JP7069640B2 - Movable devices, head-up displays, laser headlamps, head-mounted displays, vehicles and optical scanning methods - Google Patents

Description

The present invention relates to mobile devices, head-up displays, laser head lamps, head-mounted displays, vehicles and optical scanning methods.

With the development of micromachining technology, the development of MEMS (Micro Electro Mechanical Systems) devices manufactured by microfabrication of silicon and glass is progressing. As one of the MEMS devices, a small movable device in which a movable portion and an elastic beam portion provided with a reflective surface are integrally formed on a substrate to deflect and scan a light beam is known.

In such a movable device, a movable portion having a light reflecting surface is formed so as to be swingable around the first and second axes orthogonal to each other, and the movable portion swings around each axis to emit light. A lithage scan within the target area is disclosed (see, for example, Patent Document 1).

However, in the Lissajous scanning in which the scanning light draws a Lissajous figure, the locus of the scanning light in the scanning plane, that is, the scanning lines may be rough and dense. Such coarseness and density cause resolution variation and color unevenness in the image formed by the scanning light, which is a factor of deteriorating the image quality.

The present invention has been made in view of the above points, and an object of the present invention is to reduce the density of scanning lines in the resage scanning region.

The movable device according to one aspect of the disclosed technique is directly or indirectly connected to the mirror portion having a light reflecting surface and the mirror portion according to the input first and second drive signals. The first and second movable parts include first and second movable parts that rotate around the first and second axes orthogonal to each other, and the first and second movable parts are provided with first and second cantilever levers, respectively, and are predetermined. A movable device that scans light in two dimensions with the number of frames of the above, a first movable portion having a piezoelectric portion that rotates the mirror portion around the first axis, and a circumference of the first axis of the mirror portion. A first detecting means for detecting the angle of rotation of the light, a second movable part having a piezoelectric part for rotating the mirror part around the second axis, and rotation of the mirror part around the second axis. A second detection means for detecting an angle is provided, and at least one of the first detection means and the second detection means has a detection piezoelectric element and is based on the output of the first detection means. A first elastic coefficient adjusting means for adjusting the elastic coefficient of the first movable portion, and a second elastic coefficient adjusting means for adjusting the elastic coefficient of the second movable portion based on the output of the second detecting means . The first elastic coefficient adjusting means is provided so as to form a layer with or adjacent to the first detecting means in the first cantilever , and the second elastic coefficient adjusting means is provided. The second cantilever is provided so as to form a layer with or adjacent to the second detection means, and the frequency of the first drive signal is the frequency of the second drive signal and the number of frames. The value is determined based on the above and is not divided by the frequency of the second drive signal.

In the resage scanning region, the density of scanning lines can be reduced.

It is a schematic diagram of an example of an optical scanning system. It is a hardware block diagram of an example of an optical scanning system. It is a functional block diagram of an example of a control device. It is a flowchart of an example of the process which concerns on an optical scanning system. It is a schematic diagram of an example of an automobile equipped with a head-up display device. It is a schematic diagram of an example of a head-up display device. It is a schematic diagram of an example of an image forming apparatus equipped with an optical writing apparatus. It is a schematic diagram of an example of an optical writing device. It is a schematic diagram of an example of an automobile equipped with a laser radar device. It is a schematic diagram of an example of a laser radar device. It is a schematic diagram of an example of a laser headlamp. It is a perspective view of the appearance of an example of a head-mounted display. It is a figure which partially illustrates the structure of a head-mounted display. It is a schematic diagram of an example of a packaged movable device. It is a top view when viewed from the + Z direction as an example of the movable device of 1st Embodiment. It is a figure explaining the conventional example of the drive signal and the scanning line of a movable device. It is a figure explaining the drive signal of the movable device of 1st Embodiment. It is a figure explaining an example of the scanning line of the movable device of 1st Embodiment. It is a figure explaining the drive signal of the movable device of 2nd Embodiment. It is a figure explaining an example of the scanning line of the movable device of 2nd Embodiment. It is a top view which is seen from the + Z direction as an example of the movable device of 3rd Embodiment. It is sectional drawing explaining an example of the structure of the elastic modulus adjustment part and the detection piezoelectric element in the movable device of 3rd Embodiment. It is a figure explaining the change of the resonance frequency with the voltage applied to the elastic modulus adjustment part. It is a functional block diagram of an example of the control device of 3rd Embodiment. It is a flowchart which shows an example of the processing of the control apparatus of 3rd Embodiment. It is a figure explaining the relationship between the resonance frequency and the amplitude of rotation. It is a top view when viewed from the + Z direction as an example of the movable device which made the 1st movable part a double-sided beam structure. It is a top view when viewed from the + Z direction as an example of the movable device which made the 1st and 2nd movable part a double-bearing beam structure. It is a top view which is seen from the + Z direction as an example of the movable device which moves only around the 1st axis. It is a top view when viewed from the + Z direction as an example of the movable device which moves only around the 2nd axis.

Hereinafter, embodiments of the present invention will be described in detail.

[Optical scanning system]
First, the optical scanning system to which the movable device of the present embodiment is applied will be described in detail with reference to FIGS. 1 to 4. FIG. 1 shows a schematic diagram of an example of an optical scanning system. As shown in FIG. 1, the optical scanning system 10 is a system in which the light emitted from the light source device 12 is deflected by the reflecting surface 14 of the movable device 13 under the control of the control device 11 to lightly scan the scanned surface 15. be.

The optical scanning system 10 includes a control device 11, a light source device 12, and a movable device 13 having a reflecting surface 14.

The control device 11 is an electronic circuit unit including, for example, a CPU (Central Processing Unit) and an FPGA (Field-Programmable Gate Array). The movable device 13 is, for example, a MEMS (Micro Electromechanical Systems) device having a reflecting surface 14 and capable of moving the reflecting surface 14. The light source device 12 is, for example, a laser device that irradiates a laser. The surface to be scanned 15 is, for example, a screen.

The control device 11 generates a control command for the light source device 12 and the movable device 13 based on the acquired optical scanning information, and outputs a drive signal to the light source device 12 and the movable device 13 based on the control command. The light source device 12 irradiates the light source based on the input drive signal. The movable device 13 moves the reflecting surface 14 in at least one of the uniaxial direction and the biaxial direction based on the input drive signal.

As a result, for example, by controlling the control device 11 based on the image information which is an example of the optical scanning information, the reflective surface 14 of the movable device 13 is reciprocated in a predetermined range in the biaxial direction and is incident on the reflective surface 14. An arbitrary image can be projected on the surface to be scanned 15 by deflecting the irradiation light from the light source device 12 around one axis and scanning the light. The details of the movable device and the details of the control by the control device of this embodiment will be described later.

Next, a hardware configuration of an example of the optical scanning system 10 will be described with reference to FIG. FIG. 2 is a hardware configuration diagram of an example of the optical scanning system 10. As shown in FIG. 2, the optical scanning system 10 includes a control device 11, a light source device 12, and a movable device 13, each of which is electrically connected. Of these, the control device 11 includes a CPU 20, a RAM 21 (Random Access Memory), a ROM 22 (Read Only Memory), an FPGA 23, an external I / F 24, a light source device driver 25, and a movable device driver 26.

The CPU 20 is an arithmetic unit that reads programs and data from a storage device such as the ROM 22 onto the RAM 21 and executes processing to realize overall control and functions of the control device 11.

The RAM 21 is a volatile storage device that temporarily holds programs and data.

The ROM 22 is a non-volatile storage device that can retain programs and data even when the power is turned off, and stores processing programs and data executed by the CPU 20 to control each function of the optical scanning system 10. There is.

The FPGA 23 is a circuit that outputs a control signal suitable for the light source device driver 25 and the movable device driver 26 according to the processing of the CPU 20.

The external I / F 24 is, for example, an interface with an external device, a network, or the like. The external device includes, for example, a host device such as a PC (Personal Computer), and a storage device such as a USB memory, an SD card, a CD, a DVD, an HDD, and an SSD. Further, the network is, for example, a CAN (Controller Area Network) of an automobile, a LAN (Local Area Network), the Internet, or the like. The external I / F 24 may be configured to enable connection or communication with an external device, and an external I / F 24 may be prepared for each external device.

The light source device driver 25 is an electric circuit that outputs a drive signal such as a drive voltage to the light source device 12 according to the input control signal.

The movable device driver 26 is an electric circuit that outputs a drive signal such as a drive voltage to the movable device 13 according to an input control signal.

In the control device 11, the CPU 20 acquires optical scanning information from the external device or network via the external I / F 24. The configuration may be such that the CPU 20 can acquire optical scanning information, and the optical scanning information may be stored in the ROM 22 or FPGA 23 in the control device 11, or the SSD or the like may be newly stored in the control device 11. A storage device may be provided and the optical scanning information may be stored in the storage device.

Here, the optical scanning information is information indicating how the surface to be scanned 15 is optical-scanned. For example, when displaying an image by optical scanning, the optical scanning information is image data. Further, for example, when optical writing is performed by optical scanning, the optical scanning information is write data indicating the writing order and the writing location. In addition, for example, when object recognition is performed by optical scanning, the optical scanning information is irradiation data indicating the timing and irradiation range of irradiating the light for object recognition.

The control device 11 can realize the functional configuration described below by the instruction of the CPU 20 and the hardware configuration shown in FIG.

Next, the functional configuration of the control device 11 of the optical scanning system 10 will be described with reference to FIG. FIG. 3 is a functional block diagram of an example of the control device 11 of the optical scanning system.

