The signaling element of a safety edge is normally used to safeguard a point at which people or objects may be trapped or crushed or which poses a collision risk. It must be ensured that the movement is reliably halted in all applications and that the maximum permissible forces acting on a person are never exceeded when the safety edge is tripped. The most important parameters for selecting a suitable safety edge are the required safety category according to DIN EN 954-1, the speed of the potentially hazardous movement, the stopping path of the parts causing the hazard and the specific profile data of the safety edge.
Safety Category DIN EN 954-1 specifies five categories defining the requirements to be met by the safety-related parts of the control systems. The applicable category is determined by assessing the risk for a particular application. If a product standard exists, it already defines the requirements to be met.
Limitation of the Forces Occurring The force acting on a person or object depends on several factors. The permissible forces depend on which part of the body is exposed to the risk. These are defined in type C standards and must correspond to the risk assessment. The stopping path of the parts causing the hazard must be determined first. When a Stop command is given by the safety device, the control system and braking system require a certain time in order to bring the movement to a complete halt. The stopping path is consequently determined by the speed of the movement, the response time of the control system and the performance of the braking system. It should therefore be measured under the worst possible conditions conceivable. The minimum overtravel required by the safety edge is determined from the measured or given stopping path at maximum operating speed. The standard DIN EN 1760-2 mentions multiplication with a safety factor of at least 1.2. If the application involves extremely frequent actuation, care should be taken to choose a signaling element that recovers its original shape as quickly as possible. Attention must also be paid to the construction of the opposite edge.
Choice of Equipment When the stopping path and speed are known, the force-travel diagrams of the safety edges can be used to select the safety device with the required overtravel and the required operating speed. The stopping response of the machine may have to be improved if a device with sufficient overtravel cannot be found.
