JP2006220745A - Micromirror scanner and laser optical scanner using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a micromirror scanner in which a micromirror is always swung at a constant swing angle even when temperature varies. <P>SOLUTION: The micromirror scanner 10 comprises: a micromirror device 1 provided with a swingably supported micromirror and electrodes for driving to swing the micromirror by electrostatic force; an AC power source 2 which applies an AC voltage between the electrodes; a light detection element 3 disposed at a predetermined position at which the reflected light L' of laser light L emitted toward the micromirror is scanned according to the swing of the micromirror; a calculation; and a control device 4 which detects the deviation of a timing at which the reflected light is detected with the light detection element from a predetermined timing, converts the detected deviation into the swing angular variation of the micromirror, and adjusts the value of the AC voltage to correct the converted swing angular variation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a micromirror scanner configured to oscillate a micromirror using an electrostatic force generated by applying an AC voltage, and a laser beam scanning device using the micromirror scanner, and more particularly to a micromirror generated by a change in temperature. The present invention relates to a micromirror scanner capable of correcting fluctuations in the deflection angle of the micromirror so that the micromirror can always be swung at a constant deflection angle even when the temperature changes, and a laser beam scanning apparatus using the micromirror scanner.

  Conventionally, a polygon mirror scanner has been widely used as a scanning mechanism of a laser beam scanning device used in a printer, a copying machine, a projector, or the like using a laser. Such a polygon mirror scanner includes a polygonal columnar polygon mirror that is driven to rotate about an axis, and scans the laser beam by sequentially reflecting the laser beam emitted from the laser light source on the reflecting surface of the polygon mirror. Is possible.

On the other hand, in recent years, MEMS (Micro Electro Mechanical Systems) which realizes miniaturization of various mechanical elements by applying technology in a semiconductor manufacturing process such as silicon instead of the polygon mirror scanner in response to a request for miniaturization of an apparatus Various micromirror scanners manufactured using technology have been proposed (see, for example, Patent Documents 1 and 2). Such a micromirror scanner includes a micromirror supported on a silicon base material so as to be swingable by a suspension beam, and an electrode to which an AC voltage for swinging the micromirror is applied. The micromirror is oscillated by an electrostatic force generated by applying an AC voltage between the electrodes. A large micromirror deflection angle (oscillation angle range) can be obtained even with a small driving force by a resonance phenomenon caused by applying an AC voltage having a frequency that matches the natural frequency (resonance frequency) of the micromirror. It is possible.
JP 2002-31376 A JP 2003-15064 A

  However, in the micromirror scanner using the resonance phenomenon of the silicon substrate as described above, the Young's modulus of the silicon substrate changes due to temperature change, and the resonance characteristics (maximum resonance frequency) change accordingly. When the dynamic frequency is constant (when the frequency of the AC voltage to be applied is constant), there is a problem that the deflection angle of the micromirror fluctuates due to temperature change. For example, even if the temperature of the micromirror changes, the oscillation frequency does not change unless the frequency of the AC voltage to be applied is changed, but as the temperature of the micromirror increases as shown in FIG. There is a problem that the deflection angle of the micromirror becomes small. If the deflection angle of the micromirror varies in this way, the range in which the reflected light of the laser beam irradiated toward the micromirror is scanned varies. Therefore, when it is necessary to scan the laser beam at a constant frequency as in a laser printer, the oscillation frequency of the micromirror must also be constant. As a result, the scanning range varies depending on the temperature as described above. The problem of end up occurs.

  In Patent Documents 1 and 2, there is no disclosure or suggestion about the temperature dependency of the deflection angle of the micromirror as described above, and therefore there is no disclosure or suggestion of correcting the fluctuation of the deflection angle of the micromirror. .

  The present invention has been made to solve such a problem of the prior art, corrects fluctuations in the deflection angle of the micromirror caused by temperature changes, and always maintains a constant deflection angle even when the temperature changes. It is an object of the present invention to provide a micromirror scanner capable of swinging a laser beam and a laser beam scanning device using the same.

  In order to solve such a problem, the present invention provides a micromirror supported so as to be swingable, and an AC power source for applying an AC voltage between electrodes for swinging the micromirror using an electrostatic force. A photodetecting element disposed at a predetermined position where reflected light of laser light irradiated toward the micromirror is scanned in accordance with oscillation of the micromirror, and the light And a calculation control device that adjusts a voltage value of an AC voltage applied by the AC power source based on a timing at which the reflected light is detected by the detection element. A deviation amount between the timing when the reflected light is detected and a predetermined timing is detected, the detected deviation amount is converted into a deflection angle fluctuation amount of the micromirror, and the conversion is performed. There is provided a micro mirror scanner, characterized by adjusting the voltage value of the AC voltage so as to correct the the deflection angle variation.