As shown in FIG. 3, the control device 11 has a control unit 30 and a drive signal output unit 31 as functions.

The control unit 30 is realized by, for example, a CPU 20, FPGA 23, or the like, acquires optical scanning information from an external device, converts the optical scanning information into a control signal, and outputs the optical scanning information to the drive signal output unit 31. For example, the control unit 30 acquires image data as optical scanning information from an external device or the like, generates a control signal from the image data by a predetermined process, and outputs the control signal to the drive signal output unit 31. The drive signal output unit 31 is realized by the light source device driver 25, the movable device driver 26, and the like, and outputs a drive signal to the light source device 12 or the movable device 13 based on the input control signal.

The drive signal is a signal for controlling the drive of the light source device 12 or the movable device 13. For example, in the light source device 12, it is a drive voltage that controls the irradiation timing and irradiation intensity of the light source. Further, for example, in the movable device 13, it is a drive voltage that controls the timing and the movable range of moving the reflective surface 14 of the movable device 13.

Next, the process of optical scanning the surface to be scanned 15 by the optical scanning system 10 will be described with reference to FIG. FIG. 4 is a flowchart of an example of processing related to the optical scanning system.

In step S11, the control unit 30 acquires optical scanning information from an external device or the like. In step S12, the control unit 30 generates a control signal from the acquired optical scanning information and outputs the control signal to the drive signal output unit 31. In step S13, the drive signal output unit 31 outputs a drive signal to the light source device 12 and the movable device 13 based on the input control signal. In step S14, the light source device 12 irradiates light based on the input drive signal. Further, the movable device 13 moves the reflecting surface 14 based on the input drive signal. By driving the light source device 12 and the movable device 13, light is deflected in an arbitrary direction and light is scanned.

In the optical scanning system 10, one control device 11 has a device and a function of controlling the light source device 12 and the movable device 13, but the control device for the light source device and the control device for the movable device It may be provided separately.

Further, in the optical scanning system 10, one control device 11 is provided with a function of a control unit 30 of a light source device 12 and a movable device 13 and a function of a drive signal output unit 31, but these functions exist as separate bodies. For example, a drive signal output device having a drive signal output unit 31 may be provided separately from the control device 11 having the control unit 30. In the optical scanning system 10, a movable device 13 having a reflecting surface 14 and a control device 11 may be used to configure an optical deflection system that performs optical deflection.

[Image projection device]
Next, the image projection device to which the movable device of the present embodiment is applied will be described in detail with reference to FIGS. 5 and 6.

FIG. 5 is a schematic view of an embodiment of an automobile 400 equipped with a head-up display device 500, which is an example of an image projection device. Further, FIG. 6 is a schematic view of an example of the head-up display device 500.

The image projection device is a device that projects an image by optical scanning, for example, a head-up display device.

As shown in FIG. 5, the head-up display device 500 is installed near, for example, a windshield (windshield 401, etc.) of an automobile 400. The projected light L emitted from the head-up display device 500 is reflected by the windshield 401 and heads toward the observer (driver 402) who is the user. As a result, the driver 402 can visually recognize the image or the like projected by the head-up display device 500 as a virtual image. A combiner may be installed on the inner wall surface of the windshield so that the user can visually recognize the virtual image by the projected light reflected by the combiner.

As shown in FIG. 6, in the head-up display device 500, laser light is emitted from red, green, and blue laser light sources 501R, 501G, and 501B. The emitted laser light passes through an incident optical system composed of collimator lenses 502, 503, 504 provided for each laser light source, two dichroic mirrors 505, 506, and a light amount adjusting unit 507. It is deflected by a movable device 13 having a reflecting surface 14. Then, the deflected laser beam is projected onto the screen via a projection optical system including a free curved mirror 509, an intermediate screen 510, and a projection mirror 511. In the head-up display device 500, the laser light sources 501R, 501G, 501B, the collimator lenses 502, 503, 504, and the dichroic mirrors 505 and 506 are unitized by an optical housing as a light source unit 530.

The head-up display device 500 projects the intermediate image displayed on the intermediate screen 510 onto the windshield 401 of the automobile 400, so that the intermediate image is visually recognized by the driver 402 as a virtual image.

The laser light of each color emitted from the laser light sources 501R, 501G, and 501B is regarded as substantially parallel light by the collimator lenses 502, 503, and 504, respectively, and is combined by two dichroic mirrors 505 and 506. The combined laser light is two-dimensionally scanned by the movable device 13 having the reflecting surface 14 after the light amount is adjusted by the light amount adjusting unit 507. The projected light L two-dimensionally scanned by the movable device 13 is reflected by the free curved surface mirror 509, corrected for distortion, and then condensed on the intermediate screen 510 to display an intermediate image. The intermediate screen 510 is composed of a microlens array in which microlenses are two-dimensionally arranged, and magnifies the projected light L incident on the intermediate screen 510 in microlens units.

The movable device 13 reciprocates the reflecting surface 14 in the biaxial direction, and two-dimensionally scans the projected light L incident on the reflecting surface 14. The drive control of the movable device 13 is performed in synchronization with the light emission timing of the laser light sources 501R, 501G, and 501B.

The head-up display device 500 as an example of the image projection device has been described above, but the image projection device may be a device that projects an image by performing optical scanning by a movable device 13 having a reflecting surface 14. .. For example, it is mounted on a projector that is placed on a desk or the like and projects an image on a display screen, or is mounted on a mounting member mounted on an observer's head or the like, and is projected onto a reflection / transmission screen of the mounting member, or an eyeball is used as a screen. The same can be applied to a head-mounted display device or the like that projects an image.

Further, the image projection device is not only a vehicle or a mounting member, but also a moving object such as an aircraft, a ship, or a mobile robot, or a work robot that operates a drive target such as a manipulator without moving from the place. It may be mounted on a non-moving body.

[Optical writing device]
Next, the optical writing device to which the movable device of the present embodiment is applied will be described in detail with reference to FIGS. 7 and 8.

FIG. 7 is an example of an image forming apparatus incorporating the optical writing apparatus 600. Further, FIG. 8 is a schematic diagram of an example of an optical writing device.

As shown in FIG. 7, the optical writing device 600 is used as a constituent member of an image forming device represented by a laser printer 650 or the like having a printer function using a laser beam. In the image forming apparatus, the optical writing device 600 performs optical writing on the photoconductor drum by lightly scanning the photoconductor drum, which is the surface to be scanned 15, with one or a plurality of laser beams.

As shown in FIG. 8, in the optical writing device 600, the laser light from the light source device 12 such as a laser element passes through an imaging optical system 601 such as a collimator lens and then is transferred by a movable device 13 having a reflecting surface 14. It is deflected axially or biaxially. Then, the laser beam deflected by the movable device 13 passes through a scanning optical system 602 including a first lens 602a, a second lens 602b, and a reflection mirror portion 602c, and then passes through a surface to be scanned 15 (for example, a photoconductor drum or a photosensitive paper). ) Is irradiated and optical writing is performed. The scanning optical system 602 forms a spot-shaped light beam on the scanned surface 15. Further, the movable device 13 having the light source device 12 and the reflecting surface 14 is driven under the control of the control device 11.

As described above, the optical writing device 600 can be used as a component of an image forming device having a printer function by laser light. Further, by making the scanning optical system different so that optical scanning can be performed not only in the uniaxial direction but also in the biaxial direction, the laser beam is deflected to the thermal media to scan the light, and the laser label device for printing by heating and the like. It can be used as a constituent member of the image forming apparatus of.

Since the movable device 13 having the reflecting surface 14 applied to the optical writing device consumes less power for driving than the rotary multifaceted mirror using a polygon mirror or the like, the power saving of the optical writing device can be achieved. It is advantageous. Further, since the wind noise when the movable device 13 vibrates is smaller than that of the rotating polymorphic mirror, it is advantageous for improving the quietness of the optical writing device. The optical writing device requires an overwhelmingly smaller installation space than a rotating multi-sided mirror, and the amount of heat generated by the movable device 13 is small, so that it is easy to miniaturize, which is advantageous for miniaturizing the image forming device. be.

[Object recognition device]
Next, the object recognition device to which the movable device of the present embodiment is applied will be described in detail with reference to FIGS. 9 and 10.

FIG. 9 is a schematic view of an automobile equipped with a laser radar device, which is an example of an object recognition device. Further, FIG. 10 is a schematic diagram of an example of a laser radar device.

The object recognition device is a device that recognizes an object in the target direction, and is, for example, a laser radar device.

As shown in FIG. 9, the laser radar device 700 is mounted on, for example, an automobile 701, and by light-scanning the target direction and receiving the reflected light from the object 702 existing in the target direction, the object is received. Recognize 702.

As shown in FIG. 10, the laser light emitted from the light source device 12 is reflected through an incident optical system composed of a collimeter lens 703, which is an optical system whose divergent light is substantially parallel light, and a plane mirror 704. The movable device 13 having the surface 14 scans in one or two axial directions. Then, the object is irradiated to the object 702 in front of the apparatus via the projection lens 705 or the like which is a projection optical system. The drive of the light source device 12 and the movable device 13 is controlled by the control device 11. The reflected light reflected by the object 702 is photodetected by the photodetector 709. That is, the reflected light is received by the image pickup element 707 via the condenser lens 706 or the like which is an incident light detection light receiving optical system, and the image pickup element 707 outputs the detection signal to the signal processing device 708. The signal processing device 708 performs predetermined processing such as binarization and noise processing on the input detection signal, and outputs the result to the ranging circuit 710.

