Report - PEER - University of California, Berkeley

controller. Although the system as a whole controls force function, internally theactuator operates in closed-loop displacement control. Hence, there is no need for anadditional force feedback loop to ensure stability. More details on these developmentsare presented elsewhere by Reinhorn et al., 2004.7. DISTRIBUTED REAL-TIME ARCHITECTUREThe real-time hybrid system is implemented using a distributed architecture that usesShared Random Access Memory Network (SCRAMNET TM ), a very low-latencyreplicated shared memory fiber optic network. The architecture of hardware-softwarecontroller (see right side of Figure 3) allows for flexibility in the design of the realtimeoperating system and in the implementation of the components used. There arethree units which form the controller:1. The Compensation Controllerwhich contains the cascade controlloop for force control presentedabove. This controller alsocompensates for time-delays thatare inherent in the physicalsystem.2. The Real-time Simulator whichsimulates the computational substructures.The architecturehas been designed so that thissimulator could be seamlesslyMTS ActuatorController (STS)MTS Hydraulic PowerController (HPC)MTS Shake TableController (469D)SCRAMNET ICONTROL OFLOADING SYSTEMCompensation ControllerxPC TargetOptionalNetwork SimulatorReal-time SimulatorSCRAMNET IIHYBRID CONTROLLERUB-NEES NODEOptionalGeneral PurposeData AcquisitionSystemData AcquisitionFigure 7. Computational infrastructure.replaced by one at a remote location or a Supercomputer, if necessary.3. The Data Acquisition System (DAQ) that is used for feedback from theexperimental substructure as well as for archiving information during the test. .The controller operates in a synchronous-asynchronous manner. The controllerwas developed to allow parallel operations of each of the three units while sharingonly essential information through a “pool” memory provided by the 1µsec updaterate SCRANNET. Each individual component / unit operates at each own time rate,accessing the shared memory when needed, without delaying other units. Thecompensation controller is designed to compensate also for all other latencies incommunications, computing and hydraulic operations. The current implementation atUniversity at Buffalo uses the architecture shown above which allows substituting theSimulation Component with any computational device — such as a supercomputeroperating in a Grid.8. REAL-TIME HYBRID TESTING IMPLEMENTATIONA series of hybrid tests were performed on a two-story structure with the first storybuilt on the shake table and the second story simulated (see Figure 8).266