The goal of most bipedal robotics research is to develop methods of achieving a dynamically balanced gait. Most current approaches focus on maintaining the balance of the system. This paper introduces a measure called the foot placement estimator (FPE) to restore balance to an unbalanced system. We begin by developing a theoretical proof to define when a biped is stable, as well as defining the region in which stability results are valid. This forms the basis for the derivation of the FPE. The results of the FPE are then extended to a complete gait cycle using the combination of a state machine and simple linear controllers. This control system is applied to a detailed and realistic simulation based on a physical robot currently under construction. Utilizing the FPE as a measure of balance allows us to create dynamically balanced gait cycles in the presence of external disturbances, including gait initiation and termination, without any precalculated trajectories.

1.
McGeer
,
T.
, 1989, “
Powered Flight, Child’s Play, Silly Wheels and Walking Machines
,”
IEEE International Conference on Robotics and Automation- 1989
, May 14–19,
IEEE
,
Piscataway, NJ
, pp.
1592
1597
.
2.
McGeer
,
T.
, 1990, “
Passive Walking With Knees
,”
Proceedings of the 1990 IEEE International Conference on Robotics and Automation
, May 13–18,
IEEE
,
Los Alamitos, CA
, pp.
1640
1645
.
3.
Wisse
,
M.
,
Schwab
,
A.
, and
Van Der Helm
,
F.
, 2004, “
Passive Dynamic Walking Model With Upper Body
,”
Robotica
0263-5747,
22
(
6
), pp.
681
688
.
4.
Asano
,
F.
,
Yamakita
,
M.
, and
Furuta
,
K.
, 2000, “
Virtual Passive Dynamic Walking and Energy-Based Control Laws
,”
IEEE International Conference on Intelligent Robots and Systems
,
Institute of Electrical and Electronics Engineers Inc.
, Vol.
2
, pp.
1149
1154
.
5.
Koganezawa
,
K.
, and
Matsumoto
,
O.
, 2002, “
Active/Passive Hybrid Walking by the Biped Robot TOKAI ROBO-HABILIS 1
,”
Proceedings IEEE/RSJ International Conference on Intelligent Robots and Systems
,
IEEE
, Vol.
3
, Catalog No. 02CH37332C, pp.
2461
2466
.
6.
Pratt
,
J.
, 2000, “
Exploiting Inherent Robustness and Natural Dynamics in the Control of Bipedal Walking Robots
,” Ph.D. thesis, Massachusetts Institute of Technology, Cambridge, MA.
7.
Collins
,
S.
,
Ruina
,
A.
,
Tedrake
,
R.
, and
Wisse
,
M.
, 2005, “
Efficient Bipedal Robots Based on Passive-Dynamic Walkers
,”
Science
0036-8075,
307
(
5712
), pp.
1082
1085
.
8.
Vukobratovic
,
M.
, and
Borovac
,
B.
, 2004, “
Zero-Moment Point-Thirty Five Years of Its Life
,”
Int. J. Humanoid Robotics
,
1
(
1
), pp.
157
173
.
9.
Hirai
,
K.
,
Hirose
,
M.
,
Haikawa
,
Y.
, and
Takenaka
,
T.
, 1998, “
The Development of Honda Humanoid Robot
,”
Proceedings of the 1998 IEEE International Conference on Robotics and Automation
, Vol.
2
, pp.
1321
1326
.
10.
Kurazume
,
R.
,
Hasegawa
,
T.
, and
Yoneda
,
K.
, 2003, “
The Sway Compensation Trajectory for a Biped Robot
,”
2003 IEEE International Conference on Robotics and Automation
,
IEEE
, Vol.
1
, Catalog No. 03CH37422, pp.
925
931
.
11.
Lim
,
H. O.
,
Kaneshima
,
Y.
, and
Takanishi
,
A.
, 2002, “
Online Walking Pattern Generation for Biped Humanoid Robot With Trunk
,”
Proceedings -IEEE International Conference on Robotics and Automation
,
Institute of Electrical and Electronics Engineers Inc.
, Vol.
3
, pp.
3111
3116
.
12.
Vermeulen
,
J.
,
Verrelst
,
B.
,
Vanderborght
,
B.
,
Lefeber
,
D.
, and
Guillaume
,
P.
, 2006, “
Trajectory Planning for the Walking Biped “Lucy”
,”
Int. J. Robot. Res.
0278-3649,
25
(
9
), pp.
867
887
.
13.
Popovic
,
M. B.
,
Goswami
,
A.
, and
Herr
,
H.