  According to such an invention, the light detection element is disposed at a predetermined position where the reflected light of the laser beam irradiated toward the micromirror is scanned in accordance with the oscillation of the micromirror. Here, even if the temperature of the micromirror changes, the oscillation frequency of the micromirror does not change as long as the frequency of the AC voltage to be applied is constant, but the deflection angle fluctuates, so that the reflected light is detected by the photodetector. The timing to be changed also depends on the temperature of the micromirror. According to the present invention, the timing at which the reflected light is detected by the light detection element and the predetermined timing (for example, the timing at which the reflected light will be detected when the micromirror has an appropriate deflection angle are determined in advance. The shift amount (shift time) with respect to (set as timing) is detected by the arithmetic and control unit. Then, the arithmetic and control unit converts the detected deviation amount into the deflection angle fluctuation amount of the micromirror. More specifically, for example, in the arithmetic and control unit, a correspondence relationship between the deviation amount and the deflection angle variation amount is stored in advance, and the detected deviation amount is converted into the deflection angle variation amount based on the stored correspondence relationship. Will be converted to. Furthermore, the arithmetic and control unit adjusts the voltage value of the AC voltage so as to correct the converted deflection angle fluctuation amount. More specifically, for example, the arithmetic control device stores in advance a correspondence relationship (which is substantially proportional) between the voltage value of the AC voltage and the deflection angle of the micromirror, and based on the stored correspondence relationship. Therefore, the voltage value of the AC voltage is adjusted so that the fluctuation angle fluctuation amount becomes 0 (that is, the adjusted deflection angle becomes equal to the deflection angle corresponding to the predetermined timing). Therefore, according to the micromirror scanner of the present invention having the above-described configuration, fluctuations in the swing angle of the micromirror caused by changes in temperature are corrected, and the micromirror is always shaken at a constant swing angle even if the temperature changes. It is possible to move.

  The present invention is also provided as a laser beam scanning device comprising the micromirror scanner and a laser light source that emits laser light toward the micromirror included in the micromirror scanner.

  According to the micromirror scanner of the present invention, fluctuations in the deflection angle of the micromirror caused by changes in temperature are corrected, and the micromirror can always be swung at a constant deflection angle even if the temperature changes. .

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings, taking as an example the case of application to a laser printer.

  FIG. 1 is a diagram illustrating a schematic configuration of a laser beam scanning apparatus including a micro scanner according to an embodiment of the present invention. FIG. 1A illustrates a schematic configuration of the laser beam scanning apparatus, and FIG. Indicates the positional relationship of the light detection elements. As shown in FIG. 1A, a laser beam scanning apparatus 100 according to the present embodiment emits laser beam L toward a micromirror scanner 10 and a micromirror included in the micromirror scanner 10 as will be described later. A laser light source (laser diode in this embodiment) 20 is provided. In addition, the laser beam scanning device 100 according to the present embodiment sensitizes the collimator lens 30 for making the laser beam L emitted from the laser light source 20 into parallel light and the reflected beam L ′ of the laser beam L from the micromirror. An fθ lens 40 and a cylindrical mirror 50 for forming an image on the body P are provided. In the laser beam scanning device 100 having the above configuration, the reflected light L ′ of the laser beam L emitted from the laser light source 20 is printed on the photosensitive member P by swinging the micromirror included in the micromirror scanner 10. It will be scanned for minutes.

  The micromirror scanner 10 includes a micromirror device 1, an AC power supply 2, a light detection element (photodiode in the present embodiment) 3, and an arithmetic control device 4.

  FIG. 2A is a perspective view illustrating a schematic configuration of the micromirror device according to the present embodiment. 2B is a plan view showing a schematic configuration of an upper layer substrate of the micromirror device shown in FIG. 2A, and FIG. 2C is a plan view showing a schematic configuration of a lower layer substrate of the micromirror device shown in FIG. 2A. As shown in FIGS. 2A to 2C, the micromirror device 1 according to this embodiment includes an upper substrate 1A formed of a silicon material and a lower substrate 1B formed of an insulating material (for example, a glass material) stacked vertically. Has a structured. Note that the micromirror device 1 according to the present embodiment can be easily manufactured by those skilled in the art by applying a known MEMS technique such as etching or film formation. Will not be described.

