JP2006231702A - Multi-beam scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-beam scanner capable of obtaining high-quality images by making moire less conspicuous as well as preventing fluctuations in light quantity by overlapping high frequency current on an LD driving current, and a multi-beam scanner suppressed in the occurrence of a radiation noise. <P>SOLUTION: When image data are input in a resistance control part 84, the frequency of the input image data are counted. Scanning speed is read from a memory (not shown in Figure) and the lowest value of the frequency of the high-frequency current having a moire pitch of 0.3 mm or less is calculated using the read scanning speed. Then, the control amount of variable resistors 80A, 80B for reducing the frequency of the high-frequency current to a calculated lowest value is calculated, increasing or decreasing the resistance value of the variable resistors 80A, 80B based on the calculated control amount. Thereby, the high-frequency current of the calculated frequency is oscillated from respective high-frequency superimposed ICs 76A, 76B. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multi-beam scanning device, and more particularly to a multi-beam scanning device using a semiconductor laser that emits a plurality of light beams.

  A light beam emitted from a laser light source such as a laser diode (LD) is controlled in accordance with image data, and the photosensitive drum as an image carrier is rotated, and the light beam is passed through scanning means such as a polygon mirror. By repeating main scanning, an image forming apparatus that forms an electrostatic latent image on a photosensitive drum and records an image can obtain a high-quality image at a high speed. It is used.

  In the above-described image forming apparatus, in order to perform high-speed and high-density image formation, a semiconductor laser that emits a plurality of beams that are integrally formed and independently controlled (hereinafter referred to as “MSLD (multi-spot laser diode)”). ) Is used as a light source. The MSLD can be used in the scanning unit in the same way as a single beam LD. For this reason, a simple and high-performance scanning unit can be configured by using the MSLD.

  The MSLD is usually formed by juxtaposing a plurality of optical resonators having the same composition and shape on a single substrate. Therefore, the characteristics of the plurality of emission beams are extremely uniform, and the oscillation wavelengths are almost the same. Under such conditions, phase synchronization occurs due to optical coupling between the plurality of resonators due to leakage light between the optical resonators and return light from the outside of the optical resonator, so that a coherent state is easily achieved. When interference occurs between a plurality of resonators, a light intensity distribution is generated in the light emitted from the collimator lens. This distribution fluctuates if the phase of the emitted light is not stable.

  For example, as shown in FIG. 16A, in this laser emission unit, a collimator lens 106 is disposed on the light emission side of the MSLD 102 having the light emitting points 100A and 100B, and the light emission side of the collimator lens 106 is limited. An opening 114 is disposed. The limiting aperture 114 is provided for determining the beam spot diameter when the image is formed by the imaging optical system and for reducing variations in the beam spot diameter, so that the limiting aperture 114 acts equally on a plurality of beams. As described above, the collimator lens 106 is disposed at the back focus position on the optical axis.

  Since the limiting aperture 114 transmits only a part of the interference beam, the amount of light passing through the aperture varies when the phase of the light is unstable. That is, as shown in FIG. 16B, the beams emitted from the light emitting points 100A and 100B interfere with each other, and the profile after the interference changes. Therefore, the amount of light after passing through the restriction opening 114 is not constant.

  When such a laser emitting unit is used in a scanning type image forming apparatus, a light amount fluctuation may occur and appear as a visible defect on the image. For example, irregular white streaks occur when trying to form an image (for example, a full black image) in which a plurality of beams are continuously turned on. In addition, when a light amount variation occurs at the horizontal synchronization beam detection timing, a synchronization error occurs and jitter occurs in the image.

