock upon receiving an expiry signal, and outputs the image writing clock to a light modulating means that performs intensity modulation for each of the plurality of laser beams. This is a laser image recording device.

(Function) Hereinafter, the function of the laser image recording apparatus of the present invention having the above-described configuration will be described.

The present invention is based on the premise that a plurality of laser beams are not combined into one beam, but that each of the plurality of laser beams is separated in the main scanning direction. Separation here refers not only to cases where the beam spots on the imaging plane are completely separated, but also to cases where some of them overlap each other, as long as the beam detection means can distinguish and detect them. shall be included. As for the backward scanning direction, it is assumed that the positional deviation of the photosensitive material (2) is adjusted within an allowable range (for example, 1/4 dot). For convenience of explanation, a color image recording apparatus using laser beams of three colors will be described below as an example.

Now, the case where only one beam detection means is provided will be described. The image writing start position on the imaging surface of the color photosensitive material must be the same for all three laser beams.

If the scanning speed of the three laser beams is the same, that is, if laser beams with different wavelengths are used and chromatic aberration of the lens is not considered, image writing will start after the laser beam crosses the beam detection means. The time it takes for the three beams to reach the position is the same regardless of the amount of deviation between the three beams. Therefore, for each laser beam, when a predetermined time has elapsed from the time when the beam detection means detects the passage of the beam, the light modulation means corresponding to the beam modulates the laser beam with the color image signal of that beam. By starting, both beams start writing an image from the same position, and even if the beams themselves are separated, there will be no positional shift of the beam spot in the image recorded on the photosensitive material.

Next, a case will be described in which beam detection means are provided separately for each color of laser beam. In this case, since the positions of the beam detection means are different, the distance to the image writing start position is different, and the time from when the laser beam crosses the beam detection means to reaching the image writing start position is different. Become. Therefore, by setting different predetermined times for each laser beam after the beam detection means detects the passage of the beam until the light modulation means starts modulating the color image signal, three laser beams can be generated. will start writing from the same position.

In the case of one beam detection means, it outputs a detection signal every time a plurality of laser beams cross.

In the case of a plurality of photodetectors, a filter is provided on the incident surface of the photodetector, and a detection signal is output only when a beam of a pre-corresponding color crosses the photodetector.

In either case, the detection signal is applied to a synchronization signal generating means, which outputs a waveform-shaped scanning synchronization signal for each color (wavelength) of the laser beam. The scanning synchronization signal for each color is sent to a pixel clock generation means provided for each color.

Each of the pixel clock generating means generates the scanning signal from a plurality of clock signals having the same frequency as a predetermined pixel clock frequency and a predetermined phase difference based on the time point when each scanning synchronization signal is received. One clock signal that is almost synchronized with the synchronization signal is selected and output as a pixel clock signal.

Note that when the number of the plurality of clock signals is large (the phase difference is small), it is possible to reduce the time difference between the scanning synchronization signal and the first signal of the generated pixel clock signals.

This pixel clock signal is sent to a counting means provided corresponding to each pixel clock generating means. The counting means outputs a counting completion signal when it counts the sent pixel clock signals by a preset number. The time for counting this preset number is the elapse of the aforementioned predetermined time.

Therefore, when the number of beam detection means is one, the setting values of all the counting circuits are the same.

On the other hand, if a beam detection means is provided for each color of the laser beam, the set numerical value of the counting circuit will also differ depending on the setting position.

The counting completion signal of each counting means is sent to the image writing clock generation means provided corresponding to each counting means, and the image writing clock generation means generates an image writing clock at the timing of the counting completion signal. and outputs it to the optical modulation means. The light modulation means starts amplitude modulation using the corresponding color image signal based on the tarok signal. As explained above, in the present invention, even if the beam spots of multiple laser beams are misaligned, each beam starts writing on the photosensitive material from the same position, so color misregistration does not occur. become.

