Showing papers in "Journal of Intelligent and Robotic Systems in 1992"
TL;DR: This paper is concerned with a particular aspect of the resolution of this redundancy, which is its utilization to optimize the system's position and configuration during task commutations when changes occur in both task requirements and task constraints.
Abstract: Mobile manipulators are attracting significant interest in the industrial, military, and public service communities because of the potential they provide for increased efficiency in material handling and manipulation tasks. Corresponding interest has arisen in the robotics research community since the combination and coordination of the mobility of an autonomous platform with the robotic motion of a manipulator introduce complex analytical problems. One such problem arises from the particular kinematic redundancy which characterizes practical mobile manipulators. This paper is concerned with a particular aspect of the resolution of this redundancy, which is its utilization to optimize the system's position and configuration during task commutations when changes occur in both task requirements and task constraints. Basic optimization schemes are developed for cases when load and position constraints are applied at the end-effector. Various optimization criteria are investigated for task requirements including obstacle avoidance, maneuverability and several torque functions. The problem of optimally positioning the platform for execution of a manipulation task requiring a given reach is also treated. Emphasis is then placed on the multi-criteria optimization methods which are necessary to calculate the commutation configurations in sequences of tasks with varying requirements. Sample results are presented for a system involving a three-link planar manipulator on a mobile platform. The various optimization schemes are discussed and compared, and several directions (in particular the novel use of minimax optimization pioneered here for redundancy resolution) are outlined for further extensions of the methods to the general problem of motion planning and control of redundant robotic systems with combined mobility and manipulation capabilities.
53 citations
TL;DR: Many applications of robotic and teleoperated manipulator arms require operation in contact and noncontact regimes and the transition between them with special attention given to problems of flexibility in the links and drives is dealt with.
Abstract: Many applications of robotic and teleoperated manipulator arms require operation in contact and noncontact regimes. This paper deals with both regimes and the transition between them with special attention given to problems of flexibility in the links and drives. This is referred to as contact control. Inverse dynamics is used to plan the tip motion of the flexible link so that the free motion can stop very near the contact surface without collision due to overshoot. Contact must occur at a very low speed since the high frequency impact forces are too sudden to be affected by any feedback generated torques applied to a joint at the other end of the link. The effects of approach velocity and surface properties are discussed. Force tracking is implemented by commands to the deflection states of the link and the contact force. This enables a natural transition between tip position and tip force control that is not possible when the arm is treated as rigid. The effects of feedback gain, force trajectory, and desired final force level are of particular interest and are studied. Experimental results are presented on a one-link arm and the system performance in the overall contact task is analyzed. Extension to multi-link cases with potential applications are discussed.
30 citations
TL;DR: Robustness to unmodeled dynamics is achieved using a so-called composite control strategy based on a singular perturbation formulation of the manipulator dynamics together with σ-modificiation.
Abstract: In this paper we discuss the robustness of adaptive control of rigid robots and methods for improving robustness in the face of unmodeled dynamics and external disturbances. Robustness to unmodeled dynamics is achieved using a so-called composite control strategy based on a singular perturbation formulation of the manipulator dynamics together with σ-modificiation. Rigorous stability proofs are given using a composite Lyapunov function approach.
22 citations
TL;DR: The purpose of this paper is to focus on the implementation issues associated with using Petri nets for the performance analysis of discrete event dynamic systems while demonstrating several applications in manufacturing systems.
Abstract: The purpose of this paper is to focus on the implementation issues associated with using Petri nets for the performance analysis of discrete event dynamic systems while demonstrating several applications in manufacturing systems. Practical modeling issues will be discussed and several applications will be presented that illustrate the advantages and limitations of this methodology. These issues lead to the definition of several research problems in Petri nets for performance analysis.
20 citations
TL;DR: The overall control system architecture, the design and implementation of the mobility and communication functions, and results from recent testing are reviewed.
Abstract: The U.S. Army Laboratory Command, as part of the Department of Defense Robotics Testbed Program, is developing a testbed for cooperative, real-time control of unmanned land vehicles. The program entails the development and integration of many elements which allow the vehicles to perform both autonomous and teleoperated functions. The National Institute of Standards and Technology (NIST) is supporting this program by developing the vehicle control system using the Real-time Control System (RCS) architecture. RCS is a hierarchical, sensory-based control system, initially developed for the control of industrial robots and automated manufacturing systems. NIST is developing the portions of RCS that control all vehicle mobility functions, coordinate the operations of the other subsystems on the vehicle, and communicate between the vehicle and the remote operator control station. This paper reviews the overall control system architecture, the design and implementation of the mobility and communication functions, and results from recent testing.
19 citations
TL;DR: A sliding mode-based impedance controller is proposed and a simple and robust algorithm is obtained so that the targeted impedance can be accurately implemented without the exact model of the robot.
Abstract: In this paper, we discuss the problem of implementing impedance control in the presence of model uncertainties and its application to robot force control. We first propose a sliding mode-based impedance controller. The implementation of the targeted impedance, and the preservation of stability in the presence of model uncertainties, are the key issues in the proposed approach. Using sliding mode control, a simple and robust algorithm is obtained so that the targeted impedance can be accurately implemented without the exact model of the robot. The controller is designed in terms of the task space coordinates. The chattering in the sliding mode control is eliminated by using a continuous function. The problem of force control is also addressed for the impedance controlled robot. An off-line estimation method of the environment model is suggested and used in the force control scheme. The proposed impedance and force control schemes have been experimentally verified on a two degree-of-freedom direct-drive robot arm. The experimental results are presented in this paper.
16 citations
TL;DR: The paper shows that the concept of distributed positioning based on the separation of the required end-effector motion into two components according to a criterion results in the improvement of robot dynamic capabilities.
Abstract: The concept of distributed positioning is based on the separation of the required end-effector motion into two components according to a criterion. The external-to-internal transformation of the motion is made in such a way that some of the joints become responsible for the first and others for the second component. Thus, the redundancy could be compensated and the unique solution of the inverse kinematics achieved. If the separation is made according to the acceleration criterion, then the ‘smooth’ and the ‘fast’ components of the end-effector motion are obtained. The paper shows that this concept results in the improvement of robot dynamic capabilities.
14 citations
TL;DR: This paper presents the kinematic analysis and trajectory planning for a six-degrees-of-freedom end-effector whose design is based on the Stewart platform mechanism.
Abstract: This paper presents the kinematic analysis and trajectory planning for a six-degrees-of-freedom end-effector whose design is based on the Stewart platform mechanism. The end-effector is composed of two platforms and six linear actuators driven by stepper motors. A spring-loaded platform is used to provide passive compliance to the end-effector during a part assembly. A closed-form solution is derived for the inverse kinematic transformation and a computationally effective numerical solution is obtained for the forward kinematic transformation using the Newton-Raphson method. Three trajectory planning schemes, two for fine motion and one for gross motion are developed. Experimental results of tracking various test paths are presented.
14 citations
TL;DR: A rule-based framework that will automatically generate test data to achieve maximal branch coverage is presented and can be extended to include additional testing requirements and test case generation knowledge.
Abstract: Test data generation using traditional software testing methods generally requires considerable manual effort and generates only a limited number of test cases before the amount of time expanded becomes unacceptably large. A rule-based framework that will automatically generate test data to achieve maximal branch coverage is presented. The design and discovery of rules used to generate meaningful test cases are also described. The rule-based approach allows this framework to be extended to include additional testing requirements and test case generation knowledge.
14 citations
TL;DR: Some solutions to the limp material handling problem are outlined with emphasis on the ways in which sensors are sued to cope with uncertainties in the materials and handling processes in the automation of apparel manufacture.
Abstract: Research on sensory robotic assembly has been carried out at Hull University for over 12 years. Applied research is carried out in collaboration with industry and with additional support from govement research agencies. This is enhanced by longer-term, more speculative work providing the foundations for future applied research. This approach is exemplified in this paper by consideration of the automation of apparel manufacture. Some solutions to the limp material handling problem are outlined with emphasis on the ways in which sensors are sued to cope with uncertainties in the materials and handling processes.
13 citations
TL;DR: A general robust control scheme is developed that applies to systems described by a class of second-order nonlinear equations and applications to a mobile robot and a chemical stirred tank reactor are given.
Abstract: Lyapunov techniques are used to design robust controllers for nonlinear systems. The objective is to use the system structure to simplify the controller as far as possible. A general robust control scheme is developed that applies to systems described by a class of second-order nonlinear equations. Applications to a mobile robot and a chemical stirred tank reactor are given.
TL;DR: Efficient and robust Jacobian and weighted damped least squares algorithms are given which provide a method that allows full utilization of the redundancy to best achieve task requirements.
Abstract: This paper presents kinematic algorithms for resolved-rate based inverse kinematics of redundant manipulators. Efficient and robust Jacobian and weighted damped least squares algorithms are given which provide a method that allows full utilization of the redundancy to best achieve task requirements. A nominal set of task space variables is suggested and procedures for modifying this specification or their relative priorities due to changing task requirements or events are discussed. Examples are shown using a simulation of the seven degree-of-freeom Robotics Research manipulator. These simulations demonstrate the singularity robustness of the algorithms and the ability to smoothly transition between task parameterizations and relative priorities.
TL;DR: A large-scale expert supervision and control system which was developed as part of a long-term project to apply advanced concepts of CIM to a cement production plant and results in increases of the order of 4–5% in productivity and energy reduction as well as reduced plant maintenance over conventional manual control.
Abstract: The process industry and the cement industry in particular, is rapidly realising the importance of expert systems for the control of large-scale production processes which have hitherto defied solution by conventional methods. Where the operational environment of a process industry is subject to vagueness and uncertainty, then expert control offers new opportunities for increased production, fuel economy, and enhanced product quality.
TL;DR: A pattern classification and recognition approach to expert control systems is developed for use in the on-line analysis and design of dynamic systems, based on the tuning of a three-term PID controller.
Abstract: In this paper, a pattern classification and recognition approach to expert control systems is developed for use in the on-line analysis and design of dynamic systems The approach used is based on the tuning of a three-term PID controller and, hence, it is not dependent on a specific form of the process model A real-time experiment of implementing the developed controller using a microcomputer and associated hardware is presented A sample set of production rules is discussed The expert system reaches appropriate tuning parameters, using extracted features, such as oscillatory, underdamped, and exponentially monotonic properties
TL;DR: The proposed computation procedure is used to obtain the inverse kinematic position models of two robot arms: one contains only revolute joints and the other contains both revolute and prismatic joints, which give more accurate inverseKinematic velocity and acceleration models than numerical differentiation.
Abstract: The spherical wrist robot arm is the most common type of industrial robot. This paper presents an efficient analytical computation procedure of its inverse kinematics. It is based on the decomposition of the inverse kinematic problem to two less complex problems; one concerns the robot arm basic structure and the other concerns its hand. The proposed computation procedure is used to obtain the inverse kinematic position models of two robot arms: one contains only revolute joints and the other contains both revolute and prismatic joints. The 1st and 2nd time derivatives of the obtained models give more accurate inverse kinematic velocity and acceleration models than numerical differentiation. These models are verified by simulation for two different trajectories. The obtained results demonstrate the effect of the proposed procedure on reducing the necessary computation time compared to other computation techniques.
TL;DR: This paper describes the work on improving and supplementing traditional position control programming methods and describes the functionality of a complete system for programming complex robot tasks.
Abstract: The programming of robots is slowly evolving from traditional teach pendant methods to graphical Off-Line Programming (OLP) methods. Graphical simulation tools, such as OLP, are very useful for developing and testing robot programs before they are run on real industrial equipment. OLP systems are also used to develop task level programs. Traditional OLP systems, however, suffer from the limitations of using only position control which does not account for inherent robot inaccuracies and dynamic environments. This paper describes our work on improving and supplementing traditional position control programming methods. A baseline OLP system was implemented at NIST's Automated Manufacturing Research Facility (AMRF). Experience gained in implementing this system showed that an effective OLP system must accurately simulate the real world and must support sensor programming to compensate for real-world changes that cannot be simulated. The developed OLP geometric world model is calibrated using robot mounted ultrasound ranging sensors. This measurement capability produces a baseline geometric model of relatively good static accuracy for off-line programming. The graphical environment must also provide representations of sensor features. For this specific application, force is simulated in order to include force based commands in our robot programs. These sensor based programs are able to run reliably and safely in an unpredictable industrial environment. The last portion of this paper extends OLP and describes the functionality of a complete system for programming complex robot tasks.
TL;DR: This paper gives a methodology, PROLOG code, as well as an example of an explanation facility EN applicable to most neural networks, based on a general explanation degree calculation in a multilayer neural network, and on input node characterization grammars for synthesis of explanation text.
Abstract: This paper give a methodology, PROLOG code, as well as an example of an explanation facility EN applicable to most neural networks It involves How?, Why? and TRACE facilities, and is based on a general explanation degree calculation in a multilayer neural network, as well as on input node characterization grammars for synthesis of explanation text
TL;DR: A robust position tracking controller that yields an exponentially stable position tracking error result, and a robust force tracking controllers that yields adjustable bounds on the force tracking error are discussed.
Abstract: In this paper, a control architecture is developed for the closed chain motion of two six-joint manipulators holding a rigid object in a three-dimensional workspace. Dynamic and kinematic constraints are combined with the equations of motion of the manipulators to obtain a dynamical model of the entire system in the joint space. Reduced-order dynamic equations are then developed with regard to the position and force control variables. Robust control laws are then determined such that the force and position control design is decoupled. The control laws that will be discussed are: a robust position tracking controller that yields an exponentially stable position tracking error result, and a robust force tracking controller that yields adjustable bounds on the force tracking error.
TL;DR: The problem of camera calibration from the perspective of hand-eye integration (henceforth referred to as the Camera-Robot (CR) problem), is addressed and results obtained from a least-squares fit using pseudo-inverse technique and a three layer neural network are compared.
Abstract: The problem of camera calibration from the perspective of hand-eye integration (henceforth referred to as the Camera-Robot (CR) problem), is addressed in this paper. Mapping results obtained from a least-squares fit using pseudo-inverse technique and a three layer neural network are compared. The calibration matrix is developed to map the image coordinates of an IRI D256 vision processor equipped with a CCD camera directly on to the coordinates for an IBM 7540 SCARA manipulator. One transformation is obtained by performing a least-squares fit using pseudo-inverse technique on a set of one hundred data points which relates two-dimensional (2D) image coordinates to corresponding twodimensional robot coordinates. The CR problem is also approached by using the same data points on a neural network. The results not only demonstrate the ability of neural networks to ‘learn’ the transformation to a reasonable accuracy, but also from the basis for a relatively simple method of adaptive self-calibration of robot-vision systems. In a broader sense, the proposed method can be used to calibrate a variety of robotic sensors that are typically used in a flexible manufacturing environment.
TL;DR: An algorithm for path tracking of two robot arms with end-effectors gripping a common inertial load that avoids singularities, because there is no need of using the inverse kinematics.
Abstract: This paper presents an algorithm for path tracking of two robot arms with end-effectors gripping a common inertial load. The path is generated as a sequence of elementary motions. The most important feature of the present algorithm is that it avoids singularities, because there is no need of using the inverse kinematics. Direction and proximity criteria are introduced. Holonomic constraints are formulated for the position and orientation of the two end-effectors. The application of parallel processing methods to path tracking according to the previous algorithm is presented. The algorithm is implemented in the Alliant FX/80 parallel machine.
TL;DR: The tramming control algorithm design described is in concert with hierarchical architecture design principles developed at National Institute of Standards and Technology (NIST), referred to as the Real-time Control Systems (RCS) methodology.
Abstract: The drive toward increased safety for coal miners has led to the development of computer-assisted methods of underground coal mining. The development of control architectures for the control of the movement of continuous mining machines (tramming control) is an important part of this overall effort. The tramming control algorithm design described is in concert with hierarchical architecture design principles developed at National Institute of Standards and Technology (NIST), referred to as the Real-time Control Systems (RCS) methodology. The algorithm design allows for the control of both cutting and free-space movement by a continuous mining machine and allows for a high degree of human operator interaction.
TL;DR: It is found that Cartesian servo algorithms which use the transpose of the Jacobian and model-based gravity compensation, provide easy programmability and accurate reproduction of stiffnesses over a wide range.
Abstract: The programmability of Cartesian stiffness in Cartesian servo control algorithms that do not use explicit force feedback is examined. A number of Cartesian algorithms are implemented and evaluated on a commercial seven degree-of-freedom robot arm, using the NASREM robot control system testbed. It is found that Cartesian servo algorithms which use the transpose of the Jacobian and model-based gravity compensation, provide easy programmability and accurate reproduction of stiffnesses over a wide range. When dynamic behavior is a consideration, dynamic damping control, augmented to include a parameterization of the manipulator self-motion, provides superior performance and programmability.
TL;DR: The scatter degree technique is a local feature detection in pattern recognition that provides a simple and efficient method to obtain a robust vector by measuring the relation of the valley points and the peak points.
Abstract: The scatter degree technique to be introduced in this paper is a local feature detection in pattern recognition. It provides a simple and efficient method to obtain a robust vector by measuring the relation of the valley points and the peak points. Combining this technique with neural networks, one can achieve good results in the recognition and classification of noisy or partially invisible patterns.
TL;DR: The robots in automation may be used to serve their surrounding equipment such as transporting, loading, and unloading simple objects, but for some tasks, two or more robots working together may be required to achieve the assigned goals.
Abstract: The robots in automation may be used to serve their surrounding equipment such as transporting, loading, and unloading simple objects. For some tasks, two or more robots working together may be required to achieve the assigned goals. In this situation, coordination of the robots for a concerted action becomes a necessity. In addition, the joint torque distribution among the robots is desirable to avoid overloading.
TL;DR: A genetic manufacturing environment is considered, with emphasis on small-lot, discrete, and asynchronous type of manufacturing systems rather than high volume and continuous type.
Abstract: A genetic manufacturing environment is considered. The emphasis is on small-lot, discrete, and asynchronous type of manufacturing systems rather than high volume and continuous type. Two classes of scheduling policies are proposed to render the machine stable. The policies are of feedback type. The decision is made in real-time and on-line.
TL;DR: A theoretical solution for modeling the tasks and the practical solutions implemented for controlling two six-axis arms in a real experiment for manipulating objects with two robotic arms, when force control is necessary.
Abstract: The goal of this paper is to present solutions for manipulating objects with two robotic arms, when force control is necessary. The applications we are interested in are the transport and assembly of rigid objects, the deformation, transport and assembly of flexible objects, and the assembly in space of two objects, with each being held by one arm. We present a theoretical solution for modeling the tasks and the practical solutions we have implemented for controlling two six-axis arms in a real experiment. In each case, the task is described by a position vector and a force vector, which are used jointly in a hybrid position/force control scheme. The position vector consists of the absolute position/orientation of a frame attached to the manipulated object(s), and of the relative position/orientation of the end effectors. The force vector includes external and internal forces and moments acting on the object(s). This solution allows us to use the same task description for various complex applications; this feature is very interesting for real experiments, since it reduces the programming burden. We have experienced this advantage when implementing our method on a real experimental setup, which is described in the paper and with which we have carried out several experiments.
TL;DR: Simulation results show that without model errors, all advanced control schemes can achieve higher tracking accuracy than PD control and heuristic control proves to be the most robust control scheme in case of mixed model and measurement errors.
Abstract: Various advanced control strategies are applied to a direct-drive SCARA robot and studied in computer simulations. Besides computed torque control and direct adaptive control, heuristic optimal control, a new path control scheme for robotic manipulators, is included in the comparison study. PD control, the traditional robot control method, is used for generating a comparing baseline. While all schemes are applied for the same tracking task, the effect of modelling errors and measurement noise is considered in robot performance evaluation. Simulation results show that (1) without model errors, all advanced control schemes can achieve higher tracking accuracy than PD control; (2) with a random measurement error of 1%, computed torque and direct adaptive control methods are inferior to PD control; (3) heuristic control proves to be the most robust control scheme in case of mixed model and measurement errors.
TL;DR: This work experimentally characterize the motors in an Adept-2 manipulator, and develops a linearizing and decoupling controller which allows torque specification.
Abstract: The ability to command actuator torque is necessary to perform research into robot control. Commercial manipulators using direct-drive actuators offer high performance, but do not allow specification of actuator torque. We experimentally characterize the motors in an Adept-2 manipulator, and develop a linearizing and decoupling controller which allows torque specification. Torque ripple is 13%.
TL;DR: A method for tracking moving image features by combining spatial and temporal edge information with model-based feature information that makes use of a high temporal sampling rate with respect to spatial changes of the image features and operates in a real-time multi-processing environment.
Abstract: This paper describes a method for tracking moving image features by combining spatial and temporal edge information with model-based feature information. The algorithm updates the two-dimensional position of object features by correlating predicted model features with current image data. The results of the correlation process are used to compute an updated model. The algorithm makes use of a high temporal sampling rate with respect to spatial changes of the image features and operates in a real-time multi-processing environment. Preliminary results demonstrate successful tracking for image feature velocities between 1.1 and 4.5 pixels every image frame.
TL;DR: This paper proposes two simple adaptive control schemes of robot manipulators which consist of a feedforward term from the desired position, velocity, and acceleration trajectory based on the inverse of robot dynamics.
Abstract: This paper proposes two simple adaptive control schemes of robot manipulators. The first one is the state feedback control which consists of feedforward from the desired position trajectory, PD feedback from the actual trajectory, and an auxiliary input. The second one is the feedforward/feedback control which consists of a feedforward term from the desired position, velocity, and acceleration trajectory based on the inverse of robot dynamics. The feedforward, feedback, and auxiliary gains are adapted using simple equations derived from the decentralized adaptive control theory based on Lyapunov's direct method, and using only the local information of the corresponding joint. The proposed control schemes are computationally fast and do not require a priori knowledge of the detail parameters of the manipulator or the payload. Simulation results are presented in support of the proposed schemes. The results demonstrate that both controllers perform well with bounded adaptive gains.