Q: Can I still use risk categories?

A: No, because the general mechanical engineering industry now mainly uses PL (Performance Level). The EN-ISO13849-1 explains how to determine the PL.


Q: Which machine directive applies?

A: Currently, Machine Directive 2006/42/EC applies.


Q: Are there any obligations against unwanted manipulation of safety systems?

A: The EN-ISO14119 is a new harmonised standard that contains measures against manipulation. It also lists technical recommendations for the choice of safety components.


Q: What types of sensors are suitable for the highest safety levels, PLd and PLe?

A: All transponder-coded sensors are immediately suitable for PLd and also most of the light curtains. Reflection-based equipment such as laser scanners does not exceed PLd. Electromechanical sensors can even reach PLe, but you would have to use two for each entrance.


Q: What does a harmonised standard mean?

A: This is a Machine Directive-related standard, making it, to some extent, obligatory to apply it. On the Europe web server you can find an up-to-date list of harmonised standards.


Q: Do we have to use two sensors for each access door in the event of high risk levels (PLd or PLe)?

A: When a chain of safety components does not exceed PLc but you still have to achieve PLd, this is possible only by declaring “fault exclusion”. In that case, you need a written technical substantiation and takeover of responsibilities in accordance with EN-ISO13849-2.  You would have to ask yourself if this is desirable. You are not permitted to achieve a required level of PLe on the basis of a PLc solution. This is stipulated in EN-ISO13849-1 and EN-ISO14119.


Q: Are there any rules for bridging safety functions?

A: Safety functions can be bridged, but only subject to strict conditions, such as the use of optional operational modi, with muting, if necessary. One condition could be that you take a deadman’s switch into the hazardous area. Furthermore, there can only be single and avertable movements/speeds.


Q: What is the safety level of mats and frames?

A: Safety mats and safety frames are usually based on making contact rather than breaking contact. This equipment will achieve PLd.


Q: How do you monitor a safety mat?

A: This can be done with a special module to which the mat and a shut-off resistance of 8kOhm are connected. If the mat is empty, the module will measure 8 kOhm. If you stand on the mat, the module will measure practically 0 Ohm and will switch off the machine connected to the mat. In the event of a short circuit, the module again reads 0 Ohm and will switch off the machine. In the event of an interruption, resistance will suddenly be infinitely high and the module will switch off the machine.


Q: Does a robot always have to be surrounded by a barrier or screen?

A: If a robot is switched in automatic operation, a screen is usually required. On the one hand it will prevent people from getting near the robot and on the other hand it will prevent any risks that are inherent to the robot system (a product falling from a pneumatic gripper). In a number of specific cases, exceptions may apply, which are dependent on the risk analysis.


Q: Is a screen still required when a robot is moved at low speeds only?

A: Yes, a screen can be left out only if the robot is moved at low speeds, and the operator constantly has to press a deadman’s button in order to allow the release for movement. This option has to be available in order to be able to program the robot, for instance, but it is rarely used in a production environment.


Q: Can the robot and operator interact without having to switch off the robot by means of hardware?

A: This is possible, provided you use Safe Robots. These robots are fitted with special features that allow you to take the robot by the hand and to “guide” it, or to hand a product to the robot without a hardware switch-off.


Q: When using a robot, do you always have to maintain a PLe safety solution?

A: No, the risk analysis should give a definitive answer about this.  Robot systems are usually executed in PLd in a perfectly safe manner.


Q: Can a robot be started remotely?

A: No, unless exceptional safety measures were taken, a system cannot be started without the operator being able to ensure that no dangerous situations can occur (a person being locked up inside the system).


Q: What are the signals to read safety sensors?

A: A continuous 24V signal, and the machine will stop when the signal stops. In the case of redundancy, two contacts are used; 1 contact in the 24V circle and 1 contact in the 0V circle. There also may be two 24V identical channels, whereby pulses create diversity. They are also referred to as time signals. The latter are mainly used when safety sensors are connected to safety controls.


Q: Who checks the cable for short-circuiting, the controls or the sensor?

A: In the case of highly technological sensors, this is done by the sensor and the controls should not be doing it. In the case of electromechanical sensors with potential-free contacts, it is the task of the controls. In the latter case, the controls first have to send time signals to the contacts in the safety sensor.


Q: Can I secure all doors with PLe without carrying out a risk analysis?

A: The current Machine Directive stipulates a risk analysis is mandatory, at all times. This will prevent matters from being overlooked.


Q: Is machine safety always expensive and awkward and doesn’t it invite manipulation?

A: No, smart solutions often are simple solutions that save you money in the process. Also, if you follow the new recommendations of the EN-ISO14119, manipulation can be eliminated. The condition is that you do not merely follow the rules, but that you also creatively interpret them. Sharing knowledge is a good contribution in that respect.


Q: Can I use pictograms to warn others against unsafe situations?

A: Yes, but only as a last resort. First, the statutory obligations under the Machine Directive have to be followed, and all unsafe situations have to be ruled out in the design. Any unsafe situations that still remain have to be secured by means of technical solutions. The final step is affixing warnings on the machines in the form of pictograms.




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