JP2819437B2 - 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. 4, a disk-shaped rotor 2 having a rotating shaft 1 to the center, arranged in a ring plurality of piezoelectric 3 ₁ to 3 _n, 4 ₁ to 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. 5,
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. 6, 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.

The rotational speed of the rotor 2 is such that the larger the amplitude of the elastic wave is, the smaller the delay with respect to the traveling speed of the elastic wave is, and the amplitude of the elastic wave is, as shown in FIG. body _{3 1 ~3 n, 4 1 ~4} n resonant frequency F ₀ of the
The closer to, the larger.

As a drive control device for rotating the ultrasonic motor at a predetermined target speed at a constant speed, a rotational speed detector (eg, a rotary speed detector) connected to a rotor 2 of the ultrasonic motor as shown in FIG. The cycle (or frequency) of the signal from the encoder 11 is compared with the cycle corresponding to the target speed by the rotation speed comparing means 21, and the drive frequency control means 22 receiving the comparison output sets the oscillation frequency of the oscillator 23 to a predetermined value. A drive control device 2 that performs feedback control in such a manner that the signal period from the rotational speed detector 11 always approaches a period corresponding to the target speed.
0 is used.

In FIG. 8, reference numeral 24 denotes a phase shift circuit for converting the output signal of the oscillator 23 into drive signals having a phase difference of 90 degrees.

By this feedback control, even if the rotation speed temporarily fluctuates as shown in FIG. 9 due to, for example, a change in load, the motor rotation speed returns to the target speed in accordance with the response speed of the feedback loop. It is driven at a constant speed for a long time.

[0010]

However, when there is a sudden and large load change (A in FIG. 9), the response of the feedback loop does not follow the change in the rotational speed, and the return time t ₀ becomes extremely long. There was a problem that would.

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

[0012]

In order to solve the above-mentioned problems, a drive control device for an ultrasonic motor according to the present invention receives a detection signal from a rotational speed detector and changes the rotational speed of the ultrasonic motor to a target speed. An over-variation detecting means for detecting a change of not less than a predetermined value, and a frequency change rate for switching the change rate of the frequency of the drive signal to a larger value when the over-change detection means detects a change of not less than a predetermined value. Switching means.

[0013]

Therefore, when the fluctuation of the rotation speed exceeding the predetermined value is detected by the excessive fluctuation detecting means, the change rate of the driving frequency is increased by the frequency change rate switching means.

[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) 30 for an ultrasonic motor according to one embodiment.

In FIG. 2, reference numeral 31 denotes a CPU 4 to be described later.
A DA converter 32 that outputs a voltage corresponding to output data from 0, and 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 31. .

The reference numeral 33 designates an output signal from the VCO 32 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. 34 and 35 are phase shift circuits 33
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.

The rotor 2 of the ultrasonic motor M includes a rotor 2
A rotary encoder 36 that outputs a pulse signal having a frequency proportional to the rotational speed of the rotary encoder is connected.

Reference numeral 37 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 36 when the ultrasonic motor M rotates at the target speed is set. Is done.

The CPU 40 activates the ultrasonic motor and performs constant speed control in accordance with the processing procedure stored in the memory 41 in advance.

FIG. 1 is a flowchart showing the processing procedure of the CPU 40. Hereinafter, the operation of the drive control device 30 will be described with reference to this flowchart.

First, when the power is turned on, a start-up process (steps 1 to 4) for the ultrasonic motor M is performed.

This start-up process is a process for gradually increasing the motor rotation speed from the low speed to the target speed. First, the voltage data D to the DA converter 31 is set to the initial value D.
_It is set to ₀ (step 1).

Therefore, a two-phase AC signal having a frequency (for example, F _{1 in} FIG. 7) corresponding to the voltage data D ₀ is applied to the ultrasonic motor M. Due to the application of the AC signal, the ultrasonic motor M is gradually rotated, and a path signal having a long cycle is output from the rotary encoder 36, and the cycle t is measured (step 2).

Next, a magnitude comparison between the measured cycle t and a cycle T set in advance in the speed setting unit 37 is performed, and when the cycle t of the output pulse of the rotary encoder 36 is longer than the set cycle T, Returns to step 2 after the voltage data is increased by the predetermined sweep coefficient A (steps 3 and 4).

Hereinafter, the cycle t of the output pulse of the rotary encoder 36 becomes shorter than the set cycle. That is, the same processing (steps 2 to 4) is performed until the rotation speed of the ultrasonic motor M reaches the target speed.

As described above, when the ultrasonic motor M is started up to the target speed, the CPU 40 shifts to a constant speed control process. Even in this constant speed control process, the rotary encoder 3
6 is measured, and the measured period t
Is compared with the set period T (step 5,
6).

