JP2013160953A - Oscillating device, optical scanner using the same, image display device and control method of oscillating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillating device capable of adjusting a deviation between a phase of pulse voltage and a phase of oscillation of a movable plate with a simple method.SOLUTION: The oscillating device oscillates a movable plate 2 on a twisted spring 3 as axis by applying a pulse voltage across interdigital electrodes 2b and 4d. The pulse voltage is supplied at first predetermined time intervals. A time difference from the timing when the pulse voltage is supplied as the reference up to a timing when the swing angle of an oscillation of the movable plate 2 detected by an oscillation detection sensor 19 is zero. Comparing the measured time difference to a second predetermined time, when the difference between the time difference and the second predetermined time exceeds an allowable time difference, a feedback control is performed to increase or decrease the duty ratio of the pulse voltage so that the timing when the swing angle of the oscillation of the movable plate 2 becomes zero comes after a second predetermined time from the timing when the pulse voltage is supplied.

Description

  The present invention relates to an oscillating device using a movable structure that applies a pulse voltage to a vertical comb to oscillate a movable plate around a rotation axis, an optical scanning device using the oscillating device, and the optical scanning device. The present invention relates to a video display device used and a control method of a swing device.

  For example, as described in Patent Document 1, the applicant of the present application has a swing device including a small movable structure formed using a micromachining technique, an optical scanning device using the same device, and an image display device. Etc. are proposed. In such a movable structure, generally, the frequency of a pulse voltage for driving the movable plate of the movable structure is matched with the resonance frequency of the movable plate, and the movable plate is oscillated at the resonance frequency. Then, when the swing of the movable plate is stabilized, for example, a light beam is applied to a mirror formed on the surface of the movable plate, the light beam is reflected in a direction according to the swing angle of the mirror, and the light beam is scanned. ing.

  As described in Patent Document 2, it is known that the resonance frequency of the movable plate changes due to a temperature change. Therefore, if the frequency of the pulse voltage is changed according to the temperature change, the movable plate of the movable structure swings with a stable amplitude and frequency, that is, the phase of the pulse voltage and the phase of the swing of the movable plate are almost the same. Have been considered consistent. However, when the oscillation of the movable plate of the movable structure was measured with the temperature kept constant, a phenomenon in which the phase of the pulse voltage and the phase of the oscillation of the movable plate were shifted was confirmed. As the cause, it is considered that factors such as internal resistance of the SOI substrate constituting the movable structure and friction with air are intertwined in a complicated manner.

  The phase of the pulse voltage when the light beam is incident on the mirror in synchronization with the pulse voltage in an optical scanning device or an image display device using an oscillating device equipped with a movable structure formed using micromachining technology. If the swinging phase of the movable plate shifts, the position of the light beam scanned by the optical scanning device shifts, or the image quality of the projected video displayed by the video display device decreases. In addition, when the phase of the pulse voltage and the phase of the swing of the movable plate are shifted, a voltage is applied between the comb electrodes during a period in which the movable plate rotates so that the comb electrodes are separated from each other, and the movable plate rotates. An electrostatic force acts in a direction to suppress the above, and this becomes a resistance component. As a result, the swing angle of the movable plate becomes smaller than the pulse voltage, and the light beam cannot be scanned over a wide range.

  With respect to such problems, Patent Document 1 changes the pulse voltage application timing when the movable plate swings by adjusting the duty ratio of the pulse voltage applied between the comb-teeth electrodes of the movable structure. It has been proposed to adjust the swing angle and phase of the movable plate. However, at the time of filing of Patent Document 1, even when the movable plate of the movable structure is oscillated with the temperature kept constant as described above, the pulse is caused by factors such as internal resistance of the SOI substrate and friction with air. Since the phenomenon that the phase of the voltage and the phase of the movable plate oscillate was not clear, the oscillating angle and phase of the movable plate once adjusted may be shifted again. The improvement in image quality was slightly insufficient.

JP 2008-295174 A Japanese Patent Laying-Open No. 2005-345866 (paragraph 0055)

  The present invention has been made in view of the above-described problems, and an oscillating device capable of adjusting a phase shift of a oscillating phase of a movable plate and a phase of a pulse voltage for driving the movable plate with a simple configuration. An object is to provide an optical scanning device using an oscillating device, an image display device using the optical scanning device, and a control method of the oscillating device.

