Robust Control of Ultrasonic Motor Operating under Severe Operating Conditions

Abstract

Ultrasonic motor technology is a key system component in integrated mechatronics devices working on extreme operating conditions subjected to thermal cyclings or large thermal variations, EM disturbances, radiations, corrosion, or strong vibrations. Due to these constraints, robustness of the mechanics/electronics/control interfaces should be taken into account in the motor design. A robust controller for a travelling wave ultrasonic motor (TWUM) is considered in this study for operation in extreme environmental conditions. A simple causal model of the TWUM is introduced for identification of motor parameters. Then, an H∞ loop shaping synthesis procedure is implemented in order to obtain a good compromise between environmental robustness and motor’s performances. Finally, simulation and experimental results demonstrate the effectiveness of the proposed robust controller in extreme operating conditions. Keywords—H∞-synthesis, extreme environments, robust control, traveling wave ultrasonic motor. Nomenclature SymbolDescription Si,j,Dn,Σ Strain, Electrical displacement, Entropy Ti,j,En,θ Stress, Electrical field, Temperature s i,j,k,l Elastic compliance ǫ n,m,d θ n,i,j Electrical permittivity and piezoelectric constant pT m,α E i,j Pyroelectric and thermal expansion constant ρ C T,E θ Thermal constant (α,β), (d,q) Stator’s and rotor’s reference frames v,w,Ψ(v,w) Voltage phasor, Rotating traveling wave, Phase θc,k,R(kθc) Angular position,Contact points,Rotational matrix VNid,VTid Ideal normal and transversal velocity Vd,Vq Voltage in the (d,q) rotor’s reference frame FN ,FT Normal and tangential force N,T,f0 Real rotor speed, Torque, Friction coefficient frα, frβ Feedback forces in the (α,β)’s reference frame A,m, Force factor, Modal mass ds, c Stator’s damping term and stiffness 6