Philippe Lemoine

Identification of the payload inertial parameters of industrial manipulators

In this paper we present four methods for the identification of the inertial parameters of the load of a manipulator. The knowledge of the values of these parameters can be used to tune the control law parameters in order to improve the dynamic accuracy of the robot. They can also be exploited to verify the load transported by the robot. The methods presented have been validated using Staubli RX 90 robot. The experimentation has been carried out using data collected from the industrial control system (version CS8) of the manufacturer. This version allows to have access to joint positions, velocities and torques. The methods presented are based on solving linear system of equations using weighted least squares solution.

Identification of the dynamic parameters of the Orthoglide

This paper presents the experimental identification of the dynamic parameters of the Orthoglide, a 3-DOF parallel mechanism. The dynamic identification model is based on the inverse dynamic model, which is linear in the parameters. The model is computed in a closed form in terms of the Cartesian dynamic model elements of the legs and of the Newton-Euler equation of the platform. The base inertial parameters of the robot, which constitute the identifiable parameters, are given.

A vision-based computed torque control for parallel kinematic machines

In this paper, a novel approach for parallel kinematic machine control relying on a fast exteroceptive measure is implemented and validated on the Orthoglide robot. This approach begins with rewriting the robot models as a function of the only end-effector pose. It is shown that such an operation reduces the model complexity. Then, this approach uses a classical Cartesian space computed torque control with a fast exteroceptive measure, reducing the control schemes complexity. Simulation results are given to show the expected performance improvements and experiments prove the practical feasibility of the approach.

OpenSYMORO: An open-source software package for symbolic modelling of robots

This paper presents OpenSYMORO, an open-source software package for symbolic modelling of robots. This software package is based on previous work detailed in [1]. However, the package in [1] was developed using Wolfram Mathematica and hence required Mathematica license for use. OpenSYMORO is mainly developed using the Python programming language and the source code will be publicly available. The new version provides support to model robots with flexible joints, floating base and wheeled mobile robots. This is in addition to supporting serial, tree structure and closed-loop robots. A visualisation tool to view the structure of the robot is also included.

Estimation of the Absolute Orientation of a Five-link Walking Robot with Passive Feet

One of the main objectives of current research on walking robots is to make their gaits more fluid by introducing imbalance phases. For example, for walking robots without actuated ankles, which are under actuated in single support, dynamically stable walking gaits have been designed with success (Aoustin & Formal’sky 2003; Chevallereau et al. 2003; Zonfrilli et al. 2002; Aoustin et al. 2006; Pratt et al. 2001; Westervelt et al. 2003). Both the design of reference motions and trajectories and the control of the mechanism along these trajectories usually require the knowledge of the whole state of the robot. This state contains internal variables which are easy to measure using encoders for example, and also the absolute orientation of the robot with respect to the horizontal plane. For robots with unilateral constraints with the ground, it may not be possible to derive the latter information from internal measurements, as in the case of the absolute orientation of a biped in single support. Of course, technological solutions exist such as accelerometers, gyrometers, inertial units... But the implementation of these solutions is expensive and difficult. In order to overcome these difficulties, we propose to use a state observer which, based on the measurements of the joint variables and on a dynamic model of the robot, provides estimates of the absolute orientation of the walking robot during imbalance phases. This strategy was first validated in simulation for a three link biped without feet, using nonlinear high gain observers and a nonlinear observer based on sliding modes with a finite time convergence (Lebastard et al. 2006a) and (Lebastard et al. 2006b), for walking gaits composed of single support phases and impacts. The main drawback with this family of observers is that, when only some of the degrees of freedom are measured, a state coordinates transformation is necessary to design their canonical form (Gauthier & Bornard 1981; Krener & Respondek 1985; Bornard & Hammouri 1991; Plestan & Glumineau 1997). In this chapter, the observer is an extended Kalman filter and it is applied to SemiQuad, a prototype walking robot built at our institute. SemiQuad is a five link mechanism with a platform and two double-link legs. It is designed to study quadruped gaits where both front legs (resp. rear legs) have identical movements. Its unique front leg (resp. rear leg) acts as the two front legs (resp. rear legs) of the quadruped, so that SemiQuad can be considered as an implementation of a virtual quadruped, hence its

KINEMATIC ANALYSIS AND TRAJECTORY PLANNING OF THE ORTHOGLIDE 5-AXIS

The subject of this paper is about the kinematic analysis and the trajectory planning of the Orthoglide 5-axis. The Orthoglide 5-axis a five degrees of freedom parallel kinematic machine developed at IRCCyN and is made up of a hybrid architecture, namely, a three degrees of freedom translational parallel manipulator mounted in series with a two degrees of freedom parallel spherical wrist. The simpler the kinematic modeling of the Orthoglide 5-axis, the higher the maximum frequency of its control loop. Indeed, the control loop of a parallel kinematic machine should be computed with a high frequency, i.e., higher than 1.5 MHz, in order the manipulator to be able to reach high speed motions with a good accuracy. Accordingly, the direct and inverse kinematic models of the Orthoglide 5-axis, its inverse kinematic Jacobian matrix and the first derivative of the latter with respect to time are expressed in this paper. It appears that the kinematic model of the manipulator under study can be written in a quadratic form due to the hybrid architecture of the Orthoglide 5-axis. As illustrative examples, the profiles of the actuated joint angles (lengths), velocities and accelerations that are used in the control loop of the robot are traced for two test trajectories.

SICOMAT: A system for SImulation and COntrol analysis of MAchine Tools

Presents a software package for the simulation and the control analysis of machine tool axes. This package which is called SICOMAT (SImulation and COntrol analysis of MAchine Tools), provides a large variety of toolboxes to analyze the behavior and the control of the machine. The software takes into account several elements such as the flexibility of bodies, the interaction between several axes, the effect of numerical control and the possibility of reducing models.