In this paper, we propose a novel time-varying feedback control strategy based on the Robust Integral of the Sign of the Error (RISE). The main motivation is to enhance the tracking performance of RISE controller at high dynamic operating conditions. RISE control law ensures a semi-global asymptotic tracking without introducing severe restrictions on the uncertain and nonlinearly parametrized systems. More nonlinearities are added to the original RISE control law by replacing the static feedback gains with nonlinear ones which depend on the system state variables. The proposed contribution is implemented in real-time experiments on a non-redundant three-degrees-of-freedom parallel manipulator named Delta. Comparing to the standard RISE controller, experimental results show better tracking performances of the proposed time-varying feedback RISE controller.

This paper deals with a new dynamic formulation of parallel manipulators incorporating the actuator and friction dynamics to be utilized in control. A model-based controller, PD with computed feedforward, is implemented for a parallel robot taking into consideration the formulated dynamics. The motivation behind this contribution is to enhance the control performance by compensating the unfavourable nonlinearities abundant extensively in PKMs. Those nonlinearities may increase considerably when operating at high-speed motions. The proposed feedforward part relies on the reference trajectories instead of the measured ones improving the control performance and the computational efforts. To validate our contribution, real-time experiments are conducted on a four degree-of-freedom parallel robot named VELOCE in different operating conditions.

This paper deals with the design of a new robust adaptive controller for parallel manipulators based on sliding mode and modelbased adaptive control. More precisely, the proposed controller relies on continuous finite-time terminal sliding mode (TSM) control and the linear-in-the-parameters property of the inverse dynamics of the manipulator. The main motivation behind the proposed scheme is to improve the tracking performance of fast and accurate parallel manipulators while guaranteeing the closed-loop system's robustness. Based on the linear-in-the-parameters property of the inverse dynamics of the manipulator, an adaptive law is proposed in order to estimate in real-time the dynamic parameters of the manipulator. The proposed controller has the advantage of relying on the desired reference trajectories instead of measured ones which can improve its robustness and efficiency. To demonstrate the effectiveness of the proposed controller, real-time experiments are conducted on a four-degree-of-freedom parallel manipulator called Veloce.

In this paper, the recently developed ℒ1adaptive control strategy is experimentally validated for the first time on a parallel kinematic manipulator. The ℒ1adaptive controller is known for its decoupled estimation and control loops which enables fast adaptation while guaranteeing robustness of the closed-loop system. The control scheme is experimentally implemented on a 4-DOFs parallel kinematic manipulator. Based on the obtained experimental results, a comparative study shows that the proposed ℒ1adaptive controller outperforms the PD controller in terms of tracking performance thanks to the compensation of the nonlinearities in the adaptive controller.

This paper introduces a novel concept of an air bearing test bench for CubeSat ground testing together with the corresponding dynamic parameter identification method. Contrary to existing air bearing test benches, the proposed concept allows three degree-of-freedom unlimited rotations and minimizes the influence of the test bench on the tested CubeSat. These advantages are made possible by the use of a robotic wrist which rotates air bearings in order to make them follow the CubeSat motion. Another keystone of the test bench is an accurate balancing of the tested CubeSat. Indeed, disturbing factors acting on the satellite shall be minimized, the most significant one being the gravity torque. An efficient balancing requires the CubeSat center of mass position to be accurately known. Usual techniques of dynamic parameter identification cannot be directly applied because of the frictionless suspension of the CubeSat in the test bench and, accordingly, due to the lack of external actuation. In this paper, a new identification method is proposed. This method does not require any external actuation and is based on the sampling of free oscillating motions of the CubeSat mounted on the test bench.

In this paper, a new type of large-dimension reconfigurable suspended cable-driven parallel robots (CDPR) is introduced as a means to substitute for conventional methods of handing large and heavy parts across wide workspaces. The reconfigurability of the proposed CDPR offers better performances in term of workspace, flexibility and power consumption. A systematic procedure to solve a complex nonlinear optimization problem to find optimal reconfiguration for the robot is presented. Critical issues regarding various constraints and performance criteria are addressed. The robot can operate in offline reconfiguration or online reconfiguration modes which offer wide range of solutions to the end-users.

The paper presents a novel 5 dofs (3T-2R) parallel mechanism. The mechanism is characterized by large singularity-free workspace and particularly large rotational capability which makes it suitable for 5 face-machining and similar applications. Having all its prismatic actuators along x direction, the x-motion is independent from other dofs-only limited by prismatic actuators' strokes-constituting another major advantageous feature. Besides, an analytical direct geometric model can be easily established which is a rare feature in parallel robots. The paper introduces the novel mechanism with its inverse and direct geometric models as well as its kinematic models (forward and inverse Jacobians). Also, it discusses its singularity analysis and presents sample workspace plots evaluated based on isotropic performance regarding velocity and static force.

