An automated neck flexibility tester.

We investigate automation and control options for the neck flexibility tester (NFT) (P. McClure et al., 1998), a device originally used to measure the flexibility of the human cervical spine. The motivation is to lay the foundations for design and implementation of investigative devices that would allow studies of mechanical properties of the spine under repetitive dynamic loading. We derive the equations of motion for an automated NFT (ANFT) using a Lagrangian formulation. These equations, which represent a simplified first-order model of the dynamics, are used to simulate the ANFT using the software package Simulink. Two control schemes are examined: proportional plus integral plus derivative (PID) control and dynamic inversion. Both are simulated for setpoint and tracking control. It appears that PID control is preferred due to its simplicity of design and relative insensitivity to the dynamic model of the ANFT.