Image drawing apparatus and method for driving image drawing apparatus

Abstract

An image drawing apparatus includes a processor that scans a light beam reflected by a reflective surface on a surface to be scanned by controlling operation of a light source, a first actuator, and a second actuator. The deflection angle of the mirror section about the first axis is set as a first deflection angle, and the deflection angle of the mirror section about the second axis is set as a second deflection angle. The processor estimates the scanning trajectory of the light beam on the surface to be scanned using a first deflection angle estimation function, which is a function of the first deflection angle with respect to time, and a second deflection angle estimation function, which is a function of the second deflection angle with respect to time, and causes the light source to emit the light beam in accordance with the estimated scanning trajectory and the image information. And a second deflection angle estimation function that is a function of the second deflection angle with respect to time and that takes into account that a change in the first deflection angle with respect to time depends on the second deflection angle and that takes into account that a change in the second deflection angle with respect to time depends on the first deflection angle.

Description

Technical Field

[0001] The technology of the present invention relates to an image rendering device and a method for driving the image rendering device. Background Art

[0002] As one of the MEMS (Micro Electro Mechanical Systems) devices manufactured using silicon (Si) microfabrication technology, a micromirror device (also called a micro scanner) is known. Optical scanning devices equipped with such micromirror devices are expected to be used in image rendering devices such as laser displays and laser projectors due to their compact size and low power consumption.

[0003] The reflector portion of a micromirror device is formed to be able to swing about a first axis and a second axis that are orthogonal to each other. By swinging the reflector portion about each axis, a laser beam reflected by the reflector portion is caused to perform two-dimensional scanning. In addition, micromirror devices are known that can cause a laser beam to perform Lissajous scanning by causing the reflector portion to resonate about each axis.

[0004] In order to obtain a high-quality laser-drawn image in an image drawing apparatus using such a mirror device, it is necessary to estimate the scanning trajectory of the laser beam on the scanned surface and emit the laser beam according to the estimated scanning trajectory.

[0005] Japanese Patent Application Laid-Open No. 2013-065923 discloses a projector that projects an image into a projection area by scanning a laser beam. In this projector, the scanning trajectory of the laser beam is estimated based on image correction information including projection condition information.

[0006] International Publication No. 2012 / 011183 discloses an image generating device that displays an image by sinusoidally scanning a laser beam in main and sub-scanning directions. In this image generating device, a scanning trajectory is estimated based on a phase difference and a frequency ratio between the main and sub-scanning directions. Summary of the Invention

[0007] Technical issues to be solved by the invention

[0008] In a reflector device in which a reflector portion is formed so as to be able to swing around a first axis and a second axis that are orthogonal to each other, so-called crosstalk occurs, in which an angular change of the reflector portion around one of the first axis and the second axis affects an angular change of the reflector portion around the other of the first axis and the second axis.

[0009] Japanese Patent Application Publication No. 2013-065923 and International Publication No. 2012 / 011183 disclose methods for estimating the scanning trajectory, but neither method takes into account crosstalk between the two axes, making it difficult to accurately estimate the scanning trajectory. Consequently, the techniques disclosed in Japanese Patent Application Publication No. 2013-065923 and International Publication No. 2012 / 011183 cannot produce high-quality laser imagery.

[0010] The technical object of the present invention is to provide an image drawing device and a method for driving the image drawing device that can obtain a high-quality laser drawn image.

[0011] Means for solving technical problems

[0012] In order to achieve the above-mentioned object, the image drawing device of the present invention comprises: a light source for emitting a light beam; a reflector device including a reflector portion having a reflective surface for reflecting the light beam, a first actuator for swinging the reflector portion around a first axis, and a second actuator for swinging the reflector portion around a second axis orthogonal to the first axis; and a processor for scanning the light beam reflected by the reflective surface on a scanned surface by controlling the operation of the light source and the reflector device. In the image drawing device, the deflection angle of the reflector portion around the first axis is set to a first deflection angle, and the deflection angle of the reflector portion around the second axis is set to a second deflection angle. In the case of the second deflection angle, the processor uses the first deflection angle estimation function and the second deflection angle estimation function to estimate the scanning trajectory of the light beam on the scanned surface, and causes the light source to emit a light beam corresponding to the estimated scanning trajectory and image information. The first deflection angle estimation function is a function of the first deflection angle with respect to time, which takes into account the situation that the change of the first deflection angle with respect to time depends on the second deflection angle. The second deflection angle estimation function is a function of the second deflection angle with respect to time, and takes into account the situation that the change of the second deflection angle with respect to time depends on the first deflection angle.

[0013] Preferably, when the maximum amplitude of the first deflection angle is set to A1, the maximum amplitude of the second deflection angle is set to A2, the oscillation frequency of the reflector portion around the first axis is set to f1, the oscillation frequency of the reflector portion around the second axis is set to f2, the time is set to t, the constant is set to t0, the first deflection angle at time t is set to θ1(t), and the second deflection angle at time t is set to θ2(t), the first deflection angle estimation function and the second deflection angle estimation function are respectively expressed by equations (1) and (2).

[0014] [Formula 1]

[0015] θ1(t)=A1sin((2πf1(t+t0sin(2πf2t)))…(1)

[0016] [Formula 2]

[0017] θ2(t)=A2sin(2πf2(t+t0sin(2πf1t)))…(2)

[0018] Preferably, when the reflector portion is in a stationary state, the light beam is incident on the reflective surface perpendicularly.

[0019] The processor preferably estimates the scanning trajectory represented by coordinates x(t) and y(t) by inputting θ1(t) derived from equation (1) and θ2(t) derived from equation (2) into the coordinate conversion function represented by equation (3).

