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Communications

FIGURE 9.18 Two types of absolute control system, with absolute 457
displacement encoder and incremental displacement encoder.

rotation for each step, each position can be easily approached by the
slide. With stepping motors, only very limited speeds are possible,
depending on the resolution.
Figure 9.18 illustrates the two types of absolute control system:
one with an absolute displacement encoder and the other with an
incremental displacement encoder.

9.6.3 Absolute Control
In an absolute control system with an absolute displacement encoder,
such as an angular encoder or linear encoder, the actual value of abso-
lute position of the slide is known at any given time. The processor
receives this value and a reference value. The processor forms the arith-
metic difference between the two values. The greater the difference,