In this paper, a new control scheme based on the desired compensation adaptive control strategy for mechanical manipulators is developed. In order to estimate the unknown parameters, the adaptation law is formulated based on the inverse dynamic model and the desired trajectories instead of the actual ones. To further improve the tracking performance and the disturbance rejection ability of the original controller, the static feedback gains are replaced by nonlinear varying ones. The computed control inputs are then projected using a kinematics based projector in order to remove the internal efforts in redundantly actuated parallel kinematic manipulators that may damage the mechanical structure of the manipulator. To demonstrate its effectiveness, the proposed controller is validated through real-time experiments on Dual-V; a 3-DOFs redundantly actuated parallel kinematic manipulator. The obtained results show that the proposed controller outperforms the original one in terms of tracking errors and energy consumption.

A novel adaptive controller based on the Robust Integral of the Sign of the Error (RISE) is proposed. The RISE feedback strategy yields semi-global asymptotic tracking despite the presence of unstructured additive disturbances provided some limited assumptions on the system. To achieve better tracking performance, the RISE controller is extended with a model-based adaptive feedforward term. The addition of the feedforward term compensates for the structured uncertainties yielding reduced tracking errors and reduced control effort. The proposed controller is experimentally implemented on a 3-DOFs redundantly actuated parallel manipulator. The computed control inputs are projected using a kinematics based projector in order to remove the internal efforts that may damage the mechanical structure of the manipulator. Experimental results show a better performance of the proposed adaptive controller compared to the basic RISE controller in terms of tracking accuracy and energy consumption.

This paper deals with the kinetostatic performance evaluation regarding translational and rotational motions of general robots with mixed operational degrees of freedom (dofs). Also, robots with different types of actuators can be analyzed based on the same approach without any problem. Besides, the generality of the approach embraces serial, parallel, actuatedly or kinematically redundant robots. The paper seeks clarifying the issue and providing a relevant solution. It also clarifies some other useful points in this matter.

This paper presents the dimensional synthesis of a 4 dofs (3T-1R) actuatedly redundant parallel manipulator (called ARROW V1) based on dual criteria related to rapidity and precision. The dynamical (rapidity) criterion is the worst isotropic linear acceleration starting from rest, and the precision related criterion is the worst translational resolution amplification factor. This latter amplification factor happens to be equal to the theoretical translational repeatability and accuracy amplification factors as well. Also, other kinetostatic and dynamic performances have been evaluated for the synthesized set of geometric parameters as to validate global performances. The results are quite interesting showing a highly performant parallel kinematic machine (PKM).

This paper addresses the simplification of cable model in static analysis of large-dimension cable-driven parallel robots (CDPR). An approach to derive a simplified hefty cable model is presented. The approach provides an insight into the limitation of such a simplification. The resulting cable tension computation is then used to solve the inverse kinematic problem of CDPR. A new expression of cable length taking into account both the non-negligible cable mass and elasticity is also introduced. Finally, simulations and experiments on a large CDPR prototype are provided. The results show that taking into account both cable mass and elasticity improves the robot accuracy.

This paper presents a novel 4 dofs (3T-1R(1)) parallel redundant mechanism, with its complete study regarding inverse and direct geometric models (IGM and DGM), as well as singularity and workspace analysis. The robot is capable of performing a half-turn about the z axis (a complete turn would be theoretically possible if it were not for possible unavoidable inter-collisions in the practical case), and having all of its prismatic actuators along one direction, enables it to have an independent x motion - only limited by the stroke of the prismatic actuators. The mechanism is characterized by elevated dynamical capabilities having its actuators at base. Moreover, the performance of the robot is evaluated considering isotropy in velocity and forces.

This paper deals with the dual-space adaptive control of R4 redundantly actuated parallel manipulator for applications with very high accelerations. This controller is compared experimentally with a dual-space feedforward controller (which may have good performances for specific cases, but has crucial losses of performance when there is any operational change (such as a change of load)), for a pick-and-place task with accelerations of 30G (without payload) and 20G (with a payload of 200g). The objective of this paper is to show that the proposed dual-space adaptive controller not only keeps a very good performance independently of the operational case, but also has a better performance than the dual-space feedforward controller even when this last one is best configured to the given case.

This paper presents the locomotion approach of a novel quadruped robot which is able to carry various effectors for achieving manufacturing tasks in large workspaces. Equipped with lockers on some of the passive joints and clamping devices at the end of its limbs, this quadruped uses eight actuators for achieving manufacturing tasks as well as locomotion tasks. In the following sections, we first present the proposed robot and its two working modes. Then, the locking strategy of the robot is formulated as an optimization problem. Also, a practical method for managing the limbs swinging movement is addressed. At last, the presented approach is applied on two concrete examples. Possessing a low degree of kinematic redundancy, the proposed quadruped shows a reasonable locomotion capacity which allows it to achieve locomotion with respect to some extra constrains in its workspaces.

A robust cascade strategy combining an outer position predictive control loop and an inner H∞pressure control loop is proposed and tested on an electropneumatic testbed for parallel robotic applications. Two types of cylinders are tested, the standard double acting cylinder and the rodless one. A position/pressure difference (or force) strategy is developed and implemented. As the behavior of the nonlinear cylinders is nonlinear, a feedback linearization strategy is adopted. A Generalized Predictive Controller (GPC) is synthesized for the position outer loop and a constrained LMI based H∞controller is synthesized for the pressure inner loop. Experimental results show the feasibility of the control strategies and good performances in terms of robustness and dynamic tracking.

