Documents to download :

• ASC: Control of an hydraulic press (280 kB)

Process to control

This example is used to present our approach. It concerns the control of a hydraulic press with a vertical ram. It is composed of:

• an hydraulic ram,
• a safety-light curtain used to safeguard operators during the movements of the ram,
• a control panel used to select the mode of operation: Manual or Automatic mode.

In Manual mode, all the operations are carried out by pressing the corresponding push-buttons. As soon as a push-button is released, the ram movement stops.

In Automatic mode, the cycle starts by pressing the `Start' push-button: the ram is going down and comes back to the up position after the press operation has been done.

Inputs and Ouputs of the controller

Each movement of the ram is controlled thanks to a Boolean output ('goUp' and 'goDown'). The controller is informed of the position of the ram thanks to inputs 'up' and 'down'. The safety light curtain is connected to input 'lc' (lc=1 when the operator is not in the detection zone of the light curtain). The control panel of the press is composed of an emergency stop button (input: 'esb'), a three position center-off switch for the operating mode selection ('sbA', off: no mode selected, `sbM') and four push-buttons (inputs: 'vpb', 'spb', 'uppb' and 'dopb').

The 10 inputs of the controller are:

• up: Press ram in Up position,
• down: Press ram in Down position,
• lc: Safety light curtain not broken,
• esb: Emergency stop button,
• sbA: Three position switch in Automatic Position,
• sbM: Three position switch in Manual Position,
• vpb: 'Validation' Push-button,
• spb: 'Start' Push-button,
• uppb: 'Up' Push-button,
• dopb: Down' Push-button.

The 2 Outputs of the controller are:

• goUp: To move up the press ram,
• goDown: To move down the press ram.
  
  

Obtained results

To avoid tedious symbolic calculus and to help the designer during the different steps of this synthesis method, a prototype software tool has been developed in Python. This tool performs all the computations required for inconsistencies detection and control laws generation, that enables the designer to focus only on application-related issues.

• The proposed document presents the case study: from requirements to the control law.