Chapter 9 End Effectors ff ff 277 Copyright Goodheart-Willcox Co., Inc. allow for unevenness in a part surface, some vacuum cups are spring-loaded or mounted on a ball joint. Electromechanical Grippers Electromechanical grippers, also called magnetic grippers, are end effectors that use a magnetic fi eld created by a permanent magnet or an electromagnet to pick fi up an object. Objects that have flat, smooth, clean surfaces are the easiest to handle. fl Grippers that operate using a permanent magnet are well suited for explosive environments because they do not require an electric power source that could spark. Once a part is moved, it is released from the gripper by exerting force to pull it away from the magnetic field. fi An electromagnetic gripper is energized by a dc power source. An object is released from the gripper when the power source is interrupted. To speed up release time, the current is not cut off. Instead, the direction of current flow is fl momentarily reversed. There are certain disadvantages associated with using electromechanical grippers. These grippers can only be used to handle materials containing iron, which limits possible applications and locations. Metal shavings and other small metal particles are attracted to the magnet when parts are machined. If these metal particles accumulate on the magnet, they can scratch the surface of a part or cause misalignment of parts. The temperature of a workpiece must also be consid- ered. The effectiveness of magnetic force declines when workpieces are heated to several hundred degrees, as may be the case in some processing operations. Curved fingers Multi-cup vacuum gripper Curved fingers Pacifi c Robotics, Inc. Figure 9-9. When an object with large surface area must be grasped, a multi-cup vacuum gripper is often used. The gripper pictured also has curved fi ngers to provide additional support when moving large objects. fi