JP2003025629A - Optical scanner, its scanning method, display and laser printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a uniform scanning speed on the scanning plane easily at the time of scanning with an optical scanner by an electrical method employing a conventional pixel modulation technology. SOLUTION: The optical scanner comprises a circuit 11 for correcting image data into data depending on the scanning speed and two modulation circuits wherein each modulation circuit modulates the rising edge and falling edge of a light source modulation signal to perform toggle operation and exclusive OR of the outputs from both modulation circuits becomes the modulation signal of a light source 15. The pixel time width on the scanning plane is thereby variable depending on the scanning speed in units of minimum resolving power of the modulation circuit. Controllable emission time of the light source is constant regardless of the pixel time width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reciprocating optical scanner such as a resonance scanner, and more particularly to uniformizing a scanning speed thereof.

[0002]

2. Description of the Related Art Hitherto, various optical deflectors (hereinafter referred to as optical scanners) such as a resonance type scanner, a polygon mirror, a galvanometer and the like have been proposed, and their applications are wide-ranging such as a bar code reader, a display and an LBP.

In particular, an optical scanner utilizing resonance can be manufactured by a semiconductor manufacturing process, and attention is paid to downsizing of products. The resonance frequency is up to several tens of kH
The z and the amplitude can be ±± several tens of degrees depending on the resonance frequency.

Although there are many structures of a resonance type scanner, a scanner utilizing Lorentz force represented by Japanese Patent No. 2657769 is well known. The outline is shown in FIG. When a current i is passed through the coil in FIG. 2, a rotational torque due to the Lorentz force F is generated due to the magnetic field B generated by the permanent magnet or the like, and the mirror surface is twisted to a position where the restoring force of the torsion bar is balanced. Resonant operation becomes possible by applying this current i in alternating current at the resonant frequency of the scanner. The scanning operation is performed by irradiating a mirror formed on the scanner surface with laser light or the like from the outside.

This optical scanner utilizes resonance to vibrate the mirror. Therefore, the Q value is very high and the operation draws a sine curve. FIG. 3 shows the scan width at regular time intervals at this time. In the figure, the horizontal axis represents the angular displacement of the scanner from the negative maximum value to the positive maximum value, that is, the fluctuation time, and the vertical axis represents the amplitude. As is clear from the figure, the scan width at a constant time becomes maximum at the center of vibration and becomes narrower toward both ends. In addition, when the vibration angle is large, the influence of the fθ error becomes large. The fθ error is a phenomenon in which the scanning width is not constant because the scanning speed on the scanning surface changes depending on the location even if the laser light is scanned at a constant angular velocity.

If this is directly used for a display or the like, only an image having a non-uniform pixel width on the screen can be output, and the brightness on the screen becomes brighter as the pixel width becomes shorter.

Conventionally, these influences have been optically corrected by using an fθ lens or an arcsine lens. However, the optical correction requires a very complicated lens structure, and therefore the load on the product system design is very large, and there is also a demand for not using these in order to make the system small and simple.

On the other hand, as represented by Japanese Patent Publication No. 5-3947, a frequency divider having a frequency division ratio N and 1 / M is used.
Further, the division ratio N is variable and the frequency fo of the reference clock is fo
An electrical correction method has been proposed in which is changed to fo * (M / N) according to the change in scanning speed. In addition, there is also known a method in which a signal having a frequency of several tens of times the required frequency on the scanning surface is used as the reference clock and the frequency division ratio of the reference clock is changed according to the change in the scanning speed. .

[0009]

However, as the speed of products has been remarkably increased and tens of MHz is required as the frequency of the reference clock as in recent years, it is not possible to use a desired tens of times the frequency of the reference clock. Practically impossible. Also, in the method of varying the frequency division ratio, it is technically very difficult to increase the control speed and control accuracy of the circuit to a level where there is no problem in practical use.

The present invention has been made under such a circumstance, and it is possible to easily realize the uniformization of the scanning speed on the scanning surface by an electric method by applying the conventional pixel modulation technique. It is an object of the present invention to provide an optical scanning device, a scanning method thereof, a display device, and a laser printer capable of performing the above.

