Lionel Birglen

Kinetostatic analysis of underactuated fingers

The aim of this paper is to establish a fundamental basis for the analysis of underactuated fingers with a general approach. A new method to obtain the force capabilities of any underactuated fingers will be presented. Force capability is defined as the ability to generate an external wrench onto a fixed object with a given set of phalanges. This method is based on the introduction of two new matrices which completely describe the relationship between the input torque of the finger actuator(s) and the contact forces on the phalanges. Using this tool, one can study the conditions under which certain phalanx forces vanish, and compare different underactuation mechanisms with a rigorous approach.

SHaDe, a new 3-DOF haptic device

This paper presents a new type of haptic device using spherical geometry. The basic idea of haptic devices is to provide users with feedback information on the motion and/or force that he or she generates. Haptic devices have several potential applications such as, for example, fine compliant assembly, VR environment simulation, and high-precision teleoperation, especially in hazardous or hostile areas. The particular architecture of the spherical haptic device developed here will be presented and its advantages will be highlighted. Then, its basic kinematic properties, which shall be used for control and geometric optimization purposes, will be reviewed. The design optimization itself will then highlight some important features of the mechanism. The control scheme and real-time force feedback issues will then be presented. Finally, the results obtained with the prototype will be discussed.

Geometric Design of Three-Phalanx Underactuated Fingers

This paper studies the grasp stability of two classes of threephalanx underactuated fingers with transmission mechanisms based on either linkages or tendons and pulleys. The concept of underactuation in roboticfingers—with fewer actuators than degrees of freedom (DOF)—allows the hand to adjust itself to an irregularly shaped object without complex control strategy and sensors. With an-phalanx finger,n contacts (one for each phalanx) are normally required to statically constrain the finger. However, some contact forces may be lacking due to either the transmission mechanism, or simply the object size and position. Thus, one may define an i th order equilibrium, when the finger is in static equilibrium withi missing contacts. In this paper, the case for which n = 3 is studied with a particular emphasis on the cases for which i = 1 and i = 2. The fact that some contact forces do not appear or are negative, can lead in some cases to the ejection of the object from the hand, when no equilibrium configuration is achieved.

On the force capability of underactuated fingers

This paper studies the force capability of a particular class of underactuated fingers. Force capability is defined as the ability to create an external wrench onto a fixed object. The concept of the underactuation in robotic fingers, with fewer actuators than degrees of freedom (DOF) through the use of springs and the mechanical limits, allows the hand to adjust itself to an irregularly shaped object without complex control strategy and numerous sensors. However, in some configurations, the force distribution in an underactuated finger can degenerate. The finger can no longer apply forces on the object, leading in some cases to the ejection of the latter from the hand. This paper focuses on a 2-DOF finger and studies its ability to seize objects with a secure grasp.

Force Analysis of Connected Differential Mechanisms: Application to Grasping

In this paper, a methodology is proposed for the analysis of the force capabilities of connected differential mechanisms. These systems are the key elements used to extend the principle of underactuation in grasping from the fingers to the hand itself. The concept of under-actuation in robotic grasping—with fewer actuators than degrees of freedom (DOF)—allows the hand to adjust itself to an irregularly shaped object without complex control strategies and sensors. Several technological solutions have been proposed in the past but no theoretical background has been provided to analyze their characteristics, especially with respect to the forces generated. The purpose of this paper is to provide such a theoretical foundation and to illustrate its usefulness with examples applied to grasping. First, several differential elements are presented and studied. Second, a mathematical method to obtain the output force capabilities of connected differential mechanisms is presented. Finally, the technique presented is applied to two types of underactuated robotic hands.

Design of an Underactuated Compliant Gripper for Surgery Using Nitinol

This paper presents the development of an underactuated compliant gripper using a biocompatible superelastic alloy, namely, nitinol. This gripper has two fingers with five phalanges each and can be used as the end-effector of an endoscopic instrument. Optimization procedures are required to obtain the geometry of the transmission mechanism because of its underactuated nature and its underlying complexity. A driving mechanism further incorporated in the gripper to distribute actuation to both fingers and accomplish the grasping of asymmetrical objects without requiring supplementary inputs is also discussed. Finally, the results of numerical simulations with different materials and different grasped objects are presented and discussed.

