Fast-acting, long-stroke solenoids with two springs

It is pointed out that fast motion over a long stroke cannot be achieved with regular solenoids when the active force decreases rapidly with distance. A possible solution, a device with two oscillating springs controlled electromagnetically, is theoretically and experimentally studied. The mathematical model, based on finite-element analysis, consists of a dynamic model of motion that includes all relevant physical phenomena with the exception of eddy currents, which are evaluated separately. Tests were carried out to verify the mathematical model, quantify the possible time-versus-energy-input characteristics for a given stroke and volume, and allow the comparison of this concept with a previously studied approach in which repulsion forces are exerted on a moving permanent magnet. It is shown that the latter is superior when the actuator is required to provide mechanical work in addition to fast motion over a long stroke, while the two-spring actuator is faster and uses less energy when motion alone is desired