JP2011215325A - Optical scanning device and image display device - Google Patents

Abstract

An optical scanning device and an image display device in which a period during which a mirror unit can be driven at a constant angular velocity is lengthened when a drive signal in which a resonance component is suppressed by a low-pass filter are generated.
An optical scanning element having a resonance mode that oscillates in a direction perpendicular to a reflecting surface of a mirror unit and a drive voltage signal Sc2 in which a resonance frequency component of the resonance mode is suppressed by a low-pass filter. And a control unit 2 for swinging the shaft around the swing shaft. The control unit 2 acquires a detection signal Sd corresponding to the angle of the mirror unit 10 from the detection unit 18, performs a difference calculation between the detection signal Sd and the drive voltage signal Sc2, and based on the difference signal that is the difference result, The resonance frequency and amplitude of the resonance mode are determined. Then, the control unit 2 sets at least one parameter among the low-pass filter method, the cutoff frequency, and the order based on the resonance frequency and amplitude of the resonance mode.
[Selection] Figure 10

Description

  The present invention relates to an optical scanning device and an image display device including an optical scanning element that scans an incident light beam in a predetermined direction by a mirror portion having a reflecting surface.

  Conventionally, an optical scanning element that scans an incident light beam in a predetermined direction by a mirror part having a reflecting surface, and a control part that swings the mirror part of the optical scanning element around a swing axis by a drive signal are provided. Optical scanning devices and image display devices are known.

  As an optical scanning element used in an optical scanning device or an image display device, it has a mirror part supported by a beam part, and the mirror part is oscillated around an oscillation axis by a torsional displacement of the beam part, and a light beam is emitted by the mirror part. An optical scanning element for scanning is known (see, for example, Patent Document 1).

  However, in such an optical scanning element, since the mirror part is supported by the support part via an elastic beam part so as to be able to swing, the inherent resonance mode determined by the mirror part and the beam part and the resonance There is a resonant frequency corresponding to the mode.

  Accordingly, if the frequency component of the signal waveform that drives the mirror portion of the optical scanning element includes a resonance frequency unique to the optical scanning element, resonance vibration is excited in the optical scanning element. As a result, a resonance vibration component is superimposed on the swing of the mirror section, and the swing angular velocity of the mirror section changes from a desired one, and a situation in which optical scanning cannot be performed properly occurs (see FIG. 16). ).

  Therefore, in a conventional optical scanning device or image display device, a resonance signal is suppressed by generating a drive signal for driving the mirror portion of the optical scanning element by performing a filtering process using a low-pass filter (Patent Document 2). reference).

JP 2006-276399 A JP 2004-361920 A

  However, in the conventional optical scanning device and image display device, in order to reliably suppress the resonance frequency component to a predetermined amplitude with a certain margin in consideration of individual differences of optical scanning elements and variations such as temperature changes. The order and cutoff frequency of the low-pass filter were set. For this reason, for example, since the cut-off frequency of the low-pass filter is set to be low for all individuals, the period during which the mirror unit can be driven at a constant angular velocity (see FIG. 17) is limited. FIG. 17A shows the waveform of the drive signal before filtering by the low-pass filter, and FIG. 17B shows the waveform of the drive signal after filtering by the low-pass filter.

  The present invention has been made in view of the above-described problems, and in the case where a drive signal in which a resonance component is suppressed by a low-pass filter is generated, an optical scanning device in which a period during which the mirror unit can be driven at a constant angular velocity is increased, and An object is to provide an image display device.

  In order to achieve the above-mentioned object, the invention according to claim 1 has a mirror portion supported by a beam portion from both sides, and the mirror portion is swung around a rocking axis by a torsional displacement of the beam portion. Based on an optical scanning element having a resonance mode that scans a light beam by a mirror unit and swings at least in a direction perpendicular to the reflection surface of the mirror unit, and a drive signal in which a resonance frequency component of the resonance mode is suppressed by a low-pass filter A control unit that swings the mirror unit around the swing axis, and a detection unit that outputs a detection signal according to an angle of the mirror unit around the swing axis, and the control unit includes: A generation unit that calculates a difference between the drive signal and the detection signal and generates a difference signal that is a difference between the drive signal and the detection signal, and a determination that determines the resonance frequency and amplitude of the resonance mode from the difference signal Part A parameter setting unit configured to set at least one parameter among the low-pass filter method, the cut-off frequency, and the order based on the resonance frequency and amplitude of the resonance mode determined by the determination unit. To do.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, when the amplitude of the resonance mode determined by the determination unit is greater than a predetermined width, the parameter setting unit The amplitude of the resonance mode is made equal to or less than the predetermined width by changing the parameter.

  According to a third aspect of the present invention, in the optical scanning device according to the second aspect of the invention, the parameter setting unit uses the resonance mode in which the cutoff frequency of the low-pass filter is determined by the determination unit as the parameter. The frequency is set to the same frequency as the resonance frequency, and then the cut-off frequency of the low-pass filter is reduced based on the amplitude of the resonance mode.

  According to a fourth aspect of the present invention, in the optical scanning device according to the third aspect, the parameter setting unit cuts the low-pass filter according to a fluctuation ratio of the resonance mode amplitude determined by the determination unit. The OFF frequency is reduced.

  The invention according to claim 5 is the optical scanning device according to claim 3 or 4, wherein the parameter setting unit changes the order of the low-pass filter when a cutoff frequency of the low-pass filter becomes a lower limit. It is characterized by doing.

  The invention according to claim 6 is the optical scanning device according to claim 3 or 4, wherein the parameter setting unit changes the method of the low-pass filter when the cutoff frequency of the low-pass filter becomes a lower limit. It is characterized by doing.

  The invention according to claim 7 is the optical scanning device according to any one of claims 2 to 6, wherein the low-pass filter system includes a Bessel type, and the parameter setting unit includes the low-pass filter. As an initial value of the method, a Bessel type is set.

  The invention according to claim 8 is the optical scanning device according to any one of claims 1 to 7, wherein the parameter setting unit stores the parameter set last in the low-pass filter, and The parameter set when the optical scanning element is driven is the stored parameter.