As a method for avoiding the problem of such light quantity fluctuation, it has been proposed to superimpose a high-frequency current on the LD drive current to oscillate a longitudinal single mode in multiple longitudinal modes.
Japanese Patent No. 2879487

  However, when a high-frequency current is superimposed on the LD drive current, there is a problem that moire occurs between the frequency of the image data and the superimposed high-frequency current, resulting in a reduction in image quality. Moreover, radiation noise increases by superimposing a high-frequency current, which may cause EMC problems. EMC (Electro-Magnetic Compatibility) is the compatibility of the electromagnetic environment, and is the ability to achieve both the performance that does not interfere with other devices (EMI) and the performance that does not interfere with other devices (EMS; immunity). That is.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to superimpose a high-frequency current on an LD drive current to prevent fluctuations in the amount of light and to produce a high-quality image without making the moire inconspicuous. It is to provide a multi-beam scanning device that can be obtained. Another object of the present invention is to provide a multi-beam scanning device in which the generation of radiation noise is suppressed.

  To achieve the above object, a multi-beam scanning device of the present invention scans a semiconductor laser having a plurality of independently controlled light emitting points and a plurality of light beams emitted from each of the plurality of light emitting points. A scanning unit; a driving unit that drives the semiconductor laser by applying a driving current to each of the plurality of light emitting points based on image data; and a high-frequency superimposing unit that superimposes a high-frequency current of a predetermined frequency on the driving current; The frequency of the high-frequency current superimposed on the drive current is calculated so as not to cause visible moire due to the beat generated between the frequency of the image data and the frequency of the high-frequency current, and the high-frequency current of the calculated frequency is Control means for controlling the high-frequency superimposing means so as to be superimposed on the drive current.

  In the multi-beam scanning device of the present invention, when the driving means applies a driving current to each of the plurality of light emitting points based on the image data to drive the semiconductor laser, the high frequency superimposing means adds a high frequency current having a predetermined frequency to the driving current. Is superimposed. The control means calculates the frequency of the high-frequency current superimposed on the drive current so that a visible moire is not generated by the beat generated between the frequency of the image data and the frequency of the high-frequency current, and the high-frequency current of the calculated frequency Is controlled so as to be superimposed on the drive current. This prevents fluctuations in the amount of light and makes it possible to obtain a high-quality image without making the moire inconspicuous.

  Moreover, generation of radiation noise can be suppressed by superimposing high-frequency currents having different frequencies on the drive current for each of a plurality of light emitting points.

  As described above, according to the present invention, it is possible to superimpose a high-frequency current on the LD drive current to prevent light amount fluctuations and to obtain a high-quality image without making the moire inconspicuous. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Schematic configuration of image forming apparatus)
FIG. 17 is a schematic diagram showing the overall configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 17, in the image forming apparatus 10, the charger 44, the multi-beam scanning device 12, the developing device 46, and the transfer device 50 are arranged around the photosensitive member 42 along the rotation direction B. An electrostatic latent image is formed on the photosensitive member 12 charged by the device 44 by exposure scanning with the multi-beam scanning device 12, and a toner is attached to the electrostatic latent image by the developing device 46 to be visualized. The toner image formed on the photoconductor 12 is transferred to the paper 48 conveyed by the transfer device 50 and fixed on the paper 48 by the fixing device 52. The toner remaining on the photoreceptor 42 is removed by the cleaning blade 54.

(Configuration of multi-beam scanning device)
FIG. 1 is a perspective view showing a configuration of a multi-beam scanning device according to the present embodiment. As shown in FIG. 1, the multi-beam scanning device 12 includes a multi-spot laser diode (hereinafter referred to as MSLD) 16 in which two light emitting points 18A and 18B are formed at a predetermined interval. The two light emitting points 18A and 18B of the MSLD 16 are independently controlled by the LD driving unit 90. For this reason, the light emitting points 18A and 18B may be referred to as LDs 18A and 18B.

  A collimator lens 22, a slit 24, expander lenses 26 and 28, and a folding mirror 30 are arranged in this order on the light beam emission side of the MSLD 16. Further, fθ lenses 34 and 36 and a polygon mirror 38 are arranged in this order on the light beam reflecting side of the folding mirror 30. The MSLD 16, the collimator lens 22, and the slit 24 are integrated as a multi-beam emission unit 14.

