Permanent magnet linear motors for short strokes

It is noted that the use of new powerful permanent magnet materials such as neodymium-iron-boron alloys can greatly improve the performance of electric machines. The authors analyze the impact of their use on linear motors with particular emphasis on fast action over strokes on the order of 5 to 20 mm. Closed-form formulae which link the travel time to the stroke and heat dissipation limit of the device are established. These formulae are used to compare various machine configurations, some of which were devised specifically for this application. It is shown that permanent magnet linear motors feature very fast travel times, but can do so only at low duty cycles. For that reason, two-spring actuators, though not as fast for single motion, are superior when higher frequencies of operation are required