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PWM servodrives ‘outperform linear drives’

05 February, 2014

The Israeli company ACS Motion Control has developed a range of switching PWM (pulse width modulation) servodrives that, it says, cost less than linear servodrives, but offer better performance, as well as being smaller and more robust. The NanoPWM drives deliver sub-nanometer position jitter performance, and nanometer following errors when moving at low speeds.

The drives are based on a proprietary technology developed by ACS over the past five years. They are aimed at applications such as inspecting semiconductor wafers and flat panel displays, grinding lenses, ultrasonic scanning and air bearing stages.

Although linear servodrives offer low noise levels, wide bandwidths, and no crossover distortion or ripple current, ACS says they are bulky, costly and inefficient, and produce large amounts of heat. They also have complex power supply requirements, and are difficult to protect against faults.

Conventional PWM servodrives are small and efficient, with low heat dissipation. They cost less than linear drives, and have simple power supply requirements and good fault protection. But, says ACS, they typically suffer from high switching noise, current ripple and crossover distortion. Because of this, they are not suitable for demanding applications that need nanometre-accurate levels of jitter and following errors.

ACS claims that its new technology combines the best of the existing technologies. The company’s president Ze’ev Kirshenboim says that, compared to linear drives, they provide “better positioning and tracking performance, smaller size, higher efficiency, better reliability and lower cost.” They can also deliver higher voltages and currents, have simpler power supply requirements and offer full digital control.

Space-saving: a 100V, 15/30A NanoPWM drive (foreground) compared to a ±50V, 6/30A linear drive (background)

In tests, NanoPWM drives used to control XY tables with speeds above 1m/s, are said to have achieved standstill jitters better than ±0.3nm, and following errors of ±10nm at speeds of 100mm/s.

The drives are available as part of ACS's MC4U control modules that incorporate EtherCat motion controllers and power supplies. The drives operate from 100V supplies and can deliver currents up to 15A continuous (30A peak).




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