CASE STUDIES IN MECHATRONIC SYSTEMS:
Automatic Car Park System:
Consider the coin-operated car park system with barriers.
The main requirement of the system is that, the in-barrier is to be opened to allow the car inside if correct money (coin) is inserted in the collection box.
The out barrier is to be opened to allow the car outside, if the car is detected at the car park side of the barrier.
The automatic car park barrier along with the mechanism to lift and lower it
When the current flows through the solenoid A & the piston in the cylinder extends to move upward and causes the barrier to rotate about its pivot and thus the barrier raises to
allow the car inside.
When the current flows through the solenoid A ceases, the spring on the solenoid valve makes the contacts to open and thus makes the valve to its original position.
When the current flows through solenoid B, the piston in the cylinder moves downward end causes the barrier to get down.
Limit switches are used to detect when the barrier is down and also when fully up.
This control can be controlled by PLC
X400 – coin operated switch at entrance to car park
X401 – switch activated when entrance barrier is out
X402 – switch activated when entrance barrier is down
X403 – switch activated when car at exit barrier
X404 – switch activated when exit barrier is -up
X405 – switch activated when exit barrier is down
Y430 – solenoid on valve A for entrance barrier
Y43 1 – solenoid on valve B for entrance barrier
Y432 – solenoid on valve A for exit barrier
Y433 – solenoid on valve B for exit barrier
Six inputs (X400 to X405) is required for the PLC to sense the six limit switch position namely coin-operated switch, entrance barrier up switch, down switch, car at exit barrier
switch, exit barrier up switch, Exit barrier down switch
Whenever, a switch is operated, 0V signal is provided to the corresponding inputs and otherwise +24v signal is provided to the inputs. Four outputs (Y430 to Y433) are
required to operate the two solenoid valves A and B.
Program:
LD X400
OR Y430
ANI M100
ANI Y431
OUT Y430
LD X401
OUT T450
K 10
LD T450
OUT M100
LD M100
OR Y431
ANI X402
ANI Y430
OUT Y431
LD X403
OR Y432
ANI M101
ANI Y433
OUT Y432
LD X404
OUT T451
K 10
LD | T45 1 |
OUT | M101 |
LD | M101 |
OR | Y433 |
ANI | X405 |
ANI | Y432 |
OUT | Y433 |
END
Assume a 10 sec delay for the car is to come inside the barrier and to go outside the barrier.
These time delays provided by T450 and T451 energising their Internal relays respectively.
