JP2814147B2 - Ultrasonic motor drive controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control device for an ultrasonic motor.

[0002]

2. Description of the Related Art In recent years, ultrasonic motors have been used as a driving source for various devices because of their small size and high torque without generation of magnetism.

[0003] Ultrasonic motors, as shown in FIG. 7, a disk-shaped rotor 2 having a rotating shaft 1 to the center, a plurality of piezoelectric bodies 3 ₁ to 3 _n which are arranged annularly, 4 _{1-4 n} , 5 and a stator 8 having an elastic body 7 adhered to the upper surface of the piezoelectric sensor 6.

[0004] The piezoelectric element _{3 1 ~3 n, 4 1 ~4} n are aligned so polarities are alternately arranged, as shown in FIG. 8,
Against the left of the piezoelectric 3 ₁ to 3 _n and right piezoelectric 4 ₁ to 4 _n, apply an AC signal 90 ° phase at a frequency close to the resonant frequencies are different piezoelectric electrodes 9a, 9b, 10a, from 10b then, the piezoelectric _{3 1 ~3 n, 4 1 ~4} n is to flexural vibration in the circumferential direction, interference waves of the left and right via the piezoelectric body 5 of the intermediate, as shown in FIG. 9, the elastic body 7 An elastic wave traveling along the circumferential direction is generated on the surface of.

For this reason, the rotor 2 in contact with the elastic body 7 from above is driven to rotate in the direction opposite to the direction in which the elastic wave travels.

As the rotational speed of the rotor 2 increases, the delay with respect to the traveling speed of the elastic wave decreases as the amplitude of the elastic wave increases, and the amplitude of the elastic wave decreases as shown by the characteristic A in FIG. frequency increases closer to the piezoelectric element _{3 1 ~3 n, 4 1 ~4} n resonant frequency F ₀ of the.

Accordingly, if the variable ac signal frequencies in the range, for example, from F _a of F _b against the ultrasonic motor, the motor speed is also changed following the variable of the frequency.

In order to drive this ultrasonic motor at a constant speed, a rotational speed detector such as a rotary encoder is connected to the rotor 2, and the detected signal is compared with a value corresponding to a desired speed. According to the result, the drive frequency may be varied at a predetermined rate of change, and feedback control may be performed so that the motor rotation speed approaches the target speed.

[0009]

However, the resonance characteristics of the ultrasonic motor greatly change depending on the ambient temperature.
If particularly cold, the characteristic A at room temperature in 10, because the curve at a high resonant frequency F ₀ 'than F ₀ will be shifted as steep characteristic B, the combined frequency change rate to a normal temperature characteristic In this case, the loop response at low temperatures is significantly delayed.

On the other hand, when the temperature is adjusted to the low-temperature characteristic, the response characteristic of the loop at room temperature becomes unstable with vibration.

An object of the present invention is to provide an ultrasonic motor drive control device which solves this problem.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an ultrasonic motor drive control device according to the present invention comprises an ultrasonic motor in which the rate of change of the frequency of an AC signal is detected by a temperature sensor during constant speed control. The switching is controlled in accordance with the level of the temperature.

[0013]

Therefore, the constant speed control corresponding to the ultrasonic motor is performed at the frequency change rate corresponding to the temperature.

[0014]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing a configuration of a drive control device (hereinafter referred to as a drive control device) 20 for an ultrasonic motor according to one embodiment.

In FIG. 2, reference numeral 21 denotes a CPU 3 to be described later.
A DA converter 22 that outputs a voltage corresponding to output data from 0, 22 is a VCO (voltage controlled oscillator) that oscillates and outputs a signal whose frequency changes in the opposite direction to a change in the output voltage of the DA converter 21. .

Reference numeral 23 designates an output signal from the VCO 22 as 1 /
This is a phase shift circuit that generates an AC signal having a phase difference of 90 degrees by dividing the frequency by 4. 24 and 25 are phase shift circuits 23
Piezoelectric 3 ₁ to 3 _n of amplifying the output of the ultrasonic motor M,
4 is a driver for applying respectively to ₁ to 4 _n.

