JP2010139691A - Optical scanner and image display device equipped with the optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which the variation in phase difference detected with a detection piezoelectric element is suppressed and the phase of a reflection mirror is accurately detected and to provide an image display device using the optical scanner. <P>SOLUTION: A direct current power applying part 160 applies a direct current voltage on a second piezoelectric element 140 at least when an alternate current power applying part 150 does not apply an alternate current voltage on a first piezoelectric element 130. Namely, the polarization state of the second piezoelectric element 140 is adjusted by applying the direct current voltage on the second piezoelectric element 140 when the optical scanner 100 is not driven. Thus, the variation in phase difference is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an optical scanner used in a laser printer or an image display device, and more particularly to an optical scanner using a MEMS mirror and an image display device using the optical scanner.

  Conventionally, optical scanners have been used in laser printers and image display devices that display light by scanning light. In general, a polygon mirror, a galvano mirror, a MEMS (Micro-Electro-Mechanical Systems) mirror, or the like is used as the optical scanner. In particular, the optical scanner using the MEMS mirror needs only one light reflecting surface, and the mirror, the torsion bar, and the support frame can be integrally processed. Therefore, the optical scanner using the polygon mirror and the galvanometer mirror can be downsized. Weight reduction is possible.

Japanese Patent Application Laid-Open No. 2004-133867 describes a technique for swinging a reflection mirror by driving an elastic beam connected to the reflection mirror using a driving piezoelectric element as an example of an optical scanner using a MEMS mirror. . When scanning light by swinging the reflecting mirror, it is desirable to detect the swinging state of the reflecting mirror for the purpose of controlling the scanning timing, for example. In Patent Document 1, a detecting piezoelectric element for detecting a deformation amount associated with a bending motion of an elastic beam is provided on the elastic beam, whereby the swinging state of the reflecting mirror is detected.
JP-A-9-101474

  When an optical scanner is used for image display, high-precision operation control technology is indispensable for displaying an image. For example, by applying the technique described in Patent Document 1, the detection signal from the detection piezoelectric element is compared with the drive signal for driving the drive piezoelectric element, and the drive is performed so that the phase difference between them is in a predetermined state. A method for controlling the signal is conceivable. For this control, the amount of variation in the phase difference between the drive signal and the detection signal needs to be smaller than a predetermined value determined by requirements of various conditions such as image resolution and frame rate. For example, in the case of the optical scanner 100 disclosed in an embodiment described later, it is required to suppress the amount of variation in phase difference to about several nsec.

  The present inventor has discovered that the amount of variation in the phase difference changes depending on the elapsed time from the end of the driving of the optical scanner to the next driving. Here, the amount of variation in the phase difference is an amount representing how much the time difference between the drive signal and the detection signal varies when the optical scanner is driven in a resonance state. When the optical scanner is driven in a resonance state, the detection signal is delayed in phase by 90 ° with respect to the drive signal as shown in FIG. The optical scanner 100 used in the first embodiment to be described later is configured so that the resonance frequency is about 30 kHz. Therefore, a phase difference of 90 ° corresponds to a delay of about 8 μs in time. Ideally, as long as the optical scanner 100 is resonantly driven, the detection signal should always be detected with a delay of about 8 μs with respect to the drive signal. However, in reality, the time difference between the drive signal and the detection signal varies even though the optical scanner 100 is driven to resonate.

  FIG. 10 is a diagram illustrating the elapsed time dependence of the amount of variation in the phase difference when no DC voltage is applied in the optical scanner 100 disclosed in the embodiment described below. The vertical axis indicates how much the time difference differs from the amount of phase difference variation, that is, the time difference between the drive signal and the detection signal at the time of the initial drive when the elapsed time is 0 hour. The horizontal axis represents the elapsed time from the end of driving of the optical scanner to the next driving. FIG. 10 clearly shows that the amount of variation in the phase difference increases as the elapsed time becomes longer. The amount of variation in the phase difference after about 120 hours is about 10 nsec. In addition, the maximum value of the variation amount of the phase difference is about 16 nsec after about 480 hours.

  As described above, when an optical scanner is used for image display, it is required to detect the phase of the reflecting mirror with high accuracy while suppressing the amount of variation in phase difference. However, in reality, the amount of phase difference variation increases with the elapsed time from the end of driving of the optical scanner.

  The present invention provides an optical scanner capable of suppressing the amount of variation in phase difference detected by a detecting piezoelectric element and detecting the phase of a reflecting mirror with high accuracy, and an image display apparatus using the optical scanner. With the goal.

  In order to achieve this object, the invention described in claim 1 includes a reflection mirror that is oscillated around an oscillation axis and scans incident light in a predetermined direction, and a first mirror coupled to the reflection mirror. An elastic beam, a second elastic beam connected to the reflecting mirror at a position different from the first elastic beam, and an axis of oscillation that connects the reflecting mirror, the first elastic beam, and the second elastic beam. In order to swing around, at least one of the first elastic beam or the second elastic beam is provided, and bending displacement is generated in at least one of the first elastic beam or the second elastic beam. A first piezoelectric element; an AC power supply for applying an AC voltage to the first piezoelectric element to cause the first piezoelectric element to bend; and the first elastic beam or the second elastic element. In order to detect the bending displacement state of at least one of the beams, the first In order to adjust the polarization state of the second piezoelectric element, the second piezoelectric element that is provided in at least one of the elastic beam or the second elastic beam and generates a detection signal according to its bending motion, And a DC power supply unit that applies a DC voltage to the second piezoelectric element when no AC voltage is applied to the first piezoelectric element unit by at least the AC power supply unit.

