Motor Controller

Selecting a Motor Controller for Electrical Drives

It is often difficult to get motor manufacturers to make even slight changes in these specifications. For example, ordering a standard motor with a special rear shaft extension may result in a sharp jump in both price and lead time, assuming the vendor is willing to make the modification at all.

Some motor suppliers address the need for such special products through field modification centers located at a distributor site. These centers may offer some limited variations, usually only for brush-type motors. It is also interesting to note that the modifications these centers make do not address the overall system or the controllers. In many cases, other factors can complicate the design process, even when an off-the-shelf motor seems to provide the right performance. For example, space limitations may eliminate standard motors from consideration. Numerous applications today call for a motor built on and around the driven shaft, particularly when the system must be torsionally stiff (no belts), or have zero lost motion (no gears), or where shaft runout requirements are in millionths of an inch.

These systems are often typified by a need for high-speed accuracy (&\#177;0.001%) and are generally regulated with phase-locked servosystems where an optical tachometer feedback signal is compared to a reference frequency. The comparison generates a system error proportional to both shaft velocity and position. Typical 0-dB bandwidth is on the order of 100 to 300 rad/sec. To obtain acceptable system stability in such uses, it is necessary to minimize effects such as spring rate, or at least to place the response outside the system bandwidth.

The alternative approach of designing motors and controllers together as a system is made practical by modern motors that are basically constructed of a few common components. This allows manufacturers to make motors in a kit form that can be assembled around the drive spindle during manufacture.

The process of custom tuning all motor parameters for a given application is not as difficult as it may sound. While this philosophy suggests a generation of specials without end, there is actually considerable fallout of common parts and subassemblies when the motor, controller, and feedback devices are considered as a system.

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Motor Controller: Motor Controller Information

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