In the distance measuring circuit 710, the object is determined by the time difference between the timing at which the light source device 12 emits the laser beam and the timing at which the laser beam is received by the photodetector 709, or the phase difference for each pixel of the image pickup element 707 that receives the light. The presence or absence of 702 is recognized, and the distance information to the object 702 is calculated.

Since the movable device 13 having the reflecting surface 14 is less likely to be damaged and is smaller than the polymorphic mirror, it is possible to provide a compact radar device with high durability. Such a racer radar device can be attached to, for example, a vehicle, an aircraft, a ship, a robot, or the like, and can lightly scan a predetermined range to recognize the presence or absence of an obstacle and the distance to the obstacle.

In the above-mentioned object recognition device, the laser radar device 700 as an example has been described, but the object recognition device performs optical scanning by controlling the movable device 13 having the reflection surface 14 by the control device 11, and is a light detector. The device may be any device that recognizes the object 702 by receiving the reflected light, and is not limited to the above-described embodiment.

For example, biometric authentication that recognizes an object by calculating object information such as shape from distance information obtained by light scanning the hand or face and referring to it as a record, or recognition of an intruder by optical scanning to the target range. The same can be applied to a security sensor, a component of a three-dimensional scanner that calculates and recognizes object information such as a shape from distance information obtained by optical scanning, and outputs it as three-dimensional data.

[Laser headlamp]
Next, the laser headlamp 50 in which the movable device of the present embodiment is applied to the headlight of an automobile will be described with reference to FIG. FIG. 11 is a schematic diagram illustrating an example of the configuration of the laser headlamp 50.

The laser headlamp 50 includes a control device 11, a light source device 12b, a movable device 13 having a reflecting surface 14, a mirror 51, and a transparent plate 52.

The light source device 12b is a light source that emits a blue laser beam. The light emitted from the light source device 12b enters the movable device 13 and is reflected by the reflecting surface 14. The movable device 13 moves the reflecting surface in the XY direction based on the signal from the control device 11, and scans the blue laser light from the light source device 12b in the XY direction in two dimensions.

The scanning light from the movable device 13 is reflected by the mirror 51 and incident on the transparent plate 52. The front surface or the back surface of the transparent plate 52 is covered with a yellow fluorescent substance. The blue laser beam from the mirror 51 changes to white within the legal range of the color of the headlights as it passes through the coating of the yellow phosphor on the transparent plate 52. As a result, the front of the automobile is illuminated with white light from the transparent plate 52.

The scanning light from the movable device 13 scatters predeterminedly as it passes through the phosphor of the transparent plate 52. This alleviates the glare in the illuminated object in front of the vehicle.

When the movable device 13 is applied to the headlight of an automobile, the colors of the light source device 12b and the phosphor are not limited to blue and yellow, respectively. For example, the light source device 12b may be near-ultraviolet rays, and the transparent plate 52 may be coated with a uniform mixture of blue, green, and red phosphors of the three primary colors of light. Even in this case, the light passing through the transparent plate 52 can be converted to white, and the front of the automobile can be illuminated with white light.

[Head-mounted display]
Next, the head-mounted display 60 to which the movable device of the present embodiment is applied will be described with reference to FIGS. 12 to 13. Here, the head-mounted display 60 is a head-mounted display that can be worn on a human head, and may have a shape similar to that of eyeglasses, for example. The head-mounted display is hereinafter abbreviated as HMD.

FIG. 12 is a perspective view illustrating the appearance of the HMD 60. In FIG. 12, the HMD 60 is composed of a front 60a and a temple 60b provided in pairs on the left and right in a substantially symmetrical manner. The front 60a can be configured by, for example, a light guide plate 61, and an optical system, a control device, and the like can be built in the temple 60b.

FIG. 13 is a diagram partially illustrating the configuration of the HMD 60. Although the configuration for the left eye is illustrated in FIG. 13, the HMD 60 has the same configuration for the right eye.

The HMD 60 includes a control device 11, a light source unit 530, a light amount adjusting unit 507, a movable device 13 having a reflecting surface 14, a light guide plate 61, and a half mirror 62.

As described above, the light source unit 530 is a unitization of the laser light sources 501R, 501G, and 501B, the collimator lenses 502, 503, and 504, and the dichroic mirrors 505 and 506 by an optical housing. In the light source unit 530, the three-color laser light from the laser light sources 501R, 501G, and 501B is combined by the dichroic mirrors 505 and 506. The combined parallel light is emitted from the light source unit 530.

The light from the light source unit 530 is incident on the movable device 13 after the light amount is adjusted by the light amount adjusting unit 507. The movable device 13 moves the reflecting surface 14 in the XY directions based on the signal from the control device 11, and two-dimensionally scans the light from the light source unit 530. The drive control of the movable device 13 is performed in synchronization with the light emission timing of the laser light sources 501R, 501G, and 501B, and a color image is formed by the scanning light.

The scanning light from the movable device 13 is incident on the light guide plate 61. The light guide plate 61 guides the scanning light to the half mirror 62 while reflecting the scanning light on the inner wall surface. The light guide plate 61 is made of a resin or the like having transparency with respect to the wavelength of the scanning light.

The half mirror 62 reflects the light from the light guide plate 61 toward the back surface of the HMD 60 and emits the light toward the eyes of the wearer 63 of the HMD 60. The half mirror 62 has, for example, a free curved surface shape. The image from the scanning light is imaged on the retina of the wearer 63 by the reflection on the half mirror 62. Alternatively, the reflection on the half mirror 62 and the lens effect of the crystalline lens on the eyeball form an image on the retina of the wearer 63. Further, the spatial distortion of the image is corrected by the reflection on the half mirror 62. The wearer 63 can observe the image formed by the light scanned in the XY directions.

Since 62 is a half mirror, an image due to light from the outside world and an image due to scanning light are superimposed and observed on the wearer 63. By providing a mirror instead of the half mirror 62, the light from the outside world may be eliminated and only the image obtained by the scanning light can be observed.

[Packaging]
Next, the packaging of the movable device of the present embodiment will be described with reference to FIG.

FIG. 14 is a schematic diagram of an example of a packaged mobile device.

As shown in FIG. 14, the movable device 13 is attached to a mounting member 802 arranged inside the package member 801 and is packaged by covering a part of the package member with the transmission member 803 and sealing the package member 803. To. Further, the package is sealed with an inert gas such as nitrogen. As a result, deterioration of the movable device 13 due to oxidation is suppressed, and durability against changes in the environment such as temperature is further improved.

Details of the movable device of the present embodiment used in the optical scanning system, the head-up display, the optical writing device, the object recognition device, the laser head lamp, and the head-mounted display described above, and the details of the control by the control device. , Will be described with reference to the drawings. In each drawing, the same components may be designated by the same reference numerals and duplicate explanations may be omitted.

In the following, the optical scan centered on the first axis will be referred to as a main scan, and the optical scan centered on the second axis will be referred to as a sub scan. Further, rotation around the first and second axes, swing around the first and second axes, and movement around the first and second axes are synonymous with each other. .. Further, among the directions indicated by the arrows, the X direction indicates a direction parallel to the first axis, the Y direction indicates a direction parallel to the second axis, and the Z direction indicates a direction orthogonal to the XY plane.

[First Embodiment]
First, the configuration of the movable device of the first embodiment will be described in detail with reference to FIG. FIG. 15 is a plan view of a cantilever type movable device capable of light scanning in the two axial directions of the first axis and the second axis.

As shown in FIG. 15, the movable device 13 includes a mirror portion 100, first movable portions 101a and 101b, a first support portion 105, a second movable portion 106a and 106b, a second support portion 108, and electrodes. It has a connection portion 109 and. The mirror unit 100 that reflects incident light is an example of a mirror unit having a light reflecting surface. The first movable portions 101a and 101b are examples of the first movable portion that is directly connected to the mirror portion and rotates the mirror portion around the first axis in response to the input first drive signal. The second movable portion 106a and 106b are indirectly connected to the mirror portion, that is, via the first movable portion, and the second movable portion rotates the mirror portion around the second axis in response to the input second drive signal. This is an example of the department.

The first movable portions 101a and 101b are connected to the mirror portion 100 and rotate the mirror portion 100 around the first axis. The first support portion 105 supports the mirror portion 100 and the first movable portions 101a and 101b. The second movable portions 106a and 106b are connected to the first support portion 105, and the mirror portion 100 and the first support portion 105 are rotated around the second axis. The second support portion 108 supports the second movable portions 106a and 106b. The electrode connecting portion 109 is electrically connected to the first movable portions 101a and 101b, the second movable portions 106a and 106b, and the control device 11 that supplies the drive voltage to the first movable portion and the second movable portion. ..

In the movable device 13, for example, one SOI (Silicon On Insulator) substrate is molded by etching or the like, and the reflective surface 14, the cantilever 102a and 102b, the cantilever 107-1 to 107-12, and the cantilever 107-1 to 107-12 are formed on the molded substrate. By forming the electrode connecting portion 109 and the like, each constituent portion is integrally formed. The formation of each of the above components may be performed after molding the SOI substrate, or may be performed during molding of the SOI substrate.

In the SOI substrate, a silicon oxide layer is provided on a first silicon layer made of single crystal silicon (Si), and a second silicon layer made of single crystal silicon is further provided on the silicon oxide layer. It is a substrate. Hereinafter, the first silicon layer will be referred to as a silicon support layer, and the second silicon layer will be referred to as a silicon active layer.

