Modeling tools for conformal orthotic devices

Steven Riddle, Purdue University

Abstract

The purpose of this thesis is to advance the design of conformal orthotic devices through the development of two modeling tools to address knowledge gaps in the field. The field of human orthotics has been continually troubled by identifying successful methods of harnessing devices to the body. Past orthotics have utilized a rigid framework with minimal degrees of freedom (DOFs) driven by hard actuators attached to the body at select anchor points. Many devices design the structure and anchor points such that they reduce the degrees of freedom of a targeted joint, limiting the user's mobility and often causing the structure to slide relative to the body as much as actuate a given joint. There has been a recent shift in the orthotic field toward biologically inspired conformal structures to address the limitations of hard systems. By focusing on conformal devices that move with the body, limited DOFs and mobility restrictions can be addressed while also enabling new possibilities in human augmentation devices. Conformal orthotics have the opportunity to allow more DOFs in a joint while performing the same task as their rigid counterparts. By allowing these additional DOFs, the overall mobility of the user could be increased and more nuanced and particular interactions with the body and the environment may be possible. More channels of actuation could lead to finer joint control and enable more complicated tasks to be performed. The task of designing conformal orthotic structures can be broken into four parts: developing 3D skin strain models; identifying minimum strain contours for orthotic structures; modeling the effect of these structures on a joint's motion; and modeling how the modified joint behaves during a human task, such as locomotion. Much work has been done in each of these design fields; however, there remain several knowledge gaps in the field preventing the realization of conformal orthotics that need to be addressed. Addressing the first gap requires the creation of minimum strain contours on the skin surface using the 3D skin strain field as reference. Addressing the second gap requires modeling how conformal orthotic structures based on minimum skin strain contours affect joint parameters. Addressing the third and final gap requires modeling the effect of modified joint parameters on a given task. There is a need to improve understanding of these knowledge gaps so that conformal orthotics can be appropriately designed and implemented for a given task. To address the first and second conformal orthotic knowledge gaps, this thesis presents a modeling tool for mapping 3D skin strain on the skin surface and analyzing the effect of conformal orthotic structures on joint parameters. Joint parameters are compared to a control and conformal structures are found to have minimal impact on passive joint parameters.

Degree

M.S.M.E.

Advisors

Seipel, Purdue University.

Subject Area

Biomedical engineering|Mechanical engineering|Kinesiology

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