Article
Kinematic Analysis and Motion Planning of Cable-Driven
Rehabilitation Robots
Jingyu Zhang , Dianguo Cao and Yuqiang Wu *
Citation: Zhang, J.; Cao, D.; Wu, Y.
Kinematic Analysis and Motion
Planning of Cable-Driven
Rehabilitation Robots. Appl. Sci. 2021,
11, 10441. https://doi.org/10.3390/
app112110441
Academic Editor: Dario Richiedei
Received: 23 September 2021
Accepted: 3 November 2021
Published: 6 November 2021
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4.0/).
School of Engineering, Qufu Normal University, Rizhao 276826, China; zhangjingyuwang@163.com (J.Z.);
caodg@qfnu.edu.cn (D.C.)
* Correspondence: wyq@qfnu.edu.cn; Tel.: +86-1876-933-2022
Abstract:
In this study, a new cable-driven rehabilitation robot is designed, the overall design of the
robot is given, and the kinematic equation of the lower limbs in the supine state of the human body
is addressed. Considering that cable winders move along the rail brackets, the closed vector method
is applied to establish the kinematic model of the robot, and the relationship between the human
joint angle and the cable length change was deduced. Considering joint compliance, a fifth-order
polynomial trajectory planning method based on an S-shaped curve is proposed by introducing an
S-shaped velocity curve, and the changes in cable length displacement, velocity, and acceleration
are simulated and analyzed. Three planning methods are compared based on two indices, and
experimental verification is carried out on the rehabilitation experiment platform. The simulation
and experimental results show that the trajectory planning method presents low energy consumption
and strong flexibility, and can achieve better rehabilitation effect, which builds a good basis for the
subsequent study of dynamics and control strategy.
Keywords:
cable-driven rehabilitation robot; kinematics; trajectory planning; fifth-order
polynomial; flexibility
1. Introduction
With the number of patients with limb injuries caused by unknown diseases or
unexpected accidents increasing year by year [
1
,
2
], scientific and effective rehabilitation
therapy plays a significant role in restoring limb motor function. In the early stage of
rehabilitation, meaningful and repetitive rehabilitation training tasks can help patients
with motor dysfunction improve their muscle strength and coordination [
3
,
4
]. Traditional
rehabilitation treatment requires rehabilitation training under the guidance of rehabilitation
specialists. Due to long-term training, the rehabilitation teacher’s strength is weakened
and the movement is biased, which leads to a weakening of the rehabilitation effect. For
repetitive rehabilitation treatment, rehabilitation robots can be used instead of rehabilitation
specialists [5]. Therefore, rehabilitation robots have received great attention.
Some exoskeleton rehabilitation robots have been widely applied in rehabilitation
treatment, and help patients complete rehabilitation training more effectively through
auxiliary training and real-time status monitoring [
6
], such as ARMin [
7
], RUPERT [
8
],
and CADEN-7 [
9
]. However, the traditional exoskeleton robot has large inertia, and the
patient is prone to collide with the robot, causing secondary injury to the patient. There
are problems such as limited working space and a single training mode [
10
–
12
]. For these
reasons, in recent years, cable-driven robots have begun to attract people’s attention. They
use cables to replace rigid elements to drive limb movement. They have the characteristics
of a large working space, lower motion inertia, strong load-bearing capacity, and good
flexibility [
13
–
15
] in multiple scenarios, they can satisfy the rehabilitation needs of different
patients. In addition, when the robot is not controlled, the flexible cable can ensure that the
patient is not injured. Therefore, cable-driven rehabilitation robots have been widely used in
rehabilitation training. Ming et al. [
16
] developed a new type of cable-driven sports training
Appl. Sci. 2021, 11, 10441. https://doi.org/10.3390/app112110441 https://www.mdpi.com/journal/applsci