[0011]

In order to achieve the above object, in the present invention, an optical scanning device has the following (1) to (5).
And the display device as shown in (6) below, and the laser printer as shown in (7) below.
The scanning method in the optical scanning device is configured as in (8) below.

(1) An optical scanner, a light source of light scanned by the optical scanner, a correction data creating circuit for converting image data into correction data according to a deflection angle of the optical scanner, and the correction data creating circuit. A first modulation circuit that creates a first modulation signal by toggling the rising edge of the light source modulation signal according to the created correction data, and a light source modulation signal according to the correction data created by the correction data creation circuit. Outputs the exclusive OR of the second modulation circuit that creates the second modulation signal with the falling edge toggled, and the first and second modulation signals created by the first and second modulation circuits. And a light source drive circuit that drives the light source according to the output of the logic circuit.

(2) In the optical scanning device described in (1) above, the time width of one pixel on the scanning surface of the optical scanner is adjusted according to the deflection angle of the optical scanner. An optical scanning device in which the light emission controllable time of the light source is always made constant by increasing or decreasing by the minimum resolution unit.

(3) In the optical scanning device described in (1) above, the modulation patterns of the first and second modulation circuits are a right growth pattern that sequentially grows from the right end of the pixel and a left growth that sequentially grows from the left end of the pixel. An optical scanning device that can select patterns according to input data.

(4) The optical scanning device as described in (1) above, in which the way of changing the time width of the pixel on the scanning surface is changed for each deflection of the optical scanner.

(5) The optical scanner, the light source for generating the light scanned by the optical scanner, and the time for one pixel of the image data for modulating the light source are controlled according to the deflection angle of the optical scanner. A light scanning controllable time width of the light source that is always constant regardless of the time control of the one pixel.

(6) A display device for scanning and displaying a display surface by the optical scanning device according to any one of (1) to (5).

(7) A laser printer which scans a laser with the optical scanning device according to any one of (1) to (5).

(8) A scanning method in an optical scanning device comprising an optical scanner and a light source for generating light scanned by the optical scanner, the method comprising driving the optical scanner and modulating the light source. Controlling the time of one pixel of the image data according to the deflection angle of the optical scanner, and constantly controlling the light emission controllable time width of the light source regardless of the control of the time of the one pixel. A scanning method in an optical scanning device, comprising:

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to examples of an optical scanning device and the like. It should be noted that the present invention is not limited to the form of the apparatus, and can be implemented in the form of the method supported by the description of the embodiments.

[Embodiment 1] In Embodiment 1, a pixel modulation circuit conventionally used in a laser printing engine such as an LBP is applied to easily realize uniform electric scanning speed. Recently, a multi-beam system using a plurality of lasers has been developed in order to cope with the increase in the speed of a laser printing engine. Along with this, a pixel modulation circuit is being developed at the same time as a multi-beam compatible LSI. In the present embodiment, the pixel modulation circuit developed for two beams, that is, the pixel modulation circuit of two systems is used, so that the uniformization of the scanning speed can be easily realized.

To make the scanning speed uniform, the time for one pixel of the image data is controlled so as to change in the minimum time unit of the pixel modulation circuit, and the light emission controllable time width of the light source is always constant. Provides uniform and constant brightness scanning.

First, a method of correcting the scanning speed will be described.

As shown in FIG. 4, the vertical distance from the mirror surface of the scanner to the scanning surface is d. The deflection angle of the scanner is ± θ, and its utilization rate is rat. If the number of pixels in one scan is Nh, the width w of one pixel on the scanning surface is w.
Is

[0025]

[Equation 1] Becomes In FIG. 4, only the right half from the center of the scanning surface is shown.

From the figure, the angle Δθn at the nth pixel
Is

[0027]

[Equation 2] Becomes The time Tn for one pixel at this time is because the vibration of the scanner is a sine curve.

[0028]

[Equation 3] (Th is the resonance period of the scanner, and the unit of angle is de
g).

The time of each pixel is calculated from the equation (3), and the pixel having the shortest time in one scan is used as a reference and this is set as the cycle of the reference clock. A frequency synthesizer may be used when actually setting the frequency of the reference clock.

