JPS63148275A - Laser light scanner - Google Patents

Abstract

PURPOSE:To move an image formation position forward and backward optionally by providing a storage means for storing frequency division information on laser light and a frequency divider which varies in frequency division ratio according to the output of the storage means, and modulating image information according to the output of the frequency divider. CONSTITUTION:When a photodetection signal is inputted from an optical detector, the outputs of an N frequency divider 41b and a counter 42 are cleared and when the optical detection signal falls, the N frequency divider 41 begins to divides the frequency of a 60MHz clock (a). When the output of N frequency divider 41 rises assuming that the output initial value of a PROM 43 is 0, the counter 41 counts the rise at the time of the rising and is started up. When the output of this counter 42 rises, the input address of the PROM 43 varies and the PROM 43 supplies '1' to the N frequency divider 41. When the N frequency divider 41 reaches a counted value 15, a carry signal C is outputted and inputted to its own -LD, and a load input '1' is loaded. Consequently, a laser light scanner which can moves the image formation position forward and backward optionally is realized without using any expensive delay line.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a laser beam scanning device, and more specifically, a laser beam scanning device capable of preventing color shift in a multicolor recording laser printer. Regarding.

(Prior Art) Conventionally, image information is recorded by modulating a laser beam according to an image signal, irradiating the modulated laser beam onto an information recording medium through an optical system, and scanning and exposing the information recording medium. Laser printers that do this are known. FIG. 8 is a V configuration diagram showing an example of a conventional device of this type.

In the figure, 1 is a laser that emits a light beam, 2 is an optical modulator that modulates the light beam B emitted from the laser 1 according to an image signal, and 20 is a predetermined beam that receives the output light of optical modulation "a2". The beam expander 20 converts the beam size into a beam size of 2. The beam expander 20 is composed of, for example, an optical lens 3.4.

5 is a polygon mirror that distributes the transmitted light of the beam expander 20 in the main scanning direction, 6 is a motor that rotates the polygon mirror 5 at a constant speed, and 7 is a motor that receives the reflected light from the polygon mirror 5 and performs constant speed scanning. 8 is an information recording medium that receives the scanning light from the fθ lens 7. 9 is a position detection sensor that receives the light beam and detects the initial recording position. 10 is a sensor that winds the information recording medium 8 in the sub-scanning direction. 11 and 12 are pressure rollers that press the information recording medium 8 onto the transport roller 10.

The operation of the device configured as described above is summarized as follows.

A light beam 8 emitted from a laser 1 is modulated by a luminous intensity unit 2 according to an image signal. The light beam is converted to a predetermined beam diameter by a beam expander 20. The converted light beam is distributed in the main scanning direction of the information recording medium 8 by the polygon mirror 5, and is sent to the information storage medium 8 via the fθ lens 7.
Irradiation is directed towards the recording medium 8. At this time, when the light beam hits the position detection sensor 9, a counter (not shown) starts counting clock signals, and when the counted value reaches a predetermined value, the light beam modulated by the image signal is transferred to the information recording medium. 8. Start irradiation. L indicates the scanning line at this time. Then, when the count value of the counter reaches a predetermined value, the light beam is turned off and the exposure operation is ended. When one line of scanning is completed, the conveyance roller 10 rotates and the D
The information recording medium 8 is conveyed by one line in one scanning direction (one scanning direction, one winding direction).

A new scan is then performed. The information recording medium 8 that has been scanned and exposed is developed and fixed, and predetermined image information is recorded thereon. The optical modulator 2 can be omitted if a laser device (for example, a semiconductor laser) that can be directly modulated is used as the laser 1.

In recent years, laser beams with multiple wavelengths, for example red (R), have become popular.

2. Description of the Related Art Laser printers have been developed that enable multicolor recording by irradiating an information recording medium with green (G) and blue (B) laser beams and performing scanning exposure. This type of laser printer has a problem in that the beam spots of each wavelength are shifted on the imaging plane due to chromatic aberration of the imaging lens (fθ lens). As shown in FIG. 9, the wavelength λ1. Consider a case where laser light B of λ2 is incident on the polygon mirror 5 and its reflected light is irradiated onto the information recording medium 8 via the fθ lens 7.

