Showing papers by "Damien Chablat published in 2020"

A Translational Three-Degrees-of-Freedom Parallel Mechanism With Partial Motion Decoupling and Analytic Direct Kinematics

Abstract: According to the topological design theory and method of parallel mechanism (PM) based on position and orientation characteristic (POC) equations, this paper studied a 3-DOF translational PM that has three advantages, i.e., (i) it consists of three fixed actuated prismatic joints, (ii) the PM has analytic solutions to the direct and inverse kinematic problems, and (iii) the PM is of partial motion decoupling property. Firstly, the main topological characteristics, such as the POC, degree of freedom and coupling degree were calculated for kinematic modeling. Thanks to these properties, the direct and inverse kinematic problems can be readily solved. Further, the conditions of the singular configurations of the PM were analyzed which corresponds to its partial motion decoupling property.

A Translational Three-Degrees-of-Freedom Parallel Mechanism With Partial Motion Decoupling and Analytic Direct Kinematics

Abstract: According to the topological design theory and method of parallel mechanism (PM) based on position and orientation characteristic (POC) equations, this paper studied a 3-DOF translational PM that has three advantages, i.e., (i) it consists of three fixed actuated prismatic joints, (ii) the PM has analytic solutions to the direct and inverse kinematic problems, and (iii) the PM is of partial motion decoupling property. Firstly, the main topological characteristics, such as the POC, degree of freedom and coupling degree were calculated for kinematic modeling. Thanks to these properties, the direct and inverse kinematic problems can be readily solved. Further, the conditions of the singular configurations of the PM were analyzed which corresponds to its partial motion decoupling property.

Stiffness Analysis of a New Tensegrity Mechanism Based on Planar Dual-triangles

Abstract: The paper deals with the stiffness analysis and stability study of a new type of tensegrity mechanism based on dual-triangle structures, which actuated by adjusting elastic connections between the triangle edges. For a single segment of such mechanism, the torque-deflection relation was obtained as a function of control inputs and geometric parameters. It was proved that a single section of the mechanism can has either a single or three equilibrium configurations that can be both stable and unstable. Corresponding conditions of stability were found allowing user to choose control inputs ensuring the mechanism controllability, and the obtained results are confirmed by the simulation examples. The structure composed of two segments in serial was also analysed and an equivalent serial structure with non-linear virtual springs in the joints was proposed. It was proved that the stiffness of such structure decreases while the external loading increases, which may lead to the buckling phenomenon.

A bio-inspired 3-DOF light-weight manipulator with tensegrity X-joints *

Abstract: This paper proposes a new kind of light-weight manipulators suitable for safe interactions. The proposed manipulators use anti-parallelogram joints in series, referred to as X-joints. Each X-joint is remotely actuated with cables and springs in parallel, thus realizing a tensegrity one-degree-of-freedom mechanism. As compared to manipulators built with simple revolute joints in series, manipulators with tensegrity X-joint offer a number of advantages, such as an intrinsic stability, variable stiffness and lower inertia. This new design was inspired by the musculosleketon architecture of the bird neck that is known to have remarkable features such as a high dexterity. The paper analyzes in detail the kinetostatics of a X-joint and proposes a 3-degree-of-freedom manipulator made of three such joints in series. Both simulation results and experiment results conducted on a test-bed prototype are presented and discussed.

The Stability and Stiffness Analysis of a Dual-Triangle Planar Rotation Mechanism

Abstract: The paper deals with the stiffness analysis and stability study of equilibrium configurations for dual-triangle tensegrity mechanism, which is actuated by adjusting elastic connections between the triangle edges. For this mechanism, the torquedeflection relation was obtained as a function of control inputs and geometric parameters. It was proved that the mechanism can has either a single or three equilibrium configurations that can be both stable and unstable. Corresponding conditions of stability were found allowing user to choose control inputs ensuring the mechanism controllability. The obtained results are confirmed by the simulation examples presented in the paper.