This paper analyzes the possible contribution of actuation redundancy in obtaining very high acceleration with Parallel Kinematic Machines (PKM). This study is based on redundant and non-redundant Delta/Par4-like robots (frequently used for pick-and-place applications). The dynamic model, valid for both redundant and non-redundant robots, is used to analyze the traveling plate acceleration capabilities: (i) at zero speed and in any directions, (ii) at zero speed in the “best” direction. The results show that actuation redundancy allows to homogenize the dynamic capabilities throughout the workspace and to increase the traveling plate acceleration capability. Finally, the design of a redundant Delta/Par4-like robot optimized for typical pick-and-place trajectories is presented.

This paper presents MoonWalker, a lower limb exoskeleton able to sustain part of a user's bodyweight. This orthosis can be used for rehabilitation, to help people having weak legs, or to help those suffering from a broken leg, to walk. It can also be used as an assistive device helping people carrying heavy loads. Its main characteristic is that a passive force balancer provides the force to sustain bodyweight. An actuator is also required, but is used only to shift that force the same side as the leg in stance. Consequently, MoonWalker requires very low energy to work on flat terrains. That motor can provide also a part of the energy to climb stairs or slopes. We believe that this approach can help improving energetic autonomy of lower limb exoskeletons.

Generally, the cables of a parallel cable-driven robot are considered to be massless and inextensible. These two characteristics cannot be neglected anymore for large dimension mechanisms in order to obtain good positioning accuracy. A well-known model which describes the profile of a cable under the action of its own weight allows us to take mass and elasticity into account. When designing a robot, and choosing actuator and cable characteristics, a calculation of maximal tension has to be done. However, because cable mass has a significant effect on cable tensions, a model including cable mass has to be included in the design step. This paper proposes two methods to determine the appropriate cable and hence the maximal tensions in the cables. Applied to a large dimension robot, taking cable mass into account is proved to be necessary in comparison with an equivalent method based on the massless cable modeling. In this paper, only moving platform static equilibria are considered (slow enough motions).

The open-loop flexible modes identification of a high-speed and high-accuracy pick-and-place parallel robot is carried out based on two approaches: an ARMAX model and a subspace identification technique. Models of piezoelectric dynamics and disturbances can be obtained for many distinct operation conditions, allowing, in a future work, the conception of robust control laws.

This paper deals with the problem of unavailability of velocity measurements for the control of parallel manipulators for pick-and-place applications. As most controllers require the measurement of the joint positions as well as joint velocities, the latter need to be estimated. Three observers have been implemented while keeping the same nonlinear controller: a Lead-lag filter based observer, an Alpha-beta-gamma observer and a High-gain observer. The resulting performances obtained in Real-time experiments by each observer have been detailed and compared.

In this paper, several considerations for designing industry oriented robots which combine the mobility of legged robots and advantages of parallel mechanisms are outlined. A tripod and a quadruped with the same kind of legs are studied. The robots' kinematic models are built for achieving the machining and walking scenarios. The simulations show that: integrating some clamping devices and some lockable passive joints, six actuators are enough to build a legged manipulator which can not only perform 6-axis machining but can also walk on a curved supporting media. Using the “modified condition number” index, the two mechanisms are compared. They have similar workspaces and static wrench performances during the machining phase. During walking processes, however, their behaviors are different, and each of them shows interesting features depending on application requirement.

The property of form-closure of a grasp, as generally defined in the literature, is based on the assumption that contact points between the hand and the object are fixed in space. However, this assumption is false when considering a grasp exerted by an underactuated hand, since, in this case, it is not possible to control the position of each phalanx independently. In spite of researchers' interest in studying form-closure, none of the available published work on this subject takes into consideration the particular kinematics of underactuated hands. Actually, there are few available tools to qualify or quantify the stability of a grasp exerted by an underactuated hand; thus, the design of underactuated hands mostly results from an intuitive approach. This paper aims to reduce this gap. A classification of underactuated hands is proposed, which is based on the expression of contact forces. This highlights the influence of nonbackdrivable mechanisms introduced in the transmission of the closing motion of the hand on the stability of the grasp. After demonstrating that the original definition of form-closure is not suitable for the underactuated grasps, a more general definition is formulated, which checks the stability of the assembly ``object + hand.'' Using this new definition, a geometric method is proposed for the analysis of first-order form-closure of an underactuated grasp, as well as a simple rule to design a hand capable of achieving first-order form-closed grasps. Finally, a method is proposed for the analysis of higher order form-closure of an underactuated grasp, which is based on a first-order model of the grasp.

