Simultaneous use of Piezoelectric Transducer as Actuator and Sensor in real-time applications

摘要

The role of piezoelectric actuators in application at micro and nano scale has been growing over the past three decades. Piezoelectric actuators have high displacement resolution and large bandwidth, therefore they are used in micro and nano scale control applications. Despite enormous research and development, there are challenges in the control of piezoelectric actuators - mainly due to the intrinsic non-linear properties of hysteresis, creep and external conditions dependant complex dielectric properties of piezoelectric material. A more recent development in the control of piezoelectric actuators is simultaneous actuation and sensing of piezoelectric actuators - also called as self-sensing.In this thesis the challenge of simultaneous use of piezoelectric material as actuator and sensor is addressed. A novel method for determining the actuator strain is proposed and experimentally tested. The thesis proposal is to assume a piezoelectric stack actuator as a parallel plate capacitor and to estimate the strain/displacement of the actuator from its capacitance. The capacitance signal is intended to be used as a feedback signal for displacement control purpose.The thesis work started from the scratch - where the proposal was very unclear and needed to be studied and tested experimentally. For experiments a test setup was needed which was designed and built in a clean room environment. In the test setup capacitance of the actuator was measured. A relationship between strain and capacitance was studied from the experimental data. For capacitance measurement a simple low-noise electric circuit based on Op-Amps was designed and built. Whereas strain of the actuator was measured using an interferometer (laser sensor). Charge amplifier was used to give the control signal to the actuator. The capacitance and strain data were acquired using Speedgoat hardware and analyzed in xPC target environment of Matlab.Results show that there exists hysteresis in the capacitance-strain graph, even when the control signal is provided from a charge amplifier. Piezoelectric actuator cannot be modelled as a parallel plate capacitor, due to the fact that piezoelectric material has complex dielectric properties which are control signal's amplitude and frequency dependant and that the resistance of the actuator changes with the strain as well.