A new RCM mechanism for an ear and facial surgical application

Abstract: Since the insertion area in the middle ear or in the sinus cavity is very narrow, the mobility of the endoscope is reduced to a rotation around a virtual point and a translation for the insertion of the camera This article first presents the anatomy of these regions obtained from 3D scanning and then a mechanism based on the architecture of the agile eye coupled to a double parallelogram to create an RCM This mechanism coupled with a positioning mechanism is used to handle an endoscope This tool is used in parallel to the surgeon to allow him to have better rendering of the medium ear than the use of Binocular scope The mechanism offers a wide working space without singularity whose borders are fixed by joint limits This feature allows ergonomic positioning of the patient's head on the bed as well as for the surgeon and allows other applications such as sinus surgery

Shaking Force Balancing of the Delta Robot

Abstract: The paper deals with the shaking force balancing of the DELTA robot. The balancing of the shaking force of the DELTA robot is carried out through the center of mass acceleration minimization. The trajectories of the total mass center of moving links are defined as straight lines between the initial and final positions of the platform. Then, the motion between these positions are parameterized with "bang-bang" motion profiles. Such a motion generation allows the reduction of the maximal value of the center of mass acceleration and, consequently, leads to the reduction in the shaking force. A main advantage of this method is its simplicity and versatility. It is carried out without any modification of mass redistribution of the initial robot structure, i.e. without adding counterweights. In the case of changing trajectories or payloads, it is just necessary to provide the initial and final positions of the platform, calculate the input parameters according to the proposed method and implemented them in the robot control system. Numerical simulations illustrate the efficiency of the suggested approach.

Mechanics of compliant serial manipulator composed of dual-triangle segments

Abstract: The paper focuses on the mechanics of a compliant serial manipulator composed of new type of dual-triangle elastic segments. Both the analytical and numerical methods were used to find the manipulator stable and unstable equilibrium configurations, as well as to predict corresponding manipulator shapes. The stiffness analysis was carried on for both loaded and unloaded modes, the stiffness matrices were computed using the Virtual Joint Method (VJM). The results demonstrate that either buckling or quasi-buckling phenomenon may occur under the loading, if the manipulator corresponding initial configuration is straight or non-straight one. Relevant simulation results are presented that confirm the theoretical study.

Joint Space and Workspace Analysis of a 2-DOF Spherical Parallel Mechanism

Abstract: This paper deals with the joint space and workspace analysis of a two degree of freedom spherical parallel mechanism designed to be used to handle an endoscope. This mechanism is composed of the three legs (2USP-U) to connect the base to a moving platform. As the manipulator can get up to six solutions to the direct kinematic problem (DKP) in four aspects, non-singular assembly modes changing trajectories may exist. The aim of the paper is to check whether a regular workspace centred on home pose can be defined in such a way that no such trajectory exists in this workspace.

Safety in a Human Robot Interactive: Application to Haptic Perception

Abstract: Usually, traditional haptic interfaces, such as Virtuose 6DOF [1], are used in the design phases by engineers [2]. Such interfaces are safe. However, the user can apply a force/torque but cannot really feel textures and appreciate material quality. These interfaces have a limited workspace, low stiffness and are very expensive. New haptic interfaces using an industrial robots or a cobot (robots specially designed to work in Human-Robot environments) can be used as a haptic interface with intermittent contacts [3, 4]. For application considered in this paper, the cobot carries several specimens of texture on its end-effector, to allow contact between a finger of the user and the robot.

A New RCM Mechanism for an Ear and Facial Surgical Application

Abstract: Since the insertion area in the middle ear or in the sinus cavity is very narrow, the mobility of the endoscope is reduced to a rotation around a virtual point and a translation for the insertion of the camera. This article first presents the anatomy of these regions obtained from 3D scanning and then a mechanism based on the architecture of the agile eye coupled to a double parallelogram to create an RCM. This mechanism coupled with a positioning mechanism is used to handle an endoscope. This tool is used in parallel to the surgeon to allow him to have better rendering of the medium ear than the use of Binocular scope. The mechanism offers a wide working space without singularity whose borders are fixed by joint limits. This feature allows ergonomic positioning of the patient’s head on the bed as well as for the surgeon and allows other applications such as sinus surgery.