Since the silicon active layer has a small thickness in the Z-axis direction with respect to the X-axis direction or the Y-axis direction, the member composed of only the silicon active layer has a function as an elastic portion having elasticity.

The SOI substrate does not necessarily have to be flat and may have a curvature or the like. Further, the member used for forming the movable device 13 is not limited to the SOI substrate as long as it is a substrate that can be integrally molded by an etching process or the like and can be partially elastic.

The mirror portion 100 has, for example, a circular mirror portion substrate 100a and a reflective surface 14 formed on the + Z side surface of the mirror portion substrate 100a. The mirror portion substrate 100a is made of, for example, a silicon active layer, and the reflective surface 14 is made of a metal thin film containing, for example, aluminum, gold, silver, and the like. Further, the mirror portion 100 may be formed with ribs for reinforcing the mirror portion on the surface on the −Z side of the mirror portion substrate 100a. The rib is composed of, for example, a silicon support layer and a silicon oxide layer, and can suppress the distortion of the reflective surface 14 caused by the movement.

The first movable portions 101a and 101b have torsion bars 103a and 103b, and cantilever 102a and 102b. One end of the torsion bars 103a and 103b is connected to the mirror portion base 100a and extends in the first axial direction to movably support the mirror portion 100. One end of the cantilever 102a and 102b is connected to the torsion bar, and the other end is connected to the inner peripheral portion of the first support portion 105.

The torsion bars 103a and 103b are composed of a silicon active layer. Further, the cantilever 102a and 102b are formed by forming a lower electrode, a piezoelectric portion, and an upper electrode in this order on the + Z side surface of the silicon active layer which is an elastic portion. The upper electrode and the lower electrode are made of, for example, gold (Au) or platinum (Pt), and the piezoelectric portion is made of, for example, PZT (lead zirconate titanate) which is a piezoelectric material.

The first support portion 105 is, for example, a rectangular support formed so as to surround the mirror portion 100, which is composed of, for example, a silicon support layer, a silicon oxide layer, and a silicon active layer.

The second movable portions 106a and 106b have, for example, a plurality of cantilever 107-1 to l07-12 connected so as to be folded back. Such a structure in which a plurality of cantilever are folded is called a mianda structure. One end of the second movable portion 106a and 106b is connected to the outer peripheral portion of the first support portion 105, and the other end is connected to the inner peripheral portion of the second support portion 108. At this time, the connection point between the second movable portion 106a and the first support portion 105, the connection point between the second movable portion 106b and the first support portion 105, the connection point between the second movable portion 106a and the second support portion 108, and the second position. The connection points between the two movable portions 106b and the second support portion 108 are point-symmetrical with respect to the center of the reflective surface 14.

The cantilever 107-1 to 107-12 are formed by forming a lower electrode, a piezoelectric portion, and an upper electrode in this order on the + Z side surface of the silicon active layer which is an elastic portion. The upper electrode and the lower electrode are made of, for example, gold (Au) or platinum (Pt), and the piezoelectric portion is made of, for example, PZT (lead zirconate titanate) which is a piezoelectric material.

The second support portion 108 is composed of, for example, a silicon support layer, a silicon oxide layer, and a silicon active layer, and includes a mirror portion 100, first movable portions 101a and 101b, a first support portion 105, and second movable portions 106a and 106b. It is a rectangular support formed so as to surround the.

The electrode connecting portion 109 is formed, for example, on the + Z side surface of the second support portion 108, and is formed on the cantilever 102a and 102b, the upper electrodes of the cantilever 107-1 to 107-12, the lower electrodes, and the control device 11. It is electrically connected via electrode wiring such as aluminum (Al). The upper electrode or the lower electrode may be directly connected to the electrode connecting portion 109, or may be indirectly connected by connecting the electrodes to each other.

In the present embodiment, the case where the piezoelectric portion is formed only on one surface (the surface on the + Z side) of the silicon active layer, which is the elastic portion, has been described as an example, but the other surface of the elastic portion (for example, the surface on the −Z side) has been described as an example. It may be provided on a surface), or it may be provided on both one surface and the other surface of the elastic portion.

Further, the shape of each component is not limited to the shape of the embodiment as long as the mirror portion 100 can be moved around the first axis or the second axis. For example, the torsion bars 103a and 103b and the cantilevers 102a and 102b may have a shape having a curvature.

Further, on the + Z side surface of the upper electrodes of the first movable portions 101a and 101b, on the + Z side surface of the first support portion, on the + Z side surface of the second movable portions 106a and 106b, and the second support. An insulating layer made of a silicon oxide film may be formed on at least one of the + Z-side surfaces of the portion 108.

At this time, the electrode wiring is provided on the insulating layer, and only the connection spot where the upper electrode or the lower electrode and the electrode wiring are connected is partially removed as an opening or the insulating layer is not formed. The degree of design freedom of the first movable portions 101a and 101b, the second movable portions 106a and 106b, and the electrode wiring can be increased, and a short circuit due to contact between the electrodes can be suppressed. The silicon oxide film also has a function as an antireflection material.

Next, the details of the driving method of the first movable portion and the second movable portion of the movable device will be described.

When a positive or negative voltage is applied in the polarization direction, the piezoelectric portions of the first movable portions 101a and 101b and the second movable portions 106a and 106b are deformed in proportion to the potential of the applied voltage, such as expansion and contraction. It occurs and exerts a so-called inverse piezoelectric effect. The first movable portions 101a and 101b, and the second movable portions 106a and 106b rotate the mirror portion 100 by utilizing the above-mentioned inverse piezoelectric effect.

At this time, the angle formed by the XY plane and the reflecting surface 14 when the reflecting surface 14 of the mirror portion 100 is tilted in the + Z direction or the −Z direction with respect to the XY plane is called a deflection angle. At this time, the + Z direction is a positive runout angle, and the −Z direction is a negative runout angle.

First, a driving method by the first movable portions 101a and 101b will be described. In the first movable portions 101a and 101b, when the drive voltage is applied in parallel to the piezoelectric portions of the cantilever 102a and 102b via the upper electrode and the lower electrode, that is, at the same time, the respective piezoelectric portions are deformed. The cantilever 102a and 102b are bent and deformed by the action of the deformation of the piezoelectric portion. As a result, a driving force around the first axis acts on the mirror portion 100 through the twist of the two torsion bars 103a and 103b, and the mirror portion 100 rotates around the first axis. The drive voltage applied to the first movable portions 101a and 101b is controlled by the control device 11.

By applying a drive voltage having a predetermined waveform to the cantilever 102a and 102b of the first movable portions 101a and 101b in parallel, that is, at the same time, the mirror portion 100 is subjected to a period of the drive voltage having a predetermined waveform around the first axis. Can be rotated with.

In particular, for example, when the frequency of the applied voltage is set to about 20 kHz, which is about the same as the resonance frequency of the torsion bars 103a and 103b, the mechanical resonance caused by the twist of the torsion bars 103a and 103b is utilized to utilize the mirror. The unit 100 can be resonantly rotated at about 20 kHz.

Next, a driving method by the second movable portions 106a and 106b will be described. When the drive voltage is not applied to the second movable portions 106a and 106b, the runout angle by the second movable portions 106a and 106b is zero. Of the plurality of cantilever 107-1 to 107-6 included in the second movable portion 106a, the cantilever which is an even number from the cantilever 107-4 closest to the mirror portion 100, that is, the cantilever 107-1, 107-2, Let 107-3 be the cantilever group A. Further, among the plurality of cantilever 107-7 to 107-12 possessed by the second movable portion 106b, the cantilever which is the odd number counting from the cantilever 107-7 which is the closest to the mirror portion 100, that is, the cantilever 107-7, 107. Similarly, -8 and 107-9 are designated as cantilever group A. When the drive voltage of the cantilever group A is applied in parallel, that is, at the same time, the cantilever group A bends and deforms in the same direction, and the mirror portion 100 rotates about the second axis in the −Z direction.

Further, among the plurality of cantilever 107-1 to 107-6 possessed by the second movable portion 106a, the cantilever which is the odd number counting from the cantilever 107-4 which is the closest to the mirror portion, that is, the cantilever 107-4, 107-5. , 107-6 are designated as cantilever group B. Further, among the plurality of cantilever 107-7 to 107-12 possessed by the second movable portion 106b, the cantilever which is the even number counting from the cantilever 107-7 closest to the mirror portion, that is, the cantilever 107-10, 107- 11 and 107-12 are similarly referred to as cantilever group B. When the drive voltage of the cantilever group B is applied in parallel, that is, at the same time, the cantilever group B bends and deforms in the same direction, and the mirror portion 100 rotates about the second axis in the + Z direction.

In the second movable portion 106a or 106b, the plurality of piezoelectric portions of the cantilever group A or the plurality of piezoelectric portions of the cantilever group B are simultaneously bent and deformed to accumulate the amount of rotation due to the bending deformation of the mirror portion 100. The rotation angle around the second axis can be increased. For example, the second movable portions 106a and 106b are connected to the first support portion 105 point-symmetrically with respect to the center point of the first support portion 105. Therefore, when a driving voltage is applied to the cantilever group A, a driving force that moves in the + Z direction is generated at the connection portion between the first support portion 105 and the second movable portion 106a in the second movable portion 106a, and the first in the second movable portion 106b. A driving force that moves in the −Z direction is generated at the connection portion between the support portion 105 and the second movable portion 106b, and the amount of rotation is accumulated so that the rotation angle of the mirror portion 100 around the second axis can be increased.

