Planar kinematics analysis of a snake-like robot

This paper presents the kinematics of a planar multibody vehicle which is aimed at the exploration, data collection, non-destructive testing and general autonomous navigation and operations in confined environments such as pipelines. The robot is made of several identical modules hinged by passive revolute joints. Every module is actuated with four active revolute joints and can be regarded as a parallel 1 mechanism on a mobile platform. The proposed kinematics allows to overcome the nonholonomic kinematic constraint which characterizes typical wheeled robots, resulting into an higher number of degrees of freedom and therefore augmented actuation inputs. Singularities in the kinematics of the modules are analytically identified. We present the dimensional synthesis of the length of the arms, obtained as the solution of an optimization problem with respect to a suitable dexterity index. Simulation results illustrate a kinematic control path following inside pipes. Critical scenarios such as 135 elbows and concentric restriction are explored. Path following shows the kinematic capability of deployment of the robot for autonomous operations in pipelines, with feedback implemented by on-board sensors.