[0020] [Formula 3]

[0021]

[0022] Preferably, the processor causes the reflector portion to resonate around the first axis and the second axis respectively.

[0023] The driving method of an image drawing device of the present invention comprises: a light source for emitting a light beam; a reflector device including a reflector portion having a reflective surface for reflecting the light beam, a first actuator for swinging the reflector portion about a first axis, and a second actuator for swinging the reflector portion about a second axis orthogonal to the first axis; and a processor for controlling the operation of the light source and the reflector device to scan the light beam reflected by the reflective surface on a scanned surface. In the driving method of the image drawing device, the deflection angle of the reflector portion about the first axis is set to a first deflection angle, and the deflection angle of the reflector portion about the second axis is set to a first deflection angle. When the deflection angle is set to the second deflection angle, the first deflection angle estimation function and the second deflection angle estimation function are used to estimate the scanning trajectory of the light beam on the scanned surface, and the light source emits a light beam corresponding to the estimated scanning trajectory and image information. The first deflection angle estimation function is a function of the first deflection angle with respect to time, and takes into account the situation that the change of the first deflection angle with respect to time depends on the second deflection angle. The second deflection angle estimation function is a function of the second deflection angle with respect to time, and takes into account the situation that the change of the second deflection angle with respect to time depends on the first deflection angle.

[0024] Effects of the Invention

[0025] According to the technology of the present invention, it is possible to provide an image drawing device and a method for driving the image drawing device that can obtain a high-quality laser drawn image. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram schematically showing an image rendering device.

[0027] Figure 2 It is a diagram showing a configuration example of an optical system including an image rendering device.

[0028] Figure 3This is a three-dimensional diagram of the appearance of a micromirror device.

[0029] Figure 4 This is a top view of the micromirror device as viewed from the light incident side.

[0030] Figure 5 It is along Figure 4 Cross-sectional view taken along line AA.

[0031] Figure 6 It is along Figure 4 Cross-sectional view taken along line BB.

[0032] Figure 7 It is along Figure 4 Cross-sectional view taken along line CC.

[0033] Figure 8 It is a diagram showing an example in which the first actuator is driven.

[0034] Figure 9 It is a diagram showing an example in which the second actuator is driven.

[0035] Figure 10 Graph showing an example of the first drive signal and the second drive signal.

[0036] Figure 11 This is a block diagram showing an example of the configuration of a control device.

[0037] Figure 12 This is a diagram showing an example of a processing flow by the rendering control unit.

[0038] Figure 13 This is a diagram illustrating a scanning trajectory.

[0039] Figure 14 This is a diagram schematically illustrating a method for deriving a coordinate conversion function.

[0040] Figure 15 This is a diagram showing the structure of an experimental image drawing device.

[0041] Figure 16 This is a diagram showing a drawn image without crosstalk.

[0042] Figure 17 This figure shows an image drawn by an experimental image drawing device. DETAILED DESCRIPTION

[0043] An example of an embodiment of the technology of the present invention will be described with reference to the drawings.

[0044] Figure 1An image rendering device 10 according to one embodiment is schematically shown. The image rendering device 10 includes a micromirror device (hereinafter referred to as an MMD) 2, a control device 3, a light source 4, and a light source driver 5. The control device 3 is an example of a "processor" according to the technology of the present invention. Furthermore, the MMD 2 is an example of a "mirror device" according to the technology of the present invention.

[0045] The image drawing device 10 reflects the light beam L emitted from the light source 4 by the MMD 2 under the control of the control device 3 and optically scans the scanned surface 6, thereby drawing an image on the scanned surface 6. The scanned surface 6 is, for example, the surface of a screen.

[0046] The image rendering device 10 is applicable to, for example, a Lissajous scanning laser display. Specifically, the image rendering device 10 can be applied to laser scanning displays such as AR (Augmented Reality) glasses and VR (Virtual Reality) glasses.

[0047] MMD2 is a device that can make the reflector portion 20 (refer to Figure 3 ) A piezoelectric dual-axis driven mirror device that oscillates about a first axis a1 and a second axis a2 perpendicular to the first axis a1. Hereinafter, the direction parallel to the first axis a1 is referred to as the Y direction, the direction parallel to the second axis a2 is referred to as the X direction, and the direction perpendicular to the first axis a1 and the second axis a2 is referred to as the Z direction. Furthermore, in the present invention, "perpendicular" is not limited to the angle between the first axis a1 and the second axis a2 being strictly 90°, but also includes the case where the angle is within a range including manufacturing tolerances relative to 90°.

[0048] The light source 4 is, for example, a laser device that emits a laser beam as a light beam L. The light beam L emitted from the light source 4 travels in a direction parallel to the Z direction via an optical system described later, and vertically enters the reflecting surface 20A (see FIG. 2 ) while the reflector portion 20 of the MMD 2 is stationary. Figure 3 ).

[0049] The light source driver 5 is a drive circuit that supplies a drive current to the light source 4 according to the control of the control device 3 .

[0050] The control device 3 controls the operation of the MMD 2 and the light source 4 based on image information representing the image drawn on the scanned surface 6. The light source driver 5 supplies a drive current to the light source 4 in response to a control signal input from the control device 3, thereby causing the light source 4 to generate a light beam L. The MMD 2 oscillates the mirror unit 20 about the first axis a1 and the second axis a2 in response to the control signal input from the control device 3.

