JP2011030414A - Ultrasonic motor and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an ultrasonic motor capable of releasing fixation of a stator and a rotor without giving any unnecessary load to the motor. <P>SOLUTION: An AC voltage represented by V<SB>0</SB>cos(ωt) is applied to a second vibration member 320 when an AC power supply 42 is directly connected to a second application electrode by a switch 25, under the condition of the AC power supply 42 energized at the voltage level of V<SB>0</SB>cos(ωt). In this case, an amplitude At obtained by adding the amplitude Aa at the (A) region of a piezoelectric material 19 and the amplitude Ab at the (B) region is expressed as follows: At=(√2)A<SB>0</SB>sin(2πx/λ+π/4)cos(ωt). This equation shows a standing wave with the amplitude of (√2)A<SB>0</SB>. Consequently, when the AC power supply 42 is directly connected to the second application electrode 24 by the switch 25, the piezoelectric material 19 is vibrated with √2 times higher amplitude than the case that the AC power supply 42 is connected to a phase shifter 41 by the switch 25. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an annular ultrasonic motor that generates a rotational force using a traveling wave formed by ultrasonic vibration, and more particularly to control of an ultrasonic motor.

  2. Description of the Related Art Conventionally, an ultrasonic motor including an annular stator and an annular rotor that is pressure-bonded so as to be rotatable in the axial direction of the stator is known. The stator generates a traveling wave when a voltage is applied thereto, and the rotor is rotated by the traveling wave.

  For example, when the ultrasonic motor is not operated for a long period of time, the stator and the rotor may be fixed and the rotor may not rotate. In order to release the sticking, a method is known in which the voltage applied to the stator is temporarily increased to increase the amplitude of the traveling wave (Patent Document 1).

JP-A-4-42785

  However, the voltage applied to the stator is close to the upper limit of the voltage supply circuit, and temporarily increasing the voltage increases the load on the voltage supply circuit and shortens the life of the ultrasonic motor.

  The present invention has been made in view of this problem, and an object of the present invention is to obtain an ultrasonic motor and an ultrasonic motor control method capable of releasing the fixation between the stator and the rotor without applying an extra load to the ultrasonic motor. And

  An ultrasonic motor according to a first invention of the present application includes a stator that generates traveling waves by simultaneously applying a plurality of voltages having different phases, and a rotor that rotates by the traveling waves generated by the stator, and has the same phase for a predetermined period. A standing wave is generated in the stator by simultaneously applying a plurality of voltages having the above to the stator.

  The ultrasonic motor preferably generates a standing wave in the stator by simultaneously applying a plurality of voltages having the same phase to the stator for a predetermined period after activation.

  The ultrasonic motor further includes a detection member that detects the rotation of the rotor. When the detection member detects that the rotor is not rotating, a plurality of voltages having the same phase are simultaneously applied to the stator for a predetermined period. A standing wave may be generated.

  The stator includes a first vibration member that vibrates at a predetermined wavelength, and a second vibration member that is provided separately from the first vibration member and vibrates at a predetermined wavelength. The first vibration member and the second vibration member The ultrasonic vibration member forms a ring, and the ultrasonic motor applies a first and a second voltage having the same phase to the first and second vibration members at the same time for a predetermined period, respectively, to the standing wave on the stator. Is preferably generated.

  The stator includes a first vibration member that vibrates at a predetermined wavelength, and a second vibration member that is provided separately from the first vibration member and vibrates at a predetermined wavelength. The first vibration member and the second vibration member The vibration member may form a ring, and the ultrasonic motor may apply a first voltage and a second voltage having different phases to the first vibration member and the second vibration member, respectively, to generate a traveling wave in the stator. .

  An ultrasonic motor control method according to a second invention of the present application is an ultrasonic motor control method including a stator that generates a traveling wave and a rotor that is rotatable by the traveling wave generated by the stator, and generates the traveling wave in the stator. A step of detecting rotation of the rotor due to traveling waves, and a step of simultaneously applying a plurality of voltages having the same phase to the stator when it is detected that the rotor is not rotating.

  An ultrasonic motor control method according to a third invention of the present application is an ultrasonic motor control method including a stator that generates a traveling wave and a rotor that can be rotated by the traveling wave generated by the stator. And a step of simultaneously applying a plurality of voltages having the same phase to the stator for a predetermined period from the time of activation.

  As described above, according to the present invention, an ultrasonic motor and an ultrasonic motor control method capable of releasing the fixation between the stator and the rotor without applying an extra load to the ultrasonic motor are obtained.

1 is an exploded perspective view of an ultrasonic motor according to a first embodiment. It is the block diagram which showed the connection state of an electrode plate and a peripheral circuit. It is the rear view which looked at the electrode plate from the base. It is a flowchart which shows sticking release processing.

