Smart actuators employed in micropositioning are known to exhibit strong hysteresis nonlinearities, which may be asymmetric and could adversely affect the positioning accuracy. In this paper, the analytical inverse of a generalized Prandtl-Ishlinskii model is formulated to compensate for hysteresis nonlinearities of smart actuators. The generalized model was modified to ensure its continuity, and its validity in characterizing different hysteresis properties is briefly demonstrated by comparing the model responses with the measured data for the magnetostrictive, shape memory alloys (SMA), and piezo micropositioning actuators. Since the proposed generalized model is a mere extension of the analytically invertible classical Prandtl-Ishlinskii model, an inverse of the generalized model is formulated using the inverse of the classical model together with those of the envelope functions of the generalized play operator. The effectiveness of the inverse of the generalized model in compensating for the symmetric and asymmetric saturated hysteresis effects is subsequently investigated through simulations for a magnetostrictive and a SMA actuators, and through preliminary experiments performed on a piezo micropositioning stage. The simulation results suggest that the inverse of the generalized Prandtl-Ishlinskii model can be conveniently applied as a feedforward compensator to effectively mitigate the effects of the asymmetric and saturated hysteresis in magnetostrictive and SMA actuators. The experimental results further revealed that the proposed generalized analytical inverse model can be conveniently implemented as a real-time feedforward compensator to compensate for hysteresis nonlinearities of a piezo micropositioining stage.

Piezomicropositioning actuators, which are widely used in micropositioning applications, exhibit strong rate-dependent hysteresis nonlinearities that affect the accuracy of these micropositioning systems when used in open-loop control systems, and may also even lead to system instability of closed-loop control systems. Feedback control techniques could compensate for the rate-dependent hysteresis in piezomicropositioning actuators. However, accurate sensors over a wide range of excitation frequencies and the feedback control techniques inserted in the closed-loop control systems may limit the use of the piezomicropositioning and nanopositioning systems in different micropositioning and nanopositioning applications. We show that open-loop control techniques, also called feedforward techniques, can compensate for rate-dependent hysteresis nonlinearities over different excitation frequencies. An inverse rate-dependent Prandtl-Ishlinskii model is utilized for feedforward compensation of the rate-dependent hysteresis nonlinearities in a piezomicropositioning stage. The exact inversion of the rate-dependent model holds under the condition that the distances between the thresholds do not decrease in time. The inverse of the rate-dependent model is applied as a feedforward compensator to compensate for the rate-dependent hysteresis nonlinearities of a piezomicropositioning actuator at a range of different excitation frequencies between 0.05-100 Hz. The results show that the inverse compensator suppresses the rate-dependent hysteresis nonlinearities, and the maximum positioning error in the output displacement at different excitation frequencies.