JP5114178B2 - Method for adjusting optical scanning device - Google Patents

Description

  The present invention relates to an optical scanning apparatus and a color image forming apparatus having a vibrating mirror used in a laser raster writing optical system.

  Conventionally, it is necessary to rotate a polygon scanner at a high speed of 25000 rpm or more and with high accuracy in order to realize high-speed printing and high image quality of a color machine. On the other hand, in order to improve the image quality by reducing the diameter of the laser beam, the inscribed circle radius of the polygon mirror used in the polygon scanner and the length in the main scanning direction are relatively large, and the load of the polygon scanner is increasing. .

  Due to this high load, the power consumption of the polygon scanner increases, and the heat generation adversely affects the optical elements such as the scanning lens. Specifically, the temperature rise of the scanning lens closest to the polygon scanner. Heat generated from the polygon scanner is transferred to the optical housing, or the temperature of the scanning lens rises due to radiation. Actually, the temperature of the scanning lens is not raised uniformly, but the temperature distribution is increased especially in the main scanning direction, which is the longitudinal direction, due to the distance from the heat source (polygon scanner), the difference in the thermal expansion coefficient of each material, and the influence of airflow. Have.

  If there is a temperature distribution in the main scanning direction, particularly the shape accuracy and refractive index of the scanning lens change, the spot position of the laser beam fluctuates, and the image quality deteriorates. This problem is particularly noticeable in the case of plastics having a large coefficient of thermal expansion.

  In a color machine, since laser beams corresponding to each color (yellow, magenta, cyan, black) are scanned, temperature deviation between optical scanning devices corresponding to the respective colors becomes a problem in addition to the above problem. The temperature deviation causes a shift in the relative positional relationship between the beam spots corresponding to each color, resulting in an image color shift.

  Further, the temperature rise due to heat generation of the high-load polygon mirror induces a fine movement of the rotating body component (particularly, the polygon mirror having a large mass ratio), changes the rotating body balance, and generates vibration. Even if the parts of the rotating body (polygon mirror, flange to which the rotor magnet is fixed, shaft) have different or coincide with each other, they must be strictly controlled and inspected, such as part tolerance and fixing method. A slight movement (change in balance of the rotating body) occurred during high-temperature and high-speed rotation, which in turn resulted in increased vibration. The vibration is transmitted and amplified to an optical element (for example, a folding mirror) in the optical scanning device to generate banding, which causes image deterioration and noise.

  In order to solve the above problems, a vibrating mirror using a resonance phenomenon has been studied as a substitute for a polygon mirror deflector (see, for example, Patent Documents 1 to 4). This method has low power consumption, and has the effect of reducing the temperature rise of the scanning lens used in the optical scanning device and the temperature deviation and vibration for each optical scanning device of the color machine.

  However, the vibrating mirror uses the resonance phenomenon of the torsion beam to increase the vibration amplitude to a practical angle, so the size of the movable mirror that becomes the load is very small, compared to the conventional polygon mirror. The area of about 1/10 to 1/5 is an obstacle to the reduction of the beam spot diameter.

  Furthermore, there is a problem that the mounting accuracy of the movable mirror portion is poor with respect to a reference surface on which a scanning imaging lens such as an optical housing is mounted. In conventional polygon mirrors, machined members and bearings are integrated, so machining precision can be improved. However, vibrating mirrors are mainly separate from the movable mirror part created by the semiconductor process. This is because it is necessary to fix to the bracket or the like, and the mounting posture accuracy of the movable mirror portion deteriorates at that time.

In an optical scanning device using such a vibrating mirror, optical characteristics equivalent to those of a polygon mirror (desired laser beam diameter on the surface to be scanned. Desired laser beam necessary for achieving high image quality of 600 dpi or more. It is difficult to ensure the diameter and the main scanning / sub-scanning of 80 μm or less: 1 / e ^{2 of the} peak light quantity. Because the area of the vibrating mirror is small and the mounting posture accuracy is poor, the laser beam from the light source is vignetted to the movable mirror, and the center of amplitude of the vibrating mirror does not match the scanning lens, which is required in optical design. This is because the accuracy is not reached.

JP-A-2005-202321 JP 2007-058205 A JP 2007-171854 A JP 2007-233235 A

The present invention has been made in view of the above-described problems in the prior art. The power consumption is small, the temperature rise of the scanning lens used in the optical scanning device, and the temperature deviation and vibration for each optical scanning device of the color machine. It is an object of the present invention to provide an adjustment method of an optical scanning device that achieves a small-diameter beam spot and enables high image quality while having the original effect of a vibrating mirror that reduces the image quality.