  The light beam emitted from the MSLD 16 is collimated by the collimator lens 22, a part of the light beam is transmitted through the restriction aperture 32 of the slit 24, is expanded by the expander lenses 26 and 28, and enters the folding mirror 30. Is folded in a predetermined direction. The light beam folded back by the folding mirror 30 enters the reflecting surface 38A of the polygon mirror 38 through the fθ lenses 34 and 36 having power only in the non-scanning direction and is reflected. The polygon mirror 38 rotates in the direction of the arrow at a predetermined speed with 38C as the rotation axis, and the incident beam is deflected by this rotation, and the photoconductor 42 is scanned in the direction of the arrow A.

  On the light beam reflecting side of the polygon mirror 38, fθ lenses 34 and 36 and a folding mirror 40 are arranged in this order. The scanning speed of the light beam reflected by the reflecting surface 38A of the polygon mirror 38 is corrected by the fθ lenses 34 and 36 so that the scanning speed on the photosensitive member 42 becomes constant, and enters the folding mirror 40 and enters the photosensitive member. It is folded in the direction of 42 and irradiated to the photoreceptor 42.

  A pickup mirror 56 is arranged between the fθ lenses 34 and 36 and the folding mirror 40 and in the light beam scanning start direction. The lens 58 and the SOS sensor are disposed on the light beam reflecting side of the pickup mirror 56. 60 are arranged in this order. Of the light beams reflected by the polygon mirror 38, the light beam at the position corresponding to the scanning start end is reflected by the pickup mirror 56 and enters the SOS sensor 60. The SOS sensor 60 can detect the scan start timing for each scan.

(Circuit configuration of LD drive unit)
FIG. 2 is a circuit diagram illustrating a circuit configuration of the LD driving unit 90.

  As shown in FIG. 2, the LD drive unit 90 includes an LD drive circuit (hereinafter referred to as “LD drive IC”) 70 that outputs an LD drive current to the LDs 18A and 18B based on input image data, an LD drive current. Are provided with a high-frequency oscillation circuit 72 for superimposing a high-frequency current thereon, and frequency conversion means 74 for converting the frequency and amplitude of the high-frequency wave oscillated from the high-frequency oscillation circuit 72 The LD drive IC 70 is controlled by a controller (not shown).

  LDs 18A and 18B and PDs 19A and 19B are connected to the LD drive IC 70. The LD 18A is turned on, the light emission amount is detected by the PD 19A, and the light emission amount of the LD 18A is controlled by the LD drive IC 70 based on the detected light amount. Similarly, the light emission amount of the LD 18B is controlled based on the light amount detected by the PD 19B. The high frequency oscillation circuit 72 includes high frequency superposition ICs 76A and 76B and capacitors 78A and 78B. The high frequency superposition IC 76A is connected to the LD 18A via the capacitor 78A, and the high frequency superposition IC 76B is connected to the LD 18B via the capacitor 78B. Yes.

  As the external resistor, a variable resistor 80A for changing the frequency of the superimposed high frequency and a variable resistor 82A for changing the amplitude of the superimposed high frequency are connected in parallel to the high frequency superimposing IC 76A. Yes. Similarly, a variable resistor 80B and a variable resistor 82B are connected in parallel to the high frequency superimposing IC 76B. Each of the variable resistors 80A, 82A, 80B, and 82B is connected to a resistance control unit 84 that changes the resistance value and controls the variable resistor. The resistance control unit 84 is connected to a control panel 86 for inputting instructions to the resistance control unit 84. These variable resistors 80A, 82A, 80B, 82B and the resistance control unit 84 constitute a frequency conversion means 74.

  In the LD drive unit 90 described above, each of the variable resistors 80A, 82A, 80B, and 82B is controlled to a predetermined resistance value by the resistance control unit 84 in accordance with the input image data. The control operation of the resistance control unit 84 will be described later. In addition, an operator can input an instruction from the control panel 86 to the resistance control unit 84. For example, since the appearance of the moire changes depending on the screen actually used, when the operator looks at the printed image and visually observes the moire, the control panel 86 instructs the frequency and amplitude to be changed.

