The Analysis model of Torsion Behavior for Octopus-inspired Robotic Arm

Octopus can achieve a variety of dexterous movements at any point along its arm, such as elongating, shorting, bending, twisting, or changing the stiffness, which have been considered as an interesting model of inspiration in robotics. Among the complex behaviors, the torsion behavior is important because it provide extra degree of freedom of movement, like twisting. This paper proposed a detailed dynamic model that describes the torsion behavior of octopus arm, based on torsional vibration theory. The initial conditions and boundary conditions that explained the main features of the torsion behaviors of octopus arm are acknowledged. The mode shapes, which describe the torsional vibration frequency and type, were solved as the sum of the time and the distance from the fixed end to where the deformation happened. By comparing the mode shapes results solved by the method proposed in this paper and by FEA Soft ANSYS, the effectiveness of this method has been verified. Further torsional stresses and torsion angles of deformation and vibrations on rod can be expressed as the functions of the mode shapes and the external torque exerted on one end of the rod. This method can be applied to calculate the kinematics results of the torsion behaviors and the appropriate activations related for continuum robotic manipulators inspired by octopus arm.