  The cause of the variation in the phase difference and the reason why the amount of variation in the phase difference is time-dependent have not yet been clarified. However, the present inventor has discovered that the amount of variation in phase difference can be suppressed by adjusting the polarization state of the detecting piezoelectric element. Therefore, according to the present invention, at least when a drive signal is not input to the drive piezoelectric element, it is possible to suppress the amount of variation in phase difference by adjusting the polarization state of the detection piezoelectric element by applying a DC voltage. To do. Here, the polarization state means the degree of alignment of the electric dipole moment in the piezoelectric element. Specifically, in the polarization state, in the hysteresis curve of polarization-electric field characteristics, the residual polarization value, which is a polarization value remaining in the piezoelectric element when no external electric field is present, and the change in the polarization value is saturated with respect to the external electric field. It is represented by a physical quantity such as a saturation polarization value.

  According to a second aspect of the present invention, in the first aspect of the present invention, the direct-current power supply unit is configured to apply a direct-current voltage to the second piezoelectric element so that an electric field higher than a coercive electric field is generated in the second piezoelectric element. It is applied to the element.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the DC power supply unit has a predetermined time after the AC power supply unit starts applying an AC voltage to the first piezoelectric element. Before, application of a DC voltage to the second piezoelectric element is started.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the predetermined time is a time required for the polarization state to be saturated with respect to a DC voltage application time.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects of the present invention, the direct current power supply unit further includes at least a polarization state of the first piezoelectric element. A DC voltage is applied to the first piezoelectric element when no AC voltage is applied to the first piezoelectric element by the AC power supply unit.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the AC power supply unit swings the reflection mirror, the first elastic beam, and the second elastic beam. In order to drive resonance around the dynamic axis, a frequency adjustment unit is provided that adjusts the frequency of the alternating voltage applied to the first piezoelectric element in accordance with the detection signal.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the DC power supply unit is further applied with an AC voltage to the first piezoelectric element by the AC power supply unit. In this case, a DC voltage is applied to at least one of the first piezoelectric element and the second piezoelectric element.

  An invention according to claim 8 is an optical scanner according to any one of claims 1 to 7 for scanning light to form an image, and a light source for supplying light to the optical scanner. And an eyepiece optical system for guiding the light scanned by the optical scanner to the eyes of the user.

  In the first aspect of the present invention, the DC power supply unit applies the DC voltage to the second piezoelectric element when at least the AC power supply unit does not apply an AC voltage to the first piezoelectric element unit. That is, the polarization state of the second piezoelectric element is adjusted by applying a DC voltage to the second piezoelectric element when at least the reflecting mirror, the first elastic beam, and the second elastic beam are not swung. The Therefore, it is possible to suppress the amount of variation in phase difference.

  In the invention according to claim 2, the DC power supply unit applies a DC voltage to the second piezoelectric element so that an electric field higher than the coercive electric field is generated in the second piezoelectric element unit. As shown in FIG. 6 which will be described later, when the applied DC voltage generates an electric field lower than the coercive electric field, the polarization state, in particular, the residual polarization value changes depending on the applied DC voltage value. However, when the applied DC voltage value generates an electric field higher than the coercive electric field, the remanent polarization value hardly depends on the DC voltage value. Accordingly, since it is not necessary to finely control the direct current voltage value applied to the second piezoelectric element, it is easy to adjust the polarization state of the second piezoelectric element.

  According to the third aspect of the present invention, the application of the DC voltage to the second piezoelectric element is started a predetermined time before the application of the AC voltage to the first piezoelectric element is started. Since no DC voltage is always applied when no AC voltage is applied to the first piezoelectric element, that is, when the optical scanner is not driven, the power consumed can be reduced.

  In the invention according to claim 4, the predetermined time is a time required for the polarization state to be saturated with respect to the application time of the DC voltage applied to the second piezoelectric element. As shown in FIG. 5, which will be described later, the polarization state of the piezoelectric element changes with the application time of the DC voltage. However, if the application time exceeds a predetermined time, the polarization state does not change even if the DC voltage application time increases. In other words, the polarization state is saturated with respect to the DC voltage application time. Accordingly, since the DC voltage is applied for the minimum time necessary for adjusting the polarization state, the power consumption can be further reduced.

  According to the fifth aspect of the present invention, at least when the AC voltage is not applied to the first piezoelectric element, the DC voltage is applied to the first piezoelectric element. By adjusting the polarization state of the first piezoelectric element that swings the reflection mirror, the first elastic beam, and the second elastic beam, the amount of variation in the phase difference can be further suppressed.

  According to the sixth aspect of the invention, the optical scanner is resonantly driven by adjusting the frequency of the AC voltage for driving the optical scanner in accordance with the detection signal. The frequency adjusting unit feeds back a detection signal related to the phase of the reflecting mirror to adjust the frequency of the AC voltage. Therefore, a technique that can reduce the phase shift amount of the reflection mirror by feedback of the detection signal is effective for driving control of the optical scanner driven by resonance.

  According to the seventh aspect of the invention, even when an AC voltage is applied to the first piezoelectric element, a DC voltage is applied to at least one of the first piezoelectric element and the second piezoelectric element. As a result, the polarization state can be adjusted even after the optical scanner is driven.

  In an invention according to an eighth aspect, the optical scanner according to any one of the first to seventh aspects is used for an image display device. By suppressing the amount of variation in the phase difference detected by the detection piezoelectric element, a more precise image can be displayed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<First Embodiment>
FIG. 1 is a perspective view of an optical scanner 100 according to the first embodiment of the present invention. In FIG. 1, the optical scanner 100 is shown in a state in which a base 110 and a pedestal 120 are separated. The optical scanner 100 is configured by bonding a base 110 and a pedestal 120. Hereinafter, the structure of the base 110 and the pedestal 120 will be described.

