JP2024120962A - Mirror Scanner - Google Patents

Abstract

[Problem] To provide a mirror scanner with reduced circuit scale and cost. [Solution] The mirror scanner of the present invention comprises a mirror having a first surface that reflects light and capable of swinging around a first axis and a second axis that intersect at a predetermined angle, a permanent magnet arranged on a second surface of the mirror that is the surface opposite to the first surface, a yoke having a pair of ends arranged to face the second surface of the mirror and sandwich the permanent magnet, and a drive unit having a coil wound around the yoke, the pair of ends being arranged so that a straight line connecting the ends intersects the first axis and the second axis. [Selected Figure] Figure 1

Description

The present invention relates to a mirror scanner, and in particular to a mirror scanner that oscillates a mirror around two axes.

Scanning devices are known that deflect light while emitting it toward a predetermined area, and detect the light returning from the predetermined area to obtain various information about objects located within the predetermined area. In such scanning devices, a movable mirror such as a MEMS (Micro Electro Mechanical System) mirror is provided as the part that deflects the light. As an optical scanning device with a movable mirror, an optical scanning device in which a mirror vibrator and a permanent magnet are surrounded by upper and lower covers has been proposed (for example, Patent Document 1).

JP 2009-69676 A

In optical scanning devices such as those described above, an external force is applied to the moving part of the movable mirror using magnetism or the like, causing it to perform an oscillating motion, a reciprocating motion, or the like. For example, a typical two-axis driven movable mirror that performs raster scanning oscillates the movable mirror by combining oscillation around a high-speed axis caused by resonant driving and oscillation around a low-speed axis caused by non-resonant driving.

Non-resonant driving is a driving method that does not utilize the resonance phenomenon, and therefore requires more power than resonant driving. For this reason, the magnetic circuit for the slow axis is larger in circuit size than the magnetic circuit for the fast axis. As a result, optical scanning devices equipped with a magnetic circuit for the slow axis have the problem that the overall size of the device becomes larger due to the circuit size of the magnetic circuit.

In addition, conventional two-axis driven movable mirrors required separate and dedicated yokes and coils for oscillating around a fast axis and a slow axis. As a result, two-axis driven mirror scanners are large in size, weight, and cost.

The present invention has been made in consideration of the above points, and one of its objectives is to provide a mirror scanner that is small, weight, and cost-effective.

The invention described in claim 1 is characterized in that it comprises a mirror having a first surface that reflects light and capable of swinging around a first axis and a second axis that intersect at a predetermined angle, a permanent magnet arranged on a second surface of the mirror that is the surface opposite to the first surface, a yoke having a pair of ends arranged to face the second surface of the mirror and sandwich the permanent magnet, and a drive unit having a coil wound around the yoke, and the pair of ends are arranged so that a straight line connecting the ends intersects the first axis and the second axis.

1 is a diagram showing an overall configuration of a mirror scanner according to a first embodiment; FIG. 2 is a plan view of a mirror according to the first embodiment. 1 is a cross-sectional view of a mirror according to a first embodiment. FIG. 2 is a top view of the mirror scanner according to the first embodiment. FIG. 4 is a diagram showing a schematic view of how a coil is wound around a yoke. FIG. 13 is a diagram showing the axial torque acting on the mirror relative to the tilt angle of the yoke. FIG. 4 is a diagram showing a signal waveform of a drive signal. FIG. 4 is a diagram showing a signal waveform of a first signal. FIG. 11 is a diagram showing a signal waveform of a second signal. 3 is a diagram showing a schematic diagram of magnetic poles of a magnetic field generated when a drive signal is applied; FIG. FIG. 4 is a diagram illustrating a magnetic flux of a magnetic field generated when a drive signal is applied. 10 is a diagram showing a schematic diagram of components obtained by decomposing a combined magnetic flux in a first axis direction and a second axis direction. FIG. 11 is a diagram showing how an alternating magnetic field is generated in a magnetic circuit by application of a drive signal. FIG. 11 is a diagram showing how an alternating magnetic field is generated in a magnetic circuit by application of a drive signal. FIG. 11A and 11B are diagrams illustrating a first modified example of how the coil is wound around the yoke. FIG. 13 is a diagram illustrating a second modified example of how the coil is wound around the yoke. FIG. 13 is a diagram illustrating a third modified example of how the coil is wound around the yoke.