Further, when the rotation amount of the mirror portion 100 by the cantilever group A due to the voltage application and the rotation amount of the mirror portion 100 by the cantilever group B due to the voltage application are balanced, the rotation angle becomes zero.

By applying a driving voltage to the cantilever 107-1 to 107-12 so as to continuously repeat the above rotation, the mirror portion 100 can be rotated around the second axis. The drive voltage applied to the second movable portion is controlled by the control device 11.

By using PZT, which is a piezoelectric material, for the piezoelectric portion of the first movable portion and the second movable portion, it is possible to drive with high sensitivity at a low voltage.

Further, the second movable portion has a meander structure including a plurality of cantilever, and each cantilever has a piezoelectric portion connected to each cantilever, so that the cantilever can be uniformly changed in physical properties. The meander structure may have a shape having a curvature.

When the mirror unit 100 is irradiated with light such as a laser, the light reflected by the mirror unit 100 is scanned in the Y direction, that is, in the main scanning direction by rotation around the first axis of the mirror unit 100. Further, by rotating the mirror portion 100 around the second axis, scanning is performed in the X direction, that is, in the sub-scanning direction. This enables a two-dimensional scan of light in the XY plane.

Next, a method of driving the movable device 13 for lithage scanning of light will be described. Here, the Lissajous scanning means scanning the light so that the locus of the scanning light draws a Lissajous figure. The Lissajous figure is a plane figure drawn by a motion obtained by synthesizing simple vibrations in two directions orthogonal to each other on a plane.

First, a conventional driving method will be described. FIG. 16 shows an example of a locus of scanning light, that is, a scanning line and a driving signal thereof when resage scanning is performed by the movable device 13 when the present embodiment is not applied.

In FIG. 16, the signals 131 and 132 indicate the first and second drive signals input to the movable device 13. The signal 131 is a signal having a frequency fy for scanning light in the Y direction, and the signal 132 is a signal having a frequency fx for scanning light in the X direction. The waveforms of the signals 131 and 132 are sinusoidal.

The frequency fy is a frequency higher than the frequency fx. Further, the frequency fx is a resonance frequency in a structure in which the mirror portion 100, the torsion bars 103a and 103b, the cantilever 102a and 102b, the first support portion 105, and the cantilever 107-1 to 107-12 are integrated. The frequency fy is a resonance frequency in a structure in which the mirror portion 100, the torsion bars 103a and 103b, and the cantilever 102a and 102b are integrated.

When the signals 131 and 132 are input to the movable device 13, the mirror unit 100 of the movable device 13 resonates and rotates in the Y and X directions, and the scanning line 133 by the mirror unit 100 draws a Lissajous figure.

Here, the resage scanning has a property that the scanning lines in the scanning region are rough and dense. For example, in the scanning lines 133 of FIG. 16, in the X direction, the intervals between the scanning lines are coarse near the center, and the intervals between the scanning lines are getting smaller toward both ends. When an image is formed by such scanning light, resolution variation and color unevenness occur in the image in each region such as near the center and near both ends in the X direction, and the image quality deteriorates.

On the other hand, if resonance is not used, the efficiency of the momentum associated with the applied voltage decreases. In order to obtain a large amount of rotation of the mirror portion in order to widen the scanning angle, it is necessary to apply a large drive voltage, which leads to an increase in power consumption and component cost.

The inventor analyzed the relationship between the driving signal for the resage scanning and the scanning line, and found the following points. First, when the frequency fy of the first drive signal is a multiple or a divisor of the frequency fx of the second drive signal, the scanning lines overlap, and in the X direction, only the number of scanning lines corresponding to the ratio of the two is obtained. It is a point that cannot be done. Second, if the frequency fy is determined based on the frequency fx and the number of frames of the image and is set to a value that is not divided by the frequency fx, the overlap of the scanning lines in the X direction can be suppressed. The number of image frames is the number of images displayed per second.

The first point above will be described. When the frequency of the first drive signal is fy (Hz), the frequency of the second drive signal is fx (Hz), and the number of image frames is Nf (fps: frames per second), the number of scanning lines obtained in the X direction. A is as shown in the following equation (1).

・・・（１）
例えば、図１６の例では、信号１３１の周波数ｆｙは３０００Ｈｚで、信号１３２の周波数ｆｘは３００Ｈｚであり、この場合、周波数ｆｙは周波数ｆｘの倍数で、両者の比のｆｙ／ｆｘは１０である。フレーム数Ｎｆを３０ｆｐｓとすると、Ｘ方向における走査線の本数は、（１）式によれば２００本になるが、図１６の例では、ｆｘとｆｙの比に相当する１０本の走査線しか得られていない。２００本の走査線の多くが重なり、その結果、１０本の走査線になったと考えられる。

... (1)
For example, in the example of FIG. 16, the frequency fy of the signal 131 is 3000 Hz, the frequency fx of the signal 132 is 300 Hz, and in this case, the frequency fy is a multiple of the frequency fx, and the ratio fy / fx of the two is 10. .. Assuming that the number of frames Nf is 30 fps, the number of scanning lines in the X direction is 200 according to the equation (1), but in the example of FIG. 16, only 10 scanning lines corresponding to the ratio of fx and fy are used. Not obtained. It is considered that many of the 200 scanning lines overlapped, resulting in 10 scanning lines.

Next, the second point described above will be described. FIG. 17 shows an example of a drive signal when resage scanning is performed by the movable device 13 of the present embodiment. The signal 134 is a first drive signal for scanning light in the Y direction, and the signal 135 is a second drive signal for scanning light in the X direction. The waveforms of the signals 134 and 135 are sinusoidal. Similar to the above, the frequency fy of the signal 134 is higher than the frequency fx of the signal 135, and both the frequencies fx and fy are resonance frequencies.

FIG. 17 shows a drive signal at a time corresponding to one frame of an image having the number of frames Nf. The signal 134 is an example of a first drive signal input to the first movable portion, and the signal 135 is an example of a second drive signal input to the second movable portion.

In the movable device 13 of the present embodiment, the frequency fy of the drive signal is determined based on the frequency fx and the number of frames Nf, and is a value that is not divided by the frequency fx.

Here, "frequency fy is not divided by frequency fx" means that when frequency fy is divided by frequency fx, frequency fy cannot be divided by frequency fx, and there is no quotient of an integer whose remainder is 0. It means that. Even if the quotient of the division is a finite decimal number, it may be divisible, but to distinguish it from this, the expression "divided" is used, which does not include the case where the quotient is an integer.

Specifically, the frequency fx, the frequency fy, and the number of frames Nf have the relationship of the following equation (2).

・・・・（２）
（２）式のように周波数ｆｙを決定すると、ミラー部のＸ方向の回動とＹ方向の回動とが同期しなくなるため、Ｙ方向の回動の位相がＸ方向の回動ごとに変化する。つまり、Ｙ方向の走査の開始位置を、Ｘ方向に徐々にずらすという作用が得られる。

・ ・ ・ ・ (2)
When the frequency phy is determined as in the equation (2), the rotation in the X direction and the rotation in the Y direction of the mirror portion are not synchronized, so that the phase of the rotation in the Y direction changes with each rotation in the X direction. do. That is, the effect of gradually shifting the scanning start position in the Y direction in the X direction can be obtained.

For example, in FIG. 17, the phases of the first drive signal at the timings 136a, 136b and 136c of the same phase of the second drive signal are different from each other. This indicates that the scanning start positions of the first drive and the second drive are shifted in the X direction in the scanning area.

Such first and second drive signals are input to the movable device 13 from the drive signal output unit 31 based on the control signal output from the control unit 30 in FIG.

FIG. 18 shows scanning lines when signals 134 and 135 are input to the movable device 13. In FIG. 18, the thick solid line 137 is the start position of scanning in the Y direction. As shown, the start position of scanning in the Y direction is gradually deviated in the X direction. As a result, the overlap of the scanning lines per frame is suppressed, and the coarseness and density of the scanning lines in FIG. 18 is reduced as compared with FIG.

In other words, the density of the scanning lines is reduced in the resage scanning region. By forming an image with such scanning lines, for example, it is possible to suppress variations in resolution and color unevenness of the image and obtain an image of good quality.

In the XY plane of FIG. 18, the solid line and the dotted line drawn in the X direction or parallel to the Y direction are auxiliary lines and are irrelevant to the scanning lines.

Among the drive signal output units 31, the function of outputting the first drive signal to the first movable units 101a and 101b is an example of the first output means for outputting the first drive signal to the first movable unit. The function of outputting the second drive signal to the second movable portion 106a and 106b is an example of the second output means for outputting the second drive signal to the second movable portion.

At least one of the first output means and the second output means has a DDS (Direct Digital Synthesizer) type or a PLL (Phase Locked Loop) type frequency synthesizer. By using these, it is possible to generate a signal having an arbitrary frequency with high resolution based on the reference clock signal, and it is possible to freely set the frequency of the drive signal with high resolution.

In addition to the above, for example, the following effects can be obtained.

According to this embodiment, since resonance can be used in both the X and Y directions, a large amount of rotation can be obtained with a small drive voltage in both directions. Thereby, for example, it is possible to widen the angle of optical scanning without increasing power consumption and component cost.

[Second Embodiment]
Next, the movable device of the second embodiment will be described. The part that overlaps with the first embodiment will be omitted, and the differences will be described.

FIG. 19 shows an example of a drive signal when performing resage scanning by the movable device 13 of the present embodiment. In FIG. 19, the signal 138 is a second drive signal input to the second movable portions 106a and 106b. The waveform of the signal 138 is a triangular wave.