Assuming that the surface of the information recording medium 8 is the imaging position,
The light passing through the θ lens 7 is slightly shifted into wave λ1 light and wave 22 light. Such a phenomenon (referred to as chromatic aberration) occurs because the refractive index of the lens differs depending on the wavelength. The solid line in the figure is 21. The broken line is 22 lights. If λ1 and λ2 deviate, color misregistration will occur on the information recording medium 8, causing deterioration in image quality and a decrease in resolution due to thicker line widths. FIG. 10 is a diagram showing the state of the village shift.

For example, assuming that part A is an area irradiated with light of wavelength λl, and part 8 is an area irradiated with light of wavelength λ2, A+, B+
This area forms a color shift area, which causes the apparent line width to become thicker.

In order to eliminate such problems, the following method is adopted.

■ [Completely achromatize the θ lens (imaging lens).

■Correct chromatic aberration by delaying the pixel clog. This method is divided into correction within one clock and correction within one clock. That is, correction in units of clocks is performed by delaying data, and correction within clocks is performed by delaying the clock of the D/Δ converter.

FIG. 11 is a circuit diagram for correcting chromatic aberration. The image data is sent to the D/A converter 22 via the clock intermediate correction circuit 21.
The pixel clock is input to the D/A converter 22 as a conversion clock via the internal clock correction circuit 23. The operations of the clock unit correction circuit 21 and the intra-clock correction circuit 23 are controlled by the control circuit 24.

That is, the clock unit correction is performed by controlling the clock provided by the control circuit 24 to the clock unit correction circuit 21 to delay data. On the other hand, clock correction is performed by the control circuit 24 controlling the intra-clock correction circuit 23 and delaying the conversion clock applied from the intra-clock correction circuit 23 to the D/A converter 22.

(Problems to be Solved by the Invention) In the case of (2), a completely achromatic lens cannot be realized for light of wavelengths of three or more colors. Even in the case of two colors, it is necessary to use special materials to make lenses with little chromatic aberration, and a high degree of assembly is also required. Therefore, the yield of the fθ lens also deteriorates, leading to an increase in cost.

In the case of the method shown in ■, the pixel clock is constant, so
It is necessary to slightly move the beam, which has shifted from its original position due to chromatic aberration, to bring it to its original position.

This will be explained using FIG. 12. Assuming that the unit delay time between the basic pixel clock and the delayed pixel clock is 6°C, in order to correct color shift, the delay amount is 2Δt, 3Δt・
It is necessary to gradually increase the number of... For this reason, the delay element used in the correction circuit 13 (see Figure 11) requires an element that can delay up to Zhou Ming King in units of Δ, for example, a delay line and a selector that selects the clocks at each stage delayed by the delay line. becomes.

FIG. 13 is a diagram showing an example of a delay circuit, in which the pixel clock 1 input to the delay line 25 is delayed in steps from Δ[ to Δ().The delayed pixel clock at each stage is optimized by the selector 26. is selected and output as a delayed pixel clock.

However, such a delay line is expensive (for example, 4,000 yen for 8 taps) and has poor accuracy (for example, Δt±5% culm I!2). Furthermore, in this method, the pixel clock can be delayed and the imaging position can be shifted backward, but it cannot be moved forward.

The present invention has been made in view of these points, and
The object is to realize a Rade optical scanning device that can arbitrarily move the imaging position to the front without using an expensive delay line.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, modulates a plurality of laser beams with different wavelengths according to image information, and transmits them to an information recording medium through a deflection means and an imaging optical system. A laser beam scanning device that conducts scanning by guiding a laser beam to a laser beam, comprising a storage means for storing frequency division information of the laser beam, and a frequency divider that changes a frequency division ratio according to the output of the storage means, and the frequency divider output This feature is characterized in that the image information is modulated based on the image information.

(Function) Frequency division information of the laser beam is stored in advance, and the frequency division ratio of the pixel clock is changed (increase/decrease the pixel clock) based on the frequency division information. This allows the pixel clock to be advanced or delayed, and any chromatic aberration patterns can be corrected to eliminate color shift.

