A pair of ICs added to International Rectifier's line of iMOTIONTM integrated design platforms simplifies configuring motion control algorithms for permanent magnet or ac induction motors and their position feedback devices. Rather than use a DSP or MCU, the IRMCK201 and 203 feature a menu-driven Motion Control EngineTM (MCE) that eliminates software programming, which the company claims can cut time-to-market from around a year or more to a couple of months.
According to Toshio Takahashi, director of engineering for motion control, "The logic is in hardware, not in programming in complex software." The MCE is based on hardware logic. "All a user needs to do is configure parameters for motors and control, specifically in switches, just by writing values to a host register (EEPROM) interface," he adds.
The MCE is based on FPGA technology where gate density is not compact, dictating a large chip. But IR engineers were able to trade gate utilization with speed, linking "blocks" in the engine with a small sacrifice in speed. Takahashi says early in development "a big, dense FPGA was used in parallel, with the current loop calculated in 2 microseconds." While fast, he notes gate utilization was poor and resulted in a large-area, 1-Mgate chip. "We didn't need that speed and went to 7 microseconds. And arranging the patent-pending algorithm in hardware to reduce the number of gates needed resulted in a 250-kgate chip, 25% of the size." He adds that the surprise in development was not so much in implementing gate sequencing but in "how much uniqueness could be produced in the new algorithm for such functions as running quiet, noise free, and electrically efficient."
The IRMCK201 features encoder-feedback-based closed-loop current and velocity control for servo applications. The 203 runs encoder/resolverless and uses a unique estimator algorithm for real-time speed and position based on current feedback. The chips' fine pitch geometry (i.e. 0.5-mm pin pitch) allows for a high (33 MHz) clock rate and PWM senses motor current, eliminating the need for Hall effect sensors or current transformers.
Applications include dental drills, wafer-handling equipment, and pick-and-place machines. For example, a sinusoidal motor current that matches rotary motion (as opposed to conventional trapezoidal signals with greater losses) smoothes torque to minimize ripple in dental drills, allowing speeds up to 100k rpm with ac brushless motors. Some previous dc brushed motors experience brush flashover at 40k rpm. International Rectifier Inc.http://rbi.ims.ca/3843-582