Cylinder actuation

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As there are as many different circuit diagrams for the control of cylinders as there are different applications, only a few standard circuit diagrams are shown in this article. This products mentioned are only an example, and must be selected for the application as required.
Creating circuit diagram is made easier through the software program FluidDraw.

Stopping a pneumatic cylinder

Pneumatic cylinders need to be stopped frequently, either during the process or in case of an emergency stop. It must be possible to stop the drive at any position along the stroke, and leave it there for as long as necessary.


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A proven way of achieving this is by using a closed mid-position valve with exhaust air flow control via one-way flow control valves.
Advantage: this is a low-cost design Disadvantage: component leakages prevent permanent stoppage of the cylinder.
Exhaust air flow control valves slow the motion of the cylinders, because the air is exhausted through the valve.
It is preferable to use exhaust air flow control valves (type GRE-…) that are screwed into connections 5 + 3.


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Greater leakproofness can be achieved by storing air in the actuator using pilot-operated non-return valves (type HGL-…).


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In order to compensate for leakages, one option is to store pressure permanently in both cylinder chambers. As the piston rod has different surface areas, different pressures are used to prevent the cylinder from extending.
If the pressure was switched off, a vertical axis would suddenly drop; non-return valves must be used to prevent this from happening.


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If the system has to be vented (for example for safety reasons), this can be done via controlled non-return valves (type HGL-…).

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The cylinder can also be clamped by mechanically fixing the piston rod (e.g. with DNC-…-KP or DNCKE-... or end-position locking).


Moving pneumatic cylinders more quickly

The maximum travel speed of a cylinder can be greatly improved if the other chamber is pre-exhausted before the movement. This means that the cylinder is vented prior to an actual movement. The result is a far higher travel speed than is possible with a conventional solution.

 

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Advantage: can be implemented without a large amount of effort
Disadvantage: the kinetic residual energy in the end position may become too large and has to be absorbed via external shock absorbers.
In order to compensate for the disadvantages of a pre-vented cylinder, the cylinder can be supplied with air prior to reaching the end position, resulting in a combination of venting and pressurisation. 4 sensor signals are monitored along the pneumatic cylinder stroke. Travel from what, in the example, is the right-hand end position to sensor B, or from the left-hand end position to sensor C, is unthrottled.
When passing the sensor, the exhaust air is switched via a bistable valve to a flow control valve, thus reducing the speed when approaching the PPV cushioning.

 

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Advantages:

  • The circuit consists exclusively of standard components.
    -> Attractively priced
    -> Simple spare part procurement
  • The circuit does not affect the machine control system.
  • Up to 25% faster
  • Each stroke direction is separately adjustable.
  • EMERGENCY OFF is easy to implement. Without air and electricity, the cylinder remains where it is or moves to the end position

The following points must be observed:

  • The sensors must be activated for a sufficiently long period of time to generate a reliably long signal for the valves. In emergencies, switch lugs are required.
  • Of course, a sufficient supply of air is needed.
  • The start signal must be present to move. Otherwise, the first (false) brake valve will switch.
  • The brake valves have external auxiliary pilot air.
  • The following four parameters must be set correctly (see Installation instructions):
    - Position of the brake sensors B, C
    - Adjustment of the exhaust air flow control valves on the brake valves
    - Adjustment of the exhaust air flow control valves on the 5/3-way valve
    - Adjustment of the PPV
  • In order to avoid critical situations when starting from a central position, a soft-start valve is recommended. If it is only possible to start from the end position,then this valve is not necessary.
  • The most effective method is to mount the brake valves directly onto the end caps. However, only a very short tubing length should be used.


Links

Circuit diagram creation on the computer