JP2012118290A - Optical scanner and resonance frequency setting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner and a resonance frequency setting method which are capable of easily measuring a resonance frequency of a scanning mirror in a short time to set a driving frequency.SOLUTION: A head mount display takes a starting resonance frequency set at a start point, as a driving frequency to start the swing operation of a vertical scanning mirror due to a vertical scanning driving unit (S2). Next, the driving frequency of the vertical scanning mirror is successively changed in one direction toward a linear region (S3). When a deflection angle of the vertical scanning mirror is changed from increase to decrease (S5: YES), an increase/decrease direction of the driving frequency is switched (S11). The head mount display measures the driving frequency maximizing the deflection angle of the vertical scanning mirror, as a resonance frequency of the vertical scanning mirror (S13: YES and S21) and sets the measured resonance frequency as a driving frequency of the vertical scanning mirror in the subsequent swing operation (S22).

Description

  The present invention relates to an optical scanning apparatus that measures a resonance frequency of a scanning mirror and drives the scanning mirror according to the measured resonance frequency, and a resonance frequency setting method.

  2. Description of the Related Art Conventionally, there has been known an optical scanning device that forms an image on a surface to be scanned by driving (swinging) a scanning mirror and scanning a laser beam. In order to stably and efficiently resonate the scanning mirror, the frequency of the driving signal for driving the scanning mirror (hereinafter referred to as “driving frequency”) is set according to the resonance frequency of the scanning mirror. is required. For example, the optical scanning device disclosed in Patent Document 1 saves energy by setting the drive frequency and amplitude according to the resonance frequency.

  Even when the same scanning mirror is used, the resonance frequency of the scanning mirror varies with the usage environment such as temperature. Therefore, when driving the scanning mirror, it is desirable to measure the resonance frequency of the scanning mirror at that time and control the drive signal in accordance with the measured resonance frequency.

  A conventional method for measuring the resonance frequency will be described. First, characteristics between the driving frequency and the deflection angle of the scanning mirror will be described. When the scanning mirror is driven while changing the driving frequency, a jump phenomenon and a hysteresis phenomenon (hysteresis) occur. The jumping phenomenon is a phenomenon in which the deflection angle of the scanning mirror is suddenly increased or decreased when the drive frequency is changed. The hysteresis phenomenon is a phenomenon in which a difference occurs in a frequency at which a jump phenomenon occurs (hereinafter referred to as “jump frequency”) between when the drive frequency is gradually increased and when the drive frequency is gradually decreased.

  The case where a scanning mirror is what is called metal MEMS (details are mentioned later) is illustrated. If the scanning mirror is a metal MEMS, the jump frequency A when the drive frequency is gradually lowered is lower than the jump frequency B when the drive frequency is gradually raised. The resonance frequency is measured by measuring the swing angle while gradually decreasing the drive frequency and detecting the drive frequency at which the swing angle is maximized. The resonance frequency exists in a non-linear region between a jump frequency A when the drive frequency is gradually lowered and a jump frequency B when the drive frequency is gradually raised. Therefore, measurement may be performed while gradually decreasing the drive frequency from the jump frequency B. However, as described above, the resonance frequency varies with the usage environment such as temperature. Therefore, the conventional optical scanning device first measures the jump frequency B. Next, in consideration of fluctuations in the resonance frequency due to changes in the use environment, a frequency higher than the measured jump frequency B is set as the drive frequency at the time of startup. The drive frequency is gradually lowered from the drive frequency at the time of startup, and the drive frequency at which the deflection angle is maximized is measured as the resonance frequency. Even when so-called silicon MEMS (details will be described later) or the like is used, the above characteristics are not changed except that the magnitude relationship of the frequency is reversed from that in the case of metal MEMS.

JP-A-2005-208460

  In the conventional method, it is necessary to set the driving frequency at the time of startup considerably high in consideration of changes in the usage environment and resonance frequency due to durability deterioration. did not become. Therefore, the jump frequency B has to be measured in advance before the measurement of the resonance frequency is started. Therefore, in order to set the driving frequency by measuring the resonance frequency, there is a problem that a large amount of processing and a long processing time are required.

  An object of the present invention is to provide an optical scanning apparatus and a resonance frequency setting method that can easily set the drive frequency by measuring the resonance frequency of the scanning mirror in a short time.

  An optical scanning device according to a first aspect of the present invention includes a scanning mirror that scans a laser beam by swinging about a swing axis, a drive unit that swings the scan mirror, and a drive signal to the drive unit. Drive control means for controlling the drive means and detecting means for detecting the deflection angle of the scanning mirror, and the deflection angle changes linearly when the drive frequency of the scanning mirror is changed. An optical scanning device in which a linear region that is a driving frequency region and a nonlinear region that is a driving frequency region that includes a resonance frequency of the scanning mirror and whose deflection angle changes nonlinearly appears. The means starts the driving means with a starting resonance frequency set in advance at the time of starting as the driving frequency at the time of starting, and starts the swinging of the scanning mirror. When the moving means is activated, the first frequency changing means for sequentially changing the driving frequency of the scanning mirror from the starting frequency toward the linear region in one direction, and the first frequency changing means sets the driving frequency. When sequentially changing, the drive frequency is changed in the direction opposite to the direction changed by the first frequency changing means, triggered by the change of the deflection angle detected by the detecting means from increasing to decreasing. The second frequency changing means for sequentially changing the driving frequency at which the deflection angle detected by the detecting means becomes maximum when the second frequency changing means sequentially changes the driving frequency is the resonance frequency of the scanning mirror. And a resonance frequency setting means for measuring the frequency as a drive frequency thereafter.

  The optical scanning device according to the first aspect activates the scanning mirror driving means using a preset activation resonance frequency as a driving frequency at the time of activation. Next, the drive frequency of the scanning mirror is sequentially changed in one direction toward the linear region, and when the inflection point of the increase / decrease of the deflection angle is reached, the drive frequency is sequentially changed in the direction opposite to the changed direction. To go. Thereafter, the optical scanning device measures the drive frequency at which the deflection angle becomes maximum while changing the drive frequency as the resonance frequency of the scanning mirror, and sets the measured resonance frequency as the drive frequency. Therefore, the optical scanning device does not need to search for a resonance frequency in a wide range in consideration of a change in the resonance frequency due to a change in use environment. Furthermore, the optical scanning device does not need to measure in advance the frequency at which the jump phenomenon occurs. Therefore, the optical scanning device can easily measure the resonance frequency of the scanning mirror in a short time, and set the measured resonance frequency as the subsequent drive frequency.