, 2005, “
Ground Reference Points in Legged Locomotion: Definitions, Biological Trajectories and Control Implications
,”
Int. J. Robot. Res.
0278-3649,
24
(
12
), pp.
1013
1032
.
14.
Goswami
,
A.
, 1999, “
Postural Stability of Biped Robots and the Foot-Rotation Indicator (FRI) Point
,”
Int. J. Robot. Res.
0278-3649,
18
(
6
), pp.
523
533
.
15.
Goswami
,
A.
, 1999, “
Foot Rotation Indicator (FRI) Point: A New Gait Planning Tool to Evaluate Postural Stability of Biped Robots
,”
Proceedings 1999 IEEE International Conference on Robotics and Automation
,
IEEE
, Vol.
1
, Catalog No. 99CH36288C, pp.
47
52
.
16.
Lee
,
D.
, and
ElMaraghy
,
W.
, 1992, “
A Neural Network Solution for Bipedal Gait Synthesis
,”
IJCNN International Joint Conference on Neural Networks
,
IEEE
, Catalog No. 92CH3114-6, pp.,
763
768
.
17.
Bebek
,
O.
, and
Erbatur
,
K.
, 2004, “
A Gait Adaptation Scheme for Biped Walking Robots
,”
Eight IEEE International Workshop on Advanced Motion Control
,
IEEE
, Catalog No. 04TH8725, pp.
409
414
.
18.
Feng
,
K.
,
Chew
,
C. M.
,
Hong
,
G. S.
, and
Zielinska
,
T.
, 2005, “
Bipedal Locomotion Control Using a Four-Compartmental Central Pattern Generator
,”
IEEE International Conference on Mechatronics and Automation, ICMA 2005
,
Institute of Electrical and Electronics Engineers Computer Society
,
Piscataway, NJ
, pp.
1515
1520
.
19.
Chevallereau
,
C.
,
Abba
,
G.
,
Aoustin
,
Y.
,
Plestan
,
F.
,
Canudas-De-Wit
,
C.
,
Westervelt
,
E.
, and
Grizzle
,
J.
, 2003, “
RABBIT: A Testbed for Advanced Control Theory
,”
IEEE Control Syst. Mag.
0272-1708,
23
(
5
), pp.
57
79
.
20.
Horak
,
F. B.
, and
Nashner
,
L. M.
, 1986, “
Central Programming of Postural Movements: Adaptation to Altered Support-Surface Configurations
,”
J. Neurophysiol.
0022-3077,
55
(
6
), pp.
1369
1381
.
21.
Raibert
,
M. H.
, 1986,
Legged Robots That Balance
,
MIT Press
,
Cambridge
.
22.
Townsend
,
M. A.
, 1985, “
Biped Gait Stabilization Via Foot Placement
,”
J. Biomech.
0021-9290,
18
(
1
), pp.
21
38
.
23.
Khallil
,
H. K.
, 2002,
Nonlinear Systems
, 3rd ed.,
Prentice-Hall, Upper Saddle River
,
NJ
.
24.
Pratt
,
J.
, and
Tedrake
,
R.
, 2006, “
Velocity-Based Stability Margins for Fast Bipedal Walking
,”
First Ruperto Carola Symposium in the International Science Forum of the University of Heidelberg Entitled “Fast Motions in Biomechanics and Robots,”
pp.
299
324
.
25.
Pratt
,
J.
,
Carff
,
J.
,
Drakunov
,
S.
, and
Goswami
,
A.
, 2006, “
Capture Point: A Step Toward Humanoid Push Recovery
,”
Proceedings of the 2006 IEEE-RAS International Conference on Humanoid Robots
,
Genoa
,
Italy
.
26.
Essen
,
H.
, 1993, “
Average Angular Velocity
,”
Eur. J. Phys.
0143-0807,
14
(
5
), pp.
201
205
.
27.
Hunt
,
K. H.
, and
Crossley
,
F. R. E.
, 1975, “
Coefficient of Restitution Interpreted as Damping in Vibroimpact
,”
ASME J. Appl. Mech.
0021-8936,
42
(
2
), pp.
440
445
.
28.
Gilardi
,
G.
, and
Sharf
,
I.
, 2002, “
Literature Survey of Contact Dynamics Modelling
,”
Mech. Mach. Theory
0094-114X,
37
(
10
), pp.
1213
1239
.
29.
Bliman
,
P.-A.
, and
Sorine
,
M.
, 1995, “
Easy-To-Use Realistic Dry Friction Models for Automatic Control
,”
Proceedings of the Third European Control Conference, ECC 95
, Vol.
4
, pp.
3788
3794
.
You do not currently have access to this content.