By Dr Martin Kidman, safety specialist, SICK UK

safety laser scanners, and switching between protection fields.

FIELD SWITCHING A laser scanner is a safety device that that uses a spinning infrared laser beam in combination with ‘time of flight’ measuring to form a detection field, as in figure 1. Protection fields can be created using


magine you have two bungee ropes of different lengths for two bridge

locations, one 80 metres and the other 150 metres high. The ropes comply with the highest standards and also have an additional safety rope for the unlikely event that the bungees snap. However, every week both ropes are

packed away into the same box. Can you imagine what would happen if the 150 metre length bungee was sent to the 80 metre bridge? Therefore you would think that some extra safety precautions should be taken when choosing a rope. In virtually any potentially dangerous

situation, there are two parts of the safety equation to consider: Firstly, is the hardware inherently safe? Secondly, is the way it is used safe? All too often, machinery is designated as safe to the appropriate levels and yet the safety function of the wider system of which it forms a part has not been properly assessed. A good example of this is

Figure 1: Safety laser scanner

Figure 2: Safety laser scanner fields

One feature of the safety laser scanner

which industry finds very useful for both safety and productivity is the ability to change fields whilst in normal operation.

WINDING MACHINE A simple way to explain this is to look at a winding machine, as in figure 3. Generally, winding machines are used for wrapping a material (tape, plastic, metal etc.) onto a spool, bobbin or reel. At high speed, winders can be dangerous as they have drawing in capability and may also have other hazards such as an actuated knife. One application for a safety laser scanner could be to safely detect a person approaching the machine to slow down/shut down the energy to the drive providing the rotation and maybe


complementary software in order to safely detect people when they enter the field. Warning fields can also be set up for diagnostics and non-safe detection, as in figure 2.

activate a breaking system. However, human interaction is usually required in modes such as: • Slow speed • Maintenance • Roll change • Splice initiation Therefore, it is a very useful function to be able to switch between different size fields on the safety laser scanner. A VERY important question that may be

overlooked in this application is what criteria are being used in order to make the decision to switch the fields? I.e. who chooses which length bungee rope to use…? What if, for example, there was a fault

in the signals telling the scanner which mode the machine is currently in, or a fault in the signal telling the scanner what speed the reel is spinning at? In other words, if a small field was selected for slow speed, but the machine was actually running at full speed then it is likely that the machine would have a risk associated with it that could cause workers harm and therefore would not be in compliance with the latest laws. The law requires you to do everything

‘reasonably practicable’ to protect people from harm, therefore the selection of a field needs to have a safety integrity or performance level assigned to it.

FUNCTIONAL SAFETY AND ES ISO 13849 Where the effect of a protective measure is dependent on the correct function of a control system, the term ‘functional safety’ is used. To implement functional safety, the Type B harmonised standard EN ISO 13849 can be applied (we’re choosing this standard for our example, rather than IEC 62061, which is not discussed here). EN ISO 13849 sets out the general

principles, design and validation of Safety-Related Parts of Control Systems (SRP/CS). To ensure a safe system, it is


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