JP7510555B2 - Optical scanning device, optical scanning method, and program - Google Patents

Description

The present invention relates to a device for scanning light from a light source.

Devices that display images by scanning laser light are known. In laser scanning projection devices, a desired image is projected onto a projection surface by scanning modulated laser light in horizontal and vertical directions with a scanning mirror. In this type of device, in order to compensate for the effects of the scanning mirror, whose mechanical characteristics are temperature-dependent, a distortion sensor that detects distortion caused by the rotation of the scanning mirror is provided on the scanning mirror, and the output signal from the distortion sensor, which is a signal indicating the rotational position of the scanning mirror, is used to control the driving of the scanning mirror to be constant and to control the timing of the emission of the laser light.

For example, Patent Document 1 discloses a laser projection display device that performs temperature compensation for the temperature dependency of the transfer characteristics of a mirror rotation angle signal in addition to the temperature dependency of the mechanical characteristics of the scanning mirror. The device in Patent Document 1 has a scanning mirror that reflects and two-dimensionally scans the laser light emitted from a laser light source, and a sensor that detects the rotation angle of the scanning mirror, and controls the driving of the scanning mirror based on a sensor signal output from the sensor. In this case, the temperature compensation unit compensates for the temperature dependency of the transfer characteristics of the signal transmission path that transmits the sensor signal using the temperature measured by a thermometer placed near the scanning mirror.

JP 2018-101040 A

Generally, when a MEMS (Micro Electro Mechanical Systems) mirror is used as a scanning mirror, the MEMS mirror is driven in the main scanning direction by the resonant frequency of the MEMS mirror (this is called "resonant driving"), and in the sub-scanning direction by a frequency lower than the resonant frequency (this is called "linear driving"). In the case of resonant driving, driving is possible with little power, while in the case of linear driving, a relatively large amount of power is required.

For example, in an electromagnetic MEMS mirror, a relatively large current must be passed through the coil when increasing the mirror's swing angle by linear drive, which causes the coil to heat up instantaneously. The heat generated by the coil is greatest at the upper and lower ends of the scanning range, and the MEMS mirror and the sensor that detects the mirror's rotation angle are affected by this heat. In this case, even if an attempt is made to detect the temperature of the MEMS mirror with a thermometer as in Patent Document 1, it is difficult to detect such instantaneous temperature changes. As a result, appropriate correction cannot be made according to the scanning position in the sub-scanning direction, and the drive of the MEMS mirror in the main scanning direction cannot be kept constant. As a result, depending on the scanning position in the sub-scanning direction, the timing of emitting the laser light during scanning in the main scanning direction may deviate from the desired position.

The above is one example of a problem that the present invention aims to solve. The present invention aims to always maintain appropriate light emission timing when scanning in the main scanning direction.

The invention described in the claims is an optical scanning device comprising: a light source that outputs a light beam; a scanning mirror that reflects the light beam on a reflecting surface and scans the light beam in the horizontal and vertical directions; a scanning unit having a drive unit that rotates the scanning mirror; a detection unit that detects the scanning position of the light beam in the horizontal direction and the scanning position of the light beam in the vertical direction; and a correction unit that calculates a delay time corresponding to the time from the start of driving the scanning mirror in the horizontal direction to the start of outputting the light beam based on the maximum amplitude Vmax of the light beam in the vertical direction and the displacement of the scanning position of the light beam in the vertical direction, and corrects the output period of the light beam in the horizontal scan using the delay time.

The invention described in the claims is an optical scanning method executed by an optical scanning device including a light source that outputs a light beam, a scanning mirror that reflects the light beam on a reflecting surface and scans the light beam in horizontal and vertical directions, and a scanning unit having a drive unit that rotates the scanning mirror, and includes a detection step of detecting the scanning position of the light beam in the horizontal direction and the scanning position of the light beam in the vertical direction, and a correction step of calculating a delay time corresponding to the time from the start of driving the scanning mirror in the horizontal direction to the start of outputting the light beam based on the maximum amplitude Vmax of the light beam in the vertical direction and the displacement of the scanning position of the light beam in the vertical direction, and correcting the output period of the light beam in the horizontal scan using the delay time.

