ROBOTICS ENGINEERING AND APPLICATIONSDepartment ofMechanical Engineering

1. INTRODUCTIONAn end effector is a device that attaches to the wrist of the robot arm and enables thegeneral-purpose robot to perform a specific task. It is sometimes referred to as the robot's "hand."Most production machines require special purpose fixtures and tools designed for a particularoperation, and a robot is no. exception. The end effector is pan of that special-purpose tooling fora, robot. Usually, end effectors must be custom engineered for the particular task which is to beperformed. This can be accomplished either by designing and fabricating-the device fromscratch, or by purchasing a commercially available device and adapting it to the application. Thecompany installing the robot can either do the engineering work itself or it can contract for theservices of a firm that does this kind of work.Most robot manufacturers have special engineering groups whose function is to designend effectors and to provide consultation services to their customers. Also, there are a growingnumber of robot systems firms which perform some or all of the engineering work to installrobot systems. Their services would typically include end effector design.1.1 TYPESOF END EFFECTORSThere are wide assortmentsofendeffectorsrequired toperformthevarietyofdifferent workfunctions.Thevarious typescanbedividedintotwomajor categories:1.Grippers2.ToolsGrippers are end effectors used to grasp and hold object. The objects are generally workparts that are to be moved by the robot. These part-handling applications include machine loading and unloading, picking parts from a conveyor, and arranging parts onto a pallet. In addition to work parts, other objects handled by robot grippers include cartons, bottles, raw materials, and tools. We tend to think of grippers as mechanical grasping devices, but there are alternative ways of holding objects involving the use of magnets, suction cups, or other means.2Grippers can be classified as single grippers or double grippers although this classification applies best to mechanical grippers. The single gripper is distinguished by the fact that only one grasping device is mounted on the robot's wrist. A double gripper has two gripping devices attached to the wrist and is used to handle two separate objects. The two gripping devices can be actuated independently. The double gripper is especially useful in machine loading and unloading applications. With a double gripper, the robot can pick the part from the incoming conveyor with one of the gripping devices and have it ready to exchange for the finished part. When the machine cycle is completed, the robot can reach in for the finished part with the available grasping device, and insert the raw part into the machine with the other grasping device. The amount of time that the machine is open is minimized. The term multiple gripper is applied in the case where two or more grasping mechanisms are fastened to the wrist. Double grippers are a subset of multiple grippers. The occasions when more than two grippers would be required are somewhat rare. There is also accost and reliability penalty which accompanies an increasing number of gripper devices on one robot army definition, the tool-type end effector is attached to the robots wrist. One of the most common applications of industrial robots is spot welding, in which the welding electrodes constitute the end effector of the robot. Other examples of robot applications in which tools are used as end effectors include spray painting and arc welding.1.2 TYPES OF GRIPPER MECHANISMSThere are various ways of classifying mechanical grippers and their actuating mechanisms. One method is according to the type of finger movement used by the gripper. In this classification the grippers can actuate the opening and closing of the fingers by one of the following motions.

1. Pivoting movement2. Linear or translational movementIn the pivoting movement the fingers rotate about fixed pivot points on the gripper toopen and close. The motion is usually accomplished by some kind of linkage mechanism. In thelinear movement the fingers open and close by moving in parallel to each other. This isaccomplished by means of guide rails so that each finger base slides along a guide rail duringactuation. The translational finger movement might also be accomplished by means of a linkagewhich would maintain the fingers in a parallel orientation to each other during actuation.

Mechanical grippers can also be classed according to the type of kinematic device used toactuate the finger movement. In this classification we have the following types:1. Linkage actuation2. Gear-and-rack actuation3. Cam actuation