6
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-NC111 Position Control Unit is used
with a servomotor, the servomotor driver must be able to handle digital sig-
nals, and there is no need for a D/A converter. In addition, the servomotor is
connected to a tachogenerator and a rotary encoder. The Unit can thus be
used in either an open-loop or a semiclosed-loop system.
Both open-loop and semiclosed-loop systems are described in more detail on
the following pages.
Control System Principles
Section 1–4