The invention described in the claims is a program executed by an optical scanning device including a light source that outputs a light beam, a scanning mirror that reflects the light beam on a reflecting surface and scans the light beam in horizontal and vertical directions, a scanning unit having a drive unit that rotates the scanning mirror, and a computer, and causes the computer to execute a detection process of detecting the scanning position of the light beam in the horizontal direction and the scanning position of the light beam in the vertical direction, and a correction process of calculating a delay time corresponding to the time from the start of driving the scanning mirror in the horizontal direction to the start of outputting the light beam based on the maximum amplitude Vmax of the light beam in the vertical direction and the displacement of the scanning position of the light beam in the vertical direction, and correcting the output period of the light beam in the horizontal scan using the delay time.

1 shows an example of a head-up display to which the projection device of the embodiment is applied. FIG. 2 is a block diagram showing the internal configuration of the projection device. FIG. 2 is a diagram showing a configuration of a MEMS mirror. An example of a display in which multiple vertical lines are displayed is shown. An example of a display in which multiple vertical lines are displayed is shown. 2 is a block diagram showing an internal configuration of a video processing unit. FIG. 13 shows an example of a drive waveform for the MEMS mirror in the sub-scanning direction. 11 is a flowchart of a phase correction process according to an embodiment.

In one preferred embodiment of the present invention, an optical scanning device includes a light source that outputs a light beam, a scanning unit that scans the light beam in a first direction and a second direction intersecting the first direction, a detection unit that detects the emission direction of the light beam along the first direction and the second direction by the scanning unit, and a timing correction unit that corrects the start timing of the output period of the light beam in scanning along the first direction according to the emission direction of the light beam along the second direction.

In the above optical scanning device, the light source outputs a light beam, and the scanning unit scans the light beam in a first direction and a second direction intersecting the first direction. The detection unit detects the emission direction of the light beam by the scanning unit along the first and second directions, and the timing correction unit corrects the start timing of the output period of the light beam in scanning along the first direction according to the emission direction of the light beam along the second direction. This causes emission of the light beam along the first direction to start at an appropriate timing according to the emission direction of the light beam in the second direction.

In one aspect of the optical scanning device described above, the timing correction unit corrects the start timing using a correction value calculated based on the direction of scanning the light beam in the first direction, the maximum amplitude of scanning the light beam in the second direction, and the amplitude of scanning the light beam in the second direction. This allows emission of the light beam in the first direction to start at an appropriate timing according to the direction of scanning the light beam in the first direction.

In another aspect of the optical scanning device, the first direction is a direction in which the light beam is driven at the resonant frequency of the scanning unit. In this aspect, the light beam is efficiently scanned along the first direction at the resonant frequency of the scanning unit.

In another aspect of the optical scanning device described above, the scanning unit includes a scanning mirror that reflects the light beam at a reflecting surface and scans the light beam in the first direction and the second direction, and a driving unit that rotates the reflecting surface of the scanning mirror in the first direction and the second direction. In this aspect, the light beam is scanned by a scanning mirror having a reflecting surface.

Another preferred embodiment of the present invention is an optical scanning method executed by an optical scanning device including a light source that outputs a light beam and a scanning unit that scans the light beam in a first direction and a second direction intersecting the first direction, and includes a detection step of detecting the emission direction of the light beam along the first direction and the second direction, and a timing correction step of correcting the start timing of the output period of the light beam in scanning along the first direction according to the emission direction of the light beam along the second direction. This method also starts emission of the light beam along the first direction at an appropriate timing according to the emission direction of the light beam in the second direction.

Another preferred embodiment of the present invention is a program executed by an optical scanning device including a light source that outputs a light beam, a scanning unit that scans the light beam in a first direction and a second direction intersecting the first direction, and a computer, and causes the computer to execute a detection process for detecting the emission direction of the light beam along the first direction and the second direction, and a timing correction process for correcting the start timing of the output period of the light beam in scanning along the first direction according to the emission direction of the light beam along the second direction. By executing this program on a computer, the above-mentioned optical scanning device can be realized. This program can be stored in a storage medium and handled.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[Device configuration]
(Head-up display)
First, an example of a head-up display (hereinafter, referred to as "HUD") to which a projection device, which is an embodiment of the optical scanning device of the present invention, is applied will be described. Fig. 1 shows a schematic configuration of a HUD 40. As shown in Fig. 1, the HUD 40 includes a light source unit 41. The HUD 40 is attached to a vehicle including a windshield 46, a ceiling portion 47, a bonnet 48, a dashboard 49, etc.