When the waveform of the signal 138 is a sine wave, there is a time region in which the scanning speed becomes low near the turning point of the sine wave waveform, and the intervals between the scanning lines in the Y direction become dense in that time region. For example, in FIG. 18, the vicinity of both ends in the X direction corresponds to the inflection point of the sinusoidal waveform of the drive signal, and the intervals between the scanning lines in the Y direction are close. In such a case, in order to eliminate the density of the scanning lines, it is necessary to take measures such as excluding the vicinity of both ends in the X direction from the effective image area, and the entire scanning lines cannot be effectively utilized.

FIG. 20 shows an example of scanning lines when the waveform of the signal 138 is made into a triangular wave. In the case of a triangular wave, the scanning speed near the inflection point of the waveform changes linearly, so that the spacing between the scanning lines in the Y direction is prevented from becoming dense. As a result, scanning lines at equal intervals can be obtained at both ends in the X direction, and the entire scanning line can be effectively utilized.

In the XY plane of FIG. 20, the solid line and the dotted line drawn in the X direction or parallel to the Y direction are auxiliary lines and are irrelevant to the scanning lines.

[Third Embodiment]
Next, the movable device 40 of the third embodiment will be described. The part that overlaps with the first and second embodiments will be omitted, and the differences will be described.

In a movable device, the amplitude of rotation of the mirror portion may fluctuate due to fluctuations in the resonance frequency of the movable portion due to changes in ambient temperature or the like. The amplitude of rotation is synonymous with the maximum angle of rotation of the mirror portion.

Fluctuations in the amplitude of rotation reduce the quality of the image formed by the scanning light. According to the movable device 40 of the present embodiment, it is possible to suppress the influence of such fluctuations and realize stable optical scanning.

An example of the configuration of the movable device 40 of the present embodiment will be described with reference to FIG.

In FIG. 21, the cantilever 102a and 102b have elastic modulus adjusting portions 104a and 104b, respectively. Further, the cantilever 107-1 to 107-6 have an elastic modulus adjusting portion 107a, and the cantilever 107-7 to 107-12 have an elastic modulus adjusting portion 107b. Further, at least one of the cantilever 102a and 102b has a detection piezoelectric element, and at least one of the cantilever 107-1 to 107-12 has a detection piezoelectric element.

The elastic modulus adjusting portions 104a, 104b, 107a and 107b are composed of, for example, a piezoelectric actuator formed in the order of a lower electrode, a piezoelectric portion, and an upper electrode on the + Z side surface of the silicon active layer which is an elastic portion. With such a configuration, it is possible to obtain the effect that the movable portion and the elastic modulus adjusting portion can be manufactured by the same process. A heat generating part is provided in place of the piezoelectric part, and each elastic modulus adjusting part is configured by a piezoelectric actuator formed in the order of a lower electrode, a heat generating part, and an upper electrode on the + Z side surface of the silicon active layer which is an elastic part. May be good.

By applying a DC voltage to the elastic modulus adjusting portions 104a, 104b, 107a and 107b, respectively, a certain amount of deformation can be applied to the cantilever provided with the elastic modulus adjusting portion. As a result, the elastic modulus of the elastic portion of the cantilever can be changed, and the resonance frequency of the movable portion composed of the cantilever can be changed. FIG. 23 shows an example of a change in the resonance frequency of the movable portion due to the voltage applied to the elastic modulus adjusting portion.

The detection piezoelectric element is composed of, for example, a piezoelectric element formed in the order of a lower electrode, a piezoelectric portion, and an upper electrode on a surface on the + Z side of a silicon active layer which is an elastic portion. The detection piezoelectric element may be formed in the + Z direction or the −Z direction of the elastic modulus adjusting portion so as to form a layer with the elastic modulus adjusting portion provided on each cantilever. Further, it may be formed on the cantilever in a plane orthogonal to the Z direction so as to be adjacent to the elastic modulus adjusting portion.

FIG. 22 shows, as an example, a structure when the elastic modulus adjusting portion 111a and the detection piezoelectric element 111b are formed adjacent to each other on the cantilever 107-9 and 107-12 in FIG. 21. (A) is a plan view, and (b) is a cross-sectional view taken along the line AA in (a). In (b), the elastic modulus adjusting portion 111a is formed of a three-layer structure consisting of an upper electrode 111aU, a piezoelectric portion 111aP, and a lower electrode 111aL from the top. Similarly, the detection piezoelectric element 111b is also formed from the top with a three-layer structure of an upper electrode 111bU, a piezoelectric portion 111bP, and a lower electrode 111bL.

The detection piezoelectric element converts the deformation of the cantilever due to the rotation of the mirror portion 100 around the first and second axes into a voltage, and outputs the voltage to the outside through the electrode connecting portion 109. The deformation of the cantilever accompanying the rotation of the mirror portion 100 around the first and second axes is information synonymous with the angle of rotation of the mirror portion 100 around the first and second axes.

Next, an example of the functional configuration of the control device 41 of the present embodiment will be described with reference to FIG. 24. As shown in FIG. 24, the control device 41 has a control unit 42, a drive signal output unit 43, a detection signal acquisition unit 44, and a drive signal output unit 45 for elastic modulus adjustment as functions. Further, the movable device 40 has first and second movable means 40a, first and second detection means 40b, and first and second elastic modulus adjusting means 40c as functions.

The control unit 42 is realized by, for example, a CPU, FPGA, or the like, acquires optical scanning information from an external device, converts the optical scanning information into a control signal, and outputs the optical scanning information to the drive signal output unit 43. Further, the control unit 42 acquires image data as optical scanning information, generates a control signal from the image data by a predetermined process, and outputs the control signal to the drive signal output unit 43. Further, the control unit 42 generates an elastic modulus adjustment drive signal from the signal acquired by the detection signal acquisition unit 44, and outputs the elastic modulus adjustment drive signal output unit 45 to the elastic modulus adjustment drive signal output unit 45.

The drive signal output unit 43 is realized by a driver of the light source device 12, a driver of the movable device 40, and the like, and outputs a drive signal to the light source device 12 or the movable device 40 based on the control signal input from the control unit 42.

Among the drive signal output units 43, the function of outputting the first drive signal to the first movable unit is an example of the first output means that outputs the first drive signal to the first movable unit. The function of outputting the second drive signal to the second movable means is an example of the second output means that outputs the second drive signal to the second movable portion.

At least one of the first output means and the second output means has a DDS type or PLL type frequency synthesizer. By using these, it is possible to generate a signal having an arbitrary frequency with high resolution based on the reference clock signal, and it is possible to freely set the frequency of the drive signal with high resolution.

The drive signal is a signal for controlling the drive of the light source device 12 or the movable device 40. In the light source device 12, for example, it is a drive voltage that controls the irradiation timing and the irradiation intensity of the light source. Further, in the movable device 40, for example, it is a drive voltage that controls the timing at which the reflective surface 14 of the movable device 40 is moved and the movable range.

The first movable means in the first and second movable means 40a is realized by, for example, the first movable portions 101a and 101b, and the second movable means is realized by the second movable portions 106a and 106b.

The first and second detection means 40b are realized by a detection piezoelectric element provided in the cantilever, for example, inside the movable device 40.

The detection piezoelectric element possessed by at least one of the cantilever 102a and 102b detects the deformation of the cantilever accompanying the rotation of the mirror portion 100 around the first axis, that is, the angle of rotation of the mirror portion 100 around the first axis. The detection piezoelectric element possessed by at least one of the cantilever 107-1 to 107-12 is deformed by the rotation of the mirror portion 100 around the second axis, that is, the angle of rotation of the mirror portion 100 around the second axis. Is detected.

The first elastic modulus adjusting means in the first and second elastic modulus adjusting means 40c is realized from the elastic modulus adjusting units 104a and 104b, and the second elastic modulus adjusting means is realized from the elastic modulus adjusting units 107a and 107b. Each elastic modulus adjusting unit adjusts the elastic modulus of the elastic portion of the cantilever provided with each elastic modulus adjusting unit based on the signal from the elastic modulus adjusting drive signal output unit 45.

The detection signal acquisition unit 44 is realized by, for example, an A / D (Analog / Digital) converter, and the elastic modulus adjusting drive signal output unit 45 is realized by, for example, a D / A (Digital / Analog) converter.

Next, a method of detecting the fluctuation of the amplitude of rotation by the above configuration and suppressing the influence thereof will be described.

The detection piezoelectric element outputs the detection signal to the detection signal acquisition unit 44. The detection signal acquisition unit 44 A / D-converts the analog signal from the detection piezoelectric element and outputs the digital signal to the control unit 42.

The control unit 42 obtains the amplitude of rotation of the mirror unit 100 based on the output signal of the detection signal acquisition unit 44. For example, the PP (Peak To Peak) value of the change in the signal voltage according to the rotation of the mirror unit 100 is obtained, and the “signal voltage and the amplitude of the rotation of the mirror unit 100” acquired and stored in advance are obtained. Based on the data indicating "relationship between", the amplitude of rotation of the mirror unit 100 is acquired. When the plurality of cantilever has the detection piezoelectric element, the amplitude of the rotation of the mirror unit 100 is acquired based on the average value of the output signals of the plurality of detection piezoelectric elements.

The control unit 42 compares the acquired rotation amplitude of the mirror unit 100 with the specification value of the rotation amplitude of the mirror unit 100, and calculates the difference. When the difference is larger than the preset threshold value, the control unit 42 determines that the frequency of the drive signal for rotating the mirror unit 100 and the resonance frequency deviate from each other.

