bluuebunny/crossref_metadata_2025 huggingface dataset:
Model‐based control of industrial manipulators: An experimental analysis
Authors: Leahy M. B.
Published: July 2007

Model‐based control techniques for industrial robotic manipulators were experimentally analyzed. The case study for the analysis was the first three joints of a PUMA‐560. Development of an advanced control evaluation environment removed the computational restrictions of previous studies. The specific issues of: incomplete and/or asynchronous dynamic compensation, feedback paradigm selection, payload sensitivity, and drive systems effects were experimentally analyzed. Evaluation results clearly demonstrate that the performance improvement capability of model‐based control is not restricted to research robots. A model‐based controller with complete feedforward compensation and sliding mode feedback reduced the maximum tracking error by at least a factor of five when compared to feedback alone. End‐effector payload invariant tracking only requires mass information. Tracking performance is not dependent on dynamic compensation at the servo rate. Evaluation results provide insight for adaptive control law design and a baseline to compare their performance against.
An adaptive scheme for robot joint trajectory generation
Authors: Hsia T. C. , Guo Z. Y. , Li L.
Published: July 2007

It has been shown recently that robot inverse kinematic transformation can be easily carried out by using a nonlinear dynamic system called “joint space command generator.” In this paper, an adaptive version of the command generator is proposed. The main feature of this command generator is that the inverse Jacobian is estimated on‐line (using least‐squares algorithms), thus the explicit form of the inverse Jacobian is not required. Since the Jacobian is dependent on the end‐effector orientation representation, the adaptive command generator is then inherently flexible in accommodating any choice of orientation representation during Cartesian trajectory planning. The only knowledge required is the forward kinematics of the robot. Thus inverse kinematic transformation of robot trajectories can be carried out with a minimum amount of kinematic information. Extensive simulation studies of the proposed scheme have been carried out which showed that the adaptive command generator is computationally feasible and highly accurate. Different orientation representations have been tested with equal success. Some typical simulation results are presented to illustrate the performance of the adaptive command generator.
A case study of two‐robot‐arm workcell material handling
Authors: Hemami A. , Ranjbaran F. , Cheng R. M. H.
Published: July 2007

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.
Linearized dynamic models of robot manipulators in cartesian space
Authors: Li Chang‐Jin
Published: July 2007

This article presents development of the linearized dynamic models of robot manipulators in Cartesian space. A clever method is proposed to formulate the linearized dynamic models of robot manipulators in Cartesian space. Efficient methods are developed to compute various matrices involved in the models (or the manipulator sensitivity matrices in Cartesian space), such as the Jacobian matrix and the first and second derivatives of it with respect to time as well as the manipulator sensitivity matrices in joint space. The proposed methods are simple and systematic and have computational complexity of the order O(n2) only, where n is the number of degrees‐of‐freedom of the manipulator.
Hybrid control: A constrained motion perspective
Authors: Mills James K.
Published: July 2007

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.
Modal sensitivity analysis of planar robots, based on a simplified CMS approach
Authors: Jen C. W. , Johnson D. A.
Published: July 2007

The modal properties of industrial robots have become a major issue following the increasing demand for faster, lighter manipulators. In this article, the basic in‐plane and out‐of‐plane modal analysis of a planar robot with revolute joints is conducted via component mode synthesis (CMS) using a limited number of low‐order monomials as mode shapes for the different links, and an automatic coordinate reduction procedure in the assembly phase which accounts for the physical characteristics of the joints. This model is then used to study the effect of variations in configuration, payload and various physical parameters on the natural frequencies of the robot. As regards the influence of physical parameter variations, frequency sensitivity coefficients are evaluated in a straightforward manner requiring only one eigenvalue analysis, and allow to determine the eigenvalue variations. It is observed that relatively large variations of parameters can be accommodated using these sensitivity coefficients.
A new repetitive controller for mechanical manipulators
Authors: Sadegh Nader , Guglielmo Kennon
Published: July 2007

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.
Mobile robot map making using sonar
Authors: Zelinsky A.
Published: July 2007

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 applyingsonar 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.
Robotic capability determined from planes of motion
Authors: Parkin Robert E.
Published: July 2007

A consequence of the specification of robots using kinematically simple joints is a simplified kinematic analysis. The analysis is performed here in terms of points and planes; i.e., the point/plane method. It is shown that the capability of a robot is completely specified by its planes of motion; the logical position space of a robot is defined in terms of these planes, and capability is presented in tables.
A new and efficient transform for curve detection
Authors: Liang Ping
Published: July 2007

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.
Periodic gaits for the CMU Ambler
Authors: Dwivedi Suren N. , Mahalingam Swaminathan
Published: July 2007

The configuration of the Carnegie‐Mellon University Ambler, a six‐legged autonomous walking vehicle for exploring Mars, enables the recovery of a trailing leg past the leading leg to reduce the energy expenditure in terrain interactions. In this article, gaits developed for this unprecedented configuration are described. A stability criterion has been developed that ensures stability of the vehicle in the event of failure of any one of the supporting legs. Periodic gaits developed for the Ambler utilize the Ambler's unique abilities and continuously satisfy the stability criterion.
Homeostatic control for a mobile robot: Dynamic replanning in hazardous environments
Authors: Arkin Ronald C.
Published: July 2007

A longstanding goal of robotics has been to introduce intelligent machines into environments dangerous to humans. These environments also pose hazards to the robots themselves. By embedding sensing devices as a means for monitoring the internal state of the robot, dynamic plan reformulation can occur in situations that threaten the existence of the robot. A method exploiting an analogy to the endocrine control system is forwarded as the preferred method for homeostatic control—the maintenance of a safe internal environment for the machine. Examples are given describing the impact of fuel reserve depletion and global temperature stress. A methodology using signal schemas as a means to supplement the existing motor schema control found in the Autonomous Robot Architecture (AuRA) is presented.
Cooperation without communication: Multiagent schema‐based robot navigation
Authors: Arkin Ronald C.
Published: July 2007

Multiagent robotics affords the opportunity to solve problems more efficiently and effectively than any single agent could achieve. Nonetheless, communication bottlenecks between agents pose potentially serious drawbacks in coordinated behavior. In this research, we demonstrate the efficiency of multiagent schema‐based navigation for object retrieval. Primitive motor behaviors are specified for each of the individual robotic agents, which produce safe task‐achieving action in an unstructured environment. When implemented over several identical units, retrieval is facilitated in the absence of interagent communication as evidenced by spontaneous recruitment of several agents to accomplish a task. Simulation results are provided to demonstrate these effects. Extensions to other task‐achieving behaviors are also feasible.
Two‐dimensional orientation sensor
Authors: Partaatmadja O. , Benhabib B. , Kaizerman E. , Dai M. Q.
Published: July 2007

The development of a two‐dimensional noncontact electrooptical orientation sensor is addressed in this article. The sensor is based on the intensity measurement of modulated light signals reflected from the surface of an object. The transducer of the proposed sensor was designed based on the optimal mechanical‐design parameters obtained in the first stage of our research, where results were reported for one‐dimensional inclination angle measurements. Experiments undertaken in the second stage of our research, and reported herein, verify the operational principle of the two‐dimensional sensor, which yielded acceptable performance characteristics. An important characteristic of this orientation sensor is the distance‐independent inclination‐angle measurements (i.e., output signals utilized to estimate the two inclination angles are independent of the sensor's distance to the object's surface).
Linearized dynamic models for trajectory control of robot manipulators
Authors: Swarup A. , Gopal M.
Published: July 2007

To make an appropriate choice of linear model for the development of real‐time control of robot manipulators, four direct linearization schemes have been studied here on the basis of computation and accuracy. Accuracy is assured in the state linearization method, whereas the rate linearization method leads to a satisfactory trade‐off between computational effort and accuracy. In the case of high‐velocity motions, a combination of state and rate linearization is proposed.
Optimal redundancy resolution of a kinematically redundant manipulator for a cyclic task
Authors: Choi Byoung Wook , Won Jong Hwa , Chung Myung Jin
Published: July 2007

This article proposes a method for the global optimization of redundancy over the whole task period in a kinematically redundant manipulator. The necessary conditions based on the calculus of variations for integral‐type criteria result in a second‐order differential equation. For a cyclic task, the boundary conditions for conservative joint motions are discussed. Then, we reformulate a two‐point boundary value problem to an initial value adjustment problem and suggest a numerical search method based on the iterative optimization for providing a globally optimal solution using the gradient projection method. Since the initial joint velocity is parameterized with the number of redundancy, we only search parameter values in the parameterized space using the configuration error between the initial and final time. We show through numerical examples that multiple nonhomotopic extremal solutions satisfying periodic boundary conditions exist according to initial joint velocities for the same initial configuration. Finally, we discuss an algorithm for topological liftings of the paths and demonstrate the generality of the proposed method by considering the dynamics of a manipulator.
Procedure for manipulator inverse kinematics computation and proper pseudoinverse perturbation
Authors: Mayorga R. V. , Wong A. K. C. , Ma K. S.
Published: July 2007

In this article, an efficient procedure for the proper pseudoinverse perturbation and the numerical inverse kinematics computation of robot manipulators is presented. The approach is based on solving a linear system of equations and using an original scheme for the appropriate perturbation of the pseudoinverse matrix in the next iteration. The resultant algorithm is tested on the simulation of an industrial robot manipulator. From the results obtained, it is observed that the proposed approach compares favorably with the approaches using a Gaussian elimination procedure and with pseudoinverse robustness based on a manipulability measure.
Model extension and refinement using pose recovery techniques
Authors: Kumar Rakesh , Hanson Allen R.
Published: July 2007

Visual measurements of modeled 3‐D landmarks provide strong constraints on the location and orientation of a mobile robot. To make the landmark‐based robot navigation approach widely applicable, it is necessary to automatically build the landmark models. A substantial amount of effort has been invested by computer vision researchers over the past 10 years on developing robust methods for computing 3‐D structure from a sequence of 2‐D images. However, robust computation of 3‐D structure, with respect to even small amounts of input image noise, has remained elusive. The approach adopted in this article is one of model extension and refinement. A partial model of the environment is assumed to exist and this model is extended over a sequence of frames. As will be shown in the experiments, prior knowledge of the small partial model greatly enhances the robustness of the 3‐D structure computations. The initial 3‐D model may have errors and these are also refined over the sequence of frames. © 1992 John Wiley & Sons, Inc.
Passive stereo range imaging for semi‐autonomous land navigation
Authors: Matthies Larry
Published: July 2007

Many navigation tasks, such as the use of unmanned vehicles for planetary exploration or defense reconnaissance, require onboard range sensors to automatically detect obstacles in the path of a vehicle. Passive ranging via stereo triangulation, orstereo vision, is a very attractive approach to obstacle detection because it is nonemissive, nonmechanical, nonscanning, and compatible with stereographic viewing by human operators. However, several problems have restricted the practicality of stereo ranging in the past, including limitations on the speed, reliability, and generality of existing stereo matching algorithms. This situated has changed, because the Jet Propulsion Laboratory (JPL) recently demonstrated the first semi‐autonomous, robotic traverses of natural terrain to use stereo vision for obstacle detection, with all computing onboard the vehicle. This article reviews the main algorithmic paradigms for stereo vision, describes a near realtime stereo vision system developed at JPL, and presents experimental results that demonstrate the emerging practically of stereo vision for obstacle detection in semi‐autonomous land navigation. © 1992 John Wiley & Sons, Inc.
Inertial navigation sensor integrated motion analysis for autonomous vehicle navigation
Authors: Roberts Barry , Bhanu Bir
Published: July 2007

Many types of existing vehicles contain an inertial navigation system (INS) that can be utilized to greatly improve the performance of motion analysis techniques and make them useful for practical military and civilian applications. This article presents the results obtained with a maximally passive system of obstacle detection for ground‐based vehicles and rotorcraft. Automatic detection of these obstacles and the necessary guidance and control actions triggered by such detection will facilitate autonomous vehicle navigation. Our approach to obstacle detection employs motion analysis of imagery collected by a passive sensor during vehicle travel to generate range measurements to world points within the field of view of the sensor. The approach makes use of INS data and scene analysis results to improve interest point selection, the matching of the interest points, and the subsequent motion‐based range computations, tracking, and obstacle detection. In this article, we concentrate on the results obtained using lab and outdoor imagery. The range measurements that are made by INS integrated motion analysis are compared to a limited amount of ground truth that is available. © 1992 John Wiley & Sons, Inc.
Stability and control aspects of flexible link robot manipulators during constrained motion tasks
Authors: Mills James K.
Published: July 2007

The effect of robotic manipulator structural compliance on system stability and trajectory tracking performance and the compensation of this structural compliance has been the subject of a number of publications for the case of robotic manipulator noncontact task execution. The subject of this article is the examination of dynamics and stability issues of a robotic manipulator modeled with link structural flexibility during execution of a task that requires the robot tip to contact fixed rigid objects in the work environment. The dynamic behavior of a generalndegree of freedom flexible link manipulator is investigated with a previously proposed nonlinear computed torque constrained motion control applied, computed based on the rigid link equations of motion. Through the use of techniques from the theory of singular perturbations, the analysis of the system stability is investigated by examining the stability of the “slow” and “fast” subsystem dynamics. The conditions under which the fast subsystem dynamics exhibit a stable response are examined. It is shown that if certain conditions are satisfied a control based on only the rigid link equations of motion will lead to asymptotic trajectory tracking of the desired generalized position and force trajectories during constrained motion. Experiments reported here have been carried out to investigate the performance of the nonlinear computed torque control law during constrained motion of the manipulator. While based only on the rigid link equations of motion, experimental results confirm that high‐frequency structural link modes, exhibited in the response of the robot, are asymptotically stable and do not destabilize the slow subsystem dynamics, leading to asymptotic trajectory tracking of the overall system. © 1992 John Wiley & Sons, Inc.
Forward kinematics of walking machines with pantograph legs based on selections of independent joints
Authors: Zhang Chang‐De , Song Shin‐Min
Published: July 2007

This article studies the forward kinematics of walking machines with pantograph legs. The walking machine is supported by three legs and each leg has 3 degrees of freedom (dof). Because the body has 6 dof motion, only 6 joint variables among the 9 are independent. Thus, there are 84 possible ways to select the 6 independent joint variables. It is shown that the complexity of the forward position solutions is very much dependent on the selection of independent joints. In the category of3:2:1(the 3 numbers denote the number of independent joints at each of the supporting legs), all 54 combinations give closed‐form solutions. Among the 27 combinations ofcategory 2:2:2, 10 possess closed‐form solutions, 16 yield to higher‐order polynomials, and 1 gives no solutions. The 3 combinations ofcategory 3:3:0give no solutions. The results are useful to control and simulation of walking machines and other parallel systems consisting of pantograph subchains such as parallel manipulators, multifingered hands, and multiply coordinated manipulators. © 1992 John Wiley & Sons, Inc.
Redundant grasps, redundant manipulators, and their dual relationships
Authors: Kerr D. R. , Griffis M. , Sanger D. J. , Duffy J.
Published: July 2007

This article presents a meaningful, practical, and theoretically sound solution that solves the problem of grasping a rigid object with a hand that has redundant (>6) grasping contacts. This is accomplished by introducing compliance at each contact point in such a way as to provide the engineer with the capabilities of object manipulation via controlled forces at the contact points. This method of solution is adapted straight‐away to compute the static forces generated in the legs of a redundant in‐parallel manipulator that equilibrates a wrench applied to the moving/platform or end‐effector. In a way similar to the redundant grasping problem, this is accomplished by introducing the knowledge of the compliances that exist in the legs. The solution thus obtained stems from physical parameters that model the in‐parallel manipulator. The in‐depth study of the duality between the statics of in‐parallel manipulators and the kinematics of serial manipulators reveals a meaningful, practical, and theoretically sound solution for the inverse kinematics of a redundant serial manipulator. This is accomplished by incorporating the knowledge of the compliances that exist or are desired to exist in the joints of the manipulator. (For instance, the torsional compliance in revolute joints or the linear compliance in prismatic joints.) Such information provides a physically meaningful model of the serial manipulator that in turn yields a physically meaningful set of joint increments for a given end‐effector twist. © 1992 John Wiley & Sons, Inc.
Linear learning control of robot motion
Authors: Qu Zhihua , Dorsey John , Dawson Darren M. , Johnson Roger W.
Published: July 2007

For the trajectory following problem of a robot manipulator, a new linear learning control law, consisting of the conventional proportional‐integral‐differential (PID) control law, with respect to position tracking error, and an iterative learning term is provided. The learning part is a linear feedback control of position, velocity, and acceleration errors (PDD2). It has been shown that, under the proposed learning control, the position, velocity, and acceleration tracking errors are asymptotically stable in the presence of highly nonlinear dynamics. The proposed control is robust in the sense that exact knowledge about nonlinear dynamics is not required except for the bounding functions on their magnitudes. Further, neither is linear approximation of nonlinear dynamics nor repeatability of robot motion required.
Grasp synthesis for planar and solid objects
Authors: Chen Yu‐Che , Walker Ian D. , Cheatham John B.
Published: July 2007

This article presents an analysis of the mechanics for multifingered grasps of planar and solid objects. We present a method that is intuitive and computationally efficient. We combine the search for finger grasp positions with finger (manipulation and squeezing) force calculations into a single method. Physically, the squeezing and frictional effects between the fingers and the grasped objects are fully visualized through our approach. Mathematically, we reduced the complexity of finger force calculations when comparing our scheme with previously available schemes. Examples are used to illustrate the effectiveness and efficiency of our scheme. Based upon the analysis of grasp mechanics, an algorithm for quantatively choosing the grasp points is proposed to ensure stable grasps.
Dynamic model of robot manipulator in explicit form formulation with dual vectors and the notion of augmented body
Authors: Baklouti M. , Castelain J. M.
Published: July 2007

This article deals with the dynamic model formulation and computation in explicit form of the inverse dynamic model of a robot manipulator constituted with a simple kinematic chain. We go on with the studies of Pennock and Giordano using the dual vectors, and we introduce the notion of augmented body. Our aim is to obtain the computation of the inverse dynamic model in explicit form with an almost minimal number of arithmetical operations to allow the dynamic control synthesis in real time. The method proposed here requires two steps of computation: first, an intrinsic theoretical computation; second, an extrinsic practical computation using dual matrices. This method is then applied to the robot manipulator COMAU‐POLAR 6000 and compared with the method of Renaud, considered until now the most performant method. This comparison leads to the same number of arithmetical operations with both methods.
Micro‐telerobot for manipulation of microscopic objects immersed in a liquid layer
Authors: Wang P. K. C.
Published: July 2007

A micro‐telerobot for manipulating microscopic objects such as macromolecules and living microorganisms immersed in a liquid layer is proposed. The basic idea is to inject a small number of microscopic solid ferromagnetic or magnetostrictive particles into the liquid layer either before or after the insertion of the microscopic objects to be manipulated. They serve as end‐effectors for the micro‐telerobot. These end‐effectors are activated and steered by an electromagnetic probe located outside the liquid layer. A nonlinear mathematical model describing the dynamic behavior of the micro‐telerobot is developed. It is shown that the equilibrium state of an activated end‐effector is unstable. The use of a linear feedback control for stabilization is explored. Appropriate values for the feedback gains are obtained with the aid of computer simulation using the nonlinear mathematical model. The article concludes with a discussion of the physical implementation of the proposed micro‐telerobot. © 1993 John Wiley & Sons, Inc.
Parallel computation of symbolic robot models and control laws: Theory and application to transputer networks
Authors: Kirćanski N. , Petrović T. , Vukobratović M.
Published: July 2007

New computer architectures based on large numbers of processors are now used in various application areas ranging from embedded systems to supercomputers. Efficient parallel processing algorithms are applied in a wide variety of applications such as simulation, robot control, and image synthesis. This article presents two novel parallel algorithms for computing robot inverse dynamics (as well as control laws) starting from customized symbolic robot models. To gain the most benefit from the concurrent processor architecture, the whole job is divided into a large number of simple tasks, each involving only a single floating‐point operation. Although requiring sophisticated scheduling schemes, fine granularity of tasks was the key factor for achieving nearly maximum efficiency and speedup.

The first algorithm resolves the scheduling problem for an array of pipelined processors. The second one is devoted to parallel processors connected by a complete crossbar interconnection network. The main feature of the proposed algorithms is that they take into account the communication delays between processors and minimize both the execution time and communication cost. To prove the theoretical results, the algorithms have been verified by experiments on an INMOS T800 transputer‐based system. We used four transputers in serial and parallel configurations. The experimental results show that the most complicated dynamic control laws can be executed in a submilisecond time interval. © 1993 John Wiley & Sons, Inc.
Method for kinematic calibration of stewart platforms
Authors: Zhuang Hanqi , Roth Zvi S.
Published: July 2007

A Stewart platform is a six degrees of freedom parallel manipulator composed of six variable‐length legs connecting a fixed base to a movable plate. Like all parallel manipulators, Stewart platforms offer high force/torque capability and high structural rigidity in exchange for small workspace and reduced dexterity. Because the solution for parallel manipulators' forward kinematics is in general much harder than their inverse kinematics, a typical control strategy for such manipulators is to specify the plate's pose in world coordinates and then solve the individual leg lengths. The accuracy of the robot critically depends on accurate knowledge of the device's kinematic parameters. This article focuses on the accuracy improvement of Stewart platforms by means of calibration.

Calibration of Stewart platforms consists of construction of a kinematic model, measurement of the position and orientation of the platform in a reference coordinate frame, identification of the kinematic parameters, and accuracy compensation. A measurement procedure proposed in this article allows a great simplification of the kinematic identification. The idea is to keep the length of the particular leg, whose parameters are to be identified, fixed while the other legs change their lengths during the measurement phase. By that, redundant parameters can be eliminated systematically in the identification phase. The method also shows the estimation of each leg's parameters separately because the measurement equations are fully decoupled, which results in a drastical reduction of the computational effort in the parameter identification. Simulation results assess the performance of the proposed approach. © 1993 John Wiley & Sons, Inc.
A family of stewart platforms with optimal dexterity
Authors: Pittens Kenneth H. , Podhorodeski Ron P.
Published: July 2007

Stewart platform configurations (architectures and poses) optimizing local dexterity are investigated. The condition number of the Jacobian matrix is used to quantify the dexterity of the manipulator. For a platform‐centered Jacobian reference location and a given characteristic length for scaling purposes, a two‐parameter family of optimal configurations is shown to exist. Two suitable architectural parameters defining the family are identified and properties of the optimal configurations are discussed. The optimization results are shown to be easily extended for other Jacobian reference locations and for other singular value‐based local dexterity measures. It is suggested that the existence of a two‐parameter family of optimal local configurations could be exploited to aid in the resolution of optimal architectures for global measures.
Review and unification of reduced‐order force control methods
Authors: Grabbe M. T. , Carroll J. J. , Dawson D. M. , Qu Z.
Published: July 2007

In this article, we compare some of the recent methods developed for simultaneous position and force control of a single n‐link constrained robot manipulator. Mathematical models of the constrained manipulator are introduced and the advantages and disadvantages of the associated control formulations are discussed. The similarities between each of the proposed formulations are also highlighted. Finally, a transformation is presented that generalizes the methods of decoupling force from the position dynamics.
Dynamic analysis and control of a stewart platform manipulator
Authors: Lebret G. , Liu K. , Lewis F. L.
Published: July 2007

The Stewart platform is a six‐axis parallel robot manipulator with a force‐to‐weight ratio and positioning accuracy far exceeding that of a conventional serial‐link arm. Its stiffness and accuracy approach that of a machine tool yet its workspace dexterity approaches that of a conventional manipulator. In this article, we study the dynamic equations of the Stewart platform manipulator. Our derivation is closed to that of Nguyen and Pooran because the dynamics are not explicitly given but are in a step‐by‐step algorithm. However, we give some insight into the structure and properties of these equations: We obtain compact expressions of some coefficients. These expressions should be interesting from a control point of view. A stiffness control scheme is designed for milling application. Some path‐planning notions are discussed that take into account singularity positions and the required task. The objective is to make the milling station into a semiautonomous robotic tool needing some operator interaction but having some intelligence of its own. It should interface naturally with part delivery and other higher‐level tasks.
Exact methods for determining the kinematics of a stewart platform using additional displacement sensors
Authors: Cheok Ka C. , Overholt James L. , Beck Ronald R.
Published: July 2007

The Stewart platform (SP) is a parallel closed‐kinematic chain robotic mechanism that is capable of providing high structural and positional rigidity. Because of its unique capability, the platforms have been employed in many control engineering applications such as simulator shakers, robotic manipulators, etc. However, a main problem often found in the implementation of a real‐time controller for the platform is the lack of an efficient algorithm for solving its highly nonlinear forward kinematic transformation (FKT), where one seeks to find the translational and orientational altitudes of the moveable platform from knowing the lengths of the platform linkages. This article describes two new direct and exact methods for computing the translational and rotational displacements of an SP by employing extra transnational displacement sensors (TDSs), in addition to the existing TDSs for the six links of the SP. The key for the approach lies in knowing where to employ the TDSs for determining positional vectors of strategic platform locations. By taking advantage of a tetrahedral geometry, closed‐form solutions for the FKT can then be derived and directly evaluated. The new methods produce accurate solutions with only minimal computation necessary. The advantages and disadvantages of the proposed methods are discussed and compared to an existing method. The exact methods are being investigated for an on‐line implementation of a nonlinear adaptive control system and redundancy scheme for a 25‐ton Stewart platform‐based Crew Station/Turret Motion Base Simulator (CS/TMBS) at the U.S. Army Tank‐Automotive Command (TACOM).
The NIST robocrane
Authors: Albus James , Bostelman Roger , Dagalakis Nicholas
Published: July 2007

The Robot Systems Division of the National Institute of Standards and Technology (NIST) has been experimenting for several years with new concepts for robot cranes. These concepts utilize the basic idea of the Stewart platform parallel link manipulator. The unique feature of the NIST approach is to use cables as the parallel links and to use winches as the actuators. As long as the cables are all in tension, the load is kinematically constrained and the cables resist perturbing forces and moments with equal stiffness to both positive and negative loads. The result is that the suspended load is constrained with a mechanical stiffness determined by the elasticity of the cables, the suspended weight, and the geometry of the mechanism. Based on these concepts, a revolutionary new type of robot crane, the NIST ROBOCRANE, has been developed that can control the position, velocity, and force of tools and heavy machinery in all six degrees of freedom (x, y, z, roll, pitch, and yaw). Depending on what is suspended from its work platform, the ROBOCRANE can perform a variety of tasks. Examples are: cutting, excavating and grading, shaping and finishing, lifting, and positioning. A 6‐m version of the ROBOCRANE has been built and critical performance characteristics analyzed.
Six‐degree‐of‐freedom active vibration isolation using a stewart platform mechanism
Authors: Geng Zheng , Haynes Leonard S.
Published: July 2007

Intelligent Automation, Inc. has performed a study of a six‐degree‐of‐freedom (dof) active vibration isolation system based on a Stewart platform mechanism to be used for precision control of a wide range of space‐based structures as well as earth‐based systems. This article presents part of the study results, which includes a new Terfenol‐D actuator design and analysis, a design of a Stewart platform as a vibration isolation device, and robust adaptive filter algorithms for active vibration control. Prototype hardware of a six‐dof active vibration isolation system has been implemented and tested. About 30 dB of vibration attenuation is achieved in real‐time experiments.
Single‐input/single‐output transfer functions for a flexible slewing link
Authors: Barbieri Enrique
Published: July 2007

Truncated linear models based on constrained and unconstrained mode expansions for a flexible link with torque actuation at its hub led us to examine the behavior of theopen‐loop‐zerosof five commonly used single‐input single‐output transfer functions. We arrive at new conclusions with regard to minimum‐ and non‐minimum‐phase zeros, and passivity of the transfer functions. The flexible‐to‐rigid inertia (FRI) ratio plays an important role in the determination of these characteristics. This article illustrates how the zero locations of some of the transfer functions are dramatically affected by the FRI ratio. We also investigate the performance of a hub angle, hub rate, and relative tip position static feedback controller based on a reduced‐orderconstrainedmode model when applied to both unconstrained and constrained mode models of the same dimension. Simulations indicate that the constrained model can be stable while the unconstrained model is not for high FRI ratios. Our findings can provide useful information to designers in cases where the controller is sensitive to the location of the plant's zeros.
Friction modeling and compensation for an industrial robot
Authors: Phillips Stephen M. , Ballou Kevin R.
Published: July 2007

This article describes the detailed friction modeling of the General Electric GP132 industrial robot. Friction is an area whose importance is often discounted in the development of control systems because it is thought to be insignificant or unmodelable. This work demonstrates that friction does have a predictable structure, and that significant performance improvement can be realized through its proper compensation. Experiments performed to determine the static, Coulomb, and viscous friction of the GP132 are presented. In addition to these components, the robot is shown to have significant gravity load‐dependent and position‐dependent friction. The accuracy of the friction models are verified through several experiments and are shown to be considerably better than previously formulated models.
New approach for aggregating multi‐sensory data
Authors: Basir O. A. , Shen H. C.
Published: July 2007

The task of sensory data fusion may involve the aggregation of sensory measurements that may be from different phenomenological domains and that, in many cases, could embrace some conflicting information cues. It is rather a challenge to find suitable strategies by which measurements obtained by the different sensors of the system can be aggregated so that a consistent interpretation of these measurements is achieved. In this article, we present a novel approach to achieve this goal. A recursive group utility function that is capable of bringing the group of sensors into consensus is used. After each sensor in the group gathers information relevant to the sensory task, the group engages in what we call the uncertainty estimation stage. This is an information theorybased process that allows each sensor to assess its self‐uncertainty and the conditional uncertainties of other sensors. This process facilitates the computation of a weighting scheme that operates recursively on sensor observations until the group reaches a consensus. Whenever new observations are made, the uncertainty estimates of sensors are updated and used to compute a new weighting scheme. To demonstrate the efficacy and to show how the methodology works, the article discusses how the method can be used to tackle the multi‐sensor object identification problem. © 1993 John Wiley & Sons, Inc.
Efficient robot arm modeling for computer control
Authors: Megahed Said M.
Published: July 2007

This article presents a comparative study of the required number of arithmetic operations necessary for computing robot arm models using the Denavit‐Hartenberg symbolic notation and a proposed one. The proposed notation is based on the idea of describing the motion of a robot joint by a pair matrix and the geometry of a link by a shape matrix. This notation needs the use of two coordinate systems for each joint or link. The results prove that the proposed notation reduces the computation time of robot models. For a 6‐degrees of freedom robot arm, the computation times of kinematic position, velocity, and dynamic models are reduced respectively by 20%, 5%, and 2%, respectively. The two notations have the same effects on computing the inverse models. © 1993 John Wiley & Sons, Inc.
Reactive behaviors of fast mobile robots
Authors: Zapata René , Lépinay P. , Thompson P.
Published: July 2007

This article addresses the modeling of the reactive behaviors of a mobile robot moving in unstructured and dynamic environments. The main focus is on the software structure devoted to obstacle avoidance when geometric models do not exist and when obstacles can be dynamic. The first part concerns the model of the robot/environment interaction. This model is based on the definition of theinteraction component(deformable virtual zone) of aninternal stateof the robot and leads to avoidance‐oriented control laws. The second part describes the derivation of the state equation and one of its implementations on a fast outdoor mobile robot. © 1994 John Wiley & Sons, Inc.
Identification of a trajectory generator model for the PUMA‐560 robot
Authors: Tondu Bertrand , El‐zorkany Hany
Published: July 2007

In this article, work on the experimental identification of a model of the trajectory generator of a PUMA‐560 robot is reported. The model developed is based on theoretical work reported in the literature and the necessary parameters are obtained experimentally. The resulting model is validated versus the corresponding actual robot motions. All experiments are based on the use of a 3D non‐contact position sensor to record the motions of the robot end‐effector. © 1994 John Wiley & Sons, Inc.
Effect of tension parameters and intervals on splines‐under‐tension based robot trajectory planning
Authors: Yi Seung‐Jong , Kim Kyuil
Published: July 2007

The new trajectory planner using cubic spline functions under tension in joint coordinates is developed and implemented in the 6 dof articulated robot with a parallel drive arm mechanism to improve the smoothness of the joint trajectories and positioning accuracy of the manipulator. Also, the optimal selection of the tension parameter and time interval selection schemes are investigated in this study. © 1994 John Wiley & Sons, Inc.
Design and control of a three‐degrees‐of‐freedom, in‐parallel, actuated manipulator
Authors: Pfreundschuh George H. , Sugar Thomas G. , Kumar Vijay
Published: July 2007

The mechanics, design, and control of a 3–degrees‐of‐freedom, in‐parallel, pneumatically actuated manipulator are presented. The manipulator consists of two platforms connected by three serial chains. The kinematic design is such that the three relative degrees of freedom between the two plates allow the manipulator to accomodate uncertainties and sustain impacts while contacting and interacting with unknown environments. In particular, the manipulator is naturally compliant in translation along the approach direction as well as in rotations about axes perpendicular to the approach direction, while it is stiff in other directions. In this article, an overview of the manipulator kinematics, a description of the manipulator system and the associated hardware, and experimental results on the dynamic behavior of a prototype are presented. © 1994 John Wiley & Sons, Inc.