Control of lumbar spine flexion-extension movement by PD controller and feedback linearization method

The role of motor control in development of low back pain is subject of many researches both in theoretical and experimental fields. In this work flexion-extension movement of lumbar spine have been controlled by three different methods, including feedback linearization (FBL), PD control and their combinations. The model involves 7 links: 1 link for pelvis, 5 links for lumbar vertebrae and 1 link for trunk. Torque actuators have been used on each joint to make them follow desired trajectory. In linear control method, equations of motion have been linearized with respect to upright position and then control signals have been applied in the direction of eigenvectors. Robustness of each method against noises, sensory delay and parameters uncertainty have been investigated. Desired trajectory of each joint has been produced by Central Pattern Generators (CPGs), which was the subject of our previous work. The results show that PD controller in comparison with feedback linearization method is more robust in presence of noise and parameters uncertainty, but FBL controller is better when we have sensory delay. Combination of these methods leads to better control in all three simulations.