Jean-Pierre Merlet

• Doctor of Engineering
• Research Director at National Institute for Research in Computer Science and Control

A cable-driven parallel robot (CDPR) has n cables whose lengths are used to control the pose of the platform. We assume here that n > 6 and that the cables have elasticity and mass i.e. are sagging cables. In that case the inverse kinematics (IK, i.e. finding the cable lengths to reach a given platform pose) has usually an infinite number of soluti...

A cable-driven parallel robot (CDPR) has n cables whose lengths are used to control the pose of the platform. We assume here that n > 6 and that the cables have elasticity and mass i.e. are sagging cables. In that case the inverse kinematics (IK, i.e. finding the cable lengths to reach a given platform pose) has usually an infinite number of soluti...

A classical planar cable model has been presented in the Irvine textbook and is being used, for example, for the modeling of cable-driven parallel robot. It provides 2 equations involving parameters of the cable material, namely its Young modulus and its linear density, assumed here to be known, and 5 physical parameters namely the coordinates of o...

Direct kinematics (DK) is one of the most challenging problem for cable-driven parallel robot (CDPR) with sagging cables. Solving the DK in real-time is not an issue provided that a guess of the solution is available. But difficulties arise when all DK solutions have to be determined (e.g. in the design phase of the CDPR). Continuation and interval...

Sagging cable-driven parallel robots (CDPRs) are often modeled by using the Irvine's model. We will show that their configurations may be unstable, and moreover, that assessing the stability of the robot with the Irvine's model cannot be done by checking the spectrum of a stiffness matrix associated with the platform motions. In this article, we sh...

We are considering cable-driven parallel robot (CDPR), where the legs of the robot are constituted of cables that can be independently coiled/uncoiled. We show that whatever the size of the CDPR is we may have slack cables so that using a sagging cable model that takes into account both the mass and elasticity of the cables will improve the positio...

Cable-driven parallel robots (CDPR) use cables to move a platform. These cables can be coiled/uncoiled by winches and are all attached to the platform. We are considering here a specific class of CDPR, called N-1 which has N cables that are all attached to the platform at the same point B. With 2 cables we get a planar 2-dof robot while with N ≥ 3...

To overcome the physical limitations of mechanical bone cutting in minimally invasive surgery, we are developing a miniature parallel robot that enables positioning of a pulsed laser with an accuracy below 0.25 mm and minimizes the required manipulation space above the target tissue. This paper presents the design, control, device characteristics,...

Determining what will be the maximal cable tensions of a cable-driven parallel robot (CDPR) when it moves over a given workspace is an important step in the design phase as it will allow to choose the cable diameter and to provide a requested information for tuning the CDPR actuation. In this paper we consider a suspended N-1 CDPR with n cables whe...

Solving the kinematics of CDPR is complex as soon as cable sagging is taken into account. We are considering here CDPRs having 2 cables whose extremities are attached at the same point on the platform (i.e. CDPRs allowing only translational motion). Regarding the cables we assume that they are non-elastic but have a mass so that they will exhibit s...

Determining what will be the maximal cable tensions of a cable-driven parallel robot (CDPR) when it moves over a given workspace is an important step in the design phase as it will allow to choose the cable diameter and to provide a requested information for tuning the CDPR actuation. In this paper we consider a suspended N-1 CDPR with n cables whe...

Solving the kinematics of CDPR is complex as soon as cable sagging is taken into account. We are considering here CDPRs having 2 cables whose extremities are attached at the same point on the platform (i.e. CDPRs allowing only translational motion). Regarding the cables we assume that they are non-elastic but have a mass so that they will exhibit s...

We consider a 3 dof translational cable-driven parallel robot (CDPR) with 4 cables connected at the same point on the load. We assume that the CDPR has a small or medium size and uses synthetic cables so that the elasticity of the cable material is negligible. We will investigate the forward kinematics (FK) of such a CDPR (i.e. determining the CDPR...

The uncertainties arising from the fabrication and operation of mechanisms, specifically the four-bar linkage, significantly affect the expected performance of the mechanism. To accommodate uncertainties during the dimensional synthesis of the four-bar linkage, the desired coupler curve response is described by any number of precision point element...

