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Proximity perception is a technology that has the potential to play an essential role in the future of robotics. It can fulfill the promise of safe, robust, and autonomous systems in industry and everyday life, alongside humans, as well as in remote locations in space and underwater. In this survey article, we cover the developments of this field from the early days up to the present, with a focus on human-centered robotics. In this domain, proximity sensors are typically deployed in two scenarios: first, on the exterior of manipulator arms to support safety and interaction functionality, and second, on the inside of grippers or hands to support grasping and exploration. Therefore, based on this observation, in the beginning of this article, we propose a categorization to organize the use cases of proximity sensors in human-centered robotics. Then, we devote effort to present the sensing technologies and different measuring principles that have been developed over the years, also providing a summary in form of a table. Following, we review the literature regarding the applications that have been proposed. Finally, we give an overview of the most important trends that will shape the future of this domain. [ABSTRACT FROM AUTHOR]

A control design framework for the coupled stability problem in robotics is presented. The proposed framework fundamentally generalizes the conventional passivity-based approaches to the coupled stability problem. In particular, it allows for stabilization of not necessarily passive robot-environment interaction where both the manipulator and the environment are dissipative systems with quadratic supply rates. In contrast with existing results, the proposed framework can be used in combination with an arbitrary robot’s tracking control algorithm, and its stabilizing action when in contact with environment does not affect the robot’s trajectory tracking performance in free space. The framework is based on the recently developed nonplanar conic systems formalism and generalized scattering-based stabilization methods. A detailed design example is presented which illustrates the capabilities of the proposed method. [ABSTRACT FROM AUTHOR]

This article presents a unified mathematical approach for modeling, identifying, and solving the friction-inclusive dynamics of robotic mechanisms driven by sliding contact transmission systems. This approach is applied to the most common industrial screw-based drives: 1) the worm drive, 2) the simple lead screw drive, and 3) the antibacklash lead screw drive. The resulting dynamics, handily transferable to single and multiple degree of freedom (DoF) manipulators, are complemented with an algorithm for the solution of the forward dynamics problem as well as a framework for friction identification based on nonlinear optimization. The presented theory is experimentally tested on single-DoF screw-based drives for a variety of payloads and at different operation speeds. Simulation and parameter identification results using the classical Coulomb model, the Coulomb model with Stribeck friction, and the Armstrong model with Stribeck friction, rising static friction, and frictional memory are compared with experimental data, showcasing the effectiveness of the presented approach toward framing the concepts of friction and motion transmission into a robotics setting. [ABSTRACT FROM AUTHOR]

The effect of Brownian motion on maneuvering of micro-objects in a fluid medium is one of the fundamental differences between micro-manipulation and robotic manipulators in the physical world. Besides, due to the limitation of feasible sensors and actuators in micro-manipulation, current control techniques for manipulation of micro-objects or cells are mostly dependent on the physical properties of target micro-objects or cells. In this paper, we propose the first stochastic control technique to achieve simultaneous orientation and transportation of micro-objects with Brownian perturbations. Several micro-particles which are optically trapped and driven by laser beams are utilized as fingertips to first grasp a target micro-object. Cooperative control of robot-assisted stage and the fingertips is then performed to achieve the control objective, in which the target micro-object is transported toward a desired position by using the robot-assisted stage, and at the same time, it is oriented toward a desired angular position by using the fingertips. This paper provides a stochastic control framework for simultaneous orientation and transportation of micro-objects with arbitrary types in the micro-world, and thus bringing micro-manipulation using optical tweezers closer to robotic manipulation in the physical world. Rigorous mathematical formulation and stability analysis for simultaneous orientation and positioning feedback control of micro-objects in the presence of the stochastic perturbations are derived, and experimental results are also presented. [ABSTRACT FROM AUTHOR]

This paper presents a new dynamic programming (DP) approach to the optimal path following problem. The method rests on an interpolation in the phase plane so that the resulting joint accelerations and joint torques are continuous. This allows for taking into account limits on the joint jerks and torque rates in addition to joint velocities, accelerations, torques, and the mechanical power. Most methods proposed in the literature yield values of optimal trajectories at discrete sampling times so that this must be interpolated subsequently to the trajectory optimization. This causes violations of the joint jerk and torque rate limits. The proposed method does not suffer from this problem, which is a main feature of this approach. Unlike most of the previously proposed methods, joint jerk and torque rate limits are addressed with a reasonable increase in the computation time of DP algorithms. Special attention is given to experimental validation of the optimization results. The presented experimental results confirm the importance of taking the motor torque characteristics as well as the Coulomb and viscous friction into account. Neglecting these effects (as most previous publications did) leads to trajectories that cannot be performed by real manipulators. Apart from DP, other approaches with smaller computation times exist. However, most of these methods are either limited to the time optimal case (which might not always be the desired criterion) and are not able to handle all earlier mentioned constraints or cannot take into account viscous friction effects. Apart from that a sequential convex programming (SCP) approach exists, which accounts for the same constraints as the presented approach. Therefore, the proposed DP approach is compared to this SCP method and an example is presented where the time optimal trajectory is performed by a real manipulator. [ABSTRACT FROM AUTHOR]

