The linkage passes the position where the connecting link, the pivot and the jaw are in line. Past that point any load trying to open the jaws pushes the linkage further into the stop rather than back towards the piston. Holding then comes from geometry, and the air supply is only needed to make and break the position, not to maintain it.

It holds mechanically, which is a different claim from being a safety device. The jaws will not release on loss of pressure, but the assessment still has to cover what happens to the robot arm carrying it, whether the part can rotate within the jaws, and how the cell is recovered. Toggle grippers are widely accepted for load retention on air failure and are not a substitute for a rated restraint.

Three reasons overlap there: the fixture has to hold heavy sheet without power, weld spatter attacks anything that slides, and the clamping load needed is high relative to the space available. An enclosed toggle linkage with a spatter-resistant body meets all three, and the high mechanical advantage means a small bore produces the load.

By applying air to the opening port, which drives the linkage back through the dead point. Manual release is not usually possible by pulling on the jaws, because the geometry resists exactly that. Cells that need a recovery route fit a manual override valve or a hand pump on the opening line.

Only up to the point of closure. Pressure sets how much force is available to drive the linkage through the dead point and how firmly it is held against its stop, but once locked the retained load is a function of the mechanism and the part. This is the opposite of a parallel gripper, whose holding force tracks pressure directly.

The mechanical stop that defines the locked position, and the pivot pins. As the stop wears, the linkage travels slightly further past centre, the jaws close a fraction more, and eventually the unit clamps a nominal part more tightly than intended or refuses to accept one at the top of its tolerance.

Yes, and it usually should be. A magnetic piston with reed or solid-state sensors on the body reports the piston position, from which locked and released states are inferred. Because the mechanism can hold with no pressure, position sensing is often the only way the controller knows the true state of the clamp.