Branch-and-Bound Method for Just-in-Time Optimization of Radar Search Patterns

Abstract: Set covering is a well-known problem in combinatorial optimization. The objective is to cover a set of elements, called the universe, using a minimum number of available covers. The theoretical problem is known to be generally NP-difficult to solve [1], and is often encountered in industrial processes and real-life problem. In particular, the mathematical formulation of the set cover problem is well-suited for radar search pattern optimization of modern radar systems.

Singularity and workspace analysis of 3-SPS-U and 4-SPS-U tensegrity mechanisms

Abstract: This article analyzes the singularities and workspace of two tensegrity mechanisms that employ a passive universal joint and either three or four tension springs These two architectures are correlated to 3-SPS-U and 4-SPS-U parallel mechanisms for determining their geometric equations By fixing the limits of prismatic joints, the workspace for the mechanisms is generated and the parallel singularities are analyzed Based on the singularity boundaries obtained from the workspace, the joint limits are modified to generate the maximal singularity free workspaces for both the architectures A comparison is done based on the tilt limits obtained from the workspace of the mechanisms The mechanism with the maximum tilt limits is implemented for a piping inspection robot to pass through pipe bends and junctions

Shaking Force Balancing of the Orthoglide

Abstract: The shaking force balancing is a well-known problem in the design of high-speed robotic systems because the variable dynamic loads cause noises, wear and fatigue of mechanical structures. Different solutions, for full or partial shaking force balancing, via internal mass redistribution or by adding auxiliary links were developed. The paper deals with the shaking force balancing of the Orthoglide. The suggested solution based on the optimal acceleration control of the manipulator's common center of mass allows a significant reduction of the shaking force. Compared with the balancing method via adding counterweights or auxiliary substructures, the proposed method can avoid some drawbacks: the increase of the total mass, the overall size and the complexity of the mechanism, which become especially challenging for special parallel manipulators. Using the proposed motion control method, the maximal value of the total mass center acceleration is reduced, as a consequence, the shaking force of the manipulator decreases. The efficiency of the suggested method via numerical simulations carried out with ADAMS is demonstrated.

Investigation of the Stresses Exerted by an Exosuit of a Human Arm

Abstract: If a wheelchair could be considered as a better solution than an exoskeleton for the mobility of people suffering from neuromuscular diseases, there is a relevance to use a soft wearable exoskeleton (or exosuit) to assist the upper limbs in order to perform daily tasks such as having a drink, a pencil. It is imperative to limit the stresses generated by the exosuit on human. Numerical tests are proposed to investigate the possible technology choices to design the exoskeleton to limit these stresses. These numerical tests are based on the study of the inverse dynamic model of the human arm and its exosuit. A trajectory of the hand is defined and we deduce the cable tension to track this trajectory. Two decoupled planes are considered for the numerical tests, the sagittal plane where a flexion of the forearm with respect to the upper arm, and the frontal plane where abduction and adduction movements are possible. We assume that the human arm cannot provide any effort. The results show that the position of the anchor points at the shoulder and the orientation of the cable for the abduction movement have an influence to limit the stresses. However, these stresses are important on the shoulder.

Evaluating the Effect of Crutch-using on Trunk Muscle Loads

Abstract: As a traditional tool of external assistance, crutches play an important role in society. They have a wide range of applications to help either the elderly and disabled to walk or to treat certain illnesses or for post-operative rehabilitation. But there are many different types of crutches, including shoulder crutches and elbow crutches. How to choose has become an issue that deserves to be debated. Because while crutches help people walk, they also have an impact on the body. Inappropriate choice of crutches or long-term misuse can lead to problems such as scoliosis. Previous studies were mainly experimental measurements or the construction of dynamic models to calculate the load on joints with crutches. These studies focus only on the level of the joints, ignoring the role that muscles play in this process. Although some also take into account the degree of muscle activation, there is still a lack of quantitative analysis. The traditional dynamic model can be used to calculate the load on each joint. However, due to the activation of the muscle, this situation only causes part of the load transmitted to the joint, and the work of the chair will compensate the other part of the load. Analysis at the muscle level allows a better understanding of the impact of crutches on the body. By comparing the levels of activation of the trunk muscles, it was found that the use of crutches for walking, especially a single crutch, can cause a large difference in the activation of the back muscles on the left and right sides, and this difference will cause muscle degeneration for a long time, leading to scoliosis. In this article taking scoliosis as an example, by analyzing the muscles around the spine, we can better understand the pathology and can better prevent diseases. The objective of this article is to analyze normal walking compared to walking with one or two crutches using OpenSim software to obtain the degree of activation of different muscles in order to analyze the impact of crutches on the body.

