posted on 2014-04-01, 11:34authored byM. L. Rahman
Recent developments in switching theory have not
been adequately exploited for industrial control applications.
Consequently, the design of most industrial control
systems is carried out on an intuitive basis. The aim
of this study was to develop systematic techniques for the
logical design of sequence controllers, which control the
repetitive occurrences of a number of machine operations
taking place in a definite order. Machine operations, for
this study, were broadly divided into two classes, namely,
pulse mode operations involving switching on or off of
various control elements, and level mode operations for
which the control output is maintained to hold the
controlled position of the control element (like a spring
return actuator).
The design of a sequence controller for a large
number of actuators has been simplified by an approach in
which the controller is realised by a number of subsystems.
Two standard circuits, namely, a standard actuator control
circuit and an actuator control module have been developed
-for level mode operations; the realisation of the controller
using these circuits is straightforward and does not
require an expertise in switching circuit theory. Two
different circuit modules, a 'combinational module' and a
'sequential module', have been developed for cascade
realisation of sequence controllers for pulse mode
operations. A generalised model of programmable sequence
controllers (PSC's), which are suitable for industries
requiring frequent changes in the sequence of operations,
has been proposed. The basic tape realisation of the PSC,
in which the controller reads information from a tape
and executes the corresponding operation, has been
extended to control a larger number of operations. A
systematic study has been carried out for an asynchronous
sequential circuit realisation of a PSC using read-only
memories (ROIiP s). A considerable reduction in the memory
capacity of the ROM has been achieved by generating the
present state variables by a counter.
Control systems were constructed for the experimental
verifications of some of the theoretical results;
the machine operations for testing the systems were
simulated by electronic circuits. The study provides a
general basis to systematise the design of sequence
controllers for industrial automation.
History
School
Mechanical, Electrical and Manufacturing Engineering