JP2008193874A - Ultrasonic motor controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To handle an ultrasonic motor in the same manner as motors with linear input/output characteristics by additionally constituting a circuit with simple structure. <P>SOLUTION: A phase difference controller 13 in the controlling circuit 11 of the ultrasonic motor includes a linear conversion circuit 13a converting an input signal, and a phase difference controlling circuit 13b to generate a control signal to an ultrasonic motor USM on receipt of the signal from the linear conversion circuit. The linear conversion circuit 13a has a linear conversion characteristic in the output of the ultrasonic motor USM with respect to the input signal to the phase difference controller 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic motor control device.

  Ultrasonic motors are used in a wide range of fields such as robots, precision machine tools, automotive electrical equipment, lens drive for camera autofocus, and computer-related equipment. It is considered that.

  Regarding medical equipment, for example, an actuator in an MRI apparatus is required to be a non-magnetic material and not to generate electromagnetic noise. As such, pneumatic, hydraulic, hydraulic Etc. However, in the case of such a pressure type, although a relatively large torque is advantageous, an electromagnetic valve or an electromagnetic actuator is used for control, and these are installed outside the MRI room. In some cases, a long pipe is required and there is a problem in responsiveness. Also, the stick-slip phenomenon that occurs in the cylinder is a big problem for precise position control. For this reason, the pressure method is difficult to use as an MRI actuator. As in the case of application to an MRI apparatus, an ultrasonic motor is suitable for a requirement for an actuator that is made of a non-magnetic material and does not generate electromagnetic noise.

  There are two types of ultrasonic motors: standing wave type and traveling wave type. Currently, the traveling wave type is mainly used from the viewpoint of durability and the like. There are three components: a piezoelectric vibrator, an elastic body, and a moving body. When an elastic body is excited by ultrasonic vibration generated from the piezoelectric vibrator, the elastic body vibrates at a specific frequency, and the vibration wave is elastic. Progress continuously throughout the body. At this time, the mass on the surface of the elastic body becomes an elliptical motion, and the moving body proceeds in the form of receiving a thrust and moving just as the wave carries the object.

  FIG. 1 shows the structure of an ultrasonic motor. An ultrasonic motor 1 includes an annular slider (rotor) 2, an annular piezoelectric vibrator 3 that generates ultrasonic vibrations, and an annular ring bonded to the upper surface thereof. And a stator composed of the elastic vibration member 4. The slider 2 is overlapped on an elastic vibrator 4 of a stator having a comb-like groove formed on the upper surface. A bearing 6 rotatably supports the shaft 5 attached to the slider 2, and the bearing 6 is attached to a case 7 having a hole through which the shaft 5 passes.

  FIG. 2 shows a portion of the piezoelectric vibrator 3, and the piezoelectric vibrating body 3 is divided into two regions A and B in the circumferential direction, and the regions A and B are adjacent to each other at an interval of half the wavelength λ. Polarization processing is alternately performed in the thickness direction for each matching section, and the region A and the region B are spaced so that the phase is shifted by three-quarter wavelengths.

  When the piezoelectric vibrator 3 is excited by applying a high-frequency voltage having a phase difference of φ to the regions A and B, the standing waves generated in the portions of the elastic vibrator 4 corresponding to the regions A and B of the stator are mutually Interfering and synthesizing, the excitation wave is transmitted to the elastic vibrating body 4 bonded to the piezoelectric vibrator 3, and a traveling wave traveling in one direction is created. When the slider 2 is pressed against the elastic vibrator 4 of the stator at a constant pressure, a frictional force is generated between the slider 2 and the stator, and the slider 2 is opposite to the traveling direction of the traveling wave of the stator by the frictional force. As a result, the ultrasonic motor 1 is driven. Then, the driving force of the ultrasonic motor 1 is converted into the rotational force of the load via the shaft 5.

  Compared with electromagnetic motors, ultrasonic motors do not generate a magnetic field and are not affected by external magnetic fields, and are superior in electromagnetic compatibility. However, it has the advantages of being able to obtain a large holding torque without power supply from the outside when it is stationary, and extremely low operating noise. In addition to having different nonlinear input characteristics, the dynamic characteristics vary greatly depending on the driving conditions (load, temperature, etc.), the control circuit is complicated, and friction drive is used for the operating principle Therefore, there is a disadvantage that the life is short.

