EP1922772A1

EP1922772A1 - Circuit and method for controlling a piezoelectric or electrostrictive actuator

Info

Publication number: EP1922772A1
Application number: EP06793205A
Authority: EP
Inventors: Bernhard Gottlieb; Andreas Kappel; Juan Manuel Roldan Gomez; Tim Schwebel; Carsten Wallenhauer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2005-09-05
Filing date: 2006-09-05
Publication date: 2008-05-21
Also published as: DE102005042107A1; US20080218027A1; WO2007028784A1

Abstract

The invention relates to a circuit and/or a corresponding method for controlling a piezoelectric or electrostrictive actuator (P) having a series-connected driver stage (G) which provides a control signal which is used to drive the piezoelectric actuator (P). A reference capacitor (M), which is used to measure a charge (qP) of the actuator (P), is serially connected to the actuator (P). The reference capacitor (M) is used as a series capacitor in order to measure the actuator charge (qA(T) = qP(t)) of the piezoelectric actuator. The output variable is a voltage which is proportional to the actuator charge. Said voltage is guided to an A/D-converter and is processed further in a digital manner or guided directly to a analogue controller.

Description

description

Circuit and method for driving a piezoelectric or electrostrictive actuator

The invention relates to a circuit for controlling a piezoelectric or electrostrictive actuator according to the preamble features of claim 1 and to a method for driving a piezoelectric or electrostrictive actuator with such a circuit.

Piezoelectric actuators are used in many ways as actuators. For the use of these actuators an adapted to the application electronics is required, which can control the actuator with high accuracy and efficiency. Depending on the requirements, such a control electronics can have a very high complexity and significantly increase the costs of the entire drive system.

In a drive system based on such an actuator, the precise, controlled or controlled change of actuator length is the basis of the function. The length change is determined by parameters such as actuator charge, actuator charge history and actuator temperature. To control the actuator therefore the knowledge of the charge-time function is of crucial importance. For precise control of the actuator, a control loop based on the charge of the actuator is generally used. Thus, a functional block for measuring the charge of the piezoelectric actuator is an important part of the mechatronic system.

So far, the charge measurement was performed on piezoelectric actuators via the intermediate step of measuring the Aktorstromes with subsequent integration. For this purpose, a shunt resistor in series with the actuator is switched to zero potential. The actuator current is converted via the resistor into a proportional voltage drop. The voltage is integrated in a second step. The integration takes place either analog or digital via an upstream A / D converter, through an FPGA or a microcontroller.

The circuit and software costs and thus the costs for the function block for charge measurement are comparatively high in the known variant mentioned. In particular, the A / D conversion must be done in response to the drive signal with a high sampling rate. Digital integration requires additional resources in a microcontroller or FPGA. An adaptation to lower accuracy requirements depending on the application is limited in this approach possible.

The object of the invention is to simplify a circuit for driving a piezoelectric or electrostrictive actuator in terms of their structure or a method for driving a piezoelectric or electrostrictive actuator with such a circuit, in particular a cost reduction and, if necessary, allows an adaptation to lower requirements should be.

This object is achieved by a circuit for driving a piezoelectric or electrostrictive actuator having the features of patent claim 1 or by a method for controlling a piezoelectric or electrostrictive actuator having the features of claim 13.

Advantageous embodiments are the subject of dependent claims.

Accordingly, a circuit for driving a piezoelectric or electrostrictive actuator with an upstream driver stage for providing a drive signal for driving the actuator is preferred, wherein the actuator is followed by a reference capacitance for measuring a charge of the actuator in series. Particularly advantageous is a circuit in which the driver stage and the reference capacitance are connected to a common reference potential.

Particularly advantageous is a circuit in which a

Voltage drop across the reference capacitance can be tapped as an output signal proportional to the charge of the actuator. In particular, a circuit is advantageous in accordance with

u _A (t) = --q _M (t)

the output signal u _A (t) is proportional to a quotient of a reference capacitance value C _{M of} the reference capacitance with <3 _M (t) as the charge of the reference capacitance.