The light source unit 41 is installed on the ceiling 47 inside the vehicle cabin via support members 43a and 43b, and emits light that constitutes an image showing information that assists driving toward the combiner 44. Specifically, the light source unit 41 generates an original image (real image) of the display image within the light source unit 41 using an internal projection device 42, and emits light that constitutes the image to the combiner 44, allowing the driver to view a virtual image Iv through the combiner 44.

The combiner 44 projects the display image emitted from the light source unit 41 and reflects the display image to the driver's eye point Pe, thereby displaying the display image as a virtual image Iv. The combiner 44 has a support shaft 45 installed on the ceiling 47 and rotates around the support shaft 45 as a support shaft. The support shaft 45 is installed, for example, on the ceiling 47 near the upper end of the front window 46, in other words, near the position where a sun visor (not shown) for the driver is installed. The support shaft 45 may be installed in place of the sun visor described above.

(Projection device)
Next, the projection device 42 will be described. Fig. 2 is a block diagram showing the internal configuration of the projection device 42. As shown in Fig. 2, the projection device 42 includes an image signal input unit 2, a video processing unit 3, a frame memory 4, a ROM (Read Only Memory) 5, a RAM (Random Access Memory) 6, a laser driver 7, a MEMS driver 8, a laser light source unit 9 having a MEMS mirror 95, a microlens array 13, a field lens 14, a timing controller 21, and an MCU (Micro Controller Unit) 22. The projection device 42 is used in the HUD 40 and emits light constituting a display image to a combiner 44.

The image signal input unit 2 receives an image signal Si input from the outside and outputs it to the image processing unit 3. The image processing unit 3 writes the image data input from the image signal input unit 2 into the frame memory 4, reads it out as needed in accordance with the drive timing of the MEMS mirror 95, and sequentially transmits control signals corresponding to the brightness of each pixel of the image data for each color of red (R), green (G), and blue (B) to the laser driver 7.

The timing controller 21 controls the timing of reading image data from the frame memory 4 of the image processing unit 3. The timing controller 21 also controls the operation timing of the MEMS driver 8 based on the scanning position information Sc output from the MEMS mirror 95.

The ROM 5 stores control programs and data for the operation of the video processing unit 3. The RAM 6 serves as a work memory when the video processing unit 3 is operating, and various data is sequentially read and written into it.

The laser driver 7 generates a signal to drive a laser element provided in the laser light source unit 9 described later. The laser driver 7 includes a red laser drive circuit 71, a blue laser drive circuit 72, and a green laser drive circuit 73.

The red laser drive circuit 71 drives the red laser element LD1 based on a control signal output by the video processing unit 3. The blue laser drive circuit 72 drives the blue laser element LD2 based on a control signal output by the video processing unit 3. The green laser drive circuit 73 drives the green laser element LD3 based on a signal output by the video processing unit 3.

The MEMS driver 8 controls the MEMS mirror 95 based on a signal output by the timing controller 21. The MEMS driver 8 includes a servo circuit and a driver circuit. The servo circuit controls the operation of the MEMS mirror 95 based on a signal from the timing controller 21. The driver circuit amplifies the control signal for the MEMS mirror 95 output by the servo circuit to a predetermined level and outputs it.

The laser light source unit 9 outputs laser light based on a drive signal output from the laser driver 7. Specifically, the laser light source unit 9 includes a red laser element LD1, a blue laser element LD2, a green laser element LD3, collimator lenses 91a-91c, reflecting mirrors 92a-92c, and a light receiving unit 24. The laser light source unit 9 is an example of a light source of the present invention.

The red laser element LD1 outputs red laser light (also called "red laser light Lr"), the blue laser element LD2 outputs blue laser light (also called "blue laser light Lb"), and the green laser element LD3 outputs green laser light (also called "green laser light Lg"). The collimator lenses 91a-91c collimate the red, blue, and green laser light Lr, Lb, and Lg, respectively, and emit them to the reflecting mirrors 92a-92c. The reflecting mirror 92b reflects the blue laser light Lb. The reflecting mirror 92c transmits the blue laser light Lb and reflects the green laser light Lg. The reflecting mirror 92a reflects a portion of the red laser light Lr and transmits the remaining portion. The reflecting mirror 92a also transmits a portion of the blue and green laser light Lb and Lg and reflects the remaining portion. In this way, the red laser light Lr that has passed through the reflection mirror 92a and the blue and green laser lights Lb, Lg that have been reflected by the reflection mirror 92a are incident on the MEMS mirror 95. In addition, a portion of the red laser light Lr, blue laser light Lb, and green laser light Lb is irradiated onto the light receiving unit 24.

