Print the worksheet   Open the simulator

Worksheet: pneumatics

Material: the free pneumatics simulator at examrobotic.com (examrobotic.com/en/tools/pneumatics-simulator). Time: about 40 minutes.

Aim: work out a cylinder's force, tell monostable and bistable valves apart, understand what each flow control slows down and follow a sequence with its GRAFCET.

1. Cylinder force

1. The cylinder is Ø32 mm (804 mm²) with a Ø12 mm rod (691 mm² annular area). Work out at 6 bar (0.6 N/mm²):
   Extending force: ________ N    Retracting force: ________ N
2. Why is the retracting force smaller?
3. Load 30 kg and lower the pressure until it will not lift. Write down the pressure: ______ bar. Check it with F = P × A, adding about 20 N of friction.
4. With 40 kg, write down the time going up (______ s) and coming down (______ s). Why does it come down faster?

2. Valves and flow controls

5. With the monostable valve, hold Y1 and let go. What returns the valve to rest? What happens if the power fails?
6. With the bistable valve, tap Y1. Why does the cylinder not return? How do you bring it back?
7. Give an application that suits each valve type:
   Monostable: ____________________
   Bistable: ____________________
8. Close the front line flow control to 10 %. Which movement slows down? Why that one and not the other?

3. The A+ B+ A− B− sequence

9. Fill in the table: which sensor allows each movement.

   Movement	Coil	Starts when…
   A+
   B+
   A−
   B−

10. With continuous cycle ticked, press Stop halfway through a cycle. Where does the machine stop, and why is that right?
11. Press «Surprise fault» three times. For each one, write down which step it stops at and what you saw.

Answers (for the teacher)

1. Extending: 0.6 × 804 ≈ 482 N. Retracting: 0.6 × 691 ≈ 415 N.
2. Because the rod takes up part of the piston area in the front chamber.
3. 30 kg weighs about 294 N; with 20 N of friction you need about 314 N: P = 314 / 804 ≈ 0.39 N/mm², about 4 bar. Below that, it does not lift.
4. Coming down, the weight helps the air; going up, it works against it. There is more spare force coming down, so it moves faster.
5. The spring. If the power fails, the coil loses its supply and the cylinder returns to rest.
6. The bistable valve has memory: it stays in the last position. It returns with the other coil, Y2.
7. Monostable: a cylinder that must return to a safe position if the power fails (a pusher, a door). Bistable: a gripper that must not drop the part when the power fails.
8. Extending slows down. While the rod extends, the air escapes through the front line, and the flow control restricts the exhaust air (meter-out).
9. A+: A Y1, on Start with a0·b0. B+: B Y1, when a1. A−: A Y2, when b1. B−: B Y2, when a0. The cycle ends with b0.
10. It finishes the cycle and stops with both cylinders back. Nothing is left halfway and it is ready to start again.

Possible faults: a1 moved (A extends, stops at step 1), b1 moved (stops at step 2 with B out), a0 cable cut (will not start), B coil Y2 open (stops at step 4, with the coil green and B out) and A front flow control closed (at step 1 the valve changes, but A does not move).