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Loveless, Amy L (2003) DELINEATION OF IN-VITRO SPINAL KINETICS USING A ROBOTICS-BASED TESTING SYSTEM. Master's Thesis, University of Pittsburgh. (Unpublished)

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Delineation of the load-displacement characteristics of osteoligamentous spinal specimens has become fundamental to the investigation of spinal biomechanics. Traditionally, in-vitro kinetic parameters of the spine have been obtained through flexibility tests employing open or closed loop "load control" methods, or stiffness tests employing "displacement control" methods-each control method having attendant advantages and disadvantages. On the other hand, the combination load control and displacement control methods into a new, "hybrid control" method have advantages over load control or displacement control alone. Further, physical evidence such as presence of certain receptors suggests that the human body may employ a type of hybrid control method in the control of spinal movements.In the present study, a robotics-based spine testing system with hybrid control was developed to delineate the in-vitro kinetics of lumbar spine specimens. The testing system was validated experimentally using a physical rigid-body-spring model of a spine specimen, as well as analytically by computer simulations in Matlab. For systematic study, the two components making up a hybrid control algorithm were analyzed separately: the outer "displacement control" loop, and the inner "load control" loop. The outer loop applies a rotation (e.g., flexion/extension) to the specimen, while the inner loop minimizes unwanted coupled forces (e.g., anterior/posterior shear and axial tension/compression).The performance of existing standard hybrid control algorithms was tested in terms of a number of parameters, including peak force, work done to a specimen, and number of iterations. Based on these tests, a number of proposed changes to improve algorithm performance were identified. Updating the user-defined center of rotation (COR) to reflect a specimen's COR was found to improve performance of the displacement control part of the hybrid control algorithm, while using a more completely populated stiffness matrix improved performance of the load control part. The re-combination of the displacement control and load control loops into the fully constituted hybrid control algorithm revealed interesting interactions between these control components that suggest a basis for spinal dysfunction.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Loveless, Amy Lall51@pitt.eduALL51
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairGilbertson, Lars Glarss@pitt.eduLARSS
Committee MemberKang, James D
Committee MemberSmolinski, Patrick J
Committee MemberCham, Rakie
Date: 3 September 2003
Date Type: Completion
Defense Date: 22 July 2003
Approval Date: 3 September 2003
Submission Date: 7 August 2003
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Bioengineering
Degree: MSBeng - Master of Science in Bioengineering
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: rigid body kinematics
Other ID:, etd-08072003-120101
Date Deposited: 10 Nov 2011 19:57
Last Modified: 15 Nov 2016 13:48


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