Applying model mediation method to a mobile robot bilateral teleoperation system experiencing time delays in communication

Teleoperation systems consist of two subsystems namely, the master and the slave. Master is used by the human operator to send commands to the slave to achieve a task. In bilateral teleoperation, the interaction forces acquired from the slave sub-system is sent to the master to increase the level of tele-presence. In this kind of a setting, data has to be transferred through a communication line in which package losses and time delays occur. Such deficiencies in the communication line results in stability problems in the system. In this paper, HIPHAD desktop haptic device as the master sub-system and an omni-directional mobile robot as the slave subsystem is used to develop an unlimited workspace teleoperation system. The system’s stability and tracking performance under a constant time delay is measured for direct teleoperation and when model mediation method is applied to ensure stability. The results of the tests are given and the conclusions are derived.The Scientific and Technological Research Council of Turke

Position / force control of systems subjected to communicaton delays and interruptions in bilateral teleoperation

Thesis (Master)--Izmir Institute of Technology, Mechanical Engineering, Izmir, 2012Includes bibliographical references (leaves: 65-68)Text in English; Abstract: Turkish and Englishix, 76 leavesTeleoperation technology allows to remotely operate robotic (slave) systems located in hazardous, risky and distant environments. The human operator sends commands through the controller (master) system to execute the tasks from a distance. The operator is provided with necessary (visual, audio or haptic) feedback to accomplish the mission remotely. In bilateral teleoperation, continuous feedback from the remote environment is generated. Thus, the operator can handle the task as if the operator is in the remote environment relying on the relevant feedback. Since teleoperation deals with systems controlled from a distance, time delays and package losses in transmission of information are present. These communication failures affect the human perception and system stability, and thus, the ability of operator to handle the task successfully. The objective of this thesis is to investigate and develop a control algorithm, which utilizes model mediated teleoperation integrating parallel position/force controllers, to compensate for the instability issues and excessive forcing applied to the environment arising from communication failures. Model mediation technique is extended for three-degrees-of-freedom teleoperation and a parallel position/force controller, impedance controller, is integrated in the control algorithm. The proposed control method is experimentally tested by using Matlab Simulink blocksets for real-time experimentation in which haptic desktop devices, Novint Falcon and Phantom Desktop are configured as master and slave subsystems of the bilateral teleoperation. The results of these tests indicate that the stability and passivity of proposed bilateral teleoperation systems are preserved during constant and variable time delays and data losses while the position and force tracking test results provide acceptable performance with bounded errors

Disturbance observer based bilateral control systems

Bilateral teleoperation is becoming one of the far reaching application areas of robotics science. Enabling a human operator the ability to reach and manipulate a remote location will be possible with the various applications of bilateral control. In that sense, ideal bilateral control allows extension of a person's sensing to a remote environment by a master slave structure. So, the coupled goals of bilateral control is to enforce the slave system track the motion generated on the master system and to reflect the forces from the slave system. This thesis investigates the current state of the art in bilateral teleoperation. For that purpose, design and analysis of bilateral control is made based on the use of disturbance observers. First, a known control structure is investigated in the context of acceleration control. Following this, a case study is made to show a different application of bilateral control, namely grasping force control. Performance improvement in bilateral control is also studied and correspondingly, a novel functional observer is proposed for better estimation of velocity, acceleration and disturbance. In the second half of the thesis, bilateral control with time delay is realized. Design is made via separating the position and force into two different loops. For position control under time delay, a previously proposed control scheme is used in which use of communication disturbance observer with convergence terms was discussed. Observation made about the divergence from the master reference under contact motion is analyzed and a model following control structure is proposed to eliminate the remaining disturbance from the slave plant. For force control under time delay, first the response of a local controller is analyzed. In order to improve the system transparency, a new method is proposed in which environment stiffness was used for force control loop rather than the delayed slave force. In this structure, estimation of environment stiffness was made via an indirect adaptive control scheme. The analyzed structures were also tested experimentally under a master slave system consisting of 1 DOF linear motors. Experiments show the validity of the contributions made for bilateral control with and without time delay

Passive Control Architectures for Collaborative Virtual Haptic Interaction and Bilateral Teleoperation over Unreliable Packet-Switched Digital Network

This PhD dissertation consists of two major parts: collaborative haptic interaction (CHI) and bilateral teleoperation over the Internet. For the CHI, we propose a novel hybrid peer-to-peer (P2P) architecture including the shared virtual environment (SVE) simulation, coupling between the haptic device and VE, and P2P synchronization control among all VE copies. This framework guarantees the interaction stability for all users with general unreliable packet-switched communication network which is the most challenging problem for CHI control framework design. This is achieved by enforcing our novel \emph{passivity condition} which fully considers time-varying non-uniform communication delays, random packet loss/swapping/duplication for each communication channel. The topology optimization method based on graph algebraic connectivity is also developed to achieve optimal performance under the communication bandwidth limitation. For validation, we implement a four-user collaborative haptic system with simulated unreliable packet-switched network connections. Both the hybrid P2P architecture design and the performance improvement due to the topology optimization are verified. In the second part, two novel hybrid passive bilateral teleoperation control architectures are proposed to address the challenging stability and performance issues caused by the general Internet communication unreliability (e.g. varying time delay, packet loss, data duplication, etc.). The first method--Direct PD Coupling (DPDC)--is an extension of traditional PD control to the hybrid teleoperation system. With the assumption that the Internet communication unreliability is upper bounded, the passive gain setting condition is derived and guarantees the interaction stability for the teleoperation system which interacts with unknown/unmodeled passive human and environment. However, the performance of DPDC degrades drastically when communication unreliability is severe because its feasible gain region is limited by the device viscous damping. The second method--Virtual Proxy Based PD Coupling (VPDC)--is proposed to improve the performance while providing the same interaction stability. Experimental and quantitative comparisons between DPDC and VPDC are conducted, and both interaction stability and performance difference are validated

Hydraulisen puomin voimatakaisinkytketty etäohjaus

Teleoperation has been under study from the mid 1940s, when the first mechanical master-slave manipulators were built to allow safe handling of nuclear material within a hot cell. Since then, need to operate within dangerous, out of reach, uncomfortable, or hazardous environments has then motivated researchers to study teleoperation further. In this thesis, teleoperation of a hydraulic manipulator with electrically driven master manipulator was studied. The workspace of the hydraulic slave manipulator is 5 m in height and it can reach 3 m. The master manipulator has a workspace approximating full arm movement pivoting at the shoulder. Further, the slave manipulator is capable of lifting over 1000 kg, while the master manipulator can lift only 2 kg. Objective of this thesis is to implement virtual decomposition control (VDC) type controller to the master manipulator and create communication channel for the two manipulators. The VDC approach is a subsystem model based feedforward controller. Similar controller for the slave manipulator has been implemented previously. Performance of the developed teleoperation system will be evaluated with experimental implementation measuring the free space motion tracking in two degrees of freedom motion. Results from the experimental implementation indicate accurate motion tracking between the two manipulators. Experimental results indicate less than 15 mm position error between the two manipulators, which considering the size of the HIAB can be considered promising

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

Performance and stability of telemanipulators using bilateral impedance control

A new method of control for telemanipulators called bilateral impedance control is investigated. This new method differs from previous approaches in that interaction forces are used as the communication signals between the master and slave robots. The new control architecture has several advantages: (1) It allows the master robot and the slave robot to be stabilized independently without becoming involved in the overall system dynamics; (2) It permits the system designers to arbitrarily specify desired performance characteristics such as the force and position ratios between the master and slave; (3) The impedance at both ends of the telerobotic system can be modulated to suit the requirements of the task. The main goals of the research are to characterize the performance and stability of the new control architecture. The dynamics of the telerobotic system are described by a bond graph model that illustrates how energy is transformed, stored, and dissipated. Performance can be completely described by a set of three independent parameters. These parameters are fundamentally related to the structure of the H matrix that regulates the communication of force signals within the system. Stability is analyzed with two mathematical techniques: the Small Gain Theorem and the Multivariable Nyquist Criterion. The theoretical predictions for performance and stability are experimentally verified by implementing the new control architecture on a multidegree of freedom telemanipulator

Architectural study of the design and operation of advanced force feedback manual controllers

A teleoperator system consists of a manual controller, control hardware/software, and a remote manipulator. It was employed in either hazardous or unstructured, and/or remote environments. In teleoperation, the main-in-the-loop is the central concept that brings human intelligence to the teleoperator system. When teleoperation involves contact with an uncertain environment, providing the feeling of telepresence to the human operator is one of desired characteristics of the teleoperator system. Unfortunately, most available manual controllers in bilateral or force-reflecting teleoperator systems can be characterized by their bulky size, high costs, or lack of smoothness and transparency, and elementary architectures. To investigate other alternatives, a force-reflecting, 3 degree of freedom (dof) spherical manual controller is designed, analyzed, and implemented as a test bed demonstration in this research effort. To achieve an improved level of design to meet criteria such as compactness, portability, and a somewhat enhanced force-reflecting capability, the demonstration manual controller employs high gear-ratio reducers. To reduce the effects of the inertia and friction on the system, various force control strategies are applied and their performance investigated. The spherical manual controller uses a parallel geometry to minimize inertial and gravitational effects on its primary task of transparent information transfer. As an alternative to the spherical 3-dof manual controller, a new conceptual (or parallel) spherical 3-dof module is introduced with a full kinematic analysis. Also, the resulting kinematic properties are compared to those of other typical spherical 3-dof systems. The conceptual design of a parallel 6-dof manual controller and its kinematic analysis is presented. This 6-dof manual controller is similar to the Stewart Platform with the actuators located on the base to minimize the dynamic effects. Finally, a combination of the new 3-dof and 6-dof concepts is presented as a feasible test-bed for enhanced performance in a 9-dof system