  Thereby, a high-frequency current having a predetermined frequency and amplitude is oscillated from each of the high-frequency superposition ICs 76A and 76B. The LD drive current output from the LD drive IC 70 is superimposed on the high frequency current oscillated from the high frequency superposition IC 76A and applied to the LD 18A, and the high frequency current oscillated from the high frequency superposition IC 76B is superposed on the LD 18B. Applied. That is, in the LD driving unit 90, different high frequency currents can be superimposed on the LD driving currents for driving the LD 18A and the LD 18B, respectively.

  In the above description, the example in which the resistance value is varied to change the frequency and amplitude of the high-frequency current has been described. However, the frequency and amplitude of the high-frequency current can be changed by other methods depending on the high-frequency superposition IC and circuit to be used. .

  Furthermore, the frequency conversion means 74 preferably has a function of selecting high frequency superposition from the control panel 86, that is, turning on / off the high frequency. Defects due to interference can be seen by looking at the copy sample, and the defects do not necessarily occur because they differ depending on the ambient temperature and the image taken. Since high-frequency moire that is difficult to see when high-frequency is superimposed is generated, it is effective to select whether or not superimposition is necessary.

(Optimum frequency of high-frequency current)
FIG. 3 is a schematic diagram showing the configuration of an experimental apparatus for confirming the effect of high-frequency superposition.

  As shown in FIG. 3, the multi-beam scanning device 12 including the LDs 18 </ b> A and 18 </ b> B, the LD driver IC 91, the fθ lenses 34 and 36, the polygon mirror 38, and the folding mirror 40 is disposed on the substrate 21.

  In the vicinity of the LDs 18A and 18B, PDs 19A and 19B for detecting the amount of light emitted by the LDs are arranged, respectively. An oscilloscope 92 is connected to the PDs 19A and 19B. When the LDs 18A and 18B are turned on, a beam is simultaneously incident on the PD 19, and a current corresponding to the amount of received light is generated. The generated current waveform is measured by an oscilloscope 92.

  The LD driver IC 91 is mounted on the substrate 93 and connected to the LDs 18A and 18B and the controller 96, respectively. In response to an instruction from the controller 96, the LD driver IC 91 performs LD lighting for APC, LD lighting for SOS search, and LD lighting in the image scan range. A function generator 94 is electrically connected to the LDs 18A and 18B via a predetermined circuit mounted on the substrate 93. The function generator 94 functions as a high frequency oscillation circuit that superimposes a high frequency current on the LD drive current.

  FIG. 4 is a circuit diagram of a portion P surrounded by a dotted line in FIG. This circuit includes resistors 95A and 95B and capacitors 97A and 97B. The drive current of the LD 18A output from the LD driver IC 91 is applied to the LD 18A through the resistor 95A, and the drive current of the LD 18B passes through the resistor 95B. And applied to the LD 18B. At this time, the high-frequency current generated by the function generator 94 is superimposed on the drive current of the LD 18A via the capacitor 97A, and is also superimposed on the drive current of the LD 18B via the capacitor 97B. In this circuit configuration, the same high-frequency current is superimposed on the LD drive current for driving the LD 18A and LD 18B, respectively.

  FIG. 5 is a diagram showing a current waveform measured by the oscilloscope 92 when the LD is lit in the image scan range. Before superposition of the high-frequency current, as shown in FIG. 5A, the upper part of the waveform is deformed, and the light amount fluctuation occurs in one line. On the other hand, after superposing the high-frequency current, as shown in FIG. FIG. 6 is a diagram showing a current waveform measured by the oscilloscope 92 when the LD for SOS detection is turned on. In this case as well, before the high-frequency current is superimposed, the light amount fluctuation occurs as shown in FIG. 6A, but after the high-frequency current is superimposed, as shown in FIG. 6B. Does not show fluctuations in light intensity. From these results, it is understood that the fluctuation of the light emission amount of the LD 18A and LD 18B is prevented by superimposing the high frequency current on the LD drive current.

