Pressure Mat Safety Distances [Apr 2012]

April 10, 2012 6:19 am

When designing machine safeguarding, one must consider approach speed, reaction times, and the possibility of stepping behind or bypassing the safety device. While we accept these requirements for safety light curtains, we often forget the same principles apply to safety mat installations.
The operator must not be able to reach the nearest danger point before the machine has stopped. This is accomplished by the proper calculation of the safety distance for installation of safety mats.
Safety Distance FormulaS = K x (T1 + T2) + (1200mm – 0.4H)­­Where, S is the minimum distance (in mm) from the danger zone to the detection point, line, plane or zone. K is a parameter (in mm per second), derived from data on approach speeds of the body.T1 is the maximum time between the actuation of the sensing function (tactile mat) and the switching off of the safety enabling outputs (e.g. the output signal switching device OSSO of the safety module)
T2 is the response time of the machine, i.e. the time required to stop the machine or remove the risks after receiving the signal from the safety controller.
H is the distance (in mm) above the floor (for safety mats this term is usually 0)The safety distance for a safety mat can generally be calculated as follows:S = 1600 mm/s x (T1 + T2) + 1200mm
Safety Distance Calculation ExampleCalculating the safety distance for a machine for which the stop time is 117.5 ms, the response time of the tactile mat and safety module is 70 ms, and the tactile mats are at floor level.S = 1600 mm/s x (0.07 s + 0.1175 s) + 1200 mmS = 1600 mm/s x (0.1875 s) + 1200 mmS = 300 mm + 1200 mmS = 1500 mmn
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