  The optical scanning device may further include a torsion beam portion that supports the scanning mirror and a substrate that supports the torsion beam portion. The driving unit may be a vibrating body that is provided on the substrate and oscillates by applying a voltage to induce a plate wave on the substrate to swing the mirror unit. In this case, it is preferable that the first frequency changing unit sequentially increases the driving frequency, and the second frequency changing unit sequentially decreases the driving frequency. Under the above conditions, the jump frequency A when the drive frequency is gradually decreased is lower than the jump frequency B when the drive frequency is gradually increased. The resonance frequency exists between the jump frequency A and the jump frequency B when the drive frequency is gradually lowered. Therefore, the optical scanning device can measure the resonance frequency by an appropriate method according to the characteristics of the scanning mirror by increasing and decreasing the driving frequency.

  The drive control means includes a temperature acquisition means for acquiring the temperature of the scanning mirror, a parameter indicating the amount of change in the resonance frequency according to the temperature of the scanning mirror, and the temperature of the scanning mirror acquired by the temperature acquisition means. And a calculating means for calculating and setting the starting resonance frequency using the resonance frequency previously measured by the measuring means. The activation unit may activate the drive unit at the activation resonance frequency set by the calculation unit. In this case, the optical scanning device can start the measurement process from the optimum drive frequency even when the resonance frequency changes due to the influence of temperature change and change with time. The possibility of failing to measure the resonance frequency is also low.

  The second frequency changing means may reduce the amount of change in the driving frequency once as the increasing rate of the deflection angle of the scanning mirror that increases by changing the driving frequency is smaller. In the non-linear region near the resonance frequency, the rate of increase in the deflection angle of the scanning mirror decreases as the drive frequency approaches the resonance frequency. Therefore, the optical scanning device can measure the resonance frequency more accurately and set the optimum drive frequency by reducing the amount of change of the drive frequency once as the increase rate of the deflection angle is smaller.

  The first frequency changing means may decrease the amount of change in the driving frequency once as the increasing rate of the deflection angle of the scanning mirror that increases by changing the frequency is larger. When it is detected that the deflection angle of the scanning mirror changes from increase to decrease while changing the frequency by the first frequency changing means, a jump phenomenon occurs before the change from increase to decrease occurs. Therefore, the rate of increase of the deflection angle increases every time the drive frequency is changed. Therefore, the first frequency changing means can accurately grasp the change from the increase in the swing angle to the decrease by decreasing the change amount of the drive frequency once as the increase rate of the swing angle is larger.

  The drive control means controls the amplitude of the drive signal and adjusts the deflection angle of the scanning mirror according to a predetermined condition when the resonance frequency is set to the drive frequency by the resonance frequency setting means. May be further provided. The optical scanning device can adjust the deflection angle of the scanning mirror while driving the scanning mirror at an optimum driving frequency according to the resonance frequency of the scanning mirror. Accordingly, the optical scanning device can accurately drive the scanning mirror according to the resonance frequency.

  A resonance frequency setting method according to a second aspect of the present invention includes a scanning mirror that scans a laser beam by swinging around a swing axis, a drive unit that swings the scan mirror, and a drive that drives the drive unit. Drive control means for supplying a signal to control the drive means and detection means for detecting the deflection angle of the scanning mirror, and when the drive frequency of the scanning mirror is changed, the deflection angle is linear By the drive control means of the optical scanning device, a linear region that is a region of the driving frequency that changes and a nonlinear region that is a region of the driving frequency that includes the resonance frequency of the scanning mirror and whose deflection angle changes nonlinearly appear. Resonance frequency setting method to be executed, starting the driving means with a starting resonance frequency set in advance at the time of starting as a driving frequency at the time of starting, and starting the oscillation of the scanning mirror A first frequency changing step for sequentially changing the driving frequency of the scanning mirror from the starting frequency toward the linear region when the driving means is started in the starting step; When the drive frequency is sequentially changed in the frequency change step, the direction changed in the first frequency change step is triggered by the change of the deflection angle detected by the detection means from increase to decrease. A second frequency changing step for sequentially changing the driving frequency in the reverse direction, and a driving frequency at which the deflection angle detected by the detecting means is maximized when the driving frequency is sequentially changed in the second frequency changing step. Is measured as the resonance frequency of the scanning mirror, and the subsequent resonance frequency setting step is used as the drive frequency. It is equipped with a.

  According to the resonance frequency setting method according to the second aspect, the optical scanning device activates the scanning mirror drive means using the activation resonance frequency set in advance as the drive frequency at the time of activation. Next, the drive frequency of the scanning mirror is sequentially changed in one direction toward the linear region, and when the inflection point of the increase / decrease of the deflection angle is reached, the drive frequency is sequentially changed in the direction opposite to the changed direction. To go. Thereafter, the optical scanning device measures the drive frequency at which the deflection angle becomes maximum while changing the drive frequency as the resonance frequency of the scanning mirror, and sets the measured resonance frequency as the drive frequency. Therefore, the optical scanning device does not need to search for a resonance frequency in a wide range in consideration of a change in the resonance frequency due to a change in use environment. Furthermore, the optical scanning device does not need to measure in advance the frequency at which the jump phenomenon occurs. Therefore, the optical scanning device can easily measure the resonance frequency of the scanning mirror in a short time, and set the measured resonance frequency as the subsequent drive frequency.

1 is a diagram showing an external configuration of a head mounted display 1. FIG. 2 is a block diagram showing an electrical configuration of the head mounted display 1. FIG. It is explanatory drawing explaining the process in which the display part 10 inject | emits the image light 5. FIG. 2 is a perspective view of a vertical scanning system 20. FIG. 6 is a graph showing the relationship between the drive frequency and the deflection angle when metal MEMS is used for the vertical scanning mirror 21. It is a flowchart of the drive process which CPU111 performs. It is a flowchart of the start frequency calculation process performed during a drive process. 6 is an explanatory diagram of a change amount parameter table stored in a flash memory 54. FIG. 4 is an explanatory diagram of data immediately before a previous stop stored in a flash memory 54. FIG. It is explanatory drawing which shows the relationship between the raise amount of drive frequency, the fall amount, and the increase amount of a deflection angle. It is explanatory drawing of the raise amount determination table memorize | stored in ROM112. It is explanatory drawing of the fall amount determination table memorize | stored in ROM112. It is a flowchart of the process during a drive performed during a drive process.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The drawings to be referred to are used for explaining technical features that can be adopted by the present invention. The configuration of the apparatus, the flowcharts of various processes, and the like described in the drawings are not intended to be limited to these, but are merely illustrative examples.

  In the following, description will be given by taking the head mounted display 1 which is one of the optical scanning devices as an example. The head mounted display 1 is a retinal scanning display that scans a laser beam modulated according to an image signal, emits it as image light, and directly projects an image on the retina of at least one eye of a user. However, the present invention is not limited to the head mounted display 1. The present invention can be applied to any optical scanning device that scans with laser light for displaying an image. For example, the present invention can also be applied to a screen scanning type image display apparatus that emits and projects a scanned laser beam on a screen to be projected.

