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Session 1520

Use of Excel and MATLAB to Design General Linkage Systems for Orthopedic Devices

Bob Fithen, Debra Conry, Jason Leavell

Arkansas Tech / Jaeco Orthopedic / Arkansas Tech Graduate

Abstract

This paper describes a generalized method for calculating the static and dynamic behavior of orthopedic systems. The orthopedic system under consideration is a flexor hinge hand splint, an assistive device for individuals who have limited use of their hands due to spinal cord injury. Typically, these systems take force from wrist movement and translate this force to the fingertips for gripping. However, for those individuals who cannot supply enough force from the wrist, a small motor-based device can be added. In designing such a device, concerns arose over the force applied in the linkages and joints of the system. It became necessary to analyze how the forces on the linkage system varied throughout its range of motion. To accomplish this analysis, a MATLAB code1 was written and was later translated into Excel (using Visual Basic Macros).

The MATLAB code borrowed numerical techniques from a variety of sources. The numerical techniques used include root finding methods, Boolean or connectivity matrices, and cross products for use in moment balance equations. A general outline of the overall approach is as follows. Each pin joint is labeled numerically and a 3-D vector to each pin is constructed. Each link in the overall linkage system is numbered as well. A connectivity matrix is constructed describing which pin joints are members of which link. This numerical configuration is exactly that which exists within the finite element method. When the orthopedic device begins its movement the connectivity matrix never changes. However, the position of each pin joint will change relative to other points on the linkage. During the movement of the system rigid links must remain rigid. Rigid links yield constraint equations in that all pins on that link remain the same distance from each other. For well-constructed linkage systems, specification of one link’s motion will in turn describe the motion of all links on the system. Throughout the range of motion, the force in each link and pin joint is calculated based on the applied torque of a motor system.

1. Introduction

In the course of seeking an engineering degree all students at Arkansas Tech University must complete a senior design course2. The final product of this course is usually a Proceedings of the 2001 American Society for Engineering Education Annual Conference & Exposition Copyright © 2001, American Society for Engineering Education

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Fithen, R. (2001, June), Use Of Excel And Matlab To Design General Linkage Systems For Orthopedic Devices Paper presented at 2001 Annual Conference, Albuquerque, New Mexico. 10.18260/1-2--9947