JPH02101974A - Ultrasonic motor drive - Google Patents

Abstract

PURPOSE:To drive an ultrasonic motor with constant torque by detecting the mechanical arm current of the ultrasonic motor and performing amplitude control of the mechanical arm such that an output torque signal obtained based on an actual rotational speed and a noload rotational speed calculated on the basis of the detected mechanical arm current will match with a preset output torque. CONSTITUTION:In an ultrasonic motor where a frequency voltage is applied onto piezoelectric bodies 9, 10 to excite an elastic wave in a vibrating body 23 comprising the piezoelectric bodies 9, 10 and an elastic body so as to move a moving body 24 arranged on the vibrating body 23 while pressure contacting therewith, the rotation tends to decrease as the load torque increases. Output of the ultrasonic motor is obtained based on the difference between an actual rotational speed under some mechanical arm current amplitude (g) and noload rotational speed at that mechanical arm current (f), and the mechanical arm current amplitude (g) is controlled by a frequency control system such that the output torque of the ultrasonic motor will match with a set value. By such an arrangement, output torque can be controlled constant without requiring a torque sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic motor device that generates driving force using a piezoelectric couple.

Conventional technology In recent years, various types of ultrasonic vibrations have been excited using electro-mechanical transducers using piezoelectric pair ceramics, etc.
Ultrasonic motors that obtain rotational or running motion are attracting attention because they have a high energy density.

FIG. 4 shows an exploded perspective view of the ultrasonic motor. Mobile body 24
The piezoelectric bodies 21 and 22, which are radially polarized in the bottom disk shape of the vibrating body 23 in contact with
A driving signal d of several tens of kHz with a temporal phase difference of 900 is applied to each of the piezoelectric bodies 21 and 22 by shifting and gluing them together.
, e, standing waves are generated in the piezoelectric body 21, 22 with phases different from each other by 90'' both temporally and spatially.

When the amplitudes of the two standing waves are made equal, the standing waves are combined in the vibrating body 23 to generate a bending vibration wave that travels in the circumferential direction. 25 and 26 are electrode parts.

Also, 27 is a spring, and 29 is a screw (Japanese Patent Laid-Open No. 60-19
Publication No. 0178).

FIG. 5 shows that point A of the vibrating body 23 is caused by the traveling wave to
w, shows an elliptical motion of the short axis 2u, and when the moving body 24 installed under pressure on the piezoelectric body 23 comes into contact with the apex of the ellipse, v = f1 in the opposite direction to the traveling direction of the wave.
It shows that it is moving at a speed of 1u (f is the frequency of the traveling wave). The moving body 22 is driven in a direction opposite to the direction of wave propagation due to the frictional force between it and the vibrating body 23, and when the work done to the outside cannot be ignored with respect to this frictional force, the moving body 24 and the vibrating body A slip occurs between 23 and the velocity becomes smaller than V.

Figure 2 is an electrical equivalent circuit diagram of the piezoelectric body 21 or 22, which is considered to be a parallel combination of capacitance C@ that does not contribute to the piezoelectric effect, and capacitance C, R, that contributes to the piezoelectric effect. The current flowing through C6 is called the electric arm current, and L,
The current flowing through C1 and H is called a mechanical arm current. The mechanical arm current and the short axis amplitude 2u are in a proportional relationship. The mechanical arm admittance Y (s) is given by the following equation.

(S is Laplace operator s=j 2πf) Y(s)=(
s/L)/(s'+(R/L)s+(1/LC,))
In the formula, the resonant frequency is I/(2πLC+)
is given by Even if the voltage and frequency applied to the piezoelectric body 11.12 are constant, the electrical admittance of the piezoelectric body 11.12 changes due to changes in ambient temperature and mechanical load (R, L, C+ change). ) Movement speed changes.

As explained above, the moving speed of the ultrasonic motor is determined by the product of the frequency W of the traveling wave and the short axis U of the elliptical motion, and the size of the short axis U is proportional to the mechanical arm current. The fluctuation range of the short axis U is larger than the fluctuation range of the frequency W, and the moving speed is determined almost by the mechanical arm current.

If the mechanical load on the piezoelectric body 21, 22 is constant, the electrical impedance is constant, and if the voltage and frequency are constant, the mechanical arm current is constant.

Problems to be Solved by the Invention As mentioned above, conventionally, in order to keep the rotation speed constant, the mechanical arm current, which is known to be approximately proportional to the rotation speed, has been controlled to match the set value. . However, in addition to controlling the rotation speed, motors are used for
There are cases where it is desired to control the output torque to a required value, but so far not much attention has been paid to controlling the output torque of the ultrasonic motor.

In view of the above prior art, the present invention provides a device for driving an ultrasonic motor with constant torque.