This paper introduces the Quadriglide, a Schonflies motion generator module for 5-axis machine-tools. The targeted application is high speed milling of long aeronautic parts, in particular thin ones, instead of toxic and dangerous chemical milling. Quadriglide is described and its kinematics derived. Then, a preliminary optimization is done to achieve the best actuation stiffness in a prescribed workspace with large tilting angles (thetas = plusmnpi/4). Workspace plots of the optimized module are shown at the end of the paper.

This paper introduces a new two-degree-of-freedom parallel manipulator producing two translations in the vertical plane. One drawback of existing robots built to realize those dof is their lack of rigidity along the transversal axis, another one being their limited ability to provide very high acceleration. Indeed, these architectures cannot be lightweight and stiff at the same time. The proposed architecture is a spatial mechanism which guarantees a good stiffness along the transversal axis. This parallel architecture is composed by two actuated kinematic chains, and two passive chains built in the transversal plane. The key feature of this robot comes from the passive chains which are coupled for creating a kinematic constraint: the platform stays in one plane. A stiffness analysis shows that the robot can be lighter and stiffer than a classical 2 dof mechanism. A prototype of this robot is presented and preliminary tests show that accelerations above 40 g can be achieved while keeping a low tracking error.

Cable-driven robots are currently extensively studied. Generally, for this type of manipulators, cables are considered to be massless and inextensible. But for large working volume applications, their mass cannot be neglected. Based on a well-known model which describes the profile of a cable under the action of its own weight, the inverse and forward kinematics of minimally constrained cable-driven manipulators can be numerically computed. This paper studies the effects of taking cable mass into account by comparison to classical massless cable model. It highlights the real effects of such a model on cable lengths to reach a given position. The effects on cable tensions are also studied.

This paper deals with nonlinear dual mode adaptive control of a redundant manipulator for a pick-and-place scenario with high acceleration (20 G). For performance comparisons, a conventional Proportional-Derivative (PD) controller has also been implemented. In this context, the experimental testbed is not equipped with velocity sensors. Therefore, a high-gain observer has been implemented to estimate the articular velocities. Real-time experiments show the performance improvements obtained by the proposed control approach in comparison to the conventional one.

This paper discusses the mechanical kinematics solutions and design aspects of the biped robot SHERPA, a bipedal platform able to walk and carry load. Starting from the analysis of the human lower limbs, we figure out that 6 DOF per leg are fundamental for a correct walking motion and can be adopted in a mechanical design of a humanoid robot. A close investigation of the joints leads us to a novel modular mechanical design, with a parallel architecture mechanism characterized by and high degree of interchangeable components. The robot is using twelve high performance hollow shaft electrical actuators acting in pairs in a parallel manner, a remote compact and transparent actuation with zero-backlash cable transmissions, 2 DOF differential joints between each segment of the limb and a light-weight carbon fiber skeleton modeling and mimic the anatomy of the human legs. The modular 2 DOF cable differential joint has been implemented at the hip, knee and ankle level. Using our approach, actuation is more transparent (back-drivable, with low inertia) and will allow SHERPA to interact with the environment more smoothly which leads to better walking ability.

This paper presents an optimal design of a parallel manipulator aiming to perform pick-and-place operations at high speed and high acceleration. After reviewing existing architectures of high-speed and high-acceleration parallel manipulators, a new design of a 4-DOF parallel manipulator is presented, with an articulated traveling plate, which is free of internal singularities and is able to achieve high performances. The kinematic and simplified, but realistic, dynamic models are derived and validated on a manipulator prototype. Experimental tests show that this design is able to perform beyond the high targets, i.e., it reaches a speed of 5.5 m/s and an acceleration of 165 m/s2. The experimental prototype was further optimized on the basis of kinematic and dynamic criteria. Once the motors, gear ratio, and several link lengths are determined, a modified design of the articulated traveling plate is proposed in order to reach a better dynamic equilibrium among the four legs of the manipulator. The obtained design is the basis of a commercial product offering the shortest cycle times among all robots available in today's market.

This paper presents the design and the optimization of a parallel machine-tool composed of (i) an 3-dof actuated parallel mechanism (a linear Delta) and (ii) a 6-dof measuring parallel mechanism (a Gough platform).The measuring mechanism is used to control the actuated mechanism. The interest to use a measuring device independent of the actuation device is shown and the modeling of both devices used for the optimization is explained. Then, the optimization of both mechanisms is presented. The optimization of the actuated mechanism is performed to have an homogeneous behavior in velocity while the goal of the measuring device optimization is to obtain the best resolution for the measuring system evaluated at the tool level.

This paper reports the first results of an ongoing work which aims at providing numerical tools useful to the design of a family of high speed parallel robots. The objective is to find sets of feasible values for the design parameters unlike more usual design procedures relying on optimization techniques. These tools are mainly based on interval analysis and take into account the dynamics of the parallel robots. Moreover, they can deal with bounded uncertainties that affect some physical parameters involved in the dynamics. Following the statement of the design problems considered, a general method is presented. Then, this method is illustrated with the study of a 2-DOF parallel robot.