Cable-Driven Parallel Robots (CDPRs) have been little used so far for collaborative tasks with humans. One reason is the lack of solutions to guarantee the safety of the operators in case of failure. Therefore, this paper aims to determine the possible failures of CDPRs when they are used for collaborative work with humans and to provide technical...

Positioning accuracy of cable-driven parallel robots is influenced by many factors such as geometry, actuator sensor accuracy and disturbances in the applied wrench. Another uncertainty source is the elasticity of the cables. While the influence of many factors may be decreased by calibration and/or sensor fusion, elasticity parameters are difficul...

Uncertainties are inherent in the fabrication and operation of mechanisms. In terms of the four-bar linkage, uncertainties in the geometric parameters result in non-exact solutions for the coupler point. A design description which accounts for bounded uncertainties is termed an appropriate design. Appropriate analysis routines are analysis routines...

Kinematics position problems in planar parallel continuum mechanisms, whose elements are elastic rods undergoing nonlinear large deformations, are ruled by a system of nonlinear differential equations. Under some conditions, those rods can be modelled as Kirchhoff rods whose equations can be solved using elliptic integrals. The resolution has to be...

Cable lengths is an important input for determining the state of a CDPR. Using drum with helical guide may be appropriate for small or medium-sized CDPR but are problematic for large one. Another issue is the initialization of the cable length as measurements based on drum rotation are incremental. We propose to address automatic initialization and...

This paper focuses on the problem of the initial-pose estimation by means of proprioceptive sensors (self-calibration) of suspended under-actuated Cable-Driven Parallel Robots (CDPRs). For this class of manipulators, the initial pose estimation cannot be carried out by means of forward kinematics only, but mechanical equilibrium conditions must be...

Cable model has a strong influence on the complexity of the kinematic analysis of cable-driven parallel robots (CDPR). The most complete elasto-static model relies on Irvine equation that takes into account both the elasticity and the deformation of the cable due to its own mass and has been shown to be very realistic. This model is complex, non al...

Although workspace is essential for the design and control of cable-driven parallel robots very few works have been devoted to this topic when sagging cables are considered, most probably because of the complexity of the cable model. In this paper we consider a CDPR with 6 sagging cables whose lengths have a limited maximal value. We propose an alg...

Cable model has a strong influence on the complexity of the kinematic analysis of cable-driven parallel robots (CDPR). The most complete model relies on Irvine equation that takes into account both the elasticity and the deformation of the cable due to its own mass and has been shown to be very realistic. This model is complex, non algebraic and nu...

Cable model has a strong influence on the complexity of the kinematic analysis of cable-driven parallel robots (CDPR). The most complete model relies on Irvine equation that takes into account both the elasticity and the deformation of the cable due to its own mass and has been shown to be very realistic. This model is complex, non algebraic and nu...

Finding the workspace of cable driven parallel robots (CDPR) with sagging cables (i.e. elastic and deformable cables) is a problem that has never been fully addressed in the literature as this is a complex issue: the inverse kinematics may have multiple solutions and the equations that describe the problem are non-linear and non algebraic. We addre...

Direct kinematics (DK) of cable-driven parallel robots (CDPR) based only on cable lengths measurements is a complex issue even with ideal cables and consequently even harder for more realistic cable models. A natural way to simplify the DK solving is to add sensors. We consider here sensors that give a partial or complete measurement of the cable d...

Although workspace is essential for the design and control of cable-driven parallel robots very few works have been devoted to this topic when sagging cables are considered, most probably because of the complexity of the cable model. In this paper we consider a CDPR with 6 sagging cables whose lengths have a limited maximal value. We propose an alg...

Solving the direct kinematics (DK) of cable-driven parallel robots (CDPR) based only on the cable length measurements is a demanding problem that is still not well mastered, especially for robots having sagging cables. A model-based approach may be used to solve this problem but the model parameters and measurements are uncertain, thereby leading t...

Uncertainties are an inherent element in all mechanisms, arising from the manufacturing and assembly process or even from the operation of the device. In terms of synthesis routines for mechanisms, uncertainties are generally neglected since they are difficult to account for. In this work, the concept of appropriate design is utilized to develop ro...

Cable-driven parallel robot (CDPR) have a kinematics that is usually complex as soon as there are possible deformation of the cable due to elasticity or cable mass. The classical approach to solve the kinematics in that case is to inject a cable model in the kinematics equations, that are then solved. According to the cable model this solving may b...