The following describes in detail preferred embodiments of the present invention. In the following descriptions of each embodiment and in the accompanying drawings, the same reference numerals are used to refer to substantially the same or equivalent parts.

Figure 1 is a perspective view showing the overall configuration of a mirror scanner 100 according to this embodiment. The mirror scanner 100 is an optical scanning device that deflects light by periodically oscillating a movable mirror.

The mirror scanner 100 has an optical deflector 10 that deflects light, and a magnetic circuit 20 that is a magnetic field generating source that generates a magnetic field to oscillate the optical deflector 10.

In the mirror scanner 100 of this embodiment, the magnetic field generated by the magnetic circuit 20 is applied to the optical deflector 10, causing the optical deflector 10 to oscillate. The mirror scanner 100 is, for example, a magnetically driven MEMS (Micro Electro Mechanical System) device in which the optical deflector 10 operates due to a change in the magnetic field.

The magnetic circuit 20 has a yoke 21 made of a soft magnetic material, for example, an electromagnetic steel sheet. The yoke 21 has, for example, a C-shape or a U-shape consisting of a pair of core parts 21A, a connecting part 21B that connects the pair of core parts 21A, and a pair of end parts 21C. The pair of end parts 21C are located on the opposite side to the part connected to the connecting part 21B of the pair of core parts 21A.

The magnetic circuit 20 also has a coil 23 wound around the connecting portion 21B of the yoke 21. The coil 23 is wound around the connecting portion 21B using, for example, a continuous steel wire.

The magnetic circuit 20 also has a drive circuit 25 that applies a current as a drive signal to the coil 23 to generate a magnetic field from the yoke 21. In this embodiment, the drive circuit 25 applies an AC current to the coil 23 as a drive signal. This causes an AC magnetic field to be generated from each of the pair of ends 21C of the yoke 21. In other words, the pair of ends 21C of the yoke 21 have the property of being a magnetic field generating end that generates a magnetic field.

In this embodiment, the yoke 21 functions as an electromagnet when a current is applied to the coil 23 by the drive circuit 25. That is, the magnetic circuit 20 in this embodiment has an electromagnet that generates an AC magnetic field.

Figure 2 is a plan view of the optical deflector 10. Figure 3 is a cross-sectional view of the optical deflector 10 taken along line 3-3 in Figure 2. The configuration of the optical deflector 10 will be explained using Figures 2 and 3.

In this embodiment, the optical deflector 10 has an optical reflecting surface 10S, which is a mirror that is reflective to a specific light. In other words, the optical deflector 10 is a MEMS mirror in which the optical reflecting surface 10S oscillates around a first oscillation axis AX and a second oscillation axis AY.

The optical deflector 10 includes a support portion 11, a movable portion 12 supported by the support portion 11 so as to be capable of swinging, and a permanent magnet 13. The permanent magnet 13 swings the movable portion 12 in response to changes in the magnetic field.

The movable part 12 has a movable frame 12A supported by the support part 11 in a state in which it can oscillate around the first oscillation axis AY. In this embodiment, the movable frame 12A is an annular frame body, and is connected to and supported by the support part 11 by a torsion bar 11X that extends along the second oscillation axis AX.

The movable part 12 also has a movable plate 12B that is disposed inside the movable frame 12A and supported by the movable frame 12A in a state in which it can oscillate around the second oscillation axis AY. In this embodiment, the movable plate 12B is a flat member, one of whose surfaces functions as the light reflecting surface 10S. The movable plate 12B is also connected to and supported by the movable frame 12A by a torsion bar 12Y that extends along the second oscillation axis AY.

