Interval Analysis and Reliability in Robotics

A robot is typical of systems that are inherently submitted to uncertainties although they should be highly reliable (i.e. for a robot used in surgical applications). The sources of uncertainties are the manufacturing tolerances of the mechanical parts constituting the robot which make the real robot always different from its theoretical model and control errors. We exhibit properties of a robot that are sensitive to the uncertainties and we present methods, using mainly interval analysis, that allow one to manage these uncertainties to ensure the reliability of the robot

The necessity of optimal design for parallel machines and a possible certified methodology

Although they have many advantages in term of positioning accuracy, stiffness, load capacity parallel machines have also a main drawback: their performances are very sensitive to their dimensioning. Hence although the choice of a given mechanical structure among the numerous possibilities that are offered for parallel machines may influence the performances of the machine the rule of thumb is: a mechanically appropriate but poorly dimensioned machine will present in general largely lower performances than a well designed machine with a mechanical architecture a priori less adequate. Optimal dimensioning of a parallel machine is hence a critical issue but also a complex one, especially if uncertainties in the manufacturing are taken into account. We will present a possible design methodology based on interval analysis and will illustrate this methodology on realistic examples

A local planner for closed-loop robot

Global motion planners have been proposed for closed-loop robot based on the same paradigm than has been proposed for serial chains. First a sparse representation of the configuration space of the robot is constructed as a set of nodes. This is somewhat more complicated than for serial chain as the closure equations of the mechanism should be satisfied. Then a motion planning query consists simply in connecting the start and goal points through an appropriate set of nodes (usually minimizing the length of the trajectory). But such motion planner should be complemented by a local motion planner that addresses the following issues: \begin{enumerate} \item ensure that two successive nodes belong to the same robot kinematic branch (otherwise connecting these nodes will require to disassemble the robot) \item verify that all poses between nodes satisfy the robot constraints (if possible taking into account the uncertainties in the robot modeling) \item eventually try to shorten the trajectory length \end{enumerate} We present such a local motion planner that addresses all three issues and illustrates its use on a Gough parallel robot

Kinematics and synthesis of cams-coupled parallel robots

We consider parallel robots, that will be called cams-coupled parallel robots, whose mobile platform has surfaces that are constrained to be in contact at a point with surfaces located on the base. Articulated passive xed length legs connect also the base to the platform while active legs allow to control the motion of the platform. We investigate the mobility of such robot and shows how the inverse and direct kinematics can be solved for arbitrary contact surfaces. We present then preliminary results regarding the synthesis of such robot

Appropriate Design of Parallel Manipulators

International audienceAlthough parallel structures have found a niche market in many applications such as machine tools, telescope positioning or food packaging, they are not as successful as expected. The main reason of this relative lack of success is that the study and hardware of parallel structures have clearly not reached the same level of completeness than the one of serial structures. Among the main issues that have to be addressed, the design problem is crucial. Indeed, the performances that can be expected from a parallel robot are heavily dependent upon the choice of the mechanical structure and even more from its dimensioning. In this chapter, we show that classical design methodologies are not appropriate for such closed-loop mechanism and examine what alternatives are possible