  As shown in FIG. 2A or 2B, the upper substrate 1A has an elliptical micromirror 11 formed at the center and is connected to both ends of the swing axis (X axis shown in FIG. 2B). Suspension beams 13A and 13B are formed through the portion 12, and the micromirror 11 is supported by the suspension beams 13A and 13B so as to be swingable around the swing axis.

  The ends of the suspension beams 13A and 13B in the swing axis direction (the end opposite to the side connected to the micromirror 11) are bonded as anchors via the hinges 15A and 15N of the S-shaped torsion bar structure. It is connected to pads 14A and 14B, respectively. The suspension beam 13A is formed with adhesive pads 14C to 14E and hinges 15B to 15G having an S-shaped torsion bar structure. The hinges 15B and 15C are adhesive pads 14C, and the hinges 15D and 15E are adhesive pads. 14D, the hinges 15F and 15G are connected to the adhesive pad 14E, respectively. Similarly, the suspension beam 13B is formed with adhesive pads 14F to 14H and hinges 15H to 15M having an S-shaped torsion bar structure. The hinges 15H and 15I are attached to the adhesive pad 14F, and the hinges 15J and 15K are attached to the suspension beam 13B. The hinges 15L and 15M are connected to the adhesive pad 14G, respectively.

  Further, swinging comb teeth 18A and 18B extending in the Y-axis direction are formed as electrodes at the ends in the direction of the axis (Y-axis shown in FIG. 2B) orthogonal to the swinging axis of the suspension beams 13A and 13B. Fixed comb teeth 19A, 19B as electrodes formed on the main body 19 of the upper substrate 1A and extending in the Y-axis direction are alternately arranged along the swing axis direction.

  On the other hand, as shown in FIG. 2C, the lower substrate 1B corresponds to the micromirror 11 so that the micromirror 11 formed on the upper substrate 1A and the suspension beams 13A and 13B can swing around the swing axis. An elliptical digging region 16 is formed at a position where the rectangular digging regions 16A and 16B are formed at positions corresponding to the suspension beams 13A and 13B. In addition, fixing pads 17A to 17H are formed on the lower substrate 1B to fix the back surfaces of the adhesive pads 14A to 14H formed on the upper substrate 1A in a state where the upper substrate 1A and the lower substrate 1B are laminated. Has been.

  In the micromirror device 1 having the configuration described above, if an AC voltage is applied from the AC power source 2 between the swing comb teeth 18A, 18B and the fixed comb teeth 19A, 19B, the swing comb teeth 18A, 18B An electrostatic force acts between the fixed comb teeth 19A and 19B, whereby the micromirror 11 swings around the swing axis while resisting the elastic force of the hinges 15A to 15N with the adhesive pads 14C to 14H as fixed ends. Will move.

  As shown in FIG. 1 (a), the AC power source 2 is connected to the electrodes (that is, the swinging comb teeth 18A and 18B and the fixed comb teeth 19A and 19B) included in the micromirror device 1, and between the electrodes AC voltage is applied to Note that the frequency (oscillation frequency) and voltage value of the AC voltage applied by the AC power supply 2 are configured to be controllable by the arithmetic and control unit 4.

  As shown in FIG. 1A, the light detection element 3 is a predetermined scanning light L ′ of the laser light L irradiated from the laser light source 20 toward the micromirror 11 according to the oscillation of the micromirror 11. It is arranged at a position, and is configured to output a detection signal to the arithmetic control device 4 when the reflected light L ′ is incident on the photoelectric conversion surface of the light detection element 3. More specifically, as shown in FIG. 1 (a) or FIG. 1 (b), the photodetecting element 3 is the end of the scanning range when the deflection angle of the micromirror 11 is the smallest due to temperature change. The reflection light L1 ′ passing through the position is disposed inward and at a position outside the reflection light L2 ′ passing through the end position of the effective scanning range (scanning range actually used as the print width). . As the light detection element 3, a light detection element for synchronizing the scanning direction (horizontal direction) used in the conventional polygon mirror scanner can be used as it is.

  As shown in FIG. 1A, the arithmetic and control unit 4 is connected to the light detection element 3 and the AC power supply 2, and the timing at which the reflected light L ′ is detected by the light detection element 3 (that is, the light detection element). 3, the voltage value of the AC voltage applied by the AC power source 2 is adjusted based on the timing at which the detection signal is output from 3. Hereinafter, the operation of the arithmetic and control unit 4 will be described more specifically with reference to FIG. 3 as appropriate.

