Feasibility, planning and control of ground-wall transition for a suctorial hexapod robot

One of the key factors that affect the efficiency and scope of work of wall-climbing robots is how the climbing robot can achieve autonomous transition between adjacent vertical planes. This paper studies the problem of ground-wall transition of a self-developed suctorial wall-climbing hexapod robot (WelCH). In view of the feasibility of the robot performing transition, this paper makes a detailed analysis of the number and property of degrees of freedom (DOFs) of the body and the foot based on reciprocal screw theory, and the results show that the robot can achieve transitional motion only when its home configuration is axisymmetric rather than radially symmetric. For realizing the robot’s ground-wall transition, based on a Sinusoid-Sigmoid-Shaped (SS-Shaped) interpolation function, the motion strategies of foot transferring and body pitching are firstly designed in detail. This interpolation method can effectively avoid the wear of the suction cups by relying on fewer essential path points. Then, the saturation-truncated method and mean filtering method are used to deal with joint constraints and abrupt changes in angular velocities. Finally, a kinematic-based adaptive sliding mode control (ASMC) is adapted to track the planned smooth trajectory, which can effectively resist bounded external disturbances. The successful transitions from the horizontal ground to the vertical wall for the robot WelCH in simulation and filed experiment demonstrate the effectiveness of the proposed strategy.