[Mechanical configuration of optical scanner 100]
The base 110 includes a reflection mirror 111, a first elastic beam 112, a second elastic beam 113, and an outer frame portion 114. Further, the substrate 110 includes a first piezoelectric element 130 and a second piezoelectric element 140, lower electrodes 131 and 141 for applying a voltage to the first piezoelectric element 130 and the second piezoelectric element 140, and upper electrodes 132 and 142. Is provided. The reflection mirror 111 formed in a substantially circular shape in plan view is provided at the center of the base 110. The first elastic beam 112 connected to one end of the reflection mirror 111 includes a reflection mirror support portion 112a, a coupling portion 112b, and a pair of beam portions 112c. The reflection mirror support part 112a has one end connected to the reflection mirror 111 and the other end connected to the coupling part 112b. The coupling portion 112b is coupled so as to be orthogonal to the reflecting mirror support portion 112a, and a pair of beam portions 112c are coupled to both ends. The pair of beam portions 112c are connected to both ends of the coupling portion 112b so that one end is orthogonal to the coupling portion 112b, and the other end is connected to be orthogonal to the outer frame portion 114. The second elastic beam 113 connected to the other end of the reflection mirror 111 includes a reflection mirror support portion 113a, a coupling portion 113b, and a pair of beam portions 113c. Since the shape of the second elastic beam 113 is symmetrical to the first elastic beam 112 with respect to the reflection mirror 111, the description thereof is omitted. The outer frame portion 114 is arranged in a square ring around the reflection mirror 111, the first elastic beam 112, and the second elastic beam 113. The reflection mirror 111, the first elastic beam 112, the second elastic beam 113, the first piezoelectric element 130, and the second piezoelectric element 140 are the reflection mirror, the first elastic beam, and the second elastic beam of the present invention. , An example of a first piezoelectric element and a second piezoelectric element.

  The first piezoelectric element 130 is provided on the base 110 to drive the reflection mirror 111, the first elastic beam 112, and the second elastic beam 113 to swing. Specifically, the first piezoelectric element 130 is formed on the lower electrode 131 formed from the upper surface of the pair of beam portions 112 c to the outer frame portion 114. That is, the first piezoelectric element 130 is fixed to the pair of beam portions 112 c and the outer frame portion 114 via the lower electrode 131. An upper electrode 132 is provided on the upper surface of the first piezoelectric element 130. When a voltage is applied between the lower electrode 131 and the upper electrode 132, the first piezoelectric element 130 is polarized and expands and contracts in the longitudinal direction of the pair of beam portions 112c. Since the first piezoelectric element 130 is fixed to the pair of beam portions 112c and the outer frame portion 114 via the lower electrode 131, the expansion and contraction of the first piezoelectric element 130 causes the pair of beam portions 112c to extend in the thickness direction of the base 110. It is converted into a bending displacement. That is, the first piezoelectric element 130 functions as a unimorph. The bending displacement of the pair of beam portions 112c is converted into a rotational torque for swinging the first elastic beam 112, the second elastic beam 113, and the reflection mirror 111 via the coupling portion 112b. Here, the two piezoelectric elements constituting the first piezoelectric element 130 are driven in reverse phase by applying AC voltages having opposite phases, that is, AC voltages having a phase shift of π.

  The second piezoelectric element 140 is formed on the lower electrode 141 formed from the upper surface of the pair of beam portions 113 c to the outer frame portion 114 in order to detect the swinging state of the reflection mirror 111. That is, the second piezoelectric element 140 is fixed to the pair of beam portions 113 c and the outer frame portion 114 via the lower electrode 141. An upper electrode 142 is provided on the upper surface of the second piezoelectric element 140. As described above, the expansion and contraction of the first piezoelectric element 130 is converted into the bending displacement of the pair of beam portions 112c, and as a result, the first elastic beam 112, the second elastic beam 113, and the reflection mirror 111 are swung. At this time, since the second elastic beam 113 is also swung, the second piezoelectric element 140 is bent and displaced. Since the second piezoelectric element 140 is bent and displaced, the second piezoelectric element 140 is polarized in the thickness direction of the base 110 due to the piezoelectric effect. As a result, a potential difference corresponding to the bending displacement amount of the second piezoelectric element 140 is generated between the lower electrode 141 and the upper electrode 142. By reading this potential difference as a detection signal from the lower electrode 141 and the upper electrode 142, the swinging state of the reflection mirror 111 is detected.

  The pedestal 120 includes a base fixing part 121. The base fixing part 121 is for fixing to the outer frame part 114 of the base 110 and has a quadrangular annular structure having the same size as the outer frame part 114. The optical scanner 110 is formed by fixing the pedestal 120 and the base 110 by bonding, anodic bonding, or the like.