In the normal pixel modulation circuit, the reference clock cycle is set in pixel units, but in this embodiment, the time for one pixel is increased in the minimum division unit of the modulation circuit according to the displacement of the scanner. Therefore, for example, if the pixel time Tn of a certain pixel is twice as long as the reference clock, the pixel has the reference clock 2
One pixel is expressed in a cycle.

When the number of divisions of the modulation circuit in the reference clock is div and the minimum value of Tn, that is, the period of the reference clock is Tbase, the number of divisions Ndiv in each pixel.
Is

[0032]

[Equation 4] Becomes

By calculating this for all pixels, the number of reference clocks required in the image area can be known, and by taking the utilization ratio rat of the deflection angle into consideration, the number of reference clocks required for one scanning can be found.

The time width during which the light source is made to emit light for this pixel time is a constant time width Tbase regardless of the pixel time. Therefore, as in the previous example, the pixel time Tn of a certain pixel
Is Tbase, the time used for light emission control is Tbase even if the time is twice as long as the reference clock (2 * Tbase). As a result, it is possible to keep the emission brightness constant in any pixel.

FIG. 5 shows the relationship between the reference clock and the pixels.
5A shows the pixel time width in the vicinity of the minimum pixel time Tn, and FIG. 5B shows the pixel time width at the position where Tn has increased to some extent. As shown in the figure, the pixel time width increases in units of the minimum division number of modulation according to the change in Tn. In the figure, the number of divisions of the modulation circuit is div = 8, but this is due to the performance of the modulation circuit, and div = 8.
It is not limited to. The time width of each pixel changes depending on the resonance frequency of the scanner, the deflection angle θ, the utilization ratio rat, and the number of pixels Nh, and can be calculated by the above equations (1) to (4).

Further, FIG. 5C shows a light emission controllable time width (gray portion in the drawing) with respect to the pixel time. Even if the time width of the pixel changes as shown in the figure, the time used for light emission does not change. In this figure, the light emission controllable portion is near the left side of the pixel, but of course it does not matter if it is in the center or on the right side.

Next, a specific system configuration will be described.

FIG. 1 is a block diagram showing the system configuration of the "optical scanning device" of this embodiment. The correction data creation circuit 11 uses the original image data 19 according to the above-described calculation.
Is a circuit for newly converting the data into data so that the scanning speed becomes constant.

Data conversion will be described here. Figure 6
(A) is original image data. This original data is converted into data corresponding to the pixel time width while keeping the data width as shown in (b). Also in this figure, the light emission controllable portion is on the left side, but it may be on the center or on the right side as described above. Then, as shown in (c), this data is reconverted only in the time interval so as to correspond to the reference clock width.

Further, in this embodiment, two modulation circuits are used. One outputs a modulation signal in which the rising edge of the drive signal of the light source is toggled, and the other one toggles the falling edge. Output a modulated signal such as This is shown in (d) and (e) of FIG.

Therefore, the modulation data 1 and the modulation data 2 input to the modulation section 12 in FIG. 1 are set as data that can obtain the modulation outputs of FIGS. 6D and 6E.

The correction data generation circuit 11 in FIG. 1 converts the original image data 19 into the modulated data 1 and the modulated data 2 after correction as described above. For this circuit, a conversion pattern may be used in which a correction pattern is calculated in advance from the resonance frequency, deflection angle, utilization rate, etc. of the scanner and stored in a memory or the like. Although not shown, displacement of the scanner is detected. It is also possible to use a device capable of automatically calculating the correction data from the utilization rate, the number of pixels, etc. by using a microcomputer, DSP, or the like.

Next, the modulator 12 will be described. Modulator 1
Reference numeral 2 includes a modulation circuit 1 and a modulation circuit 2. This modulation circuit performs modulation according to input data in units of reference clocks. As an example, the configuration is SRAM as shown in FIG.
71 and a parallel-serial conversion circuit 72. The parallel-serial conversion circuit 72 serially converts the parallel data from the SRAM 71 within the reference clock CK and outputs it as a modulation signal.