[0051] Although details will be described later, the control device 3 causes the mirror unit 20 to resonate about the first axis a1 and the second axis a2, respectively, so that the light beam L reflected by the mirror unit 20 is scanned so as to draw a Lissajous waveform on the scanned surface 6. This optical scanning method is called a Lissajous scanning method.

[0052] Figure 2 The following illustrates an example configuration of an optical system including the image rendering device 10. For example, the light source 4 is composed of a red laser diode 4R that generates a red laser beam LR, a green laser diode 4G that generates a green laser beam LG, and a blue laser diode 4B that generates a blue laser beam LB. In this embodiment, the light beam L includes the red laser beam LR, the green laser beam LG, and the blue laser beam LB. Hereinafter, when the red laser beam LR, the green laser beam LG, and the blue laser beam LB are not required to be distinguished, they are simply referred to as the light beam L.

[0053] To coordinate the optical paths of the red laser beam LR, green laser beam LG, and blue laser beam LB emitted from the light source 4, a first through third dichroic mirrors DM1 through DM3 are provided as an optical system. The first through third dichroic mirrors DM1 through DM3 coordinate the optical paths of the red laser beam LR, green laser beam LG, and blue laser beam LB, causing the beams L to travel parallel to the Z direction. Hereinafter, the optical path coordinated by the first through third dichroic mirrors DM1 through DM3 is referred to as a coordinated optical path.

[0054] A beam splitter BS and the MMD 2 are arranged on the integrated optical path. For example, the beam splitter BS is formed of a half-mirror. A portion of the light beam L traveling through the integrated optical path and incident on the beam splitter BS passes through the beam splitter BS and, when the mirror unit 20 is stationary, is perpendicularly incident on the reflective surface 20A. The light beam L is reflected by the reflective surface 20A in a direction corresponding to the angle of the mirror unit 20 and then incident on the beam splitter BS. A portion of the light beam L incident on the beam splitter BS from the MMD 2 is also reflected by the beam splitter BS and incident on the scanned surface 6.

[0055] When each pixel of the image represented by the image information includes color information, the control device 3 controls the light source driver 5 to cause each pixel to emit a laser diode corresponding to the color information among the red laser diode 4R, the green laser diode 4G, and the blue laser diode 4B.

[0056] Next, use Figures 3 to 7 An example of MMD2 will be described. Figure 3 This is a three-dimensional image of the appearance of MMD2. Figure 4 This is a top view of the MMD2 as viewed from the light incident side. Figure 5 It is along Figure 4 Cross-sectional view taken along line AA. Figure 6It is along Figure 4 Cross-sectional view taken along line BB. Figure 7 It is along Figure 4 Cross-sectional view taken along line CC.

[0057] like Figure 3 and Figure 4 As shown, the MMD 2 includes a mirror portion 20, a first support portion 21, a first movable frame 22, a second support portion 23, a second movable frame 24, a connection portion 25, and a fixed frame 26. The MMD 2 is a so-called MEMS scanner.

[0058] The reflector portion 20 includes a reflective surface 20A that reflects incident light. The reflective surface 20A is provided on one surface of the reflector portion 20 and is formed from a thin metal film, such as gold (Au), aluminum (Al), silver (Ag), or a silver alloy. The reflective surface 20A is, for example, circular, centered at the intersection of the first axis a1 and the second axis a2.

[0059] The first axis a1 and the second axis a2 exist in a plane including the reflecting surface 20A when the mirror unit 20 is stationary. The planar shape of the MMD 2 is rectangular and is line-symmetric about the first axis a1 and the second axis a2.

[0060] The first support portions 21 are disposed outside the reflector portion 20 at positions opposing the reflector portion 20 across the second axis a2. The first support portions 21 are connected to the reflector portion 20 along the first axis a1 and support the reflector portion 20 so that it can swing about the first axis a1. In this embodiment, the first support portions 21 are torsion bars extending along the first axis a1.

[0061] The first movable frame 22 is a rectangular frame that surrounds the mirror portion 20 and is connected to the mirror portion 20 along the first axis a1 via the first support portion 21. Piezoelectric elements 30 are formed on the first movable frame 22 at positions opposing each other across the first axis a1. Thus, the two piezoelectric elements 30 formed on the first movable frame 22 constitute a pair of first actuators 31.

[0062] The pair of first actuators 31 are disposed at positions facing each other across the first axis a1. The first actuators 31 cause the mirror portion 20 to swing about the first axis a1 by applying a torque about the first axis a1 to the mirror portion 20.

[0063] The second support portions 23 are disposed outside the first movable frame 22 at positions opposing each other across the first axis a1. The second support portions 23 are connected to the first movable frame 22 along the second axis a2 and support the first movable frame 22 and the mirror portion 20 so that they can swing about the second axis a2. In this embodiment, the second support portions 23 are torsion bars extending along the second axis a2.

[0064] The second movable frame 24 is a rectangular frame that surrounds the first movable frame 22 and is connected to the first movable frame 22 along the second axis a2 via the second support portion 23. Piezoelectric elements 30 are formed on the second movable frame 24 at positions opposing each other across the second axis a2. Thus, the two piezoelectric elements 30 formed on the second movable frame 24 form a pair of second actuators 32.

[0065] The pair of second actuators 32 are disposed at positions facing each other with the second axis a2 interposed therebetween. The second actuators 32 cause the mirror portion 20 to swing about the second axis a2 by applying torque about the second axis a2 to the mirror portion 20 and the first movable frame 22 .

[0066] The connection parts 25 are respectively arranged at positions facing each other across the first axis a1 on the outer side of the second movable frame 24. The connection parts 25 are connected to the second movable frame 24 on the second axis a2.

