Citation: Sun, W.; Tian, X.; Song, Y.;
Pang, B.; Yuan, X.; Xu, Q. Balance
Control of a Quadruped Robot Based
on Foot Fall Adjustment. Appl. Sci.
2022, 12, 2521. https://doi.org/
10.3390/app12052521
Academic Editors: Dario Richiedei
and Adel Razek
Received: 17 December 2021
Accepted: 21 February 2022
Published: 28 February 2022
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Article
Balance Control of a Quadruped Robot Based on Foot
Fall Adjustment
Wenkai Sun, Xiaojie Tian, Yong Song * , Bao Pang, Xianfeng Yuan and Qingyang Xu
School of Mechanical, Electrical & Information Engineering, Shandong University, Weihai 264209, China;
sunwenkai@mail.sdu.edu.cn (W.S.); 200199800033@sdu.edu.cn (X.T.); pangbao@sdu.edu.cn (B.P.);
yuanxianfeng@sdu.edu.cn (X.Y.); qingyangxu@sdu.edu.cn (Q.X.)
* Correspondence: songyong@sdu.edu.cn
Abstract:
To balance the diagonal gait of a quadruped robot, a dynamic balance control method is
presented to improve the stability of the quadruped robot by adjusting its foot position. We set up
a trunk-based coordinate system and a hip-based local coordinate system for the quadruped robot,
established the kinematics equation of the robot, and designed a reasonable initial diagonal gait
through the spring inverted pendulum model. The current trunk posture of the quadruped robot is
obtained by collecting the data of its pitch and roll angle, and the foot position is predicted according
to the current posture and initial gait of the quadruped robot. To reduce the impact of one leg landing
on the ground and increase the stability of the quadruped robot, we adjust the landing point of the
robot according to the landing time difference between the diagonal legs. The proposed method can
adjust the body in such scenarios as planar walking and lateral impact resistance. It can reduce the
disturbance during the robot motion and make the robot move smoothly. The validity of this method
is verified by simulation experiments.
Keywords:
diagonal gait; quadruped robot; dynamic balance control; attitude feedback; landing
time difference
1. Introduction
Mobile robots can be divided into three types: legged-foot, caterpillar, and wheeled.
Compared with caterpillar and wheeled robots, legged-foot robots have discrete landing
locations and can choose the best landing locations for support. Therefore, legged-foot
robots have more advantages in terrain adaptability, motion flexibility, and load capacity.
They have broader application prospects in the fields of material transportation, military
investigation, field exploration, rescue, and disaster relief.
The first real quadruped robot research began in the 1960s. After more than half a
century of development, various styles of quadruped robots emerged. At present, one
of the most representative quadruped robots is the BigDog series developed by Boston
Dynamics [
1
,
2
]. They have good topographic adaptability, load capacity, impact resistance.
They can walk and trot under more complex terrain such as gravel, grassland, snow, etc.
Starting in 2015, Boston Dynamics introduced the Spot series of quadruped robots, which
are small, powerful, and flexible [
3
,
4
]. ANYmal, a quadruped robot developed by the
Swiss Federal Institute of Technology Zurich (ETH Zurich), has improved the series elastic
driver to achieve more flexible and precise moment control. It has a laser sensor and a
camera installed on its body to sense the terrain of the environment for map building and
self-positioning [
5
]. The Cheetah series quadruped robots, developed by the Massachusetts
Institute of Technology (MIT), mimic the body structure of a cheetah. It can run at high
speed, up to 6 m/s. In 2019, MIT launched Mini Cheetah, the first quadruped robot that
can flip backward. It can move horizontally, jump, climb from a fall, and flip backward
without visual aids. It has epochal significance in robotics.
Appl. Sci. 2022, 12, 2521. https://doi.org/10.3390/app12052521 https://www.mdpi.com/journal/applsci