The modulation pattern is preset in the SRAM 71 using the SRAM control signal, and is output as a serial signal as shown in FIG. 8 according to the input data. As a specific example, there are 64 types of modulation patterns that can be stored in the SRAM 71, and a serial signal obtained by dividing the reference clock into 32 is output. In this embodiment, the modulation outputs of FIGS. 6D and 6E can be obtained by presetting the pattern of lateral growth.

In the correction method of this embodiment, since the light emission controllable time is constant even when the pixel time width is large, the data according to the pixel time width in FIG. 9A is converted into the data according to the reference clock. In this case, there are no two rising edges or two falling edges within one reference clock time, as shown in FIGS. Therefore, the modulation pattern of the modulation circuit has no problem in lateral growth.

The EXOR (exclusive OR circuit) 13 takes the exclusive OR of the two modulation outputs created by the modulator 12 to form a final light source modulation signal.

The advantages of using two modulation circuits include the following points in addition to the fact that the system can be easily constructed using conventional techniques.

First, for example, when the number of divisions of the modulation circuit is used by dividing one pixel into 32, the number of divisions of one modulation circuit is 1
Since it is necessary to turn on / off the inside of the pixel at random, 32-bit modulated data is required. Such data processing causes an increase in circuit scale and makes data handling inconvenient. Further, when the data is 6 bits, the modulation can be performed only in 6 steps, and the light modulation accuracy is extremely lowered.

The light source drive circuit 14 is an exclusive OR circuit 13
Is a circuit for controlling light emission / extinction of the light source according to the drive signal of the light source, which is the output of.

The control circuit 1 produces the control signal Sdrv1 of the scanner from the reference clock CK. Of course this Sd
The cycle of rv1 is the resonance cycle Th of the scanner. Further, this signal is simultaneously output to the correction data creating circuit 11,
The correction data creation circuit 11 determines the output timing of the modulation data based on this signal.

The scanner drive circuit 17 drives the scanner 18 based on the scanner control signal Sdrv1. Although the canner 18 is of a resonance type, it may be not only the one utilizing the Lorentz force as described above but also a vibrating device such as a piezo.

A laser, an LED or the like is used as the light source 15.

As described above, according to this embodiment,
Uniformization of the scanning speed on the scanning surface can be easily realized by an electrical method by applying a conventional pixel modulation technique.

(Embodiment 2) FIG. 10 is a block diagram showing a system configuration of a "small display" which is Embodiment 2. In FIG. The present embodiment is an example in which the optical scanning device of the first embodiment is used for a display, and a resonance scanner is used for horizontal scanning, and a galvanometer or stepping motor is used for vertical scanning.

The vertical scanner 101 is driven by the drive circuit 102 by the control signal Sdrv2 generated based on the control signal Sdrv1 of the resonance scanner 18 in the control circuit 2.

By inputting this control signal Sdrv2 together with the control signal Sdrv1 of the scanner to the correction data generating circuit 11 and outputting the modulation data based on these signals, an image can be drawn at a desired position on the screen. .

In the case of this type of display, TV distortion occurs in which the left and right ends of the image are concave. This can be dealt with by making the data correction amount variable for each horizontal line in the correction data creation circuit 11.

As described above, by using the optical scanning device of Example 1 (which can also be referred to as a scanning speed equalizing system) for the display system, the uniform scanning speed can be easily realized on the screen.

(Third Embodiment) FIG. 11 is a block diagram showing the arrangement of an "LBP (laser beam printer)" according to a third embodiment.

In the figure, a photodiode 116 monitors the laser light output from the semiconductor laser 115 as a laser light source. The light source drive circuit 14 controls the current applied to the semiconductor laser 115 based on the monitored light quantity so that the output from the photodiode 116 becomes a predetermined value.

The beam detector 111 formed of a light receiving diode detects the information writing start position on the photosensitive drum 114 by the laser beam, and the horizontal synchronizing signal generating circuit 11
2 generates a horizontal synchronizing signal Hsync based on the output of the beam detector 111.