  According to a ninth aspect of the present invention, there is provided a light source that emits a light beam having an intensity corresponding to an image signal, a first optical scanning element that scans the light beam emitted from the light source in a first direction at a relatively high speed, A mirror portion supported by the beam portion from both sides, and the mirror portion is swung around a swing axis by the torsional displacement of the beam portion, and the light beam scanned by the first optical scanning element is A second optical scanning element having a resonance mode that scans at a relatively low speed in a second direction substantially orthogonal to the first direction and swings at least in a direction perpendicular to the reflecting surface of the mirror portion; Based on the second drive signal, the first optical scanning element is operated and the resonance frequency component of the resonance mode is suppressed by a low-pass filter, and the mirror portion of the second optical scanning element is swung around the swing axis. A control unit to be moved, and A detection unit that outputs a detection signal according to an angle of the rotation portion around the swing axis, and the control unit calculates a difference between the second drive signal and the detection signal, and performs the second drive A generation unit that generates a difference signal that is a difference between a signal and the detection signal, a determination unit that determines a resonance frequency and an amplitude of the resonance mode from the difference signal, and a resonance frequency of the resonance mode that is determined by the determination unit And a parameter setting unit that sets at least one parameter among the low-pass filter method, the cut-off frequency, and the order based on the amplitude and the amplitude.

  According to a tenth aspect of the present invention, in the image display device according to the ninth aspect, the light beam scanned by the first optical scanning element and the second optical scanning element is incident on a user's eye and the utilization is performed. An image corresponding to the image signal is projected onto a person's retina.

  According to the present invention, the parameters of the low-pass filter are set based on the resonance frequency and amplitude of the resonance mode. Therefore, even when there is an individual difference or a temperature change in the optical scanning element, the resonance mode is sufficiently attenuated. The low-pass filtering characteristic can be determined so as to secure a wide band as much as possible while keeping it. For this reason, the period which can drive a mirror part with a fixed angular velocity can be lengthened.

It is a figure which shows the structure of the optical scanning device which concerns on one Embodiment of this invention. It is a figure which shows the waveform of the drive signal which drives the optical scanning element shown in FIG. It is a figure which shows the angle change of a mirror part of the optical scanning element shown in FIG. It is a figure which shows the specific structure of the optical scanning element shown in FIG. It is the equivalent circuit of the detection part comprised by a piezoresistive element. It is a figure which shows the change of the resistance value of a piezoresistive element by torsional displacement. It is a figure which shows the change of the resistance value of a piezoresistive element by the displacement of a longitudinal vibration. It is a figure which shows the change of the resistance value of a piezoresistive element by the displacement of a twist and a longitudinal vibration. It is explanatory drawing of the offset of the detection voltage output from the detection part in the state shown in FIG. It is a figure which shows the structure of the control part shown in FIG. It is a figure which shows an example of a target angle table. It is a figure which shows the relationship between a drive voltage signal and a target angle. It is a figure for demonstrating operation | movement of the waveform adjustment part shown in FIG. It is a figure for demonstrating operation | movement of the waveform adjustment part shown in FIG. It is a figure which shows the structure of the image display apparatus which concerns on one Embodiment of this invention. It is a figure which shows the rocking | fluctuation state of a mirror part when resonance vibration generate | occur | produces in an optical scanning element. It is a figure for demonstrating the restriction | limiting of the period which can drive a mirror part by fixed angular velocity.

[1. Optical scanning device]
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the optical scanning device will be described first, and then the image display device will be described.

[1.1. Overview of optical scanning device]
First, the optical scanning device according to the present embodiment will be described. FIG. 1 is a diagram showing a configuration of an optical scanning device, FIG. 2 is a diagram showing a waveform of a drive signal, and FIG. 3 is a diagram showing a change in angle of a mirror part.

  As shown in FIG. 1, the optical scanning device 1 includes a control unit 2 that controls the entire optical scanning device 1 and a light source unit 3 that emits a luminous flux having an intensity corresponding to a drive signal Sa output from the control unit 2. And an optical scanning element 4 that scans the light beam emitted from the light source unit 3 in a predetermined direction.

  The control unit 2 generates a drive signal Sb that is a drive current for forcibly driving the mirror unit 10 of the optical scanning element 4 in a non-resonant manner, and the current waveform is a sawtooth waveform. A signal Sb is applied to the optical scanning element 4. As shown in FIG. 2, the sawtooth drive signal Sb is a signal in which the period of transition from the maximum level to the minimum level is sufficiently shorter than the period of transition from the minimum level to the maximum level. The mirror unit 10 of the optical scanning element 4 is configured to rotate around the swing axis Ly at an angle corresponding to the signal level of the drive signal Sb. The mirror unit 10 of the optical scanning element 4 is shown in FIG. As shown, it swings in a sawtooth shape around a swing axis Ly described later based on the signal waveform of the drive signal Sb.

[1.2. Specific Configuration of Optical Scanning Element 4]
Next, a specific configuration of the optical scanning element 4 will be described. FIG. 4 is a diagram showing a specific configuration of the optical scanning element 4.

  As shown in FIG. 4A, the optical scanning element 4 includes a mirror part 10 having a reflecting surface 10a, a pair of beam parts 11a and 11b, a pair of support parts 12a and 12b, a fixed part 13a, 13b and a base 14, and the mirror 10 is swung around the swing axis Ly to scan the light flux.

  The pair of beam portions 11a and 11b extend along the swing axis Ly and support each side of the mirror portion 10 with elasticity, and the mirror portion 10 is supported by the swing displacement Ly by its torsional displacement (twist deformation). It can swing around. Further, the pair of support portions 12a and 12b support the other ends of the pair of beam portions 11a and 11b with elasticity at the central portion thereof, and both fixed portions 13a and 13b fixed to the base 14 at both ends. It is fixed to. Thus, the mirror part 10 is supported by the pair of beam parts 11a and 11b and the pair of support parts 12a and 12b so as to be swingable.