  A schematic configuration of the head mounted display 1 will be described with reference to FIG. The head mounted display 1 includes at least an injection device 2, an eyepiece unit 3, and a head mounting unit 4. The emission device 2 emits image light 5 (see FIG. 3) to the eyepiece 3 in accordance with the image signal. The position of the eyepiece 3 with respect to the injection device 2 is fixed. The eyepiece unit 3 includes a half mirror 38 (see FIG. 3). The eyepiece 3 transmits the external light 6 from the outside by the half mirror 38 and reflects the image light 5 emitted from the emission device 2 toward the user's eyes. That is, the eyepiece unit 3 causes the image light 5 incident from the side of the user and the external light 6 incident from the outside to be incident on the user's eyes. As a result, the user can visually recognize an image based on the image light emitted from the ejection device 2 in addition to the actual field of view.

  The electrical configuration of the head mounted display 1 will be described with reference to FIG. The head mounted display 1 includes a display unit 10, an input unit 40, a communication unit 43, a control unit 50, a video RAM 53, a flash memory 54, and a power supply unit 55.

  The display unit 10 is a part that allows the user to visually recognize an image. The display unit 10 includes a drive signal controller 11, a laser group 13, and a laser driver group 12. The drive signal controller 11 includes a CPU 111, a ROM 112, and a RAM 113. In the drive signal controller 11, various processes for driving the display unit 10 are performed by the CPU 111 reading out the program stored in the ROM 112. Specifically, the drive signal controller 11 receives an image signal from the control unit 50 and outputs a drive signal (luminance signal) to the laser driver group 12 in accordance with the input signal. Further, the drive signal controller 11 determines conditions (for example, the drive frequency and the swing angle of the vertical scan mirror 21) for swinging the vertical scan mirror 21 and the horizontal scan mirror 26 described later, and the vertical scan drive unit 23 and A drive signal is output to the horizontal scanning drive unit 28 (details will be described later). The laser group 13 includes a blue output laser (B laser) 131, a green output laser (G laser) 132, and a red output laser (R laser) 133. The laser group 13 outputs blue, green, and red laser beams. The laser driver group 12 controls the laser group 13 according to the drive signal received from the drive signal controller 11 and causes the laser group 13 to output laser light. That is, the control unit 50 performs overall control of the head mounted display 1, and the drive signal controller 11 controls image display processing according to an image signal input from the control unit 50.

  The display unit 10 includes a vertical scanning mirror 21, a vertical scanning driving unit 23, a horizontal scanning mirror 26, and a horizontal scanning driving unit 28. The vertical scanning mirror 21 scans the laser beam output from the laser group 13 in the vertical direction (main scanning direction in the present embodiment) by swinging around the swing axis. The vertical scanning drive unit 23 causes the vertical scanning mirror 21 to resonate and oscillate at high speed in accordance with the drive signal received from the drive signal controller 11. The horizontal scanning mirror 26 further scans the laser light that has been two-dimensionally scanned in the vertical direction by the vertical scanning mirror 21 in the horizontal direction (sub-scanning direction of the present embodiment). The horizontal scanning drive unit 28 swings the horizontal scanning mirror 26 at a low speed according to the drive signal received from the drive signal controller 11.

  The display unit 10 includes a BD (beam detect) sensor 31 and a BD signal detection circuit 32. The BD sensor 31 detects the laser beam reflected by the vertical scanning mirror 21 (laser beam scanned in the main scanning direction). That is, the BD sensor 31 is provided for detecting a reference position (reference timing) in the main scanning direction of the laser light. The BD signal detection circuit 32 outputs a BD signal to the drive signal controller 11 when the BD sensor 31 detects that the laser beam has reached a predetermined position. The drive signal controller 11 detects the deflection angle that is the maximum value of the scanning angle of the vertical scanning mirror 21 based on the input result of the BD signal. Further, the drive signal controller 11 determines the timing for outputting the laser light from the laser group 13 based on the input result of the BD signal.

  The display unit 10 includes a temperature sensor 33. The temperature sensor 33 detects the temperature around the vertical scanning mirror 21 and outputs the detected temperature to the drive signal controller 11. The drive signal controller 11 determines a starting resonance frequency, which is a driving frequency when starting the vertical scanning mirror 21, based on the temperature input from the temperature sensor 33.

  The input unit 40 is a part that receives input of various operation instructions from the user. The input unit 40 includes an operation button group 41 and an input control circuit 42. The input control circuit 42 detects that the button of the operation button group 41 has been operated. The input control circuit 42 is electrically connected to the control unit 50 and outputs information related to button operations to the control unit 50.

  The communication unit 43 is a part that transmits and receives image information and the like. The communication unit 43 includes a communication module 44 and a communication control circuit 45. The communication module 44 transmits and receives image information and the like by wireless communication or wired communication with an external device. The communication control circuit 45 controls the operation of the communication module 44. The communication control circuit 45 is electrically connected to the control unit 50 and causes the control unit 50 to acquire image information.

  The control unit 50 controls the entire head mounted display 1. The control unit 50 includes a CPU, a ROM, and a RAM (not shown). In the control unit 50, various processes for controlling the operation of the head mounted display 1 are performed by reading out the program stored in the ROM by the CPU. In the video RAM 53, image data included in the image information is developed. The flash memory 54 stores various setting values of functions used in the head mounted display 1.

  The power supply unit 55 includes a battery 56 and a charge control circuit 57. The battery 56 is a rechargeable battery serving as a power source for driving the head mounted display 1. The charge control circuit 57 controls power supply from the battery 56 to the head mounted display 1 and controls charging of the battery 56 from a charging adapter (not shown).

  With reference to FIG. 3, the outline of the process in which the display unit 10 emits the image light 5 will be described. The display unit 10 includes a light source unit 18, a collimating optical system 19, a vertical scanning system 20, a first relay optical system 24, a horizontal scanning system 25, and a second relay optical system 29.

  The light source unit 18 includes a drive signal controller 11, a laser driver group 12, a laser group 13, a collimating optical system 14, a dichroic mirror group 15, a coupling optical system 16, and a BD signal detection circuit 32. For example, the drive signal controller 11 reads out the image signal of the image data developed in the video RAM 53 by the control unit 50 for each pixel constituting the image to be displayed, and generates a luminance signal 35 that is a drive signal. A vertical drive signal 36 and a horizontal drive signal 37 are generated. The drive signal controller 11 converts the generated luminance signal 35 (B luminance signal 351, G luminance signal 352, and R luminance signal 353) into the laser driver group 12 (B laser driver 121, G laser driver 122, and R laser driver 123). Output to. Further, the vertical drive signal 36 is output to the vertical scan drive unit 23, and the horizontal drive signal 37 is output to the horizontal scan drive unit 28. However, the drive signal controller 11 controls the vertical drive signal 36 and the horizontal drive signal 37 based on the timing at which the BD signal is input from the BD signal detection circuit 32 (the timing at which the laser beam reaches a predetermined position). At the same time, the timing for outputting the luminance signal 35 to the laser driver group 12 is determined.