The reason why there is room for color shift when writing on photosensitive materials is due to the time difference between the scanning synchronization signal and one pixel clock signal, but the maximum value of this time difference is due to the phase difference between multiple clock signals. , and the pixel shift at that time is equal to the number of clock signals used for the pixel clock period. That is, if the pixel clock period is lps,
The phase difference between each signal of multiple clock signals is 200ns
(i.e. when using 5 clock signals)
When the time is 1/100 ns (that is, when an IO clock signal is used), it is a 1/10 dot.

Therefore, if the phase difference between each signal is made smaller (that is, the number of clock signals used is increased), the positional deviation of the beam spot due to the above-mentioned time difference becomes negligible.

(Example) Hereinafter, an example in which the present invention is applied to a color image recording device will be described based on the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a scanning situation of a beam having a color shift in the present invention, in which a horizontal synchronization sensor l for detecting a passing beam is provided at a position on the left side (left margin) facing the photosensitive material I3. , red (R) laser beam I
A situation is shown in which the O1 green (G) laser beam 11 and the blue (B) laser beam 12 start scanning sequentially across the horizontal synchronization sensor.

Now, when three laser beams of R, G, and B cross the horizontal synchronization sensor 1, a beam detection signal as shown in FIG. 6(a) is obtained from the horizontal synchronization sensor 1.

This beam detection signal is sent to the synchronization signal generation circuit 2, where the waveform is shaped to obtain the scanning synchronization signal shown in FIG. 6(b). Among these scanning synchronization signals, the signal marked with R is sent to the pixel clock generation circuit 3, the signal marked with G is sent to the pixel clock generation circuit 3', and the signal marked with B is sent to the pixel clock generation circuit 3. The signal is sent to the clock generation circuit 3. In parallel with this, a reference pixel clock signal having the same frequency as the preset pixel clock frequency is applied from the crystal oscillator 4 to the pixel clock generation circuits 3, 3', and 3. A plurality of clock signals having a predetermined phase difference are formed by a delay circuit within.

The pixel clock generation circuits 3, 3', and 3'' select one clock signal that is substantially synchronized with the horizontal periodic signal from among the plurality of clock signals based on the time point when the horizontal synchronization signal arrives. These pixel clock signals are applied to the corresponding counting circuits 5, 5/1 and 5, respectively.In each counting circuit, the horizontal synchronization sensor I and the clock signal on the photosensitive material I3 are applied. Counts the pixel clock signals by the number of pixels corresponding to the scanning distance from the image writing start position, and outputs a counting completion signal when the counting is completed, corresponding to counting circuits 5, 5', and 5, respectively. The image write clock generation circuits 6, 6', and 6'' generate image write clocks, and the image write clocks are sent to the corresponding AOMs 7, 7', and 7.
Send to. The image write clock generation circuit of this embodiment generates an image write clock by taking the logical product of the count completion signal from the counting circuit and the pixel clock signal from the pixel clock generation circuit. Each AOM driver amplitude-modulates each laser beam over a fixed period of time from the time when the image writing clock arrives, using a color image signal synchronized with the image writing lock that is input separately.

FIG. 3 is a block diagram of the pixel clock generation circuit in this embodiment, showing an example of the circuit structure that can suppress the positional deviation of the beam spot (hereinafter referred to as jitter) to 1/16 or less of the image clock. In the figure, Ill is a latch circuit 11 that receives clocks TO to T7 at its data input.
2 is a latch circuit which receives clocks T8 to T15 at its data input.

These latch circuits are latched at the rising edge of the horizontal synchronizing signal pulse H5. 113 is the output OQ of the latch circuit 111
144 is a latch circuit 11 which receives 7Q at data inputs D0 to D and converts it into a 3-bit code signal.
2 output OQ~7Q is received by data human power D0~D7 and 3
This is an encoder that converts into a bit code signal. 11
5 is a data selector that receives the modulated output YA-Yc of the encoder 113 at its data select input 5A-8o and the clock TI-T8 at its data inputs D0 to D7; 116 also receives the modulated output YA-Yc of the encoder 114 for its data select Input SA-S c has clocks T9 to T1.
5. This is a data selector that receives TO to data inputs D0 to D. The outputs Y of these data selectors 115 and 116 are input to an OR gate 117, and the OR gate 11
7 as an image clock.