[Control Circuit Configuration of Optical Scanner 100]
FIG. 2 is a block diagram showing a circuit configuration for driving the optical scanner 100. The AC voltage application unit 150 includes a phase comparator 151, a low-pass filter 152, a voltage controlled oscillator 153, a phase shifter 154, and a comparator 155. The phase comparator 151 compares the drive signal for driving the first piezoelectric element 130 shaped by the phase shifter 154 and the comparator 155 described later with the detection signal generated from the second piezoelectric element 140, The phase difference voltage corresponding to the phase difference is output to the low-pass filter 152. The low-pass filter 152 integrates and smoothes the phase difference voltage from the phase comparator 151. The phase difference voltage smoothed by the low-pass filter 152 is input to the voltage controlled oscillator 153 as a VCO control voltage. The voltage controlled oscillator 153 generates an alternating voltage for driving the first piezoelectric element 130. The voltage controlled oscillator 153 outputs a sine wave having a frequency corresponding to the VCO control voltage from the low-pass filter 152 to a signal superimposing circuit 190 and a phase shifter 154 described later as a drive signal. As shown in FIG. 4 to be described later, when the optical scanner 100 is in a resonance state, the phase difference between the drive signal and the detection signal is shifted by π / 2. The phase shifter 154 adjusts the phase of the input drive signal so that the phase of the input drive signal and the detection signal matches when the optical scanner 100 is in a resonance state, and outputs the adjusted signal to the comparator 155. The comparator 155 compares the potential 0V with the drive signal, and outputs a positive predetermined potential if the potential of the drive signal is 0V or higher, and a negative predetermined potential if the potential of the drive signal is 0V or lower. That is, the comparator 155 shapes the input drive signal into a rectangular wave and inputs it to the phase comparator 151. The phase comparator 151, the low pass filter 152, the voltage controlled oscillator 153, the phase shifter 154, and the comparator 155 form a phase synchronization circuit, and function to keep the oscillation of the optical scanner 100 at a predetermined oscillation frequency. Although not shown in FIG. 2, the AC voltage application unit 150 supplies a control signal to the voltage-controlled oscillator 153 and the function of adjusting the amplitude of the drive signal by boosting or stepping down the output drive signal. And has a function of adjusting the frequency of the drive signal. The AC voltage application unit 150 described above is an example of the AC power supply unit of the present invention, and the phase synchronization circuit formed by the phase comparator 151, the low-pass filter 152, the voltage control oscillator 153, the phase shifter 154, and the comparator 155 is the present invention. It is an example of the frequency adjustment part.

  The DC voltage application unit 160 applies a DC voltage to the signal superimposing circuit 190 and the second piezoelectric element 140. The second piezoelectric element 140 is directly applied with a DC voltage from the DC voltage application unit 160 between the upper electrode 142 and the lower electrode 141. On the other hand, the signal superimposing circuit 190 superimposes the drive signal output from the voltage controlled oscillator 153 and the DC voltage from the DC voltage applying unit 160, and the superimposed voltage is applied to the first piezoelectric element 130, that is, the upper electrode 132. Applied between the lower electrode 131. In other words, the DC voltage application unit 160 applies a DC voltage to the first piezoelectric element 130 via the signal superimposing circuit 190. Hereinafter, in the present embodiment, the DC voltage applied to the first piezoelectric element 130 means a DC voltage from the DC voltage application unit 160 applied via the signal superimposing circuit 190. The signal superimposing circuit 190 superimposes the direct current voltage from the direct current voltage application unit 160 and the drive signal from the voltage controlled oscillator 153, and outputs a drive signal in which the direct current voltage is superimposed on the first piezoelectric element 130. The drive signal on which the DC voltage output from the signal superimposing circuit 190 is superimposed is obtained by extending and contracting the first piezoelectric element 130 in the longitudinal direction of the beam portion 112c, thereby reflecting the first elastic beam 112, the second elastic beam 113, and the reflection. The mirror 111 is driven to swing. The detection signal from the second piezoelectric element 140 is input to the phase comparator 151 and compared with the drive signal shaped into a rectangular wave by the phase comparator 151. The signal processing circuit 170 outputs a control signal to control the DC voltage application circuit 160 and the AC voltage application unit 150 according to the flowchart shown in FIG. The signal processing circuit 170 is configured to receive a detection signal, a phase difference voltage, and the like from the AC voltage application unit 150 for the control operation. With the control circuit configuration described above, the optical scanner 100 can be resonantly driven. The DC voltage application unit 160 can apply a DC voltage to the first piezoelectric element 130 and the second piezoelectric element 140 while a drive signal is input to the first piezoelectric element 130 as described above. It is also possible to apply a DC voltage to the first piezoelectric element 130 and the second piezoelectric element 140 when no drive signal is input to the first piezoelectric element 130. The DC voltage application unit 160 described above is an example of the DC power supply unit of the present invention.

[Driving Method of Optical Scanner 100]
FIG. 3 is a flowchart illustrating a flow in which the signal processing circuit 170 controls the application of voltage to the first piezoelectric element 130 and the second piezoelectric element 140. Before the driving signal is input to the first piezoelectric element 130, the signal processing circuit 170 transmits a control signal to the DC voltage application unit 160, thereby supplying the DC voltage to the DC voltage application unit 160. Application is performed to the second piezoelectric element 140 (step S100). The signal processing circuit 170 determines whether a predetermined time required for the polarization state to saturate with respect to the DC voltage application time has elapsed since the DC voltage was applied to the first piezoelectric element 130 and the second piezoelectric element 140. Is determined (step S101). If the predetermined time has not elapsed, the DC voltage is continuously applied to the first piezoelectric element 130 and the second piezoelectric element 140 until the predetermined time has elapsed (N in step S101). When the predetermined time has elapsed (Y in step S101), the signal processing circuit 170 transmits a control signal to the AC voltage application unit 150, thereby causing the voltage controlled oscillator 153 to oscillate a drive signal having an amplitude of 5V (step S101). S102). The oscillated drive signal is input from the AC voltage application unit 150 to the signal superimposing circuit 190 and superimposed on the DC voltage and then input to the first piezoelectric element 130.

