Journal of Robotics, Networking and Artificial Life, Vol. 1, No. 4 (March 2015), 261-264

Biped Robot Research at Waseda University
Kenji Hashimoto

Research Institute for Science and Engineering, Waseda University,#41-304, 17 Kikui-cho, Shinjuku-ku, Tokyo 162-0044, Japan
Atsuo Takanishi

Department of Modern Mechanical Engineering, Waseda University,
TWIns Room# 3C-202, 2-2, Wakamatsu-cho, Shinjuku-ku, Tokyo 162-8480, Japan
E-mail: contact@takanishi.mech.waseda.ac.jp
www.takanishi.mech.waseda.ac.jp/top/index.htm

Abstract
Waseda University has researched on biped robots since 1967. This paper describes our latest biped robots: (i)WABIAN-2, (ii) a biped running robot, and (iii) WL-16. WABIAN-2 is a biped humanoid robot and has realized ahuman-like walk with the knees stretched by utilizing a 2-DOF waist mimicking a human’s pelvic motion. We aredeveloping a new biped humanoid robot which can jump and run by utilizing a pelvic movement and leg elasticity.
WL-16 is a human-carrying biped vehicle.
Keywords: Biped walking, Running, Humanoid robot, Legged robot, Walking chair

1. Introduction
Waseda University has researched on biped robots since
1967 and has been one of the leading research sites forhumanoid robots since the late Prof. Ichiro Kato and hiscolleagues started the WABOT Project in 1970. We
have developed a variety of humanoid robots including
WABOT-1 which is the first full-scale human-like robot
made in 1973 and the biped humanoid robot WABIAN
in 1997.
This paper describes our latest biped robots,
WABIAN-21 (WAseda BIpedal humANoid - No. 2), arunning robot2 and WL-163 (Waseda Leg - No. 16).
2. Biped Humanoid Robot, WABIAN-2
We have developed a biped humanoid robot named
WABIAN-2 as a human motion simulator to mimic
human’s motions and mechanisms (see Fig. 1).

WABIAN-2 has 41 degrees of freedom (DoF) (a 3DoF neck, a 2-DoF trunk, two 7-DoF arms, two 3-DoF
hands, a 2-DoF waist, two 6-DoF legs and two 1-DoF
feet having passive toe joint). Its height is 1480 mm
with 63.8 kg weight. So far, WABIAN-2 has realized ahuman-like walk with the knees stretched, heel-contact
and toe-off motion by utilizing a foot mechanism havinga passive toe joint and a 2-DOF (Roll, Yaw) waist
mimicking a human’s pelvic motion. A notable featureof human walking is that the vertical ground reaction
force (GRF) has two peaks. Two peaks do not appear
when a robot walks with bending the knees. On theother hand, during the knee-stretched walking, we canfind two peaks of the vertical ground force which aresimilar to the human ones as shown in Fig. 2.
WABIAN-2 can contribute to quantitatively
evaluate welfare and rehabilitation instruments such as awalk-assist machine, an artificial leg and so on instead

Published by Atlantis Press
Copyright: the authors261

of human subjects. As one of the applications as thehuman motion simulator, we carried out walking
experiments with a walk-assist machine4 (see Fig. 3).
Generally, an armrest of a walk-assist machine is set toequal height of a user’s elbow. It is also known that theseverer his/her disability is, the lower we should set thearmrest. Measuring the current value of the actuators at(a) Overview(b) DOF configuration

the knee joints and the forces and torques applied to thearms and legs, we can calculate the energy consumption
at knee joints and the load to arms. Then we found thefact with quantitative data that the lower we set theheight of the armrest, the less the load of knees is. Thisis a good example that human motion simulator canevaluate empirical facts quantitatively. From the resultsof these experiments, we confirmed that we canevaluate welfare and rehabilitation instruments
quantitatively with a human motion simulator.
We also use WABIAN-2 to clarify the function of
the foot arch structure.5 We developed a human-likefoot mechanism that mimics the changes of theelasticity of the medial longitudinal arch with thechange of the arch height during walking. As
experimental results using the biped humanoid robot,
WABIAN-2 mounted on the human-like footmechanism, we confirmed that the arch elasticity could
absorb a foot-landing force at the plantar contact phase.
Furthermore, the windlass mechanism which causedchange of the arch height contributed to a strong thrustat the push-off phase.

Fig. 1. Biped humanoid robot, WABIAN-2.

3. Biped Running Robot

Fig. 2. Ground reaction force during the knee-stretchedwalking. Two peaks appear like the human ones.

Fig. 3. Quantitative evaluation of walk-assist machine.

