Article
The WL_PCR: A Planning for Ground-to-Pole Transition of
Wheeled-Legged Pole-Climbing Robots
Yankai Wang , Qiaoling Du *, Tianhe Zhang and Chengze Xue
Citation: Wang, Y.; Du, Q.; Zhang, T.;
Xue, C. The WL_PCR: A Planning for
Ground-to-Pole Transition of
Wheeled-Legged Pole-Climbing
Robots. Robotics 2021, 10, 96. https://
doi.org/10.3390/robotics10030096
Academic Editor: Dario Richiedei
Received: 25 May 2021
Accepted: 12 July 2021
Published: 27 July 2021
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State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering,
Jilin University, 2699 Qianjin Street, Changchun 130012, China; wangyk19@mails.jlu.edu.cn (Y.W.);
thzhang20@mails.jlu.edu.cn (T.Z.); xuecz20@mails.jlu.edu.cn (C.X.)
* Correspondence: duql@jlu.edu.cn
Abstract:
Hybrid mobile robots with two motion modes of a wheeled vehicle and truss structure
with the ability to climb poles have significant flexibility. The motion planning of this kind of robot
on a pole has been widely studied, but few studies have focused on the transition of the robot
from the ground to the pole. In this study, a locomotion strategy of wheeled-legged pole-climbing
robots (the WL_PCR) is proposed to solve the problem of ground-to-pole transition. By analyzing
the force of static and dynamic process in the ground-to-pole transition, the condition of torque
provided by the gripper and moving joint is proposed. The mathematical expression of Centre of
Mass (CoM) of the wheeled-legged pole-climbing robots is utilized, and the conditions for the robot
to smoothly transition from the ground to the vertical pole are proposed. Finally, the feasibility of this
method is proved by the simulation and experimentation of a locomotion strategy on wheeled-legged
pole-climbing robots.
Keywords: ground-walking robot; pole-climbing robot; locomotion control; load analysis
1. Introduction
Climbing robots have significant potential applications in industry, which can be used
to inspect and maintain large structures, such as dams [
1
], bridges [
2
], hulls [
3
], and large
industrial boilers [
4
]. Therefore, great efforts have been made to develop robots that can
climb in truss structures [
5
,
6
]. On the other hand, due to their high speed and high energy
efficiency, wheeled vehicles have existed and developed for hundreds of years. How to
integrate the best performance of two completely different mobile systems into a hybrid
platform is a hot topic in robot research, which provides more possibilities for improving
the robot’s ability to adapt to the environment [
7
–
9
]. In order to solve this problem, this
paper studies the mechanism of wheeled-legged robots and how the motion planning
of hybrid motion contributes to the motion control scheme for the hybrid locomotion of
wheeled-legged robots.
The hybrid motion system with wheels improves the flexibility and environmental
adaptability of the system and provides more gait. The Centaur robot is equipped with
wheel steering and articulated legs to adjust its supporting gait in response to unknown
disturbances [
7
]. The design method of hybrid legged/wheeled mobile robots is demon-
strated, and the walking, rolling, gliding and skating motions were generated by the novel
trajectory optimization formulation [8]. A Transleg was installed with four transformable
leg-wheel mechanisms, similar to the compliant spine mechanism, which can realize the
turning movement in legged-wheeled mode and the jumping gait in legged mode [
9
]. By
adding the wheel structure to improve the mechanism of the PCR [
10
], the research on gait
control can improve the flexibility and environmental adaptability of the PCR [10].
From the perspective of structural design, pole-climbing robots can be divided into
three types: soft climbing robots, legged climbing robots, and wheeled climbing robots.
The inspiration of the soft climbing robot is inspired by bionics. The soft climbing robot is
Robotics 2021, 10, 96. https://doi.org/10.3390/robotics10030096 https://www.mdpi.com/journal/robotics
