Design of a Minimally Actuated Lower Limb Exoskeleton with Mechanical Joint Coupling

Powered lower limb exoskeletons have traditionally used four or more powered joints to provide ambulation assistance for individuals with spinal cord injury.Exoskeletons with numerous powered joints commonly lost some excellent features of passive orthoses and further decreased utility due to added weight and increased control complexity.This work adopts joints coupling mechanism to design a powered exoskeleton to minimize the number of actuated joints and control complexity.Unlike conventional powered exoskeletons,the joint-coupled-powered exoskeleton only has a single motor-actuated joint for each exoskeleton leg in conjunction with a unique knee coupled system to enable their users to walk,sit,and stand.And two types of joint coupled systems are designed,respectively,hip-knee coupled and knee-ankle coupled.The joint-coupled-powered exoskeleton system allows a single actuator to power the hip motion,and allows activate knee motion through the coupled motions of the hip or ankle.More specifically,when the mechanical coupled system is activated,the knee joint is unlocked,resulting in synchronized hip-knee or ankle-knee flexion and extension.The coupling mechanism is switched on and off at specific phases of the gait(the stance phase and the swing phase)to generate the desired motions.The research work proves that minimal actuated robotic systems with joint coupled could achieve safe and natural walking.

Morphological parameters of both surfaces of coupled joint

Twenty one joints were made with Brazilian tests and each surface was scanned by the Talysurf CLI 2000. Morphological characteristics of joint surface were quantified by statistical and textural parameters. By the contrast of these parameters between both sides of each coupled joint, the following conclusions are drawn. The upper and lower surfaces of coupled joints have approximately equal values of Sp（maximum height of joint surface）, Sa（arithmetic mean height of joint surface） and Sq（root mean square height of joint surface）, but the Ssk（skewness of the height distribution of joint surface） values of the two surfaces of a coupled joint are different, one is positive while the other is negative. The Saj（auto-correlation length） parameter values of both surfaces of each coupled joint are quite close, and the S^（texture aspect ratio） values have the same situation to the Sal parameter, but the same parameters of different surfaces have big differences which illustrates its own characteristics of each joint. The two surfaces of each coupled joint have similar values of θp （mean profile angle） which can be used to deduce the value of θp each other.

Can coordination variability identify performance factors and skill level in competitive sport? The case of race walking

Background:Marginal changes in the execution of competitive sports movements can represent a significant change for performance success.However,such differences may emerge only at certain execution intensities and are not easily detectable through conventional biomechanical techniques.This study aimed to investigate if and how competition standard and progression speed affect race walking kinematics from both a conventional and a coordination variability perspective.Methods:Fifteen experienced athletes divided into three groups(elite,international,and national) were studied while race walking on a treadmill at two different speeds(12.0 and 15.5 km/h).Basic gait parameters,the angular displacement of the pelvis and lower limbs,and the variability in continuous relative phase between six different joint couplings were analyzed.Results:Most of the spatio-temporal,kinematic,and coordination variability measures proved sensitive to the change in speed.Conversely,non-linear dynamics measures highlighted differences between athletes of different competition standard when conventional analytical tools were not able to discriminate between different skill levels.Continuous relative phase variability was higher for national level athletes than international and elite in two couplings(pelvis obliquity—hip flex/extension and pelvis rotation—ankle dorsi/plantarflexion) and gait phases(early stance for the first coupling,propulsive phase for the second) that are deemed fundamental for correct technique and performance.Conclusion:Measures of coordination variability showed to be a more sensitive tool for the fine detection of skill-dependent factors in competitive race walking,and showed good potential for being integrated in the assessment and monitoring of sports motor abilities.

Bearing capacity and failure behavior of disconnectable coupling joint with double row wedges(DCJD)used in the prestressed internal bracing

A disconnectable coupling joint with double row wedges(DCJD)is a crucial component of the prestressed internal bracing in subway foundation pits.However,only a few studies have been conducted on the bearing capacity of the joints;moreover,the yield load and compression stiffness of DCJDs are typically determined from experience.The aim of this study was to quantitatively determine the bearing capacity and propose accurate formulas for calculating the yield load and compression stiffness of DCJDs.Hence,a DCJD was selected from a foundation pit in Beijing,China,and loading experiments were conducted under axial force.Load–displacement and load–strain curves were obtained,and the failure modes of the joint were analyzed.The experimental results were verified through several finite element models.Subsequently,parametric analyses were performed to investigate the effects of the dimensions of the key position on the DCJD’s bearing capacities.Moreover,regression analysis was used to obtain the formulae for estimating the initial compression stiffness and yield load of the DCJD.Finally,the fitting formulae results were compared with the numerical and experimental results.The comparisons showed that the fitting formulae were highly accurate in estimating the bearing capacity of the DCJD.

Research of air-cushion isolation effects on high arch dam reservoir

A three-dimensional （3D） finite element model of air-cushion isolated arch dam is presented with the nonlinear gas-liquid-solid multi-field dynamic coupling effect taken into account.In this model,the displacement formulation in Lagrange method,pressure formulation in Euler method,nonlinear contact model based on Coulomb friction law are applied to the air-cushion,reservoir and contraction joint domain,respectively.The dynamic response of Jinping I arch dam with a height of 305 m is analyzed using the seismic records of the Wenchuan Earthquake in 2008.Numerical results show that the air-cushion isolation reduces significantly the hydrodynamic pressure as well as the opening width for the contraction joints of high arch dam.

Two-dimensional thermoelasticity solution for functionally graded thick beams

Two-dimensional thermoelasticity analysis of functionally graded thick beams is presented using the state space method coupled with the technique of differential quadrature. Material properties vary continuously and smoothly through the beam thickness, leading to variable coefficients in the state equation derived from the elasticity equations. Approximate laminate model is employed to translate the state equation into the one with constant coefficients in each layer. To avoid numerical instability, joint coupling matrices are introduced according to the continuity conditions at interfaces in the approximate model. The differential quadrature procedure is applied to discretizing the beam in the axial direction to make easy the treatment of arbitrary end conditions. A simply-supported beam with exponentially varying material properties is considered to validate the present method. Numerical examples are performed to investigate the influences of relative parameters.