This paper presents a new pneumatically driven underactuated hand with two fingers and 3 phalanxes per finger. Two evidences have led the design of this hand. Firstly, the use of pneumatic energy facilitates the underactuation of the hand, indeed a single T-connector suffices to share out one input among two outputs. Secondly, non-backdrivable mechanisms have to be used in the transmission of phalanx's motion so that the hand is capable of producing form-closed grasps. This latter design principle is justified using a newly developed method that permits to study the form-closure property of a grasp exerted by an underactuated hand. Moreover, the intriguing ejection phenomenon is avoided thanks to non-backdrivable mechanisms that prohibit any backward motion of phalanxes when correctly positioned. An original mechanism called the "pneumatic parallelogram" is described, it enables the hand to perform fine pinch grasps. Finally, the optimal design of both fingers is addressed with respect to the force-isotropy of the finger and the positiveness of phalanx forces

This paper presents a new method to study the capability of an underactuated hand to produce form-closed grasps. First, the stability behaviours of different underactuated parallel-jaw grippers are analyzed and compared according to their actuation and transmission mechanisms. Then, both notions of 1st order and 2nd order form-closure are revisited for underactuated hands, since in this particular case the assumption of fixed contacts made in the original definition is false. Therefore, constraints imposed by non-backdrivable mechanisms are introduced into the model of the whole grasp. Finally, a simple geometrical condition, necessary and sufficient for 1st order form-closure is proposed. This permits to conclude on the minimum number of non-backdrivable mechanisms required to produce 1st order form-closed grasps using an underactuated hand

This paper introduces Heli4 a new 4 degree-of-freedom parallel robot. It is inspired by the Delta architecture, but was designed to overcome its limitations, using an articulated traveling plate. Unlike most articulated traveling plates, Heli4's traveling plate is very compact. Among other positive aspects is its symmetrical design. This paper gives the geometrical models, and particularly the forward position relationship which can be obtained in a closed form. In a third part, a detailed study of the robot singularities is made by taking into account the not-so-classic internal singularities.

This paper introduces the dynamic modeling and the identification of Par4, a four-degree-of-freedom parallel manipulator producing Schonflies motions (three translations and one rotation about a fixed axis). First of all, this paper presents how this robot is developed with the goal of reaching very high speed. Indeed, it is an evolution of Delta, H4 and I4 robots architectures: it keeps their advantages while overcoming their drawbacks. Experimentations done with the prototype prove that the robot is able to reach very high accelerations (15 G) and to perform an adept cycle in 0.25 s. In order to improve its dynamic accuracy, a dynamic control could be necessary. Thus, this paper presents the dynamic modeling of the manipulator using a simplified Newton-Euler approach. The originality of this computation is to model the traveling as two separated parts and to determine the dynamic effects applied on each of them. Finally, since a dynamic control requires a good evaluation of dynamic parameters, an experimental dynamic identification is presented

This paper deals with a particular family of lower mobility parallel kinematic manipulators. The four degrees of freedom of the end-effector consist of three translations plus one rotation with a high tilting angle. Robots belonging to this family are first introduced, and a common parameterization is established. Then an extended kinematic model is proposed for this family of robots using a new Jacobian matrix. Relevant information about robot kinematic singularities, internal singularities, and possible end-effector motions can be obtained by resorting to this matrix. The efficiency of this method is proven by applying it to several traveling-plate architectures corresponding to already built robot prototypes. The results of the expected behavior are compared with the prototype's real behavior. The goal of this paper is to show that internal (or constraint) singularities can occur in lower mobility parallel kinematic manipulators, and to underline the influence they have during the design stage.

The H4 robot is a four-degree of freedom (dof) parallel machine. The purpose of this work is to evaluate the H4 stiffness, ie the displacement response of the tool controlled point when it is submitted to a given force using an analytical method. A stiffness analysis based on analytical calculations is performed. It has the advantage to be rather fast and easy to integrate into a design optimization. This method allows to compute stiffness matrix of parallel robots and takes into account particularity of parallel robots with articulated traveling plate. Some numerical results are presented at the end of this paper for the H4 first prototype.

Nowadays an important research effort is devoted to lower mobility parallel manipulators. The existing solutions often suffer from parallel mechanisms drawbacks, i.e. small workspace and limited rotation capability. A new concept of parallel manipulators providing Schoen flies motions (motions of well-known SCARA robot) is introduced in this paper. The proposed manipulator, based on the idea of articulated traveling plate explored by the authors, has an unlimited rotation capability without using motion transformation, ampli fication neither redundancy.

This paper deals with the design of a controller and its implementation in a mini-rotorcraft toy with 3 rotors. A new original low-cost tilt angle sensor is introduced and kinematic and dynamic models are developed and implemented with the aim of developing an autopilot mode to stabilize and maintain hovering flight on demand. The result has to fit into a low-cost microcontroller and run in real-time.

