When taking an elevator, you want to get from one floor to another smoothly and safely. In elevator drives, sophisticated motion control enables the elevator to stop at a specified position and decelerate smoothly until it comes to a complete stop. A lack of fine-grained motion control can cause an elevator to stop between floors, which can make elevator occupants feel dizzy, uncomfortable, or unsafe.

Robots, computer numerical control machines, and factory automation equipment all require precise position control via servo drives, and in many cases also speed control in order to properly manufacture products and maintain workflow.

Many aspects of industrial drives are important to achieving precise motion control, which involves the three fundamental subsystems in real-time control design, namely sensing, processing, and actuation. This article discusses examples of supporting technologies for each subsystem.

induction

Without precise position and velocity sensing, precise motion control cannot be achieved. Sensing can include motor shaft angular position and speed sensing or conveyor belt linear position and speed sensing. Designers often use incremental optical encoders, with a few hundred to a thousand slots per revolution, to sense position and velocity. These encoders are typically interfaced to microcontrollers (MCUs) via quadrature encode pulses (QEP), thus requiring a QEP interface capability.

In contrast, absolute encoders are significantly more accurate, typically have a higher number of slots per revolution, and are precision mounted to provide absolute angular position. The sensed position is converted into a digital representation and encoded according to standard protocols. Examples of such protocols are Tamagawa’s T-Format and iC-Haus GmbH’s Bidirectional Serial Synchronous (BiSS) C. Previously, you also needed a field-programmable gate array (FPGA) to interface with such encoders, but now more and more MCUs have this capability as well (as shown in Figure 1 below). Since the T-Format and BiSS C protocols are generally compatible with popular communication ports or interfaces such as the Serial Peripheral Interface (SPI), Universal Asynchronous Receiver Transmitter (UART), or Controller Area Network (CAN) common on most MCUs, the Protocols are different, so they often require customizable logic blocks or proprietary processing units.

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