  The signal processing circuit 170 determines whether or not the detection signal exceeds a predetermined threshold voltage preset in the signal processing circuit 170 (step S103). When the detection signal does not exceed the predetermined threshold voltage (N in step S103), the signal processing circuit 170 changes the frequency of the drive signal by transmitting a control signal to the AC voltage application unit 150 (step S104). Specifically, the signal processing circuit 170 changes the frequency from 27 kHz to 33 kHz, and searches for a frequency at which the voltage of the detection signal exceeds a predetermined threshold voltage.

  The voltage value of the detection signal changes according to the frequency of the drive signal. It is possible to roughly determine whether or not the optical scanner 100 is in a resonance state based on a change in the voltage value of the detection signal. Hereinafter, the reason will be described with reference to FIG. The upper diagram of FIG. 4 is a diagram showing the relationship between the frequency of the drive signal and the amplitude gain that represents the magnitude of the deflection angle of the reflection mirror 111. The optical scanner 100 of this embodiment is manufactured so that the resonance frequency is 30 kHz. Therefore, when the frequency of the drive signal is 30 kHz, the optical scanner 100 is resonantly driven and the amplitude gain is maximized. The amplitude gain decreases as the frequency of the drive signal increases from 30 kHz. The magnitude of the deflection angle of the reflection mirror 111 is reflected as the magnitude of the voltage value of the detection signal. Therefore, it is possible to roughly determine whether or not the optical scanner 100 is in a resonance state by checking the voltage value of the detection signal.

  When the detection signal exceeds a predetermined threshold voltage (Y in step S103), the signal processing circuit 170 transmits a control signal to the AC voltage application unit 150, thereby causing the voltage control oscillator 153 to have a drive signal having an amplitude of 40V. Is oscillated (step S105). The oscillated drive signal is input from the AC voltage application unit 150 to the signal superimposing circuit 190 and superimposed on the DC voltage and then input to the first piezoelectric element 130. The signal processing circuit 170 determines whether or not the phase difference between the detection signal and the drive signal is 90 ° (step S106). When the phase difference is not 90 ° (N in step S106), the signal processing circuit 170 changes the frequency of the drive signal by transmitting a control signal to the AC voltage application unit 150 (step S107), and the phase difference is 90. Find the frequency that will be °.

  The relationship between the phase difference between the detection signal and the drive signal and the frequency of the drive signal is shown in the lower diagram of FIG. When the frequency of the drive signal and the resonance frequency of the optical scanner 100 are equal, that is, when the optical scanner 100 is in the resonance state, the phase difference between the detection signal and the drive signal is 90 °. The phase difference between the detection signal and the drive signal becomes smaller than 90 ° as the frequency of the drive signal becomes lower than the resonance frequency, and becomes larger than 90 ° as the frequency becomes higher than the resonance frequency. Therefore, it is possible to determine whether or not the optical scanner 100 is in a resonance state by examining the phase difference between the detection signal and the drive signal.

  When the phase difference between the detection signal and the drive signal is 90 ° (Y in step S106), the optical scanner 100 is driven to resonate. When the driving of the optical scanner 100 is finished (Step S108 is Y), the signal processing circuit 170 transmits a control signal to the AC voltage application unit 150 and stops outputting the drive signal (Step S109). Thereafter, the signal processing circuit 170 transmits a control signal to the DC voltage application unit 160 to stop the output of the DC voltage (step S110).

[Improvement of phase difference variation]
FIG. 4 shows how much variation in phase difference can be suppressed by applying a DC voltage to the first piezoelectric element and the second piezoelectric element before a drive signal is transmitted to the first piezoelectric element. This will be described with reference to FIGS.

  FIG. 5 shows that a DC voltage of 5 V is applied to a sample of a piezoelectric element having the same configuration as the first piezoelectric element 130 and the second piezoelectric element 140 used in the present embodiment for 0 minutes, 5 minutes, 10 minutes, and 15 minutes. , 20 minutes, the polarization state ratio (ΔP%) is a diagram showing how to change. The horizontal axis represents the elapsed time from the start of application of a DC voltage of 5V. The vertical axis represents the ratio between the polarization state of the sample before application of the DC voltage and the polarization state of the sample after application of the DC voltage. The saturation polarization value Pm indicated by a black circle and a straight line in FIG. 5 showed a substantially uniform value even when the DC voltage application time was changed. On the other hand, the remanent polarization value Pr indicated by a black square and a dotted line in FIG. 5 rapidly increases until the DC voltage application time is 5 minutes and gradually increases from 5 minutes to 10 minutes. The remanent polarization value Pr hardly changes after the DC voltage application time exceeds 10 minutes. Accordingly, it is considered that the DC voltage application time is appropriately 10 minutes or more.

  FIG. 6 is a diagram showing how the polarization state ratio (ΔP%) changes when a DC voltage of 0 V, 5 V, 10 V, 15 V, and 20 V is applied to the sample for 10 minutes. The horizontal axis represents the amount of DC voltage applied to the sample for 10 minutes. Similarly to FIG. 5, the vertical axis represents the ratio between the polarization state of the piezoelectric element sample before application of the DC voltage and the polarization state of the piezoelectric element material after application of the DC voltage. The saturation polarization value Pm and the remanent polarization value Pr are shown in FIG. 6 using the same symbols as in FIG. The saturation polarization value Pm showed a substantially uniform value even when the applied DC voltage amount was changed. On the other hand, the remanent polarization value Pr increases rapidly until the applied DC voltage amount is 5V, and shows a slight decrease from 5V to 10V. The remanent polarization value Pr hardly changes in the region where the applied DC voltage amount is 10 V or more. Therefore, it is considered that an appropriate DC voltage value of 10 V or more is appropriate. Note that the piezoelectric element used in the optical scanner 100 in this embodiment is configured to generate an electric field equal to the coercive electric field when the potential difference between the upper electrode and the lower electrode is about 8V. Therefore, it can be considered from FIG. 6 that it is appropriate to apply a voltage equal to or higher than the voltage value at which the coercive electric field is generated to the piezoelectric element.

