Robert B. Gorbet

Passivity-based stability and control of hysteresis in smart actuators

The past decade has seen an increase in the use of smart materials in actuator design, notably for inclusion in active structures such as noise-reducing paneling or vibration-controlled buildings. Materials such as shape memory alloys (SMAs), piezoceramics, magnetostrictives and others all offer exciting new actuation possibilities. However, all of these materials present an interesting control challenge due to their nonlinear hysteretic behavior in some regimes. We look at the energy properties of the Preisach hysteresis model, widely regarded as the most general hysteresis model available for the representation of classes of hysteretic systems. We consider the ideas of energy storage and minimum energy states of the Preisach model, and derive a passivity property of the model. Passivity is useful in controller design, and experimental results are included showing control of a differential shape memory alloy actuator using a passivity-based rate controller.

General stability criteria for a shape memory alloy position control system

This paper deals with the L/sub 2/ stability of a shape memory alloy actuated position control system, based on a single wire under constant axial load. Presuming a controller has certain specific dissipativity characteristics, it is shown that system stability can be guaranteed for a large class of controllers. In particular, the results can be used to show stability under approximated PID, PI and PD control. The result is used to find a stabilizing PI controller, and the corresponding experimental data is shown.

Closed-Loop Position Control of Preisach Hystereses

We discuss closed-loop control of hysteretic systems having Preisach representations. We apply dissipativity methods, the key component of which is the determination of an appropriate supply rate. The concept of cyclo-dissipation is used to identify a new supply rate for Preisach hystereses and dissipativity with respect to this supply rate is shown. The result is useful in the design of output feedback controllers, and complements a previous result using feedback of the output derivative. We consider the specific example of a shape memory alloy actuator and identify a class of controllers which provide stability of position feedback with current as the control variable. This demonstrates one way in which system dynamics that couple with hysteresis can be included in controller design.

Memory alloy actuator

The phase change in shape memory alloys (SMA) is highly nonlinear, and the development of advanced position ing applications for SMA actuators benefits from the availability of good models of this behaviour. One phenomenological model for SMA transformation kinetics is Madill’s model, which has recently been extended to include the effect of time varying stress. This extension allows for the modelling of stress disturbances and the simulation and prediction of stress-strain behaviour. In this work, we couple the phase kinetics of the extended model with a series-based mechanical model which includes both shape memory and superelastic behaviour. This coupled model is inverted and used to investigate different control architectures for sine tracking and stress disturbance rejection for an SMA actuator with constant load. Open-loop model-inverse feedforward control is compared with simple PI feedback and the combination of feedforward plus feedback. The results show in particular that using complicated inverse models does not always bring the expected increase in perfor mance, and that other limitations of SMA actuators can negate the benefit of model-inverse feedforward.

Design and Testing of a Thermally Stable Filter Using Bimetal Compensation

In this paper, it is proposed that a variable length bimetal tuning screw can be used to compensate for temperature drift in waveguide resonators and filters constructed from high CTE materials such as aluminum. A method is proposed for designing and tuning a bimetal tuning screw. A method is also proposed for applying this approach to filter compensation. Experimental results are provided for a compensated aluminum cavity, and filter. Temperature drift in the resonator is reduced to -0.382 ppm/degC from -23 ppm/degC. Experimental results are provided for a narrow-band inductive-iris Chebyshev band-pass filter demonstrating a reduction in temperature drift from -23 ppm/degC to 2.35 ppm/degC.

Shape memory alloy temperature compensation for resonators

In this paper we present a method for designing temperature compensated cavity resonators using shape memory alloys (SMAs). This paper gives a formula for the temperature drift of resonant frequency, which is valid for any conductor-loaded cavity regardless of its shape. This formula is combined with a field perturbation model and used to derive mechanical design constraints from a temperature drift constraint. Experimental results are given that confirm the feasibility of the proposed design approach.

INFLUENCE OF INITIAL STATE ON OPEN-LOOP REJECTION OF INPUT NOISE IN A PIEZOCERAMIC STACK ACTUATOR

Abstract Actuators made from so-called smart materials have been proposed in the literature, for inclusion in mechatronic systems used in shape control of various surfaces. At the lowest level, this shape control problem can be thought of as a number of distributed regulation problems. Because of the hysteresis non-linearity present in these actuators, there are an infinite number of system states corresponding to a particular output regulation set point. This adds complexity to the regulation design problem, and it was shown in past work that, unlike memory-less systems, using one of these states in particular resulted in better open-loop rejection of input noise. This result was shown in simulation only, for a shape memory alloy actuator. This paper furthers the investigation of the effect of initial state on output regulation, by showing the same result holds for piezoceramic actuators, and includes critical experimental confirmation using a piezoceramic stack actuator. Suggested topic area: #5 Mechatronics components and devices Possible alternate area: #2 Control of mechatronic systems

Nonlinear Macro Drive Model Identification for a Macro-Micro Positioning System

Abstract This paper deals with the identification and control of the macro drive of a macro-micro positioning system with mechanical nonlinearities. The experimental system consists of a modified ink-jet printer, modeled as a sliding mass actuated by a D C. motor. The linear dynamics are assumed separable from saturation and friction nonlinearities. Coulomb friction is approximated as a dead zone and linearized through its inverse, allowing for MLS identification of the remaining linear dynamics. The dead-zone friction model is then tuned to accurately reflect experimental results, and a full nonlinear model is formed. The resulting model is used as a basis to design a controller.

Effect of lnitial State on Output Regulation of Actuators with Preisach Hystereses

Abstract Actuators made from so-called smart materials have been proposed in the literature, for use in shape control of various surfaces. At the lowest level, this shape control problem can be thought of as a number of distributed regulation problems. Because of the hysteresis non-linearity present in these actuators, there are an infinite number of input values corresponding to a particular output regulation setpoint. One might then ask the question, not relevant to memory-less systems, whether there is some advantage to regulating about one of these states in particular. This work begins to investigate the answer to this question, with the finding that for any given desired output, there is one state in particular at which the system has a better natural (open-loop) rejection of normally-distributed noise at its input.