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Design of Controling Algorithm for Optimization of Trunk Trajectory during 3D Dynamic Activities while Considering Stability Requirements

Khorsand Vakilzadeh, Majid | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40908 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Parnianpour, Mohamad; Asghari, Mohsen
  7. Abstract:
  8. Low back pain is a common medical problem around the world afflicting 80% of the population some time in their life. Low back injury can result from a loss of torso stability. This investigation seeks to apply existing methods to new applications and to develop new methods to assess spinal stability during its dynamical activities. In this study, firstly, optimization method is utilized as an appropriate explanation of role of nervous system in controlling of spine movements. Spine which is a complex structure of vertebrae and cartilage has been modeled by a 3D inverted pendulum with a ball and socket joint at L5/S1 incorporated with 18 muscle fascicles. Planning of point-to-point spine motion is performed by optimization method in two separate steps to solve kinematics and kinetic redundancies available in spine structure. In the first step, kinematics redundancy is solved by parameterized expression of each degrees of freedom based on a complete set of basis functions augmented by a time series. In the second step, coactivation of muscles is predicted by utilizing static optimization along with stability constraint. In view point of equilibrium point hypothesis, stability of spine during its motion can be seen as that of selecting muscle parameters to shape a particular potential energy function suitable for a 3D motion of spine. Utilizing of Lyapunov sense introduces spine velocity toward an equilibrium point as a helpful item for stabilizing it in a close vicinity of equilibrium point. In this study, spinal stability has been investigated by utilizing both viewpoints. Computational motor control shows optimal control could provide a strong framework for designing flexible motions with a combination of mentioned steps rather that optimization method. Hence, direct collocation method is used to convert an optimal control problem to a common optimization problem to be accompanied with stability constraint. Finally, spindles provide necessary feedback to correct spine trajectory during its point-to-point movement.

  9. Keywords:
  10. Spine Stability ; Optimal Control ; Direct Collocation Method ; Control Algorithm

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