  Permanent magnets 15 a and 15 b are arranged in proximity to two sides parallel to the swing axis Ly of the mirror unit 10. The direction of the magnetic field formed by the permanent magnets 15a and 15b is parallel to the reflecting surface 10a of the mirror unit 10 in a stationary state and is perpendicular to the swing axis Ly. Further, as shown in FIG. 4B, a coil 16 is formed on the back surface of the mirror portion 10 opposite to the reflecting surface 10a. The electrode of the coil 16 is connected to the control unit 2 via two beam portions 11a and 11b. With this configuration, when a drive current is passed through the coil 16, Lorentz force acts on the coil 16. For example, a Lorentz force acts on the lower half of the coil 16 from the swing axis Ly in the drawing as viewed from the front side of the paper, and a Lorentz force acts on the back side of the paper as viewed from the drawing. . As a result, a rotational torque is generated in the mirror portion 10 about the swing axis Ly. Therefore, by controlling the magnitude of the current of the drive signal Sb output from the control unit 2, the angle around the swing axis Ly of the mirror unit 10 can be controlled.

  The optical scanning element 4 is further provided with piezoresistive elements R1 to R4 as a detection unit 18 that detects an angle around the swing axis Ly of the mirror unit 10. The pair of piezoresistive elements R1 and R3 are disposed symmetrically with respect to the swing axis Ly on the support portion 12a. The piezoresistive element R1 is arranged on the support part 12a on the fixed part 13a side, and the piezoresistive element R3 is arranged on the support part 12a on the fixed part 13b side. Similarly, the pair of piezoresistive elements R2 and R4 are disposed symmetrically with respect to the swing axis Ly on the support portion 12b. The piezoresistive element R2 is arranged on the support part 12b on the fixed part 13a side, and the piezoresistive element R4 is arranged on the support part 12b on the fixed part 13b side.

  The resistance value of one pair of piezoresistive elements R1 and R3 changes depending on the stress field generated in the vicinity of the swing axis Ly according to the torsional displacement generated in the beam portion 11a, and the other pair of piezoresistive elements. The resistance values of the elements R2 and R4 change depending on the stress field generated in the vicinity of the swing axis Ly according to the torsional displacement generated in the beam portion 11b.

  As shown in FIG. 4C, the pair of piezoresistive elements R1 and R3 are arranged in series between the power supply potential Vc and the ground potential GND. Similarly, the pair of piezoresistive elements R4 and R2 are arranged in series with the power supply potential Vc and the ground potential GND. That is, one end of the piezoresistive elements R1 and R4 is connected to the power supply of the power supply potential Vc, and the other end is connected to one end of the piezoresistive elements R2 and R3. The other ends of the piezoresistive elements R2 and R3 are connected to the ground of the ground potential GND.

  FIG. 5 is an equivalent circuit of the detector 18 configured by the piezoresistive elements R1 to R4 shown in FIG. As shown in the figure, the detection unit 18 uses a connection point between a pair of piezoresistive elements R1 and R3 as a first output node N1, and a connection point between the other pair of piezoresistive elements R4 and R2 as a second output node. N2. The control unit 2 receives the voltage VPR + of the first output node N1 and the voltage VPR− of the second output node N2, and the voltage of the first output node N1 with reference to the voltage of the second output node N2. Is a detection signal Sd (= [VPR +] − [VPR−]). When the drive signal Sb is not applied to the optical scanning element 4, that is, when the current value of the drive signal Sb is 0 [A], the resistance values of the piezoresistive elements R1 to R4 are not changed, and the piezoresistive element R1. When the initial resistance values of .about.R4 are the same, the detection signal Sd is 0V.

  Here, each of the piezoresistive elements R1 to R4 has a characteristic that the resistance value increases due to compressive stress and the resistance value decreases due to tensile stress. Changes. Here, it is assumed that the piezoresistive elements R1 to R4 have the same material and the same shape, and the same characteristics.

  For example, as shown in FIG. 6, when the mirror section 10 is inclined at an angle θ about the swing axis Ly, the resistance values of the piezoresistive elements R1 and R2 increase due to compressive stress, and the piezoresistive elements R3, R3, The resistance value of R4 decreases due to the tensile stress. Therefore, the voltage VPR + of the first output node N1 decreases, the voltage VPR− of the second output node N2 increases, and the detection signal Sd becomes positive. The detection signal Sd increases as the angle θ of the mirror unit 10 around the swing axis Ly increases. On the other hand, when the mirror unit 10 is tilted in the direction opposite to the direction shown in FIG. 6, the detection signal Sd has a negative polarity, and the detection signal Sd increases as the angle of the mirror unit 10 about the swing axis Ly increases.

  As described above, the tilt direction of the mirror unit 10 from the equilibrium state shown in FIG. 4 can be found from the polarity of the detection signal Sd, and the tilt angle of the mirror unit 10 can be found from the magnitude of the detection signal Sd. Using this principle, the control unit 2 detects the actual tilt angle of the mirror unit 10 around the swing axis Ly by the detection signal Sd.

  As shown in FIG. 7A, the optical scanning element 4 has a resonance mode (hereinafter referred to as a longitudinal resonance mode) of longitudinal vibration that swings in a direction perpendicular to the reflecting surface 10a. In this longitudinal resonance mode, for example, as shown in FIG. 7B, when the mirror portion 10 is displaced, compressive stress is generated in all of the piezoresistive elements R1 to R4, and the resistance value increases uniformly. . Therefore, the detection signal Sd does not change. Further, when the mirror portion 10 is displaced in the direction opposite to the direction shown in FIG. 7B, tensile stress is generated in all of the piezoresistive elements R1 to R4, and the resistance value thereof uniformly decreases. Therefore, the detection signal Sd does not change.

  On the other hand, as shown in FIG. 8, the mirror unit 10 is twisted and displaced, and the mirror unit 10 is tilted about the swing axis Ly (see FIG. 6). It is assumed that resonance (see FIG. 7) occurs in the direction. At this time, the compressive stress to the piezoresistive elements R1 and R2 due to torsional displacement becomes larger than that shown in FIG. 6, and the resistance value further increases. On the other hand, the tensile stress applied to the piezoresistive elements R3 and R4 due to torsional displacement is smaller than that shown in FIG. 6, and the resistance value decreases. The initial value of the resistance value at this time, that is, the rate of change from the equilibrium state of the beam portions 11a and 11b is larger in the piezoresistive elements R1 and R2 than in the piezoresistive elements R3 and R4. As a result, the detection signal Sd is further lowered compared to the state shown in FIG. The lowering degree increases as the torsional displacement generated in the mirror unit 10 increases. On the other hand, when a force that is displaced in the direction opposite to the direction shown in FIG. 7 acts due to resonance, the detection signal Sd rises more than in the state shown in FIG. The degree of increase increases as the torsional displacement generated in the mirror unit 10 increases.