In order to achieve the above object, a rocking device according to the present invention comprises:
A movable plate, a swing shaft that pivotally supports the movable plate and acts as a torsion spring when the movable plate swings, a frame that supports the swing shaft, and the movable plate A first side that is different from the side on which the pivot shaft is provided and a second side that faces the first side of the side of the frame are provided so as to mesh with each other and drive the movable plate A movable structure provided with a plurality of comb electrodes for generating electrostatic force to
A swing detection sensor for detecting timing when the swing angle of swing of the movable plate becomes zero;
An oscillating device comprising a control circuit for controlling a voltage and a duty ratio of a pulse voltage applied between the comb electrode on the movable plate side and the comb electrode on the frame side,
The control circuit includes:
Raising the pulse voltage at a first predetermined time interval;
Using the timing at which the pulse voltage was raised as a reference, measure the time difference until the swing angle of the swing of the movable plate detected by the swing detection sensor becomes zero,
The measured time difference is compared with a second predetermined time, and if the difference between the time difference and the second predetermined time exceeds an allowable time difference, the swing vibration of the movable plate detected by the swing detection sensor is detected. Feedback control is performed to increase or decrease the duty ratio of the pulse voltage so that the timing when the angle becomes zero is after the second predetermined time from the timing when the pulse voltage is raised.

  The control circuit searches for a duty ratio value corresponding to a difference between the time difference and the second predetermined time from among a plurality of pulse voltage duty ratio values stored in advance in a lookup table. It is preferable to adjust the duty ratio of the pulse voltage based on the value of the duty ratio.

  Alternatively, the control circuit predicts the timing at which the swing angle of the movable plate is next detected from the timing at which the swing angle of the movable plate detected by the swing detection sensor is zero, It is preferable to adjust the duty ratio of the pulse voltage so that the value of the pulse voltage becomes zero at the predicted timing.

The swing detection sensor includes a detection electrode constituted by a part of comb electrodes among a plurality of comb electrodes provided on the frame, and when the movable plate swings, Detecting the electrostatic capacitance between the meshed comb electrodes of the movable plate,
Preferably, the control circuit determines that the swing angle of the movable plate is zero when the electrostatic capacitance detected by the swing detection sensor is maximized.

  It is preferable that the control circuit can change the voltage of the pulse voltage in accordance with the change amount of the duty ratio.

  Furthermore, it is preferable that the control circuit can change the frequency of the pulse voltage when the frequency of oscillation of the movable plate is different from a predetermined frequency.

  The second predetermined time is preferably ½ of the first predetermined time.

  In addition, an optical scanning device according to the present invention is characterized by including a swinging device having any one of the above-described configurations and a mirror formed on the main surface of the movable plate.

  Further, an image display device according to the present invention includes a swing device having any one of the above configurations, a mirror formed on a main surface of the movable plate, a light source that makes a light beam incident on the mirror, A light source driving circuit for driving a light source, and the control circuit outputs a video signal synchronized with a rising timing of the pulse voltage to the light source driving circuit using video data input from the outside. Features.

Moreover, the control method of the rocking device according to the present invention includes:
A movable plate, a swing shaft that pivotally supports the movable plate and acts as a torsion spring when the movable plate swings, a frame that supports the swing shaft, and the movable plate A first side that is different from the side on which the pivot shaft is provided and a second side that faces the first side of the side of the frame are provided so as to mesh with each other and drive the movable plate A voltage of a pulse voltage applied between the comb electrode on the movable plate side and the comb electrode on the frame side, having a movable structure including a plurality of comb electrodes for generating electrostatic force And a control method of a swinging device that swings the movable plate by controlling the duty ratio,
Detecting the timing when the swing angle of the swing of the movable plate becomes zero,
Raising the pulse voltage at first predetermined time intervals;
Using the timing at which the pulse voltage is raised as a reference, measure the time difference until the timing at which the detected swing angle of the movable plate becomes zero,
The measured time difference is compared with a second predetermined time, and if the difference between the time difference and the second predetermined time exceeds an allowable time difference, the swing vibration of the movable plate detected by the swing detection sensor is detected. Feedback control is performed to increase or decrease the duty ratio of the pulse voltage so that the timing when the angle becomes zero is after the second predetermined time from the timing when the pulse voltage is raised.

