JP2019161901A - Ultrasonic actuator - Google Patents

Abstract

To realize an ultrasonic actuator with high power weight ratio.SOLUTION: An ultrasonic actuator (100) includes: a rotor (110) having a curved surface at least partially; and at least a pair of ultrasonic transducers (120) disposed with the rotor (110) interposed therebetween at positions of mutually symmetric points with a center of the rotor (110) as a symmetry point. Each of the plurality of ultrasonic transducers (120) has a tip portion in contact with the curved surface.SELECTED DRAWING: Figure 1

Description

  The following disclosure relates to ultrasonic actuators.

  In recent years, ultrasonic actuators that combine a spherical driven body and a piezoelectric element that drives the driven body with multiple degrees of freedom have been put into practical use because it is suitable for realizing movements of robot joints and the like. Expected. Conventionally, in such an ultrasonic actuator, in order to reduce the sliding resistance of the member supporting the driven body with respect to the driven body, the spherical rotor is held by combining a plurality of ring type ultrasonic transducers that generate traveling waves. It is driven (see, for example, Patent Document 1).

JP 2010-166722 A (released July 29, 2010)

  However, in the conventional technology as described above, the vibration generated in each of the plurality of ring-type ultrasonic transducers becomes a frictional resistance against the rotation of the spherical rotor, thereby reducing the efficiency of the actuator and increasing the number of components and increasing the mass. Was. Therefore, the ultrasonic actuator has a problem that the power-to-weight ratio, which is the ratio of output to mass, is low.

  An object of one embodiment of the present disclosure is to realize an ultrasonic actuator having a high power way ratio.

  In order to solve the above-described problem, an ultrasonic actuator according to an aspect of the present disclosure includes a rotor having a curved surface at least in part and a position that is point-symmetric with respect to the center of the rotor. And at least one pair of ultrasonic transducers arranged with the rotor interposed therebetween, and each of the plurality of ultrasonic transducers has a configuration in which a tip portion thereof is in contact with the curved surface.

  According to one aspect of the present disclosure, an ultrasonic actuator having a high power way ratio can be realized.

1 is a diagram illustrating a schematic configuration of an ultrasonic actuator according to Embodiment 1. FIG. It is a disassembled perspective view of an ultrasonic transducer | vibrator. (A)-(d) is the figure which showed the drive aspect of the ultrasonic transducer | vibrator, respectively. (A)-(d) is a figure which shows the rotation direction of the rotor by the vibration of an ultrasonic transducer | vibrator, respectively. It is a figure which shows another example of the vibration direction of an ultrasonic transducer | vibrator, and the rotation direction of a rotor. It is a figure which shows another example of the vibration direction of an ultrasonic transducer | vibrator, and the rotation direction of a rotor. It is a figure which shows the practical example of an ultrasonic actuator. 6 is a diagram illustrating a schematic configuration of an ultrasonic actuator according to a second embodiment. FIG. (A)-(c) is a figure which shows the rotational operation of a rotor, respectively.

Embodiment 1
Hereinafter, the first embodiment will be described in detail. FIG. 1 is a diagram illustrating a schematic configuration of an ultrasonic actuator 100 according to the first embodiment. As shown in FIG. 1, the ultrasonic actuator 100 includes a rotor 110 and a pair of ultrasonic transducers 120 (120A, 120B). The ultrasonic actuator 100 includes a preload mechanism 130. However, the application of the preload may be performed by another component such as a structure or the like, and does not need to be handled by an independent component.

  The rotor 110 is configured to have a curved surface at least partially. In the first embodiment, the rotor 110 is a sphere, and the surface of the sphere forms the curved surface. Although details will be described later, the rotor 110 is held freely rotatable by at least one pair of ultrasonic transducers 120.

  The two ultrasonic transducers 120 forming a pair are arranged with the rotor 110 interposed therebetween at positions that are symmetric with respect to the center of the rotor 110 that is a sphere. In addition, each of the plurality of ultrasonic transducers 120 has a tip portion 124 in contact with the surface of the rotor 110.