The present invention provided to solve the above problems is as follows.
[1] Light source means (light source 10) that emits a laser beam, a vibrating mirror (vibrating mirror 11) that deflects and scans the laser beam from the light source means, and a laser beam that is deflected and scanned toward the surface to be scanned. A scanning imaging optical system (lenses 14 and 17 and mirror 16) that illuminates, and two light receiving elements (not shown) that receive the laser beam provided at positions near both ends of the scanning region of the laser beam with the scanning center in between. the light receiving element PD1, PD2) and, in the adjustment method of the optical scanning apparatus including the (optical scanning device 5), the two first time intervals of the output pulses of the light receiving element and the second light receiving element of the light receiving element time interval and (time interval a, B) of the output pulse of match so on, and the output pulse width and (pulse width PA of the first output pulse width and the second light receiving element of the light receiving element, PB) The adjustment method of the optical scanning device (FIGS. 1, 4 and 4) is characterized in that the mounting posture (posture of the bracket 471) in the rotational direction about the swing axis of the vibrating mirror is adjusted so that the is constant. FIG. 6).
[2] Control means for making the amplitude of the amplitude waveform of the oscillating mirror constant based on output signals from the two light receiving elements, and the amplitude of the amplitude waveform of the oscillating mirror is controlled to be constant by the control means. The adjustment method of the optical scanning device according to [1], wherein the mounting posture in the rotation direction about the vibrating mirror swinging axis is adjusted in a state where the vibration mirror is pivoted .
[3] The above-mentioned [1] or [1], further comprising arithmetic means for measuring a time interval and / or output pulse width of each output pulse in the output signals of the two light receiving elements a plurality of times and averaging the measured time. The method for adjusting an optical scanning device according to [2] .
[4] After adjusting the mounting posture in the rotational direction around the swing axis of the vibrating mirror based on the output signal from the light receiving element, the scanning lens position of the scanning imaging optical system (lens 14) is adjusted. The method of adjusting an optical scanning device according to any one of [1] to [3], wherein the adjustment is performed by moving in the main scanning direction (FIG. 1).
[5] As the light source means, a plurality of light source devices (light source devices 10Y, 10M, 10C, and 10K) are provided, and each laser beam emitted from the plurality of light source devices is a single oscillating mirror (oscillating mirror 11). ), A plurality of scanned surfaces are deflected and scanned, and the two light receiving elements (light receiving elements PD1 and PD2) are connected to one of the plurality of scanned surfaces (photosensitive member 3K). The method for adjusting an optical scanning device according to any one of [1] to [4], wherein the optical scanning device is disposed only in an image optical system (lenses 14, 17K, mirror 16K) (FIG. 5). 1).
[6] The adjustment of the optical scanning device according to any one of [1] to [5] , wherein the laser beam that scans the light receiving element is a laser beam that has passed through the scanning imaging optical system. Method (Figure 1 ).

According to the present invention, inherent effect (low power consumption, low noise) of vibration mirror while having, or high quality 600 dpi, adjustment of the optical scanning device to achieve a beam spot diameter of the small diameter corresponding high definition A method can be provided.
Further, according to the present invention, it is possible to eliminate the influence of jitter on the output signal of the light receiving element, substantially improves the accuracy of adjustment, more stable small-diameter beam spot diameter secured possible optical scanning A method for adjusting the apparatus can be provided.
Further, according to the present invention, also to reduce the effect against electrical noise, such as generated in collision voluntarily, substantially improved the adjustment precision, capable of more stable small-diameter beam spot diameter secured An adjustment method of the optical scanning device can be provided.
Further, according to the present invention, it is possible to widen the adjustment range can substantially provide a stable method for adjusting the diameter of the beam spot diameter ensure capable optical scanning device with higher accuracy.
Further, according to the present invention, miniaturization of instrumentation置全body, adjustment method Ru can provide an optical scanning device which realizes reduction in power consumption (energy saving).

The configuration of the optical scanning device according to the present invention will be described below.
FIG. 1 is a perspective view showing a configuration example of an optical scanning device according to the present invention.
In this configuration example, the optical scanning device 5 appropriately adds four photosensitive members 3Y, 3M, 3C, and 3K (hereinafter, subscripts Y, M, C, and K to the reference numerals) in the image forming apparatus shown in FIG. , Y: yellow, M: magenta, C: cyan, and K: black) are arranged above the image forming units arranged in parallel. The optical scanning device 5 includes four light sources corresponding to each color, light deflecting means (vibrating mirror 11) for deflecting and scanning a laser beam from each light source, and four photosensitive drums 3Y, 3M, 3C, and 3K. A scanning imaging optical system that leads to the surface to be scanned is provided, and these components are housed in an optical housing (not shown).

  The light source 10 which is a light source means has four “light source devices” each composed of a semiconductor laser and a coupling lens so as to correspond to each color (10Y, 10M, 10C, 10K). Each of the four semiconductor lasers in the light source emits a light beam for writing each color component image of yellow, magenta, cyan, and black. The light beam emitted from each semiconductor laser is converted into a light beam form (parallel light beam or weak divergent or converging light beam) suitable for the subsequent optical system by the coupling lens, and the sub-circular lens 12 passes through the folding mirror 13 to obtain a secondary light beam. The beam is focused in the scanning direction and formed as a line image in the vicinity of the deflection reflection surface of the oscillating mirror 11 serving as a deflection scanning means in the main scanning direction.

  A laser transmitting member (not shown) is disposed on the incident side with respect to the oscillating mirror 11, and each light beam from the light source 10 side enters the oscillating mirror 11 through the laser transmitting member. Next, the deflected light beams for the four colors deflected in the same direction by the swing of the vibration mirror 11 are transmitted through the first lens 14 constituting the scanning lens group of the scanning imaging optical system.

