Self-sensing method for output force of piezoelectric actuator

Abstract

The invention discloses a self-sensing method for output force of a piezoelectric actuator. An integrator used for obtaining surface charges of a piezoelectric actuator wafer is included, the integrator comprises an operational amplifier and an integrating capacitor; a self-sensing expression of output force of piezoelectric actuator is shown in corresponding formula in which Fest is the self-sensing force of the piezoelectric actuator, C and uout are the integrating capacitance and the output voltage of the integrator respectively, alpha is the charge-displacement coefficient, RP is the insulation resistance of the piezoelectric actuator, u is the driving voltage applied to the piezoelectric actuator, QDA is the dielectric absorption charge of the piezoelectric actuator wafer, and iBIAS is the bias current of the operational amplifier. According to the invention, influence of the leakage resistance of the wafer in the piezoelectric actuator on the self-sensing precision can be eliminated needless of connecting a feedback capacitor in the integrator with a resistor in parallel; moreover, the dielectric absorption of the piezoelectric actuator wafer and the bias current of an operational amplifier forming the integrator are compensated, and the self-sensing precision of the output force of the piezoelectric actuator can be further improved.

Description

technical field [0001] The invention belongs to the technical field of precision drive, relates to a piezoelectric actuator in a precision drive system, in particular to a self-sensing method for the output force of a piezoelectric actuator. Background technique [0002] Piezoelectric actuators are actuators capable of producing nanoscale motion precision and resolution. Compared with other forms of actuators such as electromagnetic, magnetostrictive, electrostatic, electrothermal, shape memory alloy, etc., piezoelectric actuators have the advantages of small size, high stiffness, fast response, large output force, high displacement resolution, It has the advantages of no heat, no noise, etc., so it is widely used in precision drive systems. For example, a stacked piezoelectric actuator (consisting of multilayer piezoelectric ceramic wafers mechanically connected in series and electrically connected in parallel) is used to drive a flexible hinge mechanism tool holder, there...

AI Technical Summary

Problems solved by technology

The implementation principle and circuit structure of the bridge method are simple, but it has the following disadvantages: it is only suitable for dynamic driving conditions, but not for static or low-frequency driving conditions. This is because: piezoelectric ceramic chips are not ideal insulators, but have certain Leakage resistance, leakage current will be generated during the working process, the leakage current will destroy the balance of the bridge under static or low frequency conditions, and when the balance of the bridge is destroyed, the stability of the system will deteriorate; compared with the driving voltage , the sensing voltage is small

[0007] 1) In order to eliminate the influence of the leakage current generated by the leakage resistance of the piezoelectric ceramic chip on the self-sensing accuracy, a resistor is connected in parallel to both ends of the feedback capacitor in the integrator to meet the C P × R P =C×R (this formula is the balance condition for eliminating chip leakage current, C P , R P are the capacitance and leakage resistance of the chip in the piezoelectric actuator respectively, C and R are the feedback capacitance and feedback resistance of the integrator respectively), because the leakage resistance R of the chip in the piezoelectric actuator P often reaches 10 10 Ω or more, so that the feedback resistor R of the integrator should reach 10 7 Ω or more, such a high-value resistor is difficult to purchase, and often needs to be realized through multiple series connections; and, due to the leakage resistance R of the chip in the piezoelectric actuator P Vulnerable to changes due to the influence of ambient temperature and humidity, so as to meet the requirements of C P × R P =C×R, the feedback resistor R of the integrator should be adjusted frequently, which makes the integrator method more difficult to implement and the adjustment process is cumbersome

[0008] 2) Neglecting the dielectric absorption generated by the chip in the piezoelectric actuator under the action of voltage

But in fact, the piezoelectric ceramic chip will produce dielectric absorption under the action of voltage, thereby generating charges on the surface of the chip, which will not cause the piezoelectric actuator to generate output force, but will cause the operational amplifier constituting the integrator to generate output Voltage, thereby reducing the self-sensing accuracy of the piezoelectric actuator output force

[0009] 3) Neglecting the bias current of the operational amplifier that makes up the integrator

But in fact, there is a bias current in any operational amplifier, which will cause the output of the integrator to reduce the self-sensing accuracy of the piezoelectric actuator output force

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