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Frequently Asked Questions
Why is torque sized from inertia rather than from part weight?
Because the drive has to accelerate the part and the jaws up to speed and then stop them against a fixed stop. A light part held far from the axis carries more rotational inertia than a heavier one held close in, so two parts of the same mass can need very different torques. The impact at the stop is where undersized units fail.
How does air get to the jaws while the head is turning?
Through drilled passages and a rotating seal inside the body, so the supply enters the fixed part and crosses to the moving part internally. This is the main structural difference from bolting a gripper onto a separate rotary actuator, where a hose has to loop and flex through every cycle and becomes the first thing to fail.
Can the rotation angle be changed after installation?
On most units, yes. Adjustable stops set the end positions within the drive's total travel, usually with a shock absorber alongside to take the energy out before the stop is reached. Total travel is fixed by the mechanism, so a 180 degree unit can be set to less but not to more.
What is the effect of combining both functions in one body?
It removes an interface, a bracket and a set of hoses, and it shortens the cycle because grip and turn can overlap. It also couples the two: a fault in the rotary seal shows up as a gripping problem, and a change to the jaws changes the inertia the drive sees. Cells that need to tune the two independently sometimes still prefer separate units.
Where does backlash come from and does it matter?
From the rack and pinion mesh and the stop clearance. It matters when the part is placed into a close-fitting fixture, because the angular error at the jaw tip is the backlash multiplied by the finger radius. Vane drives have less gear backlash but a wider tolerance on the stop position, so neither is automatically tighter.
How is the cycle sequenced so the part is never released mid-turn?
By interlocking on the gripper's own position sensors rather than on elapsed time. The controller confirms the jaws are closed before rotation is commanded, and confirms the rotation has reached its stop before release. Time-based sequencing is what produces parts flung across a cell when the air supply pressure drops.
What limits how fast one of these can run?
The energy the stops and shock absorbers can absorb each cycle, and the heat that builds in them. Manufacturers publish a maximum cycle rate that already accounts for this, and it falls as the rotating inertia rises - so a unit rated for a fast cycle with a small part will not hold that rate with a long finger set.