
Presence sensing devices or presence sensors are press brake safety devices. The operator holds one end of the metal sheet of the work piece whereas the other end is being made in the die. In case a foreign object is detected, the sensor will initiate the retraction process or stop the ram motion and his protects the employee or the operator. They are the most effective safeguards for clutch presses. In case of any interruptions in the sensing field, they automatically initiate to stop the machine process. They are commonly called as light curtains which uses the photoelectric sensing concept. The light curtains use an array of infrared beams around the machines to form a perimeter. When the beams are interrupted, a kill switch is activated which stops the machine until the perimeter is reset. There are various types of presence sensors, namely, photoelectric (optical sensing), electromechanical, radiofrequency (capacitance), pullback, safety trip controls (safety tripod, pressure sensitive body bar and safety tripwire), restraint (holdback), two hand trip, gate and two hand control.