KUbot 1

KUbot Specification

Research for Humanoid Robots

■ Running Pattern Generation of Humanoid Robots

Two running patterns are generated independently in the sagittal plane and in the frontal plane and the two patterns are then combined. When a running pattern is created with resolved momentum control in the sagittal plane, the angular momentum of the robot about the Center of Mass (COM) is set to zero, as the angular momentum causes the robot to rotate. However, this also induces unnatural motion of the upper body of the robot. To solve this problem, the biped was set as a virtual under-actuated robot with a free joint at its support ankle, and a fixed point for a virtual under-actuated system was determined. Following this, a periodic running pattern in the sagittal plane was formulated using the fixed point. The fixed point is easily determined in a numerical approach. In this way, a running pattern in the frontal plane was also generated.

Fig. 1 Scheme of Running Pattern Generation

Fig. 2 Scheme of Running Pattern Generation

In an experiment, a humanoid biped known as KHR-2 ran forward using the proposed running pattern generation method. Its maximum velocity was 2.88 km/h.

■ Control Algorithm for Running Humanoid Robots

We describes online balance controllers for running in a humanoid robot and verifies the validity of the proposed controllers via experiments. To realize running in the humanoid robot, the overall control structure is composed of an offline controller and an online controller. The main purpose of the online controller is to maintain dynamic stability while the humanoid robot hops or runs. The online controller is composed of the posture balance control in the sagittal plane, the transient balance control in the frontal plane, and the swing ankle pitch compensator in the sagittal plane. The posture balance controller makes the robot maintain balance using an IMU (inertial measurement unit) sensor in the sagittal plane. The transient balance controller makes the robot keep its balance in the frontal plane using gyros attached to each upper leg. The swing ankle pitch compensator prevents the swing foot from hitting the ground at unexpected times while the robot runs forward. HUBO2 was used for the running experiment. It was designed for the running experiment, and is lighter and more powerful than the previous walking robot platform, HUBO.

Fig. 1 Overall Control Algorithm

With the proposed controllers, HUBO2 ran forward stably at a maximum speed of 3.24km/h and this result verified the effectiveness of the proposed algorithm.

■ Push Recovery Algorithm

We describe the stabilization of a hopping humanoid robot against a disturbance. In the proposed scheme, the method of control is selected according to the size of the disturbance. A posture balance controller is used when the disturbance is small, and the posture balance controller and a foot placement method are activated together when the disturbance is large. A simplified model is used to develop the novel controller for the foot placement method, and a linearized Poincare map for single hopping is made. The control law is designed using the pole placement method.

Fig. 1 Overall Control Algorithm

The proposed method is verified through simulation and experiment. In the experiment, HUBO2 hops well against various disturbance.

from Robotics and Control Laboratory. Kookmin University

http://rclab.kookmin.ac.kr