Jc John Compter

Analysis Method of the Dynamic Force and Torque Distribution in the Magnet Array of a Commutated Magnetically Levitated Planar Actuator

This paper concerns the analysis of the dynamic forces and torques acting on the magnets in a Halbach permanent magnet array of a magnetically levitated moving-magnet planar actuator. A new analysis tool is presented which predicts the dynamic force and torque distribution on the magnet array. This design tool uses lookup table data, which are generated by numerically solving the Lorentz force and torque integral, to describe the force and torque between each magnet and coil in the topology. It offers a fast and accurate solution for the analysis of magnetically levitated planar actuators. The results for two different commutation methods are presented.

Three-Dimensional Analytical Calculation of the Torque Between Permanent Magnets in Magnetic Bearings

In the high-precision industry, accurate vibration isolation and magnetic levitation are extremely important. As a result, high-performance vibration isolation and magnetic bearings based on permanent magnets are increasingly considered. This paper proposes improved analytical expressions for the torque on cuboidal permanent magnets applied to a magnetic bearing. These novel expressions are valid for any relative magnet position, especially when surfaces of the different magnets are in the same plane. Further, the torque can be obtained with respect to any reference point. Although these equations seem rather complicated, they enable an extremely fast and accurate calculation of the torque on a permanent magnet in the presence of a magnetic field of another permanent magnet. These properties enable a fast design and optimization process of such bearings using fully analytical expressions.

Modelling of a linear PM machine including magnetic saturation and end effects: Maximum force to current ratio

The use of linear permanent-magnet (PM) actuators increases in a wide variety of applications because of their high force density, robustness and accuracy. These linear PM motors are often heavily loaded during short intervals of high acceleration, so that magnetic saturation occurs. This paper models saturation and end effects in linear PM motors using magnetic circuit models. The saturating parts of the magnetic circuit are modelled as nonlinear reluctances. Magnetomotive forces represent the currents and the magnets. This paper shows that when saturated, a negative d-axis current increases the force developed by the motor. Although the increase is not large, it is nevertheless useful, because a negative d-axis current also results in a decrease in the amplifier rating. Further, the trajectory for the maximum force to current ratio is derived. The correlation between the calculated and the measured force justifies the model.

Measurement method for determining the magnetic hysteresis effects of reluctance actuators by evaluation of the force and flux variation

A measurement method is presented which identifies the magnetic hysteresis effects present in the force of linear reluctance actuators. The measurement method is applied to determine the magnetic hysteresis in the force of an E-core reluctance actuator, with and without pre-biasing permanent magnet. The force measurements are conducted with a piezoelectric load cell (Kistler type 9272). This high-bandwidth force measurement instrument is identified in the frequency domain using a voice-coil actuator that has negligible magnetic hysteresis and eddy currents. Specifically, the phase delay between the current and force of the voice-coil actuator is used for the calibration of the measurement instrument. This phase delay is also obtained by evaluation of the measured force and flux variation in the E-core actuator, both with and without permanent magnet on the middle tooth. The measured magnetic flux variation is used to distinguish the phase delay due to magnetic hysteresis from the measured phase delay between the current and the force of the E-core actuator. Finally, an open loop steady-state ac model is presented that predicts the magnetic hysteresis effects in the force of the E-core actuator.

Improvement of the dynamic performance of an AC linear permanent magnet machine

This paper discusses the controller design and test approaches leading to the performance improvement of a brushless 3-phase AC synchronous permanent magnet linear machine. The feasible controller design concept for the linear machine is presented and further implemented in Simulink and dSPACE. Two controllers, a PD and a PID-controller, are designed to reach high position accuracy during constant speed operation without a settling time. The controllers for the linear machine are implemented and the theoretical results are verified.

Analysis of the parasitic forces and torques in coreless linear motors

This paper concerns the analysis of parasitic forces and torques in coreless or air-cored linear synchronous motors with a U-shaped stator due to variation of the permanent magnet properties, manufacturing tolerances and power amplifier offsets. The parasitic forces and torques are analyzed using a 3D semi-analytical model based on surface charge modeling of the permanent magnets and numerical integration of the Lorentz force. Monte-Carlo simulations have been applied to carry out the tolerance analysis. Gaussian distributions of the tolerances are assumed. The paper shows that variation of the magnet properties, incorrect mounting of the translator and offsets in power amplifiers are the main cause of parasitic forces in this type of linear motors.

Ampere's Circuital 3-D Model for Noncuboidal Magnets

Analytical equations describing the three-dimensional field of permanent magnets are attractive tools for the optimization of permanent-magnet based structures. The shape of the magnets determines to a high extent the type of solution. The objective of this research is to find the equations describing the field of a pyramidal frustum, based on the Biot-Savart law. We develop analytical equations describing the field of current carrying sheets. These equations make it possible to treat the field of any permanent-magnet shape with a uniform magnetization and flat surfaces.

Innovative Actuator with Two Controlled Degrees of Freedom for Precision Technology Applications

The paper presents the integrated topology of the innovative actuator with two-controlled degrees of freedom (translation and rotation). For the purposes of analysis, design and optimization the analytical description of the actuator is proposed. The model is based on the theory of magnetic equivalent circuit (MEC). It yields values of magnetic field that are needed for the force and torque calculation by the Lorentz equation. The magnetic field, force and torque of the actuator are verified by a precise finite element (FE) model as well as by experiment. The comparison of the results shows that the predictive analysis of the actuator by the suggested MEC model estimates the magnetic field in the air gap, total force and torque of the actuator with acceptable accuracy.

Force analysis of linear induction motor for magnetic levitation system

This paper presents the analyses of thrust and normal forces of linear induction motor (LIM) segments which are implemented in a rotating ring system. To obtain magnetic levitation in a cost effective and sustainable way, decoupled control of thrust and normal forces is required. This study includes the design of a static test setup from which the measurement results are compared and verified with the derived analytical methods and finite element simulations. The comparison shows significant correlation of the thrust and normal forces as function of the slip frequency.