[0067] The fixed frame 26 is a rectangular frame body surrounding the second movable frame 24 , and is connected to the second movable frame 24 via a connecting portion 25 on the second axis a2 .

[0068] Furthermore, a pair of first angle detection sensors 11A and 11B are provided on the first movable frame 22 near the first support portion 21, at positions opposing each other across the first axis a1. Each of the first angle detection sensors 11A and 11B is comprised of a piezoelectric element. The first angle detection sensors 11A and 11B convert the force applied by the first support portion 21 as the mirror portion 20 rotates about the first axis a1 into a voltage and output a signal. Specifically, the first angle detection sensors 11A and 11B output a signal corresponding to the angle of the mirror portion 20 about the first axis a1.

[0069] Furthermore, a pair of second angle detection sensors 12A and 12B are provided on the second movable frame 24 near the second support portion 23, at positions opposing each other across the second axis a2. Each of the second angle detection sensors 12A and 12B is comprised of a piezoelectric element. Each of the second angle detection sensors 12A and 12B converts the force applied by the deformation of the second support portion 23 as the mirror portion 20 rotates about the second axis a2 into a voltage and outputs a signal. Specifically, the second angle detection sensors 12A and 12B output a signal corresponding to the angle of the mirror portion 20 about the second axis a2.

[0070] exist Figure 3 and Figure 4 In FIG, wiring and electrode pads for providing drive signals to the first actuator 31 and the second actuator 32 are omitted from the illustration. Figure 3 and Figure 4In the figure, wiring and electrode pads for outputting signals from the first angle detection sensors 11A, 11B and the second angle detection sensors 12A, 12B are also omitted. A plurality of electrode pads are provided on the fixing frame 26 .

[0071] like Figure 5 and Figure 6 As shown, the MMD 2 is formed, for example, by etching an SOI (Silicon On Insulator) substrate 40. The SOI substrate 40 comprises a first silicon active layer 41 made of single crystal silicon, a silicon oxide layer 42 provided on top of the first silicon active layer 41, and a second silicon active layer 43 made of single crystal silicon provided on the silicon oxide layer 42.

[0072] The mirror portion 20, first support portion 21, first movable frame 22, second support portion 23, second movable frame 24, and connection portion 25 are formed from the second silicon active layer 43 remaining after etching away the first silicon active layer 41 and silicon oxide layer 42 from the SOI substrate 40. The second silicon active layer 43 functions as a resilient elastic portion. The fixed frame 26 is formed from three layers: the first silicon active layer 41, silicon oxide layer 42, and second silicon active layer 43.

[0073] The first actuator 31 and the second actuator 32 include a piezoelectric element 30 on a second silicon active layer 43. The piezoelectric element 30 has a stacked structure in which a lower electrode 51, a piezoelectric film 52, and an upper electrode 53 are stacked in this order on the second silicon active layer 43. An insulating film is provided on the upper electrode 53, but this is not shown in the figure.

[0074] The upper electrode 53 and the lower electrode 51 are formed of, for example, gold (Au) or platinum (Pt). The piezoelectric film 52 is formed of, for example, PZT (lead zirconate titanate), a piezoelectric material. The upper electrode 53 and the lower electrode 51 are electrically connected to the control device 3 via wiring and electrode pads.

[0075] A driving voltage is applied from the control device 3 to the upper electrode 53. The lower electrode 51 is connected to the control device 3 via wiring and electrode pads, and is given a reference potential (for example, a ground potential).

[0076] When a positive or negative voltage is applied in the polarization direction, the piezoelectric film 52 deforms (e.g., expands and contracts) in proportion to the applied voltage. In other words, the piezoelectric film 52 exhibits the so-called inverse piezoelectric effect. The piezoelectric film 52 exhibits the inverse piezoelectric effect when a driving voltage is applied to the upper electrode 53 from the control device 3, causing the first actuator 31 and the second actuator 32 to displace.

[0077] like Figure 7As shown, the first angle detection sensor 11A is similarly constructed from a piezoelectric element 30 comprising a lower electrode 51, a piezoelectric film 52, and an upper electrode 53 stacked on the second silicon active layer 43. When a force (pressure) is applied, the piezoelectric film 52 is polarized in proportion to the pressure. In other words, the piezoelectric film 52 exhibits a piezoelectric effect. When a force is applied due to the deformation of the first support portion 21 as the mirror portion 20 rotates about the first axis a1, the piezoelectric film 52 exhibits a piezoelectric effect, generating a voltage.

[0078] The first angle detection sensor 11B has the same structure as the first angle detection sensor 11A, and thus is not shown in the figure. Furthermore, the second angle detection sensors 12A and 12B have the same structure as the first angle detection sensor 11A, and thus are not shown in the figure.

[0079] Figure 8 The example shown here is of a case where a torque about the first axis a1 is generated in the first actuator 31 by expanding the piezoelectric film 52 of one of the pair of first actuators 31 and contracting the piezoelectric film 52 of the other. In this manner, one and the other of the pair of first actuators 31 are displaced in opposite directions, causing the mirror portion 20 to rotate about the first axis a1.

[0080] and, Figure 8 This is an example of driving the first actuators 31 in a resonant mode in which the displacement directions of the pair of first actuators 31 and the rotational direction of the mirror unit 20 are in opposite phases. Alternatively, the first actuators 31 may be driven in a resonant mode in which the displacement directions of the pair of first actuators 31 and the rotational direction of the mirror unit 20 are in the same phase.

