Actions for Dynamic control of fracture experiments with complex specimens : design and analysis of tight controllers

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Dynamic control of fracture experiments with complex specimens : design and analysis of tight controllers

Author
Corynen, G. C.
Published
United States : [publisher not identified], 1978.
[Oak Ridge, Tennessee] : [U.S. Atomic Energy Commission], 1978.
Physical Description
microfiche : negative ; 11 x 15 cm

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Summary
Using control theory concepts that relate to the design of a closed-loop system, a specific control system problem dealing with controlling crack propagation in solid specimens is analyzed. In the process of analyzing this problem, it is shown how general control theory concepts work to solve a specific problem. This is done in a tutorial manner to aid experimentalists who may not be familiar with the control theory concepts relevant to their work. Starting with a preliminary design using available equipment, all parts and their relationship to the whole are analyzed. Studies on improving the weakest subsystem, the servovalve driver, on reducing the total error in the system, and on obtaining a stiff system (insensitive to specimen dynamics) are described. An important feature in the control strategy was a particular mix of force feedback and feedforward load-cancellation control, which not only provided a highly responsive and flexible system, but was essential in obtaining a stiff system. With linear and nonlinear stability criteria, it is shown that the linear version of the system has comfortable phase and gain margins and that the complete nonlinear system exhibits a stable and acceptable limit cycle. In addition to expressions for system stiffness that are valid when the specimen dynamics are unknown, an expression is developed that explicitly accounts for the influence of load compliance on overall system compliance. At this point, the system, although not yet in its final stage, is extremely stiff and strongly resistant to any loading effects. It has zero steady-state effort to step and ramp inputs, and servovalve saturation is the principal contributor to dynamic errors. Areas that need further study are outlined such as specimen behavior sensing, experimental validation of the design, and computation and simulation of the model.
Report Numbers
UCRL-52387
Other Subject(s)
Collection
U.S. Atomic Energy Commission depository collection.
Note
DOE contract number: W-7405-ENG-48
OSTI Identifier 5147822
Research organization: California Univ., Livermore (USA). Lawrence Livermore Lab.
View MARC record | catkey: 47038007