RU2025882C1 - Device for control over piezoelectric motor - Google Patents

Abstract

FIELD: electric motor drives. SUBSTANCE: control over rotational speed of piezoelectric motor is conducted by adjustment of angle of phase shift of voltage across free electrodes in function of speed error signal by means of controlled phase inverter 6 which results in increased efficiency. In proposed device piezoelectric motor 1, switch 7, amplifier 8, phase inverter 6, power amplifier 9 form circuit of positive feedback, i.e. self-excited generator of excitation voltage of piezoelectric motor is realized which provides for following of working frequency in region of resonance value. Piezoelectric motor 1, feedback pickup 2, comparator 3, unit 5 of frequency control phase inverter 6, power amplifier 9 and switch 7 form phase-frequency circuit of adjustment of rotational speed of motor. EFFECT: increased efficiency of control over rotational speed of motor. 3 dwg

Description

 The invention relates to piezoelectronics, in particular to control devices for piezoelectric engines (PED), and can be used in a variety of applications where the use of piezoelectric motors is promising, for example, in devices for magnetic recording and reproduction of sound, video and digital information, microrobots, etc. .

 Known devices that implement one-dimensional (amplitude and frequency) methods of controlling the speed of the SEM [1]. These devices contain only amplitude or frequency controls.

 The main disadvantage of devices that implement one-dimensional methods is a sharp limitation of the working range of the disturbing effects due to the lack of elements and operations that monitor the resonant frequency of the motor.

 A known control device PED [2]. This device includes regulators of the amplitude and frequency of the excitation voltage of the SEM, as well as a controlled voltage generator, an excitation current sensor and a phase detector that generates a phase error signal. The method underlying the implementation of this device provides amplitude control of the speed of rotation of the SEM with simultaneous tracking of the resonant frequency when the load moment changes. Tracking is performed by working out the phase error signal.

 This device is designed for a push-type PED with excitation of longitudinal-bending vibrations of a piezoelectric resonator and, due to differences in characteristics, cannot be used to control a piezoelectric motor with excitation of contour oscillations. The latter, for example, is characterized by a significant dependence of the phase angle of the current and voltage at the resonant frequency on disturbing influences. This makes it impossible to track the resonant frequency by working out a signal proportional to the deviation of the phase angle of the current and the PED excitation voltage from the set value (phase error signal). Another disadvantage of the device is the limited ability to increase efficiency and, as a consequence, the reliability of control. This is due to the use of the amplitude method of controlling the engine speed. For example, in the case of using the most economical key power amplifier, the regulation of the amplitude of the excitation voltage is carried out by changing the supply voltage of this amplifier using a sequential control element. This leads to a sharp decrease in the efficiency of the device due to losses on this element.

 The last of the considered devices is the closest in technical essence to the proposed solution (prototype).

 The aim of the invention is to provide reverse, increasing efficiency and reliability control.

 The goal is achieved by the fact that in addition to the rotational speed sensor, power amplifier (AM) and the comparison element (ES), a selective amplifier (IU) and a controlled phase shifter (UVB) are introduced. These elements make it possible to realize the operation of the phase shift of the voltage on the free electrodes of the piezoelectric resonator, which is necessary to fulfill the self-excitation conditions at a frequency corresponding to the position of the operating point on the working slope of the speed-frequency characteristic regardless of the magnitude of external disturbances (e.g., load moment). Thus, the operability of the control is ensured during reverse operation, as well as in conditions of strong disturbances (practically with changes in the load moment in the entire operating range allowed by the engine characteristics). Using these elements, the operation of changing the frequency of the self-excitation voltage in the direction of compensation of the mismatch signal in speed by adjusting the angle of the phase shift of the voltage on the free electrodes as a function of this signal is realized. This operation is carried out at low power consumption, which ensures high efficiency of the device and increases the reliability of control. In this case, the efficiency of the device with the SEM increases by 10-15%.

 From the above it is seen that the claimed features satisfy the criteria of "novelty" and "materiality of differences."

 Figure 1 presents a block diagram of a device; figure 2 - characteristics of the PED, illustrating its operation and representing the dependence on the free electrodes, the speed of the motor, as well as the phase shift of the excitation voltage and on the free electrodes on the frequency, taken for fixed values of the load moment M and the amplitude of the excitation voltage A; figure 3 shows the kinematic diagram of the SEM with the excitation of loop oscillations, which shows the location and switching of the electrodes of the piezoresistor.

