Kinematic analysis of the 3-RPR parallel manipulator

The aim of this paper is the kinematic study of a 3-RPR planar parallel manipulator where the three fixed revolute joints are actuated. The direct and inverse kinematic problem as well as the singular configuration is characterized. On parallel singular configurations, the motion produce by the mobile platform can be compared to the Reuleaux straight-line mechanism

Working and Assembly Modes of the Agile Eye

This paper deals with the in-depth kinematic analysis of a special spherical parallel wrist, called the Agile Eye. The Agile Eye is a three-legged spherical parallel robot with revolute joints in which all pairs of adjacent joint axes are orthogonal. Its most peculiar feature, demonstrated in this paper for the first time, is that its (orientation) workspace is unlimited and flawed only by six singularity curves (rather than surfaces). Furthermore, these curves correspond to self-motions of the mobile platform. This paper also demonstrates that, unlike for any other such complex spatial robots, the four solutions to the direct kinematics of the Agile Eye (assembly modes) have a simple geometric relationship with the eight solutions to the inverse kinematics (working modes)

Torque minimization of the Delta parallel robot

National audienceThis paper proposes a new solution to the problem of torque minimization of the Delta robot. The suggested approach involves connecting to the initial structure a secondary mechanical system, which generates a vertical force applied to the platform of the robot. The conditions for optimization are formulated by the minimization of the root-mean-square and maximum values of the input torque due to the static and dynamic loads. The numerical examples show the efficiency of the suggested torque minimization approach

Accuracy Analysis of 3T1R Fully-Parallel Robots

International audienceParallel robots with Shoenflies motions (also called 3T1R parallel robots) are increasingly being used in applications where precision is of great importance. Clearly, methods for evaluating the accuracy of these robots are therefore needed. The accuracy of well designed, manufactured, and calibrated parallel robots depends mostly on the input errors (sensor and control errors). Dexterity and other similar performance indices have often been used to evaluate indirectly the influence of input errors. However, industry needs a precise knowledge of the maximum orientation and position output errors at a given nominal configuration. An interval analysis method that can be adapted for this purpose has been proposed in the literature, but gives no kinematic insight into the problem of optimal design. In this paper, a simpler method is proposed based on a detailed error analysis of 3T1R fully-parallel robots that brings valuable understanding of the problem of error amplification

Pantopteron: a New Fully-Decoupled 3-DOF Translational Parallel Robot for Pick-and-Place Applications

International audienceIn this paper, a novel 3-DOF fully decoupled translational parallel robot, called the Pan-topteron, is presented. This manipulator is similar to the Tripteron Cartesian parallel manipulator, but due to the use of three pantograph linkages, an amplification of the ac-tuators displacements is achieved. Therefore, equipped with the same actuators, the mobile platform of the Pantopteron moves many-times faster than that of the Tripteron. This amplification is defined by the magnification factor of the pantograph linkages. The kinematics, workspace and constraint singularities of the proposed parallel robot are studied in detail. Design considerations are also discussed and a possible prototype is illustrated.

Self Motions of the Pantopteron

International audienceIn this paper, the self motions of a novel 3-DOF fully de-coupled translational parallel robot, called the Pantopteron, are presented. The Pantopteron is similar to the well-known Car-tesian parallel manipulator (Tripteron), but due to the use of pantograph linkages, an amplification effect is achieved. Therefore, equipped with the same actuators, the mobile platform of the Pantopteron moves faster than that of the Trip-teron. This amplification is defined by the magnification factor of the pantograph linkages. The self motions are probably the most critical types of singularities a manipulator can meet. Therefore it is of utmost importance to have a good knowledge of them. Design considerations are also discussed in order to create Pantopterons without self motions

Singularity Analysis of Zero-Torsion Parallel Mechanisms

International audienceThis paper presents the singularity analysis of four 3-DOF symmetric zero-torsion parallel mechanisms. These mechanisms are composed of three identical legs ending with a spherical joint that is constrained to move in one of three equally spaced plane intersecting at one line. The computation of the singularity loci is based on the degeneracy of the system of screws applied on the platform by the legs. The whole study is based on the use of a special orientation representation, previously introduced under the name of Tilt-and-Torsion angles. This representation is briefly introduced. Then the interdependence between the Cartesian coordinates of the general class of parallel mechanisms is derived. Finally, the singularity loci are derived and the size of the workspace taking into account all singular configurations is shown

Pantopteron-4: a New 3T1R Decoupled Parallel Manipulator for Pick-and-Place Applications

International audienceIn this paper, a novel 4-DOF decoupled parallel manipulator with Schoenflies motions, called the Pantopteron-4, is presented. This manipulator is able to perform the same movements as the Isoglide4 or the Quadrupteron, but, due to its architecture which is made of three pantograph linkages, an amplification of the movements between the actuators and the platform displacements is achieved. Therefore, having the same actuators for both robots, the Pantopteron-4 displaces (theoretically) many-times faster than the Isoglide4 or the Quadrupteron, depending on the magnification factor of the pantograph linkages. Thus, this mechanism is foreseen to be used in applications where the velocities and accelerations have to be high, as in pick-and-place. First, the kinematics of the Pantopteron-4 is presented. Then, its workspace is analyzed. Finally, a prototype of the mechanism is shown and conclusions are given

Changing Assembly Modes without Passing Parallel Singularities in Non-Cuspidal 3-R\underline{P}R Planar Parallel Robots

This paper demonstrates that any general 3-DOF three-legged planar parallel robot with extensible legs can change assembly modes without passing through parallel singularities (configurations where the mobile platform loses its stiffness). While the results are purely theoretical, this paper questions the very definition of parallel singularities.Comment: 2nd International Workshop on Fundamental Issues and Future Research Directions for Parallel Mechanisms and Manipulators, Montpellier : France (2008

Optimum Static Balancing of a Parallel Robot for Medical 3D-Ultrasound Imaging

International audienceStatic balancing of mechanical systems is useful and required in many situations. The objective of such balancing is the compensation of gravitational forces in order to achieve a static equilibrium. A balanced system becomes safer and actuators are reduced in size. However, balancing a system requires numerous complex mechanical add-ons or unavoidable addition of mass. This is the reason why methods of partial static balancing have been developed and applied in practice. In this paper, a newly designed parallel robot for medical 3D-ultrasound imaging is required to be statically balanced without complicated design modifications. Simple mechanical add-on that is optimally designed can reduce substantially the effect of gravity. The efficiency of these suggested solutions is illustrated by numerical simulation of the robot