At the position where the laser light is emitted from the laser light source unit 9, a microlens array 13 and a field lens 14 are provided. The MEMS mirror 95 reflects the laser light incident from the reflection mirror 92a toward the microlens array 13, which is an example of an EPE (Exit Pupil Expander). The MEMS mirror 95 basically operates to scan the microlens array 13 under the control of the MEMS driver 8 in order to display an image (hereinafter referred to as an "input image") input to the image signal input unit 2, and outputs scanning position information at that time (such as information on the mirror angle) to the timing controller 21 as scanning position information Sc. The MEMS mirror 95 is an example of a scanning unit of the present invention.

The microlens array 13 has multiple microlenses arranged therein, and laser light reflected by the MEMS mirror 95 is incident on it. The field lens 14 enlarges the image formed on the emission surface of the microlens array 13 and projects it onto a projection surface (not shown). For example, when the projection device 42 is used as a light source for a head-up display, the field lens 14 emits light that constitutes a display image to a combiner or the like.

The light receiving unit 24 is composed of a photodetector, receives the combined light of the red laser light Lr, blue laser light Lb, and green laser light Lb, and outputs a signal Sd indicating a voltage corresponding to the intensity of the combined light to the MCU 22. The MCU 22 controls the laser driver 7 to start and stop the emission of each of the laser light sources LD1 to LD3 based on the voltage value output from the light receiving unit 24.

(MEMS mirror)
Next, a description will be given of the configuration of the MEMS mirror 95. Fig. 3 is a top view of the MEMS mirror 95. As shown in Fig. 3, the MEMS mirror 95 mainly has a fixed frame 31, a frame portion 32, a mirror portion 33, magnets 34A to 34D, X-axis torsion bars 35A and 35B, Y-axis torsion bars 36A and 36B, and piezoelectric sensors 37V and 37H.

The fixed frame 31 is a structure for supporting the frame portion 32, and is formed from a metal material or a semiconductor material such as silicon. The fixed frame 31 has a frame shape with an internal gap. The frame portion 32 has a frame shape with an internal gap. The frame portion 32 is connected to the fixed frame 31 via the X-axis torsion bars 35A and 35B, and can freely swing (rotate) relative to the fixed frame 31 with the X-axis torsion bars 35A and 35B as the rotation axis.

The wiring pattern extending from the fixed frame 31 via the X-axis torsion bars 35A and 35B forms a coil 38 on the surface of the frame part 32 along the frame shape of the frame part 32. The mirror part 33 is a disk-shaped member with a reflective film formed on its surface that reflects incident light, and is connected to the frame part 32 via the Y-axis torsion bars 36A and 36B. The mirror part 33 can freely swing with respect to the frame part 32, with the Y-axis torsion bars 36A and 36B as the axis of rotation. The magnets 34A to 34D are arranged around the frame part 32, and generate a magnetic field in the horizontal direction (hereinafter referred to as the "H direction" or "main scanning direction") and the vertical direction (hereinafter referred to as the "V direction" or "sub-scanning direction") in the area where the coil 38 formed on the frame part 32 exists.

A piezoelectric sensor 37V, which is a strain sensor, is provided near the X-axis torsion bar 35B, and a piezoelectric sensor 37H, which is a strain sensor, is provided near the Y-axis torsion bar 36B. The piezoelectric sensor 37V is a V-direction sensor that detects the position of the mirror section 33 in the V direction, and outputs a voltage corresponding to the amount of twist and the direction of twist of the X-axis torsion bar 35B. The piezoelectric sensor 37H is an H-direction sensor that detects the position of the mirror section 33 in the H direction, and outputs a voltage corresponding to the amount of twist and the direction of twist of the Y-axis torsion bar 36B. The piezoelectric sensors 37H and 37V are examples of the detection section of the present invention.