  The light beam for writing the black component image (for example, the position of the upper end of the lens) is reflected by the mirror 16K, passes through the second lens 17K constituting the scanning lens group, and forms a drum-like photoconductive material that forms the actual state of the scanned surface. Is condensed as a light spot on the photoconductor 3K, and the surface of the photoconductor 3K is optically scanned in the direction of the arrow. The materials of the scanning lens groups 14 and 17K are made of a plastic material with an aspherical shape that is easy and low in cost, and specifically, a synthetic material mainly composed of polycarbonate or polycarbonate having low water absorption, high transmittance, and excellent moldability. Resins are preferred.

  Similarly to the above, the light beams for writing the respective color component images of yellow, magenta, and cyan are reflected by the mirror, transmitted through the lens, formed as a light spot on the photosensitive member, and scanned in the same arrow direction for each color. . By this optical scanning, an electrostatic latent image of a color component image corresponding to each photoconductor is formed. The optical elements corresponding to the colors other than black are not numbered, but the parts with “K”, which is an abbreviation for black, are optically the same for yellow, magenta, and cyan. Placed in position.

  These electrostatic latent images are visualized with a corresponding color toner by a developing device and transferred onto the intermediate transfer belt 2. At the time of transfer, the color toner images are superimposed on each other to form a color image. This color image is transferred and fixed on a sheet-like recording medium. The intermediate transfer belt 2 after the color image transfer is cleaned by a cleaning device.

  As described above, the optical scanning device 5 in FIG. 1 uses the oscillating mirror 11 of the deflection scanning unit to cause the light beams emitted from a plurality of light source devices corresponding to two or more color component images constituting a color image to be the same. The lens 14 that deflects and scans in the direction and transmits each deflected light beam through the first lens 14 of the scanning and imaging optical system in common for each color, and the lens provided in each scanning and imaging means (writes a black component image) In the case of a scanning imaging optical system, a lens 17K) is used to individually focus light toward the surface to be scanned corresponding to each color component image for optical scanning, and has four scanning imaging means corresponding to each color component. .

  Here, each color laser beam incident on the reflecting surface of the vibrating mirror 11 has a desired angle with respect to the sub-scanning direction (so-called oblique incidence optical system). Specifically, the maximum color laser beam is set to be 5 ° or less. When the incident angle is 5 ° or more, the scanning line is greatly bent on the surface to be scanned, and the diameter of the laser beam is increased, resulting in image deterioration. On the other hand, when the laser beams of each color are not incident obliquely and are incident horizontally (oblique incidence angle 0 °), a large width in the sub-scanning direction of the reflecting surface is required, which increases the load on the vibrating mirror and causes the vibration frequency. There is a problem that can not be high.

Next, the vibrating mirror 11 will be described in detail.
FIG. 2 is a detailed view of the vibrating mirror 11 as an embodiment, and FIG. 3 is an exploded perspective view thereof. FIG. 4 shows a vibrating mirror unit 470 that is mounted on an optical housing.
The oscillating mirror 11 includes a movable portion 441 that forms a mirror surface on the surface and forms a vibrator, a torsion beam 442 that supports the rotating portion, and a frame 446 that forms a support, and a Si substrate is cut out by etching. Is formed.

  As an example, the wafer is manufactured using a wafer in which two substrates of 60 μm and 140 μm called SOI substrates are bonded in advance with an oxide film interposed therebetween. First, a torsion beam 442, a vibration plate 443 on which a planar coil is formed, a reinforcing beam 444 forming a skeleton of a movable part, a frame 447, and the like by a dry process using plasma etching from the surface side of a 140 μm substrate (second substrate) 461 The remaining part is left to the oxide film, and then the movable mirror part 441 and the frame 447 are left by anisotropic etching such as KOH from the surface side of the 60 μm substrate (first substrate) 462. The other portion is penetrated to the oxide film, and finally, the oxide film around the movable portion is removed and separated to form the structure of the vibrating mirror (FIGS. 2A and 3). Here, the torsion beam 442 and the reinforcing beam 444 had a width of 40 to 60 μm.

  The inertia moment I of the vibrator is preferably small in order to increase the deflection angle. On the other hand, since the mirror surface is deformed by the inertial force, the embodiment has a structure in which the movable portion is thinned. Further, an aluminum thin film is vapor-deposited on the surface side of the 60 μm substrate 462 to form a reflection surface. On the surface side of the 140 μm substrate 461, a terminal 464 wired with a coil pattern 463 and a torsion beam with a copper thin film, and for trimming The patch 465 is formed (FIGS. 2A and 2B). Naturally, a configuration may be adopted in which a thin film permanent magnet is provided on the diaphragm 443 side and a planar coil is formed on the frame 447 side.

  On the mounting substrate 448, a frame-shaped pedestal 466 for mounting the frame 447 and a yoke 449 formed so as to surround the movable mirror portion 441 are disposed. And a pair of permanent magnets 450 that generate a magnetic field in a direction perpendicular to the rotation axis are joined (FIG. 3).

  The oscillating mirror 11 is mounted on the base 466 with the mirror surface facing up, and a Lorentz force is generated on each side parallel to the rotation axis of the coil pattern 463 by passing an electric current between the terminals 464, and the torsion beam 442 is twisted. When a rotational torque T for rotating the movable mirror unit 441 is generated and the current is cut off, the movable mirror unit 441 returns to the horizontal state by the return force of the torsion beam 442.

