Backpacks are essential for travel but carrying a load during a long journey can easily cause muscle fatigue and joint injuries. Previous studies have suggested that suspended backpacks can effectively reduce the energy cost while carrying loads. Researchers have found that adjusting the stiffness of a suspended backpack can optimize its performance. Therefore, this paper proposes a stiffness-adjustable suspended backpack; the system stiffness can be adjusted to suitable values at different speeds. The stiffness of the suspended backpack with a 5-kg load was designed to be 690 N/m for a speed of 4.5 km/h, and it was adjusted to 870 and 1050 N/m at speeds of 5.5 and 6.5 km/h, respectively. The goal of this study was to determine how carrying a stiffness-adjustable suspended backpack affected performance while carrying a load. Six healthy participants participated in experiments where they wore two backpacks under three conditions: the adjustable-stiffness suspended backpack condition (S_A), the unadjustable-stiffness suspended backpack condition (S_UA), and the ordinary backpack condition (ORB). Our results showed that the peak accelerations, muscle activities, and peak ground reaction forces in the S_A condition were reduced effectively by adjusting the stiffness to adapt to different walking speeds; this adjustment decreased the metabolic cost by 4.21 ± 1.21% and 2.68 ± 0.88% at 5.5 km/h and 4.27 ± 1.35% and 3.38± 1.31% at 6.5 km/h compared to the ORB and S_UA, respectively.
Upper limb paralysis and movement disorders resulting from neurologic injuries can be treated with an upper limb exoskeleton robot that assists with movement retraining. Cable-driven exoskeletons have been widely studied because of their lightness, compact structure, low cost, and long-distance power transmission. However, the problems of shoulder squeeze force and system stability have not been solved. In this article, we present a prototype parallel cable-driven shoulder mechanism with series springs. The theoretical analysis suggests that the stability of the mechanism is improved compared with that of the previous mechanism, and the effects of stiffness, upper limb weight, and mechanism parameters on the shoulder joint extrusion pressure are analyzed by simulation and experimental results. The results show that this mechanism plays an important role in reducing or eliminating the shoulder squeeze pressure and improving the stability of the mechanism. Moreover, the mechanism has good portability and can be combined with other exoskeletons to facilitate various robot-assisted upper limb rehabilitation training.
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