JP2010028974A - Ultrasonic motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic motor which can suppress wear caused by friction between a vibrator and a driven body during the driving of the ultrasonic motor to attain a stable and low speed driving. <P>SOLUTION: In the ultrasonic motor, a two-phase drive signal is applied to the vibrator to generate an elliptic vibration, and the drive force obtained from the elliptic vibration is applied to friction-drive the driven body. The ultrasonic motor includes a signal generation circuit 25 generating the two-phase drive signal, and a signal control circuit 23 controlling to switch the phase difference between the two-phase drive signals for a plurality of times so as to change the drive state of the ultrasonic motor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultrasonic motor that uses vibration of a vibrator such as a piezoelectric element.

  In recent years, ultrasonic motors using vibrations of vibrators such as piezoelectric elements have attracted attention as new motors that replace electromagnetic motors. Compared with conventional electromagnetic motors, this ultrasonic motor has low speed and high thrust without gears, high holding force, long stroke and high resolution, quietness, magnetic There are advantages such as no noise and no influence of magnetic noise.

  In an ultrasonic motor, an ultrasonic transducer is pressed against a driven member that is a relative motion member via a driving element that is a friction member, so that a frictional force is generated between the driving element and the driven member. The driven member is driven by this frictional force. In addition, since the friction drive is performed in this way, the ultrasonic motor has a problem of wear on the frictional member. Naturally, this wear problem leads to a durability problem of the ultrasonic motor.

  By the way, for example, an ultrasonic motor used for an AF operation of a lens in a camera or the like requires highly accurate position control. More specifically, in an ultrasonic motor used for such position control, stable driving at low speed is desired.

  As a driving method of the ultrasonic motor that realizes low-speed and stable driving in this way, there can be mentioned intermittent driving in which the driving signal of the ultrasonic motor is periodically turned on / off. According to such a conventional driving method, when the ultrasonic motor is operated at a low speed, a burst signal in which both the interval and the width are set constant is used as the driving signal. Therefore, the strong frequency component of the burst signal becomes constant, and annoying noise corresponding to the frequency is generated.

  In view of such circumstances, Patent Document 1 discloses the following technique. That is, Patent Document 1 discloses a moving body that is placed in contact with a drive body composed of an elastic body and a piezoelectric body by applying an AC voltage as a drive signal to excite an elastic traveling wave. A burst signal in which at least one of the width of the burst signal or the interval between burst signals is changed so that the average speed of the movable body is substantially constant as a drive signal to the piezoelectric body. Is applied as a drive signal, and an ultrasonic motor drive method is disclosed.

According to the technique disclosed in Patent Document 1, there is provided an ultrasonic motor driving method capable of reducing unpleasant noise and performing a somewhat stable low speed operation. Specifically, according to the ultrasonic motor driving method disclosed in Patent Document 1, the ultrasonic motor driving body is driven by a burst signal, and at least one of the interval and the width of the driving burst signal is changed. Thus, the strong frequency component of the driving burst signal is dispersed. Thus, by dispersing the frequency of the generated noise, the annoying noise that is generated is reduced and stable low-speed driving is realized.
Japanese Patent Publication No. 7-89748

  As described above, according to the ultrasonic motor driving method disclosed in Patent Document 1, intermittent driving is performed in order to reduce annoying noise and realize stable low-speed driving.

  On the other hand, in driving an ultrasonic motor, a surface (contact surface) related to the friction is easily worn by friction generated between the vibrator and the driven body during driving. Here, in the intermittent driving adopted in the ultrasonic motor driving method disclosed in Patent Document 1, the amplitude of vibration generated in the vibrator changes abruptly when the application of the drive signal is started and when the application is stopped. . For this reason, slip occurs between the vibrator and the driven body, and the contact surface is more easily worn.

  The present invention has been made in view of the above circumstances, and suppresses wear caused by friction between the vibrator and the driven body when the ultrasonic motor is driven, and realizes a stable low-speed drive. The object is to provide a sonic motor.

In order to achieve the above object, an ultrasonic motor according to the first aspect of the present invention comprises:
An ultrasonic motor that applies a two-phase drive signal to a vibrator to generate elliptical vibration in the vibrator, obtains a driving force from the elliptical vibration, and frictionally drives a driven member;
Drive signal generating means for generating the two-phase drive signal;
Phase difference control means for performing control to switch the phase difference between the two-phase drive signals a plurality of times so as to change the drive state of the ultrasonic motor;
It is characterized by comprising.

  ADVANTAGE OF THE INVENTION According to this invention, the ultrasonic motor which suppresses the abrasion which arises by the friction between a vibrator | oscillator and a to-be-driven body at the time of the drive of an ultrasonic motor, and implement | achieves the stable low-speed drive can be provided.

  Hereinafter, an ultrasonic motor according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, for convenience of explanation, the ultrasonic motor and the driving device for driving the ultrasonic motor are regarded as separate devices independent of each other, and the configuration constituted by these devices is an ultrasonic motor. This will be described as a system. However, such a designation is merely a designation for convenience of description, and may be regarded as a single ultrasonic motor including the driving device.

  FIG. 1 is a block diagram showing a schematic configuration example of an ultrasonic motor system.

  As shown in FIG. 1, the ultrasonic motor system 1 includes an ultrasonic motor 2 and a drive device 3 that drives the ultrasonic motor 2. The ultrasonic motor 2 includes an ultrasonic vibrator 4 and a driven body 5 that is driven by the ultrasonic vibrator 4.

  As shown in FIG. 2, the ultrasonic transducer 4 has a rectangular parallelepiped shape formed by laminating a plurality of sheet-like internal electrodes (not shown) provided on one side of a piezoelectric ceramic sheet 7 having a rectangular plate shape. The piezoelectric laminated body 9 and two frictional contacts 10 provided, for example, by being bonded to the surface of the piezoelectric laminated body 9 facing the driven body 5 are provided.

  Note that reference numeral 11 denotes an external electrode. All internal electrodes (not shown) arranged at the same position of the same type of piezoelectric ceramic sheet 7 are connected to each external electrode 11. Thereby, internal electrodes (not shown) arranged at the same position of the same type of piezoelectric ceramic sheet 7 are set to the same potential.

  The external electrode 11 is connected to a controller (not shown) via wiring (not shown). The wiring may be any wiring as long as it is flexible, such as a lead wire or a flexible substrate.

  Hereinafter, the operation of the piezoelectric laminate 9 will be described.

  First, the four external electrodes 11 formed on one end surface in the longitudinal direction of the piezoelectric laminate 9 are internal electrodes (not shown) corresponding to C− and C + which are C phases for vibration detection in order from the upper side in FIG. ), External electrodes 11 connected to internal electrodes (not shown) corresponding to B− and B + which are B phases for driving. On the other hand, the two external electrodes 11 formed on the other end surface in the longitudinal direction of the piezoelectric laminate 9 are external electrodes 11 connected to internal electrodes (not shown) corresponding to A + and A− for driving A phase. It is.

  Here, when an alternating voltage having the same phase and corresponding to the resonance frequency or a frequency in the vicinity thereof is applied to the A phase and the B phase, primary longitudinal vibration as shown in FIG. 3 is excited. Further, when an alternating voltage corresponding to the resonance frequency is applied to the A phase and the B phase in opposite phases, a secondary bending vibration as shown in FIG. 4 is excited. 3 and 4 are diagrams showing computer analysis results by the finite element method.

  Here, when the primary longitudinal vibration is generated in the piezoelectric laminate 9, the friction contact 10 is displaced in the length direction of the piezoelectric laminate 9 (X direction shown in FIG. 3). On the other hand, when secondary bending vibration is generated in the piezoelectric laminate 9, the friction contact 10 is displaced in the width direction of the piezoelectric laminate 9 (Z direction shown in FIG. 4).

  Therefore, a drive alternating voltage having a frequency corresponding to a resonance frequency whose phase is shifted by 90 ° or a frequency in the vicinity thereof is applied to each of the external electrodes 11 corresponding to the A phase and the B phase. As a result, in the piezoelectric laminate 9, primary longitudinal vibration and secondary bending vibration are generated at the same time, and clockwise or counterclockwise substantially elliptical vibration is generated at the position of the friction contact 10 (arrow in FIG. 2). C).

  In addition, electric charges corresponding to the longitudinal vibration generated in the ultrasonic vibrator are excited by the detection internal electrode (not shown), whereby the longitudinal electrode passes through the external electrode 11 of the C phase (C +, C). A signal proportional to vibration (hereinafter, this signal is referred to as “vibration detection signal”) is detected. This vibration detection signal is supplied to the driving device 3 (see FIG. 1) and used for controlling the ultrasonic transducer 4 and the like.

  Hereinafter, the drive device 3 will be described in detail. FIG. 5 is a diagram illustrating a schematic internal configuration of the driving device 3. As shown in FIG. 5, the driving device 3 includes an oscillation circuit (reference signal generation means) 21, a control CPU 22, a signal control circuit 23, a parameter table 24, a signal generation circuit 25, and a signal output control circuit 26. A phase difference detection circuit 28, a drive circuit 30, an encoder 33, and an encoder signal processing circuit 35.

  The oscillation circuit 21 generates a reference signal (clock signal) and outputs it to a signal control circuit 23, a signal generation circuit 25, a signal output control circuit 26, and a phase difference detection circuit 28. The reference signal will be described in detail later with reference to FIG.

  The parameter table 24 includes a driving frequency of the ultrasonic transducer 4, a phase difference between the A phase and the B phase (the phase difference is 90 ° in a “driving period” described later), an initial position of the ultrasonic motor 2, and Stores parameters such as stop position.

  The control CPU 22 sets various parameters (frequency, phase difference, etc.) in the parameter table 24 and controls the drive signal of the ultrasonic transducer 4. Also, various parameters (phase difference, encoder count value, etc.) are read from the parameter table 24, and position control, speed control processing, etc. are performed. That is, the control CPU 22 creates a frequency command value for the reference drive signal, a phase difference command value for the A phase and the B phase, and the like based on the parameter table 24 and a feedback value from the phase difference detection circuit 28 to be described later, and outputs it. To do.

  The signal control circuit 23 generates a reference drive signal S2, which is a pulse signal of a predetermined frequency, based on the reference signal S1 input from the oscillation circuit 21 and the frequency command value input from the control CPU 22. Is output to the signal generation circuit 25. Here, the control CPU 22 provides the signal control circuit 23 with a frequency command value for setting the frequency of the reference drive signal to the resonance frequency of the ultrasonic transducer 4 or a frequency in the vicinity thereof. Accordingly, the signal control circuit 23 outputs a reference drive signal having a frequency substantially the same as the resonance frequency of the ultrasonic transducer 4. The signal b shown in FIG. 6 is an example of the reference drive signal S2. The cycle of the reference drive signal is an integral multiple of the cycle of the reference signal.

  More specifically, the signal control circuit 23 includes a frequency control circuit, a phase difference control circuit, and a pulse edge delay control circuit.

  The signal control circuit 23, as the frequency control circuit, generates a reference drive signal that determines the frequency of the drive signal based on the frequency setting value in the parameter table 24 and based on the number of pulses of the reference signal that is the output of the oscillation circuit 21. Output.

  As the phase difference control circuit, the signal control circuit 23 is based on the set value of the phase difference in the parameter table 24, and is based on the number of pulses of the reference signal that is the output of the oscillation circuit 21, and is the A phase that is two drive signals. The phase difference between the signal and the B phase signal is controlled.

  The signal output control circuit 26 can directly control the output order of the output of the signal generation circuit 25 from the control CPU 22 via the signal output control circuit 26, the output order of the A phase signal, and the B phase signal. Further, the signal output control circuit 26 controls the number of pulses of the drive signal output from the signal generation circuit 25 and the output pause time for performing intermittent drive based on the set value set in the parameter table 24.

  Based on the reference drive signal S2 and the phase difference command value of the A phase and B phase from the control CPU 22, the signal generation circuit 25 has an A phase reference drive signal and a B phase reference drive signal having a phase difference of 90 °. And generate The output ON / OFF control is performed by the signal output control circuit 26.

  Here, FIG. 6 is a diagram illustrating an example of a driving reference signal in the “driving period (phase difference 90 ° period)” of the ultrasonic motor according to the present embodiment. Although details will be described later, in the ultrasonic motor according to the present embodiment, “driving period (phase difference of 90 ° period)” and “non-driving period (phase difference of 0 ° or 180 ° period)” alternate. The drive method to switch to is adopted.

  In the “drive period (phase difference 90 ° period)”, the A-phase and B-phase drive alternating signals are generated separately for the plus side and the minus side. A signal d shown in FIG. 6 is an example of a driving alternating signal on the A phase plus side, a signal e shown in FIG. 6 is an example of a driving alternating signal on the B phase plus side, and a signal f shown in FIG. FIG. 6 shows an example of a negative drive alternating signal, and a signal g shown in FIG. 6 is an example of a negative B phase drive alternating signal.

  As shown in FIG. 6, during the normal driving of the ultrasonic motor according to the present embodiment, the phase difference between the A phase and the B phase is 90 °, and the plus driving alternating signal and the minus driving are performed. The alternating signal is positive and negative and is 180 degrees out of phase.

  The signal generation circuit 25 generates an A-phase plus drive alternating signal, a B-phase plus drive alternating signal, an A-phase minus drive alternating signal, and a B-phase minus drive alternating signal, respectively. The alternating signal is output to the drive circuit 30.

  As shown in FIG. 7, the drive circuit 30 includes an H bridge circuit 31 composed of switching elements and a coil 32 for impedance matching and boosting. When various drive alternating signals are input from the signal generating circuit 25 to the drive circuit 30, the drive alternating voltages OUTA +, OUTA−, OUTB +, and OUTB− are output according to the truth table shown in FIG.

  At this time, since the drive circuit 30 has the coil 32, the drive alternating signal which is a pulse signal is converted into a waveform close to a sine wave by the action of the coil 32, and the A phase and B phase drive close to the sine wave An alternating voltage is applied to the A-phase (A +, A−) and B-phase (B +, B−) external electrodes 11 provided in the ultrasonic transducer 4.

  Here, the longitudinal vibration excited by the ultrasonic transducer 4 is detected by the internal electrode 8 of the C phase (C +, C−), and an electric signal proportional to the longitudinal vibration is detected by the C phase (C +, C−). Is input to the phase difference detection circuit 28 via the external electrode 11.

  Further, any one drive alternating signal (for example, a drive alternating signal on the A phase plus side) is input from the signal generation circuit 25 to the phase difference detection circuit 28. The phase difference detection circuit 28 detects the phase difference between the vibration detection signal input via the external electrode 11 of the ultrasonic transducer 4 and the drive alternating signal input from the signal generation circuit 25, The phase difference is stored in the parameter table 24.

  Next, a driving method of the ultrasonic motor 2 realized by the driving device 3 having the above-described configuration will be described. First, a reference signal is input from the oscillation circuit 21 to the signal control circuit 23 when the ultrasonic motor 2 is activated. On the other hand, the control CPU 22 reads the driving frequency of the ultrasonic motor 2 set in the parameter table, and gives this frequency to the signal control circuit 23 as a frequency command value.

  Further, the control CPU 22 reads the phase difference between the A phase and the B phase set as initial values from the parameter table 24, and gives this to the signal generation circuit 25. As a result, the signal control circuit 23 generates the reference drive signal S <b> 2 set at the resonance frequency of the ultrasonic transducer 4 or a frequency in the vicinity thereof and outputs it to the signal generation circuit 25.

  In the signal generation circuit 25, the reference drive signal corresponding to the A phase (A +, A−) having a predetermined phase difference based on the reference drive signal S2 and the phase difference from the control CPU 22 and the B phase (B +, B−). A corresponding reference drive signal is generated.

  The A-phase and B-phase drive alternating signals are converted into sine wave drive alternating voltages by the drive circuit 30 and applied to the external electrodes 11 of the ultrasonic transducer 4. As a result, longitudinal vibration and bending vibration as shown in FIGS. 3 and 4 are simultaneously excited in the ultrasonic vibrator, and elliptical vibration is formed in the friction contact 10 so that the driven body is relatively moved. Moved.

  The longitudinal vibration excited by the ultrasonic transducer 4 is detected by the C-phase internal electrode 8 and the external electrode 11, and the vibration detection signal is input to the phase difference detection circuit 28. The phase difference detection circuit 28 detects the phase difference between the longitudinal vibration excited by the ultrasonic transducer 4 and the A-phase driving alternating signal output from the signal generation circuit 25, and an electric signal corresponding to the phase difference. Is output to the control CPU 22. When the count number notified from the encoder signal processing circuit 35 reaches a preset count number, the control CPU 22 determines that the driven body 5 has moved to a desired position, and instructs the signal generation circuit 25 to stop driving. Is output. As a result, the drive alternating signal is not output from the signal generation circuit 25, so that the vibration of the ultrasonic transducer 4 gradually converges and stops.

  Hereinafter, “driving period (phase difference 90 ° period)” and “non-driving period (phase difference 0 ° or 180 ° period)”, which are one of the main features of the ultrasonic motor driving method according to the present embodiment, are described. Will be described in detail. In order to make it easier to understand the special effects obtained by this driving method, burst driving and its operation that have been conventionally performed will be described first.

  FIG. 9 is a diagram illustrating an example of drive signal application timing in conventional burst driving. As shown in the figure, in the conventional burst drive, the drive signal is switched to ON / OFF periodically (by alternately providing the drive signal ON period and the drive signal OFF period), and the normal speed state And a state where the speed is zero or extremely small are periodically repeated.

  In conventional burst driving, low speed driving is realized by reducing the speed of the ultrasonic motor on average by such driving control. However, in such a drive, the amplitude of vibration generated in the ultrasonic transducer changes abruptly when the application of the drive signal is started and when the application is stopped, and therefore, between the ultrasonic transducer and the driven body. Slip occurs, and wear of these members easily proceeds.

  In addition, in order to make the speed of the ultrasonic motor 0 or extremely low, for example, the following driving method can be mentioned.

That is, in addition to ON / OFF switching of the drive signal,
(Driving method 1) The frequency of the driving signal is removed from the resonance frequency.

(Drive method 2) The pulse duty of the drive signal is reduced.

  However, such a driving method has the following problems. According to the above (Method 1), since the frequency of the drive signal is removed from the resonance frequency, the vibration amplitude of the ultrasonic transducer is rapidly changed. This promotes wear due to friction between the ultrasonic transducer and the driven body. According to the above (Method 2), when the pulse duty is set to 0, it is substantially the same as switching the drive signal to OFF, and thus has the same problem.

  In view of the circumstances as described above, the following driving method is adopted in the present embodiment.

  That is, in the present embodiment, the drive state is changed by changing the phase difference between two drive signals having different phases applied to the ultrasonic transducer 4. That is, by changing the phase difference between the two-phase drive signals, the speed is set to 0 or an extremely small speed state without rapidly changing the vibration amplitude of the ultrasonic motor.

  Specifically, by changing the phase difference between the two-phase drive signals, the ratio between the longitudinal vibration and the bending vibration excited by the ultrasonic transducer 4 is changed. In other words, changing the phase difference between the two-phase driving signals in this way means that an elliptical shape when the ultrasonic transducer 4 is driving the driven body 5 (the elliptical shape 101 shown in FIG. 10 is changed). Is equivalent to changing That is, by performing such drive control, without sudden change in the vibration amplitude of the ultrasonic motor 2 (suppressing wear of both members due to friction between the driven body 5 and the friction contact 10). The driving speed of the ultrasonic motor 2 can be reduced to 0 or extremely low.

  In other words, in the ultrasonic motor according to the present embodiment, the driving force of the ultrasonic motor is changed by changing the above-described elliptical shape. Thereby, the above-described speed change is realized while suppressing wear of the member related to the friction.

  Specifically, the ratio of longitudinal vibration and bending vibration generated in the ultrasonic transducer 4 is changed by changing the phase difference of the drive signal input to the external electrode 11 provided in the ultrasonic transducer 4. . Specifically, the phase difference of the drive signal is set in the parameter table 24, and based on the setting of the parameter table 24, the phase difference between the two-phase drive signals output from the signal generation circuit 25 by the signal control circuit 23, In this case, the phase difference between the drive signals input to the A phase and the B phase of the ultrasonic transducer 4 is controlled.

  Further, the period when the phase difference between the two phases is periodically switched can also be set in the parameter table 24. Based on the setting, the output of the signal generation circuit 25 is controlled by the signal control circuit 23. The phase difference between the A-phase drive signal and the B-phase drive signal applied to the sonic transducer 4 can be switched at the set cycle.

  Specifically, for example, the following method can be given as a method for switching the phase difference.

  Here, the phase difference in the “driving period (phase difference 90 ° period)”, which is a period in which normal driving as described with reference to FIG. 6 is performed, is defined as a first phase difference. On the other hand, the phase difference in the “non-driving period (phase difference 0 ° or 180 ° period)” in which the driving force (speed) is 0 or an extremely small driving force (speed) is defined as a second phase difference. In the present embodiment, drive control is performed to alternately switch between the first phase difference and the second phase difference at a predetermined period.

  By the way, as the second phase difference, that is, the phase difference that makes the driving force (speed) zero, for example, the following phase difference can be cited. That is, the phase difference in which the vibration of the ultrasonic transducer 4 is only longitudinal vibration and the phase difference in which the vibration of the ultrasonic transducer 4 is only flexural vibration. That is, examples of the phase difference between the A-phase drive signal and the B-phase drive signal include 180 ° and 0 °. Hereinafter, drive control in the case of taking these phase differences will be described in detail.

≪When the second phase difference is 180 ° ≫
FIG. 11 shows drive control when the first phase difference, which is a phase difference during driving, is 90 °, and the second phase difference, which is a phase difference that makes the driving force (speed) 0, is 180 °. FIG.

  As shown in the figure, in the period of the first phase difference (phase difference 90 °), the ultrasonic transducer 4 is driven to draw an elliptical locus that drives the driven body 5. On the other hand, in the period of the second phase difference (phase difference 180 °), the ultrasonic transducer 4 performs only the bending vibration described above, and thus does not drive the driven body 5 substantially.

  Therefore, the speed of the ultrasonic motor includes a period of the first phase difference (phase difference 90 °) and a period of the second phase difference (phase difference 180 °) as shown in the lowermost stage in FIG. It repeats alternately (refer to graph 151 in the figure). Thereby, the speed in the period of the first phase difference (phase difference 90 °) and the speed in the period of the second phase difference (phase difference 180 °) are averaged. Such a stable low-speed drive.

≪When the second phase difference is 0 ° ≫
FIG. 12 shows drive control when the first phase difference, which is the phase difference during driving, is 90 °, and the second phase difference, which is the phase difference that makes the driving force (speed) 0, is 0 °. FIG.

  As shown in the figure, in the period of the first phase difference (phase difference 90 °), the ultrasonic transducer 4 is driven to draw an elliptical locus that drives the driven body 5. On the other hand, in the period of the second phase difference (phase difference 0 °), the ultrasonic transducer 4 only performs the above-described longitudinal vibration, and thus does not substantially drive the driven body 5.

  Accordingly, the speed of the ultrasonic motor includes a period of the first phase difference (phase difference 90 °) and a period of the second phase difference (phase difference 0 °) as shown in the lowermost stage in FIG. It is alternately repeated (see graph 161 in the figure). As a result, the speed in the first phase difference (phase difference 90 °) period and the speed in the second phase difference (phase difference 0 °) period are averaged. Such a stable low-speed drive.

  As described above, according to the present embodiment, the ultrasonic motor that suppresses wear caused by friction between the vibrator and the driven body when the ultrasonic motor is driven and realizes stable low-speed driving. Can be provided. Furthermore, according to the ultrasonic motor according to the present embodiment, noise generated due to a rapid change in vibration can be suppressed, so that a silent effect can also be obtained.

  Note that the effect of the ultrasonic motor according to the present embodiment is that the driving device that requires particularly high-precision positioning, for example, the last positioning during AF driving of the lens of the camera or the low-speed and high-precision driving of the microscope stage, etc. This is particularly noticeable when applied to a drive device that requires smooth driving.

  The present invention has been described based on one embodiment. However, the present invention is not limited to the above-described embodiment, and various modifications and applications are possible within the scope of the gist of the present invention. It is.

[Modification]
In the drive control described above in the embodiment, not only the first phase difference and the second phase difference are simply switched, but also the first phase difference (θ shown in FIG. It is of course possible to continuously sweep from ₁ ) to the second phase difference (θ ₂ shown in FIG. 13).

  In other words, a plurality of phase differences are inserted between the first phase difference and the second phase difference so that the driving force (speed) is different from that at the time of the phase differences. Needless to say, drive control may be performed such that the first phase difference (or the second phase difference) is switched to the second phase difference (or the first phase difference) via the phase difference.

  Further, the above-described embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effect described in the column of the effect of the invention Can be extracted as an invention.

1 is a block diagram showing a schematic configuration example of an ultrasonic motor system according to an embodiment of the present invention. The figure which shows the example of 1 structure of an ultrasonic transducer | vibrator. The figure which shows the longitudinal vibration of a piezoelectric laminated body. The figure which shows the bending vibration of a piezoelectric laminated body. The figure which shows the internal schematic structure of a drive device. The figure which shows an example of a reference signal. The figure which shows the example of 1 structure of a drive circuit. The figure which shows the truth value table of the input-output value when various drive alternating signals are input into the drive circuit from the signal generation circuit. The figure which shows an example of the application timing of the drive signal in the conventional burst drive. The figure which shows typically an example of the ellipse shape when the ultrasonic transducer | vibrator is driving the to-be-driven body. The state of drive control in the case where the first phase difference that is the phase difference during driving is 90 ° and the second phase difference that is the phase difference that makes the driving force (speed) 0 is 180 ° is shown. Figure. The state of drive control in the case where the first phase difference that is the phase difference during driving is 90 ° and the second phase difference that is the phase difference that makes the driving force (speed) 0 is 0 ° is shown. Figure. The figure which shows the concept of the drive control of the ultrasonic motor which concerns on one modification.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... Ultrasonic motor system, 2 ... Ultrasonic motor, 3 ... Drive apparatus, 4 ... Ultrasonic vibrator, 5 ... Driven body, 7 ... Piezoelectric ceramic sheet, 8 ... Internal electrode, 9 ... Piezoelectric laminated body, 10 ... Friction contact, 11 ... external electrode, 21 ... oscillation circuit, 22 ... control CPU, 23 ... signal control circuit, 24 ... parameter table, 25 ... signal generation circuit, 26 ... signal output control circuit, 28 ... phase difference detection circuit, DESCRIPTION OF SYMBOLS 30 ... Drive circuit, 31 ... H bridge circuit, 32 ... Coil, 33 ... Encoder, 35 ... Encoder signal processing circuit

Claims (7)

An ultrasonic motor that applies a two-phase drive signal to a vibrator to generate elliptical vibration in the vibrator, obtains a driving force from the elliptical vibration, and frictionally drives a driven member;
Drive signal generating means for generating the two-phase drive signal;
Phase difference control means for performing control to switch the phase difference between the two-phase drive signals a plurality of times so as to change the drive state of the ultrasonic motor;
An ultrasonic motor comprising:   The ultrasonic motor according to claim 1, wherein the phase difference control unit performs control to switch the phase difference at a predetermined cycle. The phase difference control means includes
A first phase difference that is the phase difference corresponding to a state of frictionally driving the driven member;
A second phase difference that is the phase difference corresponding to a state in which the driven member is not frictionally driven;
The ultrasonic motor according to claim 2, wherein control is performed to switch the frequency at a predetermined cycle. The phase difference control means includes
When switching between the first phase difference and the second phase difference at a predetermined period,
The ultrasonic motor according to claim 3, wherein control is performed to continuously switch via a phase difference between the first phase difference and the second phase difference.   The ultrasonic motor according to claim 3, wherein the second phase difference is a phase difference at which a driving force of the driven member in the traveling direction becomes zero.   The ultrasonic motor according to claim 3, wherein the second phase difference is a phase difference that causes only longitudinal vibration in the vibrator.   The ultrasonic motor according to claim 3, wherein the second phase difference is a phase difference that causes only bending vibration in the vibrator.

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