Robots In Spine Biomechanics

loutclankedAI and Robotics

Nov 13, 2013 (3 years and 8 months ago)

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Robots In Spine Biomechanics

Wafa Tawackoli, Michael A.K. Liebschner

Department of Bioengineering

Rice University

Motivation


Everyday activities


Trauma (i.e. Car accident, Sports)


Occupational (
$54 billion/year)



Relatively low impact office duties


High impact manual labor


Osteoporosis
(~$13 billion/year)

Approximately 700,000 vertebral
fractures occur each year in USA

In vitro

study of human spine for various
complex physiological loading.

Prediction of stress fracture risk

Anatomy



Cortical Shell (rim)

Trabecular bone

Vertebra

Posterior Elements

Cramer, 1995


Intervertebral

Disc

Annulus fibrosus

Nucleus pulposus,

Facet Joint

COR

Primary Goals

To understand the biomechanical behavior of spinal
segments under complex physiological loading


3D motion path


Simulation of
in vivo

complex
loading


Investigate stress fracture risk
base on physiological loading

A 3D coordinate system




Total of 6 load components may
be applied


Three forces


Three moments


Each load component may
produce 6 displacement
components


Three translations


Three rotations



36 load displacement curves can
be generated

+ Z Rotation

+ X Rotation

+ Y Rotation

+ X Direction

+ Z Direction

+ Y Direction

Complications


Mechanical Properties are difficult to
ascertain.


Spine movies in a complex 3
-
Dimensional
pattern.


However, it is important to apply such
complex motion during
in vitro

studies.

Biomechanical Methods

1.
In vivo experiments
(including imaging
studies, i.e. stereoradiography)
(Tibrewan, Pearcy)

2.
Mechanical Testing
(Panjabi, Hansson, Adams)

3.
Computational Modeling
(finite element
analysis)
(Uppala, Williams)

Biomechanical Methods (cont’d)


Mechanical Testing Devices


Pulley system
(
Crawford, Panjabi, Patwardhan
)


Uniaxial system
(Adams, Panjabi, Brickmann)



(Servo
-
Hydraulic or Pneumatic)


Mechanical Testing Methods


Uniaxial compression/tension


Shear


Bending
(Flexion, Extension, Lateral, Torsion)


Compressive axial preload

(Follower Load)

Biomechanical Methods (cont’d)

Spine Testing Machine:


Pulley system


Linear servo actuator (Parker
-
EBT 50)


6 DOF Transducer (ATI
-
Omega 160)


Bi
-
axial tilt sensor (range of ~60
o
)


Optical tracking system


Compressive axial preload capability
(up to 2250 N)

Sagittal View

ATI
-
160

Dead Weights

Extension

Flexion

Force

Force

U
-
Shape Bracket

Cable

guide

Side View

Top View

Biomechanical Methods (cont’d)

Limitations

Measurement of spinal rigidity in single plane
is very complex



Unconstrained Motion
-

6 Degrees of Freedom (DOF)


2 DOF applied force + moment


Lack of knowledge of disc degeneration (tears or
lesions)

Our Approach

Measurement of spinal rigidity under complex loading
(
Fatigue, Creep, Stress Relaxation)


Decrease DOF of unconstrained motion


Increase DOF of applied forces and moments


Apply helical axis of motion (path of minimum
resistance)


Load and displacement boundary conditions.

Concept of KUKA Robotic Arm


6 Degree of Freedom


PC computer


Windows based program (GUI
software)


Manual and automatic control


Simple modular system

Base frame

Rotating column

Link arm

Arm

Wrist

Coordinate Systems

Coordinate systems (can be defined
by the operator):



Sensor & Tool coordinate systems



Base coordinate system



Virtual coordinate system

Sensing and Control Process (1)

Hybrid Control = { load control & displacement control }

NZ

EZ

Load

Displacement

Sensing and Control Process (2)

Forces and torques measured by the
ATI transducer can be re
-
calculated
to a virtual coordinate system in
order to sense the real effecting
forces and torques between spinal
segment and the transducer.

The optical tracking system
allows for comparison in
movement between each
vertebra.

Motion Envelope

Top View of Motion Envelope

Ω

φ

Boundary condition (i.e. Bending moment of 5 N.m.)


Foundation Points

(Manually determined)

Reference (Home)
Position

Conclusion


Human spine is a complex system
therefore complex
motion behavior is expected


Hybrid control for biomechanical testing is
recommended


6DOF robotic testing system can be applied to the
delineation of
in vitro

spine kinetics

Acknowledgment


Computational and Experimental Biomechanics Lab


KUKA USA Robotics


KUKA Development Labs


ATI Industrial Automation


Joe Gesenhues

(Ryon Engineering Lab, Rice University)


Thank You

Robots in
Biomechanics

Research