  The LD starts laser oscillation when the drive current exceeds the threshold current (Ith). Therefore, as shown in FIG. 7, when a high frequency current is superimposed on the LD drive current, it is necessary to give the LD drive current an amplitude that reaches the threshold current (Ith). The sine curve below the graph shows this.

  In the following, the moire pitch may be referred to as “beat cycle”, and the cycle of image data may be referred to as “pixel cycle”. Further, the period of image data is the modulation period of image data. Moire is generated between the frequency of the image data and the frequency of the high-frequency current when a high frequency modulated at a higher speed than the image data is superimposed. Moire is a kind of spatial frequency beat phenomenon that occurs when two regular patterns are combined.

  For example, FIG. 9A shows a beat that occurs between the frequency of the image data and the frequency of the high-frequency current. This beat cycle corresponds to the pitch of moire. When the frequency of the image data is 25.62 MHz and the frequency of the high frequency is 26.7 MHz, when the sine waves of both frequencies are added, a beat with a period of about 1 mm pitch is obtained. The one-dot chain line is the frequency of the image data, the broken line is the high frequency, and the solid line is the frequency of the image data plus the high frequency. FIG. 9B is an enlarged view of the horizontal axis range (one pixel period is equivalent to 42.3 μm).

  As shown in the following equations (1) and (2), the moire pitch can be obtained from the frequency of the image data to be written, the frequency of the applied high frequency, and the speed of the beam to be scanned.

Image data frequency-high frequency = moiré frequency (1)
Moire pitch = scanning speed x (1 / moire frequency) Equation (2)
More specifically, when the frequency of the image data is 25.62 MHz, the frequency of the applied high frequency is 26.7 MHz, and the scan speed is 1.084666 mm / μs, the pitch of the moire generated at the two frequencies is 1. .04mm.

  FIG. 10 shows a waveform obtained by multiplying the waveform when the pixel cycle is equivalent to 600 SPI and instantaneously writing by a sine wave having a high frequency of 26.7 MHz. The amplitude is offset so that the minimum value becomes zero. In this case, the light intensity changes to periodicity as in FIG. From FIG. 10, it can be seen that the pitch of moire generated at two frequencies is 1.06 mm.

  11 and 12 are diagrams showing beats when the frequency of the applied high-frequency current is multiplied by an integer. FIG. 12B is a partially enlarged view of the horizontal axis of FIG. On the other hand, FIG. 13 shows an example in which the beat cycle is reduced. The pitch of the generated moire is 0.17 mm. As described above, the pitch of the generated moire differs depending on the frequency of the applied high-frequency current.

  FIG. 14 is a graph in which the pixel frequency and the visibility of the lines (moire) are normalized. The vertical axis in FIG. 14 is contrast, and the horizontal axis is the number of lines per unit length. The contrast is expressed by (MAX amplitude−MIN amplitude) / average amplitude.

  The curve shown in FIG. 14 is a plot of the same streak for each line pitch (cycle / mm). A smaller value on the vertical axis means that a streak is visible even with a small change. As can be seen from the figure, the 1 mm pitch is the most visible and becomes difficult to see regardless of whether the pitch is large or small. At 3 cycles / mm, that is, 0.3 mm pitch, streaks are observed to the same extent as when changes 9 times larger than 1 mm pitch are shown.

  With the multi-beam scanning device shown in FIGS. 1 and 2 mounted on the image forming apparatus, an image was formed by superimposing a high frequency current on the LD drive current. It was found that even when the image quality of the actually formed image was confirmed, the stripes having a pitch of 0.3 mm could not be visually recognized. Therefore, moire can be made inconspicuous by setting the pitch of moire to 0.3 mm or less.

  In the experiment, commonly used 175-line, 200-line, and 300-line screens were used, and the density was changed in the range of 20% to 50% with respect to the solid black copy. As a result of image formation, it was confirmed that 0.3 mm or less was visually visible. Note that pixel intervals corresponding to screens of 175 lines, 200 lines, and 300 lines are 0.145 mm, 0.127 mm, and 0.08 mm. When there is a certain amount of pixel shift, the smaller the pixel interval, the greater the change with respect to the shift. Therefore, the 300-line screen is more susceptible to moire.

