A safety solution for hand-fed platen presses has been developed using an array of light beam sensors and a modular safety control monitoring system. The solution was a joint collaboration between Pilz Automation Technology and SCA Display UK which manufactures Point-of-Display products at its Shenstone plant.
The factory uses one hand-fed platen press, which is used for short runs and one-off customer specials.
Ian Clews, facilities manager at Shenstone, says: “With two fatalities in the UK in recent years, users of these machines need to review their safety systems.”
“A typical hand-fed platen press closes with a tremendous force, often with the operator’s body in close proximity. This means operator safety is extremely critical.”
The overall safety solution is based on Pilz’s PNOZmulti modular safety system. PNOZmulti is multifunctional, freely configurable and is suitable for monitoring safety functions such as Emergency-Stop, safety gates and light barriers, as well as performing standard control functions. Rather than hard wiring, safety circuits can be generated on a PC using PNOZmulti’s intuitive configuration software. This configuration can then be stored on a memory card and downloaded to the PNOZmulti base unit.
The solution incorporates a PNOZmulti base unit, with input and output expansion modules to control all aspects of machine safety and control. “We wrote a functional specification for the press, then engineered a solution based on these functional safety requirements. We supplied all the hardware,” states Robinson.
The hand-fed platen press at Shenstone is fitted withgeneral purpose safety devices such as trip bars, interlocked guards, right and left hand emergency stops, safety mat, front safe edge, lumbar bar, safety gate key switch, left and right side light curtain. All these devices have the same functional safety requirements, to prevent all hazardous movement by ensuring that the clutch safety valve is de-energised and that the main motor is stopped, and to prevent unintended restart. The target safety integrity level for each General Safety Function is SIL 3 (EN 62061), equivalent to PLe according to EN ISO 13849-1.
The machine uses an array of Pilz PSENop4S light beams. The light beam array detects a violation of the danger zone while the press is closing. This is achieved by sequentially muting the laser beams as the press closes. If any beam is broken before it has been muted, the press clutch safety valve is de-energised immediately bringing the hazardous movement to a stop. Once the final beam has been broken (press closed) the beams remain muted until the press cam switch has operated, signalling that the press is at the ‘home’ position. The muting points are derived from the simulation of press position carried out within the PNOZmulti control system. The application also includes checking that the press cam switch operates correctly in each press cycle.