Motion Modeling and Control of Lower Limb Exoskeleton Based on Max-Plus Algebra

Zuojun Liu,Cuifeng Qin,Shiping Wen

doi:10.1155/2021/8538787

Zuojun Liu, Cuifeng Qin + Show 1 more

Open Access

https://doi.org/10.1155/2021/8538787

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Abstract

Max-plus algebra is a special method to describe the discrete event system. In this paper, it is introduced to describe the motion of lower limb exoskeleton. Based on the max-plus algebra and the timed event graph, the walking process of exoskeleton is modelled. The max-plus algebra approach can describe the logical sequence and safety condition in the walking process, which cannot be achieved via other conventional modelling approaches. The autonomous control of lower limb exoskeleton system is studied via the model based on max-plus algebra. In the end, an FSM (finite state machine) controller embedded with the max-plus algebra model is proposed, and the experiments show ideal speed and gait/phase period control effect, as well as the good safety and stable performance.

Highlights

Exoskeleton robot is a wearable robot that can be used to enhance people’s ability, realize the rehabilitation training of patients, and assist people in various operations
E mathematic model of a system describes the dynamic characteristics and the relationship between the variables in the system, which is the fundamental of exoskeleton control. e model of exoskeleton and its stability analyses in most literature is based on the conventional Newton Euler method or Lagrange method [3, 4]
While the conventional approaches are suitable for the continuous system, which build the model to describe the dynamic relation between the angles, speed, and torque in each gait phase. e main aim of this paper is to introduce a new modelling approach for the researchers in this field, with no hint that the conventional approaches are no longer useful

Summary

Introduction

Exoskeleton robot is a wearable robot that can be used to enhance people’s ability, realize the rehabilitation training of patients, and assist people in various operations. In this paper, the analysis and control of lower limb exoskeleton is consider in the way of discrete event system, in which the max-plus algebra is used for modelling. By using the max-plus algebra method, this paper aims to improve the control performance in terms of safety of lower limb exoskeleton. It would provide a new research thought for the safety and gait/phase control of lower limb exoskeleton. In another word, it will show the advantage of max-plus model over the conventional dynamics models in the control of lower limb exoskeleton.

Preliminary of Max-Plus Algebra

Walking Process in Timed Event Graph

Lower Limb Exoskeleton System

Walking Process Modeling via MaxPlus Algebra

Autonomous Control

Finite State Machine Control and Max-Plus Algebra Model

Conclusion