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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. Everyday activities

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Robots In Spine Biomechanics

Wafa Tawackoli, Michael A.K. Liebschner

Department of Bioengineering

Rice University

  • In vitro study of human spine for various complex physiological loading.
  • Prediction of stress fracture risk
  • 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

Annulus fibrosus

Posterior Elements

Nucleus pulposus,

Facet Joint


Cortical Shell (rim)

Trabecular bone



Cramer, 1995

primary goals
To understand the biomechanical behavior of spinal segments under complex physiological loadingPrimary Goals
  • 3D motion path
  • Simulation of in vivo complex loading
  • Investigate stress fracture risk base on physiological loading
a 3d coordinate system
A 3D coordinate system

+ Z Rotation

  • 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

+ X Direction

+ Z Direction

+ X Rotation

+ Y Rotation

+ Y Direction

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

Mechanical Testing (Panjabi, Hansson, Adams)

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

Biomechanical Methods
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


Bending (Flexion, Extension, Lateral, Torsion)

Compressive axial preload (Follower Load)

Biomechanical Methods (cont’d)
biomechanical methods cont d1
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 d2

Top View

Side View



U-Shape Bracket

Biomechanical Methods (cont’d)





Sagittal View


Dead Weights

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.

Our Approach
concept of kuka robotic arm



Link arm

Rotating column

Base frame

Concept of KUKA Robotic Arm
  • 6 Degree of Freedom
  • PC computer
  • Windows based program (GUI software)
  • Manual and automatic control
  • Simple modular system
coordinate systems
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
Sensing and Control Process (1)





Hybrid Control = { load control & displacement control }

sensing and control process 2
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
Motion Envelope


Reference (Home) Position


Foundation Points

(Manually determined)

Top View of Motion Envelope

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

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

Computational and Experimental Biomechanics Lab

KUKA USA Robotics

KUKA Development Labs

ATI Industrial Automation

Joe Gesenhues(Ryon Engineering Lab, Rice University)

thank you
Thank You

Robots in Biomechanics