SU765911A1 - Device for control of piezoelectric motor - Google Patents

Description

device, the output of the latter through the key of the analog signals is connected to the control input of the frequency controller, and the output of the threshold device through the one-shot is connected to the control input of the key; the output of the main corrective device is connected to the power amplifier via an adder, the other input of which is connected by an auto-oscillator through the second additional correction device.

FIG. 1 shows a diagram of a control device (stabilization) of a piezoelectric speed; in fig. 2 is a characteristic of a piezoelectric motor, illustrating the operation of the device and representing the dependence of the supply current and speed of the piezoelectric motor on frequency, taken for a series of fixed values of the load moments M and the amplitudes of the supply voltage A.

The device contains a piezoelectric 1, a piezoresonator (PR) which is powered by a power amplifier 2. A frequency controller 3 is connected in series with the PR (in the simplest case, a series resonant circuit tuned by voltage or current). The PR of the motor 1, the frequency controller 3 and the power amplifier 2 form a positive feedback loop of the sinusoidal oscillator, the frequency defining element of which is the frequency controller system - the PR of the motor. The signal applied to the control (upper, see Fig. 1) input of the frequency control allows you to tune its resonant frequency by 1-5%. At low load moments, when as seen from FIG. 2, the quality factor of the PR is high; the quality factor of the system is the frequency regulator — PR is determined by the properties of the latter. When the signal on the control input of the frequency control changes, the resonant frequency of the current of this system and, therefore, the frequency of the oscillator changes within 1-5% relative to the resonant frequency of the current PR. This is enough to establish the operating frequency of the dvGgatel near the resonant frequency of the corresponding speed-frequency characteristic in the operating range of load moments and amplitudes of the supply voltage. If the load moments are significant (M M, see Fig. 2), the quality factor of the PR drops, and the resonant frequency of the current and the quality factor of the system, the frequency manager of the PR, is determined by the properties of the frequency controller. The parameters of the latter are selected in such a way that the normal operation of the autogenerator continues under the ET1PC conditions. A sensor is connected to the piezo motor 1

4, the frequency of the output voltage of which is proportional to the speed of rotation of the piezoelectric motor. The signal from the output of the feedback sensor is converted into a series of rectangular voltage pulses using a driver 5. A similar function is performed by the driver 6 for the reference frequency generator 7 to set the speed. Shaper signals 5 and 6

A frequency subtraction unit 8 is generated, generating a pulse train whose duty cycle is proportional to the difference in the phase angles of the input signals of the block. The signals of the block 8 and the former 6 affect the inputs of the phase detector 9 performed on the basis of an integrator with a storage capacity. The output voltage of the phase detector, which is proportional to the integral of the engine speed deviation from the reference, through the dynamic driver 10, which implements the proportional-differentiating element, and the analog key

5 signals 11 acts on frequency controller 3, i.e. on the frequency of the excitation voltage, and through the correction device 12 and the adder 13 to the power amplifier 2,

changing the voltage amplitude of a piezoelectric transducer. The transfer function of the correction device 12 is selected in accordance with the required control law (in this case, PI). The second input of the adder 13 receives a signal from a correction device 14, made on the basis of a frequency-voltage converter and producing a signal proportional to the absolute value of the derivative of the frequency of the oscillator with respect to time.

 The threshold device 15 is a Schmidt trigger. His entrance

connected to the output of the phase detector, and the signal at its output appears at the moment when the derivative of the output voltage of the phase detector 9, i.e. rotation speed

piezoelectric motor, exceeds the specified level in absolute value. The signal of the threshold device 15 triggers the one-shot 1b. A voltage pulse generated at the output of the one-shot 16 opens the key 11, thereby blocking the signal to the control input of the frequency control. As a result, the operating frequency shifts in the direction of the frequency of the initial setting of the frequency controller.

(i.e., the frequency settings of the frequency controller when there is no signal at its upper input). After the end of the pulse at the output of the one-shot 16, the switch 11 again closes the frequency control loop.

Let us consider how the process of tracking a given rotational speed proceeds with changes in load torque. At low load moments, the speed-frequency dependence has a sharply resonant, high-frequency character. Under these conditions, for the normal functioning of the system, it is necessary to monitor the operating point as a function of the load moment near the frequency corresponding to the maximum speed. At the same time, the operating point must be located on the preselected slope of the resonant velocity-frequency characteristic and must not change to another slope so that the dynamic stability of the system is not affected by a change in the sign of the feedback in the frequency control loop. Suppose that in the initial state the loading moment is equal to M, and the operating point is in the position см (see Fig. 2). Since the rotation speed is close to the given {I1o, oie), the signals at the outputs of the threshold device 15 and the one-shot 1 b are missing, the key 11 is closed and the control (upper) input of the frequency control 3 passes the signal from the dynamic driver 10, maintaining the excitation voltage frequency f corresponding to the operating point. At the same time, the signal from the output of the correction device 12 is sufficient for the required amplitude A-J, the exciting voltage. Due to the fact that the operating frequency does not change, there is no signal at the output of differentiating link 14.

With an abrupt change in the loading moment up to the value of M M, the error signal from the output of the phase detector, which is formed by corrective devices 10 and 12, tends to reduce the frequency and increase the amplitude of the exciting voltage. When the frequency at the output of the correction device 14 changes, a signal arises that inhibits the growth of the amplitude of the exciting voltage. Since the correction device 10 is a proportional-differential link, and partly influenced by the signal of the device 14, the frequency impact is ahead of the amplitude . Thus, the presence of an additional correction device 10 is fundamentally necessary. Otherwise, large fluctuations of the instantaneous velocity may occur, since due to the displacement of the resonant frequencies with variations in the moment, the operating point will be deep down on the slope of the speed-frequency characteristic (for example, in the position in Fig. 2). At the end of the transition process, new values will be established,

the amplitudes and frequencies of the exciting voltage (Aj. and f 2, respectively, Fig. 2), and the operating point will be in a position close to point 2 near the resonance corresponding to the speed-frequency characteristic

rather than in a position, for example, 2 t I, for the reason that the effect on amplitude caused by a change in frequency and produced by the reference number}) by another link 10 is ahead of the effect on

0 amplitude caused by the speed deviation and produced by the correction device 12. Thus, the introduction of an additional correction device 14 ensures the position of the operating point near the resonant frequency of the speed-frequency characteristic, which is essential for increasing the efficiency, as well as

0 that some types of piezoelectric motors start to work unstably as a result of parametric excitation of parasitic mechanical oscillations of the PR, if the operating frequency is far from resonance. Corrective devices 10,12 and 14 are designed so that during the transition process the signals at the output of the phase detector 9 do not exceed the response threshold of the device 15. Similarly

0 the system works even if the new value of the load moment is so great that the resonant properties of the characteristic speed and frequency become poorly pronounced. For example, when changing the load moment to the value of M- (see Fig. 2), the operating point from position 1 will move to position 3

0

Suppose that in the initial state, the operating point is in position 2 and there is an abrupt load shedding to the value M M ,. Directly after a load drop, the speed will drop, and

5, in response to this signal at the output of the correction device 10, tends to reduce the operating frequency, which in turn will contribute to a reduction in speed. As a result

0, the error signal at the output of the phase detector 9 exceeds the response threshold of the device 15, the one-shot 16 activates and the key 11 blocks the passage of the signal of the correcting device 10 to the control input of the frequency control 3, Setting the frequency control in the absence of a signal at the control input is selected in such a way that the operating frequency of the oscillator in this case is greater than f (see Fig. 2). The duration of the output pulse of the one-shot is negligible compared to the transient process of changing the speed. Therefore, the release of key 11 is sufficiently short so as not to lead to noticeable fluctuations in speed. After the end of the Impullca of the one-shot 16, the key 11 is closed, and the regulation process will take place: Tzzhe, as in the previously discussed case of stepwise increase in load. At the same time, the signal at the output of the device 14, which appears during the change of the working frequency, will help to reduce the amplitude of the exciting voltage, so that at the end of the transient process the operating point of the eye.

zhets in position

The device 15 is selected slightly lower than the level corresponding to the tolerance t speed from the task. The described device without significant changes can be used in case of choosing the speed-frequency characteristic in the quality of the working left slope, as well as to control the speed of piezoelectric motors with another charge arrangement of resonant characteristics speed-frequency and piezoresonator-frequency current. To do this, it is only necessary to set the frequency control frequency setting in the absence of a signal at its control input. By. In comparison with known devices, the proposed device has the following technical and economic advantages (according to test results):

increasing the stability of the speed of rotation of the piezoelectric motor (with an error of 0.1% for the average speed and 0.01% for the instantaneous);

extending the range of load moments within which the desired stability of the rotational speed is maintained (from Mxx to about Mk);

preservation of performance in a wide range of changes in external conditions (temperature, humidity), as well as in conditions of change (for example, as a result of wear) of such internal parameters of the engine, such as pressing force, properties of a piezoresonator;

increase in efficiency when engines are operating in the electric drive system by about 15%.

The use of the device will make it possible to use a piezoelectric drive as a high-speed drive in installations of various purposes, for example, in magnetic recording-reproducing installations, which will reduce their cost, reduce size, increase the quality of recording-reproduction, and increase reliability.

Claims (2)

1. Sandler A.S., Sarbatov R.S. automatic frequency control of asynchronous motors. M., Energie, 1974., P. 34-158. 2.Sb. Vibrotechnics. Scientific works of universities of the Lithuanian SSR, 1972, 3/16 /, p. 296-307 (prototype).