280 Industrial Robotics Fundamentals Copyright Goodheart-Willcox Co., Inc. 9.4 End Effector Design To determine the type of end effector needed to do a job, a study must be per- formed to evaluate the operation, the workpiece(s), and the environment. The end effector may be subjected to extreme temperatures or make contact with abrasive or corrosive materials. Special protective materials and shielding devices may be necessary to protect the manipulator. Objects to be moved may vary in shape, size, and weight. The workpieces may also change in shape, size, or weight during a process. The end effector must be able to adjust to such changes. Other conditions to be considered are the fragility of the workpiece, the surface fi nish, and the type of material used to construct the fi workpiece. For example, if an object is made of ferrous material (one that contains iron), a magnetic gripper may be used. Additional considerations, such as problems involving inertia, center of mass, gripping force, or friction between the part and the gripper, may need to be addressed. Other concerns might involve part orientation, gripper sensing capa- bilities, or interaction with other equipment. 9.4.1 Desirable Characteristics End effectors should be designed with the appropriate desirable characteristics. The end effector should have the strength necessary to carry out the required tasks and be able to withstand rigorous use. End effectors should be equipped with measures to guard against damage from strain. Breakaway devices remove the end effector from the work area using mechanical fuses, detents, or preloaded springs. A breakaway device should be installed to prevent damage to the robot’s arm or wrist if the end effector becomes stuck. End effectors that use friction to hold objects are not typically prone to damage caused by excessive strain because the grasped object will slip out of the gripper when an opposing force is applied. However, an opposing force of this type could cause joint slippage and alter the accuracy of the robot’s positioning. Robots may use overload sensors. An overload sensor is a device that detects r obstructions or overload conditions within fractions of a second. The sensor signals the controller to shut down the robot before damage occurs. Unlike break- away joints, an overload sensor does not have parts to be replaced after it operates and does not require reprogramming. Another desirable characteristic is compliance. Compliance is the ability of an end effector to tolerate misalignment of mating parts. For the assembly of close- fi tting parts, this characteristic is essential. Compliance prevents the part from fi jamming, wedging, and wearing. Some end effectors have a certain amount of compliance built into their design. End effectors that lack this capability may use a remote center compliance (RCC) device. This device is installed in the wrist of the robot and helps to compensate for workpiece misalignment or irregularities. Robots equipped with an RCC device can perform precise tasks, such as inserting bearings into a housing with a clearance of only 0.0005″ (0.013 mm). ″ 9.4.2 Custom-Designed End Effectors In addition to standard grippers and tools, custom end effectors can be designed for a particular application, Figure 9-11. Custom-designed end effectors broaden the range of tasks that robotic equipment can perform.