  The preload mechanism 130 is configured as a part of a housing (not shown) of the ultrasonic actuator 100. The preload mechanism 130 is configured to apply preload between the pair of ultrasonic transducers 120 in a direction in which the mutual distance decreases. In the configuration in which the ultrasonic actuator 100 includes a plurality of pairs of ultrasonic transducers 120, the preload mechanism 130 is configured so that preload can be applied in a direction in which the mutual distance between the ultrasonic transducers 120 is reduced. It is desirable that

[Configuration of the ultrasonic transducer 120]
FIG. 2 is an exploded perspective view of the pair of ultrasonic transducers 120. As shown in FIG. 2, the ultrasonic transducer 120 has a vibrating body 121. The vibrating body 121 is made of a metal such as stainless steel and has a ground potential. The vibrating body 121 is a hollow prism-shaped member, and piezoelectric elements 125 to 128 are provided on each of the four side surfaces of the vibrating body 121. In addition, the vibrating body 121 is covered with piezoelectric elements 125 to 128 on all four side surfaces.

  The piezoelectric elements 125 to 128 are plate-like elements having a property of causing a stress change when a voltage is applied, and are fixed to each side surface of the vibrating body 121. The piezoelectric elements 125 to 128 can be formed of a material such as ceramics or quartz, for example.

  A tip portion 124 of the ultrasonic transducer 120 facing the rotor 110 is formed separately from the vibrating body 121 and is attached to the tip of the vibrating body 121. The front end portion 124 can be formed in, for example, a truncated cone shape, and the surface on the side in contact with the rotor 110 has a concave shape corresponding to the curved surface of the rotor 110.

  In the ultrasonic actuator 100, at least one pair of ultrasonic transducers 120 disposed with the rotor 110 sandwiched between the tip portion 124 having a concave shape corresponding to the curved surface of the rotor 110 in contact with the curved surface of the rotor 110. Thus, the rotor 110 is held. Thereby, it can be set as the structure where the spherical rotor 110 is hard to remove | deviate from the ultrasonic transducer | vibrator 120 holding the rotor 110. FIG. Therefore, the rotor 110 can be freely rotated and stably held by a pair of ultrasonic transducers 120 arranged with the rotor 110 in between, with the center of the rotor 110 as a symmetric point, with the rotor 110 interposed therebetween. can do.

  On the rear end side of the vibrating body 121 opposite to the front end side, a holding post 123 is provided in a state of being inserted into the hollow portion of the vibrating body 121 and fitted into the hollow portion. The holding post 123 is a rod-like member, and includes a structure for preventing the vibrating body 121 from rotating with respect to the holding post 123, for example, a key groove. Although not shown, the holding post 123 is held by the casing of the ultrasonic actuator 100, and preload by the preload mechanism 130 to the ultrasonic transducer 120 is applied via the holding post 123.

  In the first embodiment, the pair of ultrasonic transducers 120 are arranged in a point-symmetrical position with respect to the center of the rotor 110, that is, on a straight line that is mirror-symmetric with respect to the rotor 110. For this reason, the preload mechanism 130 may be configured to sandwich the holding posts 123 of the pair of ultrasonic transducers 120, and the structure can be simplified.

  FIGS. 3A to 3D are views showing driving modes of the ultrasonic transducer 120, respectively. FIG. 3A shows the configuration of the piezoelectric elements 125 to 128 of the ultrasonic transducer 120. As shown to (a) of FIG. 3, the piezoelectric elements 125-128 have plate-shaped upper electrode 125A-128A and lower electrode 125B-128B, respectively. The upper electrodes 125A to 128A are provided to cover the upper half of the piezoelectric elements 125 to 128, and the lower electrodes 125B to 128B are provided to cover the lower half of the piezoelectric elements 125 to 128.

  The upper electrodes 125 </ b> A to 128 </ b> A and the lower electrodes 125 </ b> B to 128 </ b> B are connected to each other diagonally across the vibrating body 121 and are at the same potential. Further, in each of the piezoelectric elements 125 to 128, the upper electrodes 125A to 128A and the lower electrodes 125B to 128B arranged vertically are configured not to be electrically connected to each other.

  The ultrasonic transducer | vibrator 120 expands-contracts the part corresponding to this electrode in the piezoelectric elements 125-128 by supplying a voltage to the upper electrodes 125A-128A or the lower electrodes 125B-128B. Thereby, the vibrating body 121 vibrates.

  Driving signals common to the lower electrodes of the opposing piezoelectric elements 125 to 128 are supplied to the upper electrodes 125A to 128A of the piezoelectric elements 125 to 128. For example, the common alternating voltage Va is supplied to the upper electrode 125A of the piezoelectric element 125 and the lower electrode 127B of the piezoelectric element 127. A portion corresponding to the upper electrode 125A of the piezoelectric element 125 is deformed (stretched) according to the applied voltage Va.