  According to the above configuration, the timing at which the pulse voltage rises is always constant, and the timing at which the swing angle of the swing of the movable plate becomes zero by feedback control that increases or decreases the duty ratio of the pulse voltage is Is converged so as to be after the second predetermined time from the timing of starting. As a result, even if the phase of the pulse voltage and the phase of the swing of the movable plate are shifted due to factors such as internal resistance of the SOI substrate constituting the movable structure and friction with air, the phase of the pulse voltage within a short period of time. And the oscillation phase of the movable plate are synchronized again. Therefore, in the optical scanning device and the video projection device using the movable structure, it is possible to improve the scanning position of the light beam and the image quality of the projected video.

  Hereinafter, a swing device, an optical scanning device using the same device, an image display device, and a control method of the swing device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration example of a video display apparatus according to the present embodiment. Note that the hardware configurations of the oscillating device, the optical scanning device, and the video display device according to the present embodiment are basically the same as those of the conventional example described in Patent Document 1, and the control method is different.

  The video display device 100 includes a mirror element 1 having a mirror formed on the surface of a movable structure, and an optical scanning device 10 as an oscillating device having a control circuit 14 that applies a voltage for driving the mirror element 1. The light source 30 is configured to make light incident on the mirror element 1, the light source driving circuit 40 that drives the light source 30, and a power source (not shown) that supplies power to and drives each part of the apparatus. The control circuit 14 of the video display device 100 creates a video signal based on video data input from the outside, and the light source driving circuit 30 causes the light beam L to enter the mirror element 1 from the light source 30 based on the video signal. The mirror element 1 is driven, the light beam L is reflected on the external projection surface, and the light beam is scanned on the external projection surface, thereby projecting the image S on the screen.

  Except for the light source 30 and the light source drive circuit 40, the mirror element 1, the control circuit 14, and the fluctuation detection sensor 19 constitute the optical scanning device 10. The control circuit 14 includes, for example, a CPU, a ROM, a RAM, and the like, and functions as a frequency control unit 15, a voltage control unit 16, and a duty ratio control unit 17. In the video display device 100, a so-called biaxial type capable of two-dimensionally scanning the light beam L in the horizontal direction (main scanning direction) and the vertical direction (sub-scanning direction) is used as the mirror element 1. On the other hand, the optical scanning device 10 is not limited to the biaxial type, but may be a uniaxial type that scans the light beam L only in the main scanning direction. In the following, in order to facilitate understanding, a uniaxial optical scanning device will be described as an example.

  2 and 3A and 3B show the configuration of the uniaxial mirror element 1. FIG. The mirror element 1 includes, for example, a conductive first silicon layer 11a and a second silicon layer 11b, and an insulating oxide film layer 11c joined between the first silicon layer 11a and the second silicon layer 11b. This is a small movable structure configured by forming the SOI substrate 11 to be formed using a micromachining technique or the like. A substantially rectangular movable plate 2 is provided at the center of the mirror element 1, and both side portions of the movable plate 2 are pivotally supported by thin beam-shaped torsion springs 3 arranged coaxially with each other. A rectangular annular frame 4 is formed around the movable plate 2 so as to surround the movable plate 2. One end of the torsion spring 3 is connected to the frame 4. That is, the movable plate 2 is pivotally supported by the frame 4 via a torsion spring 3 serving as a shaft. A plurality of comb electrodes 2b are formed on the side of the movable plate 2 on the first side that is not formed with the torsion spring 3 and is free when swinging. Further, a plurality of comb-shaped electrodes 4b formed in a comb-like shape that meshes with the comb-shaped electrodes 2b are formed on the second side of the frame 4 that faces the first side. An electrostatic force for driving the movable plate 2 is generated by applying a predetermined voltage between a comb electrode 2b on the movable plate 2 side and a drive electrode 4d described later on the comb electrode 4b on the frame 4 side. . As shown in FIG. 3B, the movable plate 2, the torsion spring 3, the comb electrode 2b on the movable plate 2 side, and the comb electrode 4b on the frame 4 side are all formed on the first silicon layer 11a. Has been. Further, portions of the frame 4 other than the comb electrodes 4b are formed in the first silicon layer 11a, the oxide film layer 11c, and the second silicon layer 11b. When the movable plate 2 is in a stationary state where it is not driven, the movable plate 2, the torsion spring 3 and the frame 4 are arranged substantially horizontally.