When a magnetic field is applied to the permanent magnet 13 so that the torsion bar 11X twists in its circumferential direction, the movable frame 12A and the movable plate 12B swing around the first swing axis AX while being supported by the support part 11. When a magnetic field is applied to the permanent magnet 13 so that the torsion bars 11X and 12Y twist in their circumferential direction, the movable frame 12A swings around the first swing axis AX, and the movable plate 12B swings around the first swing axis AX and the second swing axis AY.

In this embodiment, the permanent magnet 13 is fixed on the other surface of the movable plate 12B (the surface opposite to the surface that functions as the light reflecting surface 10S). In addition, for example, the support part 11 and the movable part 12 in the optical deflector 10 are made of a semiconductor material and can be formed, for example, by processing a semiconductor wafer.

Figure 4 is a top view of the mirror scanner 100 according to this embodiment, as viewed from a direction perpendicular to the light reflecting surface 10S. Note that the connection portion 21B of the yoke 21 and the coil 23 are not shown here.

The yoke 21 is arranged so that each of the pair of ends 21C faces the second surface of the movable plate 12B of the optical deflector 10, and the straight line A1 connecting the centers of the pair of ends 21C is inclined at a predetermined angle with the first oscillation axis AX and the second oscillation axis AY, for example, at an angle θ<45° with respect to the second oscillation axis AY.

The yoke 21 is positioned so that the straight line A1 overlaps the intersection of the first oscillation axis AX and the second oscillation axis AY in a direction perpendicular to the light reflecting surface 10S of the optical deflector 10. A permanent magnet 13 is disposed on the second surface of the movable plate 12B of the optical deflector 10 at a position corresponding to the intersection of the first oscillation axis AX and the second oscillation axis AY.

The yoke 21 is also arranged so that a pair of ends 21C are symmetrically positioned on the line A1 with the permanent magnet 13 at the center. That is, the yoke 21 is arranged so that the pair of ends 21C of the yoke 21 sandwich the permanent magnet 13.

In other words, the mirror scanner 100 has a mirror having a light reflecting surface 10S that reflects light and capable of swinging around a first swing axis AX and a second swing axis AY that intersect at a predetermined angle, a permanent magnet 13 arranged on a second surface of the light deflector 10 that is the surface opposite the light reflecting surface 10S, a yoke 21 having a pair of ends 21C that face the second surface of the light deflector 10 and are arranged to sandwich the permanent magnet 13, and a magnetic circuit 20 having a coil 23 wound around the yoke 21, and the pair of ends 21C are arranged so that a straight line connecting the ends intersects the first swing axis AX and the second swing axis AY.

The permanent magnet 13 is arranged at a position that overlaps with the intersection of the first oscillation axis AX and the second oscillation axis AY when viewed from a direction perpendicular to a plane including the first oscillation axis AX and the second oscillation axis AY on the second surface of the optical deflector 10, and each of the pair of ends 21C is arranged to face the permanent magnet 13.

Figure 5 is a schematic diagram showing the configuration of the coil 23 in the yoke 21. The coil 23 is wound continuously in the same direction around the connecting portion 21B of the yoke 21, for example, using a common winding. By winding the coil 23 in this manner, when an AC current I is passed through the coil 23 in a predetermined direction (for example, the direction shown by the arrow in Figure 5), an AC magnetic field is generated such that one of the pair of ends 21C of the yoke 21 becomes a north pole and the other becomes a south pole.

Referring again to FIG. 4, the mirror scanner 100 of this embodiment generates an AC magnetic field to resonate the optical deflector 10 so that it oscillates at high speed around the second oscillation axis AY, and to non-resonate so that it oscillates at low speed around the first oscillation axis AX. That is, in this embodiment, the second oscillation axis AY is the high speed axis, and the first oscillation axis AX is the low speed axis. Therefore, by irradiating light to the light reflecting surface 10S of the optical deflector 10, the light reflecting surface 10S reflects the light and scans the reflected light in the direction of the second oscillation axis AY at high speed while scanning the reflected light in the direction of the first oscillation axis AX at low speed. This makes it possible to raster scan the reflected light with the light reflecting surface 10S of the optical deflector 10.

