UNTANGLING WIRING CHALLENGES

A three-phase sensorless, brushless motor requires only three wires to function. But once Hall effect devices are introduced as feedback, motors require a minimum of eight wires — and an encoder quickly raises the wire count to ten or twelve in a harness.

Much confusion arises from incorrectly connected wires between the motor and amplifier. Systems relying on feedback devices such as encoders and Hall effect devices add complexity. As the number of wires increase, so does the chance of incorrectly connecting from point A to point B. "Many support calls stem from user-created cabling that inverts the phase relationship of the motor leads or feedback devices," explains Dell. Amplifiers for brushed motors are fairly interchangeable. However, for brushless motors they do require careful consideration if not purchased from the same motor manufacturer.

"To reduce wire count associated with encoders, some manufacturers offer linear Hall effect devices that provide absolute positioning within one revolution of a rotary brushless motor without an encoder — absolute or augmented incremental style. The absolute positioning allows stable and proper sinusoidal commutation with minimal wires," says Dell. "Brushless motors come with different Hall effect sensor styles, producing digital or analog output. Too, commutation sequences can vary from one motor manufacturer to the next." Motor wiring orientation is easily changed to accommodate the amplifier, but changing the logic level of Hall effect devices may be more difficult. Purchasing from one manufacturer is one approach to ensuring all components will work together with little optimization.

If required, tuning sophisticated amplifiers for a brushless motor is not overly complex; it just requires patience. Torque amplifiers regulate current in the motor based upon a PID loop. An amplifier that scales motor velocity with applied input voltage incorporates a velocity PID loop surrounding the current PID loop. "In both cases, software setup makes the process far more enjoyable than using potentiometers," says Dell.

MANUALS AND DISPLAYS

Because programmming in code can be labor intensive, straightforward control switches and manuals are on the rise. "Increasingly, control units have plain-English readout displays for easier programming and troubleshooting; others use symbols or letters to communicate parameters and fault codes. But the latter requires a symbols key — which isn't very user friendly," argues Medinger. "Intuitive command languages allow users to create the program that affects the required motion," Dell agrees.

Newer screens display multiple lines of text, and in larger font for those with vision impairment. Most are now are 128 x 64 pixels or larger. "Even color screens are on the rise, as the cell phone industry has made small screens less expensive," explains Lovelace. With text instead of the old P parameters, there's almost no need for a manual. "User can read what is about to change, without having to recall — Was that P34 or P43? And with the cost of memory continually falling, more languages can be stored individual drives without affecting final drive price."

9.29.2006 UPDATE: ONLINE-EXCLUSIVE: Forgiving with electronics

Electronics can also eliminate the need for precise mechanical arrangements. For example, traditional sensors require precise part positioning ensure they are detecting the correct part area. Often, this requires motion control engineers to focus time and energy to slow and constrain motion of the part to make sure that it is inspected correctly. "But sensors that ‘understand’ what parts look like don’t require precise part positioning. This speeds up the line, and speeds up integration," says Keating. The same applies to pneumatic systems. Often operators use wrenches to adjust shock absorbers for fine tuning stop/start cylinder or mini slide motion.
"Another approach is intelligent, electronic stroke setting. This places the shock absorber inside the hard stop, allowing deceleration of the load without returning to end positioning during maintenance," says O'Neill.
But while electronics eliminate physical connections, they complicate connectivity. Cables connect sensors to a power source, so long distances require more cabling, which must be installed in a way that doesn't create a tripping hazard. "But wireless sensor technology will address this problem in some applications," predicts Kielblock. Similarly, it can be difficult to wire sensors to two sides of a conveyor. In these situations, opposed-mode sensors -- those with the emitter and receiver in separate units -- are inconvenient. "Here, sensors that include the emitter and receiver in one unit are a better choice," says Kielblock.