  The movable plate 2 has its center of gravity located in the vicinity of the axis connecting the center lines of the two torsion springs 3 on both sides of the movable plate 2, and is driven by the comb electrode 2 b on the movable plate 2 side and the comb electrode 4 b on the frame 4 side. By generating an electrostatic force between the electrodes 4d, it swings while maintaining a balance with the torsion spring 3 as a rotation axis. On the main surface of the movable plate 2 (the surface not joined to the oxide film layer 11c), a mirror 2a for reflecting light incident from the outside of the mirror element 1 is formed. The mirror 2a is a metal film such as aluminum or gold selected according to the type of the light beam L emitted from the light source 30 or the like.

  The first silicon layer 11a constituting the frame 4 is divided into a plurality of electrically insulated portions by a plurality of insulating grooves 9 reaching the oxide film layer 11c. The first portion is a support portion 4a to which a torsion spring 3 is connected, and the second portion is a drive electrode that generates an electrostatic force for driving the movable plate 2 together with the comb electrode 2b on the movable plate 2 side. 4d, and the third portion is a detection electrode 4c constituting a swing detection sensor described later. That is, the comb electrode 4b formed on the frame 4 side is divided into a drive electrode 4d for generating a driving force and a detection electrode 4c for detecting swing. Electrode pads 7a and 7b are formed on the fixed electrode portion 4e connected to the support portion 4a and the drive electrode 4d, respectively. Therefore, the comb-teeth electrode 2b is connected to the electrode pad 7a via the support portion 4a of the frame 4, the torsion spring 3, and the movable plate 2. The drive electrode 4d is connected to each of the four electrode pads 7b via the fixed electrode portion 4e. As a result, the potential of the comb electrode 2b on the movable plate 2 side and the potential of the drive electrode 4d on the frame 4 side are controlled independently of each other. The electrode pads 7a and 7b are formed in the same process by using the same metal film as the mirror 2a, for example.

  The comb electrode 2b on the movable plate 2 side and the comb electrode 4b on the frame 4 side are, for example, arranged and arranged so as to mesh with each other while maintaining an interval of several micrometers. For example, in a state where the comb electrode 2b on the movable plate 2 side is connected to the ground potential via the electrode pad 7a on the frame 4, the control circuit 14 causes the comb electrode 4b on the frame 4 side to pass through the electrode pad 7b. Among them, the potential of the drive electrode 4d is changed, whereby a pulse voltage is applied between the comb electrode 2b and the drive electrode 4d. When a voltage is applied between the comb electrode 2b and the drive electrode 4d, an attractive force (hereinafter referred to as drive force) due to electrostatic force is generated between the comb electrode 2b and the drive electrode 4d.

  By the way, the movable plate 2 is generally tilted although the movable plate 2 is not in a horizontal posture and is very slightly inclined even when the movable plate 2 is stationary due to a dimensional error during molding. Therefore, when a driving force is generated between the comb-tooth electrode 2b and the driving electrode 4d, a component of the driving force in a direction perpendicular to the main surface of the movable plate 2 twists the movable plate 2 and rotates the spring 3 as a rotation axis. Acts as follows. Therefore, the movable plate 2 starts rotating even from a stationary state. Then, when the comb electrode 2b on the movable plate 2 side and the drive electrode 4d on the frame 4 side overlap, the application of voltage between the comb electrode 2b and the drive electrode 4d is stopped, and the driving force is reduced. To release. Thereafter, the movable plate 2 continues to rotate while twisting the torsion spring 3 by its inertial force. When the inertial force in the rotation direction of the movable plate 2 and the restoring force of the torsion spring 3 become equal, the rotation of the movable plate 2 in that direction stops. Almost simultaneously with the stop of the rotation of the movable plate 2, when the application of a voltage between the comb-tooth electrode 2b and the drive electrode 4d is started again, a restoring force of the torsion spring 3 and the comb-tooth electrode 2b and the drive electrode 4d are generated. Due to the driving force, the movable plate 2 starts to rotate in the opposite direction. Then, when the comb electrode 2b on the movable plate 2 side and the drive electrode 4d on the frame 4 side again overlap each other, the driving force is released. By repeating such control, the movable plate 2 swings around the torsion spring 3. Note that the duty ratio of the pulse voltage applied between the comb-teeth electrode 2b and the drive electrode 4d is initially set small, and then gradually increased to gradually increase the amplitude of oscillation.

