Showing papers in "Journal of Robotic Systems in 2005"
TL;DR: A hierarchical framework for approximately optimal control of redundant manipulators is presented, designed to yield input-output behavior that captures the task-relevant aspects of plant dynamics but has reduced dimensionality.
Abstract: We present a hierarchical framework for approximately optimal control of redundant manipulators. The plant is augmented with a low-level feedback controller, designed to yield input-output behavior that captures the task-relevant aspects of plant dynamics but has reduced dimensionality. This makes it possible to reformulate the optimal control problem in terms of the augmented dynamics, and optimize a high-level feedback controller without running into the curse of dimensionality. The resulting control hierarchy compares favorably to existing methods in robotics. Furthermore, we demonstrate a number of similarities to (nonhierarchical) optimal feedback control. Besides its engineering applications, the new framework addresses a key unresolved problem in the neural control of movement. It has long been hypothesized that coordination involves selective control of task parameters via muscle synergies, but the link between these parameters and the synergies capable of controlling them has remained elusive. Our framework provides this missing link. © 2005 Wiley Periodicals, Inc.
106 citations
TL;DR: Simulations of the proposed planning strategy for improving the safety of human-robot interaction by minimizing a danger criterion during the planning stage indicate that a criterion based on scaled mutually dependent factors generates safe, feasible paths for interaction.
Abstract: This paper presents a strategy for improving the safety of human-robot interaction by minimizing a danger criterion during the planning stage. This strategy is one part of the overall methodology for safe planning and control in human-robot interaction. The focus application is a hand-off task between an articulated robot and an inexpert human user. Two formulations of the danger criterion are proposed: a criterion assuming independent safety-related factors, and a criterion assuming mutually dependent factors. Simulations of the proposed planning strategy are presented for both 2D and 3D robots. The results indicate that a criterion based on scaled mutually dependent factors such as the robot inertia and the human robot distance generates safe, feasible paths for interaction. © 2005 Wiley Periodicals, Inc.
100 citations
TL;DR: The type synthesis of US-equivalent PMs is presented in detail to show the application of the proposed approach based on screw theory and using the concept of virtual chains.
Abstract: With the introduction of virtual chains to represent the motion patterns of 5-DOF motions, a classification of 5-DOF PMs (parallel manipulators) is proposed at first. A general method for the type synthesis of 5-DOF PMs is then proposed based on screw theory and using the concept of virtual chains. The type synthesis of US-equivalent PMs is presented in detail to show the application of the proposed approach. US-equivalent PMs are the parallel counterparts of the 5-DOF US serial manipulators. For a US-equivalent PM, the moving platform can rotate arbitrarily about a point moving along a spherical surface. The type synthesis of legs for US-equivalent PKCs (parallel kinematic chains), the type synthesis of US-equivalent PKCs, as well as the selection of actuated joints of US-equivalent PMs are dealt with in sequence. US-equivalent PKCs with and without inactive joints are synthesized. Several US-equivalent PMs as well as other classes of 5-DOF PMs with identical type of legs are obtained. © 2005 Wiley Periodicals, Inc.
88 citations
TL;DR: In this article, the matrix equation AX=XB used for hand-to-sensor calibration of robot-mounted sensors is analyzed using a geometrical approach, which leads to an original way to describe the properties of the equation and to find all of its solutions.
Abstract: In this paper, the matrix equation AX=XB used for hand to sensor calibration of robot-mounted sensors is analyzed using a geometrical approach. The analysis leads to an original way to describe the properties of the equation and to find all of its solutions. It will also be highlighted why, when multiple instances AiX=XBi (i=1,2,...) of the equation are to be solved simultaneously, the system is overconstrained. Finally, singular cases are also discussed. © 2005 Wiley Periodicals, Inc.
80 citations
TL;DR: An iterative learning rule with both predictive and current learning terms is used to overcome uncertainties and the disturbances in the system and shows that the system states, outputs, and control inputs are guaranteed to converge to the desired trajectories with or without state disturbances, output disturbances, or initial state errors.