The aging of the population and its socio-economic consequences make it necessary to find new avenues to answer future problems. It appears that robotic assistance systems could offer a relevant answer, especially as the evolution of technologies today makes these new solutions credible. However the development of robotic assistance to the person m...

Direct kinematics (DK) of cable-driven parallel robots (CDPR) based only on cable lengths measurements is a complex issue even with ideal cables and consequently even harder for more realistic cable models such as sagging cable. A natural way to simplify the DK solving is to add sensors. We consider here sensors that give a partial or complete meas...

Direct kinematics (DK) of cable-driven parallel robots (CDPR) based only on cable lengths measurements is a complex issue even with ideal cables and consequently even harder for more realistic cable models. A natural way to simplify the DK solving is to add sensors. We consider here sensors that give a partial or complete measurement of the cable d...

Uncertainties are an inherent element in all mechanisms, arising from the manufacturing and assembly process or even from the operation of the device. In terms of synthesis routines for mechanisms, uncertainties are generally neglected since they are difficult to account for. In this work, the concept of appropriate design is utilized to develop ro...

This paper presents a method of designing variable structure control systems for robots. As the on-board robot computational resources are limited, but in some cases the demands imposed on the robot by the user are virtually limitless, the solution is to produce a variable structure system. The task dependent part has to be exchanged, however the t...

This paper addresses the simulation of the state of a discrete-time controlled cable-driven parallel robot (CDPR) with nondeformable or elastic cables over a given trajectory. Being given a CDPR, an arbitrary model for the coiling system and for the control strategy, we exhibit a simulation algorithm that allows one to determine, in a guaranteed wa...

Direct kinematics (DK) of parallel robots is most of the time a difficult problem. This is true for cable-driven parallel robots (CDPR) especially if cable deformations are taken into account. If the cable model, whatever it is, is introduced in the kinematic equations we always end up with a square system of equations that is usually very difficul...

Accounting for uncertainties in the design variables of a parallel manipulator is important for a reliable analysis of a mechanism. The design of the 3-RRR planar parallel manipulator is modelled with uncertainties. Interval analysis techniques are utilised to solve for the reachable workspace and the collision-free workspace. It is necessary to en...

Solving the direct kinematics (DK) of parallel robots, i.e. finding all the possible poses of the platform for given input values, is most of the time a difficult problem. This is evidently true for cable-driven parallel robots (CDPR) that are more complex than classical parallel robot because of the unilateral nature of the cable actions but also...

Accounting for manufacturing tolerances and uncertainties in the design specifications of a parallel manipulator are important for a reliable analysis of a mechanism. Given a task, described by a desired workspace and set of wrenches to be generated at the end-effector, it is necessary to ensure that a fabricated design can achieve the desired crit...

Cable-driven parallel robot (CDPR) have a kinematics that is usually complex as soon as there are possible deformation of the cable due to elasticity or cable mass. The classical approach to solve the kinematics in that case is to inject a cable model in the kinematics equations, that are then solved. According to the cable model this solving may b...

Accounting for manufacturing tolerances and uncertainties in the design specifications of a parallel manipulator are important for a reliable analysis of a mechanism. Given a task, described by a desired workspace and set of wrenches to be generated at the end-effector, it is necessary to ensure that a fabricated design can achieve the desired crit...

The motion of mechanisms, kinematics, is one of the most fundamental aspect of robot design, analysis and control but is also relevant to other scientific domains such as biome- chanics, molecular biology, . . . . The series of books on Advances in Robot Kinematics (ARK) report the latest achievement in this field. ARK has a long history as the fir...

It is a general truth that increase of age is associated with a level of mental and physical decline but unfortunately the former are often accompanied by social exclusion leading to marginalization and eventually further acceleration of the aging process. A new approach in alleviating the social exclusion of older people involves the use of assist...

Workspace calculation for cable-driven parallel robot (CDPR) differs from the one for robots with rigid legs as the main limiting factor is the satisfaction of the mechanical equilibrium, being given a model for the cable behavior. We are considering here 6-dof CDPR with n ≥ 6 cables and are investigating the calculation of horizontal cross-section...