The increasing level of requirements in terms of performance, accuracy, repeatability and resolution in the semiconductors industry leads to several technological problems; among them the positioning accuracy and resolution are peculiarly important. In this paper, we address the crucial issue of high resolution and fast positioning mechanisms. We propose a novel type of high resolution and fast positioning mechanism, based on a macro/micro architecture composed of two stages. We focus here on the micro-stage. It is a combination of: a 3-RRR planar parallel structure (3-RRR stands for 3 kinematic chains in parallel, each chain composed of 3 revolute joints R in a serial arrangement) with deported PRR actuation (a rod connected with two revolute joints R to a linear actuator P and to the RRR chain). This architecture provides stiffness, symmetry and interesting thermal properties; Flexible R links (which avoid the drawbacks of conventional links in terms of backlash, friction, wear, stick-slip,...); and near serial-singular configuration which results in an improvement of the resolution. A modeling of inverse kinematics for position and velocity is presented. Then, an optimization is run to find the best set of geometrical parameters for the micro-stage. An articulated kinematic scheme is finally presented.

This paper introduces a new 4 degree-of-freedom parallel robot. It presents its architecture inspired by FlexPicker, an ABB machine based on the Delta architecture, while overcoming its drawbacks. This paper exposes the way to get the geometrical models, and particularly the forward position relationship which can be obtained in a closed form. In a third part, a detailed study of the robot singularities is made by taking into account the not-so-classic internal singularities. Design conditions are obtained for isostatic and over-constrained cases. The robot optimization and its workspace are finally presented.

In this paper, an original approach is proposed for the kinematic calibration of parallel mechanisms. The originality lies in the use of vision to get information on all parts of the mechanism, i.e. its end-effector as well as its legs. Metrological redundancy is therefore maximized to improve the calibration efficiency. The approach is implemented for the calibration of the I4 parallel mechanism, with the use of the Jacobian matrix. No accurate camera location is needed so that the experimental procedure is easy to achieve. The calibration algorithm is detailed and experimentally demonstrated more efficient than other calibration methods based on legs observation or end-effector observation.

This paper presents new force performance indexes adapted to parallel mechanisms with actuation redundancy (PMAR) especially parallel wire-driven manipulators (where only tensile forces in cables are possible). Such performance indexes might be used for optimization purpose. At first, the operational force polytope is established. It is the accurate representation of admissible operational forces from the kinetostatic analysis point of view. A way to efficiently compute it is given. The obtained description of the polytope is the same as in (Krut S. et al., March-April 2004), but regarding forces. As a consequence the reader is free to use any of the indexes introduced in (Krut S. et al., March-April 2004). From the authors' point of view the "maximum operational isotropic force" is well adapted to characterize parallel wire-driven manipulators' force behavior. The way to compute it is established. At last, this index is computed for several parallel wire-driven manipulators.

This paper deals with the design and dynamic control simulation of a new type and dynamic control simulation of a new type of 4-DOFs parallel mechanism providing 3 translations and 1 rotation for high-speed handling and machining. This parallel mechanism is named as H4. A model-based dynamic control scheme is developed to improve the accuracy of the trajectory tracking. A simplified dynamic model is used for the H4 robot to decrease the cost of computation. A dynamic simulation is performed using ADAMS/sup TM/. In addition, the adept motion is used as a benchmark test to evaluate the effect of the dynamic control. The simulation results show that the dynamic control dramatically improves the trajectory tracking accuracy.

The new generation of implanted neuroprostheses allows muscles to be controlled with fine accuracy, high selectivity and the repeatability of the muscle's response can be achieved. Thus, the closed loop control of such systems becomes possible. The SUAW project succeeded in the implantation of an advanced neuroprosthetic device on two patients, but the movement generation remains open loop and is tuned empirically. Nevertheless, the good results obtained give us the opportunity to envisage the system evolves towards closed loop control and automatic synthesis of the stimulation patterns generating the desired movement. To achieve this goal, some preliminary researches have to be carried out, beginning with a specific modelling that can be used in the context of functional electrical stimulation (FES). The main issues concern muscle modelling including the interaction with the skeleton, fatigue, FES parameters as inputs, and the identification of dynamic parameters, and afterwards, the motion synthesis and the closed loop control based on this model. Besides, the scientific approach is the same as in robotics so that the theoretical tools used in the control theory are the same and directly applicable. This paper describes the results obtained in the previous project SUAW and how we attempt, through the new project DEMAR, to enhance the global performances of the system.

This paper presents a new robot which produces four motions for high speed handling (three translations and one rotation about a given axis in world coordinates). This machine is an evolution of H4's architecture. First, H4's advantages are recalled, and some limitations are mentioned. To compensate for these limitations a new design of the traveling plate is proposed. A description of the whole mechanism is given. The structure's ability to provide Scara motions is presented. Geometrical conditions that must be followed in order to obtain desired motions are discussed. Kinematics models are derived. The design of the first prototype is described.

This paper deals with the experimental identification of the dynamic parameters of parallel machines. The dynamic parameters are estimated by using the weighted least squares solution of an over determined linear system obtained from the sampling of the dynamic model along a closed loop exciting trajectory. Experimental results are exhibited for the H4 robot, a fully parallel structure providing 3 degrees of freedom (DOF) in translation and 1 DOF in rotation. A comparative study is performed depending on the available measurements, i.e., different sensor locations (motor, end effector).