Here, for example, as shown at t ₁ in FIG.
If the motor rotation speed is equal to the target speed, it is determined that t = T, and the process returns to step S5.

Also, a slight change in the load causes t in FIG.
_If the rotation speed increases as at ₂ o'clock, it is determined that t <T, and if it is determined that this variation does not exceed the predetermined value α, the voltage data is subtracted and updated by B (B is positive). ), And the drive frequency is increased by an amount corresponding to B (steps 7 and 8).

The processing of steps 5 to 8 is repeated until t ₃ when the motor rotation speed increased by the load fluctuation reaches the target speed.

Conversely, if the rotation speed slightly decreases, such as at t ₄ , it is determined that t> T, and if it is determined that this variation does not exceed the predetermined value α, the voltage data is changed to B And the drive frequency is lowered by an amount corresponding to B (steps 9 and 10).

[0032] Also the process of step 5-10 is performed repeatedly until t ₅ the motor rotation speed is restored to the target speed.

Also, due to a sudden and large change in load,
When a sharp drop in motor speed exceeding t ₆ at a predetermined value alpha (or increase) is determined (over fluctuation detecting means), voltage data value greater C than B (e.g., three times the B) component only The frequency is updated (frequency change rate switching means), and the drive frequency is changed by an amount corresponding to C (steps 11 and 1).
2). The initial value D ₀ , the sweep coefficient A, the data B and C, and the predetermined value α of the voltage data are stored in the memory 41 in advance.

Therefore, the variable control of the drive frequency is repeated at a frequency change rate several times that of the steady state, and the motor rotational speed returns to the target speed in a short time.

In the following, the control of the driving frequency is similarly performed according to the magnitude and direction of the fluctuation of the motor rotation speed, and the ultrasonic motor is driven at a constant speed.

[0036]

[Other Embodiments] In the above embodiment, the frequency change rate of the drive frequency is switched by changing the increase / decrease constant of the voltage data from the CPU 40.
The reference voltage of 1 or the voltage-oscillation frequency characteristic of the VCO 32 may be switched.

In the above embodiment, the change rate of the drive frequency is switched when there is a change exceeding the predetermined value α. However, when there is a change exceeding the predetermined value β, the change rate becomes larger than C. The drive frequency may be variably controlled at a rate.

In the above embodiment, the comparison between the motor rotation speed and the target speed and the control of the oscillation frequency for the VCO are performed by the CPU.
However, the present invention is not limited thereto, and the present invention can also be applied to a drive control device that controls these using an analog comparator or an operational amplifier.

[0039]

As described above, the drive control apparatus for an ultrasonic motor according to the present invention is capable of controlling the frequency change in the normal constant speed control state when the rotational speed of the ultrasonic motor fluctuates by more than a predetermined value with respect to the target speed. Since the frequency of the drive signal is variably controlled at a frequency change rate larger than the rate, it is possible to return to the target speed in a very short time even if there is a sudden and large load change.

[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 diagram for explaining an operation of a main part of one embodiment.

FIG. 4 is a schematic perspective view showing a configuration of an ultrasonic motor.

FIG. 5 is a front view of a main part of the ultrasonic motor.

FIG. 6 is a schematic diagram for explaining the operation of the ultrasonic motor.

FIG. 7 is a diagram showing characteristics of an elastic wave amplitude with respect to a driving frequency of an ultrasonic motor.

FIG. 8 is a diagram showing a configuration of a conventional device.

FIG. 9 is a diagram for explaining the operation of the conventional device.

[Explanation of symbols]

 Reference Signs List 30 ultrasonic motor drive control device 32 VCO 33 phase shift circuit 36 rotary encoder 37 speed setting device 40 CPU M ultrasonic motor

Claims (1)

(57) [Claims] And detecting a rotation speed of the ultrasonic motor whose rotation speed changes in accordance with the frequency of the drive signal based on a detection signal from a rotation speed detector connected to a rotor of the ultrasonic motor. An ultrasonic wave that varies the frequency of the drive signal at a predetermined rate of change in accordance with a result of comparison between the detected rotational speed and a preset target speed to bring the rotational speed of the ultrasonic motor closer to the target speed In the motor drive control device, an over-variation detection unit that receives a detection signal from the rotation speed detector and detects that the rotation speed of the ultrasonic motor has changed by a predetermined value or more with respect to a target speed; And a frequency change rate switching means for switching the rate of change of the frequency of the drive signal to a larger value when a change equal to or more than the predetermined value is detected by the change detecting means. Motion control device.