A rotary encoder 26 for outputting a pulse signal having a frequency proportional to the rotation speed of the rotor 2 is connected to the rotor 2 of the ultrasonic motor.

Reference numeral 27 denotes a temperature sensor that outputs a signal corresponding to the temperature of the ultrasonic motor M. Reference numeral 28 denotes an output of the temperature sensor 27, and a signal shown in FIG.
This is an AD converter that outputs bit temperature data.

Reference numeral 29 denotes a speed setting device for setting the steady speed (target speed) of the ultrasonic motor M. The pulse set T of the rotary encoder 26 when the ultrasonic motor M rotates at the target speed is set. Is done.

As shown in FIG. 4, the CPU 30 calculates coefficient values A _{1 to} A ₄ corresponding to the temperature data from the AD converter 28.
(However, 0 <A ₁ <A ₂ <A ₃ <A ₄ ) is stored in the memory 31.
When the activation signal becomes “H” level, the VCO is activated based on the coefficient value for the temperature data at that time.
The ultrasonic motor M is started by performing the sweep of step S22.

FIG. 1 is a flowchart showing the start-up process and the constant speed process of the CPU 30. Hereinafter, the operation of the drive control device 20 will be described with reference to this flowchart.

When the activation signal for the CPU 30 becomes "H" level, the coefficient for the temperature data from the AD converter 28 is determined to be one of A _{1 to} A ₄ (steps 1 and 2).

Next, voltage data D for the DA converter 21 is set to an initial value D ₀ (Step 3).

Therefore, a two-phase AC signal having a frequency (for example, F _{c in} FIG. 10) corresponding to the voltage data D ₀ is applied to the ultrasonic motor M.

The application of the AC signal causes the ultrasonic motor M to gradually rotate, and a pulse signal having a long cycle is output from the rotary encoder 26, and the cycle t is measured (step 4).

Next, the voltage data D is increased by a value obtained by multiplying the coefficient A by a value obtained by subtracting the period T set in the speed setting unit 29 from the measured period t, and new voltage data D + A ( driving by t-T) low frequency AC signal from the F _c corresponding to is made. (Step 5).

Next, the two periods t and T are compared in magnitude. If the period of the output pulse of the rotary encoder 26 is longer than the set period T, the process returns to step 4 (step 6). Hereinafter, the same processing (steps 4 to 6) is performed until the cycle t of the output pulse of the rotary encoder 26 becomes shorter than the set cycle, that is, until the rotation speed of the ultrasonic motor M reaches the target speed.

At this time, the variation width of the voltage data every time, that is, the variation width of the frequency of the AC signal becomes smaller as the coefficient A corresponding to the temperature becomes smaller. It is later than the time, and the motor operation is reliably started without delaying this driving.

When the ultrasonic motor M is started up to the target speed in this way, the CPU 30 shifts to a constant speed control process.

[0031] After the startup process, and start timer for a predetermined time T _m, is carried out level determination of the start signal, "H"
If the level remains, the cycle t of the output pulse of the rotary encoder 26 is measured, and the measured cycle t is compared with the set cycle (steps 7 to 10).

Here, if t <T, it is determined that the rotation speed is faster than the target speed, the voltage data is subtracted and updated by AP (P is a constant), and the frequency of the AC signal increases (step 11). If t <T, it is determined that the rotation speed is lower than the target speed, and only the voltage data A and P are added and updated, and the frequency of the AC signal decreases (step 1).
2).

After the frequency is changed, it is determined whether the time has elapsed. If the time _Tm has not elapsed, the process returns to step S8. If the time has elapsed, it is determined whether the temperature data has changed. (Steps 13, 1
4). If the temperature data has changed, the coefficient is switched to a coefficient corresponding to the temperature data (frequency change rate switching means), and the timer is started again (step 15).

Therefore, if the temperature rises and the temperature data changes during the constant speed control, the rate of change of the frequency of the AC signal to the ultrasonic motor also increases, and the rotational speed of the ultrasonic motor is independent of the temperature. The constant speed control is performed stably at a substantially constant rate of change.