[0081] The deflection angle θ1(t) of the reflector portion 20 about the first axis a1 (hereinafter referred to as the first deflection angle) is controlled by a drive signal (hereinafter referred to as the first drive signal) applied to the first actuator 31 by the control device 3. The first drive signal is, for example, a sinusoidal AC voltage. The first drive signal includes a drive voltage waveform V applied to one of the pair of first actuators 31. 1A (t) and the driving voltage waveform V applied to the other side 1B (t). Driving voltage waveform V 1A (t) and driving voltage waveform V 1B (t) are in opposite phases (i.e., a phase difference of 180°).

[0082] The first deflection angle θ1 ( t ) is an angle at which the normal line of the reflecting surface 20A is inclined with respect to the Z direction on the XZ plane.

[0083] Figure 9The example shown here is one in which the piezoelectric film 52 of one of the pair of second actuators 32 is expanded and the piezoelectric film 52 of the other is contracted, thereby generating a torque about the second axis a2 in the second actuator 32. In this manner, one and the other of the pair of second actuators 32 are displaced in opposite directions, thereby rotating the mirror portion 20 about the second axis a2.

[0084] and, Figure 9 This is an example of driving the second actuators 32 in a resonant mode in which the displacement directions of the pair of second actuators 32 and the rotational direction of the mirror unit 20 are in opposite phases. Alternatively, the second actuators 32 may be driven in a resonant mode in which the displacement directions of the pair of second actuators 32 and the rotational direction of the mirror unit 20 are in the same phase.

[0085] The deflection angle θ2(t) of the reflector portion 20 about the second axis a2 (hereinafter referred to as the second deflection angle) is controlled by a drive signal (hereinafter referred to as the second drive signal) applied to the second actuator 32 by the control device 3. The second drive signal is, for example, a sinusoidal AC voltage. The second drive signal includes a drive voltage waveform V applied to one of the pair of second actuators 32. 2A (t) and the driving voltage waveform V applied to the other side 2B (t). Driving voltage waveform V 2A (t) and driving voltage waveform V 2B (t) are in opposite phases (i.e., a phase difference of 180°).

[0086] The second deflection angle θ2(t) is an angle at which the normal line of the reflecting surface 20A is inclined with respect to the Z direction on the YZ plane.

[0087] Figure 10 An example of the first drive signal and the second drive signal is shown. Figure 10 (A) shows the driving voltage waveform V included in the first driving signal 1A (t) and V 1B (t). Figure 10 (B) shows the driving voltage waveform V contained in the second driving signal 2A (t) and V 2B (t).

[0088] Driving voltage waveform V 1A (t) and V 1B (t) are expressed as follows.

[0089] V 1A (t)=V1sin(2πf d1 t)-V1

[0090] V 1B (t)=V1sin(2πfd1 t+α)-V1

[0091] Here, V1 is the amplitude voltage. d1 is the driving frequency (hereinafter referred to as the first driving frequency). t is the time. α is the driving voltage waveform V 1A (t) and V 1B In this embodiment, for example, α is set to 180°.

[0092] Driving voltage waveform V 1A (t) and V 1B (t) is applied to the pair of first actuators 31, whereby the mirror portion 20 is driven at the first driving frequency f d1 Swing around the first axis a1 (reference Figure 8 ).

[0093] Driving voltage waveform V 2A (t) and V 2B (t) are expressed as follows.

[0094] V 2A (t)=V2sin(2πf d2 t+φ)-V2

[0095] V 2B (t)=V2sin(2πf d2 t+β+φ)-V2

[0096] Here, V2 is the amplitude voltage. d2 is the driving frequency (hereinafter referred to as the second driving frequency). t is the time. β is the driving voltage waveform V 2A (t) and V 2B In this embodiment, for example, β is set to 180°. And φ is the driving voltage waveform V 1A (t) and V 1B (t) and driving voltage waveform V 2A (t) and V 2B (t) phase difference.

[0097] Driving voltage waveform V 2A (t) and V 2B (t) is applied to the pair of second actuators 32, whereby the mirror portion 20 is driven at the second driving frequency f d2 Swing around the second axis a2 (reference Figure 9 ).

[0098] First driving frequency f d1 The second driving frequency f is set to coincide with the resonance frequency of the mirror portion 20 about the first axis a1. d2The frequency is set to coincide with the resonance frequency of the mirror portion 20 about the second axis a2.

[0099] Figure 11 An example of the structure of the control device 3 is shown. The control device 3 includes a mirror control unit 3A and a drawing control unit 3B. The mirror control unit 3A includes a first drive signal generating unit 60A, a first signal processing unit 61A, a first phase shifting unit 62A, a first zero-crossing pulse output unit 63A, a second drive signal generating unit 60B, a second signal processing unit 61B, a second phase shifting unit 62B, and a second zero-crossing pulse output unit 63B.

[0100] The first drive signal generating unit 60A, the first signal processing unit 61A, and the first phase shifting unit 62A perform feedback control so that the oscillation of the mirror unit 20 about the first axis a1 is maintained in a resonant state. The second drive signal generating unit 60B, the second signal processing unit 61B, and the second phase shifting unit 62B perform feedback control so that the oscillation of the mirror unit 20 about the second axis a2 is maintained in a resonant state.

[0101] The first drive signal generating unit 60A generates a signal including the drive voltage waveform V according to the reference waveform. 1A (t) and V 1B (t) is a first driving signal, and the generated first driving signal is given to the pair of first actuators 31 via the first phase shifter 62A. As a result, the reflector portion 20 swings around the first axis a1. The first angle detection sensors 11A and 11B output signals corresponding to the angle of the reflector portion 20 around the first axis a1. The signals output from the first angle detection sensors 11A and 11B are signals corresponding to the first driving frequency f. d1 The waveform signals are similar to sine waves and are in opposite phases to each other.

