JPH02223387A - Ultrasonic motor and controller therefor - Google Patents

Abstract

PURPOSE:To control an ultrasonic motor properly according to the character of load torque by correcting the value of a target signal based on a state signal to be obtained through comparison between an input signal and an output signal from a piezoelectric element for detecting the driving state. CONSTITUTION:When a material grip command, e.g. a target position signal or a power signal, is fed from a manipulator system 4 to a gripper system 5, a gripper controller 5 rotates an ultrasonic motor 7 then the rotation is transmitted to grippers 81, 82. The grippers 81, 82 move in the direction of arrows and grip a material 9. Power signal or position signal is transmitted from a gripper mechanism section 8 to the gripper controller 5 and fed back to the command signal for an ultrasonic motor controller 6 in order to enable gripping of the material without causing breakdown. The gripper controller 5 sets a target position, a target power signal, a reference power signal, and the like, according to a grip command or a release command fed from the grip controller 5 then the gripper controller 5 operates command values for ultrasonic motors 4-7 based on the difference between thus set inputs and current position or power signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a stator comprising a piezoelectric material and an elastic material.
It is related to an ultrasonic motor device that generates traveling wave-like ultrasonic vibrations and extracts the vibration energy as rotational motion of a rotor, and in particular controls an ultrasonic motor that can quickly respond to subtle fluctuations in load torque. Related to equipment.

(Prior art) Regarding conventional ultrasonic motors and their control devices, see, for example, Automation Technology Magazine Separate Volume, 100-1, published September 1987.
Discussed on page 04. First, we will explain the second principle of driving the traveling wave type ultrasonic motor used in such conventional examples.
This will be explained using diagrams.

As shown in Fig. 2(a), when an alternating current voltage is applied to the elastic body 2, vertical vibrations like standing waves occur depending on the frequency of the applied voltage, as shown in Fig. 2(b). do. here,
When the phases of the AC voltages applied to these piezoelectric elements are electrically shifted by 90 degrees between adjacent piezoelectric elements, traveling-wave elastic vibrations are generated on the surface of the elastic body 2, as shown in Fig. 2 (Q ), the rotor 3 in contact with the ring-shaped elastic body 2 rotates, making it possible to extract mechanical output. Ultrasonic motors that operate on this principle have the advantage of being smaller, lighter, and able to obtain higher torque than conventional motors that operate on electromagnetic principles, and are being considered for application as actuators for robots and the like. However, in order to use it as a control element, it is generally necessary to use it in combination with sensors to detect rotational speed, rotor position, etc. A sensor piezoelectric element is provided on the rotor as described in the conference material "Latest technology of mechanical design of information equipment and its operation analysis" pages 97-98, and the driving voltage of the rotor and the sensor piezoelectric element are induced. The method of detecting the rotational speed from the phase difference between the voltages has been such that, for example, a pulse encoder is separately installed coaxially with the rotor to determine the rotational position.

[Problem to be solved by the invention]

In the above-mentioned known technology, in order to use an ultrasonic motor in, for example, a clipper device, depending on the shape, weight, softness, and surface roughness of the object to be gripped, It was not possible to perform control that adapted to the properties of the object, such as making the gripping claws bite into it.

In addition, in order to know the rotational position of the rotor, it is necessary to separately attach a pulse encoder, for example, and there is a problem that the size becomes large.

The object of the present invention is to provide an ultrasonic motor control device that can appropriately control the load torque of the ultrasonic motor according to the nature of the load torque;
An object of the present invention is to provide a small ultrasonic motor with a built-in rotational position detector.

[Means to solve the problem]

In order to achieve the above object, the present invention drives an ultrasonic motor using a first target signal output from a control system for the ultrasonic motor, and controls the drive voltage or voltage of the ultrasonic motor.

The value of the first target signal is corrected using a first state signal obtained by comparing the input signal of the drive amplifier and the output signal of the drive state detection piezoelectric element. Further, as the drive state detection piezoelectric element, an element with high conversion efficiency of generated voltage to pressure is used to detect minute state changes.

Furthermore, as a means for detecting the position of the rotor of the ultrasonic motor, a magnetic material having a predetermined position signal pattern is coated on the rotor, and changes in the magnetic field obtained thereby are detected to detect the rotational position of the rotor. Make it.

[Effect]

The ultrasonic motor and its drive device configured as above are
When no load torque is applied, the stator and the driving piezoelectric element are in a state close to mechanical resonance, and the vibration state of the stator is converted into pressure electricity by the sensor piezoelectric element and is extracted as an electrical signal.

Next, when a load torque is applied, the force is transmitted to the stator via the output shaft and rotor, and the corresponding force signal is detected by being superimposed on the output signal of the sensor piezoelectric element.

Since the output signal of the sensor piezoelectric element changes its amplitude, phase, etc. due to changes in load torque, by detecting changes in either or both of them and feeding it back to the input of the ultrasonic motor. , it is possible to appropriately respond to fluctuations in load torque. By using a highly sensitive piezoelectric element as the sensor piezoelectric element, the performance of the system is further improved.

Furthermore, the rotational speed, rotation angle, etc. of the ultrasonic motor can be detected using the magnetic material pattern applied on the rotor, and the rotational position of the rotor can be controlled.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This embodiment is applied to a gripper that is attached to the hand of a manipulator that performs work in a bad environment in place of a human being, and performs the functions of the human wrist. The gripper system includes a gripper control device 5, an ultrasonic motor 7 and its control device 6. It is composed of a gripper mechanism section 8. An object gripping command, that is, a target position signal, a force signal, etc., is sent to the gripper system 5 from the manipulator system 4, which is a higher-level system.
When input to the gripper control device 5, the ultrasonic motor 7
is rotated via the ultrasonic motor control device 6, and the output of the ultrasonic motor 7 is transmitted to the gripping claws 81 and 82 via a mechanical transmission system. As a result, the gripping claws 81 and 82 move, for example, in the direction shown by the arrow, and can grasp the object 9 placed between the gripping claws. In addition, the gripper mechanism section 8
Information such as force signals and position signals are transmitted to the gripper control device 5 and fed back into command signals to the ultrasonic motor control device 6 in order to grip the object without damaging it.

The gripper control device 5 sets the target position, target force signal, reference force signal, etc. according to the input gripping and releasing commands.
Command values for the ultrasonic motors 4 to 7 are calculated using the differences between these inputs and the current position and force signals.

As already explained using FIG. 2, the ultrasonic motor 7 is composed of a stator composed of a piezoelectric element 1 and an elastic body 2, and a rotor 3. 71 and 72 are driving electrodes,
Voltages having a phase difference of 90 degrees are applied to each stator to generate traveling wave type elastic vibrations on the stator, thereby rotating the rotor.

The driving section of the piezoelectric element is a variable oscillator 61, a 90-degree phase shifter 62, and a 90-degree phase shifter in the ultrasonic motor control device 6. It is composed of drivers 63 and 64, an exclusive OR element 65, and the like. The variable oscillator 61 generates a drive frequency for the piezoelectric element according to the rotational speed command signal from the converter a5.l. variable oscillator 61
The output is applied to the electrode 71 of the ultrasonic motor where it is amplified by the driver 63, and at the same time the output is amplified by the 90 degree phase shifter 62. It is also applied to the motor electrode 72 through the exclusive OR element 65 and the driver 64. Converter 51 generates a rotational direction signal in addition to the aforementioned rotational speed command signal, and transmits this to exclusive OR element 65. Depending on the logic level "1" or "0" of this rotation direction signal, the exclusive OR element 6
Since the phase of the output of the rotor 5 is reversed, the rotation direction of the rotor 3 is also reversed accordingly.

The rotational force of the ultrasonic motor 7 driven in this manner is transmitted to the gripper mechanism section 8.

The gripper mechanism 8 has gripping claws 81 and 82 that come into contact with the object 9.
．． and a transmission system that transmits the output of the ultrasonic motor 7. The rotation of the ultrasonic motor 7 is transmitted from the gear 83 connected to the rotor shaft to the gears 84 and 85, thereby rotating the four-way link mechanism.

The gripping claws 81 and 82 perform opening and closing operations.

However, the force required to grasp the object 9 is
Since the shape varies depending on the shape, weight, surface condition, etc., it is necessary to detect the gripping condition and provide feedback in order to properly grip it. Hereinafter, such feedback will be explained, and at the same time, the effects of the present invention will be clarified.

Since the rotational state of the ultrasonic motor 7 changes due to the reaction force of gripping the object 9, the ultrasonic motor is provided with a detection piezoelectric element for detecting this change.

This detection piezoelectric element is usually provided in the array of piezoelectric elements 1 shown in FIG. 2(a). The electrode 73 in FIG. 1 is a sensor electrode attached to such a detection piezoelectric element. Also, a driving piezoelectric element 1 bonded to the elastic body 2
A material with a large piezoelectric d constant, which indicates the efficiency of converting electrical energy into mechanical energy, is used for the detection piezoelectric element, and a material with a large mechanical quality coefficient Q is used for the detection piezoelectric element.

In FIG. 1, the signal from the sensor electrode 73 is passed through an amplifier 67 and a phase shifter 68, and is sent to the electrode 73 at a phase comparator 69.
1 through an amplifier 66. The phase comparator 69 outputs a signal corresponding to the phase difference between both signals, which controls the oscillation phase of the variable oscillator 61 via the converter 51. By such feedback, the phase difference between the voltage applied to the drive electrode 71 and the signal obtained from the sensor electrode 73 is controlled to be maintained at a predetermined value.

Reference numeral 74 denotes a position detector for detecting the positions of the gripping claws 81 and 82, and is mounted, for example, to the rotating shaft of the rotor 3 via a speed reducer. The signal from the position detector is combined with the target position signal sent by the manipulator system 4 and the subtractor 5
5, and the difference signal between the two is input to the converter 51 via the switch 53. Therefore 1 phase detection @74
When the output of the converter 51 matches the target position signal 41, the input of the converter 51 becomes zero. Generally, in this state, the variable oscillator 61 stops oscillating, and the movement of the first gripping claws 81 and 82 is stopped.

In an ultrasonic motor, the rotor is generally pressurized by a spring or the like against a fixed stator, so there is little concern that the rotor will slip in the opposite direction even if the input voltage is zero and the rotor loses its rotational force.

However, the above-mentioned method of controlling the rotational position of an ultrasonic motor is not suitable for applications in which an object such as a lens is moved by a predetermined amount and then stopped, such as in the case of a focusing device in a camera. However, it is insufficient for a gripper device such as that shown in FIG. That is, since the properties of the object to be gripped vary depending on its shape, weight, surface roughness, softness, etc., for example, it is recommended to dig the gripping claws into a highly flexible object. Fragile objects need to be controlled in accordance with the properties of the object, such as by gently pinching the object, and the present invention aims to provide a specific method for this purpose.

Such control is based on, firstly, how the force is changed after the gripping claws 81, 82, etc. come into contact with the object 9, and secondly, to what extent the gripping claws are bitten into the object 9. This includes two options: whether to stop it or not. Now, such control will be referred to as object adaptive control. To execute this control, it is necessary to detect that the gripping claws have contacted the object 9, and then use the ultrasonic waves generated to grip the object. A process is required to detect the reaction force of the motor 7 and calculate the force to be applied to the ultrasonic motor 7 from these detection signals.

FIG. 1 shows an example of the objective adaptive control of the present invention described above. The sensor signal taken out from the sensor electrode 73 via the amplifier 67 is compared with the ultrasonic motor drive voltage obtained from the ultrasonic motor drive electrode 71 via the amplifier 66 by the subtraction unit 60.

FIG. 3 shows an example of the internal circuit of this subtraction section 60, and the amplifier 6
The outputs of 6 and 67 are output to amplitude detection smoothing circuits 601 and 67, respectively.
602, and a subtracter 603 obtains a state signal 44 corresponding to the amplitude difference.

FIG. 4 shows the phase difference between the outputs of amplifiers 66 and 67.

This is a case where the subtraction unit 60 is configured to detect.

The outputs of amplifiers 66 and 67 are respectively output to waveform shaping circuit 60.
5 and 606 into a rectangular wave, and the OR gate 60
4 and a low-pass filter 607, it is converted into a voltage proportional to the phase difference. An adder 608 adds a DC voltage 607 for offset adjustment to the output of the low-pass filter 8807, and outputs a status signal 44.

The status signal 44 is compared with the reference force signal 43 by a comparator 52, depending on the magnitude relationship between the two signals.

Switch 53 to change the input of converter 51 to subtracter 55
From there, the output is switched to the output of the subtracter 54. The subtractor 54 outputs the difference in amplitude between the target force signal 42 and the state signal.

The above operation is set based on the following basis. When the gripping claws 81 and 82 are not touching the object 9, the subtraction unit 60 is designed so that its output is approximately zero to a minimum value. ing. The driving frequency of the ultrasonic motor 7 is set close to the mechanical resonance frequency of the motor 7, for example, slightly higher than the resonance frequency. As a result, the amplitude of the mechanical resonance changes according to the drive frequency, so the output torque of the ultrasonic motor 7 can be controlled by the drive frequency. ,
Or after that, when the object 9 is tightened, the ultrasonic motor 7
receives a braking force from the object 9 via the gripper mechanism section 8. This braking force lowers the Q value of the mechanical resonance of the ultrasonic motor 7, so the output amplitude of the sensor electrode 73 decreases and one phase changes. As a result, status signal 44 increases. Comparator 52 produces an output when this condition signal exceeds reference force signal 43 and switches switch 53. The manipulator system 4 tests the nature of the status signal 44;
The values of the target force signal 42 and reference force signal 43 are changed as appropriate. FIG. 5 is an example of a waveform diagram of the state signal 44 for explaining a method of controlling these signals.

In FIG. 5, the horizontal axis represents time t, and 10 is the gripping claw 8.
1,82 is the time when it touches the object 9.

Waveforms 441, 442, 443, etc. represent state signals 44 obtained corresponding to cases where the object 9 is hard, soft, balloon-shaped, etc., respectively. Also, the two dotted lines are
When the object 9 is hard, which represents the magnitude of the target force signal 42 and the reference force signal 43, after time 1 to, the ultrasonic motor receives a strong reaction in a short period of time, so it rises rapidly as shown by the state signal 441. When the object 9 is soft, the above-mentioned reaction is small and the rise of the state signal becomes gradual. If the object 9 is balloon-shaped, the initial reaction will be even smaller and will increase as it is compressed. In either case, when the gripping claws 81, 82 stop moving, the signal from the sensor electrode 73 decreases, so each status signal increases rapidly.

Now, consider the case where the status signal is 442.

Since the magnitudes of the state signal 442 and the reference force signal 43 match at time t1, the switch 453 is switched and the converter 5
1, the difference between the state signal 442 and the target force signal 42 is input. At this time, if the difference between the reference force signal 43 and the target force signal 42 is equal to the difference between the target position signal 41 and the output of the position detector 74, the input to the converter 51 will not be discontinuous, resulting in the smoothest transient response. is obtained. Status signal is 44
3, the switch 53 is switched at time t2.

The switching timing of the switch 53 varies greatly depending on the nature of the state signal, that is, the nature of the object 9, so if a quick grasping operation is required, it is first necessary to advance the times tl, t2, etc. For this reason, the manipulator system 4 monitors the state signal 44 and can change the values of the target force signal 43, reference force signal 43, etc. according to the rate of change.
Decrease the value of , or increase it if it is delayed.

After the switch 53 is switched to the state signal 44 side, the ultrasonic motor 7 enters the aforementioned objective adaptive control state controlled by the difference between the reference force signal 43 and the target force signal. During this time, the target force signal 42 is kept at a constant value or is changed as appropriate according to the state signal 44. When the time calculated based on the status signal 44 has elapsed, the manipulator system 4 sends a stop signal 45 to the converter 51 to stop the oscillation of the variable oscillator 61 and stop the ultrasonic motor 7.

In FIG. 1, the position signal detector 74 is also used for the following purposes. That is, although the value of the output 44 of the subtraction unit 60 is almost zero when the ultrasonic motor 7 is rotating steadily with no load, it shows a significantly large value at startup, which may cause malfunction. Therefore, it is necessary to stop the above-mentioned feedback control operation until the output of the 1-position signal detector 74 reaches a predetermined value. Therefore, the converter 51 receives a command from the manipulator 4 to start the operation, and then starts the subtractor 55. The switch 5 is set so as not to accept the signal from the subtraction unit 6o until the output of the subtractor 6o reaches a predetermined value.
3 switching operation is prohibited.

FIG. 6 shows an embodiment of the present invention in which the main part of the control operation explained using FIG. 1 is performed within the manipulator 4.

For example, a microcomputer device including an analog interface is used as the manipulator 4, and
Subtraction section 60. Phase shifter 68, phase comparator 69. Comparator 52
．． The switches 53, subtractors 54, 55, etc. are omitted because their functions are performed inside the manipulator 4. For example, signals from the drive electrode 71 and sensor electrode 73 of the ultrasonic motor are sent to the amplifier 66 and the sensor electrode 73, respectively. 67, the signal is appropriately amplified and taken into the manipulator 4, and a subtraction process corresponding to the subtraction unit 60 is performed therein, and according to the result, the target position signal 41 corresponds to the output of the subtracter 54 shown in FIG. The output of the zero position detector 74, which is switched to a value of or maintain it at a predetermined value. 6th
In the figure, unlike FIG. 1, the signal from the drive electrode 72 is also taken into the manipulator. In this way, for example, the noise component superimposed on one of the drive electrodes 71 and 72 can be
This is because by comparing the outputs of both electrodes, the signal component can be distinguished from the signal component and removed, resulting in a system that is resistant to noise.

In addition, in FIG. 6, some of the signals input to the manipulator 4 can be omitted depending on the roughness, precision, etc. of the target movement of the gripping claws 81, 82, etc. Above, since the drivers 63, 64, etc. are accompanied by an output impedance, the voltages applied to the drive electrodes 71, 72, etc. are subjected to waveform distortion due to the reaction from the object 9. Therefore, if this waveform distortion, for example amplitude distortion, phase distortion, or both, is detected within the manipulator 4, the signal from the sensor electrode 73 can be omitted.

FIG. 7 shows an embodiment in which the present invention is applied to a paper feeding section of a copying machine. The same parts as in Figure 1 have the same function. The paper feed rollers 11 and 12 are rotated by the size of the paper 13 given by the input of the target position signal 41, and the paper is fed to the transfer section. The control device 49 sets an initial value in the counter 56 based on the given paper size. Counter 56 subtracts the number of output pulses from position detector 74 from the initial value and sends the result to converter 51 via switch 53. The converter 51 calculates the drive frequency of the ultrasonic motor 7 corresponding to the above-mentioned subtraction result, drives the ultrasonic motor, and controls the paper feed roller 1.
The zero paper 13, which rotates the rollers 1 and 12, is sandwiched between the rollers 11 and 12 and sent out.

When the paper feed device 10 causes a paper jam, the load torque of the ultrasonic motor increases, and the output of the subtraction unit 60 also increases. When this output exceeds the value of the reference force signal 43, the output of the comparator 52 is inverted and the switch 53 is switched to the stop signal 45 side.
The ultrasonic motor 7 is stopped.

The configuration shown in Figure 7 eliminates the need for paper jam detectors in conventional devices, simplifying the mechanical system and reducing weight.

High reliability can be achieved.

In the prior art, an individual pulse encoder or the like has been used as the position detector 74 explained in FIGS. 1, 7, etc. However, since an ultrasonic motor does not involve electromagnetic elements, the rotational position of the motor can be easily detected by coating the rotor 3 with a magnetic material 31 and providing a detection pickup 32 on the fixed side. FIG. 8 is a cross-sectional view of an ultrasonic motor in which a position detection function is added using a rotor member. A stator 11 made of a piezoelectric element and an elastic body is fixed to a base 12. The rotor 3 is fixed to an output shaft 33 via an intermediate member. A magnetic pattern 31 corresponding to the number of rotations, two rotation angles, etc. of the rotor 3 is created on the outer circumference of the rotor 3 using a paint containing magnetic powder or the like. Reference numeral 32 denotes a detector for this magnetic pattern 32, which uses, for example, a coil wound around an iron core, and has a structure for detecting changes in the magnetic resistance of the coil created by the magnetic pattern 31. Similarly, it can also be applied to hollow type ultrasonic motors. With this configuration, there is no need to provide a position detection encoder separately from the motor, and the mechanism can be simplified and lightened.

〔Effect of the invention〕

As detailed above, when the present invention is applied, the rotational speed, output torque, etc. of the ultrasonic motor are determined based on the signal obtained by comparing the output of the sensor piezoelectric element provided on the stator with the drive voltage waveform of the ultrasonic motor. Since the command signal of the ultrasonic motor can be changed, the output of the ultrasonic motor can be appropriately controlled in response to subtle changes in load torque, such as in the case of gripper devices, printer paper feed devices, etc. .

Furthermore, by taking advantage of the fact that the ultrasonic motor can be made of non-magnetic material and providing a pattern containing magnetic powder on the rotor, the rotational speed of the ultrasonic motor can be increased.

A detector for detecting rotational position, etc. is economically built into the ultrasonic motor, and furthermore, the inertia rate of the ultrasonic motor including the detector is lowered to speed up the response speed of a control device using the ultrasonic motor. be able to.

[Brief explanation of the drawing]

4 is a circuit diagram of a subtraction unit used in an embodiment of the present invention, FIG. 5 is an operational explanatory diagram of an embodiment of the present invention, and FIG. 6 is a block diagram of a second embodiment of the present invention. FIG. 7 is a circuit diagram of a third embodiment of the present invention, and FIG. 8 is a structural sectional view of an ultrasonic motor for explaining the position detector of the present invention. 1... Piezoelectric element, 2... Elastic body, 3... Rotor,
4... Manipulator system, 5... Gripper control device. 6... Ultrasonic motor control device, 7... Ultrasonic motor, 8... Gripper machine end, 81, 82... Gripping claw,
9... Object, 71.72... Ultrasonic motor drive electrode, 51... Converter, 61... Variable oscillator, 60.
...Subtraction section, 62...90 degree phase shifter, 63.64...
- Driver, 65... Exclusive OR element, 73...
Sensor electrode, 66.67... Amplifier, 68... Phase shifter, 69... Phase comparator, 74... Position detector,
54.55...Subtractor. 53... Switch, 601, 602... Preamplifier circuit, 803... Subtraction circuit, 42... Target force signal, 4
1...Target position signal, 43...Reference force signal, 44,
441-443...Status signal, 45...Stop signal,
49...Control device, 11.12...Paper feed roller,
13...Paper, 10...Paper feeding device, 31...Magnetic pattern, 32...Magnetic pattern detector, 601,6
02... Amplitude detection smoothing circuit, 605, 606... Waveform shaping circuit, 607 Low pass filter, 56... Counter. Tomi map (intersection (b) tz map (su) Figure Tomi map 1ρ Tomi map h Figure

Claims (4)

[Claims] 1. In a control system for an ultrasonic motor including a stator using a driving piezoelectric element and an element for detecting the vibration state of the stator, the ultrasonic motor is driven by a first target signal outputted by the control system, and the ultrasonic motor is driven by a first target signal outputted by the control system. The first state signal is obtained by comparing the driving voltage of the driving piezoelectric element or the input signal of the amplifier for driving the driving piezoelectric element with the output signal of the driving state detecting element. A control system for an ultrasonic motor, comprising: modifying a value of a target signal. 2. In a control system for an ultrasonic motor including a stator including a driving piezoelectric element and an elastic body, and a piezoelectric element for detecting the driving state of the stator, the ultrasonic motor is controlled by a first target signal output from the control system. The value of the first target signal is corrected by a second state signal obtained by comparing the driving voltage of the driving piezoelectric element and the input signal of an amplifier for driving the driving piezoelectric element. A control system for an ultrasonic motor, characterized in that it does the following: 3. An ultrasonic motor characterized in that a rotational position pattern is provided on the outer periphery of the rotor using paint containing magnetic powder. 4. A control system for an ultrasonic motor, characterized in that the drive piezoelectric element and the drive state detection piezoelectric element are made of different materials, and a piezoelectric element made of a material with a small mechanical quality factor is used as the drive state detection piezoelectric element.