  The laser driver group 12 causes the laser group 13 to output intensity-modulated laser light based on the input luminance signal 35. The laser light output from the laser group 13 enters the collimating optical system 14. The three collimating lenses 141 to 143 of the collimating optical system 14 collimate each of the three colors (blue, green, and red) of laser light output from the laser group 13 into parallel light. The laser light collimated by the collimating optical system 14 enters the dichroic mirror group 15. The three dichroic mirrors 151 to 153 of the dichroic mirror group 15 combine the collimated laser beams of three colors into one laser beam. The combined laser light is guided to the optical fiber 17 by the coupling optical system 16.

  The laser light transmitted through the optical fiber 17 is collimated into parallel light by the collimating optical system 19 and enters the vertical scanning system 20. The vertical scanning system 20 of the present embodiment scans laser light in the vertical direction (main scanning direction) for each scanning line of an image to be displayed. The vertical scanning system 20 is designed to scan a laser beam at a higher speed (that is, at a higher frequency) than the horizontal scanning system 25. The laser light incident on the vertical scanning system 20 is applied to the deflection surface 22 of the vertical scanning mirror 21. The vertical scanning drive unit 23 causes the vertical scanning mirror 21 to resonate and oscillate in accordance with the vertical drive signal 36 input from the drive signal controller 11. As a result, the laser beam irradiated on the deflection surface 22 is scanned at high speed in the vertical direction. As described above, the BD sensor 31 detects the reference position (reference timing) of the laser light in the main scanning direction by detecting the laser light vertically scanned by the vertical scanning mirror 21.

  The vertically scanned laser light is incident on the horizontal scanning system 25 via the first relay optical system 24. The horizontal scanning system 25 of the present embodiment scans the laser beam in the horizontal direction (sub-scanning direction) from the first scanning line to the last scanning line for each frame of the image to be displayed. The laser light incident on the horizontal scanning system 25 is applied to the deflection surface 27 of the horizontal scanning mirror 26. The horizontal scanning drive unit 28 swings the horizontal scanning mirror 26 in accordance with the horizontal drive signal 37 input from the drive signal controller 11. As a result, the laser light applied to the deflection surface 27 is scanned in the horizontal direction.

  Of the laser beams that are two-dimensionally scanned by the vertical scanning system 20 and the horizontal scanning system 25, the image light 5 that is a laser beam for displaying an image is emitted to the half mirror 38 via the second relay optical system 29. The The image light 5 is totally reflected by the half mirror 38 and guided to the pupil 39 of the user. As a result, an image based on the image data developed in the video RAM 53 (see FIG. 2) is formed on the user's retina. The user can visually recognize an image by laser light that is two-dimensionally scanned and projected onto the retina.

  As described above, the head mounted display 1 performs two-dimensional scanning of laser light by causing the vertical scanning mirror 21 to resonate and oscillate at high speed, and the horizontal scanning mirror 26 to oscillate at a lower speed than the vertical scanning mirror 21. Let In order to efficiently resonate and swing the vertical scanning mirror 21, it is necessary to set the drive frequency for driving the vertical scanning mirror 21 to a value close to the resonance frequency of the vertical scanning mirror 21. By driving the vertical scanning mirror 21 at a driving frequency close to the resonance frequency to obtain a resonance state, driving energy enters and exits the vertical scanning mirror 21 without loss. Here, the resonance frequency of the vertical scanning mirror 21 fluctuates due to the influence of the temperature of the vertical scanning mirror 21 and changes with time. Therefore, it is desirable that the head mounted display 1 measures the resonance frequency of the vertical scanning mirror 21 at that time and sets the measured resonance frequency as the driving frequency.

  With reference to FIG. 4, the type of the vertical scanning system 20 according to the present embodiment will be described. The vertical scanning mirror 21 of the present embodiment is a so-called metal MEMS (see, for example, JP-A-2006-293116). As shown in FIG. 4, the vertical scanning system 20 includes a substrate 63, a vertical scanning mirror 21, a torsion beam portion 64, and a vertical scanning driving unit 23. The substrate 63 has a rectangular plate shape, and one end of the substrate 63 is fixed to the support portion 61. In the present embodiment, the substrate 63 is manufactured at low cost by using SUS as the material of the substrate 63. However, other materials such as invar and kovar may be used. The vertical scanning mirror 21 and the torsion beam portion 64 are integrally formed on the substrate 63 by hollowing out the substrate 63. The vertical scanning mirror 21 oscillates about an oscillation axis extending in the left-right direction in FIG. The two torsion beam portions 64 extend from the vertical scanning mirror 21 to the left and right, and connect the substrate 63 and the vertical scanning mirror 21.

  The vertical scanning drive unit 23 is disposed on the plate surface of the substrate 63 on the side facing the vertical scanning mirror 21 with respect to the space formed by the torsion beam portion 64, the vertical scanning mirror 21, and the substrate 63. The vertical scanning drive unit 23 of the present embodiment is a piezoelectric film that vibrates when a voltage is applied. However, instead of the piezoelectric film, a magnetostrictor, a permanent magnet, or the like that vibrates when a magnetic field is applied may be used as the vertical scanning drive unit 23. That is, any vibrating body that vibrates when a voltage or a magnetic field is applied can be used as the vertical scanning drive unit 23. The vertical scanning drive unit 23 induces a plate wave on the substrate 63 by vibrating by applying a voltage or a magnetic field. When a plate wave is induced on the substrate 63, the torsion beam portion 64 and the vertical scanning mirror 21 cause torsional vibration and scan with laser light.

  With reference to FIG. 5, the characteristics between the drive frequency and the deflection angle in the vertical scanning mirror 21 of the present embodiment will be described. When the vertical scanning mirror 21 is driven while changing the driving frequency, a jump phenomenon and a hysteresis phenomenon occur. The jumping phenomenon is a phenomenon in which the swing angle of the vertical scanning mirror 21 suddenly increases or decreases when the drive frequency is changed. The hysteresis phenomenon is a phenomenon in which a difference occurs in a jump frequency, which is a frequency at which a jump phenomenon occurs, between when the drive frequency is gradually increased and when the drive frequency is gradually decreased. In the graph of FIG. 5, the black line indicates the relationship between the drive frequency of the vertical scanning mirror 21 and the deflection angle when the drive frequency is gradually lowered (during a down sweep). The white line indicates the relationship between the drive frequency of the vertical scanning mirror 21 and the deflection angle when the drive frequency is gradually increased (during up sweep).

  As shown in FIG. 5, when the vertical scanning mirror 21 that is a metal MEMS is used, the swing angle rapidly decreases when the drive frequency reaches A (jump frequency A) during the down sweep. On the other hand, at the time of the up sweep, when the drive frequency reaches B (jump frequency B), the deflection angle increases rapidly. Thus, the jump frequency A at the time of down sweep is lower than the jump frequency B at the time of up sweep. In the region between the jump frequency A and the jump frequency B, the rate of increase / decrease of the swing angle is not constant, and the swing angle changes nonlinearly. Therefore, a region between the jump frequency A and the jump frequency B is called a non-linear region. On the other hand, in a region where the drive frequency is higher than the jump frequency B, the rate of increase / decrease of the swing angle is substantially constant, and the swing angle changes substantially linearly. Therefore, a region where the drive frequency is higher than the jump frequency B is called a linear region.