The drive circuit 25 applies the drive signal DS to the coil 23.

The drive signal DS has a current waveform in which a first signal, a sawtooth wave for driving the slow axis, is superimposed with a second sine wave, which is a second signal for driving the fast axis and has a smaller amplitude and a higher frequency than the sawtooth wave.

Figure 6 is a diagram showing the axial torque acting on the first and second oscillation axes AX and AY at a given inclination angle θ of the yoke 21 of the mirror scanner 100 in this embodiment.

The horizontal axis indicates the distance between the permanent magnet 13 and each of the pair of ends of the yoke 21 that face the permanent magnet 13. The vertical axis indicates the axial torque associated with each of the oscillation axes.

The curves in the figure show the cases where the inclination angle θ between the straight line A1 connecting the centers of a pair of ends 21C of the yoke 21 and the second oscillation axis AY is 0° (parallel), 5°, and 10°, respectively. Also, the solid line in the figure represents the axial torque applied to the first oscillation axis AX performing non-resonant operation, and the dashed line represents the axial torque applied to the second oscillation axis AY performing coexistent operation.

It can be seen that the axial torque acting on the first oscillating axis AX, which is the slow axis, is hardly affected by the change in axial torque due to the inclination angle θ, even when the inclination angle θ is changed from 0 to 10°. In addition, as the permanent magnet 13 and the pair of ends 21C are separated from each other, a decrease in axial torque is observed that is inversely proportional to the distance at each inclination angle θ, but no effect of the inclination angle θ is observed at any distance.

On the other hand, the axial torque applied to the second oscillating axis AY, which is the high-speed axis, increases each time the inclination angle θ is changed from 0° to 5° to 10°.

As mentioned above, the high-speed shaft that performs resonant operation can be driven with a smaller shaft torque than the low-speed shaft that performs non-resonant operation. In other words, by tilting the yoke 21 at an inclination angle θ, it is possible to obtain the shaft torque required for resonant operation without affecting the shaft torque required for non-resonant operation.

Figure 7 is a waveform diagram showing the current waveform of the drive signal DS. Figure 8 shows a sawtooth wave for driving the slow axis, which is the first signal. Figure 9 shows a sine wave for driving the fast axis, which is the second signal. Amplitude AML shows the amplitude for the slow axis, which corresponds to the sawtooth wave for driving the slow axis. Amplitude AMH shows the amplitude for the fast axis, which corresponds to the sine wave for driving the fast axis.

The sawtooth wave, which is the first signal shown in FIG. 8, is a signal for scanning the first oscillation axis AX with light in the slow scanning direction in raster scanning. In this embodiment, the first signal scans the slow scanning direction in one direction, and has a section with a steep slope that moves the light reflecting surface to the scanning start position, and a section that moves the light reflecting surface from the scanning start position to the scanning end position at a predetermined speed.

The sine wave, which is the second signal shown in FIG. 9, is a signal for scanning the second oscillation axis AY with light in the high-speed scanning direction in raster scanning. Since the second oscillation axis AY of the optical deflector 10 is resonantly driven, the sine wave has a frequency that matches the resonant frequency of the second oscillation axis AY. Since resonant driving does not require as much power as non-resonant driving, the amplitude of the sine wave, which is the second signal, can be reduced so as not to affect the driving of the first oscillation axis AX by the first signal.

As mentioned above, the drive signal DS has a signal waveform as shown in Figure 7, in which a first signal, a sawtooth wave for driving the low-speed axis, and a second signal, a sine wave for driving the high-speed axis, are superimposed.

In other words, the first signal has a larger amplitude and a smaller frequency than the second signal.

The first signal is a sawtooth wave and the second signal is a sine wave.

Figure 10 is a schematic diagram showing the magnetic poles that are generated at a pair of ends 21C of the yoke 21 when a magnetic field is generated by application of the drive signal DS.

