Stair Climbing Stabilization of the HRP-4 Humanoid Robot using Whole-body Admittance Control

Abstract

We consider dynamic stair climbing with the HRP-4 humanoid robot as part of an Airbus manufacturing use-case demonstrator. We share experimental knowledge gathered so as to achieve this task, which HRP-4 had never been challenged to before. In particular, we extend walking stabilization based on linear inverted pendulum tracking [1] by quadratic programming-based wrench distribution and a whole-body admittance controller that applies both end-effector and CoM strategies. While existing stabilizers tend to use either one or the other, our experience suggests that the combination of these two approaches improves tracking performance. We demonstrate this solution in an on-site experiment where HRP-4 climbs an industrial staircase with 18.5 cm high steps, and release our walking controller as open source software. 1 Corresponding author: stephane.caron@lirmm.fr 1 https://github.com/stephane-caron/lipm walking controller/ 2 Performance and safety certification requirements are yet to be defined 3 Controllers reported by Honda include the model ZMP control strategy [2], [3] where saturation of ZMP constraints triggers recovery CoM accelerations and a corresponding update of the walking pattern [4], [5]. This integration of a switching control law with replanning behavior makes these controllers more advanced than linear feedback controllers.

Capturability-Based Pattern Generation for Walking With Variable Height

“…To test our method in dynamic simulations and compare it to the existing, we extend the C++ LIP-based stair climbing controller from [39]. This controller consists of two main components: a LIP-based pattern generator by model predictive control (i.e.…”

“…Kajita et al applied it to 10-cm high steps in [40]) but can become problematic for higher steps. From experiments on the HRP-4 robot, [39] rather chose to decompose the constraint in two horizontal plane segments, introducing the vertical height variation at toe liftoff. These segments could be further decomposed for better adaption to terrain, but as of today there is no known algorithm for this.…”

Humanoid Robots in Aircraft Manufacturing: The Airbus Use Cases

“…The combination of these tasks realizes an overall whole-body admittance control scheme. The resulting stabilizer proved effective for both walking and climbing the factory staircase, whose step height is 18.5cm; see [26] for further details.…”

“…HRP-4 was able to lift itself up on its left leg but not on its right one due to a mechanical limitation issue. We consequently selected footsteps to use only the left leg for lifting phases [26].…”

Sensitivity of Legged Balance Control to Uncertainties and Sampling Period

“…Biped and quadruped robots are beginning now to master the skill of walking dynamically in most standard situations [2], [4], [9]. This suggests that more widespread commercial use of such robots will soon be possible.…”