This paper introduces Eureka, a new parallel mechanism providing five motions: three translations plus two rotations. This device is able to reach high tilting angles (/spl plusmn/90/spl deg/ about a first given axis and a whole revolution about the following axis). This is due to actuation redundancy and to the specific traveling plate. Kinematic models are derived. Due to its particular shape the forward geometrical model is also derived easily. A plot of its well conditioned workspace is given. Practical designs, free of self-collisions, are shown.

The forward kinematic model (FKM) of a redundantly actuated robot is not unique: if each actuator is equipped with an encoder, there are more joint data than strictly necessary for computing nacelle position. It is then possible to fuse competitive data to find the nacelle position. This paper proposes then a method based on a probabilistic approach to determine how computing the FKM to obtain, in terms of probability, the lowest Cartesian error.

This paper presents an efficient application of a model based predictive control in parallel mechanisms. A predictive functional control strategy based on a simplified dynamic model is implemented. Experimental results are shown for the H4 robot, a fully parallel structure providing 3 degrees of freedom (dof) in translation and 1 dof in rotation. Predictive functional control, computed torque control and PID control strategies are compared in complex machining tasks trajectories. The tracking performances are enlightened.

This paper presents a new family of fully-parallel robots producing motions of the Schoenflies displacements subgroup (three translations and one rotation about a given axis in world coordinates) for high-speed handling and machining. First, the structure's ability to provide this four-degrees-of-freedom motion is presented. Then, two of its possible designs are analyzed: the symmetrical and the asymmetrical one. Constructive designs are then presented. Some of the prototype's preliminary control results are given to prove the H4 robot's efficiency.

This paper presents a novel and safe robotic system for skin harvesting, the first one in reconstructive surgery. It is intended to significantly improve the performance of surgeons who do not regularly perform this operation; the tool, called dermatome, is mounted at the tip of a dedicated robot that precisely controls the pressure on the skin and the harvesting velocity. In this paper, the harvesting task is analyzed and the safety constraints are summarized. Then, the mechanical structure and the functions of the control system are described. Finally, in vivo experimental results on pigs are reported and discussed.

Twice (tilling device with wide capacity), a new amplification device able to double the tilting angle of a parallel mechanism, is presented. A singularity analysis is carried out: it proves that Twice can give a huge tilting angle to parallel kinematic machines. Finally, practical implementation features are discussed.

This paper introduces a control strategy based on redundant sensors that leads to parallel robots accuracy enhancement. The method is presented in general, then applied to a 4-DOF parallel robot. Practical implementation issues, simulation results and experimental validation are addressed.

This paper deals with a path planning algorithm for an anthropomorphic robot that must achieve motions (straight line, circle, helix) under the constraint of passing the forearm through a fixed point. This point simulates the penetration point (trocar) in minimally invasive surgery. It has to remain fixed with respect to the patient's body. The modeling and resolution of the constraint are presented. The geometric model and path planning are proposed. Simulation results validate the algorithm.

This paper first recalls the concept of H4 parallel mechanism, and the kinematic models necessary for real-time control are derived. A simple and efficient control system based on a combination of Windows NT and RTX is used to demonstrate its performances. Results prove the efficiency of H4 serving as a high-speed pick-and-place robot.

Presents a 3-DOF redundant parallel mechanism, ARCHI, designed as a sub-part of a 5-axis hybrid machine. The redundant parallel mechanism design and its models are recalled; different ways for its control and first motion results are presented, proving the ability of ARCHI to offer an unlimited rotation capability.

The paper presents an ongoing research program in robotized reconstructive surgery. We first analyze the action of surgeons harvesting skin, in terms of speed and forces. Then we present the control strategies we have selected and implemented on a redundant robot arm. Finally we present the first experimental results obtained on an animal: this shows that robotized skin harvesting is a possible task.

A mobile robotic manipulator, i.e. a manipulator mounted on a vehicle, is a very useful system for tasks in dangerous environments. Unfortunately the use of a wheeled vehicle introduces non-holonomic constraints, and the combination of a vehicle and a manipulator generally introduces kinematic redundancy. The goal of this paper is to propose a method to determine a feasible path between two fixed configurations for a mobile manipulator whose vehicle is non-holonomic. For this purpose, we write the global displacement of the system in a symbolic way, using two representation tools: homogeneous matrices and dual quaternions. Then, we compute the corresponding joint parameters to make the desired displacement coincide with the computed symbolic displacement. The method is described and some simulation results are presented.

We have developed a robotic system to assist doctors when they are moving ultrasonic probes on the patient's skin while exerting a given effort. The probes are used to monitor arteries for cardiovascular disease prevention, namely to reconstruct the 3D profile of arteries. A preliminary feasibility study making use of an industrial robot has been made to validate the force control scheme. It has proven the interest of the robotized approach for such a medical application. In order to comply with safety constraints, a dedicated robotic system HIPPOCRATE has been designed. The paper describes the arm and the controller architectures, with emphasis on design strategies selected to meet safety requirements.