FIG. 7 is a diagram showing the elapsed time dependence of the amount of variation in the phase difference when a DC voltage is applied. Similarly to FIG. 10, the vertical axis represents the amount of variation in phase difference, and the horizontal axis represents the elapsed time from the end of driving of the optical scanner to the next driving. In FIG. 7, a DC voltage of 10 V was applied to the first piezoelectric element for 48 hours before the optical scanner 100 was driven. Immediately after the first drive at an elapsed time of 0 hours, the amount of variation in phase difference was about 4 nsec, and after about 120 hours, the amount of variation in phase difference was about 2 nsec. In FIG. 10, which shows the dependence when no DC voltage is applied, the difference in the amount of variation in phase difference between the first drive and after 120 hours is about 10 nsec. On the other hand, in FIG. 7 to which a DC voltage is applied, the difference in the amount of variation in phase difference between the initial drive and after 120 hours is about 2 nsec, which is clearly smaller than that in FIG. . That is, the amount of variation in the detected phase difference is suppressed by applying a DC voltage to the piezoelectric element.
[Description of Image Display Device 1]
The overall configuration and operation of the image display apparatus 1 using the optical scanner 100 of this embodiment will be described. FIG. 8 shows the overall configuration of the image display device 1 according to the first embodiment. The image display device 1 is a device for causing a viewer to visually recognize a virtual image by causing a light beam to enter the pupil 52 of the viewer and displaying an image on the retina 54. This device is also called a retinal scanning display.

  The image display apparatus 1 includes a light beam generation unit 2, an optical fiber 19, a collimating optical system 20, an optical scanner 100, a first relay optical system 22, a vertical scanning unit 23, and a second relay optical system 24. The light beam generation means 2 includes a video signal processing circuit 3, a light source unit 30, and an optical multiplexing unit 40. The video signal processing circuit 3 generates a B signal, a G signal, an R signal, a horizontal synchronization signal, and a vertical synchronization signal, which are elements for combining images, based on a video signal supplied from the outside.

  The light source unit 30 includes a B laser driver 31, a G laser driver 32, an R laser driver 33, a B laser 34, a G laser 35, and an R laser 36. The B laser driver 31 drives the B laser 34 so as to generate a blue light beam having an intensity corresponding to the B signal from the video signal processing circuit 3. The G laser driver 32 drives the G laser 35 so as to generate a green light beam having an intensity corresponding to the G signal from the video signal processing circuit 3. The R laser driver 33 drives the R laser 36 so as to generate a red light beam having an intensity corresponding to the R signal from the video signal processing circuit 3. The B laser 34, the G laser 35, and the R laser 36 can be configured as, for example, a semiconductor laser or a solid-state laser with a harmonic generation mechanism. The light source unit 30 described above is an example of the light source of the present invention.

  The optical multiplexing unit 40 includes collimating optical systems 41, 42, and 43 provided to collimate laser light incident from the light source unit 30 into parallel light, and a dichroic mirror 44 for multiplexing the collimated laser light. , 45, 46, and a condensing optical system 47 that guides the combined laser light to the optical fiber 19. The blue laser light emitted from the B laser 34 is collimated by the collimating optical system 41 and then enters the dichroic mirror 44. The green laser light emitted from the G laser 35 enters the dichroic mirror 45 through the collimating optical system 42. The red laser light emitted from the R laser 36 enters the dichroic mirror 46 through the collimating optical system 43. The three primary color laser beams respectively incident on the dichroic mirrors 44, 45, and 46 are reflected or transmitted in a wavelength-selective manner and are combined as one light beam, and reach the condensing optical system 47. The laser light combined as one light beam is condensed by the condensing optical system 47 and enters the optical fiber 19.

  The horizontal scanning driver 61 drives the optical scanner 100 according to the horizontal synchronization signal from the video signal processing circuit 3. The vertical scanning driver 62 drives the vertical scanning scanner 23 according to the vertical synchronization signal from the video signal processing circuit 3. The laser light is converted into a light beam scanned in the horizontal direction and the vertical direction by the scanning of the optical scanner 100 and the vertical scanning scanner 23, and can be displayed as an image. Specifically, laser light emitted from the optical fiber 19 is converted into parallel light by the collimating optical system 20 and then guided to the optical scanner 100. The laser beam scanned in the horizontal direction by the optical scanner 100 passes through the first relay optical system 22 and then enters the vertical scanning scanner 23 as parallel rays. At this time, an optical pupil is formed at the position of the vertical scanning scanner 23 by the first relay optical system 22. The laser beam scanned in the vertical direction by the vertical scanning scanner 23 passes through the second relay optical system 24 and then enters the observer's pupil 52 as parallel rays. At this time, the observer's pupil 52 and the optical pupil at the position of the vertical scanning scanner 23 are conjugated by the second relay optical system 24. The above-described second relay optical system 24 is an example of an eyepiece optical system according to the present invention.

<Modification>
The present invention is not limited to the embodiments described so far, and various modifications and changes can be made without departing from the spirit of the present invention. An example of the modification will be described below.

  In FIG. 2, the DC voltage application unit 160 applies a DC voltage to both the first piezoelectric element 130 and the second piezoelectric element 140. However, a configuration in which a DC voltage is applied only to the second piezoelectric element 140 may be adopted.