  Thus, when a longitudinal displacement is applied to the mirror unit 10 in addition to the torsional displacement, the total compressive stress and tensile stress applied to the piezoresistive elements R1 to R4 due to the torsional displacement vary depending on the state of the longitudinal displacement. That is, when longitudinal vibration due to resonance occurs while the mirror portion 10 of the optical scanning element 4 is driven in a sawtooth shape by the drive signal Sb, the detection signal Sd is as shown in FIG. Then, the difference signal Ss between the magnitude of the detection signal Sd and the magnitude of the drive signal Sb used for feedback control has a form as shown in FIG. Here, it is assumed that the resonance frequency of the longitudinal resonance mode is sufficiently higher than the frequency of the drive signal Sb.

  The control unit 2 can detect the longitudinal resonance mode based on the variation of the difference signal Ss by using such characteristics of the optical scanning element 4. That is, when longitudinal vibration due to resonance occurs while the mirror unit 10 of the optical scanning element 4 is driven in a sawtooth shape by the drive signal Sb, the difference signal Ss fluctuates, and the control unit 2 The resonance frequency and amplitude of the excited longitudinal resonance mode are detected by the fluctuation of the signal Ss.

  Then, the control unit 2 sets at least one parameter among the low-pass filter method, the cutoff frequency, and the order based on the resonance frequency and amplitude of the longitudinal resonance mode thus detected. By doing so, the parameters of the low-pass filter can be appropriately set according to individual differences of the optical scanning elements 4 or temperature changes, and the period during which the mirror unit can be driven at a constant angular velocity is longer than in the prior art. can do.

  In the above description, two pairs of piezoresistive elements R1 to R4 are used. However, a longitudinal resonance mode is detected using a pair of piezoresistive elements R1 and R3 (or a pair of piezoresistive elements R4 and R2). You may make it do. By using the two pairs of piezoresistive elements R1 to R4, the range of the detection signal Sd can be increased. However, since the range of the detection signal Sd is small with only a pair of piezoresistive elements, the detection signal Sd is voltage amplified. An amplifier may be provided between the output node N1 (N2) between the piezoresistive elements and the control unit 2.

  In the above description, each piezoresistive element R1 to R4 has been described as having a resistance value that increases due to compressive stress and a resistance value that decreases due to tensile stress. The same applies even if the resistance value increases due to stress.

[1.3 Configuration and operation of control unit 2]
As described above, the control unit 2 generates the drive signal Sb, swings the mirror unit 10 in the scanning angle range, reflects the light beam by the reflecting surface 10a of the mirror unit 10, and scans the light beam. The configuration is as shown in FIG.

  As illustrated in FIG. 10, the control unit 2 includes a target angle command generation unit 21, a conversion unit 22, a low-pass filter (LPF) unit 23, a subtraction unit 24, and a drive signal generation unit 25.

  The target angle command generation unit 21 outputs the target angle of the mirror unit 10 corresponding to the direction to be scanned by the optical scanning element 4 as a target angle command. In the target angle command generation unit 21, information on the target angle of the mirror unit 10 in one scanning period T (see FIG. 3) is stored in the internal storage unit, and the information stored in this storage unit is sequentially read out. Output as target angle command. For example, as information on the target angle of the mirror unit 10 in one scanning period, a target angle table having information from 1 to 1000th is stored in the storage unit, and information from 1 to 1000th is sequentially read out as a target angle command. Output. As described above, the target angle is in the range of + θ1 to −θ1, and the target angle table is, for example, a table as shown in FIG. Note that the target angle of the mirror unit 10 may not be stored in advance, but may be obtained by sequential calculation.

The conversion unit 22 stores a specified value α and an offset value β that define the relationship between the target angle of the mirror unit 10 and the drive voltage signal Sc1, and according to the target angle command output from the target angle command generation unit 21 The drive voltage signal Sc1 is output. In the optical scanning element 4 according to the present embodiment, as shown in FIG. 12, the drive voltage signal Sc1 and the angle of the mirror unit 10 are in a proportional relationship, and are driven based on the target angle θ and based on the following equation (1). The voltage signal Sc1 is calculated. The specified value α and the offset value β are used to generate the control voltage Sc1 so that feedback control can be performed by the detection signal Sd.
Sc1 = θ × α + β (1)
The conversion unit 22 stores therein a conversion table that defines the relationship between the target angle of the mirror unit 10 and the drive voltage signal Sc1, and based on this conversion table, the target angle of the mirror unit 10 is converted into the drive voltage signal. You may make it convert into Sc1.

  The low-pass filter unit 23 is provided for filtering and suppressing a high-frequency component of the drive voltage signal Sc1, and a plurality of low-pass filters 27a to 27e are provided therein. The low-pass filter 27a is a Bessel-type low-pass filter, the low-pass filter 27b is a Butterworth-type low-pass filter, and the low-pass filter 27c is a Chebyshev-type low-pass filter. The low-pass filter 27d is an inverse Chebyshev (Chebyshev II) type low-pass filter, and the low-pass filter 27e is a simultaneous Chebyshev-type low-pass filter. The low-pass filters 27a to 27e can set the order and cut-off frequency from the outside. In the following, when any or all of the low-pass filters 27a to 27e are referred to, the low-pass filter 27 may be used.