  When the vertical scanning mirror 21 that is a metal MEMS is used, the resonance frequency is measured by measuring the swing angle while gradually decreasing the drive frequency, and detecting the drive frequency that maximizes the swing angle. The resonance frequency exists in a non-linear region between the jump frequency A at the time of down sweep and the jump frequency B at the time of up sweep. Therefore, the resonance frequency may be measured by down sweeping from the jump frequency B. However, as described above, the resonance frequency varies due to the influence of temperature, change with time, and the like. In the conventional method of measuring the resonance frequency, the jump frequency B is first measured. Next, in consideration of fluctuations in the resonance frequency due to changes in the use environment or the like, a frequency higher than the jump frequency B is set as the drive frequency (measurement start frequency) at startup. By gradually lowering the drive frequency from the measurement start frequency, the drive frequency that maximizes the deflection angle is measured as the resonance frequency. Therefore, in the conventional method, a processing load for measuring the jump frequency B is applied, and it is necessary to search for a wide driving frequency range in consideration of the fluctuation of the resonance frequency. The head mounted display 1 according to the present embodiment can set the optimum driving frequency by measuring the resonance frequency in a short time without measuring the jump frequency B during driving. Details of the above processing will be described below.

  A drive process executed by the CPU 111 of the drive signal controller 11 will be described with reference to FIGS. Below, the process which controls the drive of the vertical scanning mirror 21 among the processes which CPU111 performs in order to control the drive of several devices, such as the laser group 13, is demonstrated. When the CPU 111 of the drive signal controller 11 inputs an instruction to start image display from the control unit 50, the CPU 111 starts the drive process shown in FIG. 5 according to the program stored in the ROM 112.

  As shown in FIG. 6, when the driving process is started, processes (S1, S2) for starting swinging of the vertical scanning mirror 21 are performed. First, a start frequency calculation process is performed (S1). In the start frequency calculation process, the unique resonance frequency of the vertical scanning mirror 21 is calculated as the start resonance frequency (measurement start frequency).

  The start frequency calculation process will be described with reference to FIG. When the start frequency calculation process is started, the change amount parameter stored in the flash memory 54 is read (S31). The change amount parameter is a parameter indicating the change amount of the resonance frequency according to the temperature of the scanning mirror. As shown in FIG. 8, the flash memory 54 stores a change amount parameter table. In the change amount parameter table, a plurality of temperatures are stored in association with the temperature of the vertical scanning mirror 21 detected by the temperature sensor 33 and the resonance frequency of the vertical scanning mirror 21 when this temperature is detected. By using the parameters in the change amount parameter table, the change rate of the resonance frequency with respect to the temperature change of the vertical scanning mirror 21 can be calculated. Processing for storing each value of the change amount parameter table will be described later with reference to FIG.

  Next, the data immediately before the previous stop stored in the flash memory 54 is read (S32). As shown in FIG. 9, the data immediately before the stop is the temperature of the vertical scanning mirror 21 (temperature T immediately before stop) and the resonance frequency (resonance frequency immediately before stop) immediately before the resonance oscillation of the vertical scanning mirror 21 was stopped last time. F) data. That is, the temperature and resonance frequency measured last time during driving of the vertical scanning mirror 21 are stored as data immediately before the previous stop. Next, the current temperature E of the vertical scanning mirror 21 measured by the temperature sensor 33 at that time is acquired (S33).

CPU111 calculates a measurement start frequency from the value acquired by S31-S33 (S34). First, the change rate Z of the resonance frequency with respect to the temperature change is calculated from the parameters in the change amount parameter table. The change ratio Z is associated with the value of the current temperature E of the vertical scanning mirror 21 from the value of the resonance frequency associated with the value of the temperature T immediately before stop (see FIG. 8) in the change amount parameter table. It is calculated by subtracting the value of the resonance frequency that is present and dividing this value by (TE). Next, the measurement start frequency is calculated by the following (Equation 1).
Measurement start frequency = resonance frequency immediately before stop F + (temperature immediately before stop T−current temperature E) × change ratio Z (Expression 1)

  That is, the CPU 111 calculates the change rate Z of the resonance frequency with respect to the temperature change using the temperature and the resonance frequency of the vertical scanning mirror 21 measured in the past. As a result, even when the resonance frequency of the vertical scanning mirror 21 changes due to an influence such as a change with time, an appropriate change ratio Z including an influence such as a change with time can be calculated. The CPU 111 uses the calculated change rate Z, the value at the time of the previous resonance oscillation stop (the temperature T immediately before the stop and the resonance frequency F immediately before the stop), and the current temperature E to thereby influence the temperature change and the change with time. An appropriate measurement start frequency can be calculated in consideration of The process returns to the driving process (see FIG. 6).

  Returning to the description of FIG. The CPU 111 sets the calculated measurement start frequency to the drive frequency at the time of activation, and activates the vertical scanning mirror 21 (S2). The calculated measurement start frequency is a specific resonance frequency of the vertical scanning mirror 21. Next, the resonance frequency is measured (S3 to S21). First, the drive frequency of the vertical scanning mirror 21 is increased by X toward a linear region larger than the jump frequency B appearing on the upper side (higher frequency side) than the nonlinear region (S3). As the value of the increase amount X, a predetermined value that is determined in advance is used if it is immediately after startup, and is thereafter determined by the processing of S7 described later.

  The CPU 111 detects the deflection angle that is the maximum value of the scanning angle of the vertical scanning mirror 21 (S4). As a method of detecting the deflection angle, a method of detecting by arranging a plurality of photodiodes arranged in the scanning direction, a method of detecting displacement of a member that drives the vertical scanning mirror 21 with a piezoelectric element, and the result of inputting a BD signal There are various methods such as a detection method based on the method, and any method may be used. As described above, the head mounted display 1 of the present embodiment detects the deflection angle using the BD signal. A technique for detecting a deflection angle using a BD signal is known (see, for example, JP-A-2006-101306). The BD signal is output when the position of the laser light in the main scanning direction reaches a predetermined position. Since the vertical scanning mirror 21 is resonantly oscillated, the CPU 111 can detect the deflection angle of the vertical scanning mirror 21 by calculating the time until the position of the laser beam reaches the predetermined position from the origin position. it can.

  The CPU 111 determines whether or not an inflection point C that is a point at which the deflection angle changes from increasing to decreasing is detected (S5). When the vertical scanning mirror 21 that is a metal MEMS is used, as shown in FIG. 10, when the drive frequency is sequentially increased from the inherent resonance frequency (starting resonance frequency) of the vertical scanning mirror 21, a jump phenomenon occurs. The swing angle turns from increasing to decreasing. The CPU 111 can detect the inflection point C by detecting the change in the deflection angle.