As described above, in the MEMS mirror 95, the mirror section 33 is rotatably connected to the fixed frame 31 by the X-axis torsion bars 35A, 35B and the Y-axis torsion bars 36A, 36B. The mirror section 33 rotates due to the action of electromagnetic force generated by the driving signal input from the MEMS driver 8 flowing through the coil 38. The MEMS mirror 95 is driven in the H direction by the resonant frequency of the MEMS mirror 95, and in the V direction by a frequency lower than the resonant frequency. When no driving signal is input, the mirror section 33 stops at a position where the X-axis torsion bar 35 and the Y-axis torsion bar 36 are in a balanced state, that is, at a neutral position. Based on the output of the piezoelectric sensors 37V, 37H, the rotational displacement of the MEMS mirror 95 is calculated and output to the timing controller 21 as scanning position information Sc indicating the scanning position of the laser light.

[Display Timing Correction]
(Phase Shift)
When the MEMS mirror 95 is used, the response of the piezo sensor 37H may be delayed or advanced, and the response of the sensor signal detection circuit may be delayed or advanced depending on the direction of rotation of the MEMS mirror 95. That is, when the light beam is scanned to the right in the H direction and when it is scanned to the left, a difference occurs in the timing of emitting the light beam that draws the input image. This phenomenon is called a "phase shift." As a result, a thin vertical line may appear as a double vertical line in the displayed image. For example, when multiple vertical lines as shown in FIG. 4A are displayed, each vertical line appears as a double line as shown in FIG. 4B. To solve this problem, the projection device 42 changes the display timing of the image when the MEMS mirror 95 is driven to the left and right, and performs phase adjustment so that the image appears as a single vertical line.

However, when the laser light is instantaneously scanned widely in the V direction in the two-axis MEMS mirror 95 as described above, a large drive current instantaneously flows through the coil 38, causing the coil 38 to heat up instantaneously. The temperature change of the MEMS mirror 95 causes changes in the response characteristics and linearity of the piezoelectric sensors 37H and 37V, crosstalk of the vertical drive signal to the horizontal output signal of the piezoelectric sensor 37H, and changes in the drive magnetic field. For this reason, when the laser light is scanned widely in the V direction, the waveform of the output signal of the piezoelectric sensor 37H changes compared to when the MEMS mirror 95 is not driven in the V direction (i.e. when the drive current is zero), and the detection error of the scanning position in the H direction of the MEMS mirror 95 increases.

When laser light (hereinafter referred to as "image light") that displays an input image is emitted in synchronization with the H-direction scanning position that includes an error, an error also occurs in the relationship between the position of the pixel of the image to be displayed and the position where the pixel is actually drawn by scanning with the MEMS mirror 95. As a result, a positional shift in the H direction occurs in the drawn image, and the amount of the positional shift depends on the V-direction scanning position of the MEMS mirror 95 and differs for each line in the H direction. Furthermore, when the image light is scanned back and forth in the H direction, the image positional shift direction does not match during the forward scan (scanning to the right) and the return scan (scanning to the left) in the H direction, and the image may be shifted in opposite directions on adjacent lines in the H direction. As a result, a problem may occur in which a single vertical line appears as a curved double line, as shown in FIG. 4(C).

Figure 5 shows an example where a single vertical line appears as a curved double line (hereafter referred to as a "curved double line"). Note that the arrow "R" indicates a vertical line drawn by scanning to the right, and the arrow "L" indicates a vertical line drawn by scanning to the left. In the example of Figure 5 (A), the phase during right scanning and the phase during left scanning are shifted in opposite directions at the top and bottom of the V direction, but are consistent at the center of the V direction. In the example of Figure 5 (B), the phase during right scanning and the phase during left scanning are shifted in opposite directions at the top and bottom of the V direction, but are consistent at the top of the V direction. In the example of Figure 5 (C), the phase during right scanning and the phase during left scanning are shifted in opposite directions at the top and bottom of the V direction, but are consistent at the bottom of the V direction.

In the example of Figure 5 (D), the phase during rightward scanning and the phase during leftward scanning are shifted in the same direction at the top and bottom of the V direction, but are consistent at the center of the V direction. In the example of Figure 5 (E), the phase during rightward scanning and the phase during leftward scanning are shifted in the same direction at the top and bottom of the V direction, but are consistent at the top of the V direction. In the example of Figure 5 (F), the phase during rightward scanning and the phase during leftward scanning are shifted in the same direction at the top and bottom of the V direction, but are consistent at the bottom of the V direction.