  Therefore, by alternately switching the direction of the current flowing through the coil pattern 463, the movable mirror unit 441 can be reciprocally oscillated. When the current switching period is made close to the natural frequency of the primary vibration mode of the structure constituting the oscillating mirror 11 with the torsion beam 442 as the rotation axis, the so-called resonance frequency f0, the amplitude is excited and a large fluctuation occurs. You can get a corner.

  The vibration mirror unit 470 shown in FIG. 4 includes a vibration mirror 11, a bracket 471 having an electrode portion 473 for fixing the posture of the vibration mirror 11 and electrically connecting to the electrode portion 455 of the vibration mirror 11, and the bracket 471. And a substrate 472 mounted on an optical housing (not shown). Note that the substrate 472 includes an electrical connector 474. Therefore, the mounting posture of the vibrating mirror 11 is adjusted by adjusting the posture (direction, inclination, etc.) of the bracket 471.

  The vibration mirror 11 has a movable part (movable mirror part 441) whose mass and inertia are very small compared to a conventional polygon mirror, so the drive part is also miniaturized, and the efficiency of the magnetic circuit is increased, and the power consumption is kept low. (The power consumption ratio of the polygon mirror is 1/10 or less). As a result, heat generation is reduced, and the temperature rise of the optical element and housing of the writing optical system can be substantially eliminated. In particular, the resin scanning lens has no local temperature distribution, and color The occurrence of color misregistration can be suppressed without changing the scanning position of the laser beam during image formation.

  Furthermore, because the mass and inertia of the movable part are small, there is little vibration (vibration due to mass imbalance) that is transmitted to the outside even when swinging (the vibration acceleration ratio of the polygon mirror is 1/100 or less). The vibration transmitted to the optical element is substantially eliminated, and the occurrence of banding (roughness variation in the sub-scanning direction) during image formation due to the vibration of the folding mirror can be eliminated.

  By the way, in the oscillating mirror 11, there is a problem that the size of the movable mirror unit 441 is very small, and the mounting accuracy of the movable mirror unit 441 (the axis in the sub-scanning direction and the oscillation (rotation) axis of the movable mirror) is poor. In the present invention, the problem is solved by adjusting the mounting posture.

  First, as shown in FIG. 5, the main part corresponding to one photoconductor of the color image forming optical scanning device shown in FIG. 1 is considered. The laser beam 60 deflected and scanned by the oscillating mirror 11 is incident on the light receiving elements PD1 and PD2 disposed within the maximum swaying angle by the scanning position of the oscillating mirror 11 at the maximum swaying angle 60a, and an output signal is generated. The position where the laser beam is scanned at the timing is 60b, and the position where the edge of the image area on the photosensitive member 3 is scanned is 60c.

  FIG. 6A shows the vibration mirror amplitude (the magnitude of the fluctuation angle of the vibration mirror) with respect to time in the configuration of FIG. Since the oscillating mirror uses a resonance phenomenon to generate a large amplitude, the amplitude of the oscillating mirror draws a sinusoidal locus with respect to time, and the scanning speed of the laser beam deflected and scanned is not constant but varies depending on the scanning position. (When there is no scanning lens). The scanning lenses 14 and 17 have f · arcsin characteristics so as to be constant even at such a scanning speed.

Here, the posture adjustment of the vibrating mirror unit is specifically performed by the following method.
First, a laser beam is emitted from the light source 10K (only one light source among the multi-beam light sources is turned on), and the vibrating mirror 11 is driven to scan the light receiving elements PD1 and PD2. Output signals as shown in the outputs of the light receiving elements PD1 and PD2 in FIGS. 6B and 6C are obtained by the scanned laser beam. The time interval (time interval) A (A ₁ , A ₂ ,... A _{n in the} figure) of two output pulses in the output signal of the light receiving element PD1 and the time of two output pulses in the output signal of the light receiving element PD2 The bracket 471 of the oscillating mirror unit 470 in FIG. 4 is rotated in the rotational direction around the oscillation axis of the movable mirror 441 so that the interval B (B ₁ ,... B _n in the figure) coincides. Adjust posture. The laser beams that scan the light receiving elements PD1 and PD2 are imaged through the scanning lenses 14 and 17K constituting the scanning imaging optical system.

In the state in which the posture is adjusted, if the center of the scanning lens in the main scanning direction and the amplitude center of the vibrating mirror do not coincide with each other, the laser beam diameter at the light receiving elements PD1 and PD2 is increased and the diameter is increased. The size of is different. At this time, the pulse width PA ₁₁ of the first pulse (or the pulse width PA ₁₂ of the second pulse) in the output signal of the light receiving element PD1 in FIGS. 6B and 6C and the light receiving element PD2 The pulse width PB ₁₁ of the first pulse in the output signal (or the pulse width PB ₁₂ of the second pulse) is different. Therefore, the posture adjustment of the bracket 471 of the vibrating mirror unit 470 is performed so that the pulse width PA ₁₁ and the pulse width PB ₁₁ are constant.