  If the inflection point C is not detected (S5: NO), the rate of increase of the deflection angle is calculated (S6). The increase rate of the deflection angle calculated in S6 is the increase amount of the deflection angle with respect to the unit increase amount of the drive frequency. The increase rate of the deflection angle is calculated by dividing the increase amount of the deflection angle that is increased as a result of increasing the drive frequency in the immediately preceding processing of S3 by the increase amount X of the drive frequency in S3.

  As shown in FIG. 10, when the driving frequency is sequentially increased from the inherent resonance frequency of the vertical scanning mirror 21, a jump phenomenon occurs immediately before the inflection point C, and the deflection angle increases rapidly. Therefore, as shown in FIG. 10, as the driving frequency approaches the frequency of the inflection point C, the deflection angle increasing ratios P1, P2, and P3 gradually increase. That is, the frequency of the inflection point C is closer as the rate of increase of the deflection angle is larger. Therefore, in order to accurately detect the inflection point C, it is necessary to reduce the amount of increase X, which is the amount of change in drive frequency, as the rate of increase in the deflection angle increases. Further, in order to quickly and efficiently bring the drive frequency close to the frequency of the inflection point C, it is necessary to increase the drive frequency increase amount X as the deflection angle increase rate decreases.

  The CPU 111 refers to the increase amount determination table (see FIG. 11) stored in the ROM 112 to determine the increase amount X of the drive frequency corresponding to the increase rate of the deflection angle (S7). As shown in FIG. 11, in the increase amount determination table, the increase rate of the swing angle and the increase amount X are associated with each other so that the increase amount X of the drive frequency decreases as the increase rate of the swing angle increases. Yes. Therefore, the CPU 111 can easily determine the increase amount X for detecting the inflection point C efficiently and accurately by referring to the increase amount determination table. When determining the increase amount X, the CPU 111 increases the drive frequency again by the determined increase amount X (S3), and repeats the determination of whether or not the inflection point C has been detected (S4, S5).

  When detecting the inflection point C (S5: YES), the CPU 111 lowers the drive frequency of the vertical scanning mirror 21 by Y (S11). That is, the direction in which the drive frequency is changed is switched from rising to falling. As the value of the descending amount Y, a predetermined value set in advance is used if it is immediately after the drive frequency is switched from increasing to decreasing. Thereafter, the value of the descending amount Y is determined in the process of S15 described later. The CPU 111 detects the deflection angle of the vertical scanning mirror 21 with the drive frequency lowered (S12). Next, the CPU 111 determines whether or not a driving frequency that maximizes the deflection angle is detected (S13). As shown in FIG. 10, when the drive frequency is sequentially lowered from the frequency of the inflection point C, the deflection angle starts to increase and decreases before the jump phenomenon occurs. The maximum deflection angle is the deflection angle at the time when the increase starts to decrease. The CPU 111 can detect the drive frequency at which the deflection angle is maximized by detecting the change in increase / decrease of the deflection angle. The drive frequency that maximizes the deflection angle is the resonance frequency of the vertical scanning mirror 21.

  If the drive frequency that maximizes the deflection angle is not detected (S13: NO), the rate of increase of the deflection angle is calculated (S14). The increase rate of the deflection angle calculated in S14 is the increase amount of the deflection angle with respect to the unit decrease amount of the drive frequency. In S14, the increase rate is calculated by dividing the increase amount of the swing angle increased as a result of the drive frequency decrease in S11 immediately before, by the drive frequency decrease amount Y in S11.

  As shown in FIG. 10, when the drive frequency is sequentially decreased from the frequency of the inflection point C, the increase rate Q1, Q2, Q3 of the deflection angle gradually decreases in the non-linear region immediately before the deflection angle becomes maximum. . That is, the smaller the rate of increase of the deflection angle, the closer the driving frequency (resonance frequency) at which the deflection angle becomes maximum. Therefore, in order to accurately detect the drive frequency at which the deflection angle is maximized, it is necessary to decrease the drive frequency decrease Y as the increase rate of the deflection angle is smaller. Further, by increasing the drive frequency decrease amount Y as the rate of increase of the deflection angle increases, the drive frequency at which the deflection angle becomes maximum can be detected quickly and efficiently.

  The CPU 111 refers to the descending amount determination table (see FIG. 12) stored in the ROM 112 to determine the descending amount Y of the drive frequency corresponding to the increase rate of the deflection angle (S15). As shown in FIG. 11, in the decrease amount determination table, the increase rate of the swing angle and the decrease amount Y are associated with each other so that the decrease amount Y of the drive frequency decreases as the increase rate of the swing angle decreases. Yes. Therefore, the CPU 111 can easily determine the descending amount Y for efficiently and accurately detecting the drive frequency that maximizes the deflection angle by referring to the descending amount determination table. When the CPU 111 determines the lowering amount Y, the CPU 111 lowers the driving frequency again by the determined lowering amount Y (S11), and repeats the detection of the driving frequency that maximizes the deflection angle (S12, S13).

  When the drive frequency that maximizes the deflection angle is detected (S13: YES), the CPU 111 measures the detected drive frequency as the resonance frequency (S21). The measured resonance frequency is set to the drive frequency of the vertical scanning mirror 21 being driven (S22). Next, the CPU 111 controls the amplitude of the vertical drive signal 36 and adjusts the deflection angle of the vertical scanning mirror 21 (S23). Specifically, if the deflection angle is smaller than a predetermined value, the CPU 111 increases the amplitude of the vertical drive signal 36 to increase the deflection angle. When the deflection angle is larger than a predetermined value, the amplitude of the vertical drive signal 36 is decreased to decrease the deflection angle. Thereafter, a process during driving is performed (S24), and the driving process ends.

  With reference to FIG. 13, the driving process will be described. In the driving process, a follow-up process is started (S41). The follow-up process is a process of controlling the drive frequency and drive amplitude in accordance with the change in the resonance frequency, and adjusting the deflection angle to the optimum value while making the drive frequency follow the resonance frequency. The follow-up process is continuously executed until the driving is completed. In the tracking process, the CPU 111 detects changes in the resonance frequency and the deflection angle by monitoring changes in the phase of the resonance oscillation operation of the vertical scanning mirror 21. The CPU 111 causes the drive frequency to follow the changed resonance frequency and controls the drive amplitude to adjust the deflection angle.

  Next, it is determined whether or not a certain time has passed (S42). The fixed time determined in S42 is measured in order to update the variation parameter table at a fixed period. If the predetermined time has not elapsed (S42: NO), it is determined whether or not a drive stop instruction by the user is input to the input unit 40 (see FIG. 2) (S43). If no stop instruction is input (S43: NO), the determinations of S42 and S43 are repeated.