  Since the life is short, the ultrasonic motor is mainly used for an application in which a driven body is moved by a predetermined distance and stopped at a target position instead of continuous driving. Further, there are three parameters for controlling the rotation of the ultrasonic motor: input frequency, voltage, and phase difference. For each parameter, the characteristics of the rotational speed as the output are (a) frequency-rotational speed in FIG. b) Voltage-rotation speed, (c) Phase difference-rotation speed, and each parameter has nonlinear characteristics, and these characteristics change depending on conditions such as load and temperature. Of the three parameters, the relationship between the phase difference and the rotational speed is relatively linear, so it is effective to change the phase difference for the speed control of the ultrasonic motor, but it is also a non-linear characteristic. This nonlinearity interferes with accurate control. No effective countermeasure has been taken to compensate for such nonlinear characteristics of input-output in the control of an ultrasonic motor.

  The control of the ultrasonic motor is disclosed in the following documents.

  Patent Document 1 includes a frequency switching unit that switches the output frequency of the power supply unit and a phase difference switching unit that switches the phase difference of the output voltage of the power supply unit in the drive control unit of the ultrasonic motor control device. Based on the deviation between the drive position detected by the position detection means and the target position, the operation of the frequency switching means and the phase difference switching means is selectively controlled by the deceleration control means, so that the ultrasonic motor can be stably operated. It is described that the stop position is accurately controlled while maintaining the above.

Patent Document 2 discloses a rotational axis determination means for a moving body to reach a target position in a vibration type actuator having three or more types of multi-degree-of-freedom vibration modes having redundancy / non-linearity in the input-output relationship. And the inverse model is used to supply a frequency signal having the phase and amplitude determined by the parameter determining means for the frequency signal for rotating the moving body around the determined rotation axis.
JP-A-4-75479 JP 2004-129458 A

  In the control of a conventional ultrasonic motor as described in Patent Document 1, the nonlinearity of the parameters when controlling the ultrasonic motor is compensated, and the input-output relationship is made linear so that the control is accurate. There was no particular consideration for doing so. Further, in the one described in Patent Document 2, it is considered to compensate for redundancy / nonlinearity by learning with a neural network in a complex system such as a multi-degree-of-freedom rotation type. It is not practical to perform such control with a rotary type because the circuit configuration becomes complicated. Therefore, it has been required to perform accurate control by compensating for the nonlinear characteristics of the ultrasonic motor with a simple configuration.

  The present invention has been made to solve the above-described problems, and an ultrasonic motor control device according to the present invention includes at least a phase difference control unit that controls a phase difference of power supplied to an ultrasonic motor in accordance with an input signal. An ultrasonic motor control unit having a linear conversion circuit that converts an input signal, and a phase difference control circuit that receives a signal converted by the linear conversion circuit and generates a control signal to the ultrasonic motor The linear conversion circuit is such that the relationship of the output of the ultrasonic motor to the input signal to the phase difference control unit is linear.

  The linear conversion circuit may be formed of a programmable logic device.

  In the present invention, the input-output characteristic of the ultrasonic motor is linear with a control circuit with a simple configuration by adding a linear conversion circuit to the input signal to the phase difference control unit in the control circuit of the ultrasonic motor. It can be the same as This linear conversion circuit can be a simple circuit configuration as a conversion table type.

  The rotational speed of the ultrasonic motor depends on three parameters: the frequency, voltage, and phase difference of the power applied to the piezoelectric vibrator, and the rotational speed changes by changing these three factors. The characteristics of the rotational speed as an output with respect to these three parameter inputs each have nonlinearity. Of the three parameters of frequency, voltage, and phase difference, the phase difference has a linear relationship with the rotational speed. Therefore, in the present invention, the input-output characteristic of the ultrasonic motor is linear with respect to the phase difference parameter. Consider a similar usage pattern.

  FIG. 4A schematically shows the configuration of the ultrasonic motor control apparatus according to the present invention. The control circuit unit 11 that is a main part of the ultrasonic motor control device includes a frequency control unit 12, a phase difference control unit 13, and a voltage control unit 14, and each of the frequency, phase difference of power supplied to the ultrasonic motor, Electric power is supplied to the ultrasonic motor USM through the amplification unit 15 and the step-up transformer 16 which are made of an FET after adjustment for controlling the voltage. FIG. 4B shows the configuration of the phase difference control unit in FIG.

  The control characteristics of the frequency control unit 12 and the voltage control unit 14 have non-linearities as shown in FIGS. In the configuration of the phase difference control unit that is generally used, the non-linearity as shown in FIG. 3C is obtained as a characteristic of the rotational speed of the ultrasonic motor with respect to the input. In the present invention, however, FIG. ), The phase difference control unit 13 includes a linear conversion circuit 13a that converts an input signal to the original phase difference control circuit 13b. When the input signal is directly input to the phase difference control circuit 13b, the output characteristics of the ultrasonic motor have non-linear characteristics. However, after the input signal is converted by the linear conversion circuit 13a, the phase difference control circuit 13b The linear conversion circuit 13a is configured such that the output characteristics of the ultrasonic motor are linear with respect to the input signal to the linear conversion circuit 13a.