  Further, when the laser beam scanning speed and the light amount are constant, the pulse width fluctuates due to a change in the laser beam diameter (FIG. 7). FIG. 7 shows an output waveform (light receiving element output waveform) and a comparator output waveform of a light receiving unit (described later) when the laser beam is scanned on the light receiving element PD1 (or PD2). A solid line 70 of the output waveform of the light receiving unit in FIG. 7 indicates a desired laser beam diameter, and a pulse width 80 is output. On the other hand, when the beam diameter is thick, the change in the amount of light per time when scanning the light receiving portion becomes gentle, so that a gentle rise like the dotted line 71 is shown and the output pulse width 81 is also enlarged. Therefore, if the relationship between the laser beam diameter and the pulse width of the output signal of the light receiving element is grasped in advance, the laser beam diameter can be specified by measuring the pulse width. In this case, it is preferable that the scanning speed and the amount of light that are premised on the conditions for actual use of the optical scanning device are unified.

As described above, the pulse widths PA ₁₁ and PA ₁₂ that are the outputs of the light receiving element PD1 have a correlation with the laser beam diameter. In order to maintain the correlation, at least the vibrating mirror 11 has an amplitude waveform. Drive control for making the amplitude constant (and light amount control for making the light amount constant) is performed so that the scanning speed when scanning the light receiving element PD1 is made constant (0.02% or less in scanning jitter). When the vibrating mirror 11 is not controlled, the scanning speed for scanning the light receiving element PD1 is not constant (or when the amount of light is not constant), and the output signal of the light receiving element PD1 is affected. As a result, the pulse width PA ₁₁ and PA ₁₂ fluctuate, and the correlation with the laser beam diameter collapses. The same applies to the light receiving element PD2. Here, after performing drive control (described later) that makes the amplitude waveform of the oscillating mirror 11 constant, the posture adjustment of the bracket 471 of the oscillating mirror unit 470 may be performed.

  When the matching of the output pulse widths of the two light receiving elements PD1 and PD2 does not fall within a desired level by adjusting the posture of the vibrating mirror unit 471, or when it is desired to reduce the beam diameter to the design limit with high accuracy of matching ( That is, when it is desired to substantially widen the adjustment range rather than adjusting only the vibrating mirror 11, the scanning lens 14 is moved in the main scanning direction (the arrow direction shown on the scanning lens 14 shown in FIG. 1) for adjustment. Is preferred. This is because the scanning lens 14 dominates the f · arcsin characteristic.

  Since the scanning speed of the oscillating mirror 11 changes sinusoidally, the scanning lens has f · arcsin characteristics so that the scanning speed is constant, but the amplitude states of the scanning lens 14 and the oscillating mirror 11 are designed. If it is not arranged at the street position, the effectiveness of the f · arcsin characteristic is deteriorated, and the scanning speed and the laser beam diameter are different from the design desired values.

  On the other hand, when the laser beam emitted from the light source 10K enters the movable mirror portion 441 of the vibrating mirror 11 through the optical element, vignetting of the laser beam may occur depending on the position of the light source 10K. This is a problem caused by the small area of the movable mirror portion 441 (in this case, the main scanning direction). In this case, after the posture adjustment of the vibrating mirror 11 has already been completed, the light source 10K is rotated around the sub scanning direction. Vignetting can be eliminated by adjusting the posture (see the arrow for the light source 10K in FIG. 1). When vignetting occurs, a change appears in the laser beam diameter (the laser beam diameter becomes thicker), so that it can be checked by measuring the pulse width as described above.

  The time intervals (A and B in FIGS. 6B and 6C) and the output pulse widths (PA and PB in FIGS. 6B and 6C) of the output signals of the light receiving elements PD1 and PD2 described above. ), And an averaging process is performed by an arithmetic means that performs an averaging process. Based on the data (time intervals A and B, output pulse widths PA and PB) after the averaging process, the attitude of the vibrating mirror 11 is determined. Adjustments should be made. As a result, the output signals from the light receiving elements PD1 and PD2 may suddenly cause variations in scanning speed due to jitter and electrical noise, so that the influence is reduced and adjustment accuracy is substantially improved. Is possible.

  Next, in order to make use of the merits of the vibrating mirror described above, the following control is essential, and a suitable example will be shown. In other words, even if the scanning lenses 14 and 17 having the characteristics as described above (f · arcsin characteristics) are used, fluctuation fluctuations of the oscillation mirror 11 as shown in FIG. 8 occur. Therefore, each control is performed so as to suppress the fluctuation. For example, when the frequency (drive signal) of the oscillating mirror 11 is constant, the amplitude waveform of the oscillating mirror 11 should be an ideal amplitude waveform (sine waveform). , (C), the phenomenon of an actual amplitude waveform deviating from the ideal amplitude waveform occurs, both of which cause the laser beam scanning position fluctuations and cause image degradation.

FIG. 8A shows amplitude fluctuation. When the amplitude is larger than the target (the same is true when the amplitude is smaller), the amplitude is corrected to the direction indicated by the arrow to obtain the amplitude of the ideal amplitude waveform. 6 (b) and (c), the time interval A (A ₁ , A ₂ ,... A _{n in the} figure) obtained from the two output signals of the light receiving element PD1 and the two outputs of the light receiving element PD2 Control is performed so that the calculated value of the time interval B (B ₁ ,... B _{n in the} figure) obtained from the signal is constant. Specifically, an average value of (A ₁ + B ₁ ) / 2, (A ₂ + B ₂ ) / 2,... (A _n + B _n ) / 2 is calculated and averaged a plurality of times (n times The average value is averaged), and control is performed so that the control target value is uniquely determined from the resonance frequency.

