In this paper, off-the-shelf algorithms f o r force/torque control are used in the context of mobile manipulation (i.e. coordinated motion of a mobile robot base and the a r m mounted o n top of it). In particular, the task of opening a door is studied. To make the solution robust, as f e w assumptions as possible are made. B y using relaxation of forces as the basic level of control, more complex information can be derived f r o m the resulting motion. In our system, the radius and the centre of rotation of the door are estimated online. This enables the complete system t o have a higher degree of autonomy in a n unknown environment. In addition, the redundancy of the robot is exploited in such a way as t o drive the system towards a desired configuration. The framework of hybrid dynamic systems is used to implement the algorithm which gives a theoretically sound framework f o r analysing the system with respect t o safety and functionality. The integration of the above approaches results in a system which can robustly locate und grasp the handle und then open the door.0-7803-6348-5/00/$10.00 02000 JEEE.
A new method is presented for identifying the local stiffness of a structure from vibration test data. The method is based on a projection of the experimentally measured flexibility matrix onto the strain energy distribution in local elements or regional superelements. Using both a presumed connectivity and a presumed strain energy distribution pattern, the method forms a well-determined linear least squares problem for elemental stiffness matrix eigenvalues. These eigenvalues are directly proportional to the stiffnesses of individual elements or superelements, including the cross-sectional bending stiffnesses of beams, plates, and shells, for example. An important part of the methodology is the formulation of nodal degrees of freedom as functions of the measured sensor degrees of freedom to account for the location offsets which are present in physical sensor measurements. Numerical and experimental results are presented which show the application of the approach to example problems.
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