Online System for Dynamic Multi-contact Motion with Impact Force Based on Contact Wrench Estimation and Current-Based Torque Control

Abstract

Humanoid robots are expected to play a big role at distress sites and disaster sites. There is a variety of multi-contact locomotion forms other than bipedal walking such as crawling through tightly, getting on the rubble by using its knees and elbows, or jumping in and rolling over the obstacles. If such multi-contact locomotion forms can be achieved, robots can reach environments that are currently unreachable, and be able to conduct tasks required at the environments. To achieve this, it is required for robots to bring various parts of its body into contact with the environment like a human. However, it is difficult for parts without 6-axis force sensors to achieve the target force while adapting to the environment against impact force. It is also difficult to measure contact wrenches without 6-axis force sensors. In this paper, by allowing the error of the contact state, we propose online system for realizing dynamic motion which impact force occurs on the parts of the whole body by contact to the environment. In the proposed system, we applied the current-based torque control for joints to make the whole body parts of the robot adapt to the environment, and we modified motion in real time to stabilize zmp by estimating contact wrenches at the contact positions where force sensors are not mounted. In addition, at the motion planning, we generated more feasible motions for a robot applying torque control by using evolutionary computation which advances the search with the behavior of torque control. We demonstrate that the proposed system is effective by showing experimental results of sitting posture locomotion using a JAXON robot in which impact force occur on the back of the thighs which have no force sensors.