FIG. 14 is an explanatory diagram of the color shift correction method according to the present invention. Assuming that the scanning direction is taken in the direction of the arrow in the figure, (a) shows the case where the beam position B2, which is deviated from the original beam position fmBl due to chromatic aberration, occurs rearward, and (b) shows the case where the beam position B2, which is deviated from the original beam position fmBl due to chromatic aberration, occurs behind the original beam position B1. Each figure shows a case where a shifted beam position B2 occurs in the front.

To correct the beam position as shown in <B), the pixel clock is delayed. In other words, if you increase the frequency division ratio N,
Advance the pixel clock to correct the beam position shown in . In other words, the frequency division ratio N should be made small. In order to achieve this purpose, we first create a basic pixel clock,
This basic pixel clock is increased or decreased.

(1) How to create a basic pixel clock In order to produce images without pixels, place a photodetector near the scanning start position outside the recording area as shown in 9 in Figure 8, and synchronize with the signal from this photodetector. and read out the image data. That is, it is necessary to generate a pixel clock synchronized with the output of the photodetector.

Generally, as a method of generating this pixel clock, the original oscillation, which is N times the pixel clock, is divided by N using the output signal of the photodetector. Therefore, in principle, jitter of 1/N of one dot always exists, but if N is made large enough, it becomes inconspicuous. 15th
The figure shows a block diagram of the pixel clock generation circuit, and FIG. 16 shows the timing chart of each part.

The frequency Nf from the oscillator 30 is shown in FIG.

The clock is output and enters the N-divided '/i31. Here, when a position detection signal as shown in FIG. 16a from the photodetector enters the N frequency divider 31 as a reset signal @R, the N
The output of the frequency divider 31 is in a reset state during this time. When the reset signal disappears, the N frequency divider 31 starts frequency division by N, and outputs a lock f of v pixels of the same jJITo as shown in FIG. 16C.

(2) Method for increasing/decreasing the basic pixel clock As is clear from FIG. 15, it is possible to increase/decrease the frequency fo of the basic pixel clock by changing the frequency division ratio N. For example, three types of frequency division ratios N+, N2
, Ns (Nh <N2 <Ns). Then, when you want to delay the pixel clock, increase the frequency division ratio to N3 (clock period To becomes longer), and when you want to advance the pixel clock, lower the frequency division ratio to N1 (clock frequency I
9] The frequency division ratio is changed for each pixel so that T o becomes shorter. Any clock synchronization pattern can be created by such frequency division ratio control.

The case shown in FIG. 15 will be explained as an example. If the pixel clock frequency at the time of NZ frequency division is f, then N.

The pixel clock frequency during frequency division is (Nz/N1>×"o
Therefore, the frequency becomes higher. The pixel clock frequency at the time of N3 frequency division becomes (N2/N5)xfO, and the frequency becomes low.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of main parts showing an embodiment of the present invention. The embodiment shown in the figure is used for a blue (B), green (G), and red (R) color laser printer, and the synchronous clock generation circuit shown in FIG. 15 is used in B and G.

This is provided in the RfU. In the figure, 40 is a blue synchronous clock generation circuit, 50 is a line synchronous clock generation circuit, and 60 is a red synchronous clock generation circuit. The blue synchronous clock generation circuit 40 includes an N frequency divider 41.60 that receives the 60M1-11 clock. A counter 42 that receives the output of the N frequency divider 41. The output of the counter 42 is received as an address, and the clock pattern for correcting color shift (Nr, N2 as described in @
, Ns frequency division) is stored in the PROM 43.

The output of PROM 43 is input to N frequency divider 41 to determine the frequency division ratio. For example, if 0 and 1.2 are respectively input to the load input of the N frequency divider 41, the frequency division ratio is 16.
．． 15.14.

Further, the blue light photodetector signal is given to the N frequency divider 41 and counter 42 as a rehit pulse. The above configuration is exactly the same for the line synchronous clock generation circuit 50 and the red synchronous clock generation circuit 60.