Particularly advantageous is a circuit with after an elapsed time T of a charge q (T) according to

with i (t) as current flowing through the actuator and through the reference capacitance. Particularly advantageous is a circuit in which a charge of the actuator q _P (t) is equal to or proportional to a charge q _M (t) of the reference capacitance.

Particularly advantageous is a circuit which is designed for approximately electroless measurement of a voltage above the reference capacitance.

Particularly advantageous is a circuit with a reset circuit which is connected for discharging the reference capacitance, wherein the reset circuit is preferably formed by a resistor connected in parallel with the reference capacitance or by a switch connected in parallel with the reference capacitance. Particularly advantageous is a circuit with a directly connected A / D converter or a directly connected analog controller.

Particularly advantageous is a circuit with a calibration circuit for reducing an error caused by drift of component parameters, wherein the calibration circuit is designed and switched so that at intervals a transmission factor in the form of a charge to a voltage drop is determined at the Referenzkapazitat ,

Advantageously, a circuit with a control or regulating device for controlling or regulating the driver stage due to a value of the measured charge of the actuator.

According to the method, a method is preferred for controlling, in particular, such a circuit with a piezoelectric or electrostrictive actuator and with a driver stage connected upstream thereof for providing a drive signal for driving the actuator, wherein the actuator is followed by a reference capacitance for measuring a charge of the actuator in series becomes.

In particular, a method is advantageous in which a voltage drop across the reference capacitance is tapped as an output signal proportional to the charge of the actuator. Particularly advantageous is a method in which a voltage across the Referenzkapazitat is measured approximately currentless. In particular, a method is advantageous in which the reference capacitance is reset by a resistor connected in parallel with the reference capacitance or by a switch connected in parallel with the reference capacitance and closed at time intervals and opened again. In particular, a method is advantageous in which, for reducing an error caused by drift of component parameters, by means of a calibration method at intervals, a transmission factor in the form of a tion to a voltage drop at the Referenzkapazitat is determined.

Particularly advantageous is a method in which the measured charge of the actuator is used to control or regulate the driver stage.

Advantageous are such a circuit or such a method in which a frequency band in the range of 1OmHz <f <IkHz is used.

Accordingly, a series capacitance is utilized as a reference capacitance for measuring an actuator charge of a piezoelectric actuator. The output variable is a voltage proportional to the actuator charge. Depending on the application, this voltage is fed to an A / D converter and further processed digitally or fed directly to an analog controller.

Such a preferred circuit for driving a piezoelectric actuator or such a method for driving a piezoelectric actuator with such a circuit have disadvantages over known embodiments. Thus, the long-term stability of the component parameters and the temperature drift of the reference capacitance are worse in comparison to a shunt resistor. An error or drift of the capacitance value has a direct influence on the measuring accuracy. As with a measurement via a shunt resistor, an error caused by drift of component parameters can also be significantly reduced when measuring by means of a reference capacitance by means of a suitable calibration circuit. The calibration circuit determines the transmission factor at longer time intervals, in particular as a transmission factor in the form of a charge to a voltage drop.

However, the benefits outweigh the disadvantages. A very simple structure is advantageous. Also advantageous is scalable accuracy at scalable costs, where cost is a choice of reference capacity. It is also advantageous that digital integration is not required, which leads to lower resource requirements.

In addition, a direct, in particular amplifierless, connection of an A / D converter (A / D: analog / digital) is advantageously possible because the signal to be measured already has a high energy.

Also advantageous is a continuous measurement, which allows a lower speed request to the A / D converter in a digital system, especially when using pulsed piezo drivers.

In addition, low demands on the reference capacitance with respect to parasitic elements are also advantageous. Parasitic elements of Referenzkapazitat have in a limited frequency band hardly adverse effect on the measurement accuracy.

An exemplary embodiment will be explained in more detail with reference to the drawing. Show it:

1 shows an exemplary circuit for driving a piezoelectric actuator,

2 is a comparison with FIG. 1 modified circuit,

Fig. 3 shows a further compared to FIG. 1 modified circuit and

4 shows a phase response and a transfer function of such a circuit.

As can be seen from FIG. 1, an essential aspect of a basic circuit is the use of a reference capacitance M connected in series with a piezoelectric actuator P for measuring a charge q _{P of} the piezoelectric actuator P. The reference capacitance M is connected in series with the piezoelectric actuator P to zero potential 0.

Through the actuator P and through the reference capacitance M, the same current i (t) flows to a driver stage G in the form of, for example, a generator. As a result, the same charge q (t) = q _P (t) or q (t) = q _M (t) is stored in both elements. In general, or for the specific reference capacitance with a reference capacitance value C _M applies

"(t) = - q (t) or u _A (t) = - q _M (t) (1)

with u (t) as a voltage of the driver stage G and C as the total capacitance value of the total capacitance. In this case, a voltage drop across the reference capacitance M is proportional to the stored charge q _{M of} the reference capacitance M. The capacitance value C _{M of} the reference capacitance M represents the proportionality factor.

The driver stage G provides a suitable drive signal, a voltage-time function or a current-time function for driving the piezoelectric actuator P. The driver stage G is connected directly to the actuator P. The actuator P is connected at its second terminal to the series-connected reference capacitance M. The zero potential 0 of the circuit represents the reference potential of the reference capacitance M. If a voltage measurement above the reference capacitance M takes place approximately without current, the following applies

T q (T) = q _p (T) = q _M (T) = \ i (t) dt + Q (t = 0) with i (t) = i _p (t) = i _M (t). (2)

Accordingly, in both capacitive elements, ie in the actuator P and in the reference capacitance M, the same charge q (t) is stored. The stored charge q (t) causes a proportional voltage drop across the reference capacitance M. The voltage drop across the reference capacitance M represents the output to the charge q _{P of} the actuator P proportional output signal u _A (t).

The determination of the charge q _{P of} the actuator P takes place, for example, in a control device C, which applies the output signal u _A (t). The control device C preferably also determines a control or regulating signal c (t) which is applied to the driver stage G for controlling or regulating the driver stage G.

Further exemplary embodiments are shown in FIG. 2 and in FIG. 3. By a reset circuit, the reference capacitance M is discharged, wherein the stored in the reference capacitance M charge q (t = 0) is set to zero. The reset can be done, for example, according to FIG. 2 with a resistor R or according to FIG. 3 with a switch S. The reset via the resistor R is particularly simple and suitable for a periodic operation of the actuator P. In this case, the circuit consisting of the actuator P, the reference capacitance M and the resistor R is a high pass. In this way, the stability of such an integrator formed, for. B. against bias currents, which would lead to a drift in an integration, improved.

Parasitic elements of the reference capacitance M form their apparent internal resistance. The parasitic resistance in series with the reference capacitance M limits as an RC element (RC: resistance capacitance) with the capacitance C _{M of} the actuator P to the use of high frequencies. The parallel parasitic resistance of the reference capacitance M and the reference capacitance M form an RC element which limits the use at low frequencies by means of high-pass behavior. With realistic component parameters for typical applications, a frequency band of in particular at least 10 MHz <f <IkHz can be used. The use of special, low-loss and therefore expensive capacities, eg. As tantalum capacities, is advantageously no longer required depending on the application. The effect of the parasitic elements of the reference capacitance _M can be simulated by setting exemplary parameters with a reference capacitance capacitance value C _M = 100 μF and an actuator capacitance value C _P = 1 μF. The parasitic resistance in series with the reference capacitance M amounts to 100 mOhms, a replacement series inductance of the reference capacitance M amounts to 30 nH and the parasitic resistance parallel to the reference capacitance M amounts to RpM = 6 Mohms. These data correspond to those of an average electrolytic capacitor. The simulation result is shown in FIG. Shown above the frequency f is the transfer function of the output voltage u _A (t) with respect to the actuator charge q _P (t). Shown here are a phase response in the upper figure and a gain in the lower figure. It turns out that the parasitic elements surprisingly have no negative influence on the measurement accuracy over a large frequency range.

Thus, experimentally confirmed, a comparable accuracy to known methods is achieved with significantly reduced circuit complexity.

Advantageously implementable, for example, is a direct, in particular amplifierless, connection of an A / D converter (A / D: analog / digital) to which the output signal u _A (t) is applied. In practice, with an exemplary reference capacitance capacitance value C _M = 470μF and an output voltage -2V <UA <2V, it can be seen that the signal to be measured already has a high energy E = CU _A.

Claims

claims

1. A circuit for driving a piezoelectric or electrostrictive actuator (P) with an upstream driver stage (G) for providing a drive signal for driving the actuator (P), characterized in that

- The actuator (P) is followed by a reference capacitance (M) for measuring a charge (q _P ) of the actuator (P) in series.

2. A circuit according to claim 1, wherein the driver stage (G) and the reference capacitance (M) to a common reference potential (0) are connected.

3. A circuit according to claim 1 or 2, wherein a voltage drop across the reference capacitance (M) as a charge (q _P ) of the actuator (P) proportional output signal (u _A (t)) can be tapped.

4. The circuit of claim 3, wherein according to

the output signal u _A (t) is proportional to a quotient of a reference capacitance capacitance value C _{M of} the reference capacitance (M) with <3 _M (t) as the charge of the reference capacitance (M).

5. A circuit according to any preceding claim, having after an elapsed time T a charge q (T) according to

with i (t) as current flowing through the actuator (P) and through the reference capacitance (M).

6. A circuit according to claim 4 or 5, wherein a charge of the actuator q _P (t) is equal to or proportional to a charge q _M (t) of the Referenzkapazitat (M).

7. A circuit according to any preceding claim, which is designed for approximately currentless measuring a voltage across the Referenzkapazitat (M).

8. A circuit according to any preceding claim, comprising a reset circuit connected to discharge the reference capacitance (M).

9. A circuit according to claim 8, wherein the reset circuit is formed by a parallel to Referenzkapazitat (M) connected resistor (R) or by a parallel to Referenzkapazitat (M) connected switch (S).

10. A circuit according to any preceding claim with a directly connected A / D converter or a directly connected analog controller.

11. A circuit according to any preceding claim comprising a calibration circuit for reducing an error caused by component parameter drift, wherein the calibration circuit is configured and switched, at intervals a transfer factor in the form of a charge to a voltage drop across the reference capacitance (M ).

12. A circuit according to any preceding claim with a

Control or regulating device (C) for controlling or regulating the driver stage (G) on the basis of a value of the measured charge of the actuator (P).

13. A method for driving a piezoelectric or electrostrictive actuator (P) with an upstream driver stage (G) for providing a drive signal to Driving the actuator (P), characterized in that

- The actuator (P) a reference capacitance (M) for measuring a charge (q _P ) of the actuator (P) is connected in series.

14. The method of claim 13, wherein a voltage drop across the reference capacitance (M) as a charge (q _P ) of the actuator (P) proportional output signal (u _A (t)) is tapped.

15. The method of claim 13 or 14, wherein a voltage across the Referenzkapazitat (M) is measured approximately currentless.

16. The method according to any one of claims 13 - 15, wherein the Referenzkapazitat (M) is reset by a parallel to Referenzkapazitat (M) connected resistor (R) or by a parallel to Referenzkapazitat (M) connected and closed at intervals and again open switch (S).

A method according to any one of claims 13 to 16, wherein to reduce an error caused by drift of component parameters, a transmission factor in the form of a charge to a voltage drop across the reference capacitance (M) is determined by a calibration method at time intervals.

18. The method according to any one of claims 13-17, wherein the measured charge of the actuator (P) is used for driving or regulating the driver stage (G).

19. A circuit according to any one of claims 1-12 or a method according to any one of claims 13-18, wherein a frequency band in the range of 1OmHz <f <IkHz is used.