444 research outputs found
Network Representation and Passivity of Delayed Teleoperation Systems
The paper proposes a general network based
analysis and design guidelines for teleoperation systems. The
electrical domain is appealing because it enjoys proficient analysis
and design tools and allows a one step higher abstraction
element, the network. Thus, in order to analyze the system by
means of network elements the mechanical system must be first
modeled as an electric circuit. Only then power ports become
apparent and networks can be defined. This kind of analysis
has been previously performed in systems with well defined
causalities, specially in the communication channel. Indeed,
a communication channel exchanging flow-like and effort-like
signals, as for instance velocity and computed force, has a
well defined causality and can thus be directly mapped as a
two-port electrical network. However, this is only one of the
many possible system architectures. This paper investigates how
other architectures, including those with ambiguous causalities,
can be modeled by means of networks, even in the lack of
flow or effort being transmitted, and how they can be made
passive for any communication channel characteristic (delay,
package-loss and jitter). The methods are exposed in the form
of design guidelines sustained with an example and validated
with experimental results
Delay compensation for nonlinear teleoperators using predictor observers
This paper presents a delay compensation technique for nonlinear teleoperators by developing a predictor type sliding mode observer (SMO) that estimates future states of the slave operator. Predicted states are then used in control formulation. In the proposed scheme, disturbance observers (DOB) are also
utilized to linearize nonlinear dynamics of the master and slave operators. It is shown that utilization of disturbance observers and predictor observer allow simple PD controllers to be used to provide stable position tracking for bilateral teleoperation. Proposed approach is verified with simulations where it is compared with two state-of-the-art methods. Successful experimental results with a bilateral teleoperation system consisting of a pair of pantograph robots also validates the proposed method
Passivity-Based Control of Human-Robotic Networks with Inter-Robot Communication Delays and Experimental Verification
In this paper, we present experimental studies on a cooperative control
system for human-robotic networks with inter-robot communication delays. We
first design a cooperative controller to be implemented on each robot so that
their motion are synchronized to a reference motion desired by a human
operator, and then point out that each robot motion ensures passivity.
Inter-robot communication channels are then designed via so-called scattering
transformation which is a technique to passify the delayed channel. The
resulting robotic network is then connected with human operator based on
passivity theory. In order to demonstrate the present control architecture, we
build an experimental testbed consisting of multiple robots and a tablet. In
particular, we analyze the effects of the communication delays on the human
operator's behavior
An Analysis of Sampling Effect on the Absolute Stability of Discrete-time Bilateral Teleoperation Systems
Absolute stability of discrete-time teleoperation systems can be jeopardized
by choosing inappropriate sampling time architecture. A modified structure is
presented for the bilateral teleoperation system including continuous-time
slave robot, master robot, human operator, and the environment with
sampled-data PD-like + dissipation controllers which make the system absolute
stable in the presence of the time delay and sampling rates in the
communication network. The output position and force signals are quantized with
uniform sampling periods. Input-delay approach is used in this paper to convert
the sampled-data system to a continuous-time counterpart. The main contribution
of this paper is calculating a lower bound on the maximum sampling period as a
stability condition. Also, the presented method imposes upper bounds on the
damping of robots and notifies the sampling time importance on the transparency
and stability of the system. Both simulation and experimental results are
performed to show the validity of the proposed conditions and verify the
effectiveness of the sampling scheme
Control of Networked Robotic Systems
With the infrastructure of ubiquitous networks around the world, the study of robotic systems over communication networks has attracted widespread attention. This area is denominated as networked robotic systems. By exploiting the fruitful technological developments in networking and computing, networked robotic systems are endowed with potential and capabilities for several applications. Robots within a network are capable of connecting with control stations, human operators, sensors, and other robots via digital communication over possibly noisy channels/media. The issues of time delays in communication and data losses have emerged as a pivotal issue that have stymied practical deployment. The aim of this dissertation is to develop control algorithms and architectures for networked robotic systems that guarantee stability with improved overall performance in the presence of time delays in communication.
The first topic addressed in this dissertation is controlled synchronization that is utilized for networked robotic systems to achieve collective behaviors. Exploiting passivity property of individual robotic systems, the proposed control schemes and interconnections are shown to ensure stability and convergence of synchronizing errors. The robustness of the control algorithms to constant and time-varying communication delays is also studied. In addition to time delays, the number of communication links, which prevents scalability of networked robotic systems, is another challenging issue. Thus, a synchronizing control with practically feasible constraints of network topology is developed.
The problem of networked robotic systems interacting with human operators is then studied subsequently. This research investigates a teleoperation system with heterogeneous robots under asymmetric and unknown communication delays. Sub-task controllers are proposed for redundant slave robot to autonomously achieve additional tasks, such as singularity avoidance, joint angle limits, and collision avoidance. The developed control algorithms can enhance the efficiency of teleoperation systems, thereby ameliorating the performance degradation due to cognitive limitations of human operator and incomplete information about the environment.
Compared to traditional robotic systems, control of robotic manipulators over networks has significant advantages; for example, increased flexibility and ease of maintenance. With the utilization of scattering variables, this research demonstrates that transmitting scattering variables over delayed communications can stabilize an otherwise unstable system. An architecture utilizing delayed position feedback in conjunction with scattering variables is developed for the case of time-varying communication delays. The proposed control architecture improves tracking performance and stabilizes robotic manipulators with input-output communication delays. The aforementioned control algorithms and architectures for networked robotic systems are validated via numerical examples and experiments
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