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.

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.

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).

Off-line robot dynamic identification methods are generally based on the use of the Inverse Dynamic Identification Model (IDIM), which calculates the joint forces/torques (estimated as the product of the known control signal - the input reference of the motor current loop - by the joint drive gains) that are linear in relation to the dynamic parameters, and on the use of linear least squares technique to calculate the parameters (IDIM-LS technique). However, as actuation redundant parallel robot are overconstrained, their IDIM has infinity of solutions for the force/torque prediction, depending of the value of the desired overconstraint that is a priori unknown in the identification process. As a result, the IDIM cannot be used for the identification procedure. On the contrary the Power Identification Model (PIM) of any types of robot manipulator has a unique formulation and contains the same dynamic parameters as the IDIM. This paper proposes to use the PIM of actuation redundant robots for identification purpose. The identification of the inertial parameters of a planar parallel robot with actuation redundancy, the DualV, is then carried out using its PIM. Experimental results show the validity of the method.

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 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.

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.

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 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 constant disturbances rejection in limit cycle tracking for an under-actuated mechanical system. The feedback controller presented in the work of Andary et al. (2008) is enhanced to handle constant disturbances by using online iterative estimation of an equivalent disturbance which is easily compensated by adding the estimated value to the output of the system. The effectiveness of the proposed method is demonstrated through real-time experiments on an inertia wheel inverted pendulum. Constant disturbances are introduced either as a weight asymmetrically fixed to the pendulum body, or by the use of a bad calibrated sensor.

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 describes the design of a gravity balanced spatial orthosis. Previous works introduced planar mechanisms only and neglected friction. They relied on counterweight or auxiliary parallelograms. The main contributions of this paper are: (i) we succeed in designing a spatial (3D) mechanism and (ii) we analyzed the effects of friction. We designed a very simple system made with two pulleys and two springs in order to ensure gravity compensation. The system is in static equilibrium whatever its posture. It has three passive degrees of freedom at the shoulder and two at the elbow. A prototype of this orthosis is presented at the end of the paper.

This paper deals with a control approach dedicated to stable limit cycle generation for underactuated mechanical systems. The proposed approach is based on partial nonlinear feedback linearization and dynamic control for optimal periodic reference trajectories tracking. Simulation results and experiments show the efficiency of the proposed approach.

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

Many underactuated grippers with fingers have been developed these last years. Their drawback is that they only ensure conditionally grasp stability. This paper presents a study of the grasp stability of an isotropic underactuated finger, which is made by two phalanxes and uses cams and tendon for actuation. The paper presents also a study of the internal forces developed in the transmission chains. The proposed model serves for the gripper using as for part dimensioning.

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 presents an improved method for the geometrical calibration of parallel robots for which the structure is based upon some parallelogram mechanisms. Its originality is to identify the complete geometry of the mechanism's parallelograms, and to compensate the positioning error of the TCP (tool centre point), due to the infinitesimal rotation of the traveling plate, induced by the parallelogram geometrical errors. The main difficulties are: (i) to derive the calibration model relative to all geometrical parameters, and (ii) to reuse the identified errors in a control model in order to compensate the positioning errors. In fact, the position relationship taking into account the full geometry of the parallelograms is difficult, not to say impossible, to derive in a close form; therefore a linear approximation of the model is proposed. The formulas necessary to run the method on a Delta robot are given. Then a simple mechanism is used to illustrate the benefits of this method compared to classical ones

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 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.

This paper presents the design of a new underactuated finger. The main characteristic of this two-degree-of-freedom / one-actuator finger is to be force-isotropic. This means that the intensity of the forces exerted at the center of each phalanx, on the grasped object, are identical. Until now, this characteristic was observed on some underactuated fingers for some very specific configurations only (mainly when the phalanxes were lined up). With the proposed finger, this characteristic remains true whatever the configuration of the phalanxes is.

This paper introduces a four-degree-of-freedom parallel manipulator dedicated to pick-and-place. It has been developed with the goal of reaching very high speed. This paper shows that its architecture is particularly well adapted to high dynamics. Indeed, it is an evolution of Delta, H4 and 14 robots architectures: it keeps the advantages of these existing robots, while overcoming their drawbacks. In addition, an optimization method based on velocity using adept motion has been developed and applied to this high speed parallel robot. All these considerations led to experimentations that proved we can reach high accelerations (13 G) and obtain a cycle time of 0.28 s.

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.

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 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 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.

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.

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.