Why should I measure Stopping Time and Distance?

...to find out which safety arrangements can be used in a certain area around a machine and where they should be located!

Stopping Time

The safety distance (how far away from the risk area a safety component must be placed) is based upon the machine’s stopping time. The basic idea is that a safety component should be placed so far from the risk area that it is not possible to enter the area before the machine has stopped.

The stopping time for manually operated machines is especially important when light beams and light curtains are used as safety components. By reflex action, the operator tries to grab or adjust if something has gone wrong in the machine tool, even if the machine has started. It is then imperative that the machine stops before the hand reaches the risk area. A short stopping distance is also of importance for getting good ergonomics.

Grabbing or adjusting is also common when using automatic machines. Usually this is done to prevent production downtime by quickly adjusting a work piece. The stopping time is also of great importance if someone trips and falls into the machine.

Stopping time, walking speed (1.6 m/s) and hand speed (2.0 m/s) is used for the calculation of safety distances. Sometimes a fixed minimum distance is also used. See the standard EN 999 for more details on the calculation of safety distances.

Stopping Distance

For safety contact strips, it is extra important that the stopping distance is monitored. In many cases an incorrect stopping distance could result in very high risks. The stopping distance is also needed during area limiting—e.g. for robots when dividing the working area into sectors.

For door sensitive edges, it is important that the stopping distance is shorter than the soft part of the sensitive edge.

Annual Checks

Wear in a machine is something that can affect braking and motors, which means that the stopping time of a machine can change with time. Certain other changes in a machine, such as changing the weight of a workpiece or alterations in pneumatic pressure, can also affect the stopping time. For these and other reasons it is important to perform an annual check on the stopping time.

Regulations and Standards

It is also important to measure the stopping time to meet the requirements set by the machinery standards, directives and regulations.

Here we can help, with our long experience in the practical application of regulations and standards, from the viewpoint of both the authorities and production. In addition, we collaborate with the standardization committees responsible for producing these standards.

One example is the revision of EN 999, which deals with the placement of safety devices around a machine based on its stopping time. When it is complete, this standard will become EN ISO 13855.

The standard is general for all types of machinery, although for some—where there is a harmonized C standard—the requirements for minimum distance and stopping time measurement will apply. For example, in the case of mechanical press tools there is also a requirement in EN 692 for how stopping time measurements are to be performed—and in the case of hydraulic press tools, this is in EN 693.