Today in almost every part of our daily life we use some kind of electronic device. Among these devices are e.g, small tools used in the kitchen as well as larger devices like a TV set or a personal computer. Because of the large quantity of such end of life products, an environmentally and economically sensible way to treat this problem must be found. Especially for expensive products containing valuable modules nondestructive disassembly and the possibility to reuse some components seems to be a promising approach. The paper describes research for autonomous disassembly of standard PC hardware. A flexible robot system is realized as a complete experimental setup in our laboratory. This demonstrates achieved abilities in the fields of image analysis and extraction and processing of information for planning of actions as well as flexible control of the disassembly process.

This paper discusses a grasp scheme for a pyramidal-like object placed on a table under the gravitational field. We assume that the contact friction is small enough to ensure that any direct grasp fails in achieving an equilibrium grasp. For an idealized 2D triangle object placed vertically on a table, we first show that a planar two-fingered hand can always achieve an equilibrium grasp under frictional contact. We also extend the basic idea to a polyhedron whose face is triangle and show two possible procedures leading to equilibrium grasps. Finally, we verify our idea experimentally for the polyhedra.

Whereas the emphasis of precision grasping only using the fingertips is placed on dexterity and sensitivity, power grasps guarantee high security and stability. But even if the task requires a power grasp, in the initial configuration the complete enveloping by the fingers is often impossible due to the position of the object in the workspace and only a fingertip grasp can be applied. Then a transition from precision to power grasping has to be performed. Based on an experimental study this paper discusses several possibilities to realize this transition by using a three-fingered dextrous hand mounted on a 6DOF robot. In particular it is distinguished between strategies requiring a coordination of robot and hand and strategies performing the transition only by the fingers like humans do.

This paper describes a motion planner that automatically avoids collisions with obstacles. A transformation of obstacles into configuration space (C-space) is not necessary. Given a polyhedral description of robot, load and environment the algorithm first computes (off-line) a graph which roughly represents the skeleton of the freespace. Due to the way of its computation this graph does not preserve connectivity, although the freespace is a connected set, which is assumed throughout this paper. Reflecting randomly at C-space obstacles a connection between subgraphs is generated. In a second step (online) a connection between a start and a goal configuration to the graph is searched for. The impact of this algorithm concerning movable obstacles is discussed. This method is general and four examples are presented to demonstrate its feasibility by applying it to different kinematic structures with 3, 6 and 12 degrees of freedom.>

Input-dependent stability was observed during torque control experiments using the first joint of the Darmstadt-HAND. The friction and compliance existing in tendon-sheath driving systems bring a hysteresis characteristic into the dependence of joint torque output on actuator displacement. While this transmission characteristic is close to the well-known backlash behavior appearing for the gears situated between a motor and load shaft, input-dependent characteristics were found to exist in the backlash region of the transmission system in the case of the use of a practical tendon length. The observed characteristic shows springlike behavior even in the backlash region and it also depends on input. Through experiments, it was confirmed that there are close relationships between the input-dependent backlash characteristics and the input-dependent stability. Based on the experiments, a description is given of the transmission characteristic in simple model equations, and the system stability is explored by using the sinusoidal-input-describing-function technique. A nondimensional stability-criterion map explaining the experimental results is shown.>