This chapter presents an introduction to the kinematics and dynamics of parallel mechanisms, also referred to as parallel robots. As opposed to classical serial manipulators, the kinematic architecture of parallel robots includes closed-loop kinematic chains. As a consequence, their analysis differs considerably from that of their serial counterpar...

Cable-driven parallel robot (CDPR) are parallel robots that use coilable cables as legs. We are interested here in suspended CDPR for which there is no cable that exert a downward force on the platform. If we assume that the cables are mass-less and not elastic it has been shown that at a given pose whatever is the number m > 6 of cables there will...

This paper addresses the problem of the forward kinematics of cable-driven parallel robots (CDPR) having elastic or non elastic cables under the assumption that the cables are submitted to small changes in their lengths compared to an initial situation at which the pose is known, a situation that is typical of a real-time forward kinematics used fo...

This paper presents an efficient interval-analysis-based algorithm to solve the direct geometrico-static problem (DGP) of underconstrained cable-driven parallel robots (CDPRs). Solving the DGP for a generic CDPR consists of finding all possible equilibrium poses of the end effector for the given cable lengths. Since cables impose unilateral constra...

We consider in this paper cable driven parallel robot (CDPR) with m catenary cables that present a significant deformation due to their elasticity and own mass and we address the kinematics of such a robot uder the assumption of static state. We show that the inverse kinematics (IK) requires to solve a square system of equations if the robot has up...

The aim of RAPP project is to provide a software platform in order to support the creation and delivery of robotic applications (RApps) targeting people at risk of exclusion, especially older people.This paper describes the user requirements of one of the three pilots defined in RAPP: mobility assistance and activity monitoring scenario. Target use...

This paper addresses the concept of redundancy for cable-driven parallel robot (CDPR). We show that although CDPR may be considered as kinematically redundant, they constitute a special class for which the self-motion manifold is 0-dimensional and that they are not not statically redundant (i.e. the tension distribution cannot be changed continuous...

This paper presents a new nonintrusive device for everyday gait analysis and health monitoring. The system is a standard rollator equipped with encoders and inertial sensors. The assisted walking of \(25\) healthy elderly and \(23\) young adults are compared to develop walking quality index. The subjects were asked to walk on a straight trajectory...

Solving the forward kinematics (FK) of parallel robots is known to be a difficult task and the problem is even more complex for cable driven parallel robot (CDPR): the system of equations that has to be solved is larger than with rigid legs as first the static equations have to be taken into account and, second because the deformation of the cables...

This paper focuses on cable-suspended parallel robots (CSPRs), a subclass of cable-driven parallel robots, and particularly on the analysis of their workspace. CSPRs present, among other interesting characteristics, large workspaces and high reconfigurability, which make them attractive for a large variety of applications, especially for pick and p...

Marionet-Assist is a CDPR designed for transfer operations. Our crane robot has a configuration that provides three translational d.o.f.. Four wires are used to control the position of the end-effector, but as they have no elasticity, only three of them at most will be under tension. For a given position, different triplet of cables under tension a...

The main advantage of CDPRs is large workspaces. However, multiple legs and large workspace are both factors for interference. We consider a CDPR platform within a 6D workspace, and as sources of interference the collisions with the robot's environment and self interference. We present two algorithms and their interval analysis-based applications t...

Robots are controlled with a discrete-time controller that includes a high-level loop for motion control and a faster internal loop that controls the actuators. We intend to simulate the behavior of the whole chain for a cable-driven parallel robot (CDPR) with linear elastic cables and we will show that such a simulation cannot be performed using c...

Our objective is to extend the assistance functionalities of the cable-driven parallel robot Marionet-Assist, designed principally for transfer operation, by allowing it to grasp usual objects (knives, box of medicines, phone, ···) by using visual servoing. Our crane robot has a configuration that provides three translational d.o.f., and a camera w...

This paper addresses the concept of cable configuration of cable-driven parallel robots (CDPR). At a given pose a cable configuration describes the state of cables, i.e. under tension or slack, and plays a major role for the cable tensions and the platform positioning errors. Being given a CDPR with non-elastic cables and a model for the coiling sy...

The 2-2 wire-driven parallel crane is the most simple planar parallel crane actuated by wires with two wires connected at two different points on the platform. We present original contributions on the kinematics of such robot, namely full in-verse kinematics, trajectory, static and singularity analysis in the joint space.

