Simon Foucault

Parallel Mechanisms of the Multipteron Family: Kinematic Architectures and Benchmarking

This paper is a contribution to an invited session on the benchmarking of parallel mechanisms. The aim of the session is to compare different existing designs and prototypes of parallel mechanisms using a common set of benchmarking criteria. First, the kinematic architectures of parallel mechanisms of the multipteron family are presented. In addition to the tripteron and the quadrupteron, the pentapteron, a five-degree-of-freedom (dof) parallel mechanism is introduced. Then, the benchmarking criteria are applied to the prototypes of the tripteron (3-dof) and the quadrupteron (4-dof) prototypes. Although the tripteron and quadrupteron parallel mechanisms have been presented elsewhere, their properties, highlighted by the benchmarking analysis presented here are revealed for the first time.

Dynamic trajectory planning of a two-DOF cable-suspended parallel robot

This paper presents a trajectory planning approach for cable-suspended parallel mechanisms. A planar two-degree-of-freedom parallel mechanism is used for the analysis. Based on the dynamic model of the suspended robot, a set of algebraic inequalities is obtained that represents the constraints on the cable tensions. Parametric Cartesian trajectories are then defined and substituted into the constraints in order to obtain global conditions on the trajectory parameters which ensure that the trajectories are feasible. Special frequencies arise from the equations that are akin to natural frequencies of pendulum-type systems. An experimental validation is also presented using a two-dof prototype. The proposed trajectory planning approach can be used to plan dynamic trajectories that go beyond the static workspace of the mechanism, thereby opening novel applications and possibilities for cable-suspended robots.

Synthesis, Design, and Prototyping of a Planar Three Degree-of-Freedom Reactionless Parallel Mechanism

This paper addresses the dynamic balancing of a planar three-degree-of-freedom parallel mechanism. A mechanism is said to be dynamically balanced if for any motion of the mechanism, the reaction forces and torques at the base are identically equal to zero, at all times. The proposed mechanism is based on legs consisting of five-bar parallelogram linkages. The balancing equations are first obtained. Then, optimization is used in order to minimize the mass and inertia of the moving links. Finally, a numerical verification of the dynamic balancing is provided and the prototype is presented.

A Friendly Beast of Burden: A Human-Assistive Robot for Handling Large Payloads

This article presents a novel robotic assistive device for the handling of large payloads. The design of the robot is based on the application of the following fundamental mechanical principles: inertia is minimized, a parallel closed-loop cable/belt routing system is used to kinematically decouple the transmission from fixed actuators and to the end-effector, and variable static balancing is used to minimize the actuation forces required for vertical motion. As a result, the device requires only low power, thereby improving safety, and can be operated manually, even in the event of a power failure (with minimum backup power for brake release). A novel force/torque sensor is also introduced along with a control algorithm based on variable admittance that provides a very intuitive interface for physical human-robot cooperation. Finally, a full-scale prototype integrating all of the above concepts is presented.

Dynamic Point-to-Point Trajectory Planning of a Three-DOF Cable-Suspended Parallel Robot

This paper presents two trajectory-planning approaches for the point-to-point motion of planar two-degree-of-freedom (dof) cable-suspended parallel mechanisms. The proposed techniques can be used to plan trajectories that extend beyond the static workspace of the mechanism. Trajectories are specified as a list of target points that must be reached in sequence, with a zero velocity at each of the target points. In the first technnique, polynomial trajectories are designed to connect the target points, while the second approach uses trigonometric functions. Both techniques ensure continuity of the accelerations. Based on the dynamic model of the robot, algebraic inequalities are obtained that represent the constraints on cable tensions. These inequalities are used to determine the feasibility of the planned trajectories. Polynomial trajectories must be discretized in order to verify feasibility, while trajectories that are based on trigonometric functions can be verified globally, based on a set of simple algebraic equations. Example trajectories are given in order to illustrate the approach. An experimental validation is also presented using a two-dof prototype, and two video extensions are provided to demonstrate the results.

A Cable-Suspended Intelligent Crane Assist Device for the Intuitive Manipulation of Large Payloads

This paper presents a cable-suspended crane system to assist operators in moving and lifting large payloads. The main objective of this work is to develop a simple and reliable system to help operators in industry to be more productive while preventing injuries. The system is based on the development of a precise and reliable cable angle sensor and a complete dynamic model of the system. Adaptive horizontal and vertical controllers designed for direct physical human-robot interaction are then proposed. Different techniques are then proposed to estimate the payload acceleration in order to increase the controller performances. Finally, experiments performed on a full-scale industrial system are presented.

On the Development of a Planar 3-DOF Reactionless Parallel Mechanism

This paper addresses the dynamic balancing of a planar three-degree-of-freedom (DOF) parallel mechanism. A mechanism is said to be dynamically balanced if, for any motion of the mechanism, the reaction forces and torques at the base are identically equal to zero, at all times. The proposed mechanism is based on legs consisting of five-bar parallelogram linkages. The balancing equations are first obtained. Then, optimization is used in order to minimize the mass and inertia of the moving links. Finally, a numerical verification of the dynamic balancing is provided and the prototype is presented.Copyright

Experimental Determination of the Accuracy of a Three-Dof Cable-Suspended Parallel Robot Performing Dynamic Trajectories

The experimental determination of the accuracy of a three-degree-of-freedom (three-dof) spatial cable-suspended parallel robot is addressed in this paper. The concept of the dynamic trajectory planning of a three-dof spatial cable-suspended parallel robot is first briefly recalled. Then, periodic trajectories are planned and an external three-dimensional measurement system is used to determine the actual trajectory of the end-effector. Linear regression is used to fit the measured trajectory with the planned trajectory and eliminate the bias error. The accuracy of the trajectories is then assessed.

uMan: A Low-Impedance Manipulator for Human–Robot Cooperation Based on Underactuated Redundancy

This paper revisits the concept of underactuated manipulator in order to significantly improve physical human–robot cooperation for the assembly industry. The main focus is to achieve intuitive and minimum effort fine manipulation, regardless of the payloads shape and weight. An underactuated manipulator—referred to as uMan—based on a macro–mini architecture is designed with a novel passive mini mechanism, which aims at minimizing the impedance, eliminating the nonlinear impedance, and decoupling the human and robot dynamics. A specific control strategy is developed to achieve these objectives, while handling the underactuated nature of the robot for cooperative and autonomous assistance. Experimental validations are provided to assess the ease of fine manipulation using a peg-in-hole task to demonstrate the safety of the device using an effective collision detection and to establish the viability of the concept for practical industrial assembly tasks.