Hip–Knee Coupling Exoskeleton With Offset Theory for Walking Assistance

Abstract

To alleviate the influence of aging on the elderly, a hip–knee coupling exoskeleton with offset theory is designed in this article to improve people’s athletic ability. With the novel design, the unique application strategy of the offset principle for hip and knee joints is developed, and a hip–knee coupling mechanism is proposed to solve the discrete power assistance problem for the knee joint. To acquire the success of the design, the mathematical model of the coupling mechanism is established to optimize the load environment of the exoskeleton system, and furthermore, an algorithm adapted to human movement is proposed to determine the monotonicity of the cam profiles. For the selection of the elastic parameters in the coupling mechanism, the sensitivity condition is proposed, and the human–machine interaction model of the KESM is further established. A man–machine coupling model was used to verify the scientificity of the exoskeleton design, and the comparison between the joint powers with or without exoskeleton indicated that the exoskeleton theoretically saved at least 20% of the human body’s energy.

Cooperativity Model for Improving the Walking-Assistance Efficiency of the Exoskeleton

“…Due to the lack of objective comparative conditions among all existing exoskeletons, the effect of the cooperativity model on the exoskeleton was indicated by comparing the walking-assistance efficiencies of the exoskeletons with the same structure but with different elastic parameters of the energy storage components. The dynamic simulations showed that there exists and only one set of elastic parameters that can be set to obtain the maximum value of the walking-assistance efficiency, which is in line with the judgment of references [ 3 , 25 ] and the maximum values were 17.95% and 18.51% respectively for the hip joint and knee joint, which are generally higher than the previous lower-limb-assistant exoskeleton [ 3 , 4 , 23 , 24 , 30 , 31 ]. In addition, to actual test the walking-assistance efficiency of the exoskeleton with the optimal parameter combinations, the respiratory metabolisms with and without the exoskeleton were compared to calculate the efficiency, in which there is a regularity between the changes of the metabolic gases [ 22 , 24 , 33 ], and the exoskeleton provided the average walking-assistance efficiency of 14.45% for more than 80% of the subjects, which slightly higher than the previous-exoskeleton tests [ 22 , 24 , 33 ].…”

“…The calculation results of each curve are shown in Figure 13 , and the walking-assistance efficiencies were 5.41%, 9.02%, 16.88%, 18.51%, and 16.72%, respectively, in which the KESM with the optimal parameter combinations exhibited the highest walking-assistance efficiency [ 3 , 25 ]. The walking-assistance efficiencies of simulation are generally higher than the previous lower-limb-assistant exoskeleton [ 3 , 4 , 23 , 24 , 30 , 31 ] but far less than the theoretical limit of walking-assistance, which is 66.72%.…”

“…The knee joint exhibits variable stiffness characteristics throughout the gait cycle [ 30 , 31 ], so discrete assistance measures should be implemented for the knee joint. During the swing period, the knee energy storage mechanism (the KESM in Figure 2 a) should not significantly interact with the knee joint and during the support period, the negative torque should be provided for the knee joint between nodes C and D, and the positive torque should be provided between nodes D and E. From the energy perspective, the joint negative work is recovered and compensated for the joint positive work ( Figure 2 b).…”

“…To ensure the centralized completion of the test, two sets of measurement equipment were used, but to avoid measurement errors, a subject could only use one set of the respiratory metabolizer ( Figure 14 a) and exoskeleton ( Figure 14 b) to complete his test. To avoid the psychological fluctuations caused by their inadaptation with the exoskeleton, the subjects were required to conduct a half-hour adaptation training after adjusting the exoskeleton to their best subjective experience according to their physiological state [ 12 , 23 , 24 , 30 , 31 ].…”

“…5, the heart rate of most subjects could be kept below 150 bpm, which shows that the tests in this paper ensure the validity of the indirect metabolic measurement. In addition, the subjects in the first group had lower heart rates in the tests with the exoskeleton than without the exoskeleton, while most subjects in the second group had higher heart rates in the tests with the exoskeleton than without the exoskeleton, which may be related to the psychological factors during the test environment, such as the nervousness, indicating that the adaptive training of the subjects in the second group did not achieve the desired effect or their interactions with the tester were not smooth and relaxed in the test [ 30 , 31 ].…”