  A common alternating voltage Vb is supplied to the lower electrode 125B of the piezoelectric element 125 and the upper electrode 127A of the piezoelectric element 127. A portion corresponding to the lower electrode 125B of the piezoelectric element 125 is deformed (expanded) according to the applied voltage Vb.

  FIG. 3B is a diagram illustrating temporal changes of the alternating voltages Va and Vb and the ultrasonic transducer 120. The upper side of FIG. 3B shows the state of the ultrasonic transducer 120 corresponding to each of the periods I to IV. In FIG. 3B, (+) and (−) in the piezoelectric elements 125 and 127 represent portions corresponding to electrodes to which voltages of each polarity are applied. The ultrasonic vibrator 120 has two natural vibrations: (i) a stretching vibration mode (see (c) of FIG. 3) and (ii) an S-shaped bending vibration mode (see (d) of FIG. 3). Has a mode.

  As shown in FIG. 3B, Va and Vb are alternating voltages whose phases differ by 90 °. When a positive voltage is applied to the piezoelectric elements 125 and 127 (period I), the piezoelectric elements 125 and 127 are extended in the direction along the long axis of the vibrating body 121. When a negative voltage is applied to the piezoelectric elements 125 and 127 (period III), the piezoelectric elements 125 and 127 are compressed in a direction along the long axis of the vibrating body 121. Since the piezoelectric elements 125 and 127 are attached to the vibrating body 121, portions corresponding to the piezoelectric elements 125 and 127 in the vibrating body 121 (portions to which the piezoelectric elements are attached) are similarly expanded / compressed.

  As a result, in the periods I and III in which the two alternating voltages Va and Vb have the same polarity, the stretching vibration mode of the vibrating body 121 shown in FIG. 3C is excited. Further, in periods II and IV in which the two alternating voltages Va and Vb have different polarities, the S-shaped bending vibration mode of the vibrating body 121 shown in FIG. 3D is excited. If the aspect ratio (width: height) of the vibrating body 121 that is a quadrangular column is 1: 4, the resonance frequencies of the stretching vibration mode and the S-shaped bending vibration mode substantially coincide.

  When the stretching vibration mode and the S-shaped bending vibration mode are excited at the same frequency, the vibrating body 121 is deformed as shown in FIG. 3B during one period (periods I to IV). The vibration excited in each vibration mode is standing wave vibration in which the position of the central portion of the long axis of the vibrating body 121 does not change. As a result of the vibration of the vibration part 121 in the periods I to IV, the tip part 124 of the ultrasonic vibrator 120 performs elliptical vibration.

  4A to 4D are diagrams showing the rotation direction of the rotor due to the vibration of the ultrasonic transducer 120, respectively. As shown in FIG. 4A, the tip portion 124 of the ultrasonic transducer 120 is in contact with the surface of the rotor 110 with a preload by the preload mechanism 130. 110 is driven by friction and rotates.

  The ultrasonic transducer 120 includes (i) a first vibration direction (z direction in (b) of FIG. 4) and (ii) a second vibration direction ((c) of FIG. 4 orthogonal to the first vibration direction. ) In the y direction). The x direction is a direction along the major axis of the ultrasonic transducer 120, and the y direction and the z direction are directions orthogonal to the x direction and orthogonal to each other. In (b) to (d) of FIG. 4, the first vibration direction (z direction) is the vibration direction toward the near side (+ z) and the back side (−z) in the figure, and the second vibration direction. (Y direction) is a vibration direction toward the upper side (+ y) and the lower side (−y) in the figure.

  In the first embodiment, a pair of ultrasonic transducers 120 are arranged with the rotor 110 interposed therebetween at positions that are point-symmetric with respect to the center of the rotor 110. For this reason, one ultrasonic transducer | vibrator 120A is vibrated so that the rotor 110 may be friction-driven toward -z direction. Then, the other ultrasonic transducer 120B is vibrated so as to frictionally drive the rotor 110 in the + z direction. As a result, as shown in FIG. 4B, the rotor 110 rotates around the y-axis.

  Also, one ultrasonic transducer 120A is vibrated so as to frictionally drive the rotor 110 in the -y direction. Then, the other ultrasonic transducer 120B is vibrated so as to frictionally drive the rotor 110 in the + y direction. Thereby, as shown in FIG. 4C, the rotor 110 rotates around the z-axis.

