Tele-manipulation under a Dynamic Environment

One of the most important problems in tele-manipulation is how to realize the human skill in performing the task by master-slave robot system. Experimental results show that, when human operator turns a crank directly, he/she actively uses the contact force along the normal direction of the crank. Although the normal contact force does not contribute to the rotation of the crank, it influences the arm-crank system's stability. In this research, we study on how to compensate the master-slave robot system to turn the crank skillfully

Design and implementation of haptic interactions

This thesis addresses current haptic display technology where the user interacts with a virtual environment by means of specialized interface devices. The user manipulates computer generated virtual objects and is able to feel the sense of touch through haptic feedback. The objective of this work is to design high performance haptic interactions by developing multi-purpose virtual tools and new control schemes to implement a PUMA 560 robotic manipulator as the haptic interface device. The interactions are modeled by coupling the motions of the virtual tool with those of the PUMA 560 robotic manipulator;The work presented in this dissertation uses both kinematic and dynamic based virtual manipulators as virtual simulators to address problems associated in both free and constrained motions. Both implementations are general enough to allow researchers with any six degree-of-freedom robot to apply the approaches and continue in this area of research. The results are expected to improve on the current haptic display technology by a new type of optimal position controller and better algorithms to handle both holonomic and nonholonomic constraints;Kane\u27s method is introduced to model dynamics of multibody systems. Multibody dynamics of a virtual simulator, a dumbbell, is developed and the advantages of the Kane\u27s method in handling the non-holonomic constraints are presented. The resulting model is used to develop an approach to dynamic simulation for use in interacting haptic display, including switching constraints. Experimental data is collected to show various contact configurations;A two-degree of freedom virtual manipulator is modeled to feel the surface of a taurus shape. An optimal position controller is designed to achieve kinematic coupling between the virtual manipulator and the haptic display device to impose motion constraints and the virtual interactions. Stability of the haptic interface is studied and proved using Lyapunov\u27s direct method. Experimental data in various positions of the robotic manipulator is obtained to justify theoretical results. A shift mechanism is then implemented on the taurus shape, thus the motions of the robotic manipulator is further constrained. The difficulties in handling the motion constraints are discussed and an alternative approach is presented

Force control of heavy lift manipulators for high precision insertion tasks

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, June 2005."May 2005." Leaf 81 blank.Includes bibliographical references (leaves 67-70).The inherent strength of robotic manipulators can be used to assist humans in performing heavy lifting tasks. These robots reduce manpower, reduce fatigue, and increase productivity. This thesis deals with the development of a control system for a robot being built for this purpose. The task for this robot is to lift heavy payloads while performing complex insertion tasks. This task must be completed on the deck of a naval vessel where possible disturbances include wind, rain, poor visibility, and dynamic loads induced by a swaying deck. The primary objective of the controller being designed here is to allow for insertion of the payload despite tight positioning tolerances and disturbances like surface friction, joint friction, and dynamic loads from ship motions. A control structure designed for intuitive interaction between the robot and operator is analyzed and shown to be stable using an established environment interaction model. The controller is shown to perform within established specifications via numerical simulation based on simple user inputs. An additional objective of this controller design is to prevent part jamming during the insertion task. With a large, powerful manipulator, the chances of a jam occurring is high. Without the use of bilateral force feedback, it will be difficult for the operator feel when these jams will occur and there will be no information about how to prevent them. This thesis analyzes the geometry and mechanics of the jamming problem and derives a control system to assist the user in preventing these jams. These methods can be extended to other insertion tasks simply by specifying the appropriate geometry.by Matthew A. DiCicco.S.M

Delay compensation in bilateral teleoperation using predictor observers

Destabilization and performance degradation problems caused by the time delay in communication channel is a serious problem in bilateral teleoperation. In particular, variability of the delay due to limited bandwidth, long distance or congestion in transmission problems has been a real challenge in bilateral teleoperation research since the internet communication has become prevalent. Many existing delay compensation techniques are designed for linear teleoperator systems. In order to implement them on real bilateral systems, the nonlinear dynamics of the robots must first be linearized. For this purpose feedback linearization is usually employed. In this thesis, the delay compensation problem is tackled in an observer framework by designing two observers. Integration of a disturbance observer to the slave side implies a linearized slave dynamics with nominal parameters. Disturbance observer estimates the total disturbance (nonlinear terms, parametric uncertainties and external disturbances) on the slave system. A second observer is designed at the master side to predict states of the slave. This observer can be designed using a variety of linear or nonlinear methods. In order to have finite-time convergence, a sliding mode observer is designed at the master side. It is shown that this observer predicts the future positions and/or velocities of the slave and use of such predictions in the computation of a simple PD control law implies stable operation for the bilateral system. Since the disturbance observer increases the robustness of the slave system, the performance of the resulting bilateral system is quite satisfactory. Force reflecting bilateral teleoperation is also considered in this thesis. Integrating the proposed observer based delay compensation technique into the well known four-channel control architecture not only stable but also transparent bilateral teleoperation is achieved. Simulations with bilateral systems consisting of 2 DOF scara robots and pantograph robots, and experiments with bilateral systems consisting of a pair of single link robots and a pair of pantograph robots validate the proposed method

Bilateral Control - Operational enhancements

A succinct definition of the word bilateral is having two sides [1]. In robotics the term bilateral control is used to define the specific interaction of two systems by means of position and/or force. Bilateral systems are composed of two sides named master and slave side. The aim of such an arrangement is such that position command dictated by master side is followed by a slave side, and at the same time the force sensation of the remote environment experienced by slave is transferred to the mater - human operator. This way bilateral system may be perceived as an “impendanceless” extension of the human operator providing the touch information of the remote (or inaccessible) environment. In a sense bilateral systems are a mechatronics extension of the teleoperated systems. There are many applications of this structure which requires critical manipulations like nuclear material handling, robotic surgery, and micro material handling and assembly. In all these applications a human operator is required to have as close to real as possible contact with object that should be manipulated or in other word the telepresence of the operator is required. In this thesis work various important aspects of bilateral control systems are discussed. These aspects include problems of (i) acquisition of information on master and slave side, (ii) analysis and selection of the proper structure of the control systems to ensure fidelity of the system behavior. The work has been done to enhance the performance of the bilateral control system by: (i) Enhancing position and velocity measurements obtained from incremental encoder having limited number of pulses per revolution. A few algorithms are investigated and their improvements are proposed; (ii) Increasing system robustness by using acceleration controller based on disturbance observer. The robust system design based on disturbance observer is known but its application requires very fast sampling and high bandwidth of the observer. In this work the discrete time realization of the observer is presented in details and selection of the necessary filters and the sampling so to achieve a good trade-off for observer realization is discussed and experimentally confirmed; (iii) Increasing the bandwidth of force sensation by using reaction force observer. For transparent operation of a bilateral system the bandwidth of force sensation is of the major interest. All force sensors do have relatively slow dynamics and observer based structures seems providing better behavior of the overall system. In this work the observer of the interaction force is examined and design procedure is established. In order to verify all of the proposed ideas a versatile bilateral system is designed and built and experimental verification is carried out on this system

The design of a control architecture for a heavy-lift precision manipulator for use in contact with the environment

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006."June 2006."Includes bibliographical references (leaves 117-121).Robotic manipulators can be used to enhance the strength and dexterity of a human user. This thesis considers the design of a controller for a heavy-lift manipulator for lifting and inserting payloads onto aircraft on the deck of a ship. The purpose of this robot is to reduce manpower requirements aboard the ship, and reduce the physical requirements for the individuals loading the payloads onto an aircraft. This particular application presents several control challenges, including structural resonances, complex interaction with the environment, high joint friction that varies over time, tight tolerances for the insertion tasks, and ship motions. This thesis builds upon previous works by Garretson [17] and DiCicco [9] by further developing an insertion control mode for intuitive human interaction with the payload of the manipulator when in contact with the environment. These control algorithms, as well as those developed in the previous work, are also validated on a laboratory manipulator. This thesis contains a detailed description of the control architecture for the heavy lift manipulator, including the insertion control mode and a position control mode for use when the manipulator is not in contact with the environment. Both architectures are validated with dynamic simulation models.(cont.) The position control response of this manipulator is shown to be improved with the implementation of friction compensation. In some joints, outputs from an adaptive friction estimator are used to make feed-forward models of friction for use during environmental contact. The position and insertion controllers are then evaluated under open-loop and human control on a laboratory manipulator.by William T. Becker, III.S.M