Preventing unintentional MCFB motions in the T1 mode

Setting up modes:

• T1 mode = setting up with reduced speed
• T2 mode = setting up without reduced speed

The ISG-MCE has no direct knowledge of the system's mode. The PLC programmer, to whom this information is available, can leave the safe state (= standstill) with the safety function blocks. The following requirement applied to compliance with EN775:

In critical state, i.e. an operator is located in the machine hazard zone and mode T1 or T2 is active, it should only be possible to command motions by means of conscious operator actions (in the case of a robot: confirmation key + START key).

In this state, release of the start key must lead only to feed hold, but not to command aborting.

The drive's enabling signals generally disappear anyway when the mode is changed from automatic to T1 or T2.

When the confirmation key is pressed, PLCopen commands are buffered, but the motion does not yet start.

The PLC programmer can then use pressing of the start key to supply the safety function block, thus ensuring the customary functionality of the start key.