Step 4: Calculating safety distance

Optoelectronic protective devices can only perform their protective function if they are installed with a sufficient safety distance from the nearest danger point of operation. The safety distance from the protective device to the point of operation must big enough that the dangerous movement will have stopped before a part of the person’s body can reach the point of operation (see also, ANS IB11.19‑2003). After calculating the safety distance it should be checked and ensured that this minimum distance allows an ergonomic operation of the machine for the operator. If this is not the case either an entire stop time of the machine or an AOPD with higher resolution must be selected.

The following overview refers to the calculation formulas of EN ISO 13855/"Safety of machinery – Positioning of protective equipment with respect to the approach speeds of parts of the human body" and the recommendations of IEC TS 62046. If the machine is the subject of a certain specification, such as machine-specific European C-standards and OSHA / ANSI standards, then reference must be made to this. This overview does not, of course, detract from the observation of the installation notes of the operating instructions.

Safety distance calculation in accordance with EN ISO 13855 and IEC TS 62046

The minimum distance of a stop-activating protective device from the nearest danger point of operation on the machine must be calculated with the following formula:

S = (K x T) + C
S The minimum safety distance in millimeters from the next point of operation to the detection point (protective field) of the protective device. An "S" of 100 mm must be observed regardless of the calculated value.
K Approach speed in millimeters per second, derived from data of the approach speeds of the body and body parts.
Speed (lower limbs): K = 1600 mm/s
Speed (upper limbs): K = 2000 mm/s
T Stopping time of the entire system (protective device response time + interface response time + machine stopping time) in seconds (IEC TS 62046 requires at least an additional 10 % on top of the determined stopping time to allow for possible deteriorations).
C An additional distance in millimeters. This additionally added distance is based on the fact that, depending on the resolution of the protective device, a body part can get a certain distance closer to points of operation before it is detected by the protective device.