J Control Theory Appl 2013 11 (3) 386–392
DOI 10.1007/s11768-013-1171-6
Adaptive walking control of quadruped robots
based on central pattern generator (CPG)
and reflex
Chengju LIU, Qijun CHEN
†
, Guoxing WANG
Department of Electronics and Information Engineering, and
Key Laboratory of Embedded System and Service Computing, Ministry of Education, Tongji University, Shanghai 201804, China
Abstract: This paper presents a central pattern generator (CPG) and vestibular reflex combined control strategy for a
quadruped robot. An oscillator network and a knee-to-hip mapping function are presented to realize the rhythmic motion for
the quadruped robot. A two-phase parameter tuning method is designed to adjust the parameters of oscillator network. First,
based on the numerical simulation, the influences of the parameters on the output signals are analyzed, then the genetic
algorithm (GA) is used to evolve the phase relationships of the oscillators to realize the basic animal-like walking pattern.
Moreover, the animal’s vestibular reflex mechanism is mimicked to realize the adaptive walking of the quadruped robot on
a slope terrain. Coupled with the sensory feedback information, the robot can walk up and down the slope smoothly. The
presented bio-inspired control method is validated through simulations and experiments with AIBO. Under the control of
the presented CPG and vestibular reflex combined control method, AIBO can cope with slipping, falling down and walk on
a slope successfully, which demonstrates the effectiveness of the proposed walking control method.
Keywords: CPG; Walking control; Quadruped robot; Vestibular reflex
1 Introduction
Recently, bio-inspired control methods have been widely
adopted to solve the challenge of locomotion control of
robots [1–2]. From the neuro-physiological evidences, it is
generally accepted that central pattern generators (CPGs)
are responsible for animals’ fundamental rhythmic activ-
ities, such as chewing, breathing, swimming and also lo-
comotion. CPGs are neuron circuits located at the spinal
cords of vertebrates which can produce coordinated oscil-
latory signals spontaneously. Moreover, the sensory inputs
and higher-level stimulator can modulate the activity of
CPGs [3–5].
The CPG-inspired methods have been extensively ex-
plored for the motion control of crawling robots [6–9].
These works confirm the superiorities of these bio-inspired
control methods. It does not require accurate information of
the robot’s model. Thanks to the limit cycle behaviour, the
amplitude and the period of the rhythmic output signals can
be easily modulated, and the system is robust with respect
to small disturbances. Multidimensional coordinate output
signals can be generated to supply a distributed control sys-
tem for the multiple degrees of freedom of a robot. More-
over, CPGs are ideally suited to integrate reflexes, and thus,
by entraining the sensory feedback from robot-environment
interaction, adaptive locomotion control signals can be gen-
erated.
The study of CPG-inspired control method for legged
robots is focused on gait pattern diversity and dynamic
walking on irregular terrain. For legged robots, to coordi-
nate so many degrees of freedom to realize adaptive walk-
ing is very difficult. Inagaki et al. [10] proposed a wave
CPG model which could change the oscillators’ number
automatically. This wave CPG model was used to control
the leg movements of an autonomous decentralized multi-
legged robot NEXUS. Zheng et al. [11] presented a control
strategy based on CPGs and postural reflex to control the
walking of quadruped robot. The oscillators are connected
to the hip joints of quadruped robot to determine the gait
patterns, and the parameters are adjusted by the trial and
error method. Quadruped walking control using CPGs and
reflexes has been extensively explored by Kimura’s group.
Their studies mainly focus on using oscillators and reflexes
to generate torque control signals [12] or phase modulation
signals [13–15] in joint space to realize dynamic walking on
irregular terrains.
Following the research line of Kimura’s group, we will
study a CPG and vestibular reflex combined control strat-
egy for a general quadruped robot. The main contributions
of this paper are as follows: 1) An effective CPG-inspired
control system is presented. CPGs are connected to the
knee joints, which is relative to the gait pattern genera-
tions of the quadruped robot. The other joint control sig-
nals are transformed through a proposed mapping func-
tion. The presented control system can reduce the number
of adjusting parameters and generate gait patterns much
more close to quadruped animals. 2) An effective param-
Received 22 August 2011; revised 23 May 2012.
†
Corresponding author. E-mail: qjchen@tongji.edu.cn. Tel.: +86-21-69589378.
This work was supported by the National Natural Science Foundation of China (No. 61203344), the International Technology Cooperation Project (No.
2010DFA12210), the China Postdoctoral Science Foundation (No. 2011M500627), the Shanghai Science and Technology Committee Talent Program
(No. 11XD1404800), and the ‘Dawn Tracking’ Program of Shanghai Education Commission, China (No. 10GG11).
c
South China University of Technology and Academy of Mathematics and Systems Science, CAS and Springer-Verlag Berlin Heidelberg 2013