[0102] The second drive signal generating unit 60B generates a signal including the drive voltage waveform V according to the reference waveform. 2A (t) and V 2B (t) The second drive signal generated is given to the pair of second actuators 32 via the second phase shifter 62B. As a result, the reflector portion 20 swings around the second axis a2. The second angle detection sensors 12A and 12B output signals corresponding to the angle of the reflector portion 20 around the second axis a2. The signals output from the second angle detection sensors 12A and 12B are the same as those having the second drive frequency f. d2 The waveform signals are similar to sine waves and are in opposite phases to each other.

[0103] The first drive signal generated by the first drive signal generating section 60A and the second drive signal generated by the second drive signal generating section 60B are phase-synchronized.

[0104] The first signal processing unit 61A generates a signal (hereinafter referred to as the first angle detection signal) from which vibration noise has been removed based on the signals output from the pair of first angle detection sensors 11A and 11B. For example, the first signal processing unit 61A generates the first angle detection signal by subtracting the signal output from the first angle detection sensor 11B from the signal output from the first angle detection sensor 11A.

[0105] The second signal processing unit 61B generates a signal (hereinafter referred to as the second angle detection signal) from which vibration noise has been removed based on the signals output from the pair of second angle detection sensors 12A and 12B. For example, the second signal processing unit 61B generates the second angle detection signal by subtracting the signal output from the second angle detection sensor 12B from the signal output from the second angle detection sensor 12A.

[0106] The first angle detection signal input from the first signal processing unit 61A is fed back to the first drive signal generating unit 60A. The first phase shifter 62A shifts the phase of the drive voltage waveform output from the first drive signal generating unit 60A. The first phase shifter 62A shifts the phase by, for example, 90 degrees.

[0107] The second angle detection signal input from the second signal processing unit 61B is fed back to the second drive signal generating unit 60B. The second phase shifter 62B shifts the phase of the drive voltage waveform output from the second drive signal generating unit 60B. The second phase shifter 62B shifts the phase by, for example, 90 degrees.

[0108] The first zero-crossing pulse output unit 63A generates a zero-crossing pulse (hereinafter referred to as the first zero-crossing pulse) ZC1 based on the first angle detection signal input from the first signal processing unit 61A. The first zero-crossing pulse output unit 63A generates the first zero-crossing pulse ZC1 when the first angle detection signal, an AC signal, crosses zero volts. The first zero-crossing pulse ZC1 is generally generated at the time θ1(t) = 0. The first zero-crossing pulse output unit 63A inputs the generated first zero-crossing pulse ZC1 to the drawing control unit 3B.

[0109] The second zero-crossing pulse output unit 63B generates a zero-crossing pulse (hereinafter referred to as the second zero-crossing pulse) ZC2 based on the second angle detection signal input from the second signal processing unit 61B. The second zero-crossing pulse output unit 63B generates the second zero-crossing pulse ZC2 when the second angle detection signal, an AC signal, crosses zero volts. The second zero-crossing pulse ZC2 is essentially generated at the time θ2(t) = 0. The second zero-crossing pulse output unit 63B inputs the generated second zero-crossing pulse ZC2 to the drawing control unit 3B.

[0110] The rendering control unit 3B estimates the scanning trajectory of the light beam L on the scanned surface 6 and controls the light source 4 to emit light according to the estimated scanning trajectory and image information. The rendering control unit 3B is composed of a processor such as a CPU (Central Processing Unit) and executes processing according to the program stored in Lout. The image information is stored in the memory 3C, for example.

[0111] Figure 12 An example of a processing flow by the drawing control unit 3B is shown. The drawing control unit 3B executes a scanning trajectory estimation step S10 for estimating a scanning trajectory and a light emission control step S20 for controlling light emission of the light source 4.

[0112] In the scanning trajectory estimation step S10 , the rendering control unit 3B first estimates the first deflection angle θ1(t) and the second deflection angle θ2(t) based on the first deflection angle estimation function represented by the following equation (1) and the second deflection angle estimation function represented by the following equation (2).

[0113] [Formula 4]

[0114] θ1(t)=A1sin(2πf1(t+t0sin(2πf2t)))…(1)

[0115] [Formula 5]

[0116] θ2(t)=A2sin(2πf2(t+t0sin(2πf1t)))…(2)

[0117] Here, A1 is the maximum amplitude of the first deflection angle θ1(t), and A2 is the maximum amplitude of the second deflection angle θ2(t). t0 is a constant derived through experiments described later. Furthermore, f1 is the oscillation frequency of the reflector portion 20 around the first axis a1, and f2 is the oscillation frequency of the reflector portion 20 around the second axis a2. The oscillation frequency f1 is related to the first drive frequency f d1 The swing frequency f2 is equal to the second driving frequency f d2 The first deflection angle estimation function and the second deflection angle estimation function represented by the above equations (1) and (2) are stored in the memory 3C, for example.

[0118] The first deflection angle estimation function is a function of the first deflection angle θ1(t) with respect to time, and takes into account the fact that the change in the first deflection angle θ1(t) with respect to time depends on the second deflection angle θ2(t). The second deflection angle estimation function is a function of the second deflection angle θ2(t) with respect to time, and takes into account the fact that the change in the second deflection angle θ2(t) with respect to time depends on the first deflection angle θ1(t). In other words, the first deflection angle estimation function and the second deflection angle estimation function are angle estimation functions that take into account the influence of so-called crosstalk, which is the effect of the angle change of the reflector portion 20 around one of the first axis a1 and the second axis a2 on the angle change of the reflector portion 20 around the other of the first axis a1 and the second axis a2.

