ACTUATOR

An actuator includes a mirror and an electromagnet. The mirror is provided with a permanent magnet and is capable of oscillating about a first axis and a second axis as oscillation axes with respect to a reference plane. The second axis is non-parallel to the first axis. The electromagnet has a yoke and a coil and applies a magnetic flux to the permanent magnet. Both ends of the yoke face each other at least partially across a gap. When viewed from a direction perpendicular to the reference plane, a center Cg of the gap does not overlap a center Cm of the permanent magnet. A current I1 for causing the mirror to oscillate with respect to the first axis and a current I2 for causing the mirror to oscillate with respect to the second axis are superimposed and flowed through the coil.

TECHNICAL FIELD

The present invention relates to an actuator.

BACKGROUND ART

In a measurement apparatus or the like that uses light to scan and measure a predetermined region, a movable mirror is used to change the direction of light emission.

Patent Document 1 describes an optical scanner in which a permanent magnet fixed to a mirror interacts with an electromagnet to generate a driving torque on the mirror.

Related Document

PATENT DOCUMENT

SUMMARY OF THE INVENTION

Technical Problem

Miniaturization of the actuator that drives the mirror is important for miniaturization of the entire measurement apparatus or the like including the actuator. On the other hand, when trying to drive the mirror with respect to two axes, two sets of electromagnets are required, and there is a problem that the size of the actuator increases.

One example of the problems to be solved by the present invention is to miniaturize an actuator that drives a mirror.

Solution to Problem

The invention according to claim1is an actuator including a mirror provided with a permanent magnet, and capable of oscillating about a first axis and a second axis non-parallel to the first axis as oscillation axes with respect to a reference plane, an electromagnet having a yoke and a coil and applying a magnetic flux to the permanent magnet, in which both ends of the yoke face each other at least partially across a gap, when viewed from a direction perpendicular to the reference plane, a center of the gap does not overlap a center of the permanent magnet, and a current for causing the mirror to oscillate with respect to the first axis and a current for causing the mirror to oscillate with respect to the second axis are superimposed and flowed through the coil.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the invention will be described with reference to the drawings. In addition, in all of the drawings, the same components are denoted by the same reference numerals, and the description thereof will not be repeated.

EMBODIMENT

FIGS.1to3are diagrams illustrating the configuration of an actuator10according to an embodiment.FIG.1is a perspective view of the actuator10,FIG.2is a side view of the actuator10, andFIG.3is a plan view of the actuator10. The x-axis, y-axis and z-axis shown in each figure are three axes orthogonal to each other. The actuator10according to the present embodiment includes a mirror20and an electromagnet30. The mirror20is provided with a permanent magnet21. The mirror20is capable of oscillating about the first axis201and the second axis202as oscillation axes with respect to the reference plane101. The second axis202is non-parallel to the first axis201. The electromagnet30has a yoke34and a coil32and applies a magnetic flux to the permanent magnet21. Both ends (end portion341and end portion342) of the yoke34face each other at least partially across a gap340. When viewed from a direction perpendicular to the reference plane101(the z-axis direction), the center Cg of the gap340does not overlap the center Cm of the permanent magnet21. A current I1for causing the mirror20to oscillate with respect to the first axis201and a current I2for causing the mirror20to oscillate with respect to the second axis202are superimposed and flowed through the coil32. A detailed description will be made below.

Oscillating the mirror20with respect to the first axis201refers to oscillating the mirror20about the first axis201as the oscillation axis, and oscillating the mirror20with respect to the second axis202refers to oscillating the mirror20about the second axis202as the oscillation axis.

The mirror20has a reflecting surface22and the permanent magnet21is fixed at the center of the surface opposite to the reflecting surface22. The first pole211, which is one of the poles of the permanent magnet21, faces the mirror20side, and the second pole212, which is the other pole of the permanent magnet21, faces the opposite side of the mirror20, that is, the side where the electromagnet30is provided. The reference plane101is a plane including the reflecting surface22of the mirror20in a state in which no current is flowing through the coil of the electromagnet30, that is, in a reference state in which the permanent magnet21receives no force.FIGS.1to3all show the reference state. The reference plane101is parallel to the xy plane.

