High-Precision Motion Mechanism And Control Of The Planar Switched Reluctance Motor

The planar switched reluctance motor (PSRM) is a new-type of planar motors, which is based on the minimum reluctance principle. The PSRM is a promising candidate for the long-stroke and high-precision planar actuators in advanced manufacturing equipments, such as the microelectronic manufacturing and ultra-precision machining, because it observably features simple structure, easy manufacture, high reliability, long stroke, and strong resilience to harsh environment. However, the previous PSRMs exhibit low moiton accuracy. Aiming at the critical scientific problem of the generation mechanism of the motion accuracy, this paper thoroughly studies the high-precision motion mechanism and control of the PSRM to provide the systematic fundamental theory and reference design to industrial applications of the PSRM.An optimal structural design is performed for the PSRM, in the synthetic consideration of the requirements to reduce the force ripple and deformation and improve the motion accuracy. Based on the desired maximum thrust force and maximum velocity, the mathematical relation of the main dimensions, electromagnetic parameters, and dynamic parameters of the mover and stator is first derived theoretically. Then, the parameters are chosen to reduce the force ripple, including the smaller pole pitch and the larger number of tooth pairs per mover, etc. The main dimensions and electromagnetic parameters of the mover and stator are further determined. Additionally, the moving platform is optimized to decrease its deformation. Furthermore, a prototype of the PSRM is developed by applying the optimal designed structure, and an experimental setup is built. The mechanical and electromagnetic characteristics are also measured and analyzed. The research results demonstrate that the thrust force, velocity, deformation, and stress of the developed PSRM meet the design requirements, and the force ripple is reduced significantly and the motion accuracy is improved effectively for the developed PSRM.A nonlinear inverse force model of the PSRM is first built by using the sparse least squares support vector machines. Then, a nonlinear thrust force model and a nonlinear normal force model of the PSRM are theoretically deduced with the magnetic equivalent circuit method, flux tube method, and virtual work principle. Futhermore, a nonlinear friction model of the PSRM is formulated utilizing the LuGre dynamic friction model. Additionally, the simulation and experiment of the four nonlinear models are carried out. Simulation and experimantal results show that the nonlinear inverse force function is able to accurately estimate the currents greater than 1 A; the average relative errors of the thrust force and normal force from both simulation and experimental measurement are less than 10%, compared to those from the nonlinear thrust force and normal force models; the average relative error of the friction from the nonlinear friction model is about 10%, compared with that from the simulation system; the accuracy of the built nonlinear models is verified. The built nonlinear models provide the fundamental theory to high-precision motion of the PSRM.By using the local sensitivity analysis theory, the normalized sensitivities of the thrust force and normal force of the PSRM with respect to the motor parameters are deduced. Additionally, the effect rules of the motor parameters on the motion accuracy are revealed for the PSRM, based on the deduced normalized sensitivities. The solution is further proposed to improve the motion accuracy of the PSRM. The research results manifest that the normalized sensitivities of the thrust force and normal force of the PSRM with respect to the stack length of the mover and stator, tooth width of the mover and stator, air gap, number of turns per phase, current, and position primarily pertain to very high sensitivity class, respectively; in ascending order by the effect of the motor parameters on the motion accuracy for the PSRM, the effect of the stack length of the mover and stator, the effect of the current, the effect of the air gap, the effect of the tooth width of the mover and stator, the effect of the position, and the effect of the number of turns per phase are listed; the percentages of the effect of the stack length of the mover and stator, current, air gap, tooth width of the mover and stator, position, and number of turns per phase on the motion accuracy are 10.12%,15.05%,17.26%,18.07%,19.27%, and 20.23%, respectively. The obtained generation mechanism and rule of the motion accuracy provide the theoretical foundation to high-precision motion control of the PSRM.The efficiency improvement of the PSRM is discussed, and an efficiency improvement method with a maximum force per ampere (MFPA) strategy of the PSRM is proposed. A constrained optimization problem with time-varying parameters is first formulated to describe the MFPA strategy. The problem is then transformed into an unconstrained problem by employing the sequential unconstrained minimization technique. A designed adaptive genetic algorithm is further introduced to solve the unconstrained optimization problem. Additionally, the simulation and experiment of the MFPA strategy are performed. The simulation and experimental results illustrate that compared with the conventional current distribution method, the proposed current distribution method with the MFPA strategy is capable of reducing copper losses greater than 10%; the efficiency of the PSRM with the MFPA strategy can be improved effectively; the smooth, fast, and accurate trajectory tracking of the PSRM is achieved with the MFPA strategy.The steady-state position errors of the proportional, proportional-derivative (PD), proportional-integral, and proportional-integral-derivative position controls of the PSRM are first derived theoretically, respectively. Then, the PD position controllers are applied to the PSRM for realizing motion control. Moreover, a model reference adaptive position controller based on the input and output is designed for the PSRM, and the stability of this controller is proved. The experiment of the model reference adaptive position control is further carried out for the PSRM. Additionally, a position control system of the PSRM with the feedforward friction compensation is built. The experiment of the system is also performed for motion control. Experimental results depict that for the PSRM with the PD positon control, the positioning with ±0.3-μm steady-state position error for the motion with a 1-μm stroke, the positioning with ±2.3-μm steady-state position error for the motion with a 290-mm stroke, and the trajectory tracking with ±56.9-μm dynamic position error for the motion with a stroke ranging from 57 to 100 mm are achieved smoothly, fast, and accurately; the PSRM with the model reference adaptive position control realizes the submicrometer positioning accuracy for the motion with a 15-mm stroke smoothly, fast, and accurately, and its steady-state position error is ±0.2 μm; compared to the PSRM without the feedforward friction compensation, the dynamic position error is reduced by greater than 33% for the PSRM with the feedforward friction compensation under the trajectory tracking; for the PSRM with the feedforward friction compensation, the achieved ±0.2-μm steady-state position error for the positioning with a 1-μm stroke and the achieved ±1.5-μm steady-state position error for the positioning with a 290-mm stroke are presented, and the PSRM is able to achieve the x- and y-axes positioning resolutions of 0.5 μm. The submicrometer positioning is achieved for the PSRM.In this paper, for the PSRM, the optimal structural design has been carried out; the mechanical and electromagnetic characteristics have been analyzed; the nonlinear models have been deduced; the generation mechanism of the motion accuracy has been revealed; the efficiency improvement method with the MFPA strategy has been proposed; the three high-precision position controllers have been designed; the prototype has been developed; the experimental verification of the proposed theories has been implemented; the micro-/nano-positioning has been achieved. The obtained high-precision motion mechanism and control of the PSRM provide the systematic fundamental theory and reference design to industrial applications of the PSRM.