The horizontal synchronizing signal Hsync is input to the correction data creating circuit 11 and the image data is output to the modulator 12 in accordance with this timing.

The synchronous clock generation circuit 113 outputs the reference clock CK in synchronization with Hsync, and the modulator 12 operates with the clock SCK synchronized with this Hsync.

As described above, by using the present invention for the LBP, it is possible to easily realize a uniform scanning speed on the photosensitive drum.

(Modification) Although each of the above embodiments uses the resonance scanner, the present invention is not limited to this, and can be implemented by using an appropriate optical scanner. Further, as the modulation patterns of the first and second modulation circuits, a right growth pattern sequentially grown from the right end of the pixel and a left growth pattern sequentially grown from the left end of the pixel may be selectable according to the input data. Depending on the application, the way of changing the time width of the pixel on the scanning surface may be changed for each deflection of the optical scanner.

[0066]

As described above, according to the present invention,
The scanning speed of the optical scanner can be easily made uniform electrically.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of a first embodiment.

FIG. 2 is a diagram showing the configuration and operation principle of a resonant scanner.

FIG. 3 is a diagram showing a scan width at regular time intervals.

FIG. 4 is a diagram showing a relationship between a deflection angle of a scanner and a position on a scanning surface.

FIG. 5 is a diagram showing a relationship between a reference clock and pixels.

FIG. 6 is a timing chart showing the operation of the first embodiment.

FIG. 7 is a block diagram showing the configuration of a modulator.

FIG. 8 is a timing diagram showing an example of modulation.

FIG. 9 is a diagram showing a relationship between a light emission controllable time and a reference clock.

FIG. 10 is a block diagram showing the configuration of the second embodiment.

FIG. 11 is a block diagram showing the configuration of the third embodiment.

[Explanation of symbols]

11 Correction data creation circuit 12 Modulator 13 Exclusive OR circuit 14 Light source drive circuit 15 light source 18 scanner 19 image data

Claims (8)

[Claims] 1. An optical scanner, a light source of light scanned by the optical scanner, a correction data creation circuit for converting image data into correction data according to a deflection angle of the optical scanner, and the correction data creation circuit. The first modulation circuit that creates the first modulation signal by toggling the rising edge of the light source modulation signal according to the correction data, and the rising of the light source modulation signal according to the correction data created by the correction data creation circuit. A second modulation circuit that creates a second modulation signal whose down edge is toggled, and outputs an exclusive OR of the first and second modulation signals created by the first and second modulation circuits. An optical scanning device comprising: a logic circuit; and a light source drive circuit that drives the light source according to an output of the logic circuit. 2. The optical scanning device according to claim 1, wherein a time width of one pixel on a scanning surface of the optical scanner is set to a minimum resolution of the first and second modulation circuits according to a deflection angle of the optical scanner. An optical scanning device, characterized in that the light emission controllable time of the light source is always constant. 3. The optical scanning device according to claim 1, wherein the modulation patterns of the first and second modulation circuits are a right growth pattern that sequentially grows from the right end of the pixel and a left growth pattern that sequentially grows from the left end of the pixel. An optical scanning device characterized by being selectable according to input data. 4. The optical scanning device according to claim 1, wherein a method of changing a time width of a pixel on a scanning surface is changed for each deflection of the optical scanner. 5. An optical scanner, a light source for generating light scanned by the optical scanner, and a time for one pixel of image data for modulating the light source is controlled according to a deflection angle of the optical scanner, An optical scanning device comprising: a control unit that constantly controls the light emission controllable time width of the light source regardless of the time control of the one pixel. 6. A display device, wherein a display surface is scanned and displayed by the optical scanning device according to any one of claims 1 to 5. 7. A laser printer which scans a laser with the optical scanning device according to claim 1. 8. A scanning method in an optical scanning device comprising an optical scanner and a light source for generating light scanned by the optical scanner, the method comprising driving the optical scanner, and an image modulating the light source. Controlling the time of one pixel of the data according to the deflection angle of the optical scanner, and constantly controlling the light emission controllable time width of the light source regardless of the control of the time of the one pixel. A scanning method in an optical scanning device characterized by the above.