Hierarchical fuzzy control to ensure stable grasping

In many robotic applications, the end effector consists of a gripper which has to execute a stable grasping while the manipulator is moving it in the workspace. Stable grasping is important to ensure the integrity of the object as well as the success of the overall performance. Accordingly, the end effector operation must be insensitive to external disturbances. End effector vertical acceleration is considered as a disturbance as it is able to induce slip on the grasped object. If the controller has information about this disturbance, the grasping can be more stable. In addition, if the controller can limit the disturbance, the grasping operation can be improved even more. Accordingly, an algorithm for limiting the end effector vertical acceleration to assurance stable grasping is proposed. The controller has an hierarchical architecture in order to avoid the curse of dimensionality and to deal with the information which is hierarchical in nature. The limit is calculated by a fuzzy controller which uses information from both the current applied force to the object and the actuator applied energy