  An ultrasonic motor 10 according to an embodiment of the present invention will be described with reference to FIGS.

  The ultrasonic motor 10 is mainly composed of an output shaft 11, a locking plate 12, a pressure spring 13, a rotor 14, a stator 15, and a base 17.

  The output shaft 11 is disposed on the rotational axis X of the ultrasonic motor 10 and transmits the rotational force of the ultrasonic motor 10 to the outside.

  The base 17 is attached to an external fixing member, and supports the output shaft 11 via a bearing (not shown) so that the output shaft 11 is rotatable with respect to the fixing member.

  The stator 15 has a disk shape and has a cylindrical hole coaxial with the central axis of the disk. The diameter of the cylindrical hole is larger than the diameter of the output shaft 11, and the stator 15 does not contact the output shaft 11. The stator 15 is fixed to the base 17 so that the center axis is coaxial with the rotation axis X of the ultrasonic motor 10.

  The locking plate 12, the pressure spring 13, and the rotor 14 have a disk shape. Each of these has a cylindrical hole coaxial with the central axis of the disk, and the central axis is provided on the rotation axis X. The locking plate 12 and the pressure spring 13 are fixed to the output shaft 11 that fits into the cylindrical holes. The rotor 14 is freely movable in the axial direction when the cylindrical hole is loosely fitted to the output shaft 11. Hereinafter, in the rotation axis X, the direction from the base 17 toward the locking plate 12 will be described as a positive direction.

  The rotor 14 and the pressure spring 13 have elasticity with respect to the rotation axis X direction. The locking plate 12 presses the rotor and the pressure spring 13 against the stator 15 with a predetermined force. The pressure spring 13 keeps the force with which the rotor 14 is pressed against the stator 15 constant.

  The stator 15 includes an elastic member 16 that is an elastic body, a piezoelectric body 19 that is a vibration member, and an electrode plate 20 that includes a flexible printed circuit board. The piezoelectric body 19 is made of a ceramic that deforms when a voltage is applied.

  The elastic member 16 is a substantially cylindrical annular body having an axis coinciding with the rotation axis X, and has conductivity. The elastic member 16 includes comb teeth 16a that are divided into 24 pieces at equal intervals in the circumferential direction. The comb teeth 16a protrude in the positive direction of the rotation axis X, and can freely vibrate in the positive and negative directions of the rotation axis X and in the circumferential direction. The top surfaces of the comb teeth 16 a are in contact with the rotor 14. The elastic member 16 has a sticking surface 27 perpendicular to the rotation axis X on the back surface of the surface from which the comb teeth 16a protrude.

  The piezoelectric body 19 is a disc-shaped annular body having an axis that coincides with the rotation axis X, and the axial length is shorter than the radial length. In addition, the piezoelectric body 19 is sandwiched between the elastic member 16 and the electrode plate 20 in the direction of the rotation axis X, and is bonded to the bonding surface 27 with an adhesive. The adhesive is preferably a resin adhesive, such as an epoxy adhesive or an acrylic adhesive. As a result, the entire surface of the piezoelectric body 19 is in close contact with the sticking surface 27.

  The electrode plate 20 has a thin disk shape and includes a hole portion 26 concentric with the disk at the center. In the electrode plate 20, a first application electrode 21, a second application electrode 24, and a ground electrode 22 are provided on the surface in contact with the piezoelectric body 19 and the elastic member 16. The first application electrode 21 is provided over substantially a half circumference of the disk, and the second application electrode 24 is provided over the other half circumference of the disk. The first application electrode 21 and the second application electrode 24 each have a portion extending to the outer periphery of the electrode plate 20. A ground electrode 22 is provided on the entire circumference of the hole 26. The ground electrode 22 has a portion extending from the hole 26 to the outer periphery of the electrode plate 20. A voltage is applied through a portion extending to the outer periphery of these electrode plates 20.

  The first application electrode 21 is directly connected to the AC power source 42. The second application electrode 24 is connected to the AC power source 42 via the phase shifter 41. The ground electrode 22 is grounded. The phase shifter 41 applies an AC voltage with the phase of the AC power supply 42 shifted by π / 2 to the second application electrode 24. The external detection device 44 is provided outside the ultrasonic motor 10, detects the rotational speed of the ultrasonic motor 10, and transmits it to the input control circuit 43. The input control circuit 43 controls the voltage and drive frequency of the AC power supply 42 according to the rotation speed transmitted from the external detection device 44. The AC voltage applied to the ground electrode 22 and the electrode plate 20 is 400 V, and the frequency is 60 kHz.

  The piezoelectric body 19 will be described with reference to FIG. FIG. 2 shows the piezoelectric body 19 viewed from the elastic member 16 side. The + and − shown in the figure are described for explanation, and do not indicate the characteristics of the charge applied to the electrode. In addition, although the power line is directly connected to the piezoelectric body 19 for the sake of explanation, the power line is actually connected to the first application electrode 21 and the second application electrode 24.