  When the predetermined time has elapsed (S42: YES), the current resonance frequency detected in the follow-up process and the current temperature detected by the temperature sensor 33 are acquired (S45). The acquired resonance frequency and temperature are associated with each other and stored in the change parameter table (see FIG. 8) of the flash memory 54, and the change parameter table is updated (S46). The CPU 111 deletes data that has passed a predetermined time since it was stored in the change amount parameter table. Accordingly, the parameters in the change amount parameter table are appropriate parameters including the influence of changes over time. The process returns to the determination in S42.

  When a drive stop instruction is input by the user (S43: YES), the current resonance frequency detected in the follow-up process and the current temperature detected by the temperature sensor 33 are acquired as in the process of S45. (S48). The acquired resonance frequency and temperature are stored in the flash memory 54 as data immediately before the previous stop (see FIG. 9). The driving of the vertical scanning mirror 21 is stopped, the processing returns to the driving processing shown in FIG. 6, and the driving processing ends.

  As described above, the head mounted display 1 according to the present embodiment activates the swinging operation of the vertical scanning mirror 21 by the vertical scanning drive unit 23 using the inherent resonant frequency of the vertical scanning mirror 21 as the driving frequency at the time of activation. To do. Next, the drive frequency of the vertical scanning mirror 21 is sequentially changed toward the linear region, and when the inflection point C of the increase / decrease of the swing angle is reached, the direction of increase / decrease of the drive frequency is switched. Thereafter, the head mounted display 1 measures the drive frequency at which the deflection angle becomes maximum while changing the drive frequency as the resonance frequency of the vertical scanning mirror 21, and sets the measured resonance frequency as the drive frequency to make the vertical The scanning mirror 21 is driven. Therefore, it is not necessary for the head mounted display 1 to search for the resonance frequency in a wide range in consideration of the fluctuation of the resonance frequency due to a change in the use environment. Furthermore, the head mounted display 1 does not need to measure in advance the jump frequency B when the drive frequency is sequentially changed (“rise” in the above embodiment). Therefore, the head mounted display 1 can easily measure the resonance frequency of the vertical scanning mirror 21 in a short time, and can use the measured resonance frequency as the subsequent drive frequency.

  The vertical scanning mirror 21 used in the above embodiment is a metal MEMS. When the metal MEMS is used, the jump frequency A when the drive frequency is gradually lowered becomes lower than the jump frequency B when the drive frequency is gradually raised. The resonance frequency exists between the jump frequency A and the jump frequency B when the drive frequency is gradually lowered. Therefore, the head mounted display 1 can measure the resonance frequency by an appropriate method according to the characteristics of the vertical scanning mirror 21 by decreasing the drive frequency after increasing the drive frequency.

  The head mounted display 1 calculates the activation resonance frequency using the temperature of the vertical scanning mirror 21, the parameter indicating the amount of change in the resonance frequency according to the temperature, and the data immediately before the previous stop (see FIG. 8). Accordingly, the head mounted display 1 can start the measurement process from the optimum driving frequency even when the resonance frequency changes due to the influence of temperature change and change with time. The possibility of failing to measure the resonance frequency is also low.

  When the head mounted display 1 measures the resonance frequency by sequentially lowering the drive frequency, the decrease amount Y of the drive frequency is decreased as the increase rate of the deflection angle is smaller. As a result, the resonance frequency can be measured more accurately and quickly, and an optimum drive frequency can be set. Further, when the head mounted display 1 detects the inflection point C by sequentially increasing the drive frequency, the increase amount X of the drive frequency is decreased as the increase rate of the deflection angle is increased. As a result, the inflection point C can be measured more accurately and quickly.

  The head mounted display 1 can adjust the deflection angle of the vertical scanning mirror 21 while driving the vertical scanning mirror 21 at an optimum driving frequency according to the resonance frequency of the vertical scanning mirror 21. Accordingly, the head mounted display 1 can accurately drive the vertical scanning mirror 21 according to the resonance frequency.

  In the above embodiment, the vertical scanning mirror 21 corresponds to the “scanning mirror” of the present invention. The vertical scanning drive unit 23 corresponds to the “drive unit” of the present invention. The CPU 111 of the drive signal controller 11 functions as the “drive control means” of the present invention. The CPU 111 that detects the deflection angle of the vertical scanning mirror 21 based on the BD signal output from the BD sensor 31 in S4, S12, etc. of FIG. 6 functions as the “detecting means” of the present invention. The CPU 111 that activates the swinging motion of the vertical scanning mirror 21 in S2 of FIG. 6 functions as “activation means”. The CPU 111 that sequentially changes the drive frequency in S3 of FIG. 6 functions as a “first frequency changing unit”. The CPU 111 that sequentially changes the drive frequency in S11 of FIG. 6 functions as a “second frequency changing unit”. The CPU 111 that measures the resonance frequency and sets the drive frequency in S13, S21, and S22 of FIG. 6 functions as “resonance frequency setting means”.

  The CPU 111 that acquires the temperature of the vertical scanning mirror 21 in S33 of FIG. 7 functions as a “temperature acquisition unit”. In S <b> 34 of FIG. 7, the CPU 111 that calculates the measurement start frequency that is the drive frequency at the time of activation functions as a “calculation unit”. The CPU 111 that adjusts the deflection angle of the vertical scanning mirror 21 in S23 of FIG. 6 functions as an “amplitude adjusting unit”.

  The process of starting the swing operation of the vertical scanning mirror 21 in S2 of FIG. 6 corresponds to a “starting step”. The process of sequentially changing the drive frequency in S3 of FIG. 6 corresponds to a “first frequency change step”. The process of sequentially changing the drive frequency in S11 of FIG. 6 corresponds to a “second frequency change step”. The process of measuring the resonance frequency and setting the drive frequency in S13, S21, and S22 of FIG. 6 corresponds to the “resonance frequency setting step”.

  It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications are possible. First, when a scanning mirror other than metal MEMS is used, the characteristic between the drive frequency and the deflection angle may be different from the characteristic illustrated in the graph of FIG. For example, when a so-called silicon MEMS is used as the vertical scanning mirror 21 instead of the metal MEMS, the characteristic between the driving frequency and the swing angle has a shape obtained by inverting the positive and negative directions of the driving frequency in the graph of FIG.

  The structure of the silicon MEMS is exemplified in Japanese Patent Application Laid-Open No. 2003-57586, for example. The silicon MEMS has a torsion spring portion that supports the scanning mirror so as to be swingable with respect to the base, and vibrates the torsion spring portion by vibrating a vibrating body provided on at least a part of the torsion spring portion. As a result, the scanning mirror is swung to scan the light. More specifically, the silicon MEMS includes a base body, a vibrating body, a first torsion spring portion, and a pair of second torsion spring portions. The second torsion spring portion is supported by the base and vibrates by a vibrating body provided so as to straddle the base. The second torsion spring part is connected to the first torsion spring part and transmits vibration to the first torsion spring part. In the first torsion spring portion, a torsional displacement is generated by the vibration transmitted from the second torsion spring portion, and the scanning mirror connected and supported by the first torsion spring portion swings. The vibrator is generally formed of silicon.

