Drive eases microstepping

If an engineer using a full-step, 5-phase motion system wants to improve performance without a complete redesign, then switching to a 5-phase system with microstepping capability may do the trick. Microstepping lets the motor stop and hold between the full or half-step positions.

The higher resolution between steps increases system performance with smoother motion. Smaller step angles tend to eliminate the jerky character of low-speed motor operation, noise at intermediate speeds, and problems with resonance. Microstepping can also reduce total system complexity and cost, by replacing or simplifying gearboxes as well as mechanics for damping of noise and vibration. However, the electronics for generating microstepping are typically more complex than electronics for full- and half-stepping.

Oriental Motor USA Corp. takes 5-phase microstepping to the next level with its new RK Series. "This system has the simplicity of a full-step system," explains Nick Johantgen, manager of engineering and technical support. "But engineers don't have to change the motor, driver, or pulse generator to start microstepping. It costs 40% less, and has circuit board that's 37% smaller than our previous design. As a result, the RK Series makes the switch from full-step to microstepping easier and less costly than ever before."

The two most important engineering challenges, Johantgen notes, were improving the microstepping performance of the motor and driver combination while reducing the cost of the overall system. Parts count and cost reduction required developing two chips: an intelligent modular power element, and a custom gate array.

The power element includes: PAM FETs (Pulse Amplitude Modulated Field Effect Transistors), INV (Inverter) FETs, pre-drivers for PAM and INV FETs, a diode bridge, overheat detection, a triac trigger element, and an inrush current-restricting triac. The custom gate array includes: the "Smooth Drive" circuitry, pulse logic function, preset current generation, electromagnetic brake control, current boosting function, and circuit protection logic.

"We expect that this lower pricing and microstepping capability will help bring more 5-phase applications to the U.S.," says Johantgen.