  The piezoelectric body 19 includes first to fifth A piezoelectric bodies 311, 313, 315, 323, and 325, and first to fifth B piezoelectric bodies 312, 314, 322, 324, and 326. When an AC voltage is applied to the first to fifth A piezoelectric bodies 311 to 325 and the first to fifth B piezoelectric bodies 312 to 326, the first to fifth A piezoelectric bodies 311 to 325 are rotated in the X direction. The first to fifth B piezoelectric bodies 312 to 326 repeat contraction and expansion in the length with respect to the rotation axis X direction.

  The first to third A piezoelectric bodies 311, 313, 315 and the first and second B piezoelectric bodies 312, 314 form a first region 310 that is a first vibrating member, and the fourth, fifth, The A piezoelectric bodies 323 and 325 and the third to fifth B piezoelectric bodies 322, 324 and 326 form a second region 320 which is a second vibration member. A neutral region 30 is provided between the first region 310 and the second region 320. No voltage is applied to the neutral region 30.

  The first application electrode 21 is attached to the first region 310, and the second application electrode 24 is attached to the second region 320. The piezoelectric body 19 and the ground electrode 22 are in contact with the back surface of the surface to which the first application electrode 21 and the second application electrode 24 are attached via the elastic member 16. Thereby, the piezoelectric body 19 is grounded. When a voltage is applied to the piezoelectric body 19, the first region 310 and the second region 320 are displaced in the direction of the rotation axis X, but the second region 320 is π / 2 with respect to the first region 310. It is displaced in the direction of the rotation axis X with a shifted phase.

  Next, the operation of the ultrasonic motor 10 will be described.

  An AC voltage is applied to the electrode plate 20, that is, the first to fifth A piezoelectric bodies 311, 313, 315, 323, 325 and the first to fifth B piezoelectric bodies 312, 314, 322, 324, 326. Then, the first region 310 and the second region 320 of the piezoelectric body 19 vibrate at a predetermined cycle according to the applied voltage. Due to this vibration, the elastic member 16 vibrates in the rotation axis direction and the circumferential direction, and a traveling wave having a wavelength λ is generated on the top surface of the elastic member 16. The rotor 14 pressed against the elastic member 16 by the pressure spring 13 is rotated by this traveling wave. The rotational force by the rotor 14 is transmitted to the outside through the output shaft 11. The shift of π / 2 between the second region 320 and the first region 310 corresponds to ¼ of the wavelength λ of the traveling wave, that is, λ / 4. The lengths in the circumferential direction of the first to fifth A piezoelectric bodies 311, 313, 315, 323, 325 and the first to fifth B piezoelectric bodies 312, 314, 322, 324, 326 are the traveling wave lengths. This corresponds to 1/2 of the wavelength λ, that is, λ / 2.

When the AC power source 42 is an AC voltage generated by V ₀ cos (ωt), when the AC power source 42 is connected to the phase shifter 41 by the switch 25, the second region 320 has V ₀ cos ((ω−π / 2). ) AC voltage from t) is applied.

At this time, the amplitude Aa in the first region 310 and the amplitude Ab in the second region 320 of the piezoelectric body 19 are based on the following equations.
Aa = A ₀ sin (2πx / λ) cos (ωt)
Ab = A ₀ sin (2π (x−λ / 4)) sin (ωt) = A ₀ cos (2πx / λ) sin (ωt)
Here, x is a coordinate having a predetermined point as the origin in the circumferential direction of the piezoelectric body 19.

The amplitude At obtained by adding the amplitude Aa in the first region 310 and the amplitude Ab in the second region 320 is expressed by the following equation.
At = Aa + Ab = A ₀ sin (2πx / λ + ωt)
Since this equation indicates that a traveling wave having an amplitude of A ₀ is generated in the stator 15, it can be seen that the rotor 14 rotates in accordance with this equation.

On the other hand, when the AC power supply 42 is an AC voltage by _V 0 cos _(ωt), the AC power supply 42 by the switch 25 is connected directly to the second application electrode 24, the second region 320 _V 0 cos (ωt ) Is applied.

At this time, the amplitude Aa in the first region 310 and the amplitude Ab in the second region 320 of the piezoelectric body 19 are based on the following equations.
Aa = A ₀ sin (2πx / λ) cos (ωt)
Ab = A ₀ sin (2πx / λ) cos (ωt)
Here, x is a coordinate having a predetermined point as the origin in the circumferential direction of the piezoelectric body 19.