  The subtracting unit 24 subtracts the voltage value of the detection signal Sd from the voltage value of the driving voltage signal Sc2 generated by removing the high frequency component by the low-pass filter unit 23, and the difference voltage between the driving voltage signal Sc2 and the detection signal Sd Is output as a differential signal Ss. This differential signal Ss becomes a resonance component of longitudinal vibration when resonance of longitudinal vibration is applied to the mirror unit 10. On the other hand, when the resonance of the longitudinal vibration is not applied to the mirror unit 10, the difference signal Ss has a value of zero. However, in actuality, a noise component exists in the detection signal Sd, and it is desirable to provide a second low-pass filter (not shown) that does not affect the resonance component of the longitudinal vibration at the output of the detection unit 18. . At this time, it is desirable that the second low-pass filter has a characteristic that does not affect the longitudinal resonance mode, and that a phase shifter that compensates for phase rotation is provided downstream of the second low-pass filter.

  The drive signal generation unit 25 generates a drive signal Sb having a current value obtained by increasing / decreasing the current value according to the difference signal Ss, and outputs the drive signal Sb to the coil 16 of the optical scanning element 4. That is, when the difference signal Ss has a positive polarity, a drive signal Sb having a current value increased by a value proportional to the signal level of the difference signal Ss is generated. When the difference signal Ss has a negative polarity, the difference signal Ss. The drive signal Sb is generated by reducing the current value by a value proportional to the signal level. The drive signal generation unit 24 can be configured by an integrator that integrates the difference signal Ss, for example. In this way, the optical scanning element 4 is driven by the drive signal Sb having a current value corresponding to the difference signal Ss and feedback control is performed, so that the mirror unit 10 of the optical scanning element 4 is oscillated with high accuracy. I have to.

  In the case where the optical scanning element 4 is not a current-driven optical scanning element but a voltage-driven optical scanning element, the drive signal generating unit 25 increases or decreases the current value according to the difference signal Ss. A value drive signal Sb is generated.

  Further, the control unit 2 has an LPF control unit 26 for setting parameters of the low-pass filter unit 23.

  The LPF control unit 26 has a function of setting parameters of the low-pass filter unit 23, and includes a resonance determination unit 31 and a parameter setting unit 32.

  The resonance determination unit 31 determines whether or not the mirror unit 10 is in a longitudinal vibration state by resonance based on the difference signal Ss. When the resonance determination unit 31 determines that the mirror unit 10 is in the longitudinal vibration state, the resonance determination unit 31 detects the resonance frequency fs and the amplitude D of the longitudinal resonance mode based on the difference signal Ss. The difference signal Ss includes a component having a frequency other than the resonance frequency fs in the longitudinal resonance mode. If the frequency component is smaller than the resonance frequency component, the resonance determination unit 31 determines that the difference signal Ss Is detected as the amplitude of the resonance mode. When the difference signal Ss includes a frequency component other than the resonance frequency fs of the longitudinal resonance mode, the resonance determination unit 31 reduces the frequency component other than the resonance frequency by a low-pass filter or the like. The amplitude D of the longitudinal resonance mode is detected. At this time, as the prior information, the resonance frequency of the longitudinal resonance mode may be predicted in advance from the component specifications, and the cut-off frequency of the low-pass filter may be set.

  The parameter setting unit 32 sets the parameters of the low-pass filter unit 23 based on the information about the resonance frequency fs and the amplitude D of the longitudinal resonance mode output from the resonance determination unit 31. The parameters of the low-pass filter unit 23 include the method of the low-pass filter 27, the cutoff frequency, and the order. Specifically, the parameters of the low-pass filter unit 23 are set by performing the following setting process of the low-pass filter 27. During the setting process of the low-pass filter 27, the target angle command is output from the target angle command generation unit 21 to the conversion unit 22, and the sawtooth drive voltage signal Sc1 is continuously output from the conversion unit 22. The The sawtooth drive voltage signal Sc1 includes a component of the resonance frequency fs of the longitudinal resonance mode.

  When the parameter setting unit 32 starts the setting process of the low-pass filter 27, first, as shown in FIG. 13, the Bessel type is set as the method of the low-pass filter 27 for the low-pass filter unit 23, and the order thereof is further set. A predetermined order (for example, 8th order) is set (step S10).

  Thereafter, the parameter setting unit 32 acquires information on the resonance frequency fs from the resonance determination unit 31 (step S11), and the cut-off frequency fc of the low-pass filter 27 is set to the same frequency as the resonance frequency fs with respect to the low-pass filter unit 23. (Step S12).

  Next, the parameter setting unit 32 sets the lower limit value fd (step S13). This lower limit value fd is a frequency that is lower than the resonance frequency fs by a preset frequency fg, and the frequency fg is determined in advance according to the method and order of the low-pass filter 27.

  Next, the parameter setting unit 32 determines whether or not the set value fc is less than or equal to the lower limit value fd (step S14). In this process, when it is determined that the set value fc is not less than or equal to the lower limit value fd (step S14: No), the parameter setting unit 32 acquires information on the amplitude D from the resonance determination unit 31 (step S15), and this time acquisition. It is determined whether or not the measured amplitude D is equal to or smaller than the previously acquired amplitude D (step S16).

  If it is determined in step S16 that the currently acquired amplitude D is equal to or smaller than the previously acquired amplitude D (step S16: Yes), the parameter setting unit 32 determines whether or not the currently acquired amplitude D is within a predetermined range. Is determined (step S17). In this process, when it is determined that the amplitude D acquired this time is within a predetermined range (step S17: Yes), the parameter setting unit 32 ends the setting process of the low-pass filter 27.

  On the other hand, if it is determined in step S17 that the amplitude D acquired this time is not within the range specified in advance (step S17: No), the parameter setting unit 32 proceeds to step S18. Similarly, when it is determined in step S16 that the currently acquired amplitude D is not less than or equal to the previously acquired amplitude D (step S16: No), the parameter setting unit 32 proceeds to step S18. In step S18, the parameter setting unit 32 reduces the set value fc by a predetermined frequency, sets it in the low-pass filter unit 23 (step S18), and returns the process to step S14. The parameter setting unit 32 does not reduce the set value fc by a predetermined frequency, but the fluctuation ratio of the amplitude D of the resonance mode determined by the resonance determination unit 31 (the amplitude D acquired this time and the amplitude D acquired last time). The set value fc may be reduced according to the difference between the two values. For example, when the fluctuation ratio of the resonance mode amplitude D is small, the reduction degree of the set value fc is increased, and when the fluctuation ratio of the resonance mode amplitude D is large, the reduction degree of the setting value fc is lowered. In this way, it is possible to quickly set the parameters of the low-pass filter 27.

