Showing papers in "Journal of Robotic Systems in 1991"
TL;DR: A sufficient condition for the stability of a desired formation pattern for a fleet of robots each equipped with the navigation strategy based on nearest neighbor tracking is developed and simple navigation strategies for robots moving in formation are derived.
Abstract: The problem of deriving navigation strategies for a fleet of autonomous mobile robots moving in formation is considered. Here, each robot is represented by a particle with a spherical effective spatial domain and a specified cone of visibility. The global motion of each robot in the world space is described by the equations of motion of the robot's center of mass. First, methods for formation generation are discussed. Then, simple navigation strategies for robots moving in formation are derived. A sufficient condition for the stability of a desired formation pattern for a fleet of robots each equipped with the navigation strategy based on nearest neighbor tracking is developed. The dynamic behavior of robot fleets consisting of three or more robots moving in formation in a plane is studied by means of computer simulation.
411 citations
TL;DR: This article presents a new approach to the problem of determining the minimum set of inertial parameters of robots based on numerical QR and SVD factorizations and on the scaling procedure of matrices, which can be applied to open loop, or graph-structured robots.
Abstract: This article presents a new approach to the problem of determining the minimum set of inertial parameters of robots. The calculation is based on numerical QR and SVD factorizations and on the scaling procedure of matrices. It proceeds in three steps:
eliminate standard inertial parameters which have no effect on the dynamic model,
determine the number of base parameters,
and
determine a set of base parameters by regrouping some standard parameters to some others in linear relations.
Different models, linear in the inertial parameters are used: a complete dynamic model, a simplified dynamic model, and an energy model. The method is general, it can be applied to open loop, or graph-structured robots. The algorithms are easy to implement. An application for the PUMA 560 robot is given.
254 citations
TL;DR: The hybrid controller combines the adaptive scheme where M, C, and g are estimated on-line with a switching term added to the controller to compensate for uncertainties in the input matrix B.
Abstract: The problem of controlling underwater mobile robots in 6 degrees of freedom (DOF) is addressed. Underwater mobile robots where the number of thrusters and control surfaces exceeds the number of controllable DOF are considered in detail. Unlike robotic manipulators underwater mobile robots should include a velocity dependent thruster configuration matrix B(q), which modifies the standard manipulator equation to: Mq + C(q)q + g(x) = B(q)u where x = J(x)q. Uncertainties in the thruster configuration matrix due to unmodeled nonlinearities and partly known thruster characteristics are modeled as multiplicative input uncertainty. This article proposes two methods to compensate for the model uncertainties: (1) an adaptive passivity-based control scheme and (2) deriving a hybrid (adaptive and sliding) controller. The hybrid controller combines the adaptive scheme where M, C, and g are estimated on-line with a switching term added to the controller to compensate for uncertainties in the input matrix B. Global stability is ensured by applying Barbalat's Lyapunov-like lemma. The hybrid controller is simulated for the horizontal motion of the Norwegian Experimental Remotely Operated Vehicle (NEROV).
128 citations
TL;DR: An adaptive control strategy for the coordinated control of an underwater vehicle and its robotic manipulator is described and the results show that the presented control system can provide the high performance of the vehicle and manipulator in the presence of unpredictable changes in the dynamics of the Vehicle and its environment.
Abstract: Remotely operated underwater robotic vehicles (URVs) have been used for various tasks: inspection, recovery, construction, etc With the increased utilization of remotely operated vehicles in subsea applications, the development of autonomous vehicles becomes highly desirable to enhance operator efficiency However, engineering problems associated with the high density, nonuniform and unstructured seawater environment, and the nonlinear response of the vehicle make a high degree of autonomy difficult to achieve The vehicles are usually equipped with mechanical manipulators that are utilized during the working mode The accurate performance of the vehicle during the working mode can be achieved by controlling the vehicle and manipulator at the same time and compensating the end-effector error due to the vehicle motion This article describes an adaptive control strategy for the coordinated control of an underwater vehicle and its robotic manipulator The effectiveness of the control system is investigated by case study The results show that the presented control system can provide the high performance of the vehicle and manipulator in the presence of unpredictable changes in the dynamics of the vehicle and its environment
107 citations
[...]