When the drive signal DS is applied, a current flows through the first coil 23, and a magnetic field is generated such that one of the pair of ends 21C of the yoke 21 becomes a north pole and the other becomes a south pole. Figure 10 shows a case where one of the pair of ends 21C of the yoke 21, which is the end shown on the upper side of the figure, becomes a north pole (shown as Na in the figure), and the other end 21C, which is the end shown on the lower side of the figure, becomes a south pole (shown as Sa in the figure).

Figure 11 is a diagram that uses vectors to show the magnetic flux of the magnetic field generated by application of the drive signal DS. Application of the drive signal DS generates a magnetic flux shown as vector S1 in the direction from magnetic pole Na to magnetic pole Sa.

The vector S1 is formed at an inclination angle θ, at which the yoke 21 is inclined relative to the second oscillation axis AY.

Figure 12 is a schematic diagram using vectors to show the components of the magnetic flux of vector S1 shown in Figure 11 resolved into the direction of the second oscillation AY (hereinafter referred to as the Y direction) and the direction of the first oscillation axis AX (hereinafter referred to as the X direction). The Y-direction component SY of the magnetic flux is the vector component equivalent to the Y-direction component of vector S1. On the other hand, the X-direction component SX of the magnetic flux is the vector component equivalent to the X-direction component of vector S1.

In this way, by applying the drive signal DS to the coil 23, a magnetic field is generated in which the magnetic flux component in the Y direction is large and the magnetic flux component in the X direction is small. Therefore, by applying such a magnetic field to the permanent magnet 13, the optical deflector 10 can be oscillated around the first oscillation axis AX by non-resonant driving (low-speed driving), which requires a relatively large amount of power, and the optical deflector 10 can be oscillated around the second oscillation axis AY by resonant driving (high-speed driving), which does not require a large amount of power.

Figures 13 and 14 are diagrams showing the generation of an alternating magnetic field in the magnetic circuit 20 by applying a drive signal DS having a signal waveform as shown in Figure 7. Figure 13 shows the magnetic poles generated at a pair of ends 21C of the yoke 21 at time A shown in Figure 7, and Figure 14 shows the magnetic poles generated at a pair of ends 21C of the yoke 21 at time B shown in Figure 7.

At time A, the yoke 21 is arranged at a predetermined inclination angle θ, so that magnetic flux flows from magnetic pole Na to magnetic pole Sa. Then, at time B, this relationship is reversed.

As described above, the drive signal DS input to the coil 23 has a waveform in which the sawtooth wave for driving the low-speed axis, which is the first signal, and the sine wave for driving the high-speed axis, which is the second signal, are superimposed. Therefore, near time A and near time B, the pair of ends 21C apply an attractive or repulsive force to the permanent magnet 13 around the second oscillation axis AY at the frequency of the sine wave of the second signal, and become a resonant driving force source for the movable plate 12B. Also, the pair of ends 21C apply an attractive or repulsive force according to the sawtooth wave to the permanent magnet 13 around the first oscillation axis AX, and become a non-resonant driving force source for the movable frame 12A. As a result, when the drive signal DS is input to the coil 23, the optical deflector 10 can be non-resonantly driven in the direction of the second oscillation axis AX and resonantly driven in the direction of the first oscillation axis AY. Therefore, the desired rotational movement (i.e., swinging movement) can be achieved overall.

In other words, the angle between the straight line A1 connecting the pair of ends 21C and the first oscillation axis AX and the second oscillation axis AY is smaller than the angle between the straight line A1 connecting the pair of ends 21C and the first oscillation axis AX, and the coil 23 receives a drive signal DS in which a first signal for driving the optical deflector 10 around the first oscillation axis AX and a second signal for driving the optical deflector 10 around the second oscillation axis AY are superimposed, causing the optical deflector 10 to oscillate.