  In this way, the pair of ultrasonic transducers 120 is arranged such that the upper electrodes 125A to 128A or the lower electrodes are oscillated in a point-symmetric manner at the contact point of the curved surface with the center of the rotor 110 as the symmetric point. A voltage is applied to the electrodes 125B to 128B. Thereby, the direction of action of the rotational force on the rotor 110 can be matched. In this way, since the pair of ultrasonic transducers 120 performs vibrational movements that do not inhibit each other's movement, each vibration of the ultrasonic transducers 120 is high without causing frictional resistance against the rotation of the rotor 110. Powerway ratio can be obtained.

  In addition, the pair of ultrasonic transducers 120 has a function of holding the rotor 110 as well as giving a rotational force to the rotor 110. Thereby, compared with the structure which hold | maintains the rotor 110 using another piezoelectric element, the frictional resistance by the holding mechanism added to the rotor 110 can be reduced, and a higher power way ratio can be obtained.

  Also, one ultrasonic transducer 120A is vibrated so as to frictionally drive the rotor 110 in the -y direction. Then, the other ultrasonic transducer 120B is vibrated so as to frictionally drive the rotor 110 in the + z direction. As a result, as shown in FIG. 4D, the rotor 110 rotates about a rotation axis inclined 45 ° from the y axis on the xy plane.

  In this way, by combining the vibration direction of the ultrasonic vibrator 120 that vibrates in the first vibration direction and the second vibration direction orthogonal to the first vibration direction, a lot of freedom is provided in the rotation direction of the rotor 110. Can have a degree.

  5 and 6 are diagrams showing another example of the vibration direction of the ultrasonic transducer 120 and the rotation direction of the rotor 110, respectively. As shown in FIGS. 5 and 6, the ultrasonic transducer 120 has a known principle (for example, Journal of the Robotics Society of Japan, vol. 16, no. 8, pp. 1115-1122, 1998 “longitudinal vibration and transverse vibration. Based on the development of a multi-degree-of-freedom ultrasonic motor based on the degeneration of “), it is possible to cause the vibrator 121 to rotate in the major axis direction. For example, the S-shaped bending motion shown in (d) of FIG. 3 is shifted in phase by 90 degrees as shown in (i) to (iv) of FIG. generate. As a result, elliptical vibration is generated at the distal end portion 124 of the vibrating body 121, and the rotor 110 performs a rotational motion with the major axis of the ultrasonic transducer 120 as the rotation axis, as shown in FIG.

  FIG. 7 is a diagram illustrating a practical example of the ultrasonic actuator 100. According to the above-described configuration, the structure of the ultrasonic actuator 100 can be simplified, and the mass can be reduced. Further, the ultrasonic actuator 100 having multiple degrees of freedom in the rotation direction of the rotor 110 can be realized. The ultrasonic actuator 100 having such a high power way tray can be employed in the flying robot 50 as shown in FIG. 7, for example. The flying robot 50 includes a pair of wings 51, a camera 52, and a housing 53. The two wings 51 are driven by two ultrasonic actuators 100, respectively. The camera 52 is a member capable of photographing the periphery of the flying robot 50, and can be configured to be a CMOS camera, for example. Note that the flying robot 50 is not limited to one camera 52, and may have a configuration including a plurality of cameras 52 or a configuration including other members such as speakers. An ultrasonic actuator 100, a battery, a drive circuit, a control circuit, and a communication circuit are accommodated in the housing 52.

[Embodiment 2]
Embodiment 2 will be described below. For convenience of explanation, members having the same functions as those described in the first embodiment are given the same reference numerals, and the description thereof will not be repeated.

  FIG. 8 is a diagram illustrating a schematic configuration of the ultrasonic actuator 200 according to the second embodiment. As shown in FIG. 8, the ultrasonic actuator 200 includes two sets of a pair of ultrasonic transducers 120 arranged with the rotor 110 sandwiched at positions that are symmetric with respect to the center of the rotor 110. I have.

  In addition, the two sets of the pair of the ultrasonic transducers 120 are arranged at positions orthogonal to each other. That is, around the rotor 110, the four ultrasonic transducers 120 are arranged at positions shifted from each other by 90 ° with the center of the rotor 110 as the center point. According to this configuration, one rotor 110 can be sandwiched between the four ultrasonic transducers 120 and stably held and driven, and the power of the ultrasonic actuator 200 can be improved.