Abstract: This paper develops a kinematic path-tracking algorithm for a nonholonomic mobile robot using an iterative learning control (ILC) technique. The proposed algorithm produces a robot velocity command, which is to be executed by the proper dynamic controller of the robot. The difference between the velocity command and the actual velocity acts as state disturbances in the kinematic model of the mobile robot. Given the kinematic model with state disturbances, we present an ILC-based path-tracking algorithm. An iterative learning rule with both predictive and current learning terms is used to overcome uncertainties and the disturbances in the system. It shows that the system states, outputs, and control inputs are guaranteed to converge to the desired trajectories with or without state disturbances, output disturbances, or initial state errors. Simulations and experiments using an actual mobile robot verify the feasibility and validity of the proposed learning algorithm. © 2005 Wiley Periodicals, Inc.
52 citations
TL;DR: The development of a collision- and self-collision-avoidance scheme for redundant manipulators is discussed in this paper and the performance of the proposed scheme is demonstrated for a seven degrees-of-freedom redundant manipulator via simulations and experiments.
Abstract: The development of a collision- and self-collision-avoidance scheme for redundant manipulators is discussed in this paper. The method is based on modeling the arm and its environment by simple geometric primitives (cylinders and spheres). A compact method of detecting collisions between two cylinders is introduced. By resorting to the notions of dual angles and dual vectors for representing the axes of cylinders in space, a characterization of different types of collisions is introduced. The performance of the proposed scheme is demonstrated for a seven degrees-of-freedom redundant manipulator via simulations and experiments. © 2005 Wiley Periodicals, Inc.
50 citations
TL;DR: The implementation of the minimum variance model is described, both for point-to-point reaching movements and for more complex trajectories involving via points, and its performance in producing humanlike movement is evaluated.
Abstract: Models of human movement from computational neuroscience provide a starting point for building a system that can produce flexible adaptive movement on a robot. There have been many computational models of human upper limb movement put forward, each attempting to explain one or more of the stereotypical features that characterize such movements. While these models successfully capture some of the features of human movement, they often lack a compelling biological basis for the criteria they choose to optimize. One that does provide such a basis is the minimum variance model (and its extension—task optimization in the presence of signal-dependent noise). Here, the variance of the hand position at the end of a movement is minimized, given that the control signals on the arm's actuators are subject to random noise with zero mean and variance proportional to the amplitude of the signal. Since large control signals, required to move fast, would have higher amplitude noise, the speed-accuracy trade-off emerges as a direct result of the optimization process. We chose to implement a version of this model that would be suitable for the control of a robot arm, using an optimal control scheme based on the discrete-time linear quadratic regulator. This implementation allowed us to examine the applicability of the minimum variance model to producing humanlike movement. In this paper, we describe our implementation of the minimum variance model, both for point-to-point reaching movements and for more complex trajectories involving via points. We also evaluate its performance in producing humanlike movement and show its advantages over other optimization based models (the well-known minimum jerk and minimum torque-change models) for the control of a robot arm. © 2005 Wiley Periodicals, Inc.
42 citations
TL;DR: In this article, it is shown that a simple control signal composed of a well-tuned (synergistic) combination of task-space position feedback (corresponding to spring-like forces) and joint velocity feedback (viscous like forces) leads to a skilled motion of reaching in a natural way without solving inverse kinematics or dynamics.
Abstract: This article challenges Bernstein's problem of redundant degrees of freedom (DOF) that remains unsolved from both the standpoints of physiology and robotics. A rather simpler but difficult control problem of movements of human-like multi-joint reaching with excess DOF is analyzed from Newtonian mechanics and differential geometry. It is shown that, regardless of ill-posedness of inverse kinematics for such a redundant system, a simpler control signal composed of a well-tuned (synergistic) combination of task-space position feedback (corresponding to spring-like forces) and joint velocity feedback (viscous-like forces) leads to a skilled motion of reaching in a natural way without solving inverse kinematics or dynamics. Fundamental characteristics of human skilled multi-joint movements such as (1) generation of a quasi-straight line trajectory of the endpoint and (2) a little “variability” in task space but notable “variability” in joint space are analyzed from the concepts of “stability on an EP (equilibrium-point) manifold” and “transferability to an EP submanifold.” It is claimed that the control signal exerts torques on joints of the whole arm just like a single virtual-spring drawing the endpoint of the arm to the target while giving a specified viscosity to each joint. This leads to an interpretation that skilled reaching movements emerge through formation of a set of neuro-motor signals exerting relevant group of muscles to generate a total potential energy equivalent to that of the spring. Discussions are presented on how such control signals in case of human reaching can be generated in a feedforward manner with capability of anticipatory adjustments of stiffness. © 2005 Wiley Periodicals, Inc.