  The control circuit 14 includes a frequency control unit 15 that controls the frequency of the pulse voltage applied between the comb electrode 2b and the drive electrode 4d, a voltage control unit 16 that controls a voltage value that is an amplitude of the pulse voltage, and a pulse voltage. A duty ratio control unit 17 is provided for controlling the duty ratio. Of the comb-teeth electrodes 4b on the frame 4 side, the detection electrodes 4c and the comb-teeth electrodes 2b on the movable plate 2 side that mesh with the detection electrodes 4c constitute a detection unit of a swing detection sensor 19 that detects the swing of the movable plate 2. The swing detection sensor 19 includes a detection electrode 4c, a comb electrode 2b, and a capacitance detection circuit that detects a capacitance between the detection electrode 4c and the comb electrode 2b. When the movable plate 2 swings, the opposing area of the detection electrode 4c and the comb-tooth electrode 2b changes according to the swing angle of the movable plate 2, so that the movable plate 2 can be determined from the capacitance detected by the swing detection sensor 19. 2 deflection angles can be estimated. More specifically, when the swing angle of the movable plate 2 with respect to the frame 4 becomes zero, the opposing area of the detection electrode 4c and the comb-tooth electrode 2b is maximized, and thus is detected by the swing detection sensor 19. It can be determined that the deflection angle of the movable plate 2 with respect to the frame 4 is zero when the electrostatic capacitance shows the maximum value. If the change in capacitance detected by the swing detection sensor 19 is monitored, the phase of swing of the movable plate 2 can be detected.

  The light source 30 includes, for example, a laser diode element and a lens, and is disposed so as to emit the light beam L toward the mirror 2 a of the mirror element 1. In the video display device 100, for example, it is necessary to output a video signal corresponding to a pixel located at the center of the screen at a timing when the swing angle of the movable plate 2 becomes zero. Therefore, the control circuit 14 creates a video signal synchronized with the pulse voltage using video data input from the outside, and outputs the video signal to the light source driving circuit 40. The light source driving circuit 40 applies a voltage to the light source 30 according to the video signal from the control circuit 14, and emits a light beam L from the light source 30 toward the mirror element 1. When the video S projected on the screen is a moving image, the number of frames projected on the screen per second is determined according to the video system. Therefore, the control circuit 14 needs to swing the movable plate 2 at a frequency corresponding to the video system.

  Next, the operation of the video display device 100 configured as described above will be described. In the video display device 100, the control circuit 14 synchronizes with the rise of the pulse voltage in a state where the movable plate 2 of the mirror element 1 can be stably oscillated at a predetermined frequency as described above. Start output. FIG. 4 shows a state in which the phase of the pulse voltage and the phase of oscillation of the movable plate 2 are synchronized. From the top, the waveform of the pulse voltage, the phase of oscillation of the movable plate 2, and the oscillation detection sensor 19 are used. Represents the capacitance value and the waveform of the video signal. The duty ratio of the pulse voltage is set to 50%, for example. In the case shown in FIG. 4, since the phase of the pulse voltage and the phase of the swing of the movable plate are synchronized, an initial state or an ideal state of a resistance component C0 = 0 described later is shown. When the swing angle of the movable plate 2 reaches the maximum, that is, when the movable plate 2 stops rotating, for example, in the clockwise direction (timing t1), the control circuit 14 starts outputting the pulse voltage (the pulse voltage is changed). Launch). Then, when the deflection angle of the movable plate 2 becomes zero (timing t2), the output of the pulse voltage is stopped (the pulse voltage is lowered). On the assumption that the phase of the pulse voltage and the phase of oscillation of the movable plate 2 are synchronized, the control circuit 14 determines the pulse voltage at intervals of the first predetermined time T according to the frequency of oscillation of the movable plate 2. The waveform is raised (the potential of the drive electrode 4d on the frame 4 side is increased). These timings t1, t3,... Are always constant unless the swinging frequency of the movable plate is changed. Timing t2 is an intermediate point between timings t1 and t3. Since the duty ratio of the pulse voltage is variable, the timing at which the waveform of the pulse voltage is lowered by the duty ratio control of the pulse voltage is not constant.