  FIGS. 9A to 9C are diagrams showing the rotation operation of the rotor 110 in the ultrasonic actuator 200, respectively. As shown in FIG. 9A, in order to cause the rotor 110 to perform a rotation operation with the z axis as the rotation axis, each ultrasonic vibrator 120 is vibrated so as to rotate the rotor 110 in the corresponding direction. This can be easily realized. In the example shown in FIG. 9A, the rotor 110 rotates counterclockwise when viewed from the + z side with the z axis as the rotation axis.

  In addition, the rotor 110 can be rotated by using the long axis of one of the two sets of the ultrasonic transducers 120 as a rotation axis. FIGS. 9B and 9C respectively show the respective cases in which the rotor 110 rotates with the long axis of the pair of ultrasonic transducers 120C and 120D disposed above and below the rotor 110 as the rotation axis. FIG. 5 is a diagram showing vibration of a sound wave vibrator 120.

  When the rotor 110 is rotated about the long axis of the ultrasonic transducers 120C and 120D as shown in FIGS. 9 (b) and 9 (c), a pair of super The acoustic transducers 120A and 120B frictionally drive the rotor 110 in a direction orthogonal to the rotation axis and in opposite directions.

  In the example shown in FIGS. 9B and 9C, the ultrasonic transducer 120A on the left side in the drawing frictionally drives the rotor 110 in the −z direction, and the ultrasonic transducer 120B on the right side in the drawing is The rotor 110 is frictionally driven in the + z direction.

  As shown in FIG. 9B, the ultrasonic transducers 120 </ b> C and 120 </ b> D on the rotation axis side can be vibrated to reduce friction with the rotor 110. For example, the friction with respect to the rotor 110 can be reduced by applying to the ultrasonic vibrators 120 </ b> C and 120 </ b> D a voltage that excites only the stretching vibration to the vibrating body 121. From the Coulomb friction law, it is considered that the average value of friction due to stretching vibration does not change as long as the preload is constant. However, the stick-slip phenomenon does not occur by exciting the stretching vibration to the vibrating body 121 of the ultrasonic vibrators 120C and 120D on the rotation axis side. For this reason, it is considered that the frictional force is reduced because the transition from the static friction to the dynamic friction with respect to the rotor 110 of the pair of ultrasonic vibrators 120A and 120B on the side not serving as the rotation axis is performed. Further, a clear reduction in frictional force has been observed in the experiments of the inventors of the present application.

  Further, as shown in FIG. 9C, the ultrasonic transducers 120C and 120D on the rotation axis side are vibrated to excite the rotational motion of the rotor 110 at the tip portion 124 of the vibrating body 121. Also good. As described in the first embodiment with reference to FIGS. 5 and 6, the ultrasonic transducers 120 </ b> C and 120 </ b> D excite S-shaped bending motions whose phases are different from each other by 90 ° on each side surface of each vibrating body 121. Thus, it can be vibrated so as to contribute to the rotational motion of the rotor 110. Thereby, the power way ratio of the ultrasonic actuator 200 can be increased.

  One aspect of the present disclosure is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims, and the technical means disclosed in different embodiments can be appropriately combined. Embodiments to be included are also included in the technical scope of the present disclosure. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

100, 200 Ultrasonic actuator 110 Rotor 120, 120A, 120B, 120C, 120D Ultrasonic vibrator 121 Vibrating body 124 Tip portion 125-128 Piezoelectric element 130 Preload mechanism

Claims (6)

A rotor having a curved surface at least in part;
And at least one pair of ultrasonic transducers arranged with the rotor in between, at a position that is point-symmetric with respect to the center of the rotor,
Each of the plurality of ultrasonic transducers has its tip portion in contact with the curved surface. The ultrasonic actuator according to claim 1, wherein the distal end portion has a concave shape corresponding to the curved surface.   3. The ultrasonic actuator according to claim 1, wherein the pair of ultrasonic transducers perform a point-symmetrical movement at a contact point of the curved surface with the center as a symmetric point. 4. The ultrasonic transducer vibrates in a first vibration direction and a second vibration direction orthogonal to the first vibration direction.
The ultrasonic actuator according to any one of claims 1 to 3, wherein:   The ultrasonic actuator according to any one of claims 1 to 4, further comprising a preload mechanism that applies a preload between the pair of ultrasonic transducers in a direction in which a mutual distance is reduced. Two sets of the above-described ultrasonic transducers are provided,
The ultrasonic actuator according to any one of claims 1 to 5, wherein the two sets of the ultrasonic transducers are arranged at positions orthogonal to each other.

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