  In order to apply a high frequency current so that the moire pitch is 0.3 mm or less according to the pixel period, the following relational expressions (3) and (4) are satisfied from the above expressions (1) and (2). The frequency of the high frequency current may be calculated.

High frequency = image data frequency × n-moire frequency (n is a natural number) (3)
Moire pitch = scanning speed × (1 / moire frequency) ≦ 0.3 mm (4)
Note that since the moire pitch increases when (frequency of image data × n) is close to the applied frequency, the applied frequency (frequency of the high-frequency current) in the case of n = 1 is substantially calculated. .

(Superimposed current control operation)
FIG. 8 is a flowchart showing the control operation of the resistance control unit 84.

  In step 100, when image data is input to the resistance control unit 84, the frequency of the input image data is counted. Next, in step 102, the scanning speed is read out from a memory (not shown), and in step 104, the high frequency current that causes the moire pitch to be 0.3 mm or less from the relational expressions (3) and (4) using the read scanning speed. The lower limit value of the frequency is calculated.

  In the next step 106, the control amounts of the variable resistors 80A and 80B for setting the frequency of the high-frequency current to the calculated lower limit value are calculated. In step 108, the resistances of the variable resistors 80A and 80B are calculated based on the calculated control amount. The value is increased or decreased, and a high-frequency current having a frequency calculated from each of the high-frequency superposition ICs 76A and 76B is oscillated.

(Radiation noise reduction effect)
Further, EMC was measured when an image was formed by superimposing a high frequency current on the LD drive current. The measurement of EMC was performed according to CISPR which is an international standard. A high frequency current of 300 MHz was superimposed on one LD 18A, and a high frequency current of 320 MHz was applied to the other LD 18B.

  The measurement results are shown in FIG. As pointed out as “noise of additional device”, 300 MHz and 320 MHz frequency waveforms were measured as noise due to high frequency superposition. In other words, the radiation noise becomes a large value because they are added at the same frequency, whereas the radiation noise level caused by the high-frequency superposition is increased by superimposing different high-frequency currents on the LD drive currents for driving the two LDs. Can be reduced.

  If a high frequency current having the same frequency is applied, the radiation noise level at that frequency increases, and the EMC allowable value of the product may not be satisfied. Considering that moire occurs between the two frequencies and the pixel frequency, it is difficult to vary the frequency of the superimposed high-frequency current, but the frequency of the high-frequency current is set so that moire does not occur at both frequencies. It is desirable to set.

  As described above, in the present embodiment, the high-frequency current is superimposed on the LD drive current, thereby preventing fluctuations in the amount of light emitted from the two light emitting points of the MSLD. Further, since the high frequency current is applied so that the moire pitch is 0.3 mm or less according to the pixel period, a high-quality image in which the moire is not conspicuous can be obtained. Furthermore, by changing the frequency of the high frequency current applied for each light emitting point, it is possible to prevent radiation noise from being generated due to high frequency superposition.