[0035]

[Other Embodiments] In the above embodiment, the period of the output pulse of the rotary encoder 26 is measured to control the speed by the CPU 30, but the present invention is also applicable to a drive control device having an analog control unit. Can be applied.

FIG. 6 shows an analog control circuit 3 according to the present invention.
5 is a circuit diagram showing a case where the present invention is applied to FIG. This control circuit 3
In 5, to output a pulse of a predetermined width synchronized with the output pulses of the rotary encoder 26 from the one-shot multivibrator circuit 36, by integrating this output with the integration circuit 37 performs the frequency-voltage conversion, and the converted output V _a , the reference voltage V _r and the analog adder 3 from the variable resistor 38
9 is configured to control the oscillation frequency of the voltage V ₀ obtained by adding VCO 22, if the rotational speed of the ultrasonic motor M is higher than the target speed (which corresponds to the reference voltage V _r) is, VCO 22 If the oscillation frequency of the VCO 22 is low, on the contrary, the oscillation frequency of the VCO 22 is lowered to always approach the target speed.

Capacitors C ₁ , C ₂ , and C ₃ provided between the input and output of the analog adder 39 are capacitors for determining the response speed of the output to the input voltage V ₀ of the VCO 22. corresponding to ₁ to a _{4 (however, C 1 <C 2 <C} 3).

The connection of the capacitors C ₂ and C ₃ is made by the switch 4 which is turned on when the temperature data from the AD converter 28 is “0”
As shown in FIG. 7, the connection is made such that the parallel capacitance increases as the temperature decreases.

Therefore, for example, at a low temperature of -20 degrees, only the reference voltage _Vr is applied to the analog adder 39, and its output changes slowly at a slow response speed due to the capacitance of C ₁ + C ₂ + C _3. To do so, the ultrasonic motor M
Constant speed control is performed by an AC signal having a small frequency change rate.

Further, in the above-described embodiment, the temperature change is detected at every predetermined time, but it may be detected at each rotation period measurement whether or not there is a temperature change.

[0041]

As described above, according to the drive control apparatus for an ultrasonic motor of the present invention, the rate of change of the frequency during the constant speed control of the AC signal applied to the ultrasonic motor is detected by the motor. Can be switched in accordance with the level of the temperature of the ultrasonic motor, so that the rotational speed of the ultrasonic motor can be constantly and stably controlled at a substantially constant rate of change regardless of the temperature.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a processing procedure according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of one embodiment.

FIG. 3 is a correspondence diagram for explaining an operation of a main part of one embodiment.

FIG. 4 is a correspondence diagram for explaining the operation of the main part of one embodiment.

FIG. 5 is a circuit diagram showing a control unit according to another embodiment of the present invention.

6 is a correspondence diagram for explaining the operation of the main part of the embodiment of FIG. 5;

FIG. 7 is a schematic perspective view showing a configuration of an ultrasonic motor.

FIG. 8 is a front view of a main part of the ultrasonic motor.

FIG. 9 is a schematic diagram for explaining the operation of the ultrasonic motor.

FIG. 10 is a diagram showing characteristics of an elastic wave amplitude with respect to a driving frequency of an ultrasonic motor.

[Explanation of symbols]

 Reference Signs List 20 ultrasonic motor drive control device 22 VCO 23 phase shift circuit 26 rotary encoder 27 temperature sensor 29 speed setting device 30 CPU M ultrasonic motor

Claims (1)

(57) [Claims] The frequency of an AC signal applied to an ultrasonic motor is varied at a predetermined rate according to a signal from a rotation detector connected to a rotor of the ultrasonic motor, and the rotation of the ultrasonic motor is controlled. In an ultrasonic motor drive control device that performs constant speed control in a direction that always brings the speed close to the target speed, a temperature sensor that detects a temperature of the ultrasonic motor, and a rate of change of a frequency of an AC signal during the constant speed control, A drive control apparatus for an ultrasonic motor, comprising: frequency change rate switching means for switching according to the level of the temperature of the ultrasonic motor detected by the temperature sensor.