LIFTING AND SHIFTING
CYLINDER A
AO
CYLINDER B
A1
F=0
4
F=0
4
12
2
14
2
1
START P.B.
1
12
3
5
2
2
B1
B0
B1
2
14
5
BO
A1
1
3
1
3
2
AO
3
1
3
1
3
2
1
3
Figure 6.6: Pneumatic Circuit Diagram for Lifting and Shifting
Signal Overlap
Signal Overlap can occur when simultaneously two active signals appear on both set
and reset pilot ports of Final Control Valve. This is due to the required sequencing of
cylinder. At the start, both signals ao and bo appear at the same time. This will not
result in any change.
4
2
14
12
5
1
3
2
2
B0
AO
1
3
6.7. Illustration of Signal over lap
1
3
Multi Cylinder Applications Signal Elimination
On analyzing the status of set signal and reset signal for final control valve for
different cylinders, it is observed that both set and reset signals could be present
simultaneously at any instant of time, depending on the sequential operation of the
cylinder. This does not permit further change in status of the valve. This situation is
termed as signal over lap. To overcome this problem signal elimination techniques are
used as listed below:
•
•
•
•
Use of Idle return lever limit switches
Use of N.O Timers
Use of Cascading with the help of reversing valves
Use of Stepper Sequencer modules
Example 2: Clamping and Riveting
•
•
•
Sheet metal components are to be riveted using two Pneumatic Cylinders. A
Clamping cylinder (A) first advance and clamps the sheet metal parts.
While the parts are clamped a second cylinder (B) advance and performs riveting
operation
The riveting cylinder retracts and finally clamping cylinder retracts
Figure: 6.8 : Clamping and Riveting Using Pneumatic Cylinders
•
•
•
Control Diagram is drawn below the motion diagram represents the status of
various signals- the limit switches used to interrogate the piston position
Signals 1.4 and 1.3 correspond to home position and extended position limit
switches of cylinder A respectively
Signals 2.2 and 2.3 correspond to home position and extended position limit
switches of cylinder B respectively
Figure 6..9 Control Diagram for Sequence A+,B+,B-, B-
Figure 6. 10 Pneumatic Control Circuit and Control Diagram
Source : http://elearningatria.files.wordpress.com/2013/10/hydraulics-and-pneumatics.pdf