[0119] Next, the rendering control unit 3B estimates the scanning trajectory by inputting the first deflection angle θ1(t) derived from the first deflection angle estimation function and the second deflection angle θ2(t) derived from the second deflection angle estimation function into the coordinate conversion function represented by the following equation (3).

[0120] [Formula 6]

[0121]

[0122] Here, x(t) and y(t) represent the coordinates of the scanning trajectory on the scanned surface 6. The coordinate conversion function represented by the above equation (3) is stored in the memory 3C, for example.

[0123] like Figure 13 As shown, the incident vector of the light beam L incident on the reflecting surface 20A of the reflector unit 20 is represented by Lin, and the scanned surface 6 is represented by a plane perpendicular to the incident vector Lin and having a distance of 1 from the reflecting surface 20A. The coordinates of the scanning trajectory are represented by the X-coordinate and Y-coordinate of the intersection point P of the Poynting vector Lout and the scanned surface 6.

[0124] In the light emission control step S20, the drawing control unit 3B controls the light source driver 5 according to the estimated scanning trajectory and image information to control the light emission of the light source 4. The drawing control unit 3B also controls the light emission timing of the light source 4 so as to synchronize the light emission timing with the first zero-crossing pulse ZC1 and the second zero-crossing pulse ZC2 input from the mirror control unit 3A.

[0125] As described above, in this embodiment, the first deflection angle θ1(t) and the second deflection angle θ2(t) are estimated using the first deflection angle estimation function and the second deflection angle estimation function that take into account the influence of crosstalk, and the scanning trajectory is estimated by performing coordinate transformation on the estimated first deflection angle θ1(t) and the second deflection angle θ2(t), so that a high-quality laser drawing image can be obtained.

[0126] [Coordinate conversion function]

[0127] Next, the coordinate conversion function will be described. Figure 14 The method for deriving the coordinate conversion function is briefly described. First, the normal vector of the reflecting surface 20A when the reflector portion 20 is stationary is set to N. Next, the normal vector after rotation when the reflector portion 20 is rotated only by the first deflection angle θ1(t) around the first axis a1 is set to N1, and the normal vector N1 is derived based on the normal vector N. Next, the normal vector after rotation when the reflector portion 20 is rotated only by the second deflection angle θ2(t) around the second axis a2 is set to N2, and the normal vector N2 is derived based on the normal vector N1. Then, the above-mentioned Poynting vector Lout is derived based on the normal vector N2, and the coordinates of the intersection point P of the Poynting vector Lout and the scanned surface 6 are derived. The coordinates of the intersection point P are expressed by the above formula (3). The above formula (3) is a coordinate conversion function that converts the first deflection angle θ1(t) and the second deflection angle θ2(t) at time t into coordinates on the scanned surface 6.

[0128] In addition, a coordinate conversion function substantially identical to equation (3) is known from Xichen Wang, Yingke Xie, Hengheng Liang, and Nianbing Zhong, “Analysis of Distortion Based on 2D MEMS Micromirror Scanning Projection System,” Micromachines, 2021, 12, 818. Retrieved from the internet at <https: / / www.mdpi.com / 2072-666X / 12 / 7 / 818 / pdf-vor>.

[0129] [First Deflection Angle Estimation Function and Second Deflection Angle Estimation Function]

[0130] Next, the first deflection angle estimation function and the second deflection angle estimation function are explained. In MMD2, the first deflection angle θ1(t) and the second deflection angle θ2(t) in principle produce crosstalk. Therefore, it is possible to consider solving the motion equation representing the motion of the universal dual-axis reflector to find the change of the first deflection angle θ1(t) and the second deflection angle θ2(t) with respect to time. However, in reality, it is difficult to analytically solve the motion equation represented by the differential equation to find the change of the first deflection angle θ1(t) and the second deflection angle θ2(t) with respect to time. Therefore, the applicant experimentally discovered a method for finding the change of the first deflection angle θ1(t) and the second deflection angle θ2(t) with respect to time.

[0131] Figure 15The structure of the experimental image drawing device 10A is shown. The experimental image drawing device 10A is provided with a connection signal generating unit 7 instead of the drawing control unit 3B. The connection signal generating unit 7 is composed of, for example, an FPGA (Field Programmable Gate Array). The first zero-crossing pulse ZC1 and the second zero-crossing pulse ZC2 are input from the reflector control unit 3A to the connection signal generating unit 7. When the first zero-crossing pulse ZC1 or the second zero-crossing pulse ZC2 is input, the connection signal generating unit 7 inputs the connection signal to the light source driver 5. The light source driver 5 supplies a driving current to the light source 4 according to the input connection signal, thereby causing the light source 4 to generate a laser beam. In the experimental image drawing device 10A, the light source 4 is, for example, a laser diode.

[0132] In experimental image plotting device 10A, screen 8 is arranged so as to be orthogonal to the optical path of light beam L emitted from light source 4. Furthermore, fθ lens 9 is arranged between screen 8 and reflector unit 20. Light beam L emitted from light source 4 passes through through-hole 8A provided in the center of screen 8, passes through the center of fθ lens 9, and is incident on reflective surface 20A of reflector unit 20. Light beam L reflected by reflective surface 20A forms an image on scanned surface 6, which is the surface of screen 8, via fθ lens 9.

[0133] Figure 16 The following shows a drawn image assuming that there is no crosstalk between the first deflection angle θ1(t) and the second deflection angle θ2(t). Assuming that there is no crosstalk, the drawn image is in the shape of a cross with two straight lines intersecting each other at right angles.