38 citations
TL;DR: In this article, a nonlinear H∞ control for robot manipulators is extended with integral terms to cope with persistent disturbances, such as constant load at the end-effector, and a modified expression for the required increment in the control signal is provided.
Abstract: In this paper, previous works on nonlinear H∞ control for robot manipulators are extended In particular, integral terms are considered to cope with persistent disturbances, such as constant load at the end-effector The extended controller may be understood as a computed-torque control with an external PID, whose gain matrices vary with the position and velocity of the robot joints In addition, in order to increase the controller robustness, an extension of the algorithms with saturation functions has been carried out This extension deals with the resulting nonlinear equation of the closed-loop error A modified expression for the required increment in the control signal is provided, and the local closed-loop stability of this approach is discussed Finally, simulation results for a two-link robot and experimental results for an industrial robot are presented The results obtained with this technique have been compared with those attained with the original controllers to show the improvements achieved by means of the proposed method © 2005 Wiley Periodicals, Inc
37 citations
TL;DR: In this paper, a methodology for the design of parallel kinematic machines with defined isotropy and stiffness is presented, where the six legs have to be divided into two groups and the legs belonging to one tern are mutually identical.
Abstract: This paper presents a methodology for the design of PKMs (parallel kinematic machines) with defined isotropy and stiffness. Partial isotropy or full isotropy can be achieved by suitable design choices. The former is useful for five axis applications, while the latter for six axis manipulators. The paper summarizes the concept of full and partial isotropy, and for a wide class of hexapods defines in analytical form the conditions to achieve it exactly. These conditions can be used to design isotropic parallel manipulators. The methodology requires that the six legs have to be divided into two groups (terns). The legs belonging to one tern are mutually identical and are positioned with radial symmetry with respect to the TCP (tool center point). The paper shows that the manipulator structure can be defined in term of 13 design parameters, the value of six of them are chosen in order to achieve the required isotropy and stiffness properties, while the remaining seven parameters can be used to optimize the structure. The design criterion here presented assures that stiffness isotropy, force, and velocity isotropy are all achieved contemporarily. This methodology can be practically applied to a large family of hexapods. © 2005 Wiley Periodicals, Inc.
32 citations
TL;DR: The proposed method for autonomous robot navigation based on homographies computed between the current image and images taken in a previous teaching phase with a monocular vision system has turned out to be especially useful to correct heading and lateral displacement, which are critical in systems based on odometry.
Abstract: We introduce a method for autonomous robot navigation based on homographies computed between the current image and images taken in a previous teaching phase with a monocular vision system. The features used to estimate the homography are vertical lines automatically extracted and matched. From homography, the underlying motion correction between the reference path and the current robot location is computed. The proposed method, which uses a sole calibration parameter, has turned out to be especially useful to correct heading and lateral displacement, which are critical in systems based on odometry. We have tested the proposal in simulation, and with real images. Besides, the visual system has been integrated into an autonomous wheelchair for handicapped, working in real time with robustness. © 2005 Wiley Periodicals, Inc.
TL;DR: A low cost positioning system using internal sensors like odometers and optical fiber gyroscopes is proposed using three simple localization algorithms based on different sensor data processing procedures.
Abstract: An autonomous mobile robot must be able to elaborate the measures provided by the sensor equipment to localize itself with respect to a coordinate system. The precision of the location estimate depends on the sensor accuracy and on the reliability of the measure processing algorithm. The purpose of this article is to propose a low cost positioning system using internal sensors like odometers and optical fiber gyroscopes. Three simple localization algorithms based on different sensor data processing procedures are presented. Two of them operate in a deterministic framework, the third operates in a stochastic framework where the uncertainty is induced by sensing and unmodeled robot dynamics. The performance of the proposed localization algorithms are tested through a wide set of laboratory experiments and compared in terms of localization accuracy and computational cost. © 2005 Wiley Periodicals, Inc.
TL;DR: In this article, the authors developed a locally elastic contact model to describe the nonlinear coupling between the contact force with friction and elastic deformation at the individual contact, and a set of compatibility equations was given so that the elastic deformations among all contacts in the grasping system result in a consistent set of displacements of the object.
