What action does a robot take to notify the PLC that it has completed its task?

Sending an output signal from the robot to the Programmable Logic Controller (PLC) is a fundamental mechanism for communication in industrial automation systems. When a robot completes its designated task, it typically issues an output signal to inform the PLC of this completion. This output can be a digital signal that the PLC interprets as a notification or status update.

In industrial environments, robots often have various outputs that can be configured to communicate specific statuses or actions. By sending an output, the robot effectively relays information about its operational state to the PLC, which can then undertake appropriate subsequent actions or processes based on this input.

The other options, while related to the overall operation of a robot and PLC system, do not properly represent the method of communication regarding task completion. Sensors and motors play roles in the operation of the robot but are not direct means of reporting task completion to a PLC in the context presented.