A Wearable Lower Limb Exoskeleton: Reducing the Energy Cost of Human Movement

Abstract

Human body enhancement is an interesting branch of robotics. It focuses on wearable robots in order to improve the performance of human body, reduce energy consumption and delay fatigue, as well as increase body speed. Robot-assisted equipment, such as wearable exoskeletons, are wearable robot systems that integrate human intelligence and robot power. After careful design and adaptation, the human body has energy-saving sports, but it is an arduous task for the exoskeleton to achieve considerable reduction in metabolic rate. Therefore, it is necessary to understand the biomechanics of human sports, the body, and its weaknesses. In this study, a lower limb exoskeleton was classified according to the power source, and the working principle, design idea, wearing mode, material and performance of different types of lower limb exoskeletons were compared and analyzed. The study shows that the unpowered exoskeleton robot has inherent advantages in endurance, mass, volume, and cost, which is a new development direction of robot exoskeletons. This paper not only summarizes the existing research but also points out its shortcomings through the comparative analysis of different lower limb wearable exoskeletons. Furthermore, improvement measures suitable for practical application have been provided.

Keywords: assisted movement; lower limb exoskeleton; metabolic cost; wearable device.

Figure 1

The periodic movement of lower limb joints. (a) Experimental scene. (b) Gait cycle. (c–e) show the vertical alternating movement of the left and right hips, knees and ankles over a period of 4 seconds. (f–h) show the hip, knee and ankle angles during the gait cycle. (i–k) show the hip, knee and ankle forces during the gait cycle. (l–n) show the hip, knee and ankle moments during the gait cycle. (o–q) show the hip, knee and ankle power during the gait cycle.

Figure 2

Characteristics of wearable exoskeletons.

Figure 3

Multi-joint powered lower limb assisted exoskeleton. (a) University of California, BLEEX [8]. (b) ExoHIKE [48]. (c) ExoClimber [48]. (d) Lockheed Martin, HULC [43]. (e) Naval Academy of Aeronautical Engineering, the third-generation prototypes [50]. (f) East China University of Technology, ELEBOT [52]. (g) University of Tsukuba, HAL-5 [59]. (h) Southwest Jiaotong University, 2012 [63]. (i) Harbin Institute of Technology, 2013 [61]. (j) Beijing University of technology [63]. (k) Harvard University, MJSE [65].

Figure 4

Single-joint powered lower limb assisted exoskeletons. (a) Harvard University, SE [66]. (b) Harvard University, TSE [67]. (c) Achilles exoskeleton [71]. (d) MIT, AAE [72]. (e) MIT, AAE [74]. (f) University of Illinois KFO [69]. (g) University of Michigan, KAFO [70]. (h) Carnegie Mellon University, AE [73]. (i) National Institutes of Health, RETCG [4]. (j) Arizona State University, DCO [68].

Figure 5

Multi-joint passive lower limb assisted exoskeletons. (a) University of Delaware, GBE [79]. (b) MIT, MLE, & SLE [81]. (c) Delft University of Technology, XPED1 & XPED2 [82,83]. (d) Zhejiang University, LEE [84]. (e) Huazhong University of science and technology, WSLEE [85]. (f) University of Ottawa, PWAE [34]. (g) Hebei University of Technology, NNLELE [88]. (h) Beijing University of Aeronautics and Astronautics, PLEE [89]. (i) Queen’s University of Canada, REE [90].

Figure 6

Single-joint passive lower limb assisted exoskeletosn. (a) Delft University of Technology, PHE [91]. (b) Tsinghua University, ES-EXO [93]. (c) Tehran University, UEFH [94]. (d) SLT, Levitation [95]. (e) MIT, Levitation [96]. (f) Chongqing University of Technology, PKAEXO [97]. (g) Hanyang University, M-ICR [98]. (h) Tohoku University, UKE [99]. (i) University of moletuwo, Sri Lanka, PPKE [100]. (j) South China University of Technology, UFLLE [101]. (k) Nanjing Southeast University, WBCAER [102]. (l) North Carolina State University, AAPE [103]. (m) Carnegie Mellon University, UE [104]. (n) University of Ottawa, UAE [105]. (o) University of Ottawa, PAE [106]. (p) Beijing Jiaotong University, PAFE [107].

Figure 7

Multi-joint lower limb assisted exoskeletons. (a) MIT, QPPLEALCW [110]. (b) US Army Natick soldier Center, LBELCAD [112]. (c) MIT, QPLELCA [3]. (d) University of Montpellier, Moonwalker [113]. (e) Yale University, QPCSCKAFO [114]. (f) Hanyang University, HEXAR, Seoul, Korea [116]. (g) Korea Atomic Energy Research Institute, UEEWLCA [118]. (h) Tokyo University of agricultural technology, QPLLEPBWS [119]. (i) Netherlands applied scientific research organization, Exobuddy [120]. (j) Italian Institute of Technology, SWDLLA [121]. (k) Italian Institute of Technology, SALLE [122]. (l) Italian Institute of Technology, SALLE [123]. (m) Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences [124].

Figure 8

Single-joint quasi passive lower limb exoskeletons. (a) Chinese Academy of Science (CAS) [125]. (b) Slovenia, CQPSE [126]. (c) University of Michigan, RoboKnee [127]. (d) Carlton University, QPKEAR [128]. (e) Italian Institute of Technology, ACCKE [130]. (f) Yale University, QPKEGE [132]. (g) Italian Institute of Technology, iT-Knee [133]. (h) Carnegie Mellon University, LTTCKE [134]. (i) Harvard University, QPKEADD [135]. (j) City University of New York, LBKE [5]. (k) Italian Institute of Technology, QPRESA [136]. (l) Harbin Institute of Technology, QPAFWRO [137]. (m) University of Texas, SATQPAE [138]. (n) Ljubljana, Slovenia, CAAE [139].

Figure 9

Classification of wearable lower limb assist exoskeleton.

Figure 10

Relationship between weight and performance evaluation results. (a) maximum load with wearable exoskeleton. (b) the metabolic reduction with wearable exoskeleton, (c) muscle activate rate reduction with wearable exoskeleton, (d) device power for powered and quasi-passive exoskeleton, (e) joint toque reduction with the device, (f) other increment with wearable exoskeleton.