Robots In Spine Biomechanics Wafa Tawackoli, Michael A.K. Liebschner Department of Bioengineering Rice University
Mar 26, 2015
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 ~60o)
• 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
ArmWrist
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