Here, the frequency division ratio of the N-divided period in the synchronous clock generation circuit is, for example, N3 = 16. N2=15. N1-14 Thorn. Here, if the frequency division ratio of Nh, . . . N3 is set to a value far different from N2, the modified portion becomes noticeable, which is not preferable. The operation of the circuit configured as described above will be explained below with reference to the timing chart shown in FIG.

When a photodetection signal from a photodetector (not shown) is input as shown in FIG. 2(A), the output of the N frequency divider 41b and the counter 42 is ) is cleared as shown. Then, when the photodetection signal falls, the N frequency divider 4
1 is the 60M l-1z clock a shown in Figure 2 (b)
Start dividing. It is assumed that the first bright injection of PR○M43 output is O. When the output of the N frequency divider 41 rises as shown in (c), the counter 42 counts this rising edge and rises as shown in (e). When the output of this counter 42 rises, the input address input 2 of the PROM 43
Convert F ROM 4314 “1” to N frequency divider 4
Give to 1.

When the N frequency divider 41 reaches a count value of 15, (
It outputs the carry signal C as shown in d), takes it into its own LD large input, and inputs it to the load input “°
1'' is loaded. As a result, the N frequency divider 41 is set to a frequency division ratio (divided by 15) according to ``1''. Next, when the output of the N frequency divider 41 rises as shown in (c), the counter 42
The output falls as shown in (e). This allows PROM
43 outputs °O''. At the next key 17 key C, 0'' is loaded into the N frequency divider 41, and the N frequency divider 41 sets the frequency division ratio (divided by 16) according to °'0''. is set to Furthermore, when the N frequency divider 41 output rises, the counter 42 output falls. This causes the PROM 43 to output °'2".

Then, in the next key t7 Lee C, 2'' is loaded into the N frequency divider 41, and the N frequency divider 41 has a frequency division ratio (145) corresponding to 2''.
).

The operation of the blue synchronous clock generation circuit 41 has been described above, but the remaining line synchronous clock generation circuits 50. The operation of the Domei clock generation circuit 60 for red is exactly the same. As described above, according to the present invention, the synchronization clock can be arbitrarily increased or decreased depending on the value of the PROM, and thereby the color shift due to the chromatic aberration of the lens can be corrected.

In this embodiment, the light detection signals of each color are taken independently, but in FIG. 8, the color shift of each color (light detection signal If this can be corrected, it is possible to create a configuration in which a photodetection signal is obtained using one specific color of light.

This will be discussed in more detail.

For example, in Figure 1, the light detection signal from red light is changed to blue.

Also used as a green detection signal. It is assumed that the beam spots of each color at the position of the position detection sensor 9 are lined up as shown in FIG. As shown in the figure, when a photodetection signal is obtained for red, the other two colors are made to match at the recording start position by combining the number of pixels in the left margin and the above-mentioned correction.

For example, if the left margin value of red is 100 clock counts, the other two colors are set to 102 clock counts for green and 98 clock counts for stomach in the example of FIG. Furthermore, since a deviation of 8[1, Δt2 remains, this is canceled in the same manner as color deviation correction.

Furthermore, if any one color is taken as a reference, it is only necessary to match it to one of the other two colors, so there is no need for PROM clock patterns for all three caps, and only two colors are required.

FIG. 4 is a block diagram of main parts showing another embodiment of the present invention, in which red is used as a reference. In the embodiment shown in the figure, the red synchronous clock generation circuit has only an N frequency divider, and here
It is used as a 5 frequency divider. The other portable synchronous clock generation circuits and line synchronous clock generation circuits are constructed so that the N frequency divider can be varied by the PROM output.

Next, a modification will be described. If correction (increase/decrease clock) is performed for each line of the same pixel, unevenness may appear in the sub-scanning direction. FIG. 5 is a diagram showing how unevenness occurs in the sub-scanning direction.

The hatched spots in the figure indicate unevenness.

To prevent this, pixels to be corrected in each line are randomly arranged. To do this, the counter section shown in FIG. 1 is divided into upper and lower sections as shown in FIG. 6, and only the upper section is reset by the position detection sensor output.

Now, the lower bits take a random value for each line, so if n pits are opened for the lower bits, 2n
The pixels to be corrected within the pixels vary randomly for each line. Alternatively, the force r can be loaded with random values by the photodetector output.

