Article
Design and Control of an Omnidirectional Mobile
Wall-Climbing Robot
Zhengyu Zhong , Ming Xu *, Junhao Xiao and Huimin Lu
Citation: Zhong, Z.; Xu, M.; Xiao, J.;
Lu, H. Design and Control of an
Omnidirectional Mobile
Wall-Climbing Robot. Appl. Sci. 2021,
11, 11065. https://doi.org/10.3390/
app112211065
Academic Editor: Dario Richiedei
Received: 28 September 2021
Accepted: 15 November 2021
Published: 22 November 2021
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College of Intelligence Science and Technology, National University of Defense Technology,
Changsha 410073, China; hnsyszzy@foxmail.com (Z.Z.); junhao.xiao@nudt.edu.cn (J.X.);
lhmnew@nudt.edu.cn (H.L.)
* Correspondence: xuming12@nudt.edu.cn; Tel.: +86-731-84574981
Abstract:
Omnidirectional mobile wall-climbing robots have better motion performance than tra-
ditional wall-climbing robots. However, there are still challenges in designing and controlling
omnidirectional mobile wall-climbing robots, which can attach to non-ferromagnetic surfaces. In this
paper, we design a novel wall-climbing robot, establish the robot’s dynamics model, and propose
a nonlinear model predictive control (NMPC)-based trajectory tracking control algorithm. Com-
pared against state-of-the-art, the contribution is threefold: First, the combination of three-wheeled
omnidirectional locomotion and non-contact negative pressure air chamber adhesion achieves om-
nidirectional locomotion on non-ferromagnetic vertical surfaces. Second, the critical slip state has
been employed as an acceleration constraint condition, which could improve the maximum linear
acceleration and the angular acceleration by 164.71% and 22.07% on average, respectively. Last,
an NMPC-based trajectory tracking control algorithm is proposed. According to the simulation
experiment results, the tracking accuracy is higher than the traditional PID controller.
Keywords:
omnidirectional mobile robot; wall-climbing robot; critical slip state; nonlinear model
predictive control; trajectory tracking
1. Introduction
The wall-climbing robot mainly consists of two modules: the locomotion module and
the adhesion module. For the locomotion types, arms and legs [
1
] are good at overcoming
obstacles but have drawbacks in velocity, wheels and chains [
2
] have advantages in contin-
uous and fast movement but cannot handle large obstacles, sliding frames [
3
] are simple
in both structure and control but move slowly compared with wheels and chains, and
wires and rails [
4
] are safe and carry a considerable payload weight but demand external
guidance and equipment. For the adhesion types, magnetic adhesion [
5
] has a strong
adhesion force but demands a ferromagnetic wall, passive suction cups [
6
] have lower
energy consumption, while active suction chambers [
7
–
9
] have stable adhesion, mechanical
adhesion [
10
–
12
] has low energy consumption and is stable but usually requires unique
construction or materials on the wall surface, and chemical adhesion [
13
] has low energy
consumption when the robot is not moving but is highly influenced by wall material.
According to the literature [
14
,
15
], there are few wall-climbing robotic systems at-
tached to non-ferromagnetic walls with omnidirectional locomotion. However, compared
against differential wall-climbing robotic systems, omnidirectional locomotion has better
motion flexibility, including omnidirectional moving with any orientation, changing orien-
tation arbitrarily during motion, and adapting to small spaces. A robot sometimes needs to
move along a specific trajectory when carrying out a task in real applications. Therefore,
trajectory tracking for ground mobile robots has been widely researched in past years.
However, the dynamic characteristics of wall-climbing robots are different from that of
ground robots because of the overturning moment caused by gravity. The difference makes
the trajectory tracking of wall-climbing robots more challenging. In this paper, we focus
Appl. Sci. 2021, 11, 11065. https://doi.org/10.3390/app112211065 https://www.mdpi.com/journal/applsci
