Use and Maintenance Manual – Pressure-sensitive bumpers type GSBPS 19/35
7.1 How to select the correct pressure-sensitive bumper
After determining the performance level in compliance with the UNI EN ISO 13849-1 Standard, the following
steps are to be scrupulously adhered to:
a) Determine the required operating speed and maximum hazardous speed. If the hazardous speed is
not indicated, then it should be measured or calculated. The point of travel when maximum speed
occurs depends on the actuation mechanism. Maximum operating speed should be higher than
maximum hazardous speed. In the contrary, please consult Gamma System for more information.
b) Determine the distance of the required minimum over-travel.
c) Determine the stop travel for hazardous parts. If stop travel is not indicated, then measure or
calculate it. The stop travel (stroke), multiplied by a suitable safety factor of at least 1.2, ensures
minimum over-travel required for the application. Where other safety factors exist, for example a
braking system subject to deterioration, a higher safety factor is to be used. Please refer to the
diagram showing the force-travel relation shown below. A very easy way to measure the stop
distance consists in temporarily inserting the position detection at a point near the point where
maximum hazardous speed occurs. Normally closed contacts for position detection are to be
connected to the stop control circuit where the commutation devices for output signal are to be
connected. Repeatedly run the machine under the severest expected conditions and measure the
distance travelled beyond the actuation point of position detection. Maximum distance measured is
to be considered as the stop distance.
d) Determine the maximum, permissible force. Maximum permissible force is indicated in Type C
Standards or in compliance with the risk assessment. Risk assessment must take into account the
body parts and the type of persons to protect (children, elder people). Furthermore, the following
parameters are to be considered: speed, shape, sensor material and maximum pressure exerted by
the device. Maximum permissible force should be as low as possible.
e) Device selection. Use data of force/travel relation or the diagrams supplied by the manufacturer to
select the safety device offering maximum operating speed required for (at least) minimum over-travel
before attaining maximum allowable force. If no device offering sufficient over-travel can be selected,
then you may need to improve the stop performance of the machine. Here below you will find the
diagram taken from Appendix B of the EN ISO 13856-3:2013 Standard where the user - according to
maximum permissible force established by the product Standard for the application which the pressure-
sensitive bumper is destined to, or according to the risk assessment - is capable of establishing whether
the stop distance of dangerous movement (e.g. powered guard) is lower than the deformation travel of
the bumper for maximum permissible force considered.
In case of actuation from one direction, it is better to use a straight bumper. In case of 45° actuation, a
shaped bumper with 135° inner angle should be used.
In case of 90° actuation, two shaped bumpers should be used, as indicated in the following diagram.
Connect the bumpers in series at the control enclosure level.
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