  In the above-described embodiment, the driving frequency of the optical scanner 100 is set to be the same as the resonance frequency. That is, the optical scanner 100 is driven to resonate. However, the optical scanner 100 may be driven at a frequency different from the resonance frequency. Since it is necessary to know the phase difference between the detection signal and the drive signal in the resonance drive, it is particularly useful in the resonance drive to suppress the variation amount of the phase difference according to the present invention. However, even when the optical scanner 100 is driven at a frequency at which the phase difference is 0 ° in FIG. 4, it may be necessary to check the phase for the purpose of knowing the scanning position of the light. Therefore, the present invention is useful even when the optical scanner is not used for resonance driving.

  In the above-described embodiment, the drive signal is input to the first piezoelectric element 130 and the detection signal is output from the second piezoelectric element 140. However, since the shape of the first piezoelectric element 130 and the shape of the second piezoelectric element 140 are the same, a drive signal is input to the second piezoelectric element 140 and a detection signal is output from the first piezoelectric element 130. A circuit configuration may be used. Alternatively, a circuit configuration as shown in FIG. 9 that can switch between the input destination of the drive signal and the output source of the detection signal may be used. FIG. 9 is a block diagram illustrating a modification of the circuit configuration for driving the optical scanner 100. In FIG. 9, the same components as those in the circuit configuration of the above-described embodiment are denoted by the same reference numerals as those in FIG. This modification is different from the above-described embodiment in that a switching circuit 180 is provided and two signal superimposing circuits 190a and 190b are provided. The switching circuit 180 selectively outputs the input drive signal to one of the first piezoelectric element 130 and the second piezoelectric element 140 in accordance with the control signal from the signal processing circuit 170, so that the optical scanner It has a function of switching a piezoelectric element for driving 100. The switching circuit 180 also has a function of inputting, to the phase comparator 151, a detection signal output from the other piezoelectric element that is not used for driving the optical scanner 100 in accordance with a control signal from the signal processing circuit 170. That is, the switching circuit 180 switches the function of the first piezoelectric element 130 and the second piezoelectric element 140 to either a piezoelectric element used for driving the optical scanner 100 or a piezoelectric element that detects the phase of the optical scanner 100. Enable. The switching circuit 180 can be configured by a single-pole two-contact switch (SPDT (Single-Pole Dual Throw) switch) using, for example, a CMOS or the like. In the circuit configuration shown in FIG. 9, when the drive signal is output from the switching circuit 180 to the first piezoelectric element 130, the drive signal is first input to the signal superimposing circuit 190 a and the direct current from the direct current voltage application unit 160. After being superimposed on the voltage, it is input to the first piezoelectric element 130. At this time, since the drive signal is not input to the signal superimposing circuit 190b, only the DC voltage from the DC voltage applying unit 160 is input to the second piezoelectric element 140 via the signal superimposing circuit 190b. On the other hand, when the driving signal is output from the switching circuit 180 to the second piezoelectric element 140, the driving signal is first input to the signal superimposing circuit 190b and superimposed on the DC voltage from the DC voltage applying unit 160. Input to the second piezoelectric element 140. At this time, since the drive signal is not input to the signal superimposing circuit 190a, only the DC voltage from the DC voltage applying unit 160 is input to the first piezoelectric element 130 via the signal superimposing circuit 190a.

  The effect of using the switching circuit 180 is that the life of the optical scanner 100 can be extended like the signal path switching means described in Patent Document 1. The piezoelectric element used for driving has a greater stress than the element used for phase detection. Therefore, the lifetime of the piezoelectric element used for driving may be shorter than the lifetime of the piezoelectric element used for phase detection. By using the switching circuit 180 and switching the piezoelectric element between driving and detection as appropriate, the lifetime of the first piezoelectric element 130 and the second piezoelectric element 140 can be adjusted to be the same. Therefore, the life of the optical scanner 100 can be extended.

  In the above-described embodiment, as shown in FIG. 3, a DC voltage is applied to the first piezoelectric element 130 and the second piezoelectric element 140 even when the drive signal is transmitted to the first piezoelectric element 130. However, the first piezoelectric element 130 and the second piezoelectric element 140 only have to be adjusted in polarization state when the optical scanner 100 is driven. Therefore, the DC voltage is applied only before the drive signal is transmitted to the first piezoelectric element 130, and the DC voltage may not be applied after the drive signal is transmitted. Alternatively, if a DC voltage is applied to the first piezoelectric element 130 and the second piezoelectric element 140 even after transmission of the drive signal, the applied DC voltage is applied as in the technique described in Japanese Patent Application Laid-Open No. 2007-25608. By adjusting the value, it is also possible to change the tension generated in the piezoelectric element and adjust the resonance frequency of the optical scanner.

  The elastic beam of the optical scanner of the above-described embodiment has a so-called bifurcated beam shape that is coupled to the pair of beam portions from the reflection mirror support portion via the coupling portion. However, other structures may be used. For example, the optical scanner may be an optical scanner having a shape in which the elastic beam is not divided into two branches, such as the optical scanner shown in FIG. 1 of US Pat. No. 6,657,764 or FIG. If a piezoelectric element is used for driving, the present invention is applicable. In the optical scanner of the above-described embodiment, the reflection mirror 111 is supported at both ends by the first elastic beam 112 connected to one end and the second elastic beam 113 connected to the other end. However, even if the reflection mirror is supported by an elastic beam only at one end, such as the optical scanner shown in FIG. 1 of Japanese Patent Application Laid-Open No. 7-65098, the optical scanner swings. The present invention can be applied if a piezoelectric element is used for detection and driving. In short, any optical scanner having a configuration in which the reflection mirror supported by the elastic beam is driven and the swing state is detected by a piezoelectric element may be used.

