Hexa Platform as Active Environment System

Abstract

IntroductionThe considerable progress made in manufacturing has made it possible to construct industrial manipulators with more and more stiff joints. This presents an obvious advantage in an unlimited space, which results in increased positioning accuracy. However, problems arise when the robot is equipped with a torque and force sensor for the purpose of a controlled action on the environment, for example in the tasks of autonomous assembly. In such cases the high environment stiffness may account for generation of big forces which have a detrimental effect on the mechanical construction of the manipulator and constrain the allowable robot velocities in cases when the robot comes into contact with the environment [3]. Therefore, passive [18] or active [16] compliance systems are introduced between the stiff manipulator and also the mostly stiff environment. They are usually added as a part at the end of the robot arm. A passive compliance uses some mechanical devices composed of springs, sliding axles and knee joints. In passive compliance devices, there is no interaction between the control computer of the robot and the compliant device. The chief drawback of such a solution is lack of information about the exact position of the object in the space [1]. Since precise positioning is a matter of prime importance in the majority of applications, active compliance systems equipped with sensors coupled with the robot control system take on great significance. One such commercial example is the DLR (German Aerospace Center) lightweight manipulator arm with torque sensors in each joint along with collision detection and safe reaction system [2]. Although the active compliance systems based on the hybrid position-force control are much more attractive than the passive solutions based on the impedance control, they present a great challenge due to occurring stability problems [20]. Additionally, it should be remembered that the presence of a passive compliance between the manipulator and the environment is required for entering into contact to be noninvasive, even if an active compliance is used [19].