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

Abstract

The robustness of biped walking in unknown and uneven terrains is still a major challenge in research. Traversing such environments is usually solved through vision-based reasoning on footholds and feedback loops—such as ground force control. Uncertain terrains are still traversed slowly to keep inaccuracies in the perceived environment model low. In this article, we present a ground force-control scheme that allows for fast traversal of uneven terrain—including unplanned partial footholds—without using vision-based data. The approach is composed of an early-contact method, direct force control with an adaptive contact model, and a strategy to adapt the center of mass height based on contact force data. The proposed method enables the humanoid robot Lola to walk over a complex uneven terrain with 6 cm variation in ground height at a walking speed of 0.5 m/s. We consider our work a general improvement on the robustness to terrain uncertainties caused by inaccurate or even lacking information on the environment.

Quintic Spline Collocation for Real-Time Biped Walking-Pattern Generation with variable Torso Height

“…An overview of the implemented hybrid position/force control is given in [26]. For this paper, we use the version specified in [27] where support for partial contacts is disabled. The inverse kinematics in SIK is based on Automatic Supervisory Control [28] to avoid collisions and minimize various penalties like vertical angular momentum.…”

“…However, this modification is not necessary and yields only slight improvements. Lastly, we point out that the ZMP trajectory is not exclusively used for planning the CoM motion, but also serves as reference input to the SIK module, for details see [27].…”

Analysis of Sensor-Based Real-Time Balancing of Humanoid Robots on Inclined Surfaces

“…Robot-walking control on a specific surface requires accurate detection of the surface-profile information [11][12][13][14][15][16][17][18]. Most of the development in this field extensively utilizes specific measured terrain information to stabilize the walking pattern [14][15].…”

“…Typically, the environment information is collected by cameras or similar vision-based sensors [19][20]. Therefore, the case of a "blind" humanoid robot, without any camera to sense the environment, can be a worst-case scenario for robot-stability control [16][17][18]. In such a case, the surface interaction with force/torque sensors, integrated under the robot feet [16], becomes an important information source for assuring robustness and stability of the robot.…”

“…In summary, the balancing of the light humanoid robots, cannot be efficiently realized using such previously proposed dynamic walking-pattern control. Further, the balancing of light-weight robots on an inclined surface is more difficult than that of a heavy-weight robot [15][16][17][18]. Under observation of the scalability rules [40], very few investigations on balancing light-weight humanoid robots on an inclined surface have been reported [41][42].…”