TL;DR: This paper presents two parallel robots that have been recently designed and one has tried to extend the principle of the DELTA mechanical structure structure to a 6-degree-of-freedom parallel robot, called the HEXA.
Abstract: This paper presents two parallel robots that have been recently designed. This first one is a 3-degree-of-freedom lightweight robot called DELTA and designed in Switzerland by EPFL. One gives the equations corresponding to different models of this robot : forward and inverse kinematics as well as inverse dynamics. The important feature of the method in deriving these models is to use a «good» set of parameters in order to simplify the equations. Based upon these considerations of simplicity, one has tried to extend the principle of the DELTA mechanical structure structure to a 6-degree-of-freedom parallel robot. One came up with a new design one called the HEXA. One presents this robot and shows that it should have the same dynamic capabilities as the DELTA, because, like this one, it can be built with light material and it can be easily modeled
65 citations
TL;DR: A new approach is developed for observing joint limits and avoiding obstacles during the trajectory planning and an alternative measure of arm “manipulability” based directly on the rank of the Jacobian is introduced.
Abstract: A review of local optimization methods for resolving joint configurations in underconstrained manipulation tasks is conducted. A new approach is developed for observing joint limits and avoiding obstacles during the trajectory planning. The methodology is used in a four-link arm example to avoid a workspace singularity and is compared with results using the extended Moore-Penrose technique. An alternative measure of arm 'manipulability' based directly on the rank of the Jacobian is also introduced.
48 citations
TL;DR: A machine vision algorithm to find the longest common subcurve of two 3-D curves is presented, of average complexity O(n) where n is the number of the sample points on the two curves.
Abstract: A machine vision algorithm to find the longest common subcurve of two 3-D curves is presented. The curves are represented by splines fitted through sequences of sample points extracted from dense range data. The approximated 3-D curves are transformed into 1-D numerical strings of rotation and translation invariant shape signatures, based on a multiresolution representation of the curvature and torsion values of the space curves. The shape signature strings are matched using an efficient hashing technique that finds longest matching substrings. The results of the string matching stage are later verified by a robust, least-squares, 3-D curve matching technique, which also recovers the Euclidean transformation between the curves being matched. This algorithm is of average complexity O(n) where n is the number of the sample points on the two curves. The algorithm has applications in assembly and object recognition tasks. Results of assembly experiments are included.
45 citations
TL;DR: Two techniques that improve existing local torque optimization methods for redundant robotic mechanisms are proposed, based on a balancing scheme, which balances a joint torque norm against a norm of joint accelerations and a torque optimization method which minimizes torques through accelerations obtained from the null-space of the Jacobian matrix.
Abstract: Two techniques that improve existing local torque optimization methods for redundant robotic mechanisms are proposed. The first technique is based on a balancing scheme, which balances a joint torque norm against a norm of joint accelerations. Expressions have been derived utilizing the Lagrangian multipliers method. The other technique is based on a torque optimization method which minimizes torques through accelerations, obtained from the null-space of the Jacobian matrix. These accelerations are balanced against the minimum-norm acceleration component in order to improve the performance. Numerical simulations have been carried out which in most cases illustrate good performance capability from the viewpoint of torque optimization and global stability.
44 citations
TL;DR: An efficient reverse analysis of three 6-degree-of-freedom (dof) subchains of the 7-dof SSRMS is presented, which has the distinct advantage that the plane can be oriented arbitrarily and, in this way, the singularity is avoided.
Abstract: An efficient reverse analysis of three 6-degree-of-freedom (dof) subchains of the 7-dof SSRMS is presented. The first subchain is formed by locking the seventh joint. The second subchain is formed by locking the second joint, while the third subchain is formed by locking the first joint (the grounded joint is counted as the first joint in the chain). There are a maximum of eight different arm configurations in each of the three subchains, and these were determined by employing a computer-efficient algorithm, which required the rooting of only at most quadratic polynomials. The algorithms were implemented, and the SSRMS was employed in an animated environment to perform and practice a number of useful tasks for Space Station servicing. The locking of the second joint has the advantage in that an operator can choose the orientation of the plane that contains the two longest links so as to avoid collisions with obstacles. However, it has the disadvantage that when the second joint angle equals 0 deg or 180 deg, the manipulator is in a singularity configuration. This plane can also be oriented by specifying the first joint angle, so that the plane can be oriented arbitrarily and, in this, the singularity is avoided.