The actuator10is a biaxial actuator and can oscillate the mirror20with respect to the first axis201and the second axis202. Thereby, the direction of the light reflected by the reflecting surface22of the mirror20can be changed two-dimensionally. In the present embodiment, the first axis201and the second axis202are substantially orthogonal or orthogonal to each other.

In the electromagnet30, the coil32is wound around at least a portion of yoke34. As current flows through the coil32, a magnetic flux is generated between an end portion341and an end portion342. By applying this magnetic flux to the permanent magnet21, it is possible to oscillate the mirror20with respect to the first axis201and the second axis202.

In the actuator10according to the present embodiment, the driving of the mirror20with respect to the first axis201and the driving of the mirror with respect to the second axis202are realized using the same electromagnet30. That is, the electromagnet for causing the mirror20to oscillate with respect to the first axis201and the electromagnet for causing the mirror20to oscillate with respect to the second axis202are not separated. By doing so, it is possible to reduce the size of the actuator10without providing electromagnets for each of the plurality of oscillation axes.

The electromagnet30is U-shaped or C-shaped. Specifically, both ends (end portion341and end portion342) of the yoke34of the electromagnet30face each other across at least a portion of the permanent magnet21when viewed from a direction perpendicular to the reference plane101. The end portion341and the end portion342are end portions where a magnetic flux is generated. The electromagnet30may be composed of a plurality of electromagnets which are configured such that the end portions where a magnetic flux is generated face each other at least partially across a gap340. That is, the yoke34and the coil32of the electromagnet30may be divided into a plurality of parts. In the examples ofFIGS.1to3, the end portion341and the end portion342are closer to the mirror20than the coil32is. Also, the coil32extends in a direction parallel to the reference plane101.

Next, with reference toFIGS.1and3, a structural body12including a mirror20, an outer frame50, and an inner frame60will now be described. The actuator10further includes an outer frame50, a torsion bar52, an inner frame60and a torsion bar62. The outer frame50and the inner frame60are connected via two torsion bars52. The inner frame60and the mirror20are connected via two torsion bars62. The outer frame50, the torsion bars52, the inner frame60, the torsion bars62, and the mirror20are integrally constructed by, for example, microfabrication of a semiconductor wafer, and the actuator10is a MEMS actuator. In the present embodiment, the electromagnet30is positioned entirely on one side of the structural body12including the outer frame50, the torsion bars52, the inner frame60, the torsion bars62and the mirror20.

For example, the outer frame50is fixed with respect to the housing (not shown) of the actuator10. The inner frame60is capable of oscillating about the first axis201as the oscillation axis with respect to the outer frame50. Two torsion bars52coincide with the first axis201. That is, the two torsion bars52overlap along the first axis201, and as the torsion bars52twist, the inner frame60oscillates with respect to the outer frame50. Also, the mirror20is capable of oscillating about the second axis202as the oscillation axis with respect to the inner frame60. Two torsion bars62coincide with the second axis202. That is, the two torsion bars62overlap along the second axis202, and as the torsion bars62twist, the mirror20oscillates with respect to the inner frame60. In the reference state described above, the torsion bars52and the torsion bars62are not twisted, and one surface of the outer frame50, the inner frame60, and the mirror20are positioned on the same plane as the reference plane101.

