Three positions, different functions
At rest, operation is not enabled. The middle position maintains an enabling signal; squeezing through to the third position removes it. This arrangement addresses both letting go and gripping more tightly when startled.
Returning from the third position must not create unintended enabling as the middle position is crossed. Actual behaviour depends on the device and its integration into Machinery safety functions and performance level.
Enabling is not a command for any movement
In a robot application, enabling is combined with manual mode and specified movement conditions. The task must allow observation, adequate clearance and control of hazards from other connected equipment.
A signal permitting operation must be distinguished from the specific command initiating it. Holding the device does not authorise any automatic sequence or protect other people in the area.
Use, ergonomics and limitations
Handle shape, operating force and posture affect whether the control can be maintained as intended. Discomfort or fatigue must be reported and addressed technically, never by tying the enabling control in position.
Programming that requires motion differs from maintenance requiring isolation. Lockout/Tagout (LOTO) and other energy-control measures remain necessary where required for the intervention.
An assessment example
A technician needs to observe a point while teaching a robot. Review checks whether she can see the full movement, could become trapped, and what happens to the gripper and associated conveyor. Looking only at the pendant button would leave these risks unresolved.
Before use, competent personnel verify all three positions and the specified response in accordance with the instructions. Replacing a pendant or changing a program requires review of compatibility with the validated function. Testing must not expose a person to hazardous movement to demonstrate that protection works.
Before authorising a task, describe which movement the technician needs, which areas must remain visible and how work will stop if visibility or positional control is lost. This helps distinguish a genuine adjustment need from an intervention that should instead be performed with energy sources isolated. Training should address that boundary explicitly.