  FIG. 3 is an explanatory diagram for explaining the operation of the arithmetic and control unit according to the present embodiment. FIG. 3A is an explanatory diagram showing fluctuations in the deflection angle of the micromirror caused by a change in temperature. (B) shows the time chart showing the fluctuation | variation of the output signal of the photon detection element which arises with the change of temperature. As shown in FIG. 3A, if the temperature of the micromirror 11 changes from T1 to T2, the deflection angle of the micromirror 11 (meaning the range of angles in which the micromirror 11 swings) means the center position C of the scanning region. The angle formed by the optical path of the reflected light L ′ passing through and the optical path of the reflected light L ′ passing through the end of the scanning region) varies from θ1 to θ2.

  More specifically, when the temperature of the micromirror 11 is T1, the reflected light L ′ passes through the point C and reaches the point C1 when the micromirror 11 swings. 3 is scanned to the left in FIG. 3A until reaching point C1 ′ after reaching point C1. Then, after reaching the point C1 ', scanning is performed in the right direction on the paper surface of FIG. 3A until reaching the point C1 via the point C. The above operation is repeated, and the reflected light L 'is reciprocally scanned on the line segment connecting the points C1 and C1'. On the other hand, when the temperature of the micromirror 11 is T2, the micromirror 11 oscillates so that the reflected light L ′ passes through the point C and scans in the right direction in FIG. 3A until reaching the point C2. Then, after reaching point C2, scanning is performed in the left direction of FIG. 3A until reaching point C2 ′ via point C. Then, after reaching the point C2 ', scanning is performed in the right direction on the paper surface of FIG. 3A until reaching the point C2 via the point C. The above operation is repeated, and the reflected light L 'is reciprocally scanned on the line segment connecting the point C2 and the point C2'.

  Here, when the temperature of the micromirror 11 changes from T1 to T2, the deflection angle changes from θ1 to θ2 as described above, but the oscillation frequency of the micromirror 11 does not change. That is, when the temperature of the micromirror 11 is T1, the time required for the reflected light L ′ to pass again through the point C, the point C1, the point C, the point C1 ′, and the point C (oscillation cycle); When the temperature of the micromirror 11 is T2, the time required for the reflected light L ′ to pass through the point C, the point C2, the point C, the point C2 ′, and the point C again is equal to the oscillation period. become. In other words, when the temperature of the micromirror 11 is T1, the time required for the reflected light L ′ to reach the point C1 after passing through the point C (1/4 of the oscillation period), and the temperature of the micromirror 11 Is the time required for the reflected light L ′ to reach the point C2 after passing through the point C (1/4 of the oscillation period) (time T shown in FIG. 3B). It becomes.

  Therefore, as long as the arrangement position of the light detection element 3 is fixed as shown in FIG. 3A, the reflected light L ′ first passes after passing the point C as shown in FIG. In the time until the point C1 or the point C2 is reached, the detection signal D1 of the light detection element 3 at the temperature T1 (the ON signal indicating that the reflected light L ′ is incident on the light detection element 3) is the temperature. It is output later than the detection signal D2 of the light detection element 3 at T2.

  The arithmetic control device 4 has a timing at which reflected light is detected by the light detection element 3 (that is, a timing at which the detection signals D1 and D2 shown in FIG. 3B are output) and a predetermined timing (FIG. 3B). (A timing at which the reference signal D shown in FIG. 1 appears) is detected. More specifically, it appears at a target timing (timing at which the reflected light L ′ will be detected by the photodetecting element 3 when the micromirror 11 has an appropriate deflection angle θ set in advance). While generating the reference signal D synchronized with the oscillation frequency of the mirror 11 (the frequency of the AC voltage applied by the AC power supply 2), the detection signal D1 (D2) of the light detection element 3 is used as the oscillation frequency of the micromirror 11 ( The signals D and D1 (D2) are detected by an appropriate comparator or the like in synchronization with the frequency of the AC voltage applied by the AC power supply 2. Then, the deviation amount (deviation time) is calculated by counting the time difference between the detected signals D and D1 (D2) with an appropriate counter or the like.

  Since the micromirror 11 swings, the reflected light L ′ is reciprocated as described above, and is incident twice on the light detection element 3 during the swing period (once in the forward path and once in the return path). It will be. As a result, the detection signal D1 (D2) of the light detection element 3 is output twice during one oscillation period. Therefore, the arithmetic and control unit 4 is provided with an appropriate frequency dividing circuit or the like to extract only the detection signal corresponding to either the forward path or the return path of the reflected light L ′, and set it as the detection signal D1 (D2). It is configured as follows.