Driving of the actuator10by the electromagnet30will now be described with reference toFIGS.1to3,5and6. First, driving about the first axis201as the oscillation axis will be described. When current flows through the coil32of the electromagnet30, a magnetic flux is generated between the end portion341and the end portion342. At this time, the end portion341and the end portion342are opposite poles to each other. Then, the orientation of the mirror20changes so that the permanent magnet21is directed toward an end portion side that is of opposite polarity to the second pole212, of the end portion341and the end portion342. For example, when the current I1flows through the coil32of the electromagnet30as shown inFIG.5, which will be described later, the orientation of the mirror20changes each time the polarity of the current switches from positive to negative or from negative to positive. Next, driving about the second axis202as the oscillation axis will be described. When current flows through the coil32of the electromagnet30, the electromagnet30pulls the permanent magnet21into the gap340side, and the torsion bars62along the second axis202are twisted. Since the twisted torsion bars try to return to their original state, the permanent magnet21moves away from the gap340when the magnitude of the current flowing through the coil32decreases. For example, when the current I2is flowed through the coil32of the electromagnet30at the resonance frequency of the mirror20as shown inFIG.6, which will be described later, the mirror20oscillates at the resonance frequency together with the permanent magnet21. Therefore, the orientation of the reflecting surface22of the mirror20can be controlled by changing the polarity and magnitude of the current flowing through the coil32.

In the actuator10according to the present embodiment, the end portion341and the end portion342have end surfaces perpendicular to the second axis202. The end portion341and the end portion342of the yoke34face each other in a direction parallel to the second axis202(y-axis direction). By doing so, it is possible to reduce crosstalk between the oscillating with respect to the first axis201and the oscillating with respect to the second axis202. However, the yoke34may be arranged such that both ends obliquely face each other with respect to the second axis202. Also, the end portion341and the end portion342may have end surfaces perpendicular to the first axis201. The end portion341and the end portion342of the yoke34may face each other in a direction parallel to the first axis201(x-axis direction). The yoke34may be arranged such that both ends obliquely face each other with respect to the first axis201.

In a case where the end portion341and the end portion342of the yoke34face each other in a direction parallel to the second axis202(y-axis direction), the torque that can be generated for driving about the second axis202as the oscillation axis is smaller than the torque that can be generated for driving about the first axis201as the oscillation axis. In contrast, in the present embodiment, the mirror20is driven to oscillate at the resonance frequency with respect to the second axis202. Therefore, it is possible to sufficiently oscillate the mirror20even with a relatively small driving torque.

Further, in the actuator10according to the present embodiment, as described above, the center Cg of the gap340does not overlap the center Cm of the permanent magnet21when viewed from a direction (z-axis direction) perpendicular to the reference plane101. Specifically, when viewed from a direction perpendicular to the reference plane101, the center of the gap340is deviated from the center of the permanent magnet21in the direction parallel to the first axis201(x-axis direction). By doing so, it is possible to increase the torque for causing the mirror20to oscillate about the second axis202as the oscillation axis. On the other hand, the center of the gap340is not deviated from the center of the permanent magnet21in the direction perpendicular to the first axis201(y-axis direction). By doing so, it is possible to reduce crosstalk between the oscillating with respect to the first axis201and the oscillating with respect to the second axis202. However, the gap340may be deviated from the center of the permanent magnet21in an oblique direction with respect to the first axis201or may be deviated from the center of the permanent magnet21in an oblique direction with respect to the second axis202.

The actuator10further includes a control unit70. The control unit70generates a signal in which the current I1for causing the mirror20to oscillate with respect to the first axis201and the current I2for causing the mirror20to oscillate with respect to the second axis202are superimposed. The control unit70is configured by including, for example, a driving circuit72and an integrated circuit40.

FIG.4is a diagram illustrating a hardware configuration of the control unit70. In this figure, the control unit70is implemented using the integrated circuit40. The integrated circuit40is, for example, a system on chip (SoC). The control unit70is configured by including an integrated circuit40and a driving circuit72.

The integrated circuit40includes a bus402, a processor404, a memory406, a storage device408, an input and output interface410, and a network interface412. The bus402is a data transmission line for the processor404, the memory406, the storage device408, the input and output interface410, and the network interface412to transmit and receive data to and from each other. A method of connecting the processor404and the like to each other is not limited to the bus connection. The processor404is an arithmetic processing unit realized using a microprocessor or the like. The memory406is a memory realized using a random access memory (RAM) or the like. The storage device408is a storage device realized using a read only memory (ROM), a flash memory, or the like.

