Gating Without Additional Muting Sensors

Until now, muting sensors have been required for the temporary bridging of protective fields. These recognize the approach of material to be conveyed to a protective field, so that it can be bridged for passage. At the same time, access for people is prevented by arranging the sensors accordingly. Muting solutions are used primarily in the intralogistics, automotive and packaging industries.

Leuze Electronic developed the Smart Process Gating process (SPG) based on the Type 4 safety light curtains of the MLC 500 series. This means that there is no need for the muting sensors. With the SPG, the first gating signal comes from the system controller (PLC), while the second is generated by the safety light curtain itself when the protective field is interrupted. SPG therefore requires knowledge of the position of the conveyed goods so that the necessary PLC control signals are available in the correct time window on the safety light curtain.

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Requirements for a safe solution

The integration of an SPG application into a system is to be considered a system solution in terms of safety. This arises from the interaction of the safety light curtain, system control and, if necessary, mechanical elements. To do this, the system builder needs experience in safety design, because, for example, he programs the gating sequence in the PLC and creates the safety system solution himself. He is therefore responsible for the implementation of the overall system. It is therefore important to take into account the safety-related requirements for an SPG installation, which are described in the corresponding instructions.

An important requirement is the knowledge of the current position of the transported goods by the system control (PLC). The PLC must know when the protective field is reached or left by the goods to be transported in order to send the necessary control signals to the safety light curtain at the right time. The knowledge of the position can be realized, for example, with active conveyor belts. This is necessary because, for example, the protective field must be interrupted within 4 s after the PLC control signal is applied. In addition, a maximum of 200 mm clearance between the goods to be transported and the light curtain is permitted when entering and exiting as long as a gating sequence is active.

A synchronization beam (first or last beam) must remain free during the entire process of the bridging function. An automatic start / restart is excluded during operation - the system may only be operated in combination with a restart interlock, as is also integrated in the MLC 530 SPG. The achievable performance level of the solution results together with the system control used. Performance level PLd is achieved together with a standard controller, performance level PLe results together with a safety controller.

Content of the article:

• Page 1: Gating without additional muting sensors
• Page 2: The principle of operation
• Page 3: Synchronization beam and fixed beam blanking

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