Mechanical design and trajectory planning of a lower limb rehabilitation robot with a variable workspace

Hongbo Wang,Zhenghui Wang,Hongnian Yu,Yongfei Feng,Victor Vladareanuv,Yaxin Du

doi:10.1177/1729881418776855

Abstract

The early phase of extremity rehabilitation training has high potential impact for stroke patients. However, most of the lower limb rehabilitation robots in hospitals are proposed just suitable for patients at the middle or later recovery stage. This article investigates a new sitting/lying multi-joint lower limb rehabilitation robot. It can be used at all recovery stages, including the initial stage. Based on man–machine engineering and the innovative design for mechanism, the leg length of the lower limb rehabilitation robot is automatically adjusted to fit patients with different heights. The lower limb rehabilitation robot is a typical human–machine system, and the limb safety of the patient is the most important principle to be considered in its design. The hip joint rotation ranges are different in people’s sitting and lying postures. Different training postures cannot make the training workspace unique. Besides the leg lengths and joint rotation angles varied with different patients, the idea of variable workspace of the lower limb rehabilitation robot is first proposed. Based on the variable workspace, three trajectory planning methods are developed. In order to verify the trajectory planning methods, an experimental study has been conducted. Theoretical and actual curves of the hip rotation, knee rotation, and leg mechanism end point motion trajectories are obtained for three unimpaired subjects. Most importantly, a clinical trial demonstrated the safety and feasibility of the proposed lower limb rehabilitation robot.

Highlights

According to the statistics from the China Disabled Persons’ Federation, in 2010 the number of patients with limb disorder was about 24.72 million in China
As the lengths of the thigh and the calf are much longer than the foot, in the following trajectory planning methods, the ankle joint motion is designed separately to obtain large ranges of motion, so here O2 is chosen as the end point, which can be expressed as xO2 1⁄4 l1 cosq[1] þ l2 cosðq[1] þ q2Þ
Compared with the present sitting/lying rehabilitation robots, lower limb rehabilitation robots (LLR-Ros) could adjust the length of the mechanical leg electrically through an innovative design of the length adjustment mechanism

Summary

Introduction

According to the statistics from the China Disabled Persons’ Federation, in 2010 the number of patients with limb disorder was about 24.72 million in China. As the lengths of the thigh and the calf are much longer than the foot, in the following trajectory planning methods, the ankle joint motion is designed separately to obtain large ranges of motion, so here O2 is chosen as the end point, which can be expressed as xO2 1⁄4 l1 cosq[1] þ l2 cosðq[1] þ q2Þ ð1Þ yO2 1⁄4 l1 sinq[1] þ l2 sinðq[1] þ q2Þ. According to the subjects’ joint ranges and leg lengths, the robot calculated the subjects’ workspace in the largest circle trajectory mode. In this experiment, the training trajectories are chosen tangent to the boundary curves S1 and S2. The simulation of the arbitrary curve trajectory planning: (a) the circular trajectory, (b) the linear trajectory, and (c) the irregular figure trajectory

20 Trajectory after interpolation

Findings

Discussion

Conclusions