When the frequency of the drive signal and the resonance frequency deviate from each other, the control unit 42 obtains and stores in advance the above-mentioned data indicating "the relationship between the amplitude of rotation and the amount of deviation of the resonance frequency". The amount of deviation of the resonance frequency is obtained from the amplitude of rotation. Further, the control unit 42 applies the amount of deviation of the resonance frequency to the elastic modulus adjusting unit based on the data indicating the “relationship between the resonance frequency and the voltage applied to the elastic modulus adjusting unit” acquired and stored in advance. Find the voltage. Then, the control unit 42 outputs a digital signal of voltage to the drive signal output unit 45 for adjusting the elastic modulus.

The elastic modulus adjusting drive signal output unit 45 D / A-converts a digital signal of the elastic modulus adjusting voltage and outputs it to the elastic modulus adjusting units 104a, 104b, 107a and 107b. Each elastic modulus adjusting portion applies a certain amount of deformation to the cantilever according to the applied voltage, and changes the elastic modulus of the elastic modulus in the cantilever to change the resonance frequency of the cantilever or the like by a predetermined amount.

The detection piezoelectric element possessed by at least one of the cantilever 102a and 102b is an example of the first detecting means for detecting the angle of rotation around the first axis of the mirror portion. The detection piezoelectric element possessed by at least one of the cantilever 107-1 to 107-12 is an example of the second detecting means for detecting the angle of rotation around the second axis of the mirror portion.

The elastic modulus adjusting units 104a and 104b are examples of the first elastic modulus adjusting means, and the elastic modulus adjusting units 107a and 107b are examples of the second elastic modulus adjusting means.

The flowchart of the above processing is shown in FIG.

First, in step S241, the control device 41 acquires optical scanning information. The optical scanning information is information indicating how the surface to be scanned is light-scanned as described above, and for example, information such as image data, the number of frames Nf of the image, the first and second drive signals, etc. included.

Subsequently, in step S243, the control unit 42 generates a drive signal and outputs the drive signal to the drive signal output unit 43 based on the optical scanning information.

Subsequently, in step S245, the drive signal output unit 43 outputs a drive signal to the light source device 12, the first and second movable means 40a.

Subsequently, in step S247, the light source device 12, the first and second movable means 40a perform optical scanning based on the drive signal.

During the optical scan, in step S249, the detection signal acquisition unit 44 acquires a signal of the rotation angle of the mirror unit 100.

Subsequently, in step S251, the control unit 42 acquires the amplitude of rotation of the mirror unit 100 from the signal of the rotation angle of the mirror unit 100. Then, the difference between the acquired rotation amplitude of the mirror unit 100 and the specification value of the rotation amplitude of the mirror unit 100 is calculated, and if the difference is larger than the threshold value, the frequency of the drive signal and the resonance frequency deviate from each other. Judge that there is.

When it is determined that the frequency of the drive signal and the resonance frequency deviate from each other, in step S253, the control unit 42 generates a drive signal for elastic modulus adjustment and outputs it to the drive signal output unit 45 for elastic modulus adjustment.

Subsequently, in step S255, the elastic modulus adjusting drive signal output unit 45 outputs the elastic modulus adjusting drive signal to the elastic modulus adjusting units 104a, 104b, 107a and 107b.

Subsequently, in step 257, the elastic modulus adjusting portions 104a, 104b, 107a and 107b adjust the elastic modulus of the elastic modulus in the cantilever.

If it is determined in step S251 that the frequency of the drive signal and the resonance frequency do not deviate from each other, the process returns to step S247 and the optical scanning is continued.

In step S259, it is determined whether to end the optical scan, and if it ends, the process ends. If not, the process returns to step S247 and the optical scan continues.

As a result, it is possible to suppress the influence of changes in the ambient temperature and realize stable optical scanning.

In the above, the detection piezoelectric element is shown as an example of the first and second detection means for detecting the angle of rotation around the first and second axes of the mirror portion, but the present invention is not limited thereto. As the first and second detection means, for example, a PD (Photo Diode) arranged outside the movable device 40 may be used. The following is an example of processing when PD is used.

The PD detects the timing at which the scanning light from the movable device 40 passes through the light receiving surface of the PD. The detection signal acquisition unit 44 A / D-converts the output signal of the PD and outputs the digital signal to the control unit 42. The control unit 42 obtains, for example, the time t required for one scan in the X direction from the digital signal output from the PD. The period of the drive signal is T, the specification value of the rotation amplitude of the mirror unit 100 is P, and the control unit 42 acquires the rotation amplitude p of the mirror unit 100 as, for example, P × t / T. can.

In addition, in order to detect the amplitude of rotation around the first and second axes, at least two PDs, one for the first axis and the other for the second axis, are required.

It is also possible to use the PD provided for synchronous detection of scanning by the movable device 40 as the first and second detection means.

Further, in the above, it has been shown that the amplitude of the rotation of the mirror unit 100 fluctuates due to the deviation of the resonance frequency, but the present invention is not limited to this. This embodiment is also applicable when the amplitude of rotation of the mirror unit 100 fluctuates due to factors other than the deviation of the resonance frequency.

For example, the angle of rotation around the first and second axes of the mirror unit is detected by a detection piezoelectric element or the like, and the amplitude of rotation of the mirror unit 100 is acquired based on the output of the detection piezoelectric element or the like. If the amplitude of rotation of the mirror unit 100 differs from or fluctuates from the specified value, the voltage applied to the elastic modulus adjustment unit while monitoring the amplitude of rotation of the mirror unit 100 based on the output of the detection piezoelectric element or the like. To adjust. As a result, the amplitude of rotation can be matched with the specified value, or fluctuation can be suppressed.

In the above, in order to detect the deviation between the frequency of the drive signal and the resonance frequency, the amplitude of rotation of the mirror unit 100 is obtained. Instead of this, the deviation between the frequency of the drive signal and the resonance frequency is determined from the phase difference between the phase of the output change of the detection piezoelectric element due to the rotation of the mirror unit 100 and the phase of the output signal of the drive signal output unit 43. It may be detected. This is because the above phase difference also changes according to the frequency shift.

The phase difference can be detected, for example, by inputting both the output signal of the detection piezoelectric element and the output signal of the drive signal output unit 43 to a lock-in amplifier circuit or the like.

When the phase difference exceeds a preset threshold value, the control unit 42 determines that the frequency of the drive signal for rotating the mirror unit 100 and the resonance frequency deviate from each other.

When the frequency of the drive signal and the resonance frequency deviate from each other, the control unit 42 acquires and stores in advance the above-mentioned phase difference based on the data indicating "the relationship between the phase difference and the amount of deviation of the resonance frequency". The amount of deviation of the resonance frequency is obtained from. Further, the control unit 42 applies the amount of deviation of the resonance frequency to the elastic modulus adjusting unit based on the data indicating the “relationship between the resonance frequency and the voltage applied to the elastic modulus adjusting unit” acquired and stored in advance. Find the voltage. Then, the control unit 42 outputs a digital signal of voltage to the drive signal output unit 45 for adjusting the elastic modulus.

The elastic modulus adjusting drive signal output unit 45 D / A-converts a digital signal of the elastic modulus adjusting voltage and outputs it to the elastic modulus adjusting units 104a, 104b, 107a and 107b. Each elastic modulus adjusting portion applies a certain amount of deformation to the cantilever according to the applied voltage, and changes the elastic modulus of the elastic modulus in the cantilever to change the resonance frequency of the cantilever or the like by a predetermined amount.

By detecting the phase difference in this way, it is possible to detect a frequency shift that is strong against disturbance noise such as vibration of the movable device 40.

Instead of the detection piezoelectric element, a PD arranged outside the movable device 40 may be used. In this case, both the output signal and the drive signal of the PD may be input to the lock-in amplifier circuit or the like.

Further, as described above, the present invention is not limited to the case where the resonance frequency deviates, and can be applied to the case where the amplitude of rotation of the mirror unit 100 fluctuates due to a factor other than the deviation of the resonance frequency. This is because the above phase difference also changes according to the amplitude of rotation.
[Fourth Embodiment]
Next, the movable device of the fourth embodiment will be described. The parts that overlap with the first to third embodiments will be omitted, and the differences will be described.

In a movable device, the use of resonance is convenient for widening the angle of optical scanning by the movable device because a large amount of movement of the mirror portion, that is, the amplitude of rotation can be obtained with a low drive voltage. However, on the other hand, in the use of resonance, there is a risk that the amplitude of rotation of the mirror portion changes significantly when the frequency of the drive signal of the movable device deviates from the resonance frequency.

For example, due to manufacturing variations, the resonance frequency may differ for each movable device, or even for the same movable device, the resonance frequency may change over time due to changes in ambient temperature or the like. When the frequency of the drive signal deviates from the resonance frequency, the amplitude of rotation changes significantly, and a desired scanning angle cannot be obtained.

The present embodiment is characterized in that a frequency deviated by a certain amount from the resonance frequency, that is, a frequency to which an offset is given is used as the frequency of the drive signal, and the mirror portion is rotated. This makes it possible to improve the robustness of optical scanning with respect to fluctuations in the frequency and resonance frequency of the drive signal.

FIG. 26 shows an example of the relationship between the frequency of the drive signal of the movable device and the amplitude of rotation of the mirror portion. In FIG. 26, the frequency fr indicated by the broken line indicates the resonance frequency, and the frequency fs indicated by the alternate long and short dash line indicates the frequency offset from the resonance frequency in the direction of the low frequency.

