An apparatus comprises a cavity coupled to a pneumatic controller configured to control pressure in the cavity; a piston configured to be pulled into the cavity when pressure in the cavity is below atmospheric pressure and to be pushed outward when pressure in the cavity is greater than atmospheric pressure; and a gripper arm mechanically coupled to the piston. The gripper arm may be configured to support a device under test. The gripper arm may be coupled to the piston through a pusher bar. The apparatus may further comprise a pneumatic control port; and a pneumatic bleed port. The pneumatic control port is coupled to the cavity, and the pneumatic bleed port is configured to bleed pneumatic pressure to atmosphere if the piston over-travels a predetermined position.