This paper proposes a modeling method for generic compliant robotic manipulators. It is based on graph theory and the port-Hamiltonian formalism, which allows a modular approach to the interconnection of rigid bodies with compliant actuators by means of kinematic pairs. This modularity enables a simple and straight-forward adaption the model when a manipulator's actuator morphology is changed. An example of a spatial three degree-of-freedom manipulator shows that this modeling method is more suitable for modeling changes in actuator placement than the traditional Euler–Lagrange method. [ABSTRACT FROM PUBLISHER]

This work presents a complete pipeline for folding a pile of clothes using a dual-armed robot. This is a challenging task both from the viewpoint of machine vision and robotic manipulation. The presented pipeline is comprised of the following parts: isolating and picking up a single garment from a pile of crumpled garments, recognizing its category, unfolding the garment using a series of manipulations performed in the air, placing the garment roughly flat on a work table, spreading it, and, finally, folding it in several steps. The pile is segmented into separate garments using color and texture information, and the ideal grasping point is selected based on the features computed from a depth map. The recognition and unfolding of the hanging garment are performed in an active manner, utilizing the framework of active random forests to detect grasp points, while optimizing the robot actions. The spreading procedure is based on the detection of deformations of the garment's contour. The perception for folding employs fitting of polygonal models to the contour of the observed garment, both spread and already partially folded. We have conducted several experiments on the full pipeline producing very promising results. To our knowledge, this is the first work addressing the complete unfolding and folding pipeline on a variety of garments, including T-shirts, towels, and shorts. [ABSTRACT FROM AUTHOR]

Time-optimal path following considers the problem of moving along a predetermined geometric path in minimum time. In the case of a robotic manipulator with simplified constraints, a convex reformulation of this optimal control problem has been derived previously. However, many applications in robotics feature constraints such as velocity-dependent torque constraints or torque rate constraints that destroy the convexity. The present paper proposes an efficient sequential convex programming (SCP) approach to solve the corresponding nonconvex optimal control problems by writing the nonconvex constraints as a difference of convex (DC) functions, resulting in convex–concave constraints. We consider seven practical applications that fit into the proposed framework even when mutually combined, illustrating the flexibility and practicality of the proposed framework. Furthermore, numerical simulations for some typical applications illustrate the fast convergence of the proposed method in only a few SCP iterations, confirming the efficiency of the proposed framework. [ABSTRACT FROM PUBLISHER]

Passivity-based control has emerged as an important paradigm for synchronization of networked robotic systems. Despite the practical utility of task-space algorithms, the previous results focused on joint-space synchronization and were primarily derived for kinematically identical manipulators. Hence, in this paper, the problem of task-space synchronization of (possibly redundant) heterogeneous robotic systems is studied. By exploiting passivity-based synchronization results that are developed previously, an adaptive control algorithm is proposed to guarantee task-space synchronization of networked robotic manipulators in the presence of dynamic uncertainties and time-varying communication delays. To demonstrate the efficacy of the proposed framework, numerical simulations and experiments are conducted with redundant and nonredundant manipulators, respectively. [ABSTRACT FROM PUBLISHER]

Flexible manipulators have many advantages over rigid robots when used in grasping tasks, owing to the characteristic flexibility of the materials used in their construction, which allow them to absorb energy during impact and make them controllable in order to limit the force applied during contact. In this paper, a two-flexible-finger gripper with a simple sensory feedback system is proposed. A generalized proportional-integral controller is implemented to acquire high control accuracy, while eliminating the need for derivatives of system output. The performance of this force feedback control system is investigated when mounted on a 6-degree-of-freedom (6-DOF) manipulator and grasping different objects. The experimental results indicate that the system proposed is able to manipulate different types of objects (both rigid and flexible) in an industrial environment by perfectly controlling the applied contact torque. [ABSTRACT FROM AUTHOR]

As we know, the dynamic visual-tracking control, which is based on the depth-independent interaction matrix, has been proposed to cope with the general 3-D motion of robot manipulators. To deal with the unknown camera parameters, an adaptive law has been designed. It is noted, however, that the designed adaptive law uses a vector signal defined by the true depths of feature points, which are unavailable when the camera parameters are unknown. Nevertheless, such an adaptive law can still be implemented by replacing the exact depths with the estimated depths, since the estimated depths can be readily calculated by using the estimated values of the camera parameters. In this case, however, we cannot definitely say whether or not the robot system can be guaranteed to achieve asymptotical stability or even stable behavior. To overcome this problem, in this paper, we redefine the mentioned vector signal using the estimated depths and show that the design based on the new vector signal can make the robot system asymptotically stable. Additionally, the existing tracking control design based on the concept of depth-independent interaction matrix is initial-state dependent. Thus, in this paper, we also modify the existing design to obtain an initial-state-independent result. To show the performance of the proposed designs, simulation results based on a two-link planar manipulator are presented. In addition, preliminary experimental results using an industrial manipulator are also given. [ABSTRACT FROM PUBLISHER]

