1. Ningbo Research Institute, Zhejiang University, Ningbo 315100, China 2. College of Mechanical Engineering, Zhejiang University, Hangzhou 310058, China
A wearable flexible knee-joint protection exoskeleton was designed, which is used for knee-joint load reduction and force assistance during body motion. The flexible knee joint was designed using solid isotropic material with penalization (SIMP) model and finite element analysis based on biomechanics features of lower limbs. The exoskeleton joint is rigid during stance period to help reduce the body weight load on the knee joint, and it shows flexibility during swing period to adapt to physiological joint kinematic characteristics of body. Therefore no extra force is loaded on the body joint. The walking assistance module was designed and added on the basis of this wearable flexible knee-joint exoskeleton mechanism. The corresponding assisting force control method was researched to realize walking assistance. The performance tests show that the knee joint protection exoskeleton can reduce the knee joint load up to 110 N. The weight of the wearable exoskeleton is 639 g, therefore the weight loss ratio is significant. The exoskeleton system with walking assistance module weights 4.8 kg. The walking test proves that the system has the ability to assist walking.
Fig.1Human motion surface and distribution of lower limb freedom
关节运动
步行运动范围[14]
运动极限[15]
髋关节旋内/旋外
1.6°/13.2°
50°/40°
髋关节屈/伸
32.2°/22.5°
120°/30°
髋关节外展/内收
7.9°/6.4°
20°/45°
膝关节屈/伸
73.5°/0°
150°/0°
踝关节背屈/趾屈
14.1°/20.6°
20°/40°
踝关节内/外翻
16.5°/25.7°
20°/35°
Tab.1Motion range of each lower limb joint
大腿长/mm
大腿围/mm
小腿围/mm
体重/kg
$ {452}_{+30}^{-29} $
$ {408}_{+51}^{-44} $
$ {353}_{+49}^{-49} $
$ 56 $
Tab.2Physical parameters of human body
Fig.2Generalized material density nephogram of flexible joint
Fig.3Design sketch of flexible exoskeleton joint
Fig.4Simulation and verification of SIMP method
Fig.5Stress and deformation nephogram after optimization
Fig.6Structure design of wearable exoskeleton
Fig.7Design of hip-joint assist mechanism
Fig.8Cable displacements and joint angles for hip joint and knee joint force assistance
Fig.9Wearing effect of exoskeleton system
Fig.10Stress equivalent sample and test data
Fig.11Test while wearing knee-joint protection exoskeleton
Fig.12Relationship between knee-joint rotation and exo-joint strain
序号
测试条件
ε1 /10?6
P /N
1
腿环接触涤纶衣物
1066
52.72
2
黏接硬橡胶接触衣物，松束缚
1150
56.87
3
黏接硬橡胶，中等束缚
1445
71.46
4
黏接硬橡胶，紧束缚
2083
103.00
Tab.3Load results of exoskeleton joint under different conditions
Fig.13Output current and rope ends displacement before and after adding one-side load
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