Furthermore, if the pixel to be corrected and the pixel not to be corrected have different gradation fj characteristics, N1. N2. It is also conceivable to prepare another γ correction table for pixels that are frequency-divided by N3.

It is also conceivable to correct the deviation from the [θ characteristic of the fθ lens at the same time as the color blurring.

As shown above, in this method, it is possible to realize a pattern of any frequency division ratio stored in the PROM in advance, and the clock 111
The accuracy of subtraction by 1 can be achieved with the accuracy of the original oscillation, and the cost is low.

Finally, I will give a concrete example. Now, it is assumed that the frequency division ratio is the same as in the previous embodiment: 14, 15, and 16, and the frequency division is based on 15. At this time, for example, as shown in Figure 7, with red as the reference, the image height (scanning signal) from the center of the fθ lens is
Then, at the point Y = 30 mm, the blue color is 150 μff!
(Forward from red, in case of Figure 14 (a)) Green is +70 μm
Assume that the beam forms an image (beyond red, in the case of FIG. 14(b)).

Pixel pitch in main scanning direction 50 μm <20 dots/+
nm), the frequency is divided by 16 (16/15) x 50 = 5
A pixel of 3.3 μm can also be divided by 14 (14/15)
A pixel of 50=46.7μm was realized, and compared to the plug type 50μm, ±3.3μmii! ii) The prime pitch can be shifted.

The number of pixels at an image height of Y=30111 m is 30×20=600 pixels based on the center of the lens.

Therefore, for helmets, 50 out of 600 pixels from 150 μm
/3.3=15 pixels divided by 16. If it is divided evenly, 400 pixels (211111) are divided once by 16.

For green, similarly, 70/3.3-21 pixels 14
Divide the frequency. If divided evenly, 288 pixels 1.4n+
m) is divided once by 14. By performing these processes, the three beam spots of B, G, and R can be made to coincide at the point 'y'-3Qn+m.

(Effects of the Invention) As described in detail above, according to the present invention, when dividing the clock, the pixel clock can be increased or decreased by appropriately changing the division ratio according to the value of FROM. , This makes it possible to match the deviations of the beam spots of each color. Therefore, it is possible to realize a laser beam scanning device that can arbitrarily move the imaging position back and forth without using an expensive delay line. According to the invention,
Eliminates color misalignment in color laser printers.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of main parts showing an embodiment of the present invention, Fig. 2 is a timing chart showing the operation of each part, Fig. 3 is a diagram showing the positional relationship of the beams of each color, and Fig. 4 is a diagram showing the positional relationship of the beams of each color. 5 is a diagram showing the occurrence of unevenness in the sub-scanning direction, FIG. 6 is a diagram showing the configuration of the counter, FIG. 7 is an explanatory diagram of a specific example of color shift, 8 is a diagram showing an example of a conventional configuration of a laser printer, FIG. 9 is a schematic diagram of color misregistration, FIG. 10 is a diagram showing a color misregistration state, FIG. 11 is a diagram showing an example of a chromatic aberration correction circuit, and FIG. 12 is a diagram showing an example of a chromatic aberration correction circuit. The figure is an explanatory diagram of the pixel clock delay state, Fig. 13 is a delay circuit diagram of the pixel clock using a delay line, Fig. 14 is an explanatory diagram of the principle of color shift correction, and Fig. 15 is an explanatory diagram of how to make the pixel clock. FIG. 16 is a timing chart of FIG. 15. 40...Blue synchronous clock generation circuit 41...N frequency divider 42...Counter 43-
P ROM 5o...Line synchronous clock generation circuit 60...Akagawa synchronous clock generation circuit Figure 14 Figure 15 Figure 16

Claims (1)

[Claims] In a laser beam scanning device that modulates a plurality of laser beams with different wavelengths according to image information, guides them to an information recording medium through a deflection means and an imaging optical system, and performs scanning, a memory that stores frequency division information of the laser beam. and a frequency divider that changes a frequency division ratio according to the output of the storage means, and is configured to modulate image information based on the output of the frequency divider. .