Leuze has recently developed a new compact, space saving design for smart process gating (SPG), which enables the bridging of a protective field without additional muting sensors. The SPG system, supplied locally and across sub-Saharan Africa by Countapulse Controls, also reduces installation and service costs.
Gerry Bryant, managing director of Countapulse Controls, says that the new Leuze safety system offers high reliability and availability, since there are no risks of misaligned or damaged muting sensors. Installation and service costs are lower because there is no set-up or alignment of muting sensors and even interrupted parts and pallets with gaps between loading can be safely transported in sequence.
“There is also reduced risk of tampering by operators,” Bryant says. “Leuze has developed the SPG on the basis of the Type 4 safety light curtains in the MLC 500 series, so muting sensors are no longer needed.”
Explaining the purpose of muting sensors, Bryant adds: “Muting allows for safe access to protected area without jeopardising the safety of the system. For example, if a pallet is moving through (in or out) of the protected areas, muting will allow the pallet to move unhindered without breaching the safety barrier, which has been created to protect the workers.”
Explaining the SPG process, Bryant says the first gating signal is sent by the process controller (PLC) to the safety light curtain shortly before the protective field is entered, to interrupt the protective device while the transported material is passing through. The second signal is, on the other hand, generated by the safety light curtain itself when the protective field is interrupted. SPG therefore requires knowledge of the position of the transported goods so that the necessary PLC control signals are within the correct time window at the safety light curtain.
“The point in time must be set such that the transported material is within 20 cm of the protective field, in order to prevent persons from slipping through,” he says. “The safety light curtain generates the second signal in the protective field during entry and bridges the protective field.”
Traditionally, according to Bryant, the protective field in a manufacturing or production cell was achieved by using safety light curtains with muting facilities. “SPG would be used in the palletising section of a bottling plant, for example. The protective field prevents access into areas which would be considered unsafe whilst production is in process,” he explains.
The system control transmits a switching signal to the safety light curtain, whereby the described distance of 200 mm between the transported goods and the light curtain is maintained. Entry into the protective field must then take place in less than four seconds. During the entry, the safety light curtain generates the second signal and bridges the protective field while the transported material is passing through.
In the basic configuration, the material must pass through in less than ten minutes, otherwise the receiver of the safety light curtain goes into an interlock state. If necessary, a timeout extension of up to 100 hours can be configured – to permit downtime, for example, during a shift change or over a weekend – without blocking the processes. When the transported material exits the protective field, the safety light curtain resets the signal.
The MLC 530 SPG safety curtain can be used in two operating modes for different conveyor speeds: a maximum speed of up to 0.6 m/s, and the other at less than 0.2 m/s. Depending on the selected operating mode, the protective field is then reactivated by the safety light curtain after one or two seconds. The transport material may not have moved more than 200 mm away from the protective field by this time.
Summarising the advantages of Leuze smart process gating, Bryant considers the difficulties that the new system overcomes. “Smart gating eliminates the need for incorporating separate muting sensors as was the case with conventional safety light curtains,” he concludes.