Abstract: Because friction is central to robotic grasp, developing an accurate and tractable model of contact compliance, particularly in the tangential direction, and predicting the passive force closure are crucial to robotic grasping and contact analysis. This paper analyzes the existence of the uncontrollable grasping forces (i.e., passive contact forces) in enveloping grasp or fixturing, and formulates a physical model of compliant enveloping grasp. First, we develop a locally elastic contact model to describe the nonlinear coupling between the contact force with friction and elastic deformation at the individual contact. Further, a set of “compatibility” equations is given so that the elastic deformations among all contacts in the grasping system result in a consistent set of displacements of the object. Then, combining the force equilibrium, the locally elastic contact model, and the “compatibility” conditions, we formulate the natural compliant model of the enveloping grasp system where the passive compliance in joints of fingers is considered, and investigate the stability of the compliant grasp system. The crux of judging passive force closure is to predict the passive contact forces in the grasping system, which is formulated into a nonlinear least square in this paper. Using the globally convergent Levenberg-Marquardt method, we predict contact forces and estimate the passive force closure in the enveloping grasps. Finally, a numerical example is given to verify the proposed compliant enveloping grasp model and the prediction method of passive force closure. © 2005 Wiley Periodicals, Inc.
TL;DR: This paper presents a hierarchical strategy for field mobile robots that incorporates path planning at different ranges that utilizes gross terrain characteristics, such as hills and valleys, to determine globally safe paths through the rough terrain.
Abstract: This paper presents a hierarchical strategy for field mobile robots that incorporates path planning at different ranges. At the top layer is a global path planner that utilizes gross terrain characteristics, such as hills and valleys, to determine globally safe paths through the rough terrain. This information is then passed via waypoints to a regional layer that plans appropriate navigation paths using regional terrain characteristics. The global and regional path planners share the same map information, but at different ranges. The motion recommendations from the regional layer are then combined with those of the reactive navigation layer to provide reactive control for the mobile robot. Details of the global and regional path planners are discussed, and simulation and experimental results are presented. © 2005 Wiley Periodicals, Inc.
TL;DR: By considering the internal forces induced by the redundant muscles, it is shown that the damping factors in each joint can be regulated and the human arm's sensory-motor control mechanism can realize humanlike quasistraight line reaching movements.
Abstract: This paper studies the human arm's sensory-motor control mechanism in reaching movements. First, we formulate both the kinematics and dynamics of a two-link planar arm model with six redundant muscles. The nonlinear muscle dynamics is modeled based on several biological understandings. We then show the stability of the overall system and perform some numerical simulations. By considering the internal forces induced by the redundant muscles, we show that the damping factors in each joint can be regulated, and as the result, it can realize humanlike quasistraight line reaching movements. In addition, we also propose the gravity compensation method at the muscle input level and present the result of numerical simulation to verify the usefulness of this method. © 2005 Wiley Periodicals, Inc.
TL;DR: Four experimental setups with hardware and software architecture description are presented: the dc motor, the magnetic levitator, the nonholomonic motion planner, the NHMP, and the graphic environment tool.
Abstract: In this paper we describe work being done at our department to make the robotics laboratory accessible to students and colleagues to execute and watch real-time experiments at any time and from anywhere. We describe a few different installations and highlight the underlying philosophy, which is aimed at enlarging the lab in all the dimensions of space, time, and available resources, through the use of Internet technologies. In particular, four experimental setups with hardware and software architecture description are presented: the dc motor, the magnetic levitator, the nonholomonic motion planner (NHMP), and the graphic environment tool. © 2005 Wiley Periodicals, Inc.
TL;DR: A new method to learn multifingered hand configuration during grasping in the presence of noise and uncertainty is proposed based on a modular architecture composed of several neural networks.
Abstract: In this paper, we propose a new method to learn multifingered hand configuration during grasping in the presence of noise and uncertainty. The developed model is composed of two modules. The first one carries out the learning of the fingers inverse kinematics. It is based on a modular architecture composed of several neural networks. Using reinforcement learning, a second neural network based model optimizes the position and orientation of the hand palm taking into account noisy sensing information. Working together these two modules exchange information to define the complete hand configuration. In order to illustrate the capabilities of the proposed model, simulation results are proposed using different kinds of objects, different levels of noise, and for a multifingered hand with different number of fingers. © 2005 Wiley Periodicals, Inc.
