Alexandre Lecours

Variable admittance control of a four-degree-of-freedom intelligent assist device

Robots are currently used in some applications to enhance human performance and it is expected that human/robot interactions will become more frequent in the future. In order to achieve effective human augmentation, the cooperation must be very intuitive to the human operator. This paper presents a variable admittance control approach to improve system intuitivity. The proposed variable admittance law is based on the inference of human intentions using desired velocity and acceleration. Stability issues are discussed and a controller design example is given. Finally, experimental results obtained with a full-scale prototype of an intelligent assist device are presented in order to demonstrate the performance of the algorithm.

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.

Computed-Torque Control of a Four-Degree-of-Freedom Admittance Controlled Intelligent Assist Device

Robots are used in different applications to enhance human performance and in the future, these interactions will become more frequent. In order to achieve this human augmentation, the cooperation must be very intuitive to the human operator. This paper proposes a computed-torque control scheme for pHRI using admittance control. The admittance model is first introduced. Then, the robot identification, the computed-torque approach and the saturation considerations are addressed. The intelligent assist device used for the experiments is then presented. Finally, experimental results that demonstrate the performance of the algorithm are provided.

Design and experimental validation of planar programmable inertia generators

This paper investigates the design and experimental development of planar programmable inertia generators. An inertia generator is a hand-held haptic device that has a programmable inertia. By moving internal masses in reaction to accelerations induced by the user, the effective inertia of the device is modified in order to render a prescribed inertia. In this paper, a one-degree-of-freedom device with one internal moving mass is first proposed. The corresponding dynamic model is developed and the rendering capabilities of the device are investigated. Then, a controller is designed to produce the appropriate motion of the internal mass in reaction to the acceleration induced by the user. A prototype is presented and experimental results are discussed. A mechanical architecture is then proposed for the design of a planar three-degree-of-freedom inertia generator. The corresponding dynamic model is derived, and it is shown that the generalized inertia matrix of the proposed mechanism is always of full rank. The rendering capabilities of the device are also investigated. Finally, simulation results obtained with the three-degree-of-freedom inertia generator are reported and discussed.

On the Development of a Programmable Inertia Generator

This paper presents a preliminary investigation on a one-degree-of-freedom programmable inertia generator. An inertia generator is a hand-held haptic device that has a programmable inertia. By moving internal masses in reaction to accelerations induced by the user, the effective intertia of the device is modified in order to render a prescribed perceived inertia. In this paper, a one-degree-of-freedom device with one internal moving mass is proposed. The dynamic modelling of the system is first presented. Then, a controller is designed to produce the appropriate motion of the internal mass in reaction to the acceleration induced by the user. A prototype is presented and experimental results are discussed.

Reactionless Two-Degree-of-Freedom Planar Parallel Mechanism With Variable Payload

A reactionless mechanism is one which does not exert any reaction force or moment on its base at all times, for any arbitrary trajectory of the mechanism. This paper addresses the static and dynamic balancing of a two-degree-of-freedom parallel planar mechanism (five-bar mechanism). A simple and effective adaptive balancing method is presented that allows the mechanism to maintain the reactionless condition for a range of payloads. Important proofs concerning the balancing of five-bar mechanisms are also presented. The design of a real mechanism where parallelogram linkages are used to produce pure translations at the end-effector is also presented. Finally, using dynamic simulation software, it is shown that the mechanism is reactionless for arbitrarily chosen trajectories and for a variety of payloads.Copyright