FEATURE MACHINE SAFETY Shining a light on some safety terms
Muting is achieved by installing additional sensors such as photocells to detect material and mute the light curtain. Integrated with a safety controller PLC such as Sick’s Flexi Soft or dedicated UE403 muting module, the muting sensors are usually installed in two beam cross formation (figure 1a) or four beam sequential arrangement, (figure 1b) Other muting methods include exit
S
afety protection can sometimes feel like the enemy of efficiency in
automation, necessitating frustrating interruptions, stops, and machine downtime. The threat of frequent line stoppages can tempt an operator into cutting corners and overriding safe procedures with potentially disastrous consequences. That’s why best-in-class machinery safety is much more than just ensuring that people are fully protected. At the same time, a well-designed system must use technology to fully enable productivity. A key capability of light curtain technology is the ability to stop a machine, such as a robot, from operating if a person enters the dangerous area while still allowing materials, products or plant to move in and out without interrupting the flow of production. However, the terminology can sometimes be confusing, especially as new technology features are developed to provide more options to streamline efficiency.
MUTING Muting is the first and most widely-used method in the industry. The muting function deactivates the protective function of a protective device temporarily but must only be possible if the passing material blocks the hazardous point.
Figure 1b Figure 1a
only, parallel muting and muting using inductive loops. There are a number of conditions that need to be met when implementing safe muting: • During muting, a safe state must be ensured by other means (material blocking access). • Muting shall be automatic.
BLANKING Sometimes when an object needs to be allowed to break the light curtain, blanking can be used. There are two main different types of blanking: Fixed blanking and floating blanking in which fixed beams are ignored or with a number of beams which can ‘float’ (move) in the field. Partial blanking, sometimes called
partial muting, can also be used if only certain beams are to be ignored on passage of material.
• Muting shall not be dependent on a
single electrical signal. • Muting shall not be entirely dependent on software signals. • An invalid combination of muting
signals shall not allow any muting state. • The muting status shall end
immediately after the material has passed through.
BYPASS/OVERRIDE To reduce downtime and prevent false trips, manual bypass and override functions can be selected by the operator under certain conditions. Bypass disables the safety function with other protection measures in place, for example in robot teaching, only operated in slow speed and using a pendant or teaching control device with a three-position enabling device in accordance with IEC 60204-1:2005. Override is a manual triggering of
muting after an error in the muting conditions so that power can be applied to the conveyor in order to get the material out of the ESPE and clear the system. Both must only be operated by a key- operated, positive-action resetting switch, with two switching contacts. Its integration must comply with EN ISO 12100 and EN 60204-1:2005, and be installed so that the entire hazardous area can be seen.
28 DECEMBER/JANUARY 2018 | AUTOMATION
DYNAMIC GUARDING All of the muting configurations above use additional sensors to deliver added functionality. Sick now provides light curtain technology that uses pattern recognition to offer customer-specific dynamic blanking in order to allow passage of material without muting. These multi-functional safety light curtains can differentiate between complex objects in the protective field and other objects, in particular, people. Process flow is no longer affected by restrictive protection, while installation cost, and the risk of malfunction with additional instrumentation, are minimised. SICK light curtains such as the Sick C4000 Fusion and C4000 Palletiser, offer configurable features such as dynamic blanking for specific objects like feet on pallets, mesh crates or trolley wheels, and direction monitoring without additional muting sensors. Other facilities include checking the number of objects in the field, the size of the objects and the gaps between them, with the option of reduced resolution for ignoring small objects like wires and wrapping which may cause false trips.
Sick provides light curtain technology that uses pattern recognition to offer customer-specific dynamic blanking
Sick
www.sick.co.uk /AUTOMATION T: 01727 831121
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