An end effector for use on a robotic arm includes a clamping assembly for clamping a workpiece, and a tool such as a drill for performing an operation on the clamped workpiece. The clamping assembly is slidably mounted on the robotic arm and self adjusts its position relative to the workpiece before a clamping operation is performed. Linear actuators independently control the movements of the clamping members. The actuators are operated by a controller, based in part on position information produced by sensors that sense the position of the clamping members.