Surgery assistance device

Abstract: A surgery assistance device (1) comprises means for offsetting a first type of rotation and a second type of rotation, a mechanism (40a) for transmitting a third type of rotation, a mechanism (40b) for transforming the third type of rotation into a translation and a resilient element (41) connected at one end to the mechanism (40a) for transmitting the third type of rotation. The mechanism (40a) for transmitting the third type of rotation is connected to a rotary motor, the rotation of the rotary motor in a first direction causing the lowering of a tool (5) and an extension of the resilient element, the rotation of the rotary motor in a second direction causing the raising of the tool (5) and a contraction of the resilient element, and when the tool (5) is in a lowered position and the rotary motor does not exert any torque, the resilient element (41) returns to an initial shape causing the raising of tool (5).

Evaluating the Effect of Crutch-Using on Trunk Muscle Loads

Abstract: Crutch is the most common tool for temporary or permanent ambulation assistance. Crutch-using transforms human kinematic chain, and therefore is hypothesized to have dynamical influence on the trunk. In this paper, two different crutch gaits were analyzed with regard to their associated risks of scoliosis. A numerical human-crutch model was constructed on the OpenSim software, then both unilateral crutch gait (denoted as single crutch walking) and bilateral crutch gait (denoted as double crutch walking) were simulated to represent the situation where ones’ right foot gets injured and bears 10% of body weight at most. The kinematics of one single moment in the weight-transferring phase were constructed through joint space. The inverse dynamics calculation and the static optimization algorithm were conducted to compute joints load and muscles activation level at this moment. Attentions were paid to eight muscle groups that are closely associated with the occurrence of scoliosis. As the results, the average muscle activation level of the eight muscle groups were 31% in the case of single crutch walking and 9% for the double crutch walking, as compared with 1% in a normal gait. Muscle activation asymmetry was more severe for single crutch gait than that of a double crutch gait. It is suggested that the unilateral crutch walking brings higher risk of scoliosis than the bilateral crutch walking in the partial weight bearing gaits.

Design of a Piping Inspection Robot by Optimization Approach

Abstract: This article presents an optimization approach for the design of an inspection robot that can move inside variable diameter pipelines having bends and junctions. The inspection robot uses a mechanical design that mimics the locomotion of a caterpillar. The existing prototype developed at LS2N, France is a rigid model that makes it feasible for working only inside straight pipelines. By the addition of a tensegrity mechanism between motor units, the robot is made reconfigurable. However, the motor units used in the prototype are oversized to pass through pipe bends or junctions. An optimization approach is employed to determine the dimensions of motors and their associated leg mechanisms that can overcome such bends. Two optimization problems are defined and solved in this article. The first problem deals with the determination of motor sizing without leg mechanisms. The second problem deals with the determination of sizing of the leg mechanism with respect to the dimensions of motor units obtained from the first problem. A 3D model of the optimized robot design is then realized using CAD software.

Shaking Force Balancing of the Orthoglide

Abstract: The shaking force balancing is a well-known problem in the design of high-speed robotic systems because the variable dynamic loads cause noises, wear and fatigue of mechanical structures. Different solutions, for full or partial shaking force balancing, via internal mass redistribution or by adding auxiliary links were developed. The paper deals with the shaking force balancing of the Orthoglide. The suggested solution based on the optimal acceleration control of the manipulator’s common centre of mass allows a significant reduction of the shaking force. Compared with the balancing method via adding counterweights or auxiliary substructures, the proposed method can avoid some drawbacks: the increases of the total mass, the overall size and the complexity of the mechanism, which become especially challenging for special parallel manipulators. Using the proposed motion control method, the maximal value of the total mass centre acceleration is reduced, as a consequence, the shaking force of the manipulator decreases. The efficiency of the suggested method via numerical simulations carried out with ADAMS is demonstrated.