Means for Solving the Problem By applying a frequency voltage to a piezoelectric body and exciting an elastic wave to a vibrating body composed of the piezoelectric body and an elastic body, the piezoelectric body is placed in pressure contact with the vibrating body. In an ultrasonic motor that moves a moving object, when the mechanical arm current amplitude is changed while the load torque is kept constant, the change in motor rotation speed approximately follows a straight line with a positive slope. . A group of straight lines showing the relationship between the rotational speed and the mechanical arm current amplitude obtained when the load torque is increased from 0 has approximately the same slope, and shows a tendency for the rotational speed to decrease as the load torque increases. That is, the rotation speed is N1 and the mechanical arm current amplitude is 1. Then, the straight line is N=AX1. +B 2 , the slope A remains almost constant even if the load torque changes, and the slope B decreases as the load torque increases.

Therefore, the no-load rotation speed for the mechanical arm current amplitude at a certain point in time is determined, and the output torque is determined from the difference between it and the actual rotation speed at that time, so this difference in rotation speed can be controlled by controlling the mechanical arm current amplitude. The output torque can be controlled at a constant level.

The output of the ultrasonic motor is determined from the difference between the actual rotation speed under an active mechanical arm current amplitude and the no-load rotation speed at that mechanical arm current amplitude, and the machine is adjusted so that this output torque matches the set output torque. By having a frequency control system that controls the arm current amplitude, it is possible to provide an ultrasonic motor device that can control the output torque to a constant level without a torque sensor.

EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. FIG. 2 shows an equivalent circuit of a piezoelectric body. A piezoelectric body 9 and a resistance element 5 are connected in series to the electrode part 7, and the electric arm of the piezoelectric body in FIG. Connect in parallel with a series connection body consisting of a piezoelectric body and a resistive element. By determining the potential difference between the resistive elements 5 and 6 of the electrode section 7 using the differential amplifier 18, the electrical arm current P is canceled out and the mechanical arm current f is detected. Since the mechanical arm current f is alternating current, the amplitude detector 17 is used to find the mechanical arm current amplitude g. When the mechanical arm current amplitude g is input to the no-load rotation speed calculator 15, a no-load rotation speed signal indicating the no-load rotation speed at the mechanical arm current amplitude g is sent to the output torque calculator 14. Also,
A pulse-like angle signal I is output from the rotation speed sensor 19 for measuring the rotation speed of the ultrasonic motor, and the angle signal i is converted into a rotation speed signal j representing the rotation speed by the F/V converter 16.
is converted to This rotational speed signal j is output torque calculator 1
4, and an output torque signal k is determined from the no-load rotational speed signal and the rotational speed signal j. This output torque signal is compared with the set output torque signal l in a comparator 13, and the frequency controller 12 outputs a frequency control signal n so that the output torque error signal m, which is the comparison result, becomes O.

The voltage controlled frequency oscillator 1 is based on the frequency control signal n,
A predetermined drive frequency signal a is output.

The 90° phase shifter 2 has a temporal phase of 90° with respect to the drive frequency signal a.
``Generate different signals, and these two AC signals b+
c is amplified by power amplifiers 3 and 4, respectively, and a drive signal e is applied to electrode parts 7 and 8 and piezoelectric bodies 9 and 10.

It is applied as d. The above is the configuration of this embodiment.

Next, the operation of this embodiment will be explained using FIG. 3. Third
The figure shows the mechanical arm current amplitude 1. when the ultrasonic motor is driven under constant load torque. It is a figure showing the relationship between (g) and motor rotation speed N. As can be seen from FIG. 3, even if the load torque (T) changes, the mechanical arm current amplitude is 1. The slope of the motor rotation speed N with respect to (g) is almost constant, and the load torque T
When increasing from =0 to T+, Ta, Ta, the constant load torque graph moves toward the smaller motor rotation speed N while keeping its slope almost constant.

Now, consider a case where the motor is driven at 22 points.

