The Design and Analysis of Reciprocating Non-Linear Electro-Mechanical Systems

Abstract

Low power reciprocating diaphragm air compressors are commonly used in medical applications where high efficiency and reliability, minimum space envelope and low cost are critical design considerations. The use of reciprocating electromagnetic linear actuators as prime-movers is preferred over other drive mechanisms such as motor/rotating cam systems due to increased reliability and reduced volume envelope. The possible topologies for such linear actuators include moving magnet, moving coil and moving iron devices. Moving magnet configurations have the advantages of improved heat dissipation and reliability, due to the absence of flying leads, than moving coil devices and have an inherent bi-directional action unlike moving iron devices. Existing systems employing moving magnet devices generally utilise open planar configurations, however these have the disadvantages of undesirable forces normal to the intended motion, poor utilisation of materials and low efficiencies. The paper considers two alternative axisymmetric moving magnet actuators, air cored [1] and iron-cored actuator. Figure 1 shows an axisymmetric schematic of the air cored device which consists of a shuttle with an axially magnetised permanent magnet, supported by a non-magnetic shaft. The stator has two opposing current carrying coils housed in a non-magnetic former. The iron cored device shown in figure 2 is a bipolar device and comprises of a soft magnetic shaft carrying two radially magnetised permanent magnet rings and a coaxial soft magnetic shell housing the opposing current carrying coils.