Ballistic walking of a humanoid with compliant wholebody

We developed a whole-body humanoid robot “Pneumat-BT”(PNEUMATics – Biped Twister) whose joints are driven by agonistic and antagonistic pairs of pneumatic artificial muscles. This joint system, which is different from that of traditional robots with motors, enables ballistic motion of a joint, acting like a pendulum when there is no actuation signal. We have proposed a control method of ballistic walking that is utilizing the body dynamics of the robot.

Fig. 1 Whole-body Humanoid Pneumat-BT

There are many studies on passive dynamic walkers(PDW) that can walk on gentle slope without any actuation, and semi-PDW. But most of existing studies of PDW and semi-PDW consider only walking in 2D plane and functions of lower leg only. Moreover, it is difficult to utilize passivity effectively if using electromagnetic motors.

In this study, we divided walking motion into sagittal, frontal, and horizontal planes for realizing 3D stable walking. Ballistic walking control is used to stabilize its walking in sagittal plane, while the stiffness of each muscles is tuned to stabilize walking in frontal and horizontal plane. We have experimentally shown that the robot can walk stably in 3D space with proposed method. Effect of the control parameter of sagittal motion is shown in Fig.2. Effect of parameters of angle and stiffness of ankle joint is shown in Fig.3.

In order to design the robot body that is suitable for walking, we have used incremental design approach, which is based on the robots of our previous versions, 2D walking robot and 3D walking robots without upperbody.
This study is reported in [narioka2008]．

Fig. 2 Parameter tuning of the sagittal motion

Fig. 3 Experimental verification of stability in the frontal plane