[0134] Figure 17 The image drawn by the experimental image drawing device 10A is shown. Since the image is formed by the fθ lens 9, the X coordinate and Y coordinate on the scanned surface 6 are represented by the first deflection angle θ1(t) and the second deflection angle θ2(t). The applicant has found that when crosstalk occurs, the drawn image is not strictly a cross shape, as shown in FIG. Figure 17 As shown in the two enlarged images in Figure 2, the depicted image deviates slightly from the cross shape. This experimental result was also reproduced in a computer simulation.

[0135] The present applicant has found that by expressing the first deflection angle θ1(t) and the second deflection angle θ2(t) by the above equations (1) and (2), the following equations can be reproduced: Figure 17 The experimental results and simulation results shown in the figure are as follows. The constant t0 in the above equations (1) and (2) was found by searching for the optimal value in a way that reproduces the experimental results. The results of the implementation in a certain MEMS device showed that the typical value of the constant t0 is t0 = 1×10 -7 When the crosstalk is large, the constant t0 tends to become large, and when the crosstalk is small, the constant t0 tends to become small.

[0136] The structure of the MMD2 shown in the above embodiment is an example. The structure of the MMD2 can be modified in various ways. For example, the first actuator 31 that causes the mirror unit 20 to swing about the first axis a1 can be arranged on the second movable frame 24, and the second actuator 32 that causes the mirror unit 20 to swing about the second axis a2 can be arranged on the first movable frame 22.

[0137] Furthermore, the hardware structure of the control device 3 can be modified in various ways. The control device 3 can be composed of one processor, or a combination of two or more processors of the same type or different types. The processor includes a CPU, a programmable logic device (PLD), and a dedicated circuit. As is well known, a CPU is a general-purpose processor that executes software (programs) to function as various processing units. PLD is a processor such as FPGA (Field Programmable Gate Array) that can change its circuit structure after manufacturing. A dedicated circuit is a processor such as ASIC (Application Specific Integrated Circuit) that has a circuit structure specially designed to perform specific processing.

[0138] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An image rendering device comprising: a light source that emits a light beam; a reflector device including a reflector portion having a reflecting surface for reflecting the light beam, a first actuator for swinging the reflector portion about a first axis, and a second actuator for swinging the reflector portion about a second axis orthogonal to the first axis; and a processor that scans the light beam reflected by the reflecting surface on a scanned surface by controlling the actions of the light source and the reflector device; In the image rendering device, When the deflection angle of the mirror portion around the first axis is set as a first deflection angle and the deflection angle of the mirror portion around the second axis is set as a second deflection angle, The processor uses a first deflection angle estimation function and a second deflection angle estimation function to estimate the scanning trajectory of the light beam on the scanned surface, and causes the light source to emit the light beam corresponding to the estimated scanning trajectory and image information. The first deflection angle estimation function is a function of the first deflection angle with respect to time, which takes into account the situation that the change of the first deflection angle with respect to time depends on the second deflection angle. The second deflection angle estimation function is a function of the second deflection angle with respect to time, which takes into account the situation that the change of the second deflection angle with respect to time depends on the first deflection angle.

2. The image rendering device according to claim 1, wherein Let the maximum amplitude of the first deflection angle be A1, let the maximum amplitude of the second deflection angle be A2, let the oscillation frequency of the oscillation of the reflector portion around the first axis be f1, let the oscillation frequency of the oscillation of the reflector portion around the second axis be f2, let time be t, let a constant be t0, let the first deflection angle at time t be θ1(t), let the second deflection angle at time t be θ2(t), in this case, The first deflection angle estimation function and the second deflection angle estimation function are respectively expressed by equation (1) and equation (2), [Formula 1] θ1(t)=A1sin(2πf1(t+t0sin(2πf2t)))…(1)[Formula 2] θ2(t)=A2sin(2πf2(t+t0sin(2πf1t)))…(2).

3. The image rendering device according to claim 2, wherein: When the reflector portion is in a stationary state, the light beam is vertically incident on the reflective surface.

4. The image rendering device according to claim 3, wherein: The processor estimates the scanning trajectory represented by coordinates x(t) and y(t) by inputting θ1(t) derived using equation (1) and θ2(t) derived using equation (2) into the coordinate conversion function represented by equation (3). [Formula 3] 5. The image rendering device according to claim 4, wherein: The processor causes the reflector portion to resonate around the first axis and the second axis respectively.

6. A method for driving an image rendering device, the image rendering device comprising: a light source that emits a light beam; a reflector device including a reflector portion having a reflecting surface for reflecting the light beam, a first actuator for swinging the reflector portion about a first axis, and a second actuator for swinging the reflector portion about a second axis orthogonal to the first axis; and The processor controls the operation of the light source and the reflector device to scan the light beam reflected by the reflective surface on the scanned surface. In the driving method of the image drawing device, The deflection angle of the mirror portion around the first axis is defined as a first deflection angle, and the deflection angle of the mirror portion around the second axis is defined as a second deflection angle. In this case, The first deflection angle estimation function and the second deflection angle estimation function are used to estimate the scanning trajectory of the light beam on the scanned surface, and the light source is caused to emit the light beam corresponding to the estimated scanning trajectory and image information. The first deflection angle estimation function is a function of the first deflection angle with respect to time, which takes into account the situation that the change of the first deflection angle with respect to time depends on the second deflection angle. The second deflection angle estimation function is a function of the second deflection angle with respect to time, which takes into account the situation that the change of the second deflection angle with respect to time depends on the first deflection angle.

Images