The amplitude At obtained by adding the amplitude Aa in the A region and the amplitude Ab in the B region is expressed by the following equation.
At = Aa + Ab = (√2) A ₀ sin (2πx / λ + π / 4) cos (ωt)
This equation shows a standing wave with an amplitude of (√2) A ₀ .

  Therefore, when the AC power source 42 is directly connected to the second application electrode 24 by the switch 25, the amplitude is (√2) times that when the AC power source 42 is connected to the phase shifter 41 by the switch 25. It can be seen that the piezoelectric body 19 vibrates.

  Next, the sticking release process will be described with reference to FIG. The sticking release process is executed when the ultrasonic motor 10 is activated.

  In step S31, it is determined whether or not the external detector 44 has detected the rotation of the ultrasonic motor 10, that is, the rotor 14. When rotation is not detected, the process proceeds to step S32. When rotation is detected, the process ends.

In step S32, the switch 25 is connected to the electrode side terminal 25a for a predetermined period, for example, zero comma several seconds, and the AC power source 42 is directly connected to the first application electrode 21 and the second application electrode 24. As a result, a standing wave having an amplitude of (√2) A ₀ is generated in the A region and the B region, and the fixation between the rotor 14 and the stator 15 is released.

  According to the present embodiment, a standing wave having a larger amplitude than the traveling wave can be generated in the stator 15, thereby generating a larger force between the rotor 14 and the stator 15 than the traveling wave. Can be made. Therefore, the pressure applied by the pressure spring 13 between the rotor 14 and the stator 15 can be temporarily relaxed, and the adhesion between the rotor 14 and the stator 15 can be released.

  The switch 25 is not connected to the electrode-side terminal 25a when the rotation of the rotor 14 is not detected at the start-up, but the switch 25 is connected to the electrode-side terminal 25a for a predetermined period or at the start-up of the rotor 14 The connection may be made until rotation is detected.

The AC voltage generated by the AC power supply 42 is not limited to V ₀ cos (ωt).

  The number of the comb teeth 16a is not limited to 24, and any value can be adopted according to the required performance for the ultrasonic motor 10.

  Further, the applied AC voltage and frequency are not limited to 400 V and 60 kHz.

DESCRIPTION OF SYMBOLS 10 Ultrasonic motor 11 Output shaft 12 Locking plate 13 Pressure spring 14 Rotor 15 Stator 16 Elastic member 16a Comb 17 Base 19 Piezoelectric body 20 Electrode plate 21 First application electrode 22 Ground electrode 24 Second application electrode 25 Switch 25a Electrode side terminal 25b Phase shifter side terminal 26 Hole 27 Sticking surface 30 Neutral region 41 Phase shifter 42 AC power supply 43 Input control circuit 44 External detection device 310 First region 320 Second region X Rotating shaft

Claims (7)

A stator in which traveling voltages are generated by simultaneously applying a plurality of voltages having different phases;
A rotor that rotates by traveling waves generated by the stator,
An ultrasonic motor that generates a standing wave in the stator by simultaneously applying a plurality of voltages having the same phase to the stator for a predetermined period.   2. The ultrasonic motor according to claim 1, wherein a plurality of voltages having the same phase are simultaneously applied to the stator for a predetermined period from the start to generate a standing wave in the stator. A detection member for detecting rotation of the rotor;
2. The standing wave is generated in the stator by simultaneously applying a plurality of voltages having the same phase to the stator for a predetermined period when the detection member detects that the rotor is not rotating. Ultrasonic motor. The stator includes a first vibrating member that vibrates at a predetermined wavelength, and a second vibrating member that is provided separately from the first vibrating member and vibrates at the predetermined wavelength,
The first vibrating member and the second vibrating member form a ring;
4. The superstructure according to claim 1, wherein a first wave and a second voltage having the same phase are simultaneously applied to the first and second vibrating members for a predetermined period to generate a standing wave in the stator. 5. Sonic motor. The stator includes a first vibrating member that vibrates at a predetermined wavelength, and a second vibrating member that is provided separately from the first vibrating member and vibrates at the predetermined wavelength,
The first vibrating member and the second vibrating member form a ring;
4. The ultrasonic motor according to claim 1, wherein first and second voltages having different phases are simultaneously applied to the first and second vibrating members to generate traveling waves in the stator. 5. An ultrasonic motor control method comprising a stator that generates a traveling wave and a rotor that is rotatable by the traveling wave generated by the stator,
Generating a traveling wave in the stator;
Detecting rotation of the rotor due to the traveling wave;
And a step of simultaneously applying a plurality of voltages having the same phase to the stator when it is detected that the rotor is not rotating. An ultrasonic motor control method comprising a stator that generates a traveling wave and a rotor that is rotatable by the traveling wave generated by the stator,
Detecting rotation of the rotor at start-up;
Applying a plurality of voltages having the same phase to the stator at the same time for a predetermined period from startup.

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