  However, as described above, factors such as the internal resistance of the SOI substrate constituting the movable structure and the friction with air are complicatedly entangled, and the phase of the pulse voltage and the phase of the swing of the movable plate shift. Occur. FIG. 5 shows a state in which the phase of the pulse voltage is shifted from the phase of the swing of the movable plate of the mirror element. As shown in FIG. 4, the control circuit 14 detects when the deflection angle of the movable plate 2 reaches the maximum, that is, when the rotation of the movable plate 2 stops, for example, in the clockwise direction (timing t1, t3...). Ideally, the output of the pulse voltage is started and the output is stopped at the same time as the deflection angle of the movable plate 2 becomes zero, but when the deflection angle of the movable plate 2 becomes zero as shown in FIG. If the pulse voltage continues to be output even after (timing tx), it acts as the resistance component C1. When this state continues, the difference between the phase of the pulse voltage and the phase of the oscillation of the movable plate 2 gradually increases.

  As described above, the swing detection sensor 19 detects the timing tx when the swing angle of the movable plate 2 with respect to the frame 4 becomes zero. In the initial state shown in FIG. 4, the timing tx at which the capacitance at which the deflection angle of the movable plate 2 becomes zero reaches the maximum value and the intermediate point t2 between the timings t1 and t3 at which the pulse voltage is raised coincide. However, as shown in FIG. 5, when the phase of the pulse voltage is shifted from the phase of the swing of the movable plate 2, the intermediate point between the timing tx at which the electrostatic capacitance reaches the maximum value and the timings t1 and t3 at which the pulse voltage is raised. t2 will not match. That is, the control circuit 14 monitors the change in the capacitance value detected by the fluctuation detection sensor 19 to determine whether the phase of the pulse voltage and the fluctuation phase of the movable plate 2 are synchronized, and The amount of deviation can be detected. Specifically, the control circuit 14 uses the timings t1, t3,... When the pulse voltage is raised as a reference, and the timing tx when the swing angle of the swing of the movable plate 2 detected by the swing detection sensor 19 becomes zero. Is measured, and the measured time difference is compared with a second predetermined time T / 2. When the difference between the time difference Δt and the second predetermined time T / 2 exceeds the allowable time difference, the timing tx at which the swing angle of the swing of the movable plate 2 detected by the swing detection sensor 19 becomes zero. The feedback control is performed to increase or decrease the duty ratio of the pulse voltage so as to be after the second predetermined time T / 2 from the timing t1, t3,. FIG. 6 shows a state in which the PWM control is performed and the duty ratio of the pulse voltage is changed to be small. By reducing the duty ratio of the pulse voltage, the resistance component is reduced from C1 to C2, so that an effective driving force for relatively swinging the movable plate 2 is increased, and the maximum deflection angle of the movable plate 2, That is, the amplitude increases.

Here, it will be described that when the resistance component C is changed, not only the amplitude of the movable plate 2 is changed but also the phase is changed. The swing of the movable plate 2 is established as a secondary resonance system model as shown in FIG. This equation of motion can be expressed as equation (1) in the case of reciprocating linear motion, and equation (2) in the case of rotational motion.

In the formula (2), I represents the moment of inertia, C represents the viscosity coefficient (resistance component), k represents the spring constant, and T represents the torque. Here, when T = T0eiωt and θ = θ0ei (ωt−φ), the equation (2) is solved, and the deflection angle θa and the phase φ are expressed by the equations (3) and (4), respectively.

  Since the equation (3) representing the swing angle θa of the oscillation includes the resistance component C in the denominator, the amplitude decreases as the resistance component increases from C0 to C1. On the other hand, since the equation (4) representing the phase φ includes the resistance component C in the numerator, the phase φ advances when the resistance component increases. Conversely, when the resistance component decreases from C1 to C2, the amplitude increases and the phase φ is delayed. Thus, by performing PWM control of the pulse voltage and changing the duty ratio, it is possible to change both the amplitude and phase of the swing of the movable plate 2 at the same time.

  Returning to FIG. 4, the video signal is synchronized with the pulse voltage. For example, the video corresponding to the pixel located at the center of the screen at the timing t2, t4... When the deflection angle of the movable plate 2 becomes zero. The output of the video signal is started when a predetermined time elapses from the rising timing t1, t3,... Of the pulse voltage so that the signal is output. The predetermined time is set to a time when the change in the angular acceleration of the swing of the movable plate 2 is reduced. Thereby, the video display apparatus 100 can project the video S in a proper size on a proper position on the screen.

