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ATI Industrial Automation Robotic End Effectors and

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					Robots In Spine Biomechanics




      Wafa Tawackoli, Michael A.K. Liebschner
           Department of Bioengineering
                 Rice University
                      Motivation
            In vitro study of human spine for various
                  complex physiological loading.
                 Prediction of stress fracture risk



Approximately 700,000 vertebral
fractures occur each year in USA
   – 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)
                               Anatomy
                                   Annulus fibrosus
                                                            Posterior Elements



               Nucleus pulposus,
                                   Facet Joint




                                      COR
                                                                  Cortical Shell (rim)


                                                             Trabecular bone



                   Intervertebral Disc                Vertebra
Cramer, 1995
             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
                     + Z Rotation

                                            Total of 6 load components may
                                             be applied
    + X Direction
                           + Z Direction
                                                Three forces
                                                Three moments
  + X Rotation                              Each load component may
                                             produce 6 displacement
                                             components
+ Y Rotation                                    Three translations
                                                Three rotations
   + Y Direction
                                            36 load displacement curves can
                                             be generated
            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)
Biomechanical Methods (cont’d)
                           Extension        Flexion   Force
     Top View




                        Force



                                                      Sagittal View
      Side View


                Cable
                guide           ATI-160
  U-Shape Bracket

                                   Dead Weights
                  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
           Wrist
Arm

                   Link arm
                              • PC computer

       Rotating column
                              • Windows based program (GUI
       Base frame

                                software)

                              • Manual and automatic control

                              • Simple modular system
                 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)

                            Displacement



    EZ



    NZ

                                            Load




Hybrid Control = { load control & displacement control }
         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
                                    Ω

    Reference (Home)
    Position




                                                     φ




                                               Foundation Points
Top View of Motion Envelope                    (Manually determined)
Boundary condition (i.e. Bending moment of 5 N.m.)
                   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