The input and output interface410is an interface for connecting the integrated circuit40to peripheral devices. In the present figure, at least the driving circuit72is connected to the input and output interface410.

The network interface412is an interface for connecting the integrated circuit40to a communication network. Such a communication network is, for example, a controller area network (CAN) communication network. A method of connecting the network interface412to the communication network may be a wireless connection or a wired connection.

The storage device408stores program modules for realizing the functions of the control unit70. The processor404realizes the function of the control unit70by reading this program module into the memory406and executing the program module.

The hardware configuration of the integrated circuit40is not limited to the configuration shown in the present figure. For example, the program module may be stored in the memory406. In this case, the integrated circuit40may not include the storage device408.

FIG.5is a graph illustrating a waveform of the current I1for causing the mirror20to oscillate with respect to the first axis201.FIG.6is a graph illustrating a waveform of the current I2for causing the mirror20to oscillate with respect to the second axis202.FIG.7is a graph illustrating a waveform of the current (I1+I2) obtained by superimposing the current for causing the mirror20to oscillate with respect to the first axis201and the current for causing the mirror20to oscillate with respect to the second axis202.

The current I1for causing the mirror20to oscillate with respect to the first axis201is, for example, a sawtooth wave or a triangular wave. The current I2for causing the mirror20to oscillate with respect to the second axis202is, for example, a sine wave. As described above, the mirror20is driven to oscillate at the resonance frequency with respect to the second axis202. The control unit70generates the driving current (I1+I2), in which the current I1and the current I2are superimposed, and the driving current is flowed from the control unit70to the coil32. By using the driving current as shown inFIG.7, the mirror20can be driven so that the light reflected by the reflecting surface22performs raster scanning. However, the waveforms of the current I1and the current I2are not limited to the examples shown inFIGS.5and6.

As described above, according to the present embodiment, the center Cg of the gap340does not overlap the center Cm of the permanent magnet21when viewed from a direction perpendicular to the reference plane101. Therefore, it is possible to realize the driving of the mirror20with respect to the first axis201and the driving of the mirror with respect to the second axis202using the same electromagnet30. As a result, it is possible to miniaturize the actuator10.

EXAMPLES

FIG.8is a graph showing a result of simulating the relationship between the position of the electromagnet30and the generated torque. In the structure shown inFIGS.1to3, the simulation was performed by changing the distance between the permanent magnet21and the yoke34to a plurality of values (the unit inFIG.8is mm) in the z direction. The horizontal axis of the graph is the distance (offset) between the center Cg of the gap340and the center Cm of the permanent magnet21as seen from the z-axis direction. The vertical axis of the graph is the magnitude of the torque generated by the electromagnet30that oscillates the mirror20with respect to the second axis202.

As shown in the present figure, in a case where there is no offset of the center Cg with respect to the center Cm, the torque was almost 0 regardless of the distance between the permanent magnet21and the yoke34. On the other hand, as the offset increased, the torque gradually increased and peaked at an offset of 2.5 mm.

FIG.9is a graph showing a result of measuring the relationship between the position of the electromagnet30and the amplitude of the mirror. In the structure shown inFIGS.1to3, the mirror20was oscillated with respect to the second axis202and the oscillation amplitude was measured. The measurements were performed for a plurality of offset values, and the driving signal was the same sine wave. When the offset was 2.5 mm, as shown in the present figure, it was possible to oscillate the mirror by nearly 60° in terms of optical oscillation angle.

As above, the embodiment and the examples are described with reference to the drawings, but these are examples of the present invention, and various other configurations other than the embodiment and the examples described above can be adopted.

This application claims priority based on Japanese Patent Application No. 2021-032420 filed on Mar. 2, 2021, the entire disclosure of which is incorporated herein by reference.

REFERENCE SIGNS LIST