FIG. 8B shows the positional relationship between the amplitude center of the amplitude waveform of the oscillating mirror 11 and the center of the scanning region, and the actual amplitude waveform has an offset with respect to the center of the scanning region (ideal amplitude waveform). It is an example showing a state. In order to eliminate the offset (corrected in the direction shown by the arrow), the time interval A of the light receiving element PD1 output as shown in FIGS. 6B and 6C (A ₁ , A ₂ ,. .. Control is performed so that the calculated values of A _n ) and the time interval B (B ₁ ,... B _{n in the} figure) of the light receiving element PD2 output are constant. Specifically, the difference of A ₁ -B ₁ , A ₂ -B ₂ ,... A _n -B _n is calculated, averaged several times (n times of differences are averaged), and the target value is calculated. Control is performed so that it becomes zero.

  FIG. 8C shows the phase fluctuation of the amplitude waveform of the oscillating mirror 11, and even if phase fluctuation (phase shift in the time axis direction) like the actual amplitude waveform shown in FIG. The reference phase clock for generating a signal for driving the vibrating mirror 11 as shown in FIGS. 6B and 6D and the light receiving element PD1 Control is performed so that the output time interval C (phase deviation) is constant. Specifically, averaging is performed a plurality of times at time intervals C1, C2,..., And control is performed so that the target value becomes zero. At this time, the output of the light receiving element PD1 that counts the time interval is preferably the output (the rear end side of A) that is the timing immediately before entering the image forming area of the two outputs. The reason for matching the phase is that the output immediately before the image writing start side (the rear end side of A) has higher accuracy (when the output at the front end side of the time interval A is used, the output within the time of A is used. Phase accuracy at the time of image formation decreases due to phase fluctuation).

  Here, since the amplitude or offset in FIGS. 8A and 8B is a phenomenon different from the ideal scanning speed, it is a scanning position shift in the main scanning direction. For example, image deterioration such as jitter in the main scanning direction (vertical line fluctuation) and main scanning magnification error is caused, which is a common problem not only for color images but also for monochrome images. On the other hand, the phase fluctuation of FIG. 8C is a particular problem when forming a color image. As shown in FIG. 1, a single oscillating mirror 11 scans a laser beam emitted from a light source of each color on a photoconductor for each color according to an image signal. Since the deflection scanning position of the laser beam changes, the sub-scanning position changes on the image (on the intermediate transfer belt), and color misregistration and color unevenness occur.

FIG. 9 is a block diagram of a control system (control means) for realizing amplitude, offset, and phase control in the optical scanning device 5 of the present invention.
The time intervals A and B are measured by counters 111 and 112, respectively, for signals output by laser beams that are deflected and scanned and scan the light receiving elements PD1 and PD2. Next, the arithmetic unit 113 compares the average of (A + B) / 2 with the target amplitude, and similarly compares the average of the difference of AB with the target offset (zero in this embodiment), and the result is the controller. To 114. The reason why each average is taken (the reason why the averaging process is performed) is to prevent the control from being performed by erroneous information such as when sudden electrical noise is mixed. In addition, the frequency | count of averaging is performed in the range of 2-10 times. This is because if it is 10 times or more, the correction timing is delayed and the control deviation is increased.

  The controller 114 calculates the correction amount of the amplitude and offset according to the comparison result, and amplifies the corrected sine wave drive signal by the drive circuit (amplifier) 110 of the oscillating mirror 11 to drive control the oscillating mirror 11 To do. The control system loop is an amplitude and offset control loop.

  Next, the phase control loop outputs the drive signal of the oscillating mirror 11 generated from the reference phase clock (reference clock) in the control state in which the amplitude and offset control work normally and each falls within a desired range with respect to the target value. The phase control loop is executed so as to cancel the phase fluctuation of the amplitude waveform of the actual oscillating mirror with respect to the ideal amplitude waveform of the deflection angle of the oscillating mirror 11 based thereon. In other words, phase control is highly accurate control over amplitude and offset control, so if all controls are executed at the same time, they will interfere with each other and drive signal fluctuations will increase and all will converge within the control target value range. Takes time. Therefore, it is possible to shorten the time until convergence within the control range by giving priority to vibration and offset control as coarse adjustment and then performing phase control as fine adjustment.

  As phase control, the phase deviation between the output signal from the light receiving element PD1 and the reference phase clock (time interval C in FIG. 6D) is detected by the phase comparator 115 and measured by the counter 116. The measurement result is converted to a DC voltage corresponding to the phase deviation by an LPF (Low Pass Filter) 117 and an integrator 118, and the phase deviation between the reference phase clock (reference clock) and the output signal of the light receiving element PD1 is determined according to the voltage amount. Control to change the phase (so-called PLL (Phase Locked Loop) control) is performed (so that the time interval C) is constant). Next, the generation of the sine wave signal with respect to the phase change generates a sine wave signal having an optimum phase according to the increment of the phase change amount (resolution) prepared in advance. As a result, the drive signal of the oscillating mirror 11 is corrected, and control is performed to cancel the phase fluctuation of the actual amplitude waveform of the oscillating mirror 11 with respect to the ideal amplitude waveform of the oscillating angle of the oscillating mirror 11.

