Computer-aided design and simulation of current sensitive electromagnetic actuators.

The thesis presents the development of CAD techniques in the design and simulation of electromagnetic actuators. It also demonstrates the application of analytical and finite element CAD techniques on the behaviour, evaluation and optimal design of current sensitive electromagnetic actuators. Both clapper and stepper motor actuators are investigated based on the magnetic saturation and polarisation principles. An analytical method is outlined and applied in the design of the actuators and their evaluation. The two scalar potential approach is investigated in 3D nonlinear magneto-static finite element computation which is used in the simulation and prediction of the performance of the actuators. A 2D nonlinear transient electromagnetic finite element method, taking account of the 3rd dimension, is developed and the actuators for time-varying current control is evaluated. A decoupled 3D finite element integral method is postulated to predict the dynamic transient response characteristics of the actuators. Analysis is used to examine the relationships of the actuator sensitivity to manufacturing tolerances which cover a wide range of design and control variables. The actuator sensitivity is quantified in terms of critical design factors and a range of airgap settings. The actuators are optimised and quantitative comparisons between the predictions and the test results for the clapper actuators are discussed. The deficiencies of the clapper type actuators are examined. Anovel approach electromagnetic actuator is proposed to obviate these deficiencies. This actuator is based on the combination of the principles of magnetic saturation and the stepper motor. A disc magnet stepper motor is investigated and employed in the actuator. The dependency of the actuator performance on specific key factors is obtained and optimised. A technique is developed to reduce detent torque to a low level. The optimal design of the stepper motor actuator is presented, together with the evaluation of its static and dynamic characteristics. Finally, an actuator combining the stepper motor and clapper actuator is postulated and evaluated. The aims of the work presented here are to: explore the use of Computer Aided Design techniques in the design and analysis of high sensitivity current-operated electromagnetic actuators; to optimise actuators and improve the sensitivity; to develop design and evaluation approaches capable of solving the magnetic actuators transient dynamic performance and practical engineering design problems; to investigate the actuators dependence on the key design parameters in order to determine the range of manufacturing tolerances and to optimise the actuator; to develop a novel magnetic actuator capable of operating with the highest possible sensitivity to current, diminishing the need for very finely machined surfaces and obviating the separate use of the toroid transformer. This also involves developing the analytical techniques.