For example, when a movable device is driven by a drive signal having a frequency fr, if the resonance frequency deviates by Δf due to a change in ambient temperature or the like, the amplitude of rotation changes by ΔAr. On the other hand, when the movable device is driven at a frequency fs offset from the resonance frequency, even if the resonance frequency deviates by the same amount of Δf as above, the amplitude of rotation is only a small change of ΔAs.

The frequency fs in FIG. 26 is an example of a frequency obtained by adding or subtracting a predetermined offset frequency from the resonance frequency of the first movable portion or the second movable portion.

As an example of the configuration of the movable device of the present embodiment, for example, the configuration of FIG. 21 can be used. As shown in FIG. 23, the resonance frequency can be changed by changing the voltage applied to the elastic modulus adjusting portions 104a, 104b, 107a and 107b, and the offset frequency is set to the resonance frequency with respect to the frequency of the drive signal. It can be added or subtracted. As a result, even if there is a difference in the resonance frequency between the movable devices or a change in the resonance frequency with time in the same movable device, it is possible to suppress the difference in the movable device and the change in the amplitude of rotation with respect to the change with time.

The above offset may be given by changing the frequency of the drive signal without changing the resonance frequency. However, in the present embodiment, since the frequency fy and the frequency fx have a predetermined relationship, it is necessary to adjust the frequency fy and the frequency fx while maintaining the predetermined relationship, which complicates the adjustment. As described above, the offset can be easily given by changing the resonance frequency.

As described above, according to the present embodiment, although the maximum amplitude of rotation using resonance cannot be obtained, it is possible to suppress a decrease in the amplitude of rotation with respect to fluctuations in the frequency of the drive signal and the resonance frequency. In other words, the robustness of optical scanning with respect to fluctuations in the frequency and resonance frequency of the drive signal can be improved.
[Modification example of the configuration of the movable device]
In the movable device 13 of FIG. 15, the cantilever 102a and 102b are formed on the −Y side with the first axis as the center. Such a structure is called a cantilever structure. On the other hand, in the movable device 13a of FIG. 27, the cantilever 102c and 102d are formed symmetrically with respect to the first axis in the ± Y direction. Such a structure is called a double-sided beam structure. As shown in FIG. 27, even when the first movable portion has a double-sided beam structure, the drive method shown in the first to fourth embodiments can be applied. In FIG. 27, 104c, 104d, 104e, and 104f are elastic modulus adjusting portions.

Further, in the movable device 13 of FIG. 15, a configuration in which the piezoelectric portion is formed only on one surface of the silicon active layer which is an elastic portion, that is, the surface on the + Z side, has been described as an example, but the present invention is not limited to this. The configuration may be provided on another surface of the elastic portion, for example, the surface on the −Z side, and the driving method shown in the first to fourth embodiments may be applied. Further, the configuration is provided on both one surface and the other surface of the elastic portion, and the driving method shown in the first to fourth embodiments may be applied.

Further, if the mirror portion 100 can be moved around the first axis or the second axis, both the first movable portion and the second movable portion are held by a beam as in the movable device 13b shown in FIG. 28. The structure may be used, and the driving method shown in the first to fourth embodiments may be applied. In FIG. 28, 110a and 110b are elastic modulus adjusting portions.

Further, as shown in FIGS. 29 and 30, the movable device 13c that can move only around the first axis and the movable device 13d that can move only around the second axis are also shown in the first to fourth embodiments. The drive method can be applied. However, in order for the movable device 13c or the movable device 13d to scan light in two directions of X and Y, it is necessary to use at least two movable devices. In FIG. 30, 100b is a light reflecting surface and 100c is a mirror portion.

Although examples of embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and various aspects are described within the scope of the gist of the present invention described in the claims. It can be transformed and changed.

10 Optical scanning system 11, 41 Control device 12, 12b Light source device 13, 13a, 13b, 13c, 13d, 40 Movable device 14 Reflection surface 15 Scanned surface 25 Light source device driver 26 Movable device driver 30, 42 Control unit 31, 43 Drive signal output unit 44 Detection signal acquisition unit 45 Drive signal output unit for adjusting elasticity 50 Laser head lamp 51 Mirror 52 Transparent plate 60 Head mount display 60a Front 60b Temple 61 Light guide plate 62 Half mirror 63 Wearer 100 Mirror unit 100a Mirror unit Substrate 101a, 101b First movable part 102a, 102b, 107-1 to 107-12 Cantilever 103a, 103b Torsion bar 104a, 104b, 107a, 107b Elasticity adjustment part 105 First support part 106a, 106b Second movable part 108th 2 Support part 109 Electrode connection part 131, 132, 134, 135, 138 Signal 133 Scan line 500 Head-up display device 650 Laser printer 700 Laser radar device 702 Object 801 Package member 802 Mounting member 803 Transmissive member

Japanese Unexamined Patent Publication No. 2012-068349

Claims (17)

A mirror portion having a light reflecting surface and a mirror portion directly or indirectly connected to the mirror portion, and the mirror portion is rotated around the first and second axes orthogonal to each other according to the input first and second drive signals. The first and second movable parts are provided with first and second cantilever, respectively, and are movable to scan light in two dimensions with a predetermined number of frames. It ’s a device,
A first movable portion having a piezoelectric portion that rotates the mirror portion around the first axis, and a first movable portion.
A first detecting means for detecting the angle of rotation of the mirror portion around the first axis, and
A second movable portion having a piezoelectric portion that rotates the mirror portion around the second axis, and a second movable portion.
A second detecting means for detecting the angle of rotation of the mirror portion around the second axis is provided.
At least one of the first detection means and the second detection means has a detection piezoelectric element.
The elastic modulus of the first movable portion is adjusted based on the output of the first detecting means , and the elastic modulus of the second movable portion is adjusted based on the output of the second detecting means. It has at least one of the second elastic modulus adjusting means and
The first elastic modulus adjusting means is provided in the first cantilever so as to form a layer with or adjacent to the first detecting means.
The second elastic modulus adjusting means is provided in the second cantilever so as to form a layer with or adjacent to the second detecting means.
The movable device is characterized in that the frequency of the first drive signal is a value determined based on the frequency of the second drive signal and the number of frames and is not divided by the frequency of the second drive signal. The claim is characterized in that it has a first output means for outputting the first drive signal to the first movable portion and a second output means for outputting the second drive signal to the second movable portion. The movable device according to 1. The movable device according to claim 2, wherein at least one of the first output means and the second output means has a frequency synthesizer of a DDS system or a PLL system. The movable device according to any one of claims 1 to 3, wherein the frequencies of the first and second drive signals have the following relationship.

However, fy is the frequency of the first drive signal, fx is the frequency of the second drive signal, and Nf is the number of frames. The movable device according to any one of claims 1 to 4, wherein at least one of the first drive signal and the second drive signal is a signal having a triangular wave waveform. One of claims 1 to 5, wherein the second movable portion is formed of a meander structure having a plurality of cantilever, and each cantilever has a piezoelectric portion connected to each cantilever. The movable device according to item 1. The first elastic modulus adjusting means has a piezoelectric portion connected to the first movable portion.
The movable device according to any one of claims 1 to 6, wherein the second elastic modulus adjusting means has a piezoelectric portion connected to the second movable portion. The first detecting means detects the phase difference between the phase of the angle change of the rotation of the mirror portion around the first axis and the phase of the first drive signal.
The second detecting means detects the phase difference between the phase of the angle change of the rotation of the mirror portion around the second axis and the phase of the second drive signal.
The movable device according to claim 6 or 7. The frequency of the first drive signal is a frequency obtained by adding or subtracting a predetermined offset frequency from the resonance frequency of the first movable portion.
The frequency of the second drive signal is a frequency obtained by adding or subtracting a predetermined offset frequency from the resonance frequency of the second movable portion, according to any one of claims 1 to 8. The movable device described. An image projection device comprising the movable device according to any one of claims 1 to 9. A head-up display comprising the movable device according to any one of claims 1 to 9. The head-up display according to claim 11, further comprising a plurality of light sources that emit a plurality of lights having different wavelengths and a synthesis means for synthesizing the lights from the plurality of light sources. A laser headlamp comprising the movable device according to any one of claims 1 to 9. A head-mounted display comprising the movable device according to any one of claims 1 to 9. The head-mounted display according to claim 14, further comprising a plurality of light sources that emit a plurality of lights having different wavelengths and a synthesis means for synthesizing the lights from the plurality of light sources. A vehicle having the head-up display according to claim 11. An optical scanning method that scans light in two dimensions with a predetermined number of frames.
A rotation step of rotating the mirror portion around the first and second axes orthogonal to each other by inputting a first drive signal and a second drive signal to the piezoelectric portions of the first and second movable portions.
Based on the detection signal output by the detection piezoelectric element possessed by at least one of the first and second movable parts, the rotation angle around the first axis or the rotation angle around the second axis of the mirror part is acquired. Acquisition process and
A generation step of generating a drive signal for elastic modulus adjustment based on the detection signal, and
In the first and second cantilever of the first and second movable parts, respectively, the elastic modulus adjustment is performed by using the elastic modulus adjusting means provided so as to form a layer or be adjacent to the detection piezoelectric element. The elastic modulus adjusting step of adjusting the elastic modulus of the first or second movable portion based on the drive signal is provided.
The optical scanning method is characterized in that the frequency of the first drive signal is a value determined based on the frequency of the second drive signal and the number of frames and is not divided by the frequency of the second drive signal. ..

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