JPH09261979A - Speed controller for ultrasonic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently control the speed even in a low speed range and to enhance the rapid response of the speed control by setting the set speed value stored in memory means as an initial set value, and steering a desired target speed to control the speed. SOLUTION: The rotating speed (target speed) of an ultrasonic motor 10 required for a microprocessor (CPU) 11 is set, and a voltage signal according to the set value is set from the CPU 11 to a V-f converting sawtooth wave forming circuit 12 as an f-D-A signal. A PWM control P-D-A signal is output according to the target speed set to the CPU 11, and speed control is conducted. Thus, the speed can be controlled by setting the speed in the direction for raising the P-D-A signal from the initial set value, i.e., the low speed range stored in the CPU 11, and the speed setting is simple with an excellent rapid response.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control device for an ultrasonic motor which controls the speed by pulse width modulation.

[0002]

2. Description of the Related Art Ultrasonic motors often perform speed control by changing the frequency (driving frequency) of the power supply pressure, but in addition, speed control can be performed by changing the voltage or phase of the power supply pressure. You can

That is, this type of motor is decelerated as the driving frequency is increased, and is accelerated as the driving frequency is decreased. The rotation speed of this motor changes in the same manner as above even if the phase of the power supply pressure is controlled.

Further, the speed can be controlled even if the voltage of the power supply voltage is changed. In this case, the higher the voltage, the higher the speed, and the lower the voltage, the slower the speed. The voltage control means for controlling the speed by changing the voltage of the power supply voltage is thus controlled by changing the power supply voltage to control the voltage level of the power voltage and pulse width modulation to change the effective value of the power voltage. Some are controlled by (PWM).

A specific example of the PWM control will be described. In a driver that operates a step-up transformer with a pulse voltage and applies an output voltage of the transformer to drive an ultrasonic motor, a pulse width of an input pulse of the step-up transformer is used. The speed is controlled by changing.

[0006]

Although it is effective to control the speed of the ultrasonic motor by changing the driving frequency,
If the drive frequency is increased so that the motor exceeds a certain control range, there is a problem that it is not suitable for low speed control of the motor because it has a characteristic that the rotation speed hardly changes.

Therefore, an object of the present invention is to propose a speed control device for an ultrasonic motor capable of sufficiently controlling the speed even in a low speed region of the motor and improving the responsiveness of the speed control. To do.

[0008]

SUMMARY OF THE INVENTION The present invention, however, relates to a speed control device for an ultrasonic motor in which a step-up transformer is operated with a pulse voltage and an output voltage of the transformer is applied to drive the step-up transformer.

Further, according to the present invention, speed control means for controlling the motor speed by pulse-width modulating the pulse voltage according to the target speed to be set, and the set speed at which the speed change starts by the pulse width modulation are detected in advance. , Memory means for storing the set speed value.

The present invention is characterized in that the set speed value stored in the memory means is used as an initial set value to set a desired target speed for speed control.

In the speed control device of the present invention thus constructed, the pulse width of the pulse voltage changes according to the target speed to be set, whereby the effective value of the output voltage of the step-up transformer changes and the motor speed changes. It is controlled according to the target speed. Since the speed control performed in this way is PWM control, it is particularly advantageous for the speed in the low speed region of the motor.

Further, since the speed control device is configured to set the target speed with the set speed value stored in the memory means, that is, the set speed value at which the speed change starts due to the pulse width modulation as the initial set value. As for the speed setting range in which the speed does not change due to pulse width modulation, the target speed can be set by skipping the setting range. As a result, the target speed can be set quickly and the speed control becomes easy. .

[0013]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a circuit of a speed control device. A CPU (microprocessor) 11 sets a required rotation speed (target speed) of an ultrasonic motor 10,
The voltage signal according to this set value is V / f from the CPU 11.
It is sent to the conversion / sawtooth wave generation circuit 12 as an fD / A signal. The CPU 11 outputs an f.D / A signal whose voltage level changes from an f.D / A signal generation unit (for example, a register) by changing the D / A setting input according to the set value.

The V / f conversion / sawtooth wave generation circuit 12 is a CPU
The voltage signal input from 11 is subjected to voltage-frequency conversion to create a sawtooth signal of frequency fn, which is sent to the distributor 13. The divider 13 shapes the sawtooth wave signal of fn into a rectangular wave while delaying the phase by 90 ° by the clock of 4fn, and divides it into four. That is, a rectangular wave signal is output from φ3 with a phase delay of 90 ° from φ1, a phase of 90 ° from φ3, a phase of φ2 from φ2, and a phase of 90 ° from φ2.

The four-divided rectangular wave signal is the AND circuit 14
It is input to the first input terminals of a to 14d. Also, the ultrasonic motor 1 is connected to the second input terminals of the AND circuits 14a to 14d.
An ON / OFF signal of 0 is input, and the pulse frequency signals output from the AND circuits 14a to 14d during the gate opening are amplified by the transistors 15a to 15d.
Input to the base.

The collectors of the transistors 15a and 15b are connected to both ends of the primary coil of the step-up transformer 16, and the collectors of the transistors 15c to 15d are the step-up transformer 1.
7 are connected to both ends of the primary coil, respectively. The output terminals of the secondary coils of the step-up transformers 16 and 17 are connected to the ultrasonic motor 10.

In addition, according to the target speed set in the CPU 11, the P / D for PWM control is controlled by the CPU 11.
/ A signal is output and this P · D / A signal is compared.
The data is sent to the first input terminal of the input terminal 19. In addition,
The CPU 11 changes the D / A setting input according to the speed setting value P. The voltage level changes from the D / A signal generator P.
D / A signal is output.

Then, the comparator 19 inputs the sawtooth wave signal sent from the V / f conversion / sawtooth wave generation circuit 12 to the second input terminal and outputs P as a result of comparison with the P.D / A signal.
It outputs a WM signal.

2 and 3 show a PWM signal output from the comparator 19, and FIG. 2 shows a case where the P.D / A signal is "0" volt and the PWM signal is fully output. Shows the case where the P · D / A signal is raised to limit the PWM signal.

Thus, the PWM signal output from the comparator 19 is input to the third input terminals of the AND circuits 14a to 14d. That is, as shown in FIG. 4, each AND circuit 14a to 14d inputs the above-mentioned PWM signal,
The pulse frequency signals Pa1, Pa2, Pb1, Pb2 whose pulse widths are changed according to the M signal are output.

Further, this speed control device is equipped with an ultrasonic wave mode.
A sensor 20 for detecting the actual rotation speed of the motor 10 is provided. The sensor 20 can be composed of an impeller rotated by the ultrasonic motor 10 and a photo interrupter outputting a pulse signal in accordance with the rotation of the impeller. This sensor-20 is an ultrasonic wave
A pulse signal corresponding to the actual speed of the controller 10 is sent to the CPU 11.

The speed control device implemented as described above has a PW
The M signal is made constant and the driving frequency is changed to control the speed, and conversely, the driving frequency is made constant and the PWM signal is changed to perform the speed control as the second control.

When the PWM signal is kept constant (eg, full output as shown in FIG. 2) and the speed is controlled by the drive frequency, the f.D / A setting input of the CPU 11 is changed to change the speed setting value. As a result, fD /
A signal from CPU 11 to V / f conversion / sawtooth wave generation circuit 12
Since the f · D / A signal is subjected to voltage-frequency conversion, a sawtooth signal having a frequency of fn is sent to the distributor 13.

As described above, the distributor 13 delays the rectangular wave signal by 90 ° and inputs it to the first input terminals of the AND circuits 14a to 14d. Therefore, at this time, the second inputs of the AND circuits 14a to 14d are input. If the ON signal is input to the terminals, the AND circuits 14a to 14d output the pulse frequency signals Pa1, Pa2, Pb1, and Pb2.

Therefore, the transistors 15a to 15d are rendered conductive in the order in which the pulse frequency signals are input to the base, and the primary coil current flows through the step-up transformers 16 and 17. As a result, the output voltage induced in the secondary coils of the step-up transformers 16 and 17 is applied to the ultrasonic motor 10 as the feeding pressures Va and Vb, and the frequencies (driving frequencies) of the feeding pressures Va and Vb are followed. Ultrasonic motor 1 at rotation speed
0 rotates.

If the target speed is changed by changing the speed setting value of the CPU 11, the power feeding pressures Va and V are changed according to the setting value.
Since the frequency of b changes, the rotation speed of the ultrasonic motor 10 increases or decreases according to the frequency.

When the speed is controlled by the PWM signal while keeping the driving frequency constant, the voltage level of the P.D / A signal changes according to the target speed set in the CPU 11,
Therefore, the PWM signal having the pulse width determined by the P · D / A signal is input to the third input terminals of the AND circuits 14a to 14d. From this, the transistors 15a-1
The pulse frequency signal input to the 5d base is P ・ D / A
The effective values of the feed pressures Va and Vb output from the step-up transformers 16 and 17 are modulated according to the signal, and the rotation speed of the ultrasonic motor 10 is increased toward the set target speed and decelerated. To do.

While the speed is being controlled as described above, the pulse signal according to the actual speed of the ultrasonic motor 10 is transmitted to the sensor.
It is input to the CPU 11 from 20, and the CPU 11 judges the state of the actual speed from this pulse signal, and detects an inappropriate control range or control point for speed control. For example, if the motor becomes low speed due to speed control by the drive frequency and the motor speed does not change even if the drive frequency is changed, CP
U11 switches to speed control by PWM control as the limit point of the control amount. If the switching point between the frequency control and the PWM control is stored in the memory of the CPU 11 in advance, it is not necessary to set the switching point by the pulse signal from the sensor-20.

FIG. 5 shows the P.D / A signal and the ultrasonic motor 10.
FIG. 6 is a characteristic diagram obtained by an experiment regarding the relationship with the rotation speed of As shown in the figure, the rotation speed of the ultrasonic motor 10 hardly changes in a predetermined range (for example, 0 to 25 mV) as the P.D / A signal increases, and the P.D / A signal increases.
It was confirmed that the signal A drastically changed as the signal A was further increased.

Therefore, in this experimental form, P · D /
The A signal is stepwise (for example, 0, 5, 10, 15, ...
・) The rotation speed starts to change by changing to P ・ D / A
A signal (eg, 30 mV) is detected, and the P.D / A signal (eg,
25 mV) as the initial setting value of the set speed value, and C
It is stored in the memory of the PU 11.

Therefore, in the subsequent speed control, P.p.m. from the initial set value (for example, 25 mV) stored in the memory.
The speed can be controlled by setting the speed in the direction of increasing the D / A signal level. For example, 0 to 20 mV
P ・ D / A within the range of 25-60 mV
Since the target speed can be set by changing the signal, speed setting becomes simple and the speed control means is excellent in responsiveness.

Further, when the initial setting value is stored in the memory as described above, when the rotation speed is within 10% with respect to the one-step change of the P.D / A signal, the variation of the rotation speed is varied. Therefore, it is preferable to determine the initial setting value when 10% or more. In this way, 10% which is a guideline for the initial setting value is {(actual speed-target speed) /
Target speed) × 100}.

On the other hand, as can be seen from FIG. 5, the motor speed with respect to the P.D / A signal changes greatly as the speed becomes slower. Therefore, in the configuration in which the P.D / A signal is set stepwise at constant intervals, It is difficult to get the target speed. Therefore, in the present embodiment, the one-step set amount of the P · D / A signal is determined by the following equation.

[0034]

[Equation 1] In this equation, it is appropriate to set Z to about 30 to 50 rpm.

FIG. 6 shows the pulse frequency signals Pa1, Pa2, Pb1 and Pb2 output from the AND circuits 14a to 14d and the power supply voltages Va and Vb when the P.D / A signal is set to "0" volt. It is the waveform diagram shown. FIG. 7 shows P.
FIG. 7 is a waveform diagram showing pulse frequency signals Pa1, Pa2, Pb1, Pb2 and power supply voltages Va, Vb when the D / A signal is increased and set to “520 mV”. As can be seen from these waveform diagrams, by changing the P.D / A signal, the power supply pressure changes, and the ultrasonic motor 10 is speed-controlled according to the P.D / A signal.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit example of a speed control device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an output operation of a PWM signal when the P · D / A signal is set to “0” volt.

FIG. 3 is an explanatory diagram showing an output operation of a PWM signal when a P · D / A signal is raised.

FIG. 4 is a time chart of a pulse frequency signal whose pulse width is modulated according to a P · D / A signal.

FIG. 5 is a characteristic diagram showing the relationship between the P · D / A signal and the rotation speed of the ultrasonic motor.

FIG. 6 is a waveform diagram showing a pulse frequency signal and a feed voltage when the P · D / A signal is set to “0” volt.

FIG. 7 is a waveform diagram showing a pulse frequency signal and a feed voltage when the P · D / A signal is raised to a predetermined value.

[Explanation of symbols]

 10 Ultrasonic Motor 11 CPU 12 V / f Conversion / Sawtooth Wave Generation Circuit 13 Distributor 14a to 14d AND Circuit 15a to 15d Transistor 16, 17 Step-up Transformer 19 Comparator 20 Sensor-

Claims (1)

[Claims] 1. A step-up transformer is operated by a pulse voltage,
In an ultrasonic motor speed control device for applying and driving the output voltage of the transformer, a speed control means for controlling the motor speed by pulse-width modulating the pulse voltage according to a target speed to be set, and a pulse width. A preset speed at which the speed change starts due to the modulation is detected in advance, and a memory means for storing the set speed value is provided, and the desired speed is set by setting the desired speed as the initial set value. The ultrasonic mode is characterized by having a controllable structure.
Speed control device.