41 citations
TL;DR: This paper presents a solution to the inverse kinematics problem for variable-geometry-truss manipulators based on a spline-like reference curve for the manipulator's shape that has a number of advantages: direct, intuitive manipulation of shape; reduced calculation time; and direct control over the effective degree of redundancy of the manipulators.
Abstract: A new class of robotic arm consists of a periodic sequence of truss substructures, each of which has several variable-length members. Such variable-geometry truss manipulators (VGTMs) are inherently highly redundant and promise a significant increase in dexterity over conventional anthropomorphic manipulators. This dexterity may be exploited for both obstacle avoidance and controlled deployment in complex workspaces. The inverse kinematics problem for such unorthodox manipulators, however, becomes complex because of the large number of degrees of freedom, and conventional solutions to the inverse kinematics problem become inefficient because of the high degree of redundancy. This paper presents a solution to this problem based on a spline-like reference curve for the manipulator's shape. Such an approach has a number of advantages: (1) direct, intuitive manipulation of shape; (2) reduced calculation time; and (3) direct control over the effective degree of redundancy of the manipulator. Furthermore, although the algorithm has been developed primarily for variable-geometry-truss manipulators, it is general enough for application to other manipulator designs.
41 citations
TL;DR: The locomotion of a quadrupedal walking machine in an obstacle-strewn environment is studied and a gait algorithm that enables the walking machine to follow the path and maintain stability is developed.
Abstract: The locomotion of a quadrupedal walking machine in an obstacle-strewn environment is studied. The path planning of the walking machine body includes the following two features : first, the path is generated based on the Bezier curve so that its shape can be easily adjusted to avoid obstacles ; second, the velocity and acceleration are assigned independently from the path generation so that the inertial terms are controllable. After the path has been generated, a gait algorithm that enables the walking machine to follow the path and maintain stability is developed. Two special cases―straight-line crab walking and turning about a fixed axis―are studied first. The general case that the walking machine is following an arbitrary curve is then studied. During walking, if the crab angle exceeds a certain limit, the gait needs to be changed in order to maintain stability. The methods for changing the gaits are discussed
TL;DR: Techniques which can be used to derive models of the open-loop dynamics for prototype Remotely Operated Underwater Vehicles (ROVs) and Autonomous Underwater vehicles (AUVs) are described.
Abstract: Models of the open-loop dynamics for prototype Remotely Operated Underwater Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) are required for performance prediction and autopilot design. This article describes techniques which can be used to derive these models. The methods may be conveniently grouped into predictive techniques i.e., those which require only vehicle design data and which predict dynamics before the prototype is built and testing techniques i.e., methods which measure open-loop dynamics from the trials performance of a prototype ROV. The relative benefits and drawbacks of the various methods are examined.
TL;DR: A new repetitive learning controller for motion control of mechanical manipulators undergoing periodic tasks is developed that does not require exact knowledge of the manipulator dynamic structure or its parameters, and is computationally efficient.
Abstract: A new repetitive learning controller for motion control of mechanical manipulators undergoing periodic tasks is developed. This controller does not require exact knowledge of the manipulator dynamic structure or its parameters, and is computationally efficient. In addition, no actual joint accelerations or any matrix inversions are needed in the control law. The global asymptotic stability of the ideal and the robust stability of the nonideal control system is proven, taking into account the full nonlinear dynamics of the manipulator. Simulation results of this algorithm applied to a realistic Scara type manipulator, which includes dry friction, pay-load inertia variations, actuator/sensor noise, and unmodelled dynamics are also presented.
TL;DR: This article describes a method of producing high-resolution maps of an indoor environment with an autonomous mobile robot equipped with sonar range-finding sensors, based on investigating obstacles in the near vicinity of a mobile robot.
