Modifying the estimated ground height to mitigate error effects on bipedal robot walking

Abstract

Classic biped walking controllers assume a perfectly flat, rigid surface on which the robot walks. While walking over unknown terrain, robots need to sense and estimate the ground location. Errors in this estimation result in an unexpected early or late ground contact of the swing foot. In this paper, we analyze how these errors affect walking stability. Based on simulation results, we propose a strategy that mitigates this effect. We show that if the ground height has an associated uncertainty, an overestimation of its value results in a more stable walk. This overestimation depends on both sensor data and the robot's dynamics. By using a reduced robot model, our strategy could be implemented into the realtime control to make the robot more robust against perception errors and irregular surfaces.

Time-variable, event-based walking control for biped robots

“…As discussed in the previous work, we consider the upper body orientation as an indicator of the robot’s stability. 18 In Figure 9, we plot the upper body orientation for two exemplary height values to compare the different cases. The normal control results in the robot tilting over for all height values over 3.4 cm (see Table 1).…”

“…13,14 Nevertheless, perception errors become larger when performing dynamic walking at higher speeds or even when walking over other kinds of nonrigid, non-flat terrain, such as grass or stones. 18 Some authors presented methods for quick trajectory regeneration 6,7 during dynamic walking that are based on balance compensation without changing the step duration. Different strategies for online modification of ZMP trajectories were proposed for the HRP-2 robot that allowed it to dynamically walk over carpet tiles, though at low walking speeds.…”

“…[12][13][14][15][16][17] In all works cited above, knowledge about the ground location is assumed and ground contact timing is predefined. Therefore, even small ground location errors have a great effect on this kind of control, 18 especially when compared to their human counterparts. 19 By planning the step durations beforehand, different kinds of errors (e.g.…”

Towards the Development of a Navigation System for a Bipedal Robot: Preliminary Analysis of the Literature

“…Most of the works reviewed so far are focused on the detection and avoidance of obstacles in static or dynamic environments, that is, the obstacles can be fixed or can be moved during the navigation of the robot. In addition, the robots are regularly navigated on 1-level flat terrain [42, 44, 45, 47, 51, 54, 56-62, 64, 66, 68-73, 75, 77-90] or multi levels [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67], even in irregular terrain [63]. The distribution of the type of land used in the experimentation of the reviewed papers is shown in Figure 3.…”

A force-control scheme for biped robots to walk over uneven terrain including partial footholds

“…Ground height estimation errors can reach the centimeter range 1,2 and have a significant effect on the performance of the overall system. 6 To compensate for such disturbances and model inaccuracies caused by the planning of the center of mass (CoM) trajectories, fast feedback loops are typically deployed. [7][8][9][10][11][12] For robots with torque-controlled joints, this is usually the position control of the CoM to track a desired reference trajectory based on the estimated robot state.…”