Circular magnetic flux: General Industry Coverage

A linear motor offers numerous mechanical advantages for a machine tool compared to a ballscrew drive, according to Greg Langenhorst, technical marketing manager for MC Machinery Systems Inc., which supplies Mitsubishi EDMs, lasers and other products. Those advantages include the elimination of backlash, lubrication requirements, pitch-error compensation and wear because a linear motor is a noncontact device.

Linear drive systems are well-established in machine tool design, but Langenhorst said Mitsubishi is the first to incorporate a linear shaft motor, rather than a linear synchronous motor with a flat-plate design, in wire EDMs. The flat-plate design, which has permanent magnets on one side and a set of copper-wrapped iron cores on the other, limits the effective magnetic flux to only half of its potential, the company reports. In contrast, the new cylindrical drive technology’s round shaft uses 360° of magnetic flux. That’s possible because round magnets are packed end-to-end in a stainless steel tube, which is surrounded by coreless copper wire housed in a “forcer.”

Courtesy of MC Machinery Systems

MC Machinery Systems’ cylindrical drive technology replaces ballscrews with linear shaft motors (above) in Mitsubishi wire EDMs, such as the MV1200R (below).

This enables the air gap between the magnets and copper wire to be significantly larger in the circular style than the flat design, Langenhorst noted. “The air gap is not as critical because we’re using the magnetic flux from all the way around those permanent magnets,” he said.