  Further, the arithmetic control device 4 stores in advance a correspondence relationship between the deviation amount (deviation time) and the deflection angle fluctuation amount (difference between the deflection angle θ1 (θ2) and the appropriate deflection angle θ). Such a correspondence relationship may be theoretically obtained based on the deflection angle θ, the oscillation frequency of the micromirror 11, the position where the light detection element 3 is disposed, or may be calculated experimentally. Then, the arithmetic control device 4 converts the calculated deviation amount (deviation time) into a deflection angle fluctuation amount based on the stored correspondence.

  Further, the arithmetic and control unit 4 has a relationship between the voltage value of the AC voltage applied by the AC power supply 2 and the deflection angle of the micromirror 11 when the temperature of the micromirror 11 is a predetermined constant temperature (for example, room temperature). Correspondence relationships are stored in advance. Such correspondence can be calculated experimentally, and is substantially proportional as shown in FIG. The arithmetic and control unit 4 then adjusts the AC voltage so that the fluctuation amount fluctuation amount becomes zero based on the stored correspondence relationship (that is, the adjusted deflection angle becomes equal to the appropriate deflection angle θ). The voltage value will be adjusted. More specifically, as shown in FIG. 4, when the deflection angle is θ1 smaller than θ (that is, when the deflection angle fluctuation amount is θ1−θ <0), the AC before adjustment is performed. While the voltage value of the voltage is increased by V−V1, when the deflection angle is θ2 larger than θ (that is, when the deflection angle variation is θ2−θ> 0), the AC voltage before adjustment is The voltage value is adjusted to be reduced by V2-V.

  Therefore, according to the micro scanner 10 having the above-described configuration, the fluctuation of the deflection angle of the micro mirror 11 caused by the temperature change is corrected, and the micro mirror 11 is always kept at a constant deflection angle θ even if the temperature changes. It can be swung. Thereby, the scanning width of the laser beam scanning device 100 that scans the laser beam at a constant frequency (the scanning width of the reflected light L ′ of the laser beam L on the micromirror 11 on the photosensitive member P) is stabilized regardless of the temperature. Therefore, it is very preferable when used as a scanning mechanism of a laser printer.

FIG. 1 is a diagram illustrating a schematic configuration of a laser beam scanning apparatus including a micro scanner according to an embodiment of the present invention. FIG. 1A illustrates a schematic configuration of the laser beam scanning apparatus, and FIG. Indicates the positional relationship of the light detection elements. FIG. 2A is a perspective view illustrating a schematic configuration of the micromirror device according to the present embodiment. FIG. 2B is a plan view showing a schematic configuration of an upper substrate of the micromirror device shown in FIG. 2A. FIG. 2C is a plan view showing a schematic configuration of a lower layer substrate of the micromirror device shown in FIG. 2A. FIG. 3 is an explanatory diagram for explaining the operation of the arithmetic and control unit shown in FIG. 1. FIG. 3 (a) is an explanatory diagram showing fluctuations in the deflection angle of the micromirror caused by a change in temperature. b) is a time chart showing the fluctuation of the output signal of the photodetecting element caused by the temperature change. FIG. 4 is a diagram schematically showing the correspondence between the voltage value of the AC voltage applied by the AC power source shown in FIG. 1 and the deflection angle of the micromirror. FIG. 5 is a diagram illustrating the relationship between the temperature of the micromirror and the deflection angle of the micromirror.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Micromirror device 2 ... AC power supply 3 ... Photodetection element 4 ... Calculation control apparatus 10 ... Micromirror scanner 11 ... Micromirror 20 ... Laser light source 100 ... Laser beam scanning device L ... Laser beam L '... Reflected beam

Claims (2)

A micromirror scanner comprising a micromirror supported so as to be swingable, and an AC power source for applying an AC voltage between electrodes for driving the micromirror to swing using an electrostatic force,
A light detecting element disposed at a predetermined position where reflected light of the laser light irradiated toward the micromirror is scanned in accordance with the swing of the micromirror;
An arithmetic control device that adjusts the voltage value of the AC voltage applied by the AC power source based on the timing at which the reflected light is detected by the photodetecting element;
The arithmetic and control unit detects a deviation amount between a timing at which the reflected light is detected by the light detection element and a predetermined timing, converts the detected deviation amount into a deflection angle fluctuation amount of the micromirror, A micromirror scanner characterized by adjusting the voltage value of the AC voltage so as to correct the converted deflection angle fluctuation amount.   A laser beam scanning apparatus comprising: the micromirror scanner according to claim 1; and a laser light source that emits laser light toward the micromirror included in the micromirror scanner.

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