 When controlling the proposed device, an excitation voltage is generated using a self-generating process, using the voltage on the free electrodes of the piezoresistor as a feedback signal. This ensures that the operating frequency is tracked near the resonance value. The fulfillment of the conditions of self-excitation in the field of operating frequencies is achieved by shifting the phase angle of the voltage on the free electrodes by a predetermined value. When the rotation speed is disconnected from the set value, this angle is regulated according to the PID law as a function of the error signal.

 The device contains a PED 1, on the shaft of which a speed sensor is fixed - a feedback sensor (DOS) 2. The output signal of the DOS, proportional to the current speed value, is supplied to one of the inputs of the ES 3, the other input of which is connected to the output of the speed setting unit (BCH) ) 4. The output signal ES is the error signal for speed ε (t) through the frequency control unit 5 and is fed to the control input of the UVB 6. The signal from the free electrodes of the piezoresonator PED through the switch (PC) 7 is fed to the input of the IU 8. The output of the IU is connected to signal input UVB 6, and UVB output - to the input of the PA 9. The output signal of the PA through PC 7 is supplied to the working electrodes of the piezoresonator PED 1.

 Blocks 1, 7, 8, 6, 9 form a positive feedback loop, i.e. they realize a self-oscillator of the excitation voltage of the SEM, which provides tracking of the operating frequency in the region of resonance value. Blocks 1, 2, 3, 5, 6, 9, 7 comprise a phase-frequency circuit for controlling the speed of rotation of the SEM.

 As PC 7 in the simplest case, a mechanical switching device in two positions and in two directions is used. Using this PC, free and working electrodes of the piezoelectric resonator PED are switched and thereby the engine is reversed.

+ K₃ ∫ U_вхdt
Коэффициенты К₁, К₂, К₃ рассчитываются из условия обеспечения требуемого качества переходного процесса регулирования скорости. Блок регулирования частоты выполнен на базе операционных усилителей. Пропорциональные, суммирующие, интегрирующие, дифференцирующие звенья реализованы по типовым схемам.The frequency control unit 5 generates a control signal for the phase angle of the voltage at the free electrodes according to the PID law as a function of the speed error signal. Regulation is carried out according to the following function:
U _out = K ₁ U _in + K ₂

+ K ₃ ∫ U _in dt
The coefficients K ₁ , K ₂ , K _{3 are} calculated from the condition of ensuring the required quality of the transition process of speed regulation. The frequency control unit is based on operational amplifiers. Proportional, summing, integrating, differentiating links are implemented according to standard schemes.

UVB 6 is made on an operational amplifier. To carry out the regulation of the phase in its composition there is a field-effect transistor operating in an adjustable resistance mode. The lower and upper limits of the phase angle change of UVB 6 are established from the requirements for fulfilling the conditions of self-excitation of the oscillator and from the requirement to maintain the stability of the speed control loop, respectively. The fact is that in the absence of restrictions from above, when φ _Σ = φ _ИУ + φ _UVB + φ _УМ > π / 2, the operating point switches to non-working - the left slope of the characteristic is speed - frequency, which leads to phase inversion and, consequently, to loss stability in the speed control loop (see figure 2). Here, φ _ИУ , φ _UVB , φ _УМ are the phase angle angles introduced by ИУ 8, UVB 6, УМ 8, respectively. On the other hand, in the absence of a lower limit, if φ _Σ = φ _ИУ + φ _UVB + φ _УМ << π / 2, the operating point is deep down on the slope of the characteristic voltage on the free electrodes - frequency (figure 2). In this case, one of the conditions for self-excitation of the oscillator ceases to be satisfied - the condition of balance of amplitudes.

 The inclusion of the device IU 8 is necessary to prevent self-excitation of the circuit at the frequencies of the parasitic modes of vibration of the piezoresonator. The resonant frequency of the DUT is selected to coincide with the center of the frequency region, within which the resonant frequencies of the piezoelectric motor are grouped for the given ranges of change of A and M and when the engine is reversed. The bandwidth of the DUT should be wider than the above frequency range and at the same time narrow enough to reliably suppress spurious frequencies. The specified condition is fulfilled when the quality factor of the electoral circuit of the PS is 3-7.

 The device operates as follows.

The amplitude of the excitation voltage is not regulated, its value is determined by the supply voltage and maintains an approximately constant value equal to A ₁ (see figure 2). In the initial state, the load moment is equal to M ₂ , and the operating point is in position a (figure 2). The speed of rotation of the PEM is close to the specified one, and the error signal at the output of the ES 3 through the frequency control unit 5 acts on the control input of the UVB 6 so that the phase balance condition φ _ИУ + φ _UVB + φ _УМ -φ ₂ = 0 is satisfied at the frequency f ₁ , providing the position of the working point on the right - the working slope of the characteristics of the speed - frequency (figure 2).

Let there be an abrupt change in the moment to a value of M ₁ > M _2. The speed of the processes of establishing the oscillator oscillation frequency is determined mainly by the inertia of the processes in the piezoelectric resonator, which, in turn, is 3-4 orders of magnitude lower than the inertia of the processes of establishing the rotation speed. Therefore, almost before the beginning of the transition process of changing the rotation speed, a new value of the oscillator frequency is established, determined from the phase balance condition φ _ИУ + φ _UVB + φ _IM -φ ₂ = 0, where φ _UVB = φ _UVB . As follows from this equation, φ ₂ tends to maintain the old value, and the operating point tends to position b, remaining on the working slope of the speed-frequency characteristic. Subsequently, in the process of developing the emerging speed error signal, the control voltage of the UVB 6 changes. As a result, the _UVB φ changes (increases) and, as a result, the oscillator frequency decreases until the speed error signal is compensated. At the end of this process, the operating point is in position b, and the frequency value is equal to φ ₂ .

Suppose that in the initial state the operating point is in the position in (Fig. 2) and the load moment is reset to the value M ₂ <M ₁ . The behavior of the system in this case is similar to that described above. Even before the beginning of the transition process of changing the speed, the frequency of the oscillator is tuned in the conditions of maintaining the initial value of φ ₂ . In this case, the working point tends to the position r, remaining on the working slope of the speed-frequency characteristic. Subsequently, as a result of working out the emerging speed error signal, the operating point moves to position a (Fig. 2).

Suppose that in the initial state M = M _{2 the} system starts up, i.e. rotation speed n = 0. If there were no maximum φ _UVB limitation, then immediately after start-up, under the action of a signal with a significant magnitude mismatch, φ _ИУ + φ _UVВ + φ _УМ > π / 2, i.e. the phase balance condition φ _ИУ + φ _UVB + φ _УМ -φ ₂ = 0 would be satisfied at frequencies corresponding to the left - inoperative slope of the speed - frequency characteristic. This would lead to a loss of stability of the speed control loop. However, in the UVF 6 scheme, a constructive restriction is introduced on the maximum angle φ _UVB , so that φ _ИУ + φ _UVB + φ _УМ ≅π / 2. In this case, immediately after start-up, the phase balance condition is satisfied at φ ₂ = π / 2, and, therefore, the self-excited oscillator is excited at a frequency f _{res. 1} (as long as n <n _ass , φ _ИУ + φ _UVB + φ _УМ = π / 2, φ ₂ = π / 2, f = f _{res. 1} ) After the rotation speed exceeds a predetermined value, φ _ИУ + φ _UVB + φ _УМ starts to decrease under the action of the speed error signal, which results in a decrease in φ ₂ and increase in frequency. This causes a decrease in rotation speed. At the end of the transition process, the operating point is in position a (figure 2).

Limiting the maximum angle φ _UVB prevents the transition of the operating point to an inoperative slope of the speed-frequency characteristic not only during start-up, but also in all other cases when rotation speed fluctuations are possible, for example, when an overshoot effect occurs.

 The introduction of new elements - UVB 6 and IU 8 - allows you to monitor the operating frequency in the region of the resonant value by organizing a self-generating process, using the voltage on the free electrodes as a feedback signal and performing a phase shift of this voltage by the amount necessary to fulfill the self-excitation conditions for a given frequency. This ensures the operability of the proposed device under reverse conditions and with changes in the load moment in the operating range. The use for this purpose of the elements described in analog devices is impossible due to differences in the characteristics of control objects.

 The organization of control of the speed of rotation of the SEM by adjusting the angle of the phase shift of the voltage on the free electrodes as a function of the signal of the error of speed, implemented using UVB 6, allows you to refuse to control the amplitude of the excitation voltage, which increases the efficiency of the device by 10-15% compared with the analog device .

Claims (1)

 A device for controlling a piezoelectric engine, comprising a speed sensor mounted on the output shaft of the piezoelectric engine and an output connected to one input of the comparison element, the other input of which is connected to the speed setting unit, and the output to the input of the speed control unit, a switch with four outputs , two of which are designed to connect to the working and free electrodes of the piezoelectric resonator of the piezoelectric motor, respectively, a power amplifier, output to which is connected to the third output of the switch, characterized in that an amplifier and a controlled phase shifter are inserted into it, the output of which is connected to the input of the power amplifier, the input of the amplifier is connected to the fourth terminal of the switch, and the output of the amplifier is connected to the signal input of the controlled phase shifter, the control input of which is connected to the output of the speed control unit.

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