Abstract: This article describes a method of producing high-resolution maps of an indoor environment with an autonomous mobile robot equipped with sonar range-finding sensors. This method is based on investigating obstacles in the near vicinity of a mobile robot. The mobile robot examines the straight line segments extracted from the sonar range data describing obstacles near the robot. The mobile robot then moves parallel to the straight line sonar segments, in close proximity to the obstacles, continually applying sonar barrier test. The sonar barrier test exploits the physical constraints of sonar data, and eliminates noisy data. This test determines whether or not a sonar line segment is a true obstacle edge or a false reflection. Low resolution sonar sensors can be used with the method described. The performance of the algorithm is demonstrated using a Denning Corp. Mobile Robot, equipped with a ring of Polaroid Corp. Ultrasonic Rangefinders.
TL;DR: The design and illustrates the performance of a single joint in terms of friction, stiffness, and in implementing variable compliance and as a closed-loop torque servo.
Abstract: An underwater manipulator is described that can exhibit a wide range of compliance through a combination of mechanical design and software control and its performance characterized. The manipulator has been used in conjunction with the JASON Remotely Operated Vehicle at full-ocean depth. The major goal of the design was to produce a manipulator that can actively control the interaction forces with the work task in the hostile deep-ocean environment. The manipulator's performance has been characterized in the lab and its overall operational utility has been confirmed during tests to depths of approximately 4000 meters, including an archaeological excavation at 700 meters depth in the Mediterranean. The manipulator uses high performance brushless DC servomotors driving the joints though low-friction, zero-backlash reductions of moderate ratio consisting of cables and pulleys. Each joint is highly backdriveable and has a large range of rotation. This approach permits a variety of force control schemes such as impedance control to be implemented with no sensors other than the displacement sensors integrated with the brushless motor. It also permits high-quality torque servomechanisms to be directly implemented. This article outlines the design and illustrates the performance of a single joint in terms of friction, stiffness, and in implementing variable compliance and as a closed-loop torque servo.
TL;DR: This article presents an improved numerical algorithm for robot inverse kinematics which is based upon the solution of the first-order differential equations arising from the manipulator's velocity Jacobian relations based on the use of the Adams-Moulton predictorcorrector scheme.
Abstract: This article presents an improved numerical algorithm for robot inverse kinematics which is based upon the solution of the first-order differential equations arising from the manipulator's velocity Jacobian relations. The use of the Adams-Moulton predictorcorrector scheme leads to a fourth-order trajectory following in the joint space. The implementation of a strict descent feature for the trajectory error at the end-effector level contributes to the robustness of the algorithm near singularities. The execution of this algorithm is about 2.7 times faster than that of Gupta and Kazerounian,16 with much of the speed up coming from the use of software optimizations. Several issues related to the accuracy, convergence, speed, real-time computation, and portability of this algorithm are discussed.
TL;DR: Experimental results indicate that an adaptation of Newton-Raphson search combined with the use of a low-noise, high accuracy camera can drastically reduce the number of image points at which computations need be made.
Abstract: Submersibles require the capability to accurately maintain their position when they are observing, photographing, or working at a site. The most direct way for an ROV or AUV to maintain position in the near bottom environment is to track or lock onto stationary objects on the ocean floor. A particular advantage of an optical stationkeeping system is its ability to use natural rather than manmade beacons. Several improvements to our previously reported optical flow methods for the detection of vehicle motion have been investigated. Experimental results indicate that an adaptation of Newton-Raphson search combined with the use of a low-noise, high accuracy camera can drastically reduce the number of image points at which computations need be made. Other experiments with an algorithm, which accounts for illumination variations that one may encounter in undersea environments, show significant improvement in the estimation of optical flow and vehicle motion.
TL;DR: A formulation of the constrained manipulator dynamics is presented in which the hybrid control design is most naturally carried out, and two hybrid control laws are proposed, a constrained motion control law already proposed in the literature and a concrete example of a three-degree-of-freedom robotic manipulator illustrates the hybrid design methodology proposed.
Abstract: Control of manipulators during execution of tasks that require the end-effector to come into contact with objects in its work environment represents an important class of control problem. Hybrid control, a concept which defines the architecture of a class of control laws has been proposed as a method with which to solve this control problem. One interpretation of the hybrid control method is within the framework of constrained motion control. Constrained motion occurs during contact by the manipulator end-effector with rigid objects in the workplace, hence the motion of the manipulator is kinematically constrained. Papers have appeared in the robotics control literature addressing hybrid control within the constrained motion context which do not explicitly use the constrained dynamic formulation that correctly describes the dynamic behaviour of the manipulator. This article serves to link results from constrained motion control and the existing literature on the hybrid control method. In this article a formulation of the constrained manipulator dynamics is presented in which the hybrid control design is most naturally carried out. This formulation of the manipulator dynamics, previously proposed in the robotics literature, is such that the generalized force and position coordinates to be controlled are mutually orthogonal. Hence, the hybrid selection matrices, a key element of the hybrid control design philosophy, are implicit in this coordinate representation. A hybrid control design methodology is then formulated based on this development. Two hybrid control laws are proposed. For each hybrid control law, the global asymptotic stability is readily established due to the natural coordinate representation. One of these hybrid control laws, a constrained motion control law already proposed in the literature, is given to illustrate the equivalence of the hybrid control design and certain existing constrained motion control methods. Finally, a concrete example of a three-degree-of-freedom robotic manipulator illustrates the hybrid design methodology proposed.
TL;DR: A new collision-avoidance scheme is proposed for autonomous land vehicle (ALV) navigation in indoor corridors that combines the maneuvering board technique used for nautical navigation with a modified version of the least-mean-square-error (LMSE) classifier in pattern recognition.
Abstract: In this article, a new collision-avoidance scheme is proposed for autonomous land vehicle (ALV) navigation in indoor corridors. The goal is to conduct indoor collisionfree navigation of a three-wheel ALV among static obstacles with no a priori position information as well as moving obstacles with unknown trajectories. Based on the predicted positions of obstacles, a local collision-free path is computed by the use of a modified version of the least-mean-square-error (LMSE) classifier in pattern recognition. Wall and obstacle boundaries are sampled as a set of 2D coordinates, which are then viewed as feature points. Different weights are assigned to different feature points according to the distances of the feature points to the ALV location to reflect the locality of path planning. The trajectory of each obstacle is predicted by a real-time LMSE estimation method. And the maneuvering board technique used for nautical navigation is employed to determine the speed of the ALV for each navigation cycle. Smooth collision-free paths found in the simulation results are presented to show the feasibility of the proposed approach.
TL;DR: A new transform for curve detection, called the Curve-Fitting Hough Transform (CFHT), is proposed, which is advantageous over the conventional HT and variants in its high speed, small storage, arbitrary parameter range, and high parameter resolution.
Abstract: A new transform for curve detection, called the Curve-Fitting Hough Transform (CFHT), is proposed. In the conventional Hough Transform (HT) and its variants, both storage and computation grow exponentially with the number of parameters. The CFHT is advantageous over the conventional HT and variants in its high speed, small storage, arbitrary parameter range, and high parameter resolution. This is achieved by fitting a segment of the curve to be detected to a small neighborhood of edge points. If the fitting error is less than a given threshold, the parameters obtained from curve fitting are used to map an edge element to a single point in the parameter space. A multidimensional ordered parameter list is used to accumulate the occurrences of the curve to be detected.
TL;DR: A classification of new connectivity properties of the free workspace of manipulators moving among obstacles is proposed, corresponding to different types of motions (point-to-point motions, following of continuous trajectories) that the manipulator can perform in the Cartesian space.
Abstract: This article presents a new topological characterization of the free workspace of manipulators moving among obstacles. The free workspace is the set of positions and orientations that the end-effector of the manipulator can reach, according to the joint limits of each of its links, and taking into account the obstacles of the environment. A classification of new connectivity properties of the free workspace is proposed, corresponding to different types of motions (point-to-point motions, following of continuous trajectories) that the manipulator can perform in the Cartesian space. For each property, a necessary and sufficient condition is given, which permits verification of the connectivity of the whole free workspace and leads to all the connected subspaces in it. These properties have been implemented in a Robotics C.A.D. system using octree representation of spaces. Some applications are presented, which show that this work is of primary interest for preparing off-line tasks, and is a new contribution to the problem of robotic cell layout design.
TL;DR: In this article, the algorithms for generating the joint position and velocity (PV) trajectories are extensively developed and application of the algorithms to a four-link revolute planar robot manipulator is demonstrated through simulation.
Abstract: New inverse kinematic algorithms for generating redundant robot joint trajectories are proposed. The algorithms utilize the kinematic redundancy to improve robot motion performance (in joint space or Cartesian space) as specified by certain objective functions. The algorithms are based on the extension of the existing “joint-space command generator” technique in which a null space vector is introduced which optimizes a specific objective function along the joint trajectories. In this article, the algorithms for generating the joint position and velocity (PV) trajectories are extensively developed. The case for joint position, velocity, and acceleration (PVA) generation is also addressed. Application of the algorithms to a four-link revolute planar robot manipulator is demonstrated through simulation. Several motion performance criteria are considered and their results analyzed.
TL;DR: A new solid model named “Hierarchical Sphere Model” (HSM) is proposed for modeling moving objects (robots) and a feasible algorithm for checking an interference between them on the basis of HSM is presented.
Abstract: In order to realize collision-free coordination of multiple robots, it is crucial to model the robots in a computer adequately and to detect existence or nonexistence of an interference between them on the basis of data structure of the robot models. Motivated by this observation, this article proposes a new solid model named “Hierarchical Sphere Model” (HSM) for modeling moving objects (robots) and presents a feasible algorithm for checking an interference between them on the basis of HSM. HSM arranges region informations in a hierarchical tree structure whose nodes correspond to spherical regions. On the basis of hierarchy of HSM, the algorithm checks only intersections between HSMs' nodes which are close to each other, and hence it works efficiently even if the objects have complicated shape. Furthermore, because a node of HSM represents a spherical region, intersection between, two nodes can be easily found just by calculating the distance between two spheres corresponding to them no matter how the objects move. Finally, the efficiency of the algorithm is demonstrated by several experiments.
TL;DR: A hierarchical graph-based mapping approach is devised to analyze the inherent parallelism in the Newton-Euler formulation at several computational levels, and to derive the features of an abstract architecture for exploitation of parallelism.
Abstract: In this article, parallel computation of manipulator inverse dynamics is investigated. A hierarchical graph-based mapping approach is devised to analyze the inherent parallelism in the Newton-Euler formulation at several computational levels, and to derive the features of an abstract architecture for exploitation of parallelism. At each level, a parallel algorithm represents the application of a parallel model of computation that transforms the computation into a graph whose structure defines the features of an abstract architecture, i.e., number of processors, communication structure, etc. Data-flow analysis is employed to derive the time lower bound in the computation as well as the sequencing of the abstract architecture. The features of the target architecture are defined by optimization of the abstract architecture to exploit maximum parallelism while minimizing architectural complexity. An architecture is designed and implemented that is capable of efficient exploitation of parallelism at several computational levels. The computation time of the Newton-Euler formulation for a 6-degree-of-freedom (dof) general manipulator is measured as 187 microsec. The increase in computation time for each additional dof is 23 microsec, which leads to a computation time of less than 500 microsec, even for a 12-dof redundant arm.
TL;DR: In numerically forming the inertia matrix, the present method is more efficient than other methods in the literature for a manipulator with five or more joints; whereas this method is also superior to the recursive Newton-Euler formulation in computing the bias vector for a manipulation with six or less joints.
Abstract: This article presents a new composite body method for numerically forming the inertia matrix and the bias vector of manipulators, which is more efficient than the other two existing types of composite body methods. The main discrepancy of this one from the existing ones is that all points in a manipulator are observed from the origin of the base frame and the distances are all measured from this origin. The required computations of the present method for the inertia matrix and the bias vector of a manipulator with n rotational joints are (10.5n2 + 38.5n - 85)M + (6n2 + 39n - 70)A and (12.5n2 + 5.5n + 3)M + (9n2 + n)A, respectively, where “M” denotes multiplications, “A” does additions. In numerically forming the inertia matrix, the present method is more efficient than other methods in the literature for a manipulator with five or more joints; whereas this method is also superior to the recursive Newton-Euler formulation in computing the bias vector for a manipulator with six or less joints.
TL;DR: Using the principle of virtual work, a force and torque relationship between the joints and end-effector is obtained and computer simulations of the resulting force/torque relationship are compared to results obtained experimentally.
Abstract: A technique to determine the relationship between the generalized joint torque and the generalized force exerted by the end-effector of a flexible link manipulator on the environment is presented. First, a systematic technique which accounts for the links' bending and torsion is used to determine the kinematic equations of the manipulator. A procedure to determine a “pseudo” Jacobian matrix which accounts for the links' flexibility is then developed. In the determination of the pseudo Jacobian matrix, partial derivatives are not used, thus reducing inaccuracies resulting from approximating the bending and torsion of the links. Using the principle of virtual work, a force and torque relationship between the joints and end-effector is obtained. To demonstrate the validity of the technique presented, computer simulations of the resulting force/torque relationship are compared to results obtained experimentally.
TL;DR: A general feedback scheme is developed for dynamically steering an AMR to a visible goal in the local obstacle-free space identified by the SSA and Simulation results are presented that demonstrate the effectiveness of the combined SSA-SCA feedback scheme.
Abstract: This article presents an algorithm for dynamically steering an autonomous mobile robot (AMR) along a collision-free path to a goal using local feedback information. A twolevel navigation algorithm is presented in which a subgoal selection algorithm (SSA) generates visible subgoals to be pursued by the steering control algorithm (SCA). An earlier article presented the SSA in detail, demonstrating how subgoals can be updated while the AMR is moving so that a continuous motion is achieved without stopping to replan the path when new sensor data become available. This study focuses on the SCA. In particular, a general feedback scheme is developed for dynamically steering an AMR to a visible goal in the local obstacle-free space identified by the SSA. We present the detailed implementation of the SCA for a conventionally steered AMR (CAMR). Simulation results are presented that demonstrate the effectiveness of the combined SSA-SCA feedback scheme. The algorithm has been successfully implemented on the NavLab at CMU.
TL;DR: This article designs and experimentally test controllers for active damping of the vibrations and stabilization of the link-tip position and develops a dynamic model for the one-mode flexible vibration control.
Abstract: This article reports experimental results in control of a one-link flexible manipulator. A d.c. drive with gear train rotates the link with a tip-mass in the horizontal plane. A “stiff” hardware servo-system tracks the commanded drive velocity. We describe the experimental setup and develop a dynamic model for the one-mode flexible vibration control. We design and experimentally test controllers for active damping of the vibrations and stabilization of the link-tip position. Results for continuous control implemented with an analog computer and a sampled-data, digital-computer control are reported. A high control performance is achieved despite the gear-train friction influence. In addition, sampled-data digital controllers for tracking control of the link reference motion are designed and tested.
TL;DR: The feasibility of the task from a kinematics point of view, and the necessary conditions and constraints for the relative set-up of the two manipulators are discussed are discussed.
Abstract: More problems are involved in collaborating multi-robot-arm systems than in single robot arms. These problems stem from mutual dynamic and kinematic effects between the arms. This work is confined to only the kinematics of two robot arms; other problems like control, force distribution, and so on are not addressed here. A particular case of a material handling problem with two collaborating robot arms loading/unloading long objects from a conveyor is studied. The feasibility of the task from a kinematics point of view, and the necessary conditions and constraints for the relative set-up of the two manipulators are discussed. These conditions originate from the working envelope of the two arms which depends on three factors: the working envelope of each individual arm, the spacing between them, and the dimensions of the workpiece. To assist this study, an efficient algorithm for determining the two-dimensional contours of the workspace of a single arm is included.
TL;DR: It is found in this study that the additional link deflection resulting from the angular deflection of a robotic revolute joint substantially contributes to the end-effector's total deflection.
Abstract: Traditionally, robotic deflection analysis for a low-weight robot has been performed based on an assumption that each link is treated as a cantilever beam, which leads to no angular deflection at a joint. In practice, a robotic intermediate joint is linearly and angularly deflected when a load is applied at the end-effector. It is found in this study that the additional link deflection resulting from the angular deflection of a robotic revolute joint substantially contributes to the end-effector's total deflection. This article presents an improved method via a combination of classical beam theory, energy methods and the concepts of differential relationships to more accurately calculate the static deflection at the end-effector. A systematic approach to deflection calculation through three different Jacobians are presented. The study also shows that the end-effector's deflection heavily depends on robotic arm configurations. The deflection is then compensated based on the selected optimum configuration. The theoretical deflection analysis is verified by experimental results. A planar two-link robot and a six-degree-of-freedom Elbow Manipulator are used for numerical illustration and calculation procedure.