In the embodiment described above, the two piezoelectric elements constituting the first piezoelectric element 130 are driven in reverse phase by applying AC voltages having opposite phases to each other, that is, AC voltages having a phase shift of π. However, the reverse-phase driving is performed, for example, on the right piezoelectric element of the two piezoelectric elements constituting the first piezoelectric element 130 in FIG. 1 and the left piezoelectric element of the two piezoelectric elements constituting the second piezoelectric element 140. Alternatively, this may be achieved by applying a reverse-phase AC voltage. Alternatively, an AC voltage having the same phase is applied to the right piezoelectric element of the two piezoelectric elements constituting the first piezoelectric element 130 and the right piezoelectric element of the two piezoelectric elements 140 constituting the second piezoelectric element 140 in FIG. May be applied to achieve in-phase driving.

1 is a perspective view illustrating an overall configuration of an optical scanner 100 according to a first embodiment. 1 is a block diagram showing a circuit configuration for driving an optical scanner 100. FIG. 7 is a flowchart for explaining a flow in which the signal processing circuit 170 controls the application of voltage to the first piezoelectric element 130 and the second piezoelectric element 140. The figure explaining the relationship between a frequency, an amplitude gain, and a phase difference. The figure which shows the change of a polarization state at the time of changing DC voltage application time. The figure which shows the change of a polarization state at the time of changing the direct-current voltage amount to apply. The figure which shows the elapsed time dependence of the dispersion | variation amount of a phase difference at the time of applying a DC voltage. The figure which shows the whole structure of the image display apparatus 1 in 1st Embodiment. FIG. 9 is a block diagram showing a modification of the circuit configuration for driving the optical scanner 100. The figure which showed the relationship between the elapsed time from the drive end of an optical scanner to the next drive in the case of not applying a DC voltage, and the amount of deviation | shift of a detection phase.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image display apparatus 2 Light beam production | generation means 3 Video signal processing circuit 3
19 Optical fibers 20, 41, 42, 43 Collimating optical system 22 First relay optical system 23 Vertical scanning scanner 24 Second relay optical system 30 Light source unit 31 B laser driver 32 G laser driver 33 B laser driver 34 B laser 35 G laser 35 R laser 40 Optical combiner 44, 45, 46 Dichroic mirror 47 Condensing optical system 52 Observer pupil 54 Retina 61 of observer Observer retina 61 Horizontal scan driver 62 Vertical scan driver 100 Optical scanner 110 Substrate 111 Reflection mirror 112 First Elastic beam 113 Second elastic beam 112a, 113a Reflecting mirror support part 112b, 113b Coupled part 112c, 113c Pair of beam part 114 Outer frame part 120 Base 121 Base fixing part 130 First piezoelectric element 131, 141 Lower electrode 132, 142 Upper part Electrode 140 Second piezoelectric element 150 Voltage applying unit 151 phase comparator 152 low pass filter 153 voltage controlled oscillator 154 phase shifter 155 the comparator 160 the DC voltage applying unit 170 signal processing circuit 180 switching circuit 190,190a, 190b signal superimposing circuit

Claims (8)

A reflection mirror that is swung around a swing axis and that scans incident light in a predetermined direction;
A first elastic beam coupled to the reflecting mirror;
A second elastic beam coupled to the reflecting mirror at a position different from the first elastic beam;
In order to oscillate the reflection mirror, the first elastic beam, and the second elastic beam about an oscillation axis, provided on at least one of the first elastic beam or the second elastic beam, A first piezoelectric element that causes bending displacement in at least one of the first elastic beam or the second elastic beam;
An alternating current power supply for applying an alternating voltage to the first piezoelectric element to cause the first piezoelectric element to bend;
In order to detect a bending displacement state of at least one of the first elastic beam or the second elastic beam, the bending beam is provided on at least one of the first elastic beam or the second elastic beam and is bent by itself. A second piezoelectric element that generates a detection signal in accordance with movement;
In order to adjust the polarization state of the second piezoelectric element, at least when the AC voltage is not applied to the first piezoelectric element by the AC power supply, a DC power supply that applies a DC voltage to the second piezoelectric element When,
An optical scanner comprising: The DC power supply unit applies a DC voltage to the second piezoelectric element so that an electric field higher than a coercive electric field is generated in the second piezoelectric element;
The optical scanner according to claim 1. The DC power supply unit starts applying a DC voltage to the second piezoelectric element a predetermined time before the AC power supply unit starts applying an AC voltage to the first piezoelectric element;
The optical scanner according to claim 1 or 2. The predetermined time is a time required for the polarization state to saturate with respect to the DC voltage application time.
The optical scanner according to claim 3. The DC power supply unit further includes the first piezoelectric element when no AC voltage is applied to the first piezoelectric element by at least the AC power supply unit in order to adjust the polarization state of the first piezoelectric element. DC voltage is applied to
The optical scanner according to claim 1, wherein the optical scanner is an optical scanner. The AC power supply unit applies to the first piezoelectric element according to the detection signal in order to drive the reflection mirror, the first elastic beam, and the second elastic beam to resonate around a swing axis. A frequency adjustment unit for adjusting the frequency of the AC voltage;
The optical scanner according to claim 1, wherein the optical scanner is an optical scanner. The DC power supply unit further applies a DC voltage to at least one of the first piezoelectric element and the second piezoelectric element even when an AC voltage is applied to the first piezoelectric element by the AC power supply unit. Apply
The optical scanner according to claim 1, wherein the optical scanner is an optical scanner. An optical scanner according to any one of claims 1 to 7, for forming an image by scanning light;
A light source for supplying light to the optical scanner;
An eyepiece optical system for guiding the light scanned by the optical scanner to the eyes of the user;
An image display device comprising: