Motion control today takes place under the guidance of computers, solid-state logic, or pneumatic sequencers. These devices can take on a variety of forms and provide control on different levels.
Controllers can be divided into four basic types. Chip-level devices consist of a few integrated circuits combined to produce signals that drive positioning equipment. Board-level devices are controllers made up of one or more circuit boards containing computer functions as well as input/output (I/O). These devices often handle control, sensing, and power drive for positioning equipment. Box-level devices generally combine displays, keyboards, computing, and I/O functions into a single enclosure. Finally, dedicated controllers include programmable logic controllers (PLCs) and pneumatic sequencers. These are designed to handle specific chores common to factory-floor control.
Devices in each of the four categories play a different role in motion control. As an overview of the technology, capabilities that typify equipment applications for each type will be outlined.
Microcontrollers
Motion controllers made with integrated circuits frequently use single-chip microcontrollers primarily for computing power. These devices are essentially computer processors, memory, and simple input/output functions combined on a single chip.
Microcontrollers developed in the past few years are frequently used in motion-control applications because they contain several features optimized for such uses. These features often include special timers and counters. The timers and counters are set up to facilitate the generation of pulse-width-modulated (PWM) waveforms used to drive motors and other industrial loads.
Additional features encountered in such microcontrollers include special facilities for both rapidly sensing signal levels on input lines, and for generating trigger signals to start external peripherals. These features are aimed at timing mechanical peripherals such as rotating machinery and for sensing signals generated by transducers such as limit switches. Additional capabilities typically include dedicated PWM outputs, watchdog timers, and high-resolution (on the order of 10-bit) analog/digital converters.
Microcontrollers now commonly built into motion-control applications include 8096, 8051, and 68HC11-type devices. These components work with either 8 or 16-bit data paths at clock rates as high as 12 MHz. The throughput and bandwidth that they provide is considered adequate for the majority of simple motion-control applications. However, newer and faster 32-bit controllers are aimed specifically at handling high-end needs.
The 32-bit parts designed for these applications often contain scaled-down computing circuits used in general-purpose 32-bit microprocessors. Keys to high performance generally include multimegabyte address space, 32-bit data handling, clock rates on the order of 16 MHz or more, and special instruction sets. Such chips directly address large memories and run lengthy programs. Controllers in this category include the 80960 and 80376.
Other features put in such devices and on peripheral chips include direct memory-access (DMA) channels, interrupt controllers, and programmable interval timers. Applications are typically those that demand numerous calculations or image recognition. Examples are robotic arm control or array processing.
