Harmonic Passive Motion Paradigm

Humans can robustly interact with external dynamics that are not yet fully understood. This work presents a hierarchical architecture of semi-autonomous controllers that can control the redundant kinematics of the limbs during dynamic interaction, even with delays comparable to the nervous system. The postural optimisation is performed via a non-linear mapping of the system kineto-static properties, and it allows independent control of the end-effector trajectories and the arms stiffness. The proposed architecture is tested in a physical simulator in the absence of gravity, presence of gravity, and with gravity plus a viscous force field. The data indicates that the architecture can generalise the motor strategies to different environmental conditions. The experiments also verify the existence of a deterministic solution to the task-separation principle. The architecture is also compatible with Optimal Feedback Control and the Passive Motion Paradigm. The existence of a deterministic mapping implies that this task could be encoded in neural networks capable of generalisation of motion strategies to affine tasks.

Machining With Redundant Kinematics

The demand for high productivity and quality combined with the need for decreasing energy consumption will substantially affect machine tool design in the future. This development is driven by a modification of process chains which is focused on resource conservation. One important contribution for that purpose is the transition towards complete machining. This approach calls for a configuration targeting major process stability as well as a structure geared towards accuracy and dynamism. The compromise between potential dynamism and machine size can be improved by using redundant drives. This paper describes models, simulation tools and the method of the development process for redundant kinematics. To highlight the different aspects of designing such machine tool structures, their development process is demonstrated on the basis of two examples, complete machining for tool- and die making and an adaptive spindle holder for micro contouring and -structuring.

Improving the stability level for on-line planning of mobile manipulators

SUMMARYThis paper presents a quadratic programming (QP) form algorithm to realize on-line planning of mobile manipulators with consideration for improving the stability level. With Lie group and screw tools, the general tree topology structure mobile robot dynamics and dynamic stability attributes were analysed. The stable support condition for a mobile robot is constructed not only in a polygonal support region, but also in a polyhedral support region. For a planar supporting region, the tip-over avoiding requirement is formulated as the tip-over prevent constraints with the reciprocal products of the resultant support wrench and the imaginary tip-over twists, which are constructed with the boundaries of the convex support polygon. At velocity level, the optimized resolution algorithm with standard QP form is designed to resolve the inverse redundant kinematics of the Omni-directional Mobile ManipulatorS (OMMS) with stability considerations. Numerical simulation results show that the presented methods successfully improve the stability level of the robot within an on-line planning process.