TL;DR: An architecture for the transmission of stereoscopic video images via network is proposed, which in the future will substitute for current image processing devices.
Abstract: This article addresses the use of stereoscopic images in teleoperated tasks. Depth perception is a key point in the ability to skillfully manipulate in remote environments. Displaying three-dimensional images is a complex process but it is possible to design a teleoperation interface that displays stereoscopic images to assist in manipulation tasks. The appropriate interface for image viewing must be chosen and the stereoscopic video cameras must be calibrated so that the image disparity is natural for the observer. Attention is given to the calculation of stereoscopic image disparity, and suggestions are made as to the limits within which adequate stereoscopic image perception takes place. The authors have designed equipment for image visualization in teleoperated systems. These devices are described and their performance evaluated. Finally, an architecture for the transmission of stereoscopic video images via network is proposed, which in the future will substitute for current image processing devices. © 2005 Wiley Periodicals, Inc.
TL;DR: Simulation and initial experimental results show that the minimum driving force change criterion can roughly capture this feature of the hand velocity profiles and, therefore, can be a reasonable candidate for modeling of humanlike reaching movements.
Abstract: This paper is concerned with the problem of trajectory formation of humanlike reaching movements. First, we review conventional criteria of optimality adopted in robotics and computational neuroscience for the prediction of reaching movements and formulate a dynamic version of the minimum hand jerk criteria. We call it a minimum driving force change criterion and check its performance for the free-space movements. Next, we test the performance of the new criterion for the movements where the human hand is geometrically constrained by the external environment, and for the movements with flexible objects. The main feature of these movements is that the hand velocity profiles are not always bell shaped. Our simulations and initial experimental results show that the minimum driving force change criterion can roughly capture this feature and, therefore, can be a reasonable candidate for modeling of humanlike reaching movements. © 2005 Wiley Periodicals, Inc.
TL;DR: This paper addresses the problem of position control of robotic manipulators in the task space with obstacles with a computationally simple class of task space regulators consisting of a transpose Jacobian controller plus an integral term including the task error and the gradient of a penalty function generated by obstacles.
Abstract: This paper addresses the problem of position control of robotic manipulators in the task space with obstacles. A computationally simple class of task space regulators consisting of a transpose Jacobian controller plus an integral term including the task error and the gradient of a penalty function generated by obstacles is proposed. The Lyapunov stability theory is used to derive the control scheme. Through the use of the exterior penalty function approach, collision avoidance of the robot with obstacles is ensured. The performance of the proposed control strategy is illustrated through computer simulations for a direct-drive arm of a SCARA type manipulator operating in both an obstacle-free task space and a task space including obstacles. © 2005 Wiley Periodicals, Inc.
TL;DR: A muscle model is used and is integrated in the optimization technique, in order to determine measurable values, like the activation and the displacement of each muscle in the system, during a real-time simulation.
Abstract: This paper deals with the development of a highly realistic human hand and forearm model. The model contains 38 muscles and 24 degrees of freedom representing the joints of the system. The adopted model has to be as close as possible to the reality of the human being hand, to address several features linked to manipulation tasks, grasping objects and daily routine movements like shaving, writing, etc. In addition, a better comprehension of the biomechanical and neuromuscular behavior of the system is aimed. This will allow having a tool for the simulation of repairing surgery, acts such as tendon transfer. In this paper, we focus on the muscle forces determination for a given task. An optimization technique is used to resolve the redundant problem over the 24 joints of the system. Also, a muscle model is used and is integrated in the optimization technique, in order to determine measurable values, like the activation and the displacement of each muscle in the system. The calculation is made during a real-time simulation. © 2005 Wiley Periodicals, Inc.
TL;DR: In this article, a collision and self-collision avoidance scheme for redundant manipulators is proposed based on modeling the arm and its environment by simple geometric primitives (cylinders and spheres).
Abstract: The development of a collision- and self-collision-avoidance scheme for redundant manipulators is discussed in this paper. The method is based on modeling the arm and its environment by simple geometric primitives (cylinders and spheres). A compact method of detecting collisions between two cylinders is introduced. By resorting to the notions of dual angles and dual vectors for representing the axes of cylinders in space, a characterization of different types of collisions is introduced. The performance of the proposed scheme is demonstrated for a seven degrees-of-freedom redundant manipulator via simulations and experiments. © 2005 Wiley Periodicals, Inc.
TL;DR: This work investigates the behavior of robots experiencing unidentified locked-joint failures in a general class of tasks characterized by point-to-point motion and develops a procedure for workspace evaluation that allows for the identification of regions in the manipulator's workspace in which tasks may be completed even with such failures.
Abstract: Robots are frequently used for operations in hostile environments. The very nature of these environments, however, increases the likelihood of robot failures. Common failure-tolerance techniques rely on effective failure detection and identification. Since a failure may not always be successfully identified, or, even if identified, may not be identified soon enough, it becomes important to consider the behavior of manipulators with unidentified failures. This work investigates the behavior of robots experiencing unidentified locked-joint failures in a general class of tasks characterized by point-to-point motion. Based on the analysis, a procedure for workspace evaluation is developed that allows for the identification of regions in the manipulator's workspace in which tasks may be completed even with such failures. © 2005 Wiley Periodicals, Inc.
TL;DR: A new map-based algorithm for the localization of vehicles operating in harsh outdoor environments is presented and a map building algorithm using observations from a scanning laser rangefinder is developed for building a polyline map that adequately captures the geometry of the environment.
Abstract: Determining the pose (position and orientation) of a vehicle at any time is termed localization and is of paramount importance in achieving reliable and robust autonomous navigation. Knowing the pose it is possible to achieve high level tasks such as path planning. A new map-based algorithm for the localization of vehicles operating in harsh outdoor environments is presented in this article. A map building algorithm using observations from a scanning laser rangefinder is developed for building a polyline map that adequately captures the geometry of the environment. Using this map, the Iterative Closest Point (ICP) algorithm is employed for matching laser range images from the rangefinder to the polyline map. Once correspondences are established, an Extended Kalman Filter (EKF) algorithm provides reliable vehicle state estimates using a nonlinear observation model based on the vertices of the polyline map. Data gathered during field trials in an outdoor environment is used to test the efficiency of the proposed ICP-EKF algorithm in achieving the localization of a four-wheel drive (4WD) vehicle. © 2005 Wiley Periodicals, Inc.
TL;DR: In this paper, forcestorque sensor-based skills for handling deformable linear objects in a manner suitable to reduce acute vibration with simple human skill inspired strategies that consist of one or two adjustment motions.
Abstract: The vibration of a deformable object is often problematic during automatic handling by robot manipulators. However, humans can often handle and damp the vibration of deformable objects with ease. This paper presents forcestorque sensor-based skills for handling deformable linear objects in a manner suitable to reduce acute vibration with simple human skill inspired strategies that consist of one or two adjustment motions. The adjustment motion is a simple open-loop motion that can be attached to the end of any arbitrary end-effector's trajectory. As an ordinary industrial robot's simple action, it has three periods, i.e., acceleration, constant speed, and deceleration period; it starts from a predicted time tightly close to a forcesmoment maximum. The predicted time for the adjustment action is generated automatically on-line based on the vibration rhythm and the data sensed by a forcestorque sensor mounted on the robot's wrist. To find the matching point between the vibrational signal of the deformable object and a template, template matching techniques including cross-correlation and minimum squared error methods are used and compared. Experiments are conducted with an industrial robot to test the new skills under various conditions. The results demonstrate that an industrial robot could perform effective vibration reduction skills with simple strategies. © 2005 Wiley Periodicals, Inc.
TL;DR: A systematic method is first presented to get isotropic parallel designs and a measure for spatial isotropy is proposed to evaluate and compare the global isotropy of obtained manipulators.
Abstract: How to obtain 6-DOF parallel manipulators with optimum global isotropy is investigated in this paper. A systematic method is first presented to get isotropic parallel designs. A measure for spatial isotropy is then proposed to evaluate and compare the global isotropy of obtained manipulators. Efficient methods to find the minimum and maximum singular values of matrices are developed to facilitate the evaluation process. © 2005 Wiley Periodicals, Inc.
TL;DR: In this article, the authors proposed a new control solution that is inspired by the biological model of motor control in voluntary movements, with special regard for situations of unpredictable contact/noncontact transitions.
Abstract: This work focuses on interaction control of robot manipulators in unstructured environments, with special regard for situations of unpredictable contact/noncontact transitions. It is basically addressed to those environments where a high level of robot adaptability is required and no information on the geometry of the environment is available. By pointing out the main limitations of standard interaction control schemes in managing situations of contact/noncontact transitions, this paper proposes a new control solution that is inspired by the biological model of motor control in voluntary movements. It consists of a combination of a feedforward loop and a proportional-derivative plus gravity compensation control in the feedback loop. The control law is named coactivation-based compliance control in the joint space since a unique function, called coactivation function, is evaluated for regulating robot visco-elasticity in an unpredictably variable environment. It resumes the mechanism of adjustable visco-elastic properties acting on the agonist and antagonist muscles of a human arm. The work also proposes a methodology for evaluating performance of interaction control schemes that is based on stiffness graphical representation through ellipses. The method replicates the experimental setup used in neuroscience to measure stiffness in human limbs. It is regarded as a powerful tool for evaluating robot behavior over space and time, since it allows both a visual representation of stiffness variation during motion and a quantitative measure of robot performance. It is shown how the method can be used to evaluate a control scheme and how it can provide indications to improve a control law. In this paper, an application to the standard compliance control in the joint space and the coactivation-based compliance control is presented. © 2005 Wiley Periodicals, Inc.
TL;DR: A new family of 4-degrees-of-freedom (DOF) parallel mechanisms with two platforms and its application to a footpad device that can simulate the spatial motions of the human foot is proposed.
Abstract: This paper proposes a new family of 4-degrees-of-freedom (DOF) parallel mechanisms with two platforms and its application to a footpad device that can simulate the spatial motions of the human foot. The new mechanism consists of front and rear platforms, and three limbs. Two limbs with 6-DOF serial joints ( P -S-P-P) are attached to each platform and are perpendicular to the base plate, while the middle limb is attached to the revolute joint that connects the front and rear platforms. The middle limb is driven by the 2-DOF driving mechanism that is equivalent to active serial prismatic and revolute joints ( Pe - Re ), or prismatic and prismatic joints ( Pe - Pe ) with two base-fixed prismatic actuators. Since the middle limb perpendicular to the base plate has 3-DOF serial joints ( Pe - Re -R or Pe - Pe -R), two new 4-DOF parallel mechanisms with two platforms can generate pitch motion of each platform, and roll and heave motions (1T-3R) or pitch motion of each platform and two translational motions (2T-2R) at both platforms, according to the type of the 2-DOF driving mechanism. Kinematic analyses of the 1T-3R mechanism were performed, including inverse and forward kinematics and velocity analysis. Based on the 1T-3R mechanism, a footpad device was designed to generate foot trajectories for natural walking. © 2005 Wiley Periodicals, Inc.
TL;DR: In this paper, an adaptive robot controller is developed that forces the end-effector of a robot manipulator to move such that the position and orientation of an object are regulated to a desired position in the camera space, despite parametric uncertainty throughout the entire robot-camera system.
Abstract: This paper considers the camera-space position and orientation regulation problem for the camera-in-hand problem via visual serving in the presence of parametric uncertainty associated with the robot dynamics and the camera system. Specifically, an adaptive robot controller is developed that forces the end-effector of a robot manipulator to move such that the position and orientation of an object are regulated to a desired position and orientation in the camera-space, despite parametric uncertainty throughout the entire robot-camera system. An extension is also provided that illustrates how slight modifications can be made to the camera-in-hand control law to achieve adaptive position and orientation tracking of the end-effector in the camera-space for a fixed-camera configuration. Simulation results are provided to illustrate the performance of the adaptive, camera-in-hand controller. © 2005 Wiley Periodicals, Inc.
TL;DR: A new system for simulating and tele-operating robot arms through the Internet, which allows many users to simulate and test positioning commands for a robot by means of a virtual environment, as well as execute the validated commands in a real remote robot of the same characteristics.
Abstract: Simulation and teleoperation tools offer many advantages for the training or learning of technological subjects, such as flexibility in time-tables and student access to expensive and limited equipment. In this paper, we present a new system for simulating and tele-operating robot arms through the Internet, which allows many users to simulate and test positioning commands for a robot by means of a virtual environment, as well as execute the validated commands in a real remote robot of the same characteristics. The main feature of the system is its flexibility in managing different robots or including new robot models and equipment. © 2005 Wiley Periodicals, Inc.