Abstract: Impact force between leg and terrain will have influence on the vertical stability of legged robots. Although passive compliance can decrease the impact force, it will bring side effects such as body vibration. To deal with it, a force feedback based active compliance controller is proposed, and its influence on the vertical stability is analyzed. Meanwhile, due to mechanical clearance, gait pattern, and terrain parameters, foot slippage may occur and then causes stability issues. Swing leg retraction is then introduced and analyzed to improve the horizontal stability of legged robots. Simulations and experiments show the effectiveness of the proposed methods and the enhancement of vertical and horizontal stability.

Key words: active compliance, stability, swing leg retraction, legged robots