The existing assembly and loads first, then the simplest mechanism, and only then drawings.
Review the existing assembly: what moves, what is fixed and where there is space
Find the simplest mechanism: in the gripper, one idler pinion and two racks
Check the stroke at 0, 25, 50, 75, 100 and 105 mm with no collisions with the frame or cylinders
Size for the worst case: one Ø25 cylinder at 6 bar drives both jaws, about 295 N per tooth
Issue drawings of the new parts and explanatory images