Locomotion design of transverse ledge brachiation robot with active wrist joint for lateral posture compensation.

A transverse ledge brachiation robot is designed to move transversely along a ledge on a vertical wall by generating energy from the swinging motion of its lower limbs. This method reduces the force required by the upper limbs to propel the robot forward. However, previously developed robots often encounter a common issue: lateral posture deviation, which is typically caused by slippage when the grippers grasp the ledge. Without compensation, this deviation can increase the risk of falling during continuous brachiation cycles. To address this problem, we propose an active wrist joint mechanism utilizing a feedback control approach as the compensator to effectively correct gripper position deviations. In our robot design, we develop a motion control strategy that coordinates the upper and lower limbs in order to maintain the swing energy that can be transferred to the subsequent cycles. Then we propose a potential energy-based phase switching condition in the motion control strategy in order to simplify the computation process. Simulation results demonstrate that the optimized parameter for compensation effectively maintains the gripper's position relative to the ledge throughout 55 brachiation cycles. Furthermore, experiment validation shows that this posture compensation reduces deviation by one-third compared to results without compensation. This study has demonstrated a 68% improvement in energy consumption efficiency for continuous transverse brachiation compared to the previous generation, as well as a 37% improvement over transverse ricochetal brachiation locomotion.