Andrés Kecskeméthy

Time-Optimal Path Planning Along Specified Trajectories

Time-optimal motion planning along specified paths is a well-understood problem in robotics, for which well-established methods exist for some standard effects, such as actuator force limits, maximal path velocity, or sliding friction. This paper describes some extensions of the classical methods which consider, on the one hand side, additional non linear constraints such as sticking friction, acceleration limits at the end-effector, as well power limits for the overall system, and on the other, general paths featuring smooth interpolation of angular acceleration as well as arbitrary multibody systems comprising multiple loops. The methods are illustrated with two applications from robotics and the mining industry.

Robust Inverse Kinematics at Position Level by Means of the Virtual Redundant Axis Method

Several techniques have been developed in the past to handle the inverse kinematics of serial robots passing through or close to singular configurations. As a common line, these approaches operate at velocity level, seeking a trade-off between tracking accuracy and joint velocity feasibility. While providing robust control, some difficulties arise in these methods for predicting end-effector errors and their spread in SE(3). In a previous paper, the virtual redundant axis (VRA) method was introduced at velocity level, by which end-effector velocity errors could be concentrated in non-controllable directions. The present paper extends the VRA method to position level, allowing for a precise motion tracking and the handling of singularity paths in the same way as regular motions.

Time-Optimal Path Planning for the General Waiter Motion Problem

This paper presents a direct solution approach for the so-called general waiter motion problem, which consists in moving a tablet as fast as possible from one pose to the other such that non of the objects resting on the tablet slides at any time. The question is akin to several industrial problems in which tangential forces are restricted due to functional reasons, such as suction grippers, motion of sensitive goods, etc. In contrast to existing approaches which parametrize the problem in configuration (joint) space, we decompose the overall task into two cascaded main components: shaping the optimal geometry of the spatial path, and finding the time optimal one-dimensional motion of the system along this path. The spatial path is parametrized using via poses in SE(3), making it possible to reduce the search space to significant physical subspaces, and to interact intuitively with the user. The overall optimization is subdivided into a series of subproblems with cost functions and search spaces of increasing fineness, such that each subproblem can be solved with the output of its predecessor. A solution of the waiter motion problem with four objects illustrates the applicability of the algorithm.

Large-amplitude base-motion compensation of a serial robot using an inertial measurement unit

This paper describes the kinematical analysis and control of a large spatial robot for base motion compensation using an inertial measurement unit. The proposed method is intended for a 6 degrees of freedom serial manipulator, which compensates a large-amplitude spatial motion at its base such that the end effector maintains to a high degree a prescribed target location. Hereby, the robot circumvents hand wrist singularities by a new virtual redundant joint approach. The overall system is tested for a KUKA KR500 system and computergenerated as well as real wave signals with large amplitudes.