It is a perspective view which shows the structure of the multi-beam scanning apparatus which concerns on this Embodiment. It is a circuit diagram which shows the circuit structure of LD drive part. It is the schematic which shows the structure of the experimental apparatus for confirming the effect of a high frequency superimposition. FIG. 4 is a circuit diagram of a portion surrounded by a dotted line in FIG. 3. (A) And (B) is a figure which shows the electric current waveform measured with the oscilloscope at the time of LD lighting in an image scanning range. (A) And (B) is a figure which shows the electric current waveform measured with the oscilloscope at the time of LD lighting for SOS detection. It is a figure which shows the IL characteristic of LD. It is a flowchart which shows the control operation of a resistance control part. (A) And (B) is a figure which shows an example of the beat generate | occur | produced between the period of a pixel, and the period of the applied high frequency. It is a figure which shows the other example of the beat generate | occur | produced between the period of a pixel, and the period of the high frequency to apply. It is a figure which shows the other example of the beat generate | occur | produced between the period of a pixel, and the period of the high frequency to apply. (A) And (B) is a figure which shows the other example of the beat generate | occur | produced between the period of a pixel, and the period of the applied high frequency. It is a figure which shows the other example of the beat generate | occur | produced between the period of a pixel, and the period of the high frequency to apply. It is the graph which normalized pixel frequency and the visibility of a line (moire). It is a figure which shows the measurement result of EMC at the time of image formation. (A) And (B) is a figure explaining the problem of the conventional laser emission unit. 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Multi-beam scanning apparatus 14 Multi-beam emission unit 16 MSLD
18A, 18B Light emitting point 21 Substrate 22 Collimator lens 24 Slit 26 Expander lens 30 Mirror 32 Restriction aperture 34 Lens 38 Polygon mirror 38A Reflecting surface 40 Mirror 42 Photoconductor 44 Charger 46 Developer 48 Paper 50 Transfer device 52 Fixing device 54 Cleaning Blade 56 Pickup mirror 58 Lens 60 Sensor 70 LD drive IC
72 High-frequency oscillation circuit 74 Frequency conversion means 76A, 76B High-frequency superposition IC
78A, 78B Capacitors 80A, 80B, 82A, 82B Variable resistor 84 Resistance control unit 86 Control panel 90 Drive unit 91 LD drive IC
92 Oscilloscope 93 Board 94 Function generator 95A, 95B Resistor 96 Controller 97A, 97B Capacitor 100A, 100B Light emitting point 106 Collimator lens 114 Limiting aperture

Claims (8)

A semiconductor laser with a plurality of independently controlled light emitting points;
Scanning means for scanning a plurality of light beams emitted from each of the plurality of light emitting points;
Driving means for driving the semiconductor laser by applying a driving current to each of the plurality of light emitting points based on image data;
High-frequency superimposing means for superimposing a high-frequency current of a predetermined frequency on the drive current;
The frequency of the high-frequency current superimposed on the drive current is calculated so as not to cause visible moire due to the beat generated between the frequency of the image data and the frequency of the high-frequency current, and the high-frequency current of the calculated frequency is Control means for controlling the high-frequency superimposing means so as to be superimposed on the drive current;
A multi-beam scanning device.   The multi-frequency according to claim 1, wherein the high-frequency superimposing unit includes a frequency adjusting unit that adjusts a frequency of the superimposed high-frequency current to a predetermined frequency, and superimposes the high-frequency current having a predetermined frequency adjusted by the frequency adjusting unit on the driving current. Beam scanning device.   3. The multi-beam scanning device according to claim 1, wherein the control unit calculates a frequency of a high-frequency current superimposed on the drive current so that a pitch of the moire is a predetermined value or less.   3. The multi-beam scanning apparatus according to claim 2, wherein the frequency adjusting means is outside a scanning unit including the semiconductor laser and the scanning means and has an ON / OFF function.   5. The multi-beam scanning device according to claim 1, wherein the high-frequency superimposing unit superimposes a high-frequency current having a different frequency for each light emitting point on a driving current applied to each of the plurality of light emitting points.   6. The high-frequency superimposing unit further includes an amplitude adjusting unit that adjusts an amplitude of a superimposed high-frequency current to a predetermined amplitude, and superimposes a high-frequency current having a predetermined amplitude adjusted by the amplitude adjusting unit on the driving current. Multi-beam scanning device.   The multi-beam scanning device according to claim 1, wherein the control unit calculates a frequency of a high-frequency current superimposed on the driving current so that a pitch of the moire is 0.3 mm or less. The multi-beam scanning device according to claim 1, wherein the control unit calculates a frequency of a high-frequency current superimposed on the drive current so as to satisfy the following relational expression.
High frequency current frequency = Image data frequency x n-Moire pitch (n is a natural number)
Moire pitch = scanning speed × (1 / moire frequency) ≦ 0.3 mm

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