  Note that the generation resolution of the sine wave signal corresponding to the phase control needs to have a high accuracy exceeding the allowable range of control, but the higher the accuracy, the higher the cost because a memory is required. Therefore, the generation resolution of the sine wave signal is set to be 50 μm or less which is visually recognized as a color shift in the sub-scanning direction.

  FIG. 10 shows a relationship with a laser beam scanned using the light receiving element PD1 as an example. The light receiving element PD1 is disposed at a position that is optically equivalent (a beam diameter and a scanning speed) to a laser beam scanned on the surface of the photosensitive member as shown in FIG. Although it is preferable to extend the scanning of the photoconductor surface, for the sake of layout, a configuration in which the laser beam scans inside the light receiving element PD1 via a folding mirror may be adopted.

  The light receiving element PD1 is composed of an amplifier circuit that amplifies an output signal from a light receiving unit made of a PIN photodiode and a comparator circuit that shapes a waveform, and is packaged as one IC with a laser beam transmitting member made of resin. In the figure, reference numeral 402a denotes a light receiving portion, 402b denotes a circuit portion, and 402c denotes an IC lead (FIG. 10A). When the scanning beam passes through the light receiving portion 402a, a comparator output signal shown in FIG. 10C is generated.

  In the dotted line area on the left side of the light receiving portion 402a in FIG. 10A, the light source device is turned off (or the flare light is dimmed to such an extent that it does not form a light amount that forms a latent image on the photoreceptor surface in the light receiving element). It is drawn like that. When the light source emits light in a region between the maximum deflection angle of the oscillating mirror 11 and the vicinity of the light receiving element PD1, ghost light due to irregular reflection of the optical components arranged in the optical scanning device 5 is generated, and the light receiving element PD1. , The noise to the signal to PD2 affects the time interval (time interval) of A, B, C, and the pulse width, and the accuracy of posture adjustment of the vibrating mirror 11 is deteriorated, malfunctioning in control and non-operation. It becomes stable. In order not to cause this problem, it is set in advance so as to be extinguished at the above timing (or dimmed to such an extent that the ghost light does not become a light amount at a level for forming a latent image on the surface of the photoreceptor in the light receiving element). Turning off or dimming can also have the effect of extending the life of a light source made of a semiconductor laser and reducing the temperature rise of the light source device. Here, “in the vicinity of the light receiving element” is a scanning position at which the time intervals A, B, and C can be normally measured without affecting the output of the comparator.

  Note that if the amount of light is reduced when the reflectance or transmittance of the optical element is reduced (deterioration with time), the rise time to the threshold voltage that determines the comparator output becomes longer (the inclination becomes slower). will have to go. Therefore, the above problem is solved by controlling the light source so that the light amount is always constant when scanning the light receiving element PD1 (or PD2).

  By the way, although the case of the sine wave has been shown as an example of the drive signal, since the number of DA conversion bits and a large-capacity memory are required to generate the sine wave, the drive signal is generated at a low cost. It is also possible to use a rectangular wave. Further, the oscillation of the oscillating mirror 11 has been described in the embodiment of the reciprocating scanning. However, since the scanning is performed so that the scanning position in the sub scanning direction approaches the maximum deflection angle end (so-called zigzag shape), When crushing of characters on both ends of the image or uneven density is a problem, it can be solved by scanning on one side (one direction).

Next, a color image forming apparatus according to the present invention will be described.
FIG. 11 is a color image forming apparatus using the optical scanning device 5 of the present invention, and is a configuration diagram of a tandem type color image forming apparatus in which a plurality of photoconductors 3Y, 3M, 3C, 3K are arranged in parallel. An optical scanning device 5, a developing device 6 (6Y, 6M, 6C, 6K), a photoreceptor 3 (3Y, 3M, 3C, 3K), an intermediate transfer belt 2, a fixing device 7, and a paper feed cassette 1 are laid out in order from the top of the apparatus. Has been.

  On the intermediate transfer belt 2, photosensitive members 3Y, 3M, 3C, and 3K corresponding to the respective colors are arranged at equal intervals in the parallel order. The photoreceptors 3Y, 3M, 3C, and 3K are formed to have the same diameter, and members are sequentially disposed around the photoreceptors according to an electrophotographic process. The photoconductor 3Y will be described as an example. A charging charger (not shown), a laser beam L1 based on an image signal emitted from the optical scanning device 5, a developing device 6Y, a transfer charger (not shown), a cleaning device (not shown), and the like. Are arranged in order. The same applies to the other photoconductors 3M, 3C, 3K. That is, in the present embodiment, the photoconductors 3Y, 3M, 3C, 3K are to be scanned surfaces set for each color, and the laser beams L1, L2, L3,. L4 is provided to correspond to each.

  The photoconductor 3Y uniformly charged by the charging charger rotates in the direction of arrow A in the drawing to sub-scan the laser beam L1, and an electrostatic latent image is formed on the photoconductor 3Y. Further, a developing device 6Y that supplies toner to the photoconductor 3Y is disposed downstream of the irradiation position of the laser beam L1 by the optical scanning device 5 in the rotation direction of the photoconductor 3, and yellow toner is supplied. The toner supplied from the developing device 6Y adheres to the portion where the electrostatic latent image is formed, and a toner image is formed. Similarly, M, Y, and K monochromatic toner images are formed on the photoreceptors 3M, 3C, and 3K, respectively. The intermediate transfer belt 2 is disposed further downstream in the rotational direction than the position where the developing unit 6Y of each photoconductor 3Y is disposed.