We are now developing a new biped humanoid robotthat can mimic various characteristics of human runningfor investigating human running mechanisms andhuman motion control. If a robot could perform motions
that would improve sports performance, it would bepossible to identify more effective human motions andcreate a novel sports coaching program.
Human running can be modeled by a spring-loaded
inverted pendulum (SLIP) model, which is composed ofa body mass and spring leg inspired by the linear
relationship between the ground reaction force and thevertical body displacement during running.6 This model
describes human running in a simple, straightforward
way and is used on the studies of biped running robots.
Moreover, the knee and ankle joints in a standing leg act
like torsion springs which emerge the leg stiffness.7
Furthermore, an important characteristic that has not yet
been reported is that a pelvic movement in the frontalplane can help to increase jumping forces.
On the basis of the analysis of human runningmotion, we propose a new model named SLIP2 (SpringLoaded Inverted Pendulum using Pelvis). This model is

Published by Atlantis Press
Copyright: the authors
262

composed of a body mass, a pelvis, and leg springs. In
this model, the knee and ankle joints in a standing leg
act like torsion springs and the pelvic sine movement
causes the resonance for hopping.
We have developed a biped running robot with apelvis and a joint stiffness adjustment mechanism thatuses two leaf springs mimicking the joint stiffness of ahuman leg during running (see Fig. 4). The robot hasrealized hopping motions by utilizing the pelvic
movement and leg elasticity.
4.

Biped Vehicle, WL-16

We consider that a biped vehicle is a viable solution in
barrier-free engineering that is much more effective andlow-cost than infrastructure improvements. Therefore,
we have developed a human-carrying biped vehicle
named WL-16 as shown in Fig. 5.
The weight of WL-16 is 74 kg including 11 kg
battery weight. Each leg mechanism has six linear
actuators and passive joints at the both sides of eachlinear actuator. The upper passive joints are commercial
universal joints which use needle bearings with littlebacklash. The lower passive joints are lightweight 3DOF spherical rolling joints, which were newly
developed in cooperation with HEPHIST Seiko Co., Ltd.
Each linear actuator consists of a 150W DC servo
motor and a ball screw. The control computer is(a) Overview(a) Overview(b) DOF configuration(b) Mechanism and sensors

Fig. 4. Biped running robot.

Fig. 5. Biped vehicle, WL-16.

Published by Atlantis Press
Copyright: the authors263

arranged at the rear of the waist. The batteries, DC servo
drives and an IMU sensor are arranged inside the waist
part. A passenger seat is on the waist, and a control stick
is mounted on the passenger seat. A passenger canchange the direction of the robot freely by using thecontrol stick.
5. Conclusions
We introduced our latest biped robots developed at
Waseda University. WABIAN-2 is the biped humanoid
robot which can walk with the knees stretched, heelcontact and toe-off motion by utilizing a footmechanism having a passive toe joint and a waist
mimicking a human’s pelvic motion. WABIAN-2 canquantitatively evaluate welfare and rehabilitation
instruments by analyzing the data from a lot of sensors
throughout the body. WABIAN-2 also can evaluate ride
quality of WL-16 (see Fig. 6). WL-16 is the bipedvehicle consisting of two Stewart Platform type legs andwaist with a passenger seat. It can be used as a
substitute for a wheel chair.
The new biped running robot is designed based on
the analysis of human running motion, and it can jumpby utilizing the pelvic movement and leg elasticity. WeFig. 6. Cooperative relation between WABIAN-2 andWL-16.

will identify more effective human motions by using therunning robot and try to create a novel sports coaching
program.
Acknowledgements
This study was conducted as part of the ResearchInstitute for Science and Engineering, Waseda
University, and as part of the humanoid project at the
Humanoid Robotics Institute, Waseda University. It wasalso supported in part by MEXT/JSPS KAKENHI(Grant Number: 24360099, 25220005 and 25709019),
SolidWorks Japan K.K., HEPHIST Seiko Co., Ltd., andDYDEN Corporation whom we thank for their financial
and technical support.
References
1. Y. Ogura, H. Aikawa, K. Shimomura, H. Kondo, A.
Morishima, H. O. Lim and A. Takanishi, Development ofa Humanoid Robot WABIAN-2, in Proc. of the 2006
IEEE International Conference on Robotics andAutomation (2006) 76-81.
2. T. Otani, M. Yahara, K. Uryu, A. Iizuka, K. Hashimoto,T. Kishi, N. Endo, M. Sakaguchi, Y. Kawakami, S. H.
Hyon, H. O. Lim and A. Takanishi, Running Model andHopping Robot Using Pelvic Movement and Leg
Elasticity, in Proc. of the 2014 IEEE International
Conference on Robotics and Automation (2014) 23132318.
3. K. Hashimoto, H. O. Lim and A. Takanishi, DisturbanceCompensation Control for Biped Vehicle, Advanced
Robotics 25 (3) (2011) 407-426.
4. Y. Ogura, H. Aikawa, K. Shimomura, H. Kondo, A.
Morishima, H. O. Lim and A. Takanishi, Development ofa humanoid robot capable of leaning on a walk-assist
machine, in Proc. of the IEEE RAS/EMBS International
Conference on Biomedical Robotics and Biomechatronics(2006) 835–840.
5. K. Hashimoto, Y. Takezaki, K. Hattori, H. Kondo, T.
Takashima, H. O. Lim and A. Takanishi, A Study ofFunction of the Human’s Foot Arch Structure Using
Biped Humanoid Robot, in Proc. of the 2010 IEEE/RSJ
International Conference on Intelligent Robots andSystems (2010) pp. 2206-2211.
6. T. McMahon and G. Cheng, The Mechanics of Running:
How does Stiffness Couple with Speed?, J. Biomechanics
23 (1990) 65-78.
7. M. Gunther, R. Blickhan, Joint stiffness of the ankle andthe knee in running, J. Biomechanics 35 (2002) 1459–1474.

Published by Atlantis Press
Copyright: the authors
264