  When the duty ratio of the pulse voltage is changed, the resistance component of the vibration of the secondary resonance system changes, and thereby the amplitude of the swing of the movable plate 2 changes. When the error is exceeded, the control circuit 14 controls the voltage control unit 16 in accordance with the change amount of the duty ratio, and increases or decreases the voltage value of the pulse voltage by a predetermined correction amount set in advance, for example. Thereby, the swing amplitude of the movable plate 2 can be made constant. Furthermore, when the oscillation frequency of the movable plate 2 is also deviated from the predetermined frequency, the control circuit 14 controls the frequency control unit 15 to change the frequency of the pulse voltage in addition to the duty ratio and voltage, Control is performed so that the swing of the movable plate 2 has a predetermined frequency.

  The duty ratio control by the duty ratio control unit 17 is, for example, according to the difference between the time difference Δt and the second predetermined time T / 2 from among the duty ratio values of a plurality of pulse voltages stored in advance in the lookup table. Alternatively, the duty ratio value may be searched, and the duty ratio of the pulse voltage may be adjusted based on the searched duty ratio value. Alternatively, from the timing tx when the swing angle of the movable plate 2 detected by the swing detection sensor 19 becomes zero, the next timing when the swing angle of the swing of the movable plate becomes zero is predicted, and at the predicted timing. The duty ratio of the pulse voltage may be adjusted so that the value of the pulse voltage becomes zero.

  As described above, according to the configuration of the present embodiment, the control circuit 14 always increases the pulse voltage at intervals of the first predetermined time T, except for changing the oscillation frequency of the movable plate 2. Since the video signal synchronized with the rise timing of the voltage is output to the light source drive circuit 40, it is not necessary to adjust the phase of the pulse voltage or shift the timing of incident light, and the control program is simplified. In addition, the duty ratio of the pulse voltage is feedback controlled even if the phase of the pulse voltage and the phase of the swing of the movable plate are out of sync due to the internal resistance of the SOI substrate constituting the movable structure or friction with air. Thus, the phase of the pulse voltage and the phase of the swing of the movable plate can be synchronized again. As a result, the phase of the video signal and the swinging phase of the movable plate 2 can be synchronized again so that the video can be displayed properly.

  As described above, the mirror element 1 has been described as being uniaxial. However, the basic control contents performed by the control circuit 14 in the biaxial mirror element 1 that is actually used in the video display device 100 are as follows. This is substantially the same as described above. That is, the control circuit 14 is configured to be able to change the duty ratio, voltage, and the like as described above for each pulse voltage for swinging the movable plate 2 around each rotation axis. With respect to the swing around each rotation axis, the phase and the swing angle can be adjusted so that the image can be displayed properly.

  In the above description, the case where the movable plate 2 is swung at a predetermined frequency corresponding to the video system has been described. However, when the movable plate 2 is swung at the resonance frequency, the movable plate 2 and the torsion spring 3 are swung. What is necessary is just to apply the pulse voltage of the frequency of about twice the resonant frequency of the vibration system comprised by these. Thereby, the swing angle of the movable plate 2 can be increased.

  Further, the shape of the movable plate 2 and the frame 4 is not limited to a rectangular shape, but may be other shapes such as a circle. The swing detection sensor is not limited to the one that detects the capacitance as described above. For example, the swing detection sensor detects the swing angle of the movable plate using a photo sensor or the like. It may be one that detects the swing angle.

1 is a block diagram illustrating a configuration example of a video display device according to an embodiment of the present invention. The perspective view which shows the mirror element used for the optical scanning device of the said apparatus. (A) is a top view of the said mirror element, (b) is the sectional view on the AA line of (a). Time chart showing the waveform of the pulse voltage, the phase of the swing of the movable plate, the capacitance value by the swing detection sensor, and the waveform of the video signal when the phase of the pulse voltage and the phase of the swing of the movable plate are synchronized . The same time chart in the state in which the phase of the pulse voltage is shifted from the phase of the swing of the movable plate. The same time chart when changing the duty ratio of the pulse voltage. The figure which shows the secondary resonance system model equivalent to the rocking | fluctuation of a movable plate.