The kinematics of wire-driven parallel robot (WDPR) is one of the most challenging problem of modern kinematics. We investigate here the kinematics of two robots with 3 and 4 wires, in a crane configuration, having specific location of the anchor point on the platform. The 4-3-1 robot has 4 wires, three of them being connected at the same anchor po...

Abstract: In this work, we present an improved biomechanical model of the knee and the muscle group involved to ensure the movement of extension of the knee joint, under an external load. The problem of redundancy is solved by presenting the problem as an optimization procedure. In order to identify the best objective function to be optimized, we c...

Clinical evaluation of frailty in the elderly is the first step to decide the degree of assistance they require. This evaluation is usually performed once and for all by filling standard forms with macro-information about standing and walking abilities. Advances in robotics make it possible to turn a standard assistance device into an augmented dev...

This paper studies the direct geometrico-static analysis of under-constrained cable-driven parallel robots with 3 cables. The task consists in finding all equilib-rium configurations of the end-effector when the cable lengths are assigned. An interval-analysis-based procedure is proposed to numerically find the real solutions of the problem for a r...

There are two main systems that can be used to coil and uncoil the wires of a wire-driven parallel robots: a rotary motor that turns a drum on which the wire is coiled or a linear motor with a pulley system. The rotary category may be divided into two sub-categories: the system with a spiral guide for the coiling, allowing only layer for the wire a...

Wire-driven parallel robot (WDPR) is a special class of parallel robot in which the rigid legs are replaced by wires, with po-tential advantages in terms of intrusivity and workspace. Although the study of WDPR seems to be a well-addressed subject, we will show that there are still numerous challenging open issues in this field. 1 Wire-driven paral...

A N −1 wire-driven parallel robot is a robot for which all the N ≥ 3 wires are connected at the same point of the platform, al-lowing to control the location of this point. We are interested in the positioning accuracy of such a robot. If the wires are not elastic we show that the influence on the accuracy of the co-location errors of the wire anch...

We consider wire-driven parallel robot with N ≥ 4 wires that are con-nected at the same point on the platform. Such robot has 3 d.o.f. but it is non re-dundant (e.g. we cannot control the tension in the wires) as there will always be only at most 3 wires under tension simultaneously. We consider in this paper three approaches that make this robot r...

We address the kinematics of the redundant N − 1 wire-driven parallel robot, i.e. a robot with N > 3 wires connected at the same point on the platform. The redundancy allows one to increase the workspace size. But we show, both theoretically and experimentally that if the wires are not elastic, then the redundancy cannot be used to control the wire...

Gait analysis and human joint motion mea-surement has been studied extensively in the recent past. Common approaches that have been used include using in-ertial sensors, multi-camera optical and IR tracking sys-tems, X-ray and fluoroscopy based imaging, force sensors, magnetic sensors and bone-fixed pins for measurement. Soft tissue artifacts (STA)...

Presentation slide of this invited talk

This paper studies under-constrained cable-driven parallel robots with three cables. A major challenge in the study of these manipulators is the intrinsic coupling between kinematics and statics, which must be tackled simultaneously. In this contribution, a general elimination procedure is provided that solves the direct geometrico-static problem,...

This paper deals with the wrench-feasible workspace (WFW) of n-degree-of-freedom parallel robots driven by n or more than n cables. The WFW is the set of mobile platform poses for which the cables can balance any wrench of a given set of wrenches, such that the tension in each cable remains within a prescribed range. Requirements of nonnegative cab...

Le maintien à domicile aussi longtemps que possible des personnes vieillissantes s'avère être la solution la plus rationnelle, tant en termes de confort que de coûts sociaux. D'où l'intérêt de dispositifs robotisés pour les assister au quotidien.

We present the overall design of ANG, a new walking aid for the elderly. The objectives of this walking aid is to provide a low-cost and low-intrusivity aid for the elderly. ANG is based on a classical 4-wheel Rollator, the two rear wheels being fixed while the two front are caster wheels. The rear wheels have been motorized, a bistable clutching m...

We present several prototypes of wire-driven parallel robots that we have recently designed and which use two different actuation schemes. Two of them have been completed and submitted to extensive tests. These tests have allowed to determine interesting open problems related to kinematics that are presented. Key wordsKinematics-wire-driven parall...