The operation of the device configured in this way will be described next.

First, it is assumed that the phases of the clocks TO to T15 shown in the diagram are shifted from each other by 1/16 as shown in FIG. Here, To is a reference image clock. Such phase-shifted clocks can be created using a delay circuit (not shown).

These clocks are latched by the horizontal synchronization signal pulse H3. At this time, the data latched by the latch circuits 111 and 112 becomes t; in synchronization with the HS pulse.

This latch data is encoded by subsequent encoders 113 and 114, and input to data select inputs of data selects 115 and 116 to select a clock whose phase is synchronized with the HS pulse.

A specific case will be explained. Assuming that the horizontal synchronizing signal pulse H5 rises at the time shown in FIG. 4, the state of the clock TO-715 at this time is latched by this HS pulse. At this time, the values to be latched are (1, 11110000000011
1). At this time, the first data selector 115 is selected by the circuit (112) that latches the T15 clock. That is, the latch output of T15 is inverter 1
18 to the G input of the data selector 115 and selects the data selector. Therefore, in this case, only the data inputs TO to T7 of the encoder 113 need to be considered.

Encode the value (11111000) at this time (
(see Figure 5) and (YA= l, YB= 0, Y
c = 1), the data selector D5 is selected, and the clock T6 is output and passes through the OR gate 117. After counting this clock by a predetermined number N, modulation of the laser is started.

In this way, no matter what time the horizontal periodic signal pulse HS rises, it is always possible to keep the predetermined count number N constant for a certain period of time.
Laser modulation (recording on the photosensitive material) can be started at the time when a time of /16 cycles or less is added, and jitter can be suppressed to 1716 or less of the image clock cycle.

By the way, the input of the data selector 115. -D7 must be selected in consideration of the delay time of elements, etc.

Adjacent clocks To-T15 differ by only one bit. Therefore, even if the latch timing deviates, the adjacent clock is selected, so there is no significant deviation from the HS pulse. Furthermore, even if the first data selector 115 is selected when the latched data of the T15 clock is '1', even if the next phase (11111111) of the clocks TO to T7 is latched, the output of the encoder 113 is (YA=]-, Ys=1,
Since the T8 clock is selected by Y c -1) and output as the image clock, a clock with an unreasonable phase will not be output as the image clock.

FIG. 6(c) shows the time interval of image writing for each color. Assuming there is no chromatic aberration in the lens, the horizontal sync sensor is 1
In this case, t1=t2-tst. If there is chromatic aberration of the lens, the time interval for writing this image is
The setting should be done taking into consideration the chromatic aberration of the lens. When three horizontal synchronization sensors are used for each color, jl,
E! , t3 are values corresponding to the scanning distances between each horizontal synchronization sensor and the image writing start position.

In this case, it is more troublesome to adjust the set value of the counting circuit than in the case of one horizontal synchronization sensor, but a circuit for discriminating R, G, and H of the synchronization signal in the synchronization signal generation circuit is not required.

In addition, as a method for separately inputting the three color beams to the three horizontal synchronization sensors, something like a dichroic mirror may be used, or a filter may be used that allows only the laser beam of each color to pass through. .

Although the above embodiment describes the case where the present invention is applied to a color image recording device, the present invention is not limited to the color image recording device of the present invention, and a gradation image is recorded by modulating each of a plurality of laser beams. It can also be used in laser image recording devices, etc.

Further, in the above embodiment, a gas laser is used as the laser light source and the light is modulated by the AOM, but a ROM may be used as the light modulation means.

Note that when a semiconductor laser is used as the laser light source, modulation can be performed by controlling the drive current of the semiconductor laser, so the semiconductor laser drive circuit serves as the optical modulation means in the present application, and AOM etc. are not required.

