Electronic Key Systems Enable Safe Mode Selection

A mode selector switch is available on almost all machines - mostly in the form of a key switch. In future, a safety-related assessment of the operating mode selection will increasingly be required. Some standards, for example for turning and grinding machines, already require this assessment. The requirement for a safety-related evaluation of the operating mode selection results from the fact that when switching from one operating mode to another, various safety-related devices on the machine are switched on and off.

Switch operating mode to setup

A very simple example of a machine with only two operating modes (automatic and set-up mode) shows why this is so: In automatic mode, a protective door is used on the machine as a safety device. The protective door is secured with a safety switch. If the door is opened, the machine switches off and goes into a safe state. For commissioning in set-up mode, however, it is necessary that the machine remains switched on even when the protective door is open - but not with all functions of the automatic mode. To do this, the operating mode of the machine is switched to setup. In this operating mode, the safety switch on the protective door is bridged so that the machine can be started up.At the same time, an enabling button is used as the safety device and the control technology is switched to a safely reduced speed. In addition, not all axes and functions are in operation.

Picture gallery

Picture gallery with 5 pictures

In this example - due to the switching of the operating mode from automatic to set-up mode - the safety device "protective door" must be switched off. At the same time, two other safety functions protect the employee: the enabling button and the reduced speed. Figure 1 should make this clear.

Different functions

An operating mode can include different functions. A single step of the machine can make sense both in automatic mode and in set-up mode: in automatic mode with the protective door closed and in set-up mode with the enabling button pressed and the speed reduced.

Switching between different safety devices must meet a performance level (PL) according to EN ISO 13849-1. Only then is it ensured that the switchover is correct. Both the C standard for lathes (EN ISO 23125) and that for grinding machines (EN ISO 16089) require a PL c for the switchover. The upcoming new standard for milling machines (EN ISO 16090) will also require a PL c.

There is no security term for keys

In order to be able to assess a mode selector switch normatively, its components must be considered. In the case of a key switch, this is initially the key itself. It is not a safety-relevant part - or is it? The German language makes us a little difficult here, because the term security is used differently. Basically, a key is a security-relevant part. However, not in the sense of EN ISO 13849-1.

For the standard, “safety” means protecting people from the machine or from an accident with the machine. In English, the term safety or functional safety is used for this type of safety. A key prevents unauthorized access to the machine from the outside and is used to switch from one operating mode to the other. There is currently no specific term or standard for this type of safety technology in the world of machines. C standards also make no demands here. However, future C standards will use the English term security for this form of security technology. However, EN ISO 13849-1 is not responsible for assessing security.

Access system

Access system for safe mode selection up to PL e

Safety device

Transponder-based access and control system

Content of the article:

• Page 1: Electronic key systems enable safe mode selection
• Page 2: No evaluation according to norm
• Page 3: Operating mode selection via touch panel
• Page 4: Electronic keys with copy protection

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