Special ICs

Manufacturers have also developed special-purpose ICs that handle tasks needed to implement both closed-loop motion control and motor speed control. Presently, three chips are available for closed-loop control, one for multiaxis contouring, and a few others for motor speed control. A general-purpose motion-control IC called the HCTL-1000 is aimed at dc, brushless dc, and stepper motors. The TTL-compatible chip is powered by a single 5-V power supply. Position and velocity control are provided by comparing the host computer-command signal with feedback data from an incremental encoder. The encoder feedback is decoded into quadrature counts and a 24-bit counter keeps track of position. As a result, neither analog compensation nor velocity feedback is necessary. On-chip software allows a choice of four control modes: position control, proportional velocity control, trapezoidal profiling, and integral velocity control. In the position-control mode, the motor moves from one point to another without velocity profiling. Proportional velocity control regulates motor speed using only gain for compensation. Dynamic pole and zero-lead compensation is not used. Actual motor velocity is compared to the specified velocity, and the error calculated. The trapezoidal mode is used for point-to-point control with velocity control. The final position, acceleration, and maximum velocity are specified. The controller then computes the signal profile needed to conform to these requirements. Motor velocity is monitored during the position change. If maximum velocity is reached before the motor moves half way to the target position, the velocity versus time waveform is trapezoidal. Otherwise it is triangular. Continuous velocity control is provided by the integral velocity control mode. Here, velocity and acceleration can be changed at any time to profile velocity in time. Once the specified velocity is reached, it is maintained until the command is changed. Another closed-loop controller, called the GL-1200, produces precise motor control using an external 10-MHz