| In contemporary society,more and more people suffer from low back pain.Low back pain(low back pain,LBP)is a common disease in orthopedics,sports medicine and rehabilitation medicine,which refers to the pain or discomfort in the back of the back and sacrum,sometimes accompanied with radiation pain in the lower extremities.Lower back pain is one of the most common health problems that influences an individual’s life quality and is a leading cause of disability.However,at present,there is still no effective diagnosis and treatment.Exoskeleton robots is a kind of wearable mechatronics device which is developed by imitating the biological exoskeleton.It can provide the wearer with body support and functional enhancement.Therefore,this paper designs a new lower back exoskeleton based on parallel mechanism for low back pain.The main work is as follows:(1)The first part is the mechanical structure design of lumbar exoskeleton based on the movement mechanism of human waist and the defects in the structure of the existing lumbar exoskeleton.This paper firstly analyzes the lumbar structure and its movement characteristics and then defines a kind of lumbar rehabilitation movement trajectory on the basis of comprehensive analysis of lumbar spine mechanism and lumbar muscle group.Based on the coupling characteristics of waist motion,a new kind of lower back exoskeleton is designed by using a 4-SPS/S spherical parallel mechanism.The relevant dimension parameters are defined.The degree of freedom of the parallel mechanism is analyzed with spiral theory.With the structure design of lumbar exoskeleton finished,the mechanical body of lumbar exoskeleton is drawn in Solidworks.(2)Considering the inherent characteristics of the parallel mechanism and the structural characteristics of the lumbar exoskeleton,kinematics and dynamics models of lumbar exoskeleton are built in this paper.The inverse kinematics is obtained by coordinate transformation,and Newton iteration method is used to get the forward kinematics of the mechanism.The correctness of the kinematics is verified by MATLAB simulation.Based on the kinematics model,the workspace of lumbar exoskeleton is obtained by Monte Carlo method.The main work of the dynamic modeling is to solve the thrust of the push rod on the human body.Finally,the dynamic model of a single push rod is carried out.The friction factors in the motor are taken into account in the modeling process and a modified LuGre friction model with uncertain parameters is proposed.(3)Based on friction compensation of every single motor,an improved mean deviation coupling control strategy is proposed to control the co-operation of the four push rods in the proposed lumbar exoskeleton.The controller consists of two parts,the cooperative control part and the single motor tracking control part.On the one hand,considering that there are four push-rod motors in the parallel mechanism,in order to improve the cooperative performance of the system,this paper proposes an improved mean deviation coupling synchronous control strategy based on the traditional synchronous control strategy.On the other hand,tracking performance of the motors is also an important factor affecting the control accuracy and stability of the whole system.In this paper,an adaptive friction compensation strategy based on nonlinear observers is proposed to track the desired displacement signal accurately.Finally,the proposed control method is simulated by MATLAB.(4)The Open Sim software is chosen to verify the effectiveness of the designed lumbar exoskeleton in power assist.Based on the analysis of its principle and key simulation techniques,the lumbar exoskeleton designed in Solidworks is first import into the software to be coupled with the human body.The muscle force during the motion of flexion and extension of the human body respectively with and without extra assistance can be calculated through inverse dynamics analysis.The availability of the mechanism can be proved by comparing the force in the two conditions. |
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