Polytopes are well-known tools to graphically represent force/motion capabilities for a manipulator. This paper focuses on the evaluation of velocity polytopes for redundant fully parallel robots for which a new intermediate space is introduced (in addition to classical joint space and task space) in order to take into account the specific kinematic relationships. In this space, additional constraint are imposed on the available velocities to be consistent with the kinematic constraints due to the redundant kinematic chains. An algorithm to correctly evaluate the task space velocity polytope is given, and numerical results are provided in the case of a planar redundant 3-DOF parallel arm.

A mobile manipulator, composed of a manipulator mounted on a vehicle, is a very useful system to achieve tasks in dangerous environments. However, it is a very complicated system to model and control. The use of a wheeled vehicle generally introduces nonholonomic constraints, and the combination of a vehicle and a manipulator generally introduces some kinematic redundancy. The aim of this paper is to investigate the use of dual quaternions for the motion generation of a mobile manipulator with a nonholonomic vehicle. In this preliminary work, only planar cases are considered. Therefore, the principles of the planar quaternion theory are recalled. The description of the system in the planar quaternion space is developed. Some simulation results are then presented.

Manipulability ellipsoids and polytopes are well-known tools to graphically represents these capabilities. This paper focuses on the evaluation of force capabilities for redundant manipulators, for which additional constraints must be imposed on the available joint torques in order to satisfy the static assumption. An algorithm to correctly evaluate the task space force polytope is given and a new definition of the force ellipsoid is proposed. The obtained results can be applied also to nonredundant manipulators in singular configurations. Numerical results are provided in the case of a planar redundant arm.

Robustness is a very important feature of robot controllers. Obviously, dynamic control is not the good way to obtain the best robustness performance, especially when the payload is unknown. Moreover, this kind of control laws are not able to compensate for Coulomb friction. Our approach is based on the variable structure control (VSC) with sliding mode, but it is well known that VSC is unstable for physical sampled systems. Therefore, the concept of fuzzy logic is used to implement fuzzy sliding mode control on our six-degree-of-freedom fast parallel robot. Both simulated and real experiments are reported in this paper.

This paper concerns the performance comparison of different control structures based on various sensors for an agricultural mobile manipulator. The robot's mobile platform is continuously advancing, pulled by a tractor while the manipulator executes local tasks. Therefore, an existing prototype has been entirely modelled which allowed us to test each control structure using a dynamic simulator. The simulation results permit to identify the best control structure for the given constraints.

Concerns the control of the deformation of a robot manipulator exerting large forces and moments on its environment. This was motivated by a real application consisting in inserting rivets with a two-arm robot (to assemble a wing or a fuselage on an airplane structure). The solution consists in performing the complete task rivet after rivet. To do so, it is necessary that the two parts be compressed together to avoid any introduction of turnings between them during drilling. Therefore, the forces that the arms have to exert exceed 1000 N. With such constraints, a position controlled robot deforms and the end-effecters are not orthogonal to the parts anymore, which is not acceptable. These deformations cannot be detected by the optical encoders mounted on the motors shafts, because they are due mainly to the flexibility of the joints. We have developed a force control scheme with explicit force feedback to compensate for these deformations by servoing the forces and moments at the level of the end-effector: the desired values are zero except for the force orthogonal to the parts being assembled. To avoid using force sensors in a production line, we propose to use a force control scheme to derive a reference model. This model furnishes at every point the position increments to be applied to the robot in order to compensate for its nondesired deformations.>

The paper presents an original hybrid position/force control scheme. The novelty of the control law lies in the absence of Cartesian position servoloop. It is shown that when one tries to implement a hybrid control based upon a previously published scheme and task description, the Cartesian position servoloop automatically disappears. This is an essential result that is taken into account to construct the control diagram. Two types of experimental results are presented. The first experiments are aimed at validating the theoretical results we have obtained; the second experiments prove the efficiency of our hybrid control.

Two parallel robots are presented. The first is a three-degree-of-freedom lightweight robot called DELTA. The equations corresponding to different models of this robot (forward and inverse kinematics as well as inverse dynamics) are given. The important feature of the method used in deriving these models is the use of a 'good' set of parameters to simplify the equations. These models have been employed to control a real DELTA with a low-cost controller. An attempt was also made to extend the principle of the DELTA mechanical structure to a six-degree-of-freedom parallel robot. A design called the HEXA has been developed. The authors present this robot and show that it should have the same dynamic capabilities as the DELTA because, like the later, it can be built with light material and can be easily modeled.>

In order to perform complex coordinated tasks with a two-arm robot, some kind of robust hybrid position/force control is necessary. As a first step towards such a control scheme, the authors present mainly the results they have obtained in simulation with a single-arm robot. They have developed a simulator which allows one to test various control algorithms. In particular, they have tested a variable structure system for the hybrid control of a Puma robot. Several experimental results are presented in this case. Controlled variables for a two-arm system are also proposed.>