Alain Jutard

A random exploration approach for automatic chamberless insertion

The stochastic approach strategy to realize the robotized in sertion of low-clearance, chamferless parts is studied in both the analytical and experimental contexts. The analytical ap proach is discussed in terms of stochastic differential equations that involve Gaussian white and colored noises processes to model a planar random search. Special attention is devoted to characterize the time required for the insertion, a random variable whose first moment calculation (i.e., the mean) is dealt with. In the mathematical modelization context adopted, it is remarkable that the calculated mean mating time grows slowly (i.e., logarithmically), with the precision required to perform an insertion. The. theoretical results are validated on a robo tized assembly system, also presented in this article. In this experimental system, the random movements are generated by pseudorandom binary sequences that, for the time scales con sidered, are large band processes. The experimental data are observed to sustain the logarithmic behavior obtained analyt ically. Hence, in addition to its simplicity and flexibility, the random strategy approach appears to be very efficient when high mating precision is required.

Geometric model of the DCR-LAI compliant device

In this paper the authors present a mathematical model of geometric and kinematic behaviour of an original passive compliant device provided with two rotation centres, called DCR–LAI system. This device is designed for a robotic assembly of parts with very small tolerances including a chamfer at the hole. The given modelisation may be used as a decision aid for the choice of a compliant device with regard to characteristics of parts being assembled.

A robot-task conformance index for the design of robotized cells

Abstract A robot-task conformance index is introduced. It applies to any manipulator and a broad scope of tasks. Bounded in the [0, 1] range, this dimensionless index is defined within or outside singularities, and remains invariant against changes in units for translations or rotations. It is based on the simultaneous diagonalization of quadratic forms accounting for the “capabilities” of the robot and the “constraints” of the task. The structural and joint properties of the robot are formulated as a repeatability ellipsoid. A sufficient task ellipsoid is construed from the tasks domain of constraints . Following the simultaneous diagonalization of both robot and task ellipsoids, minimum containing and maximum contained ellipsoids are deduced. Appropriate volume ratios of these four ellipsoids define the conformance index. Calculations performed in the diagonalized space reduce the computational burden.