In a wider sense, an end effector can be seen as the part of a robot that interacts with the work environment.
When referring to robotic prehension there are four general categories of robot grippers:[1] These categories describe the physical effects used to achieve a stable grasp between a gripper and the object to be grasped.
Vacuum cups and electromagnets dominate the automotive field and metal sheet handling.
Other principles are less used at the macro scale (part size >5mm), but in the last ten years, have demonstrated interesting applications in micro-handling.
Even more complex are ultrasonic grippers, where pressure standing waves are used to lift up a part and trap it at a certain level (example of levitation are both at the micro level, in screw- and gasket-handling, and at the macro scale, in solar cell or silicon-wafer handling), and laser source that produces a pressure sufficient to trap and move microparts in a liquid medium (mainly cells).
Two-finger grippers tend to be used for industrial robots performing specific tasks in less-complex applications.
For example, if a robot is designed to lift a round object, the gripper surface shape can be a concave impression of it to make the grip efficient.
For many physically interactive manipulation tasks, such as writing and handling a screwdriver, a task-related grasp criterion can be applied in order to choose grasps that are most appropriate to meeting specific task requirements.
The end effector of an assembly-line robot would typically be a welding head, or a paint spray gun.
A surgical robot's end effector could be a scalpel or other tool used in surgery.
Other possible end effectors might be machine tools such as a drill or milling cutters.
The end effector on the space shuttle's robotic arm uses a pattern of wires which close like the aperture of a camera around a handle or other grasping point.