In this way, to prevent a single vertical line from appearing as a curved double line, in this embodiment, when the MEMS mirror 95 is driven in the H direction, the output start timing of the image light is corrected according to the scanning position (scanning direction) of the MEMS mirror 95 in the V direction.

(Phase adjustment)
Fig. 6 is a block diagram showing the internal configuration of the image processing unit 3 shown in Fig. 2. The image processing unit 3 includes a video signal processing unit 51, an LD control unit 52, and a phase adjustment unit 53. The video signal processing unit 51 sends a MEMS control signal S11 to the timing controller 21 and sends an LD control signal S12 to the LD control unit 52 in accordance with the operation timing of the image signal input from the image signal input unit 2. The LD control unit 52 sends a drive signal S13 to the laser driver 7 for actually driving each of the laser elements LD1 to LD3 based on the LD control signal S12 supplied from the video signal processing unit 51.

The phase adjustment unit 53 corrects the output timing of the image light corresponding to the input image when the MEMS mirror 95 scans the light beam in the H direction. Basically, the phase adjustment unit 53 controls the timing of the drive signal S13 supplied by the LD control unit 52 to the laser driver 7 based on the drive start timing of the MEMS mirror 95 in the H direction, and adjusts the output start timing of the image light. Specifically, the phase adjustment unit 53 calculates a delay time _TR from the drive start time _TR0 of the MEMS mirror 95 in the horizontal right direction to the start of output of the image light. Similarly, the phase adjustment unit 53 calculates a delay time _TL from the drive start time _TL0 of the MEMS mirror 95 in the horizontal left direction to the start of output of the image light. Here, the phase adjustment unit 53 determines the delay times _TR and _TL so that the curved double line illustrated in FIG. 5 appears as a single vertical line.

In detail, the phase adjustment unit 53 determines delay times T R and T L so that the phase shift during rightward scanning and the phase shift during leftward scanning are cancelled out using the scanning position in the V direction of the MEMS mirror 95, the scanning direction in the H direction (horizontal rightward/horizontal leftward), and the scanning position in the H direction, which are supplied as a signal S14 from the timing controller 21, and supplies the delay times T _R and T _L to the LD control unit 52 as a signal S15. The LD control unit 52 outputs a drive signal S13 to the laser driver 7 based on the delay _time T _R so that the laser driver 7 starts outputting image light after the delay time T _R0 from the start time T _L0 of driving the MEMS mirror 95 in the horizontal rightward direction. Similarly, the LD control unit 52 outputs a drive signal S13 to the laser driver 7 based on the delay time T L so that the laser driver 7 starts outputting image light after the delay time T _L0 from the start time T _L0 of driving the MEMS mirror 95 in the horizontal rightward direction. This allows the laser driver 7 to draw the input image so that the vertical lines in the input image appear as a single correct vertical line. The phase adjustment unit 53 is an example of the timing correction unit of the present invention.

(How to calculate delay time)
Next, a method of calculating the delay times T _R and T _L will be described. FIG. 7 shows a driving waveform of the MEMS mirror 95 in the V direction. The horizontal axis indicates time t, and the vertical axis indicates the amplitude (displacement) v of the MEMS mirror 95 in the V direction. The vertical axis is set to zero at the center of the display screen, and the maximum amplitude in the V direction based on the center of the screen is set to V _max . In the driving waveform of FIG. 7, points P1 and P3 correspond to the upper end in the V direction of the scanning area of the light beam, that is, the upper end of the image, and point P2 corresponds to the lower end in the V direction of the scanning area of the light beam, that is, the lower end of the image. The MEMS mirror 95 scans the light beam from the upper end P1 to the lower end P2 in the V direction at time T _vpp , and then returns the light beam from the lower end P2 in the V direction to the upper end P3 in the V direction at time T _ret . The MEMS mirror 95 repeats this operation.

In this case, the delay time _TR during rightward scanning is calculated by the following formula:
_TR = _kR × _Vmax × sin(ωt + θ) + A + _kR1 × v + _kR2 × ^v2 (1)

The first term of equation (1) is a term for calculating the amount of phase shift timing correction by a trigonometric function (sine wave) using the maximum amplitude _Vmax , and " _kR " is a weighting value for this purpose. As shown in Fig. 5, the phase shift has a curved shape, so the first term is a correction amount using a sine wave. Here, "ω" is given by the following equation, and "θ" is a position shift correction value relative to the center of the screen.
ω=2π/(2×T _vpp )=π/T _vpp (2)

The "A" in the second term of formula (1) is a constant correction amount that does not depend on the amplitude v in the V direction. The third term of formula (1) is a correction amount that depends on the amplitude v in the V direction, and specifically, is the sum of a value obtained by multiplying a correction amount proportional to v by a predetermined weight value _kR1 and a value obtained by multiplying a correction amount proportional to the square of v by a predetermined weight value _kR2 . Note that correction amounts proportional to the cube or fourth power of v may also be added.

Similarly, the delay time T _L during leftward scanning is calculated by the following formula:
T _L = k _L × V _max × sin(ωt + θ) + B + k _L1 × v + k _L2 × v ² (3)

Here, the first term is a term for calculating the amount of phase shift timing correction by a trigonometric function using the maximum amplitude _Vmax , and " _kL " is a weighting value for this purpose. "ω" is given by the above equation (2).

The second term "B" in formula (3) is a constant correction amount that does not depend on the amplitude v in the V direction. The third term in formula (3) is a correction amount that depends on the amplitude v in the V direction, and specifically, is the sum of a value obtained by multiplying a correction amount proportional to v by a predetermined weight value _kL1 and a value obtained by multiplying a correction amount proportional to the square of v by a predetermined weight value _kL2 . It is to be noted that a correction amount proportional to the cube or fourth power of v may be further added.

As described above, the delay time is calculated separately for rightward and leftward scanning in the H direction because it is considered that the phase shift amount may differ between rightward and leftward scanning. Therefore, if the phase shift amount between rightward and leftward scanning is approximately the same, the same correction amount can be calculated for both scanning directions using formula (1) or (3).

In the above example, the phase adjustment unit 53 adjusts the timing at which the image light starts scanning in the horizontal right direction based on the time at which the MEMS mirror 95 starts driving horizontally to the right, and adjusts the timing at which the image light starts scanning in the horizontal left direction based on the time at which the MEMS mirror 95 starts driving horizontally to the left. Alternatively, the phase adjustment unit 53 may adjust the timing at which the image light starts scanning in the horizontal left direction based on the time at which the MEMS mirror 95 starts driving horizontally to the right. In other words, both the timing at which the image light starts scanning to the right and the timing at which the image light starts scanning to the left may be adjusted based on the time at which the MEMS mirror 95 starts driving right.

Here, _a method for setting the constants _kR , _kR1 , kR2, and A used in formula (1), the constants _kL , _kL1 , _kL2 , and B used in formula (3), and the constant θ commonly used in formula (1) and formula (3) will be described. Typically, these constants are set when the projection device 42 is manufactured and stored in the ROM 5. Specifically, an image signal Si including a plurality of vertical lines each having a vertical width of one pixel, as shown in FIG. 4A, is input to the image signal input unit 2 when the projection device 42 is manufactured, and while observing the image displayed by the projection device 42, these constants are set so that the phase shift on the image is minimized over the entire image, and are stored in the ROM 5. Note that these constants may be configured to be set by the user.

(Phase adjustment process)
Fig. 8 is a flowchart of the phase adjustment process. This process is executed by the projection device 42 shown in Fig. 2. Alternatively, this process may be realized by a computer such as a CPU executing a program prepared in advance.

First, the piezoelectric sensors 37V and 37H provided on the MEMS mirror 95 detect the drive positions of the MEMS mirror 95 in the V and H directions (step S1). Specifically, the piezoelectric sensor 37V detects the amplitude v of the MEMS mirror 95 in the V direction, and the piezoelectric sensor 37H detects the scanning direction (rightward scanning/leftward scanning) of the MEMS mirror 95 in the H direction.

Next, the phase adjustment unit 53 of the image processing unit 3 calculates delay times T R and T L by the above-mentioned formulas (1) and (3) using the amplitude v in the V direction and the scanning direction in the H direction detected in step S1, using _constants previously stored in the _ROM 5, and supplies the delay times to the LD control unit 52 (step S2). The LD control unit 52 supplies the driving signal S13, the phase of which has been adjusted by the delay times T _R and T _L , to the laser driver 7, and corrects the output timing of the image light from the laser driver 7 (step S3). In this way, the delay times T _R and T _L cancel the phase shift during rightward scanning and leftward scanning in the H direction, and it is possible to prevent the curved double line from being displayed.

[Modification]
(Variation 1)
In the above embodiment, the piezo sensor 37V is used to detect the drive position in the V direction of the MEMS mirror 95, but the method of detecting the drive position in the V direction of the MEMS mirror 95 is not limited to this. For example, the phase adjustment unit 53 of the image processing unit 3 may detect the drive position in the V direction of the MEMS mirror 95 by calculating it based on the elapsed time after the V direction drive waveform of the MEMS mirror 95 output from the MEMS driver 8 returns to the upper end of the scanning area in the V direction.

(Variation 2)
In the above embodiment, the present invention is applied to scanning of image light in a projection device, but the application of the present invention is not limited to this. For example, the present invention may be applied to a device that scans laser light in a two-dimensional direction, such as a laser radar or LiDAR (Light Detection and Ranging) that is mounted on a vehicle and detects surrounding objects.

7 Laser driver 8 MEMS driver 9 Laser light source unit 21 Timing controller 22 MCU
40 Head-up display 42 Projection device 51 Video signal processing unit 52 LD control unit 53 Phase adjustment unit 95 MEMS mirror

Claims (7)

A light source that outputs a light beam;
a scanning unit including a scanning mirror that reflects the light beam on a reflecting surface and scans the light beam in horizontal and vertical directions, and a driving unit that rotates the scanning mirror;
a detection unit that detects a scanning position of the light beam in the horizontal direction and a scanning position of the light beam in the vertical direction;
a correction unit that calculates a delay time corresponding to a time from a drive start timing of the scanning mirror in a horizontal direction to a start timing of output of the light beam based on a maximum amplitude Vmax of the light beam in the vertical direction and a displacement of a scanning position of the light beam in the vertical direction, and corrects an output period of the light beam in the horizontal direction scanning using the delay time;
An optical scanning device comprising: The optical scanning device according to claim 1, wherein the correction unit calculates, as the delay time, a first delay time corresponding to the time from when the scanning mirror starts to move to the right to when the light beam starts to be output, and a second delay time corresponding to the time from when the scanning mirror starts to move to the left to when the light beam starts to be output. The optical scanning device according to claim 1 or 2, wherein the driving unit sets the frequency at which the scanning mirror is driven in the horizontal direction to the resonant frequency of the scanning mirror. The optical scanning device according to any one of claims 1 to 3, wherein the correction unit calculates the delay time based on a correction amount expressed by a function including the maximum amplitude Vmax, a constant correction amount that is independent of the displacement of the scanning position of the light beam in the vertical direction, and at least one correction amount that is dependent on the displacement of the scanning position of the light beam in the vertical direction. An optical scanning method performed by an optical scanning device including a light source that outputs a light beam, a scanning mirror that reflects the light beam at a reflecting surface and scans the light beam in horizontal and vertical directions, and a scanning unit having a drive unit that rotates the scanning mirror, comprising:
a detection step of detecting a scanning position of the light beam in the horizontal direction and a scanning position of the light beam in the vertical direction;
a correction step of calculating a delay time corresponding to a time from a drive start timing of the scanning mirror in a horizontal direction to a start timing of output of the light beam, based on a maximum amplitude Vmax of the light beam in the vertical direction and a displacement of a scanning position of the light beam in the vertical direction, and correcting an output period of the light beam in the horizontal direction scanning using the delay time;
An optical scanning method comprising: A program executed by an optical scanning device including: a light source that outputs a light beam; a scanning mirror that reflects the light beam on a reflecting surface and scans the light beam in horizontal and vertical directions; a scanning unit having a drive unit that rotates the scanning mirror; and a computer,
a detection step of detecting a scanning position of the light beam in the horizontal direction and a scanning position of the light beam in the vertical direction;
a correction step of calculating a delay time corresponding to a time from a drive start timing of the scanning mirror in a horizontal direction to a start timing of output of the light beam based on a maximum amplitude Vmax of the light beam in the vertical direction and a displacement of a scanning position of the light beam in the vertical direction, and correcting an output period of the light beam in the horizontal direction scanning using the delay time;
A program for causing the computer to execute the above. A storage medium storing the program according to claim 6.