  When silicon MEMS is used, the graph showing the relationship between the drive frequency and the deflection angle has a shape in which the left and right sides of the graph illustrated in FIG. 5 are reversed. Even in this case, the resonance frequency can be measured in the same manner as in the above-described embodiment only by switching up and down in various processes described with reference to FIGS. For example, when silicon MEMS is used, the drive frequency may be decreased sequentially in S3 of FIG. In S7, the amount of decrease may be determined so that the amount of decrease in one driving frequency decreases as the increase rate increases. In S11, the drive frequency may be increased sequentially. In S15, the amount of increase may be determined so that the amount of increase in drive frequency once decreases as the increase rate decreases. That is, which of the up sweep and the down sweep is to be executed first may be appropriately determined according to the type of scanning mirror to be used.

  Other modifications can be made to the above embodiment. For example, in the above embodiment, the retinal scanning type head mounted display 1 is exemplified. However, the present invention can be applied to any image display apparatus that displays an image by scanning the laser beam in the main scanning direction by the resonance oscillation of the scanning mirror. 6 may be performed by an external device such as a PC connected to the image display device, and the external device may control the operation of the image display device. Needless to say, the storage device that stores the change parameter table (see FIG. 8), the data immediately before the previous stop (see FIG. 9), and the like can be changed to a storage device other than the flash memory 54. The main scanning direction may be the horizontal direction and the sub-scanning direction may be the vertical direction.

  The method for determining the measurement start frequency shown in S34 of FIG. 7 can be changed. For example, the head mounted display 1 may acquire the resonance frequency associated with the current temperature of the vertical scanning mirror 21 in the change amount parameter table shown in FIG. 8 and determine it as the measurement start frequency. The parameter may be a fixed value without updating the change amount parameter table shown in FIG.

  The head mounted display 1 of the above embodiment determines the drive frequency increase amount X and the decrease amount Y according to the increase rate of the swing angle. However, the method for determining the drive frequency increase amount X and decrease amount Y can be changed. For example, when a certain decrease in measurement accuracy can be tolerated, at least one of the increase amount X and the decrease amount Y may be a fixed value.

DESCRIPTION OF SYMBOLS 1 Head mounted display 11 Drive signal controller 21 Vertical scanning mirror 23 Vertical scanning drive part 31 BD sensor 33 Temperature sensor 36 Vertical drive signal 54 Flash memory 111 CPU

Claims (7)

A scanning mirror that scans a laser beam by swinging around a swing axis; a drive unit that swings the scan mirror; and a drive control unit that controls the drive unit by supplying a drive signal to the drive unit; Detecting means for detecting a deflection angle of the scanning mirror,
When the drive frequency of the scanning mirror is changed,
A linear region that is a region of the driving frequency where the deflection angle changes linearly;
An optical scanning device that includes a resonance frequency of the scanning mirror and a nonlinear region that is a region of a driving frequency in which a swing angle changes nonlinearly,
The drive control means includes
Starting means for starting the driving means with a starting resonance frequency set in advance as a driving frequency at the time of starting, and starting swinging of the scanning mirror;
First frequency changing means for sequentially changing the driving frequency of the scanning mirror in one direction from the starting frequency toward the linear region when the driving means is started by the starting means;
When the first frequency changing means sequentially changes the drive frequency, the first frequency changing means has changed when the deflection angle detected by the detecting means changes from increasing to decreasing. Second frequency changing means for sequentially changing the driving frequency in a direction opposite to the direction;
When the second frequency changing means sequentially changes the driving frequency, the driving frequency at which the deflection angle detected by the detecting means is maximized is measured as the resonance frequency of the scanning mirror, and is set as the subsequent driving frequency. An optical scanning device comprising: a resonance frequency setting unit. A torsion beam that supports the scanning mirror;
A substrate that supports the torsion beam portion;
The driving means is a vibrating body that is provided on the substrate and oscillates the mirror portion by inducing a plate wave in the substrate by vibrating by application of a voltage or a magnetic field,
The first frequency changing means sequentially increases the driving frequency,
The optical scanning device according to claim 1, wherein the second frequency changing unit sequentially decreases the driving frequency. The drive control means includes
Temperature acquisition means for acquiring the temperature of the scanning mirror;
Using the parameter indicating the amount of change of the resonance frequency according to the temperature of the scanning mirror, the temperature of the scanning mirror acquired by the temperature acquisition unit, and the resonance frequency previously measured by the measurement unit, Calculating means for calculating and setting a resonance frequency for use,
The optical scanning device according to claim 1, wherein the activation unit activates the driving unit at the activation resonance frequency set by the calculation unit.   2. The second frequency changing means reduces the amount of change of the driving frequency once as the increasing rate of the deflection angle of the scanning mirror that increases by changing the driving frequency is smaller. 4. The optical scanning device according to any one of 3.   5. The first frequency changing means reduces the amount of change in one drive frequency as the rate of increase in the deflection angle of the scanning mirror, which increases as the frequency is changed, is smaller. The optical scanning device according to any one of the above. The drive control means includes
When the resonance frequency is set to the drive frequency by the resonance frequency setting means, the apparatus further comprises amplitude adjustment means for controlling the amplitude of the drive signal and adjusting the deflection angle of the scanning mirror according to a predetermined condition. 6. The optical scanning device according to claim 1, wherein the optical scanning device is characterized in that: A scanning mirror that scans a laser beam by swinging around a swing axis; a drive unit that swings the scan mirror; and a drive control unit that controls the drive unit by supplying a drive signal to the drive unit; Detecting means for detecting a deflection angle of the scanning mirror,
When the drive frequency of the scanning mirror is changed,
A linear region that is a region of the driving frequency where the deflection angle changes linearly;
A resonance frequency setting method that is executed by the drive control unit of the optical scanning device in which a non-linear region that includes a resonance frequency of the scanning mirror and a drive frequency region in which a deflection angle changes nonlinearly appears.
An activation step of activating the driving means with the activation resonance frequency set in advance at the time of activation as a driving frequency at the time of activation, and starting oscillation of the scanning mirror;
A first frequency changing step for sequentially changing the driving frequency of the scanning mirror in one direction from the starting frequency toward the linear region when the driving means is started in the starting step;
When the drive frequency is sequentially changed in the first frequency change step, the change was made in the first frequency change step when the deflection angle detected by the detection means changed from increase to decrease. A second frequency change step for sequentially changing the drive frequency in a direction opposite to the direction;
When the driving frequency sequentially changes in the second frequency changing step, the driving frequency at which the deflection angle detected by the detecting means is maximized is measured as the resonance frequency of the scanning mirror, and is set as the subsequent driving frequency. A resonance frequency setting method comprising: a resonance frequency setting step.

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