This paper presents a novel approach to solve multiobjective robotic trajectory planning problems. It proposes to find the Pareto optimal set, rather than a single solution usually obtained through scalarization, e.g., weighting the objective functions. Using the trajectory planning problem for a redundant manipulator as part of a captive trajectory simulation system, the general discrete dynamic programming (DDP) approximation method presented in our previous work is shown to be a promising approach to obtain a close representation of the Pareto optimal set. When compared with the set obtained by varying the weights, the results confirm that the DDP approximation method can find approximate Pareto objective vectors, where the weighting method fails, and can generally provide a closer representation of the actual Pareto optimal set. [ABSTRACT FROM AUTHOR]

We explore global randomized joint-space path planning for articulated robots that are subjected to task-space constraints. This paper describes a representation of constrained motion for joint-space planners and develops two simple and efficient methods for constrained sampling of joint configurations: tangent-space sampling (TS) and first-order retraction (FR). FRis formally proven to provide global sampling for linear task-space transformations. Constrained joint-space planning is important for many real-world problems, which involves redundant manipulators. On the one hand, tasks are designated in workspace coordinates: to rotate doors about fixed axes, to slide drawers along fixed trajectories, or to hold objects level during transport. On the other hand, joint-space planning gives alternative paths that use redundant degrees of freedom (DOFs) to avoid obstacles or satisfy additional goals while performing a task. We demonstrate that our methods are faster and more invariant to parameter choices than the techniques that exist. [ABSTRACT FROM AUTHOR]

This paper presents the theoretical analysis and experimental investigation of actively controlled manipulation of a magnetic microbead using quadrupole magnetic tweezers. Bead dynamics, magnetic actuation, and visual measurement are analyzed. A feedback control law is developed and implemented to stabilize and steer the motion of the magnetic microbead. It is developed in two steps. First, an inverse model, which is associated with a lumped-parameter analytical force model, is derived to enable feedback linearization. Second, linear controllers are designed to achieve motion stabilization and manipulation of the magnetic microbead. A proportional-gain controller along with feedback linearization is implemented to establish a stable trapping of the magnetic bead to facilitate system calibration. Experiments are then performed to validate the derived inverse force model and theoretical analysis. In addition, a minimum-variance controller is designed and employed to reduce the variance of the bead's Brownian motion. The control performance in terms of variance reduction, nanostepping, and large-range steering is then experimentally demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, a distributed-actuation method has been newly proposed based on a simple sliding-actuation mechanism for a finger-type manipulator design. Based on the spatially distributed force on the proposed sliding-actuation mechanism, it has been shown that the distributed actuation provides additional design freedom to optimize the manipulator performance. To verify the effectiveness of the proposed method, we developed a finger-type manipulator, which consists of four links with three joints, and performed experiments. The experimental results show that the fingertip force of the developed manipulator can be effectively increased and easily managed by the distributed-actuation method. [ABSTRACT FROM AUTHOR]

A key problem in robot grasping is that of positioning the manipulator contacts so that an object can be grasped. In unstructured environments, contact positions are typically planned based on range or visual measurements that are used to reconstruct object geometry. However, because it is difficult to measure the complete object geometry precisely in common grasp scenarios, it is useful to employ additional techniques to adjust or refine the grasp using local information only. In particular, grasp control techniques can be used to improve a grasp by adjusting the contact configuration after making initial contact with an object by using measurements of local object geometry at the contacts. This paper proposes three variations on null-space grasp control: an approach that combines multiple grasp objectives to improve a grasp. Two of these variations are theoretically demonstrated to converge to force-closure configurations for arbitrary convex objects when grasping with two contacts. All variations are found to converge in simulation. Robot-grasping experiments are reported that show the approach to be useful in practice. [ABSTRACT FROM AUTHOR]

In this paper, we present a strategy for recovery from joint failures in a robot arm mounted on a mobile platform. We use the ability to reposition the base of the arm by relocating the platform and to change the position of the wrist by regrasping the scientific-tool package to provide design degrees of freedom (DOFs). The velocity and acceleration specifications of the task combine with the constraints imposed by the joint failure to yield values for these DOFs that ensure that the task can be achieved despite the joint failure. [ABSTRACT FROM AUTHOR]

In this paper, we extend the concept of dynamic manipulability to evaluate the dynamic property of multifingered grasping systems consisting of a multifingered hand and a grasped object, and propose a measure of dynamic manipulability of multifingered grasping. Similar to the original dynamic manipulability, the proposed measure evaluates the mapping from a set of realizable joint torques to a set of resultant accelerations of the grasped object, which forms an ellipsoid under a constant internal force constraint. It is clearly shown that the internal forces not only affect the volume of the ellipsoid, but also the amount of offset of the ellipsoid, while the gravity forces simply induce an offset. A new measure, i.e., omni-directionality, is introduced to add a penalty to the original manipulability measure, which simply evaluates the volume of the ellipsoid, depending on how much the ellipsoid is offset. Numerical examples by using a simple two-fingered robot hand are shown to demonstrate the effectiveness of the proposed measure. [ABSTRACT FROM AUTHOR]