The current rotation speed N2 is determined by performing F/V conversion on the angle signal i from the rotation speed sensor. Also, the current mechanical arm current amplitude I
as is determined by the amplitude detector 17. Mechanical arm current amplitude with no load 1. If Cg) is known, the no-load rotational speed N- at this time can be found. This mechanical arm current amplitude 1. (
The process of determining the no-load rotation speed from g) is performed by the no-load rotation speed calculator 15. Here, since the slope θ・ of the graph when the load torque T=O is almost equal to the slope θ? of the graph when the load torque T '' T * is almost equal, the difference between the no-load rotation speed No. and the actual rotation speed N2 is Load torque T=
The distance between the graph of O and T2 can be found, and from this distance the current torque T2 can be found. The output torque calculator 14 calculates the current torque T2 from the no-load rotational speed N@ and the actual rotational speed N2. Therefore, by making the value obtained from the no-load rotational speed N9 and the actual rotational speed N2 coincide with the set value, it is possible to drive with a constant torque. and,
If the rotation speed is constant, the output torque is mechanical arm current amplitude 1, (
g), so if the value calculated from the no-load rotation speed N@ and the actual rotation speed N2 is larger than the set value l (if the output torque is too large), then the driving frequency of the ultrasonic motor Sweeping to the high frequency side, the mechanical arm current amplitude 1. (g
) to lower the output torque. Conversely, the no-load rotation speed N
If the value obtained from 8 and the actual rotational speed N2 is smaller than the set value (if the output torque is too small), the drive frequency is swept to the lower frequency side and the mechanical arm current amplitude is set to 1. (g) to increase the output torque.

In this way, the output torque obtained from the no-load rotation speed Nl (h) and the actual rotation speed N2 (j) is compared with the set output torque l, and the drive is adjusted according to the output torque error m that is the comparison result. Constant torque drive can be achieved by changing the frequency a and controlling the mechanical arm current amplitude g.

As an effect of this example, if the relationship between the motor no-load rotation speed and the mechanical arm current amplitude is known, the no-load rotation speed can be found by obtaining the mechanical arm current amplitude, and the no-load rotation speed and the actual By keeping the value determined from the rotation speed constant, the motor can be driven with a constant torque. In this case, no special torque sensor is required. Furthermore, since the mechanical arm current amplitude is O at startup, the calculated no-load rotation speed is also O. Since the actual rotational speed at the time of startup is also 0, the rotational speed difference is O, and frequency control works in the direction of increasing the mechanical arm current amplitude, so that constant torque control works from the time of startup. Similarly, when the ultrasonic motor is stopped, the rotation speed becomes 0, so the output torque is determined by the no-load rotation speed, and the no-load rotation speed is determined by the set output torque l, so the ultrasonic motor The output torque can be controlled to be constant even when the motor is stopped.

In this example, a disc-type ultrasonic motor was used, and the mechanical arm current amplitude was used as a signal to be controlled to control the torque. However, other types of ultrasonic motors such as an annular type and a linear movement type The control target signal can also be a signal that can monitor the amplitude of the piezoelectric body of an ultrasonic motor, such as a voltage that corresponds to the strain of the piezoelectric body from an electrode provided on the piezoelectric body for a sensor. Furthermore, although the mechanical arm current is controlled by frequency in this embodiment, it can also be used to control the mechanical arm current by voltage.

Effects of the Invention As explained above, the mechanical arm current of the ultrasonic motor is detected, and the output torque signal obtained from the no-load rotation speed calculated from there and the actual rotation speed detected by the rotation speed sensor is calculated in advance. By controlling the mechanical arm current amplitude to match the set output torque, the ultrasonic motor can be driven with a constant torque.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a driving device for an ultrasonic motor according to an embodiment of the present invention, Fig. 2 is an exploded perspective view of an electric temporary type ultrasonic motor of the same motor, and Fig. 5 is an explanatory diagram of the principle of the motor. It is. 1. Electrically controlled frequency oscillator, 2. 90 degree phase shifter, 3
．． 4... Power amplifier, 9.10... Ultrasonic motor piezoelectric body, 12... Frequency controller, 13... Comparator, 14... Output torque calculator, 15... No-load rotation speed calculator, 16...
・F/V converter, 17...Amplitude detector, 18...Differential amplifier, 19...Rotational speed sensor Name of agent: Patent attorney Shigetaka Kurino゜Figure

Claims (1)

[Claims] An ultrasonic motor consists of a vibrating body made of a piezoelectric body and an elastic body, and a moving body installed in pressurized contact with this vibrating body, and an ultrasonic motor that has a phase difference of 90° at the same frequency with respect to the input frequency signal. a 90° phase shifter that generates two alternating current signals; a power amplifier for the two alternating current signals generated by the 90° phase shifter; and a machine that detects a mechanical arm current that indicates the amplitude of the piezoelectric pair of the ultrasonic motor. An arm current detector, a rotation speed detector that detects the motor rotation speed, a no-load rotation speed calculator that calculates the no-load rotation speed at the mechanical arm current, and the current rotation speed and no-load rotation speed. It has an output torque calculator that calculates the output torque, and a frequency controller that matches the output torque signal from the output torque calculator to the set output torque, and calculates the no-load rotation speed and the current rotation speed at the current mechanical arm current. 1. An ultrasonic motor drive device characterized by detecting the output torque of a motor and changing a mechanical arm current so that the requested torque and the actual output torque are equal.