Transcript ME3242 Industrial Automation

ME3242 Industrial Automation
Reference Text:
Lecturer:
Please:
Industrial Automation,
by David W. Pessen
John Wiley & Sons, 1990.
Prof Poo Aun Neow
[email protected]
Room: EA-07-32
When emailing me, please indicate
ME3242 or TM3242 in Subject.
IA - Introduction
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Sequencing with purely
pneumatic logic
Objectives:
• To learn to design purely pneumatic logic circuits
for the sequencing of pneumatic cylinders so as to
achieve automatic operation.
• We will learn to use two approaches: the Cascade
Method and the Lucas Method.
• We will also learn about some miscellaneous topics
in pneumatics such as speed control of cylinders,
operational and emergency stop operations.
IA - Introduction
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Why Pneumatics?
• Air is clean, convenient and readily available in the
factory floor. No problem with exhaust.
• Preferred for small or medium-size systems where
actuators are pneumatic cylinders.
• Often preferable to use same power medium
throughout system, avoiding need for interface.
• Several methods available for systematic design of
purely pneumatic sequencing systems.
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Review:-
Pneumatic Cylinder with Flow-control valve
For the 4/2 valve, only one box can be
operative at any time.
The right(left) box will be in operation
when the last pressure signal is -(+). If there
is no pressure signal on either side, the valve
remains at rest in its current position.
There should not be air pressure signals to
BOTH sides at the same time.
4 port, 2 position
flow control valve,
or 4/2 valve
When the right (left) box is in operation, the
cylinder retracts(extends).
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Review: Notation for specifying sequence
Sample requirement: An automatic drilling machine is
designed to have three pneumatic cylinders for automatic
operation. A typical cycle of operation is initiated by
actuating a START pushbutton. A clamp cylinder A then
retracts thereby actuating a clamp mechanism to hold the
workpiece. The drill cylinder B then extends to perform
the drilling operation at the end of which it immediately
retracts. The clamp cylinder A extends after which a third
cylinder C extends to push the workpiece away and then
retracts. The cycle is then complete.
Description of sequence:
START A+ B+ B- A- C+ CIA - Introduction
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Notation: Important note
By convention, A- is always used for the at-rest position
of Cylinder A, and A+ the other position. Thus in any
sequence, the first action of any cylinder X is always
X+, i.e. moving from rest to the other position. Note
that when at rest (initial state), a cylinder could be
either retracted or extended depending upon the
application.
A
+
A
-
+
A-
A+
IA - Introduction
A-
-
A+
6
End of Introduction
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