(Effects of the Invention) As explained above, in the apparatus of the present invention, the scanning distance between the fixedly provided horizontal synchronization sensor (beam detection means) and the image writing start position on the photosensitive material is fixed. Focusing on the fact that the beam spot of each laser beam does not have to be perfectly aligned to write, image writing is started after the time corresponding to the scanning distance has elapsed after the laser beam crosses the horizontal synchronization sensor. Even if there is a positional shift between the beam spots of multiple laser beams on the photosensitive material, resulting in multiple beams, the laser beams will start when a certain amount of time has elapsed after each beam crosses the horizontal synchronization sensor. As long as the horizontal synchronization sensor can separate and identify each beam, image writing will start from a point at the same distance from the horizontal synchronization sensor, that is, at the same position, regardless of the magnitude or order of the deviation between the beams. The advantage is that the position of the beam spot does not occur when writing into the material. Further, since the adjustment of mirrors and the like only needs to be performed in the backward scanning direction, mechanical adjustment can be easily performed.

Even when a horizontal synchronization sensor is provided for each laser beam, the time from when it crosses the horizontal synchronization sensor to when it starts writing depends on the scanning distance between each horizontal synchronization sensor and the image writing start position. If the time is set, the image writing start position on the photosensitive material will be the same for each beam, so there is an advantage that positional deviation of the beam spot will not occur.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure shows the scanning situation of a beam with color shift, Figure 3 is a specific configuration diagram of the pixel clock generation circuit, Figure 4 is a diagram showing the phase relationship of clock signals, and Figure 5 is the value decoded by the decoder. Figure 6 is a diagram showing the relationship between the scanning synchronization signal and the input terminal of the clock signal selected by it, and Figure 7 is a diagram showing the time relationship between the scan synchronization signal and the start of image writing. Figure 7 is the configuration of a conventional three-tube color laser printer. 8 is a block diagram of a conventional single-tube color laser printer, and FIG. 9 is a time relationship diagram of scan synchronization in the conventional device. l...Horizontal synchronization sensor (beam detection means), 2...
Synchronous signal generation circuit, 3.3', 3... Pixel clock generation circuit, 4...
Crystal oscillator, 5.5', 5"... Counting circuit, 6.6', 6... Image writing clock generation circuit, 7.
7'7"... AOM, 8... Polygon, 9... f-theta lens, lO... Red laser beam, 11... Green laser beam, 12... Blue laser beam, 13. ...Photosensitive material, 14.14', 14", 15.15', 15"...
Dichroic mirror, 16, 16', 16...AOM. 17... Helium-cadmium (He-Cd) white laser, 18... Red laser, l9... Green laser, 20... Blue laser, 111.112... Latch circuit, 113. 114...Encoder, 115.116...Data selector, 117...OR gate, 118...Inverter.

Claims (1)

[Claims] In an image recording device that records an image on a photosensitive material by simultaneously scanning a plurality of laser beams separated in a scanning direction in the separated state, one or a plurality of laser beams are provided corresponding to the plurality of laser beams. beam detecting means; receiving a beam detection signal from the beam detecting means; and synchronizing signal generating means for outputting a waveform-shaped scanning synchronizing signal for each of the plurality of laser beams; based on the scanning synchronizing signal; selecting one clock signal substantially synchronized with the scanning synchronization signal from a plurality of clock signals having the same frequency as a predetermined pixel clock frequency and having a phase difference, and outputting the selected clock signal as a pixel clock signal; a pixel clock generation means; a plurality of counting means for receiving a pixel clock signal from each of the pixel clock generation means and outputting a counting completion signal when counting for a predetermined number of pixels is completed; the plurality of image writing clock generating means for generating an image writing clock upon receiving a counting completion signal from each counting means, and outputting the image writing clock to the light modulating means that performs intensity modulation for each of the plurality of laser beams; A laser image recording device characterized by: