Telepresence

The control system of the MUST-SIM facility has been carefully designed to provide a flexible, reconfigurable environment for effective telepresence operation. Features are included to allow for safe operation by on-site and off-site researchers and staff, as well as for protection of valuable equipment and test specimens.

The actuators within the six DOF Loading and Boundary Conditions Boxes (LBCB) must be carefully controlled to reproduce the correct displacements and loadings dictated by the result of detailed numerical simulations which include soil-structure interaction.  Since a major feature of the NEES facility will be its flexibility, it is imperative that the testing configurations and loading profiles be rapidly reconfigurable.  As a result, a flexible, open-architecture approach to the control system implementation is desirable.  Simultaneously, there are constraints associated with the system integration that would preclude having every aspect of the control system be open-architecture.  Consequently, the control system will possess a modular hierarchical structure.

This structure possesses distinct layers or levels of control that will be utilized by the NEES facility:  network, link and servo levels.  The network level control system is the primary system associated with telepresence.  It coordinates the networked flow of information.  The link level ensures and coordinates the communication between the computers exchanging information in the networks and the controllers running the actual displacements of the actuators which change the degrees of freedom in a prescribed manner.  The servo level is concerned solely with reproducing a displacement or loading pattern communicated to it by the Link level by use of the hydraulic actuators within the LBCBs.  The reasons for the hierarchical approach are safety and flexibility.  With a hard feedback connection between the actuators and the controller, including safety switches and emergency shutdown algorithms, the possibility of a dangerously unstable testing situation is minimized.  At the same time, having remote access to the tests will be possible, albeit in a manner that is not real-time. These layers will be discussed in further detail below.

Control System

The higher level supervisory control (i.e., network control) of the system will be performed over the internet, thereby giving multiple users remote access to the MUST-SIM facility and providing telepresence. However, since unpredictable and variable latencies, as well as packet losses associated with network communication, will adversely affect direct, real-time, closed loop control of individual servo-actuators over the Internet, an alternative approach that is a much safer and more reliable one is offered. The network level component focuses on the exchange of information over a network, but this information exchange is not in real-time. The displacements and rotations of the boundary conditions are determined by the FEM simulations that are running on clusters of networked computers. Once these boundary conditions have been determined, they are sent via a network system to a remote server for the control system. This server then communicates the desired boundary conditions to the systems performing the actual real-time feedback control through the client computer.

The network layer is also concerned with the collection of data from the client computer through the Server and its remote rendering.  The client/server terminology is obtained from the particular software of choice, WinCon, which is produced by Quanser Consulting of Ontario, Canada.  Data collected from the client can be viewed remotely in a streaming fashion by the server.  In addition, the use of WebLab, another Quanser product, allows for solid model graphical visualization by any computer connected to the same network as the Server.  The visualization software is quite powerful, allowing 3D Java-based animations to be constructed and manipulated based on the incoming data.  Additionally, the data streaming is highly optimized to provide a factor of a four-fold acceleration over standard streaming video.  WinCon and WebLab will allow  NEES users to observer the results of a test both in numeric data  and graphical animation forms thereby providing realistic telepresence. The telepresence is not limited to only observation.  It is possible for NEES users to have teleoperation or telemanipulation.  Commands or controller re-configurations can be sent out via the Internet to change the basic structure of the server algorithms as well as the server/client exchange.  These include selection of monitored variables and the rate of monitoring.