In the well-known electromechanical analogy that converts between electrical and mechanical system representations, mass is the dual of a grounded capacitor. Consequently, any. electrical circuit that contains ungrounded capacitors, such as a filter, does not have a mechanical equivalent. A new mechanical system element representing a pulley-based differential transmission is proposed, which, when connected to a mass, is shown to simulate a capacitor in the general case. This new differential mass model provides an additional conceptual framework to model complex mechanical systems such as robotic manipulators. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

One important category of parallel mechanisms is the translational parallel mechanism (TPM). This paper focuses on the structural shakiness of the nonoverconstrained TPM. Such a structural shakiness is due to the unavoidable lack of rigidity of the real bodies, which leads to uncheckable orientation changes of the moving platform of a TPM. Using algebraic properties of displacement subsets and, especially, displacement Lie subgroup theory, we show that the structural shakiness of the nonoverconstrained TPM is inherently determined by the structural type of its limb chains. A structural shakiness index (SSI) for a nonoverconstrained TPM is introduced. When the set of feasible displacements of the end body of a 5-degree-of-freedom (DOFs) limb chain contains two infinities of parallel axes of rotation, we have SSI = 2; when the displacement set of the end body of a 5-DOF limb chain contains only one infinity of parallel axes of rotation, we have SSI = 1. It is proven that nonoverconstained TPMs constructed with limb chains with SSI = 1 are much less prone to orientation changes than those constructed with limb chains with SSI = 2. Based on the SSI, we enumerate limb kinematic chains and construct 21 nonoverconstrained TPMs with less shakiness. [ABSTRACT FROM AUTHOR]

A fully actuated system can execute any joint trajectory. However, if the system is underactuated, not all joint trajectories are attainable. For such systems, it is difficult to characterize attainable joint trajectories analytically. Numerical methods are generally used to characterize these. This paper investigates the property of differential flatness for underactuated planar open-chain robots and studies dependence on inertia distribution within the system. It is shown that certain choices of inertia distributions make an underactuated open-chain planar robot with revolute joints feedback linearizable, i.e., also differentially flat. Once this property is established, trajectory between any two points in the state space can be planned, and a controller can be developed to correct for errors. To demonstrate the proposed methodology in hardware, experiments with an underactuated 3-DOF planar robot are also presented. [ABSTRACT FROM AUTHOR]

Motivated by the need for greater speed, efficiency, and adaptability in climbing and walking robots, we have developed a bipedal planar robot that complements its walking and climbing capabilities with rolling. Rolling capabilities are provided by an innovative morphology, without the need for additional resources beyond those required by walking and climbing. Herein, we present the design of this robot, the development of a quasi-static rolling controller, and a comparison of experimentally obtained speed and energy data for walking versus rolling locomotion. We show that rolling can significantly improve energy efficiency over walking—as much as a factor of 5.5. We also demonstrate the ability to roll up slopes and roll over obstacles. [ABSTRACT FROM AUTHOR]

This paper introduces a novel and general real-time adaptive motion planning (RAMP) approach suitable for planning trajectories of high-DOF or redundant robots, such as mobile manipulators, in dynamic environments with moving obstacles of unknown trajectories. The RAMP approach enables simultaneous path and trajectory planning and simultaneous planning and execution of motion in real time. It facilitates real-time optimization of trajectories under various optimization criteria, such as minimizing energy and time and maximizing manipulability. It also accommodates partially specified task goals of robots easily. The approach exploits redundancy in redundant robots (such as locomotion versus manipulation in a mobile manipulator) through loose coupling of robot configuration variables to best achieve obstacle avoidance and optimization objectives. The RAMP approach has been implemented and tested in simulation over a diverse set of task environments, including environments with multiple mobile manipulators. The results (and also the accompanying video) show that the RAMP planner, with its high efficiency and flexibility, not only handles a single mobile manipulator well in dynamic environments with various obstacles of unknown motions in addition to static obstacles, but can also readily and effectively plan motions for each mobile manipulator in an environment shared by multiple mobile manipulators and other moving obstacles. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical methodology of inverse kinematic computation for 7 DOF redundant manipulators with joint limits. Specifically, the paper focuses on how to obtain all feasible inverse kinematic solutions in the global configuration space where joint movable ranges are limited. First, a closed-form inverse kinematic solution is derived based on a parameterization method. Second, how the joint limits affect the feasibility of the inverse solution is investigated to develop an analytical method for computing feasible solutions under the joint limits. Third, how to apply the method to the redundancy resolution problem is discussed and analytical methods to avoid joint limits are developed in the position domain. Lastly, the validity of the methods is verified by kinematic simulations. [ABSTRACT FROM AUTHOR]

