2008 international ansys conference · cinematically and structurally analyzed using ansys...

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2008 International ANSYS Conference

Development of a machine to test knee joint prosthesis

Adrián López Cervantes, Raúl Lesso Arroyo, Jaime Gallardo Alvarado, Daniel Aguilera Camacho.Mechanical Engineering DepartmentInstitute Technological of Celaya


Abstract and introduction

AbstractThe knee joint is one of the most important joints in the human body. Inthis paper is presented the development of a machine which simulatesthe principal movements of the human leg through a mechanismcinematically and structurally analyzed using ANSYS Workbench. Themachine has four degrees of freedom and is designed to support 155 lband analyzed the wear of a knee joint prosthesis.

IntroductionThe knee joint is one of the human body parts which is worn due to thedifferent activities in our life. When this joint is damaged (Phenomenonthe Osteoarthritis), it must be replaced for a prosthesis which has anaverage life of 50 months. For this reason, a mechanism that simulatesa gait cycle in movement and force has been developed to test thisprosthesis and understand the sort of damage that has place in theprosthesis.


Knee joint (Phenomenon the Osteoarthritis )


Hypothesis and objectives

Hypothesis:A four degrees of freedom machine is enough to simulatethe principal movements of the human knee joint, wear aknee joint prosthesis and obtain statistical data about thekind of damage in this important component.

Objectives:• Simulate the gait cycle.• Structural and dynamic analyses using ANSYS

Workbench.• Desing a load frame.• Metrological validation of the machine.


Background

• Knee joint prosthesis– A knee joint replacement is a component which

substitutes a knee joint damaged

Inserto

Digitized model for simulation


Gait cycle

Each gait cycle is divided into two periods, stance and swing. Stanceis the time when the foot is in contact with the ground, constituting 62percent of the gait cycle. Swing denotes the time when the foot is inthe air, constituting the remaining 38 percent of the gait cycle.

Heel strike Toe-off


Gait cycle

Principal movements of the knee

Varum and valgus angle

RotationFlexion-extension


Description of design

Conceptual designThe principal design of the machine is the result of aselection of several ideas. The selected idea has twoparts, one that simulates the movement of the foot andone that simulates the tibia, prosthesis and femur. Thefirst part is the one that was simulated due to it is the partwhich moves all the load.

This simulated part is a mechanism which is made ofaluminum links and revolute joints with steel bolts,nylamid block and joint using a CAD software. The lengthof the links was designed with a dynamic simulationssoftware to give the displacements of the foot in the gaitcycle.


Description of design

Links

Revolute joints

Block

BoltRevolute joints


Mechanism kinematical behavior

The mechanism was analyzed with Trigonometry to know the positionof the block and the angles of the links and Screw Algebra to knowthe angular velocities of the links and linear velocity of the block.


ANSYS Workbench Simulation

The mechanism was analyzed in two ways:• Structural analysis to know if the dimensions of the

elements were sized enough to resist the 155 lb load.• Dynamic analysis (rigid and flexible) to know the

displacements, velocities (lineal and angular), forces andtorques to select three servomotors.

Because the mechanism simulates the movement of thefoot, it had to support the reaction force of the knee.Because of the gait cycle has two critical load points, thecontact and the high point, the mechanism was analyzedin this positions.


ANSYS Workbench Simulation

Contact and High point positions

Support links


Structural analysis. Preprocessing

Material properties and behavior. Links: Aluminum, Block:Nylamid M, Bolts: structural Steel, Stiffness behavior: Flexible for all.

Element contact. Body to Body contact: Bonded, Contact surfaces:Frictionless

Mesh. Links: Body Sizing (20mm), Holes: refinement (1), Body tobody contact: Contact Sizing.

Supports. Links: Fixed support, Block: Frictionless support.Loads. The load for each position was the knee reaction force in that

particular time in the gait cycle (686.7 N and 2197.4 N).


Structural analysis. ResultsDeformation 0.48683 mm Deformation 0.48683 mm

Von-Mises Stress 137.01 MPa Von-Mises Stress 237.39 MPa


Rigid Dynamic AnalysisPreprocessing

• Stiffness behavior– Rigid for all elements

• Joints– Link-Link: Body to body revolute, Link-Block: Body to body revolute,

Link supports: Body to ground revolute, Bolts: Body to body fixed, Link-Bolt: Body to body revolute

• Earth gravity: 9806.6 mm/s²• Loads: Joint rotation (90°) on support link


• Relative Angular Velocity (1.1411rad/sec) in symmetric support links.

• Block Velocity (270.16 mm/s)

• Block Relative Displacement (480.96 mm)

Rigid Dynamic AnalysisResults


Flexible Dynamic Analysis Preprocessing

Stiffness behavior Flexible for all elements

Mesh Links: Body sizing (15 mm), Bolts: Body sizing (5 mm), Block:Body sizing (30 mm)

Loads Rotational velocity in the support links, earth gravity and thegait cycle knee joint force


Flexible Dynamic Analysis ResultsTorques in the support links (3291.3, 3301.1 and 17839 N·mm )


Physical mechanism

The mechanism was built and tested to compare thetheorical results with the measure of three strain gagesadded in the critical parts of the mechanism

Load

Strain Gages


Conclusions

• The conceptual design was developed from the commercial models of knee simulators– This design is shown to have better movements, force and easier

construction• The principal design objective was for this mechanism to produce the

gait cycle movement of the foot and transfer this movement and load at the tibia, prosthesis and femur components

• A commercial knee prosthesis was digitized with all its components in CAD to improvise the conceptual design

• Use of Simulation in ANSYS Workbench software was critical to derive the optimum values of the critical design parameters under static and dynamic conditions

References1. Introduction to ANSYS structural and rigid and flexible dynamic analysis. ANSYS Inc.2. A.C. Godesta,b, M. Beaugoninb, E. Haugb, M. Taylora, P.J. Gregsona, (2001), Simulation of a knee

joint replacement during a gait cycle using explicit finite element analysis, Journal of Biomechanics 35(2002) 267–275, Elsevier.

3. William Petty, MD, Gary J. Miller, PhD, Donald L. Bartel, (2003), PhD, About the simulation of thehuman knee joint for walking locomotion.

4. Smith PN, Refshauge KM, Scarvell JM. Development of the concepts of knee kinematics. Arch PhysMed Rehabil 2003; 84:1895-902.

2008 international ansys conference · cinematically and structurally analyzed using ansys...

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