1 Mirror element (movable structure)
2 Movable plate 2a Mirror 2b Comb electrode on movable plate 3 Torsion spring 4 Frame 4b Comb electrode on frame side 4c Detection electrode 4d Drive electrode 10 Optical scanning device 14 Control circuit 15 Frequency control unit 16 Voltage control unit 17 Duty ratio control Unit 19 Fluctuation detection sensor 30 Light source 40 Light source drive circuit 100 Video display device S Video L Light beam

Claims (10)

A movable plate, a swing shaft that pivotally supports the movable plate and acts as a torsion spring when the movable plate swings, a frame that supports the swing shaft, and the movable plate A first side that is different from the side on which the pivot shaft is provided and a second side that faces the first side of the side of the frame are provided so as to mesh with each other and drive the movable plate A movable structure provided with a plurality of comb electrodes for generating electrostatic force to
A swing detection sensor for detecting timing when the swing angle of swing of the movable plate becomes zero;
An oscillating device comprising a control circuit for controlling a voltage and a duty ratio of a pulse voltage applied between the comb electrode on the movable plate side and the comb electrode on the frame side,
The control circuit includes:
Raising the pulse voltage at a first predetermined time interval;
Using the timing at which the pulse voltage was raised as a reference, measure the time difference until the swing angle of the swing of the movable plate detected by the swing detection sensor becomes zero,
The measured time difference is compared with a second predetermined time, and if the difference between the time difference and the second predetermined time exceeds an allowable time difference, the swing vibration of the movable plate detected by the swing detection sensor is detected. An oscillating device that performs feedback control to increase or decrease the duty ratio of the pulse voltage so that the timing when the angle becomes zero is after the second predetermined time from the timing when the pulse voltage is raised. .   The control circuit searches for a duty ratio value corresponding to a difference between the time difference and the second predetermined time from among a plurality of pulse voltage duty ratio values stored in advance in a lookup table. 2. The oscillating device according to claim 1, wherein the duty ratio of the pulse voltage is adjusted based on the value of the duty ratio.   The control circuit predicts the next timing when the swing angle of the swing of the movable plate becomes zero from the timing when the swing angle of the swing of the movable plate detected by the swing detection sensor becomes zero. 2. The oscillating device according to claim 1, wherein the duty ratio of the pulse voltage is adjusted so that the value of the pulse voltage becomes zero at the same timing. The swing detection sensor includes a detection electrode constituted by a part of comb electrodes among a plurality of comb electrodes provided on the frame, and when the movable plate swings, Detecting the electrostatic capacitance between the meshed comb electrodes of the movable plate,
4. The control circuit according to claim 1, wherein the control circuit determines that a swing angle of the movable plate is zero when a capacitance detected by the swing detection sensor is maximized. 5. The swing device according to any one of the above.   5. The oscillating device according to claim 1, wherein the control circuit is capable of changing the voltage of the pulse voltage in accordance with an amount of change of the duty ratio.   7. The control circuit according to claim 1, wherein the frequency of the pulse voltage can be changed when the frequency of oscillation of the movable plate is different from a predetermined frequency. The rocking device according to the item.   The swing device according to any one of claims 1 to 6, wherein the second predetermined time is ½ of the first predetermined time.   8. An optical scanning device comprising: the oscillating device according to claim 1; and a mirror formed on a main surface of the movable plate.   8. The oscillating device according to claim 1, a mirror formed on a main surface of the movable plate, a light source that makes a light beam incident on the mirror, and driving the light source. The control circuit outputs video signals synchronized with the rising timing of the pulse voltage to the light source driving circuit using video data input from the outside. Video display device. A movable plate, a swing shaft that pivotally supports the movable plate and acts as a torsion spring when the movable plate swings, a frame that supports the swing shaft, and the movable plate A first side that is different from the side on which the pivot shaft is provided and a second side that faces the first side of the side of the frame are provided so as to mesh with each other and drive the movable plate A voltage of a pulse voltage applied between the comb electrode on the movable plate side and the comb electrode on the frame side, having a movable structure including a plurality of comb electrodes for generating electrostatic force And a control method of a swinging device that swings the movable plate by controlling the duty ratio,
Detecting the timing when the swing angle of the swing of the movable plate becomes zero,
Raising the pulse voltage at first predetermined time intervals;
Using the timing at which the pulse voltage is raised as a reference, measure the time difference until the timing at which the detected swing angle of the movable plate becomes zero,
The measured time difference is compared with a second predetermined time, and if the difference between the time difference and the second predetermined time exceeds an allowable time difference, the swing vibration of the movable plate detected by the swing detection sensor is detected. An oscillating device that performs feedback control to increase or decrease the duty ratio of the pulse voltage so that the timing when the angle becomes zero is after the second predetermined time from the timing when the pulse voltage is raised. Control method.

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