  If it is determined in step S14 that the set value fc is equal to or lower than the lower limit value fd (step S14: Yes), the parameter setting unit 32 determines whether there is a changeable order (step S19). The changeable order means an order that has not yet been set among the orders of the low-pass filter 27 that can be selected in the setting process of the low-pass filter 27. If it is determined that there is a changeable order (step S19: Yes), the parameter setting unit 32 sets the order determined to be changeable in the low-pass filter unit 23 (step S20), and the process returns to step S11. . The order of the low-pass filter 27 can be changed by increasing the order, for example. At this time, the parameter setting unit 32 desirably increases the order of the selectable low-pass filter 27 to a substantially effective order in consideration of the S / N ratio.

  If it is determined in step S19 that there is no changeable order (step S19: No), the parameter setting unit 32 determines whether there is a changeable low-pass filter 27 method (step S21). The changeable low-pass filter 27 method means a method that has not been set yet among selectable low-pass filter 27 methods in the setting process of the low-pass filter 27. For example, when the filters 22a to 22c are set, the filter 22d and the filter 22e are determined to be a method of the low-pass filter 27 that can be changed. It is desirable to select the low pass filter in order from the flat ripple characteristic of the pass band and the group delay characteristic of the pass band. For example, the Bessel low pass filter 27a and the Butterworth low pass filter 27b are selected in the order of an inverse Chebyshev low pass filter 27d, a simultaneous Chebyshev low pass filter 27e, and a Chebyshev low pass filter 27c.

  If it is determined in step S21 that there is a changeable low-pass filter 27 method (step S21: Yes), the parameter setting unit 32 sets the low-pass filter 27 method determined to be changeable in the low-pass filter unit 23. (Step S22), and the process returns to Step S11. On the other hand, if it is determined that there is no changeable low-pass filter 27 method (step S21: No), the parameter setting unit 32 ends the process.

  As described above, in the optical scanning device 1 according to the present embodiment, the parameters of the low-pass filter unit 23 are set based on the resonance frequency fs and amplitude D of the resonance mode. Even in such a case, the low-pass filtering characteristic can be determined so as to ensure as wide a band as possible while maintaining the characteristic of sufficiently attenuating the resonance mode. For this reason, the period which can drive the mirror part 10 with a fixed angular velocity can be lengthened.

  In the example of the setting process of FIG. 13, first, the predetermined method and order of the low-pass filter 27 are set for the low-pass filter unit 23, and the cutoff frequency fc having the same frequency as the resonance frequency fs is set. However, the initial value setting method is not limited to this method, and may be performed as shown in FIG. 14, for example.

  That is, in the example shown in FIG. 14, when the setting process of the low-pass filter 27 is started, the parameter setting unit 32 sets the method, order, and cut-off frequency fc of the low-pass filter 27 set in the previous setting process as they are (step). S30). At this time, if there is no previously set parameter, the parameter setting unit 32 performs the same processing as steps S10 to S12.

  Next, the parameter setting unit 32 sets the lower limit value fd as in the process of step S13 (step S31). Thereafter, the parameter setting unit 32 performs the same processing as the processing shown in FIG. The parameter setting unit 32 stores the method, order, and cutoff frequency of the low-pass filter 27 set this time in step S43 before the parameter setting process ends, and the parameter setting process ends.

  As described above, an initial value setting method in which the method, order, and cutoff frequency fc of the low-pass filter 27 set in the previous setting process may be set as they are. In this way, the parameters of the low-pass filter 27 can be set quickly.

  In the above description, the priority order is increased in order of the cut-off frequency, order, and method of the low-pass filter to change them. However, only one of these may be changed, Only two of these may be changed.

  Further, the method of the low pass filter 27 is not limited to the above five types, and other methods may be selected.

  In the above description, the signal to be compared with the amplitude of the detection signal Sd is the drive voltage signal Sc2, but the comparison target may be a signal proportional to the drive signal Sb. For example, the drive signal Sb is voltage-converted. A signal may be used. Alternatively, the drive voltage signal Sc1 may be used as a signal for comparison.

[2. Image display device]
Next, an image display apparatus including the above-described optical scanning element will be described.

  As shown in FIG. 15, the image display apparatus 100 according to the present embodiment includes a control unit 110, a light source unit 120, a scanning unit 140, a second relay optical system 180, a half mirror 185, and the like.

  The control unit 110 includes a drive signal supply unit 111, a main scanning drive signal generation unit 112, a sub scanning drive signal generation unit 113, and a main control unit 114. Based on an image signal S (for example, NTSC composite signal, component signal) input from the outside, the drive signal supply unit 111 receives RGB pixel signals 115r, 115g, and 115b of the three primary colors that are elements for forming an image. Generated in pixel units. The main scanning drive signal generating unit 112 generates and outputs a main scanning driving signal 116 used in the main scanning unit 160 so that an optical scanning element 161 (described later) of the main scanning unit 160 is in a predetermined scanning range in a resonance state. To do. Further, the sub-scanning drive signal generation unit 113 generates and outputs a sawtooth-shaped sub-scanning drive signal 117 used in the sub-scanning unit 170 in synchronization with the main scanning drive signal 116.

  The light source unit 120 is provided with an R laser driver 121, a G laser driver 122, and a B laser driver 123. The laser drivers 121, 122, and 123 supply drive currents to the lasers 124, 125, and 126 based on the R, G, and B drive signals 115r, 115g, and 115b output from the drive signal supply unit 111, respectively. To do. Each laser 124, 125, 126 emits laser light whose intensity is modulated in accordance with the drive current supplied from each laser driver 121, 122, 123. The R (red) laser light Lr, G (green) laser light Lg, and B (blue) laser light Lb emitted from the lasers 124, 125, and 126 were collimated by collimating optical systems 127, 128, and 129, respectively. Later, the light enters the dichroic mirrors 130, 131, and 132. Thereafter, the laser beams Lr, Lg, and Lb of the three primary colors are wavelength-selectively reflected and transmitted by these dichroic mirrors 130, 131, and 132, reach the coupling optical system 133, and are combined to the optical fiber cable 135. Emitted. Thus, the laser light emitted to the optical fiber cable 135 is a combination of intensity-modulated laser light of each color.

