Pierre Dauchez

HEXA: a fast six-DOF fully-parallel robot

The paper presents a new design for a six-degree-of-freedom (DOF) parallel structure dedicated to high-speed applications. The authors extend the principle of the DELTA mechanical structure in order to obtain orientations of the travelling plate. The approach which goes from the DELTA to the HEXA is first developed. Then a kinematic model of the HEXA is proposed. Finally a dynamic model of that robot is presented.<<ETX>>

Fast parallel robots

This paper presents two parallel robots that have been recently designed. This first one is a 3-degree-of-freedom lightweight robot called DELTA and designed in Switzerland by EPFL. One gives the equations corresponding to different models of this robot : forward and inverse kinematics as well as inverse dynamics. The important feature of the method in deriving these models is to use a «good» set of parameters in order to simplify the equations. Based upon these considerations of simplicity, one has tried to extend the principle of the DELTA mechanical structure structure to a 6-degree-of-freedom parallel robot. One came up with a new design one called the HEXA. One presents this robot and shows that it should have the same dynamic capabilities as the DELTA, because, like this one, it can be built with light material and it can be easily modeled

External force control of an industrial puma 560 robot

Deformations occurring in a robot working in contact with a rigid environment is a real problem in the industrial world. This problem can be solved by taking into account forces undergone by the robot at the end-effector level. The first part of this article is aimed at determining a force control scheme that satisfies this constraint and that can be implemented on a non-modified industrial robot controller. Various existing force control schemes are investigated and the reasons for discarding them are given. Then, the emphasis is put on a so-called external force control scheme, which seems to be a solution to our problem. The control law appearing in such a scheme is determined by means of a realistic robot simulator developed on a SUN workstation. A simple integral term on the force error gives acceptable results in various robot configurations. This is illustrated in the form of graphs. In a second part, the implementation of this external control scheme in a real PUMA 560 robots UNIMATE controller is presented. Certain software issues and implementation solutions are pointed out. Several experiments are described. Once again, graphs are used to show the experimental results.

Telerobotics over IP networks: Towards a low-level real-time architecture

Long distance teleoperation over asynchronous transmission links makes many classical teleoperation schemes unstable. The use of this kind of media involves varying transmission delays that may become prohibitive even at short distance. However, they are standardized, cheap and widespread over the planet. The paper presents our latest works on the improvement of teleoperation loops, by providing a low-level architecture which permits the use of classical teleoperation controls over asynchronous digital links.

A global approach for motion generation of non-holonomic mobile manipulators

A mobile robotic manipulator, i.e. a manipulator mounted on a vehicle, is a very useful system for tasks in dangerous environments. Unfortunately the use of a wheeled vehicle introduces non-holonomic constraints, and the combination of a vehicle and a manipulator generally introduces kinematic redundancy. The goal of this paper is to propose a method to determine a feasible path between two fixed configurations for a mobile manipulator whose vehicle is non-holonomic. For this purpose, we write the global displacement of the system in a symbolic way, using two representation tools: homogeneous matrices and dual quaternions. Then, we compute the corresponding joint parameters to make the desired displacement coincide with the computed symbolic displacement. The method is described and some simulation results are presented.

Fuzzy sliding mode control of a fast parallel robot

Robustness is a very important feature of robot controllers. Obviously, dynamic control is not the good way to obtain the best robustness performance, especially when the payload is unknown. Moreover, this kind of control laws are not able to compensate for Coulomb friction. Our approach is based on the variable structure control (VSC) with sliding mode, but it is well known that VSC is unstable for physical sampled systems. Therefore, the concept of fuzzy logic is used to implement fuzzy sliding mode control on our six-degree-of-freedom fast parallel robot. Both simulated and real experiments are reported in this paper.

A planar quaternion approach to the kinematic synthesis of a parallel manipulator

In this paper we present a technique for designing planar parallel manipulators with platforms capable of reaching any number of desired poses. The manipulator consists of a platform connected to ground by RPR chains. The set of positions and orientations available to the end-effector of a general RPR chain is mapped into the space of planar quaternions to obtain a quadratic manifold. The coefficients of this constraint manifold are functions of the locations of the base and platform R joints and the distance between them. Evaluating the constraint manifold at each desired pose and defining the limits on the extension of the P joint yields a set of equations. Solutions of these equations determine chains that contain the desired poses as part of their workspaces. Parallel manipulators that can reach the prescribed workspace are assembled from these chains. An example shows the determination of three RPR chains that form a manipulator able to reach a prescribed workspace.

World representation and path planning for a mobile robot

This paper is related to the problem of navigation of a mobile robot amidst obstacles. In order to easily take into account any modification of the environment, we propose a very simple representation of the obstacles, based on the use of rectangles, as well as a matrix description of the spatial relationships between the obstacles. We also present a path planner based on a A* algorithm, the features of which are specifically designed for our world of rectangles. The cost function takes into account both the length of the path and the number of turns. Some experimental results and implementation details are also given in this paper.

Task modeling and force control for a two-arm robot

The authors present solutions for manipulating objects with two robotic arms, when force control is necessary. The applications of interest are the transport and assembly of rigid objects, the deformation, transport, and assembly of flexible objects, and the assembly in space of two objects, each being held by one arm. The authors present a theoretical solution for modeling the tasks and practical solutions implemented for controlling two six-axis arms.<<ETX>>

Hybrid control of a two-arm robot for complex tasks

Abstract For many coordinated tasks, a two-arm robot cannot be properly controlled by using a simple position control scheme and therefore requires a certain form hybrid control. Uchiyama and Dauchez recently proposed a symmetric hybrid position/force scheme for the manipulation of rigid objects rigidly held. The main results of this theory are summarized in this paper, and the limitations are pointed out. Several examples in which the relative motion of the end effectors cannot be neglected are presented: manipulation of rigid objects non-rigidly held, deformation of a flexible object, and assemblies of two objects “in space”. These tasks are analyzed and attempted control schemes are given for each of them. The dynamic effects are always neglected in this preliminary theoretical approach. An experimental setup built around two six axis PUMA arms and a parallel processing controller has been installed in order to validate our theoretical results. The hardware and software of this setup are also briefly described in this paper.