Unlike traditional rigid linked robots, soft robotic manipulators can bend into a wide variety of complex shapes due to control inputs and gravitational loading. This paper presents a new approach for modeling soft robotic manipulators that incorporates the effect of material nonlinearities and distributed weight and payload. The model is geometrically exact for the large curvature, shear, torsion, and extension that often occur in these manipulators. The model is based on the geometrically exact Cosserat rod theory and a fiber reinforced model of the air muscle actuators. The model is validated experimentally on the OctArm V manipulator, showing less than 5% average error for a wide range of actuation pressures and base orientations as compared to almost 50% average error for the constant-curvature model previously used by researchers. Workspace plots generated from the model show the significant effects of self-weight on OctArm V. [ABSTRACT FROM AUTHOR]

The admittance of a manipulator can be used to improve robotic assembly. If properly selected, the admittance will regulate a contact force and use it to guide the parts to proper positioning. In previous work, procedures for selecting the appropriate admittance for single principal contact (PC) cases were identified. This paper extends this research for some of the two PC cases—those for which each contact occurs at a single point. The conditions obtained ensure that the motion that results from frictionless contact always instantaneously reduces part misalignment. We show that, for bounded misalignments, if an admittance satisfies the misalignment. reducing conditions at a finite number of contact configurations, then the admittance will also satisfy the conditions at all intermediate configurations. [ABSTRACT FROM AUTHOR]

Force feedback is necessary for accurate force control in robotic manipulators, and thus far, wrist force/torque (F/T) sensors have been used. But an important problem arises when only these types of sensors are used. In a dynamic situation where the manipulator moves in either free or constrained space, the interaction forces and moments at the contact point and also the noncontact ones are measured by the mentioned sensor. In this paper, an estimator based on a sensor fusion strategy integrating the measurements of three different sensors (a wrist FIT sensor, an inertial sensor, and joint sensors) was developed to determine the contact force and torque exerted by the manipulator to its environment. The resulting observer helps to overcome some difficulties of uncertain world models and unknown environments since it reduces the high-frequency and low-frequency spectral contents, i.e., the low-frequency component due to inertia of a heavy tool mass and the high-frequency component due to impacts. The new improvement was experimentally validated in a force/position impedance control loop applied to a Stäubli RX60 industrial robotic platform. [ABSTRACT FROM AUTHOR]

The conditions for a parallel manipulator to be flagged can be simply expressed in terms of linear dependencies between the coordinates of its leg attachments, both on the base and on the platform. These dependencies permit to describe the manipulator singularities in terms of incidences between two flags (hence, the name ‘flagged’). Although these linear dependencies might look, at first glance, too restrictive, in this paper, the family of flagged manipulators is shown to contain large subfamilies of six-legged and three-legged manipulators. The main interest of flagged parallel manipulators is that their singularity loci admit a well-behaved decomposition with a unique topology irrespective of the metrics of each particular design. In this paper, this topology is formally derived and all the cells, in the configuration space of the platform, of dimension 6 (nonsingular) and dimension 5 (singular), together with their adjacencies, are worked out in detail. [ABSTRACT FROM AUTHOR]

Many control laws for robot manipulators assume uniform boundedness of the Coriolis/centripetal matrix to insure global stability. In this paper, a new procedure to derive explicitly uniform bounds of the Coriolis/centripetal matrix is proposed. This procedure has the advantage with respect to other methods of avoiding the computation of the Christoffel symbols of first order involved in the derivation of the dynamics of the whole mechanism. To this end a new description of the Coriolis/centripetal matrix has been introduced based on fundamental matrices which exhibit structural properties of commutation and representation. [ABSTRACT FROM AUTHOR]

Visual servoing consists of steering a robot from an initial to a desired location by exploiting the information provided by visual sensors. This paper deals with the problem of realizing visual servoing for robot manipulators taking into account constraints such as visibility, workspace (that is obstacle avoidance), and joint constraints, while minimizing a cost function such as spanned image area, trajectory length, and curvature. To solve this problem, a new path-planning scheme is proposed. First, a robust object reconstruction is computed from visual measurements which allows one to obtain feasible image trajectories. Second, the rotation path is parameterized through an extension of the Euler parameters that yields an equivalent expression of the rotation matrix as a quadratic function of unconstrained variables, hence, largely simplifying standard parameterizations which involve transcendental functions. Then, polynomials of arbitrary degree are used to complete the parametrization and formulate the desired constraints and costs as a general optimization problem. The optimal trajectory is followed by tracking the image trajectory with an IBVS controller combined with repulsive potential fields in order to fulfill the constraints in real conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a natural saturating extension of the proportional-derivative (PD) with desired gravity compensation (PDdgc) control law for the global regulation of robot manipulators with bounded inputs. Compared with other algorithms previously proposed under the same analytical framework, it proves to be advantageous in several senses. First, it involves a single saturation function at each joint. Second, it does not need to discriminate the terms that shall be bounded, since these are simply all of them included within the only saturation involved at every joint. Experimental results show the effectiveness of the proposed scheme. As far as the authors are aware, no such type of natural saturating extension (i.e., involving only one saturation function at each joint, where all the terms of the controller are embedded) to the bounded input case had been previously proposed for the PDdgc scheme. Furthermore, it is shown how the proposed approach may be conceived within the framework of the energy shaping plus damping injection methodology. [ABSTRACT FROM AUTHOR]

Viscoelastic contact is a type of contact which includes, in addition to linear or nonlinear elastic response, time-dependent response due to relaxation or creep phenomena that govern the contact behavior. The characteristics of the time-dependent relaxation of such a viscoelastic contact are typically exponentially decaying functions, and exponentially growing functions for creep, respectively. Such contacts can be found in anthropomorphic robotic fingers, soft materials, viscoelastic skin with rigid core, and human fingers and feet. In this paper, the nature of viscoelastic contacts is investigated, and the evolution of their friction limit surfaces and of the pressure distributions at the contact interface are studied. Two cases commonly found in robotic grasping and manipulation are discussed. Based on the modeling formulation, it is found that the two important parameters of analysis and modeling for such contacts, i.e., the radius of contact area and the profile of pressure distribution, can be chosen using proposed coupling equations as the viscoelastic contact interface evolves with time. The new contribution of this paper includes a proposal of coupling equations between the two important parameters to describe the viscoelastic contact interface, and a study of the evolution of limit surfaces for viscoelastic contact interface due to temporal dependency, and the implication on grasp stability. It is found from the evolution of limit surfaces that when normal force is applied with typical viscoelastic contacts, grasp becomes more stable as time elapses. The modeling can be applied to the design of fingertips and the analysis of robotic grasping and manipulation involving viscoelastic fingers. [ABSTRACT FROM AUTHOR]

This paper describes a spatial-motion-constraints-generation approach for a human-machine collaborative surgical-assistant system from registered computer tomography models. We extend constrained optimization formulation incorporating task goals, anatomy-based constraints, ‘no fly zones’ etc. We use a fast potential-collision-constraint-detection method based on a 3-D surface model and covariance tree data structure. These boundary constraints, along with task behaviors and joint limits, serve as constraint conditions for constrained robot control. We are able to follow a complex path inside a human skull, phantom represented by a surface model composed of 99000 vertices and 182 000 triangles in real time. Our approach enables real-time task-based control of a surgical robot in a precise interactive minimally invasive surgery task. We illustrate our approach based on two example tasks which are analogous to the procedures in endoscopic sinus surgery, and analyze the user's performance on both teleoperation and cooperative control for one of the example tasks. The experimental results show that a robotic assistant employing our approach on spatial motion constraints can assist the user in skilled manipulation tasks, while maintaining desired properties. Our approach is equally applicable to teleoperative and cooperative controlled robots. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of position-based visual servoing in a multiarm robotic cell equipped with a hybrid eye-in-hand/eye-to-hand multicamera system. The proposed approach is based on the real-time estimation of the pose of a target object by using the extended Kalman filter. The data provided by all the cameras are selected by a suitable algorithm on the basis of the prediction of the object self-occlusions, as well as of the mutual occlusions caused by the robot links and tools. Only an optimal subset of image features is considered for feature extraction, thus ensuring high estimation accuracy with a computational cost independent of the number of cameras. A salient feature of the paper is the implementation of the proposed approach to the case of a robotic cell composed of two industrial robot manipulators. Two different case studies are presented to test the effectiveness of the hybrid camera configuration and the robustness of the visual servoing algorithm with respect to the occurrence of occlusions. [ABSTRACT FROM AUTHOR]

Classical sensor-based approaches tend to constrain all the degrees of freedom of a robot during the execution of a task. In this paper, a new solution is proposed. The key idea is to divide the global full-constraining task into several subtasks, which can be applied or inactivated to take into account potential constraints of the environment. Far from any constraint, the robot moves according to the full task. When it comes closer to a configuration to avoid, a higher level controller removes one or several subtasks, and activates them again when the constraint is avoided. The last controller ensures the convergence at the global level by introducing some look-ahead capabilities when a local minimum is reached. The robot accomplishes the global task by automatically sequencing sensor-based tasks, obstacle avoidance, and short deliberative phases. In this paper, a complete solution to implement this idea is proposed, along with several experiments that prove the validity of this approach. [ABSTRACT FROM AUTHOR]

This paper addresses the static analysis of cable-driven robotic manipulators with non-negligible cable mass. An approach to computing the static displacement of a homogeneous elastic cable is presented. The resulting cable-displacement expression is used to solve the inverse kinematics of general cable-driven robotic manipulators. In addition, the sag-induced stiffness of the cables is derived. Finally, two sample robotic manipulators with dimensions and system parameters similar to a large scale cable-driven manipulator currently under development are analyzed. The results show that cable sag can have a significant effect on both the inverse kinematics and stiffness of such manipulators. [ABSTRACT FROM AUTHOR]

By judiciously selecting the admittance of a manipulator, the forces of contact that occur during assembly can be used to guide the parts to proper positioning. This paper identifies conditions for selecting the appropriate spatial admittance to achieve reliable force-guided assembly of polyhedral parts for cases in which a single feature (vertex, edge, or face) of one part contacts a single feature of the other, i.e., all single principal contact cases. These conditions ensure that the motion that results from frictionless contact always instantaneously reduces part misalignment. We show that, for bounded misalignments, if an admittance satisfies the misalignment-reducing conditions at a finite number of contact configurations, then the admittance will also satisfy the conditions at all intermediate configurations. [ABSTRACT FROM AUTHOR]

High-precision motion of parallel manipulators depends not only on the position accuracy of each actuator, but also on the position synchronization of all actuators. This paper presents a simple synchronized control algorithm for the setpoint position control of parallel manipulators, by incorporating cross-coupling technology into a common proportional-derivative (PD) control architecture. An integrated controller is developed, consisting of a PD control and a saturated proportional-integral (S-PI) control with feedback of the differential position errors amongst actuators (defined as the synchronization errors). The controller can stabilize the motion of each actuator, and meanwhile synchronize all actuators' motionsso that both position and synchronization errors converge to zero. The control algorithm does not use the modeling parameters in the controller formulation, and thus permits easy implementation in practice. It is proved that the proposed method can guarantee global asymptotical stability of the system. Experiments conducted on a planar three-degree-of-freedom parallel manipulator demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper provides a detailed design description and technical testing results of a device for studying motor learning and rehabilitation of human locomotion. The device makes use of linear motors and a parallel mechanism to achieve a wide dynamic force bandwidth as it interacts with the leg during treadmill stepping. [ABSTRACT FROM AUTHOR]

We develop a velocity field tracking-control scheme with proportional integral force feedback to transport and manipulate deformable material with a mobile manipulator. We assume that the deformable object is a damped underactuated mechanical system. The input-to-state stability properties of its zero dynamics are used to derive bounds on the admissible end-effector velocities and accelerations. It is shown both analytically and in simulation that using deformation feedback, we can avoid exciting excessive object deformations. [ABSTRACT FROM AUTHOR]

Computation of grasps with form/force closure is one of the fundamental problems in the study of multifingered grasping and dextrous manipulation. Based on the geometric condition of the closure property, this paper presents a numerical test to quantify how far a grasp is from losing form/force closure. With the polyhedral approximation of the friction cone, the proposed numerical test can be formulated as a single linear program. An iterative algorithm for computing optimal force-closure grasps, which is implemented by minimizing the proposed numerical test in the grasp configuration space, is also developed. The algorithm is computationally efficient and generally applicable. tt can be used for computing form/force-closure grasps on 3-D objects with curved surfaces, and with any number of contact points. Simulation examples are given to show the effectiveness and computational efficiency of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Distributed manipulation systems induce motions on objects through the application of many external forces. Many of these systems are abstracted as planar programmable force fields. Quadratic potential fields form a class of such fields that lend them- selves to analytical study and exhibit useful stability properties. This paper introduces a new methodology to build quadratic potential fields with simple devices using the naturally existing phenomena of airflow, which is an improvement to the traditional use of the complicated programmable actuator arrays. It also provides a basis for the exploitation, in distributed manipulation, of natural phenomena like airflow, which require rigorous analysis and display stability difficulties. A demonstration and verification of the theoretical results for the special case of the elliptic field with airflows is also presented. [ABSTRACT FROM AUTHOR]

The learning from observation (LFO) paradigm has been widely applied in various types of robot systems. It helps reduce the work of the programmer. However, the applications of available systems are limited to manipulation of rigid objects. Manipulation of deformable objects is rarely considered, because it is difficult to design a method for representing states of deformable objects and operations against them. Furthermore, too many operations are possible on them. In this paper, we choose knot tying as a case study for manipulating deformable objects, because the knot theory is available and the types of operations possible in knot tying are limited. We propose a knot planning from observation (KPO) paradigm, a KPO theory, and a KPO system. [ABSTRACT FROM AUTHOR]

We introduce a new method for synthesizing kinematic relationships for a general class of continuous backbone, or continuum, robots. The resulting kinematics enable real-time task and shape control by relating workspace (Cartesian) coordinates to actuator inputs, such as tendon lengths or pneumatic pressures, via robot shape coordinates. This novel approach, which carefully considers physical manipulator constraints, avoids artifacts of simplifying assumptions associated with previous approaches, such as the need to fit the resulting solutions to the physical robot. It is applicable to a wide class of existing continuum robots and models extension, as well as bending, of individual sections. In addition, this approach produces correct results for orientation, in contrast to some previously published approaches. Results of real-time implementations on two types of spatial multisection continuum manipulators are reported. [ABSTRACT FROM AUTHOR]

Some in-parallel robots, such as the 3-2-1 and the 3/2 manipulators, have attracted attention because their forward kine- matics can be solved by three consecutive trilaterations. In this paper, we identify a class of these robots, which we call flagged manipulators, whose singularity loci admit a well-behaved decomposition, i.e., a stratification, derived from that of the flag manifold. Two remarkable properties must be highlighted. First, the decomposition has the same topology for all members in the class, irrespective of the metric details of each particular robot instance. Thus, we provide explicitly all the singular strata and their connectivity, which apply to all flagged manipulators without any tailoring. Second, the strata can be easily characterized geometrically, because it is possible to assign local coordinates to each stratum (in the configuration space of the manipulator) that correspond to uncoupled rotations and/or translations in the workspace. [ABSTRACT FROM AUTHOR]

Hyper redundancy, high reliability, and high task repeatability are the main advantages of binary manipulators over conventional manipulators with continuous joints, especially when manipulators are operated under tough and complex work conditions. The precise and complex movement of a binary manipulator necessitates many modules. In this case, numerically efficient inverse kinematics algorithms for binary manipulators usually require impractically large memory size for the real-time calculation of the binary states of all joints. To overcome this limitation by developing a new inverse kinematics algorithm is the objective of this research. The key idea of the proposed method is to formulate the inverse kinematics problem of a binary manipulator as an optimization problem with real design variables, in which the real variables are forced to approach the permissible binary values corresponding to two discrete joint displacements. Using the pro- posed optimization method, the inverse kinematics of 3-D binary manipulators with many modules can be solved almost in real time (say, less than a second for up to 16 modules) without requiring a large memory size. Furthermore, some manipulation considerations, such as operation power minimization, can be easily incorporated into the proposed formulation. The effectiveness of the proposed method is verified through several numerical problems, including 3-D inverse kinematics problems. [ABSTRACT FROM AUTHOR]

In this paper, the design of reactionless 3-degree-of-freedom (DOF) and 6-DOF parallel manipulators is presented. At first, the design and dynamic balancing of a novel 3-DOF parallel mechanism referred to as the parallelepiped mechanism are addressed. Two types of actuation schemes of the mechanism are considered, and the two corresponding mechanical structures are designed. The balancing equations are derived by imposing that the center of mass of the mechanism is fixed and that the total angular momentum is constant with respect to a fixed point. Optimization is performed to determine the counterweights and counter-rotations based on the balancing conditions. Numerical examples of reactionless 3-DOF parallelepiped mechanisms are given. The dynamic simulation software ADAMS is used to simulate the motion of the mechanisms and to verify that the mechanisms are reactionless at all limes and for arbitrary trajectories. Finally, the 3-DOF parallelepiped mechanisms are used as legs to synthesize reactionless 6-DOF parallel manipulators. [ABSTRACT FROM AUTHOR]

This paper studies the problem of position-tracking adaptive control for planar robotic manipulators through visual servoing under a fixed-camera configuration. The uncertain parameters enter through two separate channels: 1) through the robot dynamics in terms of constant linearly appearing Inertia values and 2) nonlinearly appearing camera calibration parameters such as the camera orientation angle and scale factor uncertainties. The associated adaptive control problem is challenged by the presence of the nonlinearly appearing uncertain camera-calibration parameters. We provide a novel solution to this problem by constructing two layers of control structures. To be specific, the inner layer is a conventional certainty-equivalence adaptive controller that stabilizes the faster robot dynamics, whereas the outer layer is a novel controller structure that is designed to handle the nonlinear parameterizations within the slower dynamics of the vision system. We prove global stability and boundedness for all of the closed-loop signals of the cascade interconnection under the relatively standard assumption of Jacobian nonsingularity. If the control objective is set-point regulation, we guarantee global asymptotic convergence for the tracking errors. On the other hand, if the desired trajectory is time-varying, we show that the closed-loop tracking errors under the action of the proposed controller converge to a residual set whose size is determined by the speed of the desired trajectory. Furthermore, we show that the size of this residual error set can be made arbitrarily small by appropriate choice of certain parameters within the controller structure. In contrast with other solutions for this problem that are documented in existing literature, we completely avoid overparameterizations and make no restrictions on the possible range of the camera orientation angle or any additional persistence of excitation requirements. The only piece of prior knowledge required for our solution is the availability of a lower bound on the camera scale factor. The effectiveness of the proposed scheme is illustrated through numerical simulations. [ABSTRACT FROM AUTHOR]

Given some geometric elements such as points and lines in R³, subject to a set of pairwise distance constraints, the problem tackled in this paper is that of finding all possible configurations of these elements that satisfy the constraints. Many problems in robotics (such as the position analysis of serial and parallel manipulators) and CAD/CAM (such as the interactive placement of objects) can be formulated in this way. The strategy herein proposed consists of looking for some of the a priori unknown distances, whose derivation permits solving the problem rather trivially. Finding these distances relies on a branch-and-prune technique, which iteratively eliminates from the space of distances entire regions which cannot contain any solution. This elimination is accomplished by applying redundant necessary conditions derived from the theory of distance geometry. The experimental results qualify this approach as a promising one. [ABSTRACT FROM AUTHOR]