End Effectors (robot hand)

End Effector
• Attached to the wrist a hand “end effector”.
• The end effector is not considered as part of the robot’s manipulator.
• An end-effector is a tool or gripping mechanism attached to the end of a robot arm used to make intentional contact with an object
or to produce the robot’s final effect on its surroundings to accomplish some task.

• Tools are used in applications where the robot must perform some processing operation on the work-part.
• In each case the robot must not only control the relative position of the tool with respect to the work as a function of time, it must also control the operation of the tool.

Grippers are end effectors used to grasp and manipulate objects during the work cycle. The objects are usually work-parts that are moved from one location to another in the cell.

Examples of Grippers
• Mechanical grippers, in which the part is held between mechanical fingers and the fingers are mechanically actuated
• Vacuum grippers, in which suction cups are used to hold flat objects
• Magnetized devices, for holding ferrous parts
• Adhesive devices, where an adhesive substance is used to hold a flexible material such as fabrics.

Grasping Force
The factors that determine the grasping force are:
– The weight of the object;
– Consideration of whether the part can be grasped about its center of mass;
– The speed and acceleration with which the robot arm moves, and the orientational relationship between the direction of movement and the position of fingers on the object;
– Whether physical constriction or friction is used to hold the part;
– Coefficient of friction between the object and the gripper fingers.