A Charge Feedback Controller for a Piezoelectric Voltage Amplifier/Driver
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0969-W03-12
A Charge Feedback Controller for a Piezoelectric Voltage Amplifier/Driver Maciej Noras, Peter McAnn, and Jerzy Kieres Trek, Inc., 11601 Maple Ridge Rd., Medina, NY, 14103
ABSTRACT In this paper, authors examine the design and implementation of a new charge feedback control circuitry for a voltage amplifier used in driving of a piezoelectric actuator. Actuators driven in the usual voltage feedback regime display a nonlinear voltage-displacement relationship, known as hysteresis. Use of the new charge feedback control circuitry resulted in significant reduction (70%) of the hysteresis-related nonlinearity. INTRODUCTION Piezoelectric actuators display hysteresis dependence in the transfer function between the applied voltage to strain or displacement of the piezo material. As a result, piezoactuators are typically operated in the limited linear range of motion to avoid errors caused by nonlinearity of the hysteresis effects. A large variety of techniques have been developed to reduce hysteresis, taking advantage of either special feedback techniques or relatively complicated mathematical modeling. One of relatively successful approaches of overcoming the hysteresis of the actuator is to use charge instead of voltage control. The problem with this approach is a slow charge accumulation in the actuator, leading to a creep in the desired displacement of the actuator (charge bias) [1,2]. I n attempts to reduce creep effect several techniques were developed, including compensating capacitance in series with the driven actuator [3], DC current source switching [4], lead compensator [5], or external feedback loop compensation with inverse transfer function programmed into a PID controller [6]. In this paper authors propose a combination of charge and voltage feedback control loops for improving creep and hysteresis reduction. The macro fiber composites (MFC) used in experiments consist of rectangular piezoceramic rods sandwiched between layers of adhesive and polyimide film, with electrodes embedded in it. The structure is mounted on the surface of the stainless steel flexible sheet that serves as a ground electrode. DESIGN OF THE PIEZO DRIVER Initial design featured two feedback loops within the amplifier structure: one that assures DC stability and creep-free performance (voltage loop) and the other providing charge-feedback information (charge loop). The charge monitor employed in the design is constructed using AD210 precision, wide bandwidth isolation amplifier (Figure 1). This particular design and its performance with a LIPCA (Lightweight Composite Piezoceramic Actuator) device was described elsewhere [7]. The following re-design presented in this work results from desire to simplify the construction of the control system by using a standard high voltage amplifier and an external circuitry that modifies the input voltage, so the actuator is driven in the charge control regime. This is an attempt to create a “snap-on” solution for conversion of voltage amplifiers used in driving piezoelectrics into charge
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