  The scanning unit 140 includes a collimating optical system 151, a main scanning unit 160, a first relay optical system 165, a sub-scanning unit 170, and the like.

  The collimating optical system 151 collimates the laser beam generated by the light source unit 120 and emitted through the optical fiber cable 135.

  The main scanning unit 160 and the sub-scanning unit 170 are arranged in the main scanning direction and the sub-scanning direction so that the laser light incident from the optical fiber cable 135 can be projected on the retina 190b of the user's eye 190 as an image. An optical system for scanning. The main scanning unit 160 includes an optical scanning element 161 that reciprocally scans incident laser light that has been collimated by the collimating optical system 151 in the main scanning direction. The sub-scanning unit 170 scans the optical scanning element 171 that scans in the main scanning direction by the main scanning unit 160 and scans the laser light incident through the first relay optical system 165 at a relatively low speed in the sub-scanning direction. Have. This sub-scanning direction is a direction substantially orthogonal to the main scanning direction. For example, the main scanning direction can be the horizontal direction and the sub-scanning direction can be the vertical direction.

  The first relay optical system 165 that relays the laser beam between the main scanning unit 160 and the sub-scanning unit 170 converges the laser beam scanned in the main scanning direction by the optical scanning element 161 on the mirror unit of the optical scanning element 171. Let The laser beam is scanned in the sub-scanning direction by the optical scanning element 171. The laser beam scanned by the optical scanning element 171 is a half mirror 185 positioned in front of the eye 190 via a second relay optical system 180 in which two lenses 180a and 180b having positive refractive power are arranged in series. And is incident on the user's pupil 190a. As a result, an image corresponding to the image signal S is projected on the retina 190b, and the user recognizes the laser light incident on the pupil 190a as an image. Further, the half mirror 185 transmits the external light L2 so as to enter the pupil 190a of the user, so that the user visually recognizes an image in which the image based on the laser light L1 is superimposed on the external scene based on the external light L2. can do. As described above, the image display device 100 is a see-through retinal scanning image display device that forms an image on the retina of the user's eye 190 by superimposing an image according to the image signal S and an outside scene.

  In the image display device 100 configured as described above, the optical scanning element 171 has the same configuration as that of the optical scanning element 4, and the sub-scanning drive signal generation unit 113 includes the control unit 2 of the optical scanning device 1 described above. Similarly, the optical scanning element 171 having the same configuration as that of the optical scanning element 4 is driven. That is, the optical scanning element 171 is provided with a detection unit that detects the angle of the mirror unit, and the sub-scanning drive signal generation unit 113 detects the sub-scanning drive signal 117 (or a signal proportional to the sub-scanning drive signal 117) and the detection unit. Since the resonance frequency fs and the amplitude D corresponding to the resonance mode are detected based on the difference signal from the signal Sd, and the parameters of the low-pass filter unit 23 are set based on the resonance frequency fs and the amplitude D, the optical scanning element Even when there are individual differences or temperature changes in 171, the low-pass filtering characteristics can be determined so as to ensure as wide a band as possible while maintaining the characteristics that sufficiently attenuate the resonance mode. For this reason, the period which can drive a mirror part with a fixed angular velocity can be lengthened.

  Here, laser light that is advantageous in terms of efficiency is used as an example of the light flux, but the light flux is not limited to laser light.

  In addition, although the detection unit that detects the angle of the mirror unit of the optical scanning element is configured by a piezoresistive element, a detection method using a piezoelectric element or a detection method using a change in capacitance may be used.

  Although the present invention has been described through the above-described embodiments, the following effects can be expected according to this embodiment.

(1) It has the mirror part 10 supported by the beam parts 11a and 11b from both sides, and the mirror part 10 is swung around the rocking axis by the torsional displacement of the beam parts 11a and 11b, and the light beam is scanned by the mirror part 10. In addition, the optical scanning element 4 (171) having a resonance mode that swings at least in the direction perpendicular to the reflecting surface 10a of the mirror unit 10 and a drive voltage signal in which the component of the resonance frequency fs of the resonance mode is suppressed by the low-pass filter 27. Based on Sc2, the control unit 2 (110) that swings the mirror unit 10 of the optical scanning element 4 (171) about the swing axis Ly, and the detection signal Sd according to the angle of the mirror unit 10 about the swing axis Ly. Is provided. Then, the control unit 2 (110) performs a difference calculation between the drive voltage signal Sc2 (drive signal Sb) and the detection signal Sd, and generates a difference signal Ss that is a difference between the drive voltage signal Sc2 and the detection signal Sd. Based on the subtraction unit 24, the resonance determination unit 31 for determining the resonance frequency resonance frequency fs and the amplitude D from the difference signal Ss, and the resonance mode resonance frequency fs and amplitude D determined by the resonance determination unit 31. Since the parameter setting unit 32 for setting at least one parameter among the method of the low-pass filter 27, the cut-off frequency, and the order is provided, even if there is an individual difference or a temperature change in the optical scanning element 4, the resonance mode The low-pass filtering characteristic can be determined so as to secure a wide band as much as possible while maintaining the characteristic of sufficiently attenuating the noise. For this reason, the period which can drive the mirror part 10 with a fixed angular velocity can be lengthened.

(2) When the resonance mode amplitude D determined by the resonance determination unit 31 is larger than the predetermined width, the parameter setting unit 32 changes the parameter of the low-pass filter 27 so that the resonance mode amplitude D is less than or equal to the predetermined width. Therefore, the vibration of the mirror unit 10 due to resonance can be reliably suppressed, and the period during which the mirror unit 10 can be driven at a constant angular velocity can be lengthened.

(3) The parameter setting unit 32 sets the cutoff frequency fc of the low-pass filter 27 as a parameter to the same frequency as the resonance frequency fs of the resonance mode determined by the resonance determination unit 31, and then the amplitude D of the resonance mode. Since the cut-off frequency fc of the low-pass filter 27 is reduced based on the above, the parameters of the low-pass filter 27 can be quickly set.