Simulation of friction stir welding using industrial robots

– The purpose of this paper is to establish a model‐based framework allowing the simulation, analysis and optimization of friction stir welding (FSW) processes of metallic structures using industrial robots, with a particular emphasis on the assembly of aircraft components made of aerospace aluminum alloys., – After a first part of the work dedicated to the kinetostatic and dynamical identification of the robotic mechanical system, a complete analytical model of the robotized process is developed, incorporating a dynamic model of the industrial robot, a multi‐axes macroscopic visco‐elastic model of the FSW process and a force/position control unit of the system. These different modules are subsequently implemented in a high‐fidelity multi‐rate dynamical simulation., – The developed simulation infrastructure allowed the research team to analyze and understand the dynamic interaction between the industrial robot, the control architecture and the manufacturing process involving heavy load cases in different process configurations. Several critical process‐induced perturbations such as tool oscillations and lateral/rotational deviations are observed, analyzed, and quantified during the simulated operations., – The presented simulation platform will constitute one of the key technology enablers in the major research initiative carried out by NRC Aerospace in their endeavor to develop a robust robotic FSW platform, allowing both the development of optimal workcell layouts/process parameters and the validation of advanced real‐time control laws for robust handling of critical process‐induced perturbations. These deliverables will be incorporated in the resulting robotic FSW technology packaged for deployment in production environments., – The paper establishes the first model‐based framework allowing the high‐fidelity simulation, analysis and optimization of FSW processes using serial industrial robots.

Type Synthesis of Linkage-Driven Self-Adaptive Fingers

This paper aims at providing a method to synthesize mechanical architectures of self-adaptive robotic fingers driven by linkages. Self-adaptive mechanisms are used in robotic fingers to provide the latter with the ability to adjust themselves to the shape of the object seized without any dedicated electronics, sensor, or control. This type of mechanisms has been known for centuries but the increased capabilities of digital systems have kept them in the shadows. Recently, because of the lack of commercial and industrial success of complex robotic hands, self-adaptive mechanisms have attracted much more interest from the research community and several prototypes have been built. Nevertheless, only a handful of prototypes are currently known. It is the aim of this paper to present a methodology that is able to generate thousands of self-adaptive robotic fingers driven by linkages with two and three phalanges. First, potential kinematic architectures are synthesized using a well-known technique. Second, the issue of proper actuation and passive element(s) selection and location is addressed.

Synthesis of Differentially Driven Planar Cable Parallel Manipulators

In this paper, the idea of using cable differentials in the architecture of planar cable-driven parallel robots is introduced. Cable differentials are a type of mechanisms with several outputs driven by a single input. Using them in cable parallel manipulators can decrease their cost and control complexity. However, due to their kinematic constrains, cable differentials cannot be arbitrarily used in the design of these manipulators. Thus, a synthesis method is proposed to tackle this issue. First, the general requirements and characteristics of differentially driven planar cable mechanisms are reviewed. Then, the advantages of using these differentials instead of typically actuated cables are shown through a comparison between differentially actuated planar cable robots and fully actuated ones. The results reveal that with the same number of actuators, using differentials may lead to larger workspaces and improved kinetostatic properties. Subsequently, the systematic synthesis of differentially driven planar cable mechanisms is presented. For this, a method to find the different arrangements of q cables in a differential is proposed. Then, valid arrangements with 2, 3, and 4 cables are investigated. Finally, several differential actuation schemes are considered and all possible differentials with q=2, 3, and 4 cables are found.

A compliant self-adaptive gripper with proprioceptive haptic feedback

Grippers and robotic hands are an important field in robotics. Recently, the combination of grasping devices and haptic feedback has been a promising avenue for many applications such as laparoscopic surgery and spatial telemanipulation. This paper presents the work behind a new self-adaptive, a.k.a. underactuated, gripper with a proprioceptive haptic feedback in which the apparent stiffness of the gripper as seen by its actuator is used to estimate contact location. This system combines many technologies and concepts in an integrated mechatronic tool. Among them, underactuated grasping, haptic feedback, compliant joints and a differential seesaw mechanism are used. Following a theoretical modeling of the gripper based on the virtual work principle, the authors present numerical data used to validate this model. Then, a presentation of the practical prototype is given, discussing the sensors, controllers, and mechanical architecture. Finally, the control law and the experimental validation of the haptic feedback are presented.