The little engine that could

Whether the integrated control card pictured in figures 2A and 2B is built for a standalone configuration, or is located on a network, certain design considerations must be kept in mind. Figure 3 shows an internal block diagram of a typical integrated motion controller. The major elements are the motion processor, the signal conditioning circuitry and the amplifier. Note that there may be other major sections including a network interface chip and a host microprocessor, depending on the overall control and communications architecture.

The motion processor is the central IC that performs most of the motion control functions. These functions include quadrature signal decoding, trajectory generation, servo loop compensation (if servo motors are used), PWM (pulse width modulation), analog, or pulse & direction motor command output generation. Other functions may include commutation, digital I/O, analog I/O, breakpoints, servo trace and motion performance monitoring.

Since about 1985 it has been possible to purchase the motion processor off-the-shelf from a number of vendors. Varying in their degree of sophistication, the number of axes supported, and the motor types they work with, these handy products provide high-level motion commands and manage all low-level interface to motion peripherals.

Motion processors connect to the outside world through a parallel microprocessor-style interface, a serial interface such as RS232 or RS485, or more recently, via networks such as CANbus. Earlyon, their motion features were not as powerful as those provided by off-the-shelf cards, but in the last five years that distinction has disappeared with the addition of S-curve profiling, dual biquad filtering, and on-board trace.