(4) Since the parameter setting unit 32 sets the cutoff frequency fc of the low-pass filter 27 according to the fluctuation ratio of the amplitude D of the resonance mode determined by the resonance determination unit 31, the parameter setting unit 32 can quickly set the parameters of the low-pass filter 27. Can be done.

(5) Since the parameter setting unit 32 changes the order of the low-pass filter 27 when the cutoff frequency fc of the low-pass filter 27 reaches the lower limit value fd, the order of the low-pass filter can be set to an appropriate order. .

(6) Since the parameter setting unit 32 changes the method of the low-pass filter 27 when the cut-off frequency fc of the low-pass filter 27 reaches the lower limit value fd, the low-pass filter can be set to an appropriate type of low-pass filter. it can. It is desirable to select the low-pass filter in order from the flat ripple characteristic in the pass band. For example, a Bessel type low pass filter 27a, a Butterworth type low pass filter 27b, an inverse Chebyshev type low pass filter 27d, a simultaneous Chebyshev type low pass filter 27e, and a Chebyshev type low pass filter 27c are selected in this order.

(7) The low-pass filter 27 includes a Bessel type, and the parameter setting unit 32 sets a Bessel type with a flat passband ripple characteristic as an initial value of the low-pass filter 27 method, thereby causing resonance. The vibration of the mirror unit 10 can be reliably suppressed, and the period during which the mirror unit 10 can be driven at a constant angular velocity can be lengthened.

(8) The parameter setting unit 32 stores the last set parameter in the low-pass filter 27, and sets the stored parameter in the low-pass filter 27 when the optical scanning element 4 (171) is driven next. The parameters of the filter 27 can be set quickly.

DESCRIPTION OF SYMBOLS 1 Optical scanning device 2 Control part 3 Light source part 4,171 Optical scanning element 10 Mirror part 10a Reflecting surface 11a, 11b Beam part
12a, 12b Support section 13a, 13b Fixing section 14 Base 18 Detection section 21 Target angle command generation section 22 Conversion section 23 Low pass filter section 24 Subtraction section 25 Drive signal generation section 26 LPF control section 27 (27a to 27e) Low pass filter 31 Resonance determination unit (determination unit)
32 Parameter setting section

Claims (10)

The mirror unit is supported by the beam unit from both sides, the mirror unit is swung around the swing axis by the torsional displacement of the beam unit, the light beam is scanned by the mirror unit, and at least the reflecting surface of the mirror unit An optical scanning element having a resonance mode that swings in a direction perpendicular to
A control unit that swings the mirror unit around the swing axis based on a drive signal in which a resonance frequency component of the resonance mode is suppressed by a low-pass filter;
A detection unit that outputs a detection signal according to an angle of the mirror unit around the swing axis,
The controller is
A generation unit that performs a difference operation between the drive signal and the detection signal and generates a difference signal that is a difference between the drive signal and the detection signal;
A determination unit for determining the resonance frequency and amplitude of the resonance mode from the difference signal;
A parameter setting unit configured to set at least one parameter among a method, a cutoff frequency, and an order of the low-pass filter based on the resonance frequency and amplitude of the resonance mode determined by the determination unit; Optical scanning device. The parameter setting unit changes the parameter of the low-pass filter to make the resonance mode amplitude equal to or less than the predetermined width when the amplitude of the resonance mode determined by the determination unit is larger than a predetermined width. The optical scanning device according to claim 1. The parameter setting unit sets the cutoff frequency of the low-pass filter as the parameter to the same frequency as the resonance frequency of the resonance mode determined by the determination unit, and then, based on the amplitude of the resonance mode, The optical scanning device according to claim 2, wherein a cutoff frequency of the low-pass filter is reduced. 4. The optical scanning device according to claim 3, wherein the parameter setting unit reduces a cutoff frequency of the low-pass filter in accordance with a fluctuation ratio of an amplitude of the resonance mode determined by the determination unit. 5. The optical scanning device according to claim 3, wherein the parameter setting unit changes the order of the low-pass filter when a cutoff frequency of the low-pass filter becomes a lower limit. 5. The optical scanning device according to claim 3, wherein the parameter setting unit changes a method of the low-pass filter when a cutoff frequency of the low-pass filter becomes a lower limit. The low-pass filter system includes a Bessel type,
The optical scanning device according to claim 2, wherein the parameter setting unit sets a Bessel type as an initial value of the low-pass filter method. 2. The parameter setting unit stores the parameter set last in the low-pass filter, and sets the parameter to be set when the optical scanning element is driven next as the stored parameter. 8. The optical scanning device according to any one of 7 to 7. A light source that emits a luminous flux having an intensity according to an image signal;
A first optical scanning element that scans a light beam emitted from the light source in a first direction at a relatively high speed;
A mirror portion supported by the beam portion from both sides, and the mirror portion is swung around a swing axis by the torsional displacement of the beam portion, and the light beam scanned by the first optical scanning element is A second optical scanning element that scans in a second direction substantially orthogonal to one direction at a relatively low speed and has a resonance mode that swings at least in a direction perpendicular to the reflecting surface of the mirror unit;
The first optical scanning element is operated based on the first driving signal, and the mirror portion of the second optical scanning element is moved based on the second driving signal in which the resonance frequency component of the resonance mode is suppressed by a low-pass filter. A control unit that swings around a moving axis;
A detection unit that outputs a detection signal according to an angle of the mirror unit around the swing axis,
The controller is
A generation unit that performs a difference operation between the second drive signal and the detection signal and generates a difference signal that is a difference between the second drive signal and the detection signal;
A determination unit for determining the resonance frequency and amplitude of the resonance mode from the difference signal;
A parameter setting unit configured to set at least one parameter among a method, a cutoff frequency, and an order of the low-pass filter based on the resonance frequency and amplitude of the resonance mode determined by the determination unit; Image display device.   A light beam scanned by the first optical scanning element and the second optical scanning element is incident on a user's eye, and an image corresponding to the image signal is projected on the user's retina. The image display device according to claim 9.

Images