Abstract
M.Ing. (Mechanical Engineering)
This dissertation presents the solution to the direction control problem of an underactuated snake robot using the amplitude modulation method. The amplitude modulation method allows for the control of the joint relative angles during the serpentine movement to produce friction forces that propel the snake robot to the desired path. In this dissertation, the snake robot equations of motion derived from the Euler-Lagrange method utilizing the joint relative angles as the generalized coordinates to decouple the equations into actuated and unactuated equations. The partial feedback linearization technique transformed the equations of motion into the control affine nonlinear system, where geometric control techniques proved the controllability of the snake robot subjected to the Coulomb friction law represented by an arctangent function.
The solutions to the equations of motion calculated from the Mathematica software for a given control law showed the state space evolution of the snake robot performing the serpentine gait. In the simulation results (without the direction control), the snake robot moved forward after few seconds from starting and its direction changed. The change in direction was due to the approximated Coulomb friction law considered using the arctangent function. This resulted in zero friction forces at the beginning, zero propelling force, and thus the snake robot did not move for some time. However, at this point, the joint angles changed according to the control law employed and the direction of the robot changed. Consequently, the snake robot was unable to track the desired straight path due to the change in direction at the beginning.
Furthermore, the dissertation considered the solution to the direction control problem using the amplitude modulation and the joint offset angle controllers. In the simulation results, both controllers stabilize the snake robot to its desired path. The direction control based on controlling the head angle determined from the line-of-sight guidance law. The guidance law allowed for the derivation of the desired head angle to track a given path. The implementation of the line-of-sight guidance law caused a difference (error) between the actual head angle and the desired head angle at the start of motion, where the snake robot was unable to track the desired path for some time for both direction controllers. For amplitude modulation, this error forced the tail link to...