  The intermediate transfer belt 2 is wound around a plurality of rollers 2a, 2b, and 2c, and is moved and conveyed in the direction of arrow B by driving a motor (not shown). By this conveyance, the intermediate transfer belt 2 is sequentially moved to the photoreceptors 3Y, 3M, 3C, and 3K. The intermediate transfer belt 2 sequentially superimposes and transfers the single color images developed by the photoreceptors 3Y, 3M, 3C, and 3K, thereby forming a color image on the intermediate transfer belt 2. Thereafter, the transfer paper is conveyed from the paper feed tray 1 in the direction of arrow C, and the color image is transferred. The transfer paper on which the color image is formed is discharged as a color image after being fixed by the fixing device 7.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

It is a perspective view which shows the structure of the optical scanning device based on this invention. It is detail drawing which shows the structure of a vibration mirror. It is a disassembled perspective view of a vibration mirror. It is a disassembled perspective view which shows the mounting state of a vibration mirror unit. It is the schematic which shows the principal part from the vibration mirror in the optical scanning apparatus of this invention to a photoreceptor. It is a figure which shows the relationship between the amplitude waveform of the vibration mirror in the optical scanning device of this invention, the output signal of a light receiving element, and a reference | standard phase clock. It is a figure which shows the relationship between the output waveform of a light receiving element, and a comparator output waveform. It is a figure which shows the mode of the fluctuation | variation of the amplitude of an amplitude waveform of an oscillation mirror, an offset, and a phase. It is a block diagram of the control means regarding the drive of a vibration mirror. It is a figure which shows the relationship between a light receiving element and the laser beam scanned. 1 is a schematic cross-sectional view showing a configuration of a color image forming apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Paper feed tray 2 Intermediate transfer belt 2a, 2b, 2c, 2d Roller 3, 3Y, 3M, 3C, 3K Photoreceptor 5 Optical scanning device 6Y, 6M, 6C, 6K Developing device 7 Fixing device 10 Light source 10Y, 10M, 10C , 10K light source means 11 vibrating mirror 12 cylindrical lens 13 folding mirror 14 first lens 16K mirror 17K second lens 60, L1, L2, L3, L4 laser beam 70, 71 light receiving element output waveform 80, 81 pulse width 110 driving Circuit 111, 112, 116 Counter 113 Operation unit 114 Controller 115 Phase comparator 117 LPF
118 integrator 402a light receiving unit 402b circuit unit 402c IC lead 441 movable mirror unit 442 torsion beam 443 diaphragm 444 reinforcing beam 446, 447 frame 449 yoke 450 permanent magnet 455, 473 electrode unit 461, 462 substrate 463 coil pattern 464 terminal 465 patch 466 Base 470 Vibration mirror unit 471 Bracket 472 Substrate 474 Electrical connector PD1, PD2 Light receiving element

Claims (6)

Light source means that emits a laser beam, a vibrating mirror that deflects and scans the laser beam from the light source means, a scanning imaging optical system that condenses the laser beam that is deflected and scanned toward the surface to be scanned, and the laser beam In an adjustment method of an optical scanning device comprising: two light receiving elements that receive the laser beams provided at positions near both ends of the scanning region with the scanning center interposed therebetween ,
Of the two light receiving elements , the time interval of the output pulses of the first light receiving element and the time interval of the output pulses of the second light receiving element coincide with each other, and the output pulse of the first light receiving element An adjusting method for an optical scanning device , wherein the mounting posture in the rotational direction about the swing axis of the vibrating mirror is adjusted so that the width and the output pulse width of the second light receiving element are constant . Control means for making the amplitude of the amplitude waveform of the oscillating mirror constant based on output signals from the two light receiving elements;
2. The mounting posture in the rotational direction about the swing axis of the vibrating mirror is adjusted in a state where the amplitude of the amplitude waveform of the vibrating mirror is controlled to be constant by the control means. The adjustment method of the optical scanning device as described . The two time intervals and / or the output pulse width of each output pulse is measured a plurality of times in the output signal of the light receiving element, characterized by having a calculating means for processing averages of claim 1 or 2 Method for adjusting optical scanning device. Based on the output signal from the light receiving element, after adjusting the mounting posture in the rotational direction around the swing axis of the vibrating mirror, the scanning lens position of the scanning imaging optical system is moved and adjusted in the main scanning direction. The method of adjusting an optical scanning device according to claim 1, wherein: A plurality of light source devices as the light source means;
Respective laser beams emitted from the plurality of light source devices are deflected and scanned on a plurality of scanned surfaces by the single vibrating mirror,
5. The two light receiving elements are arranged only in a scanning imaging optical system corresponding to one of the plurality of scanned surfaces . An adjustment method for an optical scanning device according to any one of the above. The laser beam, a method of adjusting an optical scanning device according to any one of claims 1 to 5, characterized in that the a laser beam passing through the scanning image forming optical system for scanning the light receiving element.

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