Pierre Y. Willems

Identification of the barycentric parameters of robot manipulators from external measurements

An original procedure for the estimation of the barycentric parameters of a robot is presented. This procedure requires only the processing of measurements provided by an external experimental set-up. The procedure is based on the property that the relations between the robot motion and its reactions on the bedplate are completely independent of the internal joints forces. A convincing validation experiment on a PUMA 562 is reported.

On the kinematic modelling and the parameter estimation of the human shoulder

This paper presents some results on the modelling and the corresponding parameter estimation of the human shoulder. This system consists of the clavicle, the scapula, the humerus and the various joints between these bodies and the trunk through the sternum; it will be represented as a succession of a rotational joint between the sternum and the clavicle and a constant distance joint, representing the scapula between, the clavicle and the humerus head. The parameters of this system are the components of the position vectors of the joint characteristic points (the corresponding centres of the rotations). Experimental results are presented as well as a validation of the proposed model.

On the identification of the barycentric parameters of robot manipulators from external measurements

An original procedure for the estimation of the barycentric parameters of a robot is presented. This procedure requires only the processing of measurements provided by an external experimental set-up (reactions at the bedplate, and position, velocities, and accelerations). The procedure is based on the property that the relations between the robot motion and its reactions on its bedplate are completely independent of the internal joint forces. Some identifiability issues are discussed, and a validation experiment is reported.<<ETX>>

A case study of physical diagnosis for aircraft engines

This paper examines an ongoing research and development project which deals with identification, control and diagnosis in aircraft engines. Within these topics, this paper focuses on physical diagnosis, where one of the main motivations of the project is to introduce innovation and update techniques currently used in industry. Several fault diagnosis methods are considered and compared in terms of their possible application to the project. Further details are provided for the parametric statistical approach which, according to this initial study, is one approach flexible enough and with good foundations in order to achieve the desired objectives.

Multibody Formalism Applied to Non-Conventional Railway Systems

The paper presents the main features of the AUTODYN programme developed in Louvain-La-Neuve. This multi-purpose programme, based on the virtual work principle, can be used for vehicle dynamics as well as in robotics and for other mechanical systems. The generalized coordinates describe the relative motion in the joints between bodies. A library of joints, including rail-wheel connections, with their corresponding interaction models is available. Moreover the joints can be restricted by means of user-defined constraints and some of their coordinates can have a prescribed motion. Constraints resulting from closed loops are automatically generated and the final form of the equations is obtained by using the Lagrange multipliers technique and a coordinate partioning method.

Determination of ground reaction forces and centres of pressure of both feet during normal walking on a single platform

Typically, ground reaction forces (GRFs) are recorded using floor-mounted force platforms in order to compute net joint torques. The assessment of these data during several cycles is time consuming, since the subjects must target their footsteps in order to allow adequate recording, i.e. to place only one foot per individual plate. One solution is to use a force measuring treadmill (FMT). However the FMT records the summed GRFs from both feet during the double contact phases. So the left and right GRF profiles and COPs must be computed from the global values of the GRFs and COPs. The aim of this study is to determine a new algorithm to decompose left and right measured GRF profiles and COPs from their global values, and to compare these with the independently measured GRFs and COPs.

Stability of deformable gyrostats based on Sturm's theorem.

It is shown how Sturms theorem, which provides stability criteria for linear differential equations with complex coefficients, may be used to determine the stability of a class of deformable spacecraft which includes symmetrical dual- and triple-spin satellites with flexible dissipative bearings. For dual-spin satellites, the results are equivalent to those obtained by a Liapunov analysis using a Hamiltonian-like testing function and integrals of motion. For triple-spin satellites, the results are also equivalent to those resulting from a Liapunov analysis in the particular cases where a suitable testing function can be obtained, and, in the general case, the method provides a complete set of stability criteria, which, with appropriate hypotheses, yields a simple closed-form stability condition.

Axial Gyrostats, Canonical Cases

We now have seen the qualitative nature of the osculation vectors and the polhode families on the energy ellipsoid, for all body shapes. We now turn to the development of analytical solutions for the angular velocity components. In the present section, we confine ourselves to the special case of the axial gyrostat for which h1 = h2 = 0 , h3 > 0. It is convenient to dispose first of the special body shapes, as in the case of the osculation study. For the Sphere, the axial case is the only case, so the solution given for it completely disposes of that body shape.

Stability of the Special Equilibria

We consider now the stability of Cases 2 and 3 discussed in the previous lecture, with that Case 1 falling out as a by-product. The essential symbolic preliminaries are recapitulated first.

Effects of Flexibility on Stability

We are interested in the attitude of the space vehicle with respect to a rotating reference frame. For a gravity stabilized vehicle this re ference will be the orbital frame with one axis per pendicular to the plane of the orbit and a second axis aligned with the local vertical, (Fig. 1). For satellites spinning in free-space, the reference frame will have a constant angular velocity equal to the nominal angular velocity of the system.