Estimation Of Joint Stiffness Research Articles

How Well Do Commonly Used Co-contraction Indices Approximate Lower Limb Joint Stiffness Trends During Gait for Individuals Post-stroke?

Muscle co-contraction generates joint stiffness to improve stability and accuracy during limb movement but at the expense of higher energetic cost. However, quantification of joint stiffness is difficult using either experimental or computational means. In contrast, quantification of muscle co-contraction using an EMG-based Co-Contraction Index (CCI) is easier and may offer an alternative for estimating joint stiffness. This study investigated the feasibility of using two common CCIs to approximate lower limb joint stiffness trends during gait. Calibrated EMG-driven lower extremity musculoskeletal models constructed for two individuals post-stroke were used to generate the quantities required for CCI calculations and model-based estimation of joint stiffness. CCIs were calculated for various combinations of antagonist muscle pