Wai-Chuen Gan

Position control of linear switched reluctance motors for high-precision applications

Most advanced manufacturing processes require precise motions for material transfer, packaging, assembly, and electrical wiring. To achieve precise linear motions, most of these high-performance manufacturing machines use X-Y sliding tables with permanent-magnet rotary motors and rotary to linear couplers. Though this method is the most widely used, it has disadvantages of low accuracy, complex mechanical adjustments, high cost, and low reliability. This paper describes the position control of a linear switched reluctance motor for high-performance motions in manufacturing automation. The proposed actuator has a very simple structure and it can be manufactured easily. There is no need for magnets and no limitation on the travel distance. The actuator is extremely robust and can be used in a hostile environment. A novel current-force-position lookup table is first developed to perform the force linearization. Then, a plug-in robust compensator using H/sub /spl infin// loop-shaping design is employed to improve the system robustness and the tracking performance. Experimental results of the motion system indicate that the system has fast tracking responses with good accuracy.

A Self-Tuning Regulator for the High-Precision Position Control of a Linear Switched Reluctance Motor

In the high-technology mass manufacturing industry, high-speed and high-precision motion is an indispensable element in the automated production machines. In recent years, there has been a growing tendency to employ direct drive permanent magnet linear synchronous motors in demanding motion applications. Although the overall performance is good, its implementation cost remains high. This is mostly due to the cost of the Neodymium-Boron magnets, the manufacturing of the magnetic rails, and the precision of the overall mechanics. In this paper, a much cheaper alternative is proposed-to use a low-cost linear switched reluctance motor (LSRM) and an adaptive control strategy to overcome the tolerances and difficult control characteristics inherent in the motor. The LSRM has simple and robust structure, and it does not contain any magnets. However, its force is solely drawn from the reluctance change between the coil and the steel plates. Variations on the behavior of these two elements due to different operating conditions will change the motion behavior of the motor. Also, to keep the overall cost low, the LSRM sets a marginal mechanical tolerance during its mass production. This leads to characteristic variations in the final product. Finally, since the LSRM is a direct drive motor, any variations on the motor characteristics will directly reflect on the control system and the motion output. In this paper, a self-tuning regulator (STR) is proposed to combat the difficulties and uncertain control behaviors of the LSRM. This paper first introduces the motor winding excitation scheme, the model of the LSRM, and the current control method. The LSRM system is modeled as a single-input single-output discrete model with its parameters estimated by the recursive least square (RLS) algorithm. Then, an STR based on the pole placement algorithm is applied to the LSRM for high- performance position tracking. Both the simulation investigation and the experimental verification were conducted. In both cases, the results verified that the proposed RLS algorithm can estimate the parameters with fast convergence. The STR can provide quick response and high precision which is robust to the change of system parameters. Combined with STR control, the LSRM is a low-cost solution to fast, accurate, and reliable position tracking for many demanding motion control applications.

Torque and velocity ripple elimination of AC permanent magnet motor control systems using the internal model principle

This paper addresses the problem of torque and velocity ripple elimination in AC permanent magnet (PM) motor control systems. The torque ripples caused by DC offsets that are present in the current sensors of the motor driver and the digital-to-analog converters of the motion controller are studied and formulated mathematically. These torque ripples eventually generate velocity ripples at the speed output and degrade the system performance. In this paper the torque ripples are modeled as a sinusoidal function with a frequency depending on the motor speed. The internal model principle (IMP) is then used to design a controller to eliminate the torque and velocity ripples without estimating the amplitude and the phase values of the sinusoidal disturbance. A gain scheduled (GS) robust two degree of freedom (2DOF) speed regulator based on the IMP and the pole-zero placement is developed to eliminate the torque and velocity ripples and achieve a desirable tracking response. Simulation and experimental results reveal that the proposed GS robust 2DOF speed regulator can effectively eliminate the torque ripples generated by DC current offsets, and produce a velocity ripple-free output response.

Development and control of a low-cost linear variable-reluctance motor for precision manufacturing automation

Most advanced manufacturing processes require precise linear-position control for material transfer, packaging, assembly, and electrical wiring. To achieve precise linear motion, most of these high-performance manufacturing machines use X-Y sliding tables with permanent-magnet rotary motors and rotary-to-linear couplers. Though this method is the most widely used, it has disadvantages of low accuracy, complex mechanical adjustments, high cost, and low reliability. This paper describes the use of the variable-reluctance-driving principle to construct a novel linear direct-drive actuator system for high-performance position control in manufacturing automation. The proposed actuator has a very simple structure and it can be manufactured easily. There is no need for magnets and no limitation on the traveling distance. The actuator is extremely robust and can be used in hostile environment. A novel control method, using cascade control and the force-linearization technique, is developed and implemented for precision position control of the actuator. Experimental results of the motion system indicate that the system has fast responses with good accuracy.

High-Precision Position Control of a Linear-Switched Reluctance Motor Using a Self-Tuning Regulator

High-precision position control of linear-switched reluctance motor (LSRM) is important in motion-control industry. The static model-based controller sometimes cannot give satisfactory output performance due to the inherent nonlinearities of LSRM and the uncertainties of the system. In this paper, a self-tuning regulator (STR) based on the pole-placement algorithm is proposed for high-precision position tracking of the LSRM. Following the time-scale characteristics analysis of LSRM position-tracking system and force-characteristic investigation, the position-tracking model is treated as a second-order system. Different from the static model-based control schemes, the dynamic model of the LSRM can be obtained by online estimation. Also, some practical aspects are taken into account. Owing to the unmodeled dynamics and high-frequency measurement noises, there are some oscillations in the practical control signals, and they can be reduced by a properly designed filter. Both the simulation and experimental results demonstrate that, in the control of the proposed STR, the position-tracking system can reproduce the reference signal with the desired performance in harsh ambient. These results confirm that the method is effective and robust in the high-precision position tracking of LSRM.

Design of a linear switched reluctance motor for high precision applications

This paper describes the design of a linear switched reluctance motor (LSRM) for high-speed high-precision point-to-point motions. An S-shaped curve is first chosen as the trajectory motion profile and then a simple yet effective design procedure is introduced to design the motors mechanical dimensions. Theoretical deduction and experimental results on the phase inductance and the static force generation are presented and compared with each other. The final design has a simple and robust structure. Measurements from the fabricated LSRM show that the motor has met all design specifications. The resultant LSRM is very useful in high-precision applications, especially in semiconductor fabrication machineries.

Design and simulation of a magnetic levitated switched reluctance linear actuator system for high precision application

Magnetic levitated carrier system was developed for the transportation systems. It is contact-free type; it can eliminate mechanical components (e.g. gears, guide, ball bearings), reduce the mechanical alignment and maintenance cost, satisfy environmental demand, and enable the carrier to travel at high speed with high precision and acceleration. In this paper, the investigation, design, simulation and fabrication of a magnetic levitated linear motion system are addressed, based on switched reluctance (SR). The proposed system resolves the problems of mechanical wear, friction, noise, heat generation, and ldquometal dustrdquo contamination, and it is very suitable for applications that require high-performance linear motions: from high-precision manufacturing machines, clean-room wafer carrier systems, to high-speed material transportation in factories and warehouses. The proposed system employs a novel linear machine structure which uses four coils for levitation, and three coils for propulsion. Comparing to permanent-magnet (PM) track levitation, high-temperature superconductor levitation, and other existing magnetic levitation methods, the proposed system has a much simpler structure. It can lower manufacturing cost and increase reliability. In this paper, we firstly discussed the mechanical structure of the proposed levitation system and the model of the actuators. Then, finite element analysis (FEA) was carried out for both the propulsion and levitation actuators to verify the electromagnetic characteristics of the motion system. Finally, a control algorithm, which includes PID and nonlinear force control was discussed. The levitation system was simulated by Matlab Simulink, to achieve a stable and high-precision position control. The simulation results were very satisfactory and it validated the design concept.

Short distance position control for linear switched reluctance motors: a plug-in robust compensator approach

Short distance position control (<1 mm) is an important issue in many precision position applications such as integrated circuit (IC) bonding machines. For these purposes, a novel linear switched reluctance motor (LSRM) is developed. The motors control strategy is based on a 20/spl times/20 look-up table force linearization scheme for low-cost implementation. The system performance is satisfactory for long and medium distance travels, but the systems output should be further improved for short ones. In this paper, a plug-in robust compensator is proposed to improve the tracking response of the overall system. Simulation and experimental results are presented and compared to validate the proposed robust plug-in compensator.

Magnetic Analysis of Switched Reluctance Actuators in Levitated Linear Transporters

A novel linear magnetic levitated actuator using the switched reluctance principle is addressed in this paper. This actuator can be applied to precise motion control of automation machines. The proposed system has the advantages of a simple and robust structure, and direct drive capability. The contactless structure eliminates mechanical wear, friction, noise, and heat generation. To verify the feasibility of the proposed system, the magnetic levitated force is analyzed by magnetic circuit analysis (MCA) and by finite-element analysis (FEA). A prototype structure is fabricated, and experiments are performed with the actual hardware. Results of the MCA and the FEA are both compared with the results obtained from the hardware experiments. They all agree with the proposed design methodology. This paper can form a useful reference in the design of a mechanical structure for magnetic levitated switched reluctance actuators.

Position Estimation and Error Analysis in Linear Switched Reluctance Motors

In this paper, a continuous position estimation scheme is presented for linear switched reluctance motors (LSRMs). The scheme uses diagnostic current injection into an unenergized phase to detect the motor position. This paper proposed that a new current integration index be used to quantify the measurement of current waveform. Hardware implementation results demonstrate the effectiveness of the proposed estimation scheme for the LSRM. This paper also performs a study on the accuracy of the estimated position. Through the detailed experimental data, the approach of polynomial fitting is compared with the lookup table with regard to characteristic curve representation. The estimation error distributions and their standard deviation show that the accuracy and precision are close between these two approaches.