  FIG. 5 shows a model that considers an input-output relationship for a phase difference control circuit and an ultrasonic motor as a unit. In this case, the phase difference control circuit receives the input signal r (k), generates a control signal, and supplies the control signal to the ultrasonic motor via the amplifier circuit and the step-up transformer. The rotational speed is considered as the output y (k) of the ultrasonic motor. The relationship of input r (k) -output y (k) by a general phase difference control circuit has a nonlinear characteristic as shown in FIG. 6A, but a linear conversion circuit as shown in FIG. 4B according to the present invention. The phase difference control circuit having 13a has a linear characteristic as shown in FIG.

The linear conversion circuit 13a for linearizing the characteristics of the phase difference control circuit converts the relationship r (k) -y (k) from the form shown in FIG. 6A to the form shown in FIG. 6B. Since it is a thing, it can comprise by thinking as FIG. 7, for example. FIG. 7A shows the phase difference control circuit of FIG. 5 as having a linear conversion circuit as shown in FIG. 4B. The input r (k) is converted by the linear conversion circuit 13a and s This is considered to be input to the phase difference control circuit 13b as (k). FIG. 7B is a view obtained by superimposing (a) and (b) of FIG. Here, it is assumed that φ _p corresponds to the straight line b and φ _q corresponds to the curve a for a certain value of N.

What is necessary as a function of the linear conversion circuit 13a is that the input r (k) is converted into a straight line b that has a characteristic like the curve a when r (k) is directly input to the phase difference control circuit. It is. For this purpose, the phase difference phi _p may be converted to the phi _q by the input r (k). When the phase difference becomes phi _p input r (k), by entering this with the phase difference control circuit to convert the φ _q s (k), it is in the form of curve a as the characteristic of the phase difference control circuit Therefore, the value N of the output characteristic does not change. In other words, the relationship r (k) −y (k) is equivalent to a linear characteristic due to the conversion of φ _p → φ _{q in} the linear conversion circuit.

  As such a linear conversion circuit, in the case of a circuit that handles an input signal as a digital quantity, a conversion table in which an input-output relationship is tabulated is provided, and an output obtained by converting the input signal with reference to the conversion table is generated. Can be configured. Further, such a linear conversion circuit or a control circuit unit including the linear conversion circuit can be easily configured by a programmable logic device (CPLD).

  In the present invention, in the ultrasonic motor control device, with a simple configuration that includes a linear conversion circuit for a signal input to the phase difference control unit, the ultrasonic motor control circuit is handled in the same manner as the linear characteristic. The ultrasonic motor can be controlled with high accuracy.

FIG. 3 is a partially broken view showing the structure of an ultrasonic motor. It is a figure which shows the part of the piezoelectric vibrator of an ultrasonic motor. It is a figure which shows the relationship between the control parameter and output of an ultrasonic motor, and shows the relationship of (a) frequency-rotation speed, (b) voltage-rotation speed, (c) phase difference-rotation speed. (A) It is a figure which shows schematic structure of the ultrasonic motor control apparatus by this invention, and shows the structure of the part of (b) phase difference control part. It is a figure which shows the relationship of input-output in model, seeing a phase difference control circuit and an ultrasonic motor as a unit. FIG. 5 shows an input-output relationship with respect to the model of FIG. 5, and shows a case where (a) no linear conversion circuit is provided and a case where (b) a linear conversion circuit is provided. (A) It is a figure shown about the case where the phase difference control part in FIG. 5 is provided with a linear transformation circuit, (b) What overlapped and showed (a) and (b) of FIG. 6 as an example which forms a linear transformation circuit. FIG.

Explanation of symbols

1 Ultrasonic motor 2 Slider (rotor)
3 Piezoelectric vibrator 4 Elastic vibrator 5 Shaft 6 Bearing 7 Case 11 Ultrasonic motor control circuit unit 12 Frequency control unit 13 Phase difference control unit 13a Linear conversion circuit 13b Phase difference control circuit 14 Voltage control unit 15 Amplifying unit 16 Step-up transformer

Claims (2)

  An ultrasonic motor control unit including at least a phase difference control unit that controls a phase difference of electric power supplied to the ultrasonic motor according to an input signal, the phase difference control unit converting the input signal into the linear conversion circuit and the linear conversion circuit A phase difference control circuit that receives a signal converted by the conversion circuit and generates a control signal to the ultrasonic motor, and the linear conversion circuit relates an output of the ultrasonic motor to an input signal to the phase difference control unit. An ultrasonic motor control device characterized in that is linear. The ultrasonic motor control device according to claim 1, wherein the linear conversion circuit is formed of a programmable logic device.

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