As described above, in the mirror scanner 100 of this embodiment, the magnetic circuit 20 is formed using one yoke 21 arranged so that the straight line connecting the centers of a pair of ends 21C of the yoke 21 forms a predetermined angle with the first oscillation axis AX and the second oscillation axis AY, which are the oscillation axes of the optical deflector 10. Then, a drive signal DS in which a sawtooth wave for the slow axis and a sine wave for the fast axis are superimposed is applied to the coil 23 to generate an alternating magnetic field. As a result, the mirror scanner 100 of this embodiment can perform raster scanning by oscillating the optical deflector 10 around the second oscillation axis AY at high speed and around the first oscillation axis AX at low speed.

The mirror scanner 100 of this embodiment can achieve resonant drive for the fast axis and non-resonant drive for the slow axis using a single yoke, making it possible to reduce the size, weight, and cost of the mirror scanner.

In the above embodiment, an example was described in which a drive signal was used in which a sawtooth wave for the slow axis was superimposed on a sine wave for the fast axis, but the present invention is not limited to this. Any drive signal that can oscillate the optical deflector 10 around the first oscillation axis AX and the second oscillation axis AY may be used.

In the above embodiment, a sawtooth wave is input as the first signal for scanning the first oscillation axis AX, which is the slow axis, in one direction. However, the operation direction of the first oscillation axis AX is not limited to one direction. For example, in order to utilize the bidirectional oscillation of the first oscillation axis AX in the forward and backward directions, a sine wave with a lower frequency and a larger amplitude than the second signal for the fast axis is input, making it possible to perform raster scanning using the bidirectional oscillation of the first oscillation axis AX in the forward and backward directions.

In the above embodiment, the coil 23 is wound around the connecting portion of the yoke 21 using a steel wire. However, the configuration of each coil is not limited to this.

For example, as shown in FIG. 15, the coil may be made up of a first coil 23A and a second coil 23B wound continuously using a common steel wire. That is, each of the first coil 23A and the second coil 23B can be made up of a pair of coils wound separately around a pair of core parts, rather than a single coil that is not separated as in the above embodiment.

Also, as shown in FIG. 16, the coil 23 may be composed of a first coil 23A and a second coil 23B wound around a pair of core portions 21A of the yoke 21, and a coil 23C wound around the connecting portion 21B. That is, each of the first coil portion and the second coil portion can be composed of three coils wound separately around the pair of core portions and the connecting portion of the yoke, respectively.

Also, as shown in FIG. 17, the coil 23 may be composed of a series of coils 23D having a length equal to the sum of the three coils (23A, 23B, and 23C) shown in FIG. 16. That is, each of the first coil portion and the second coil portion may be composed of a series of coils wound around a pair of core portions and a connecting portion of the yoke.

In the modified examples shown in Figures 15 to 17 above, the coils 23A to 23C are wound continuously across multiple parts using a common steel wire. However, the first, second and third coils 23A, 23B and 23C may each be wound around the pair of core parts 21A of the yoke 21 or the connecting part 21B using an independent steel wire. In other words, the first, second and third coils 23A, 23B and 23C only need to be wound so that one of the pair of ends 21C of the yoke 21 becomes the north pole and the other becomes the south pole when the drive signal DS is applied.

In other words, the coil 23 is configured so that when the drive signal DS is input, each of the pair of ends 21C has an opposite polarity to each other.

The series of processes described in the above embodiment can be performed by computer processing according to a program stored in a recording medium such as a ROM.

100 mirror scanner 10 mirror 10S light reflecting surface 11 support portion 12 movable portion 12A movable frame 12B movable plate 13 permanent magnet 20 magnetic circuit 21 yoke 23 coil 25 drive circuit

Claims (1)

a mirror having a first surface that reflects light and capable of swinging about a first axis and a second axis that intersect at a predetermined angle;
a permanent magnet disposed on a second surface of the mirror opposite to the first surface;
a driving unit including a yoke having a pair of ends arranged to face the second surface of the mirror and sandwich the permanent magnet therebetween, and a coil wound around the yoke;
having
A mirror scanner, characterized in that the pair of ends are arranged so that a straight line connecting the ends intersects the first axis and the second axis.

Images