6
automatic adjustments. The C200H-NC112 Position Control Unit can be used
in an open-loop system in conjunction with a stepping motor.
In a closed-loop system, on the other hand, the PC controls an external pro-
cess without human intervention. The servomotor provides direct feedback
so that actual values (of positions, speeds, and so on) are continuously ad-
justed to bring them more closely in line with target values. In some systems,
the digital feedback signals will be transmitted to a digital-to-analog converter
to complete the feedback loop, thereby permitting automated control of the
process.
A semiclosed-loop system is similar to a closed-loop system, except that
feedback is provided by a tachogenerator and a rotary encoder rather than
directly by the servomotor. If the C200H-NC112 Position Control Unit is used
with a servomotor, the servomotor driver must be able to handle digital sig-
nals. There is therefore no need for a D/A converter. Here, the servomotor is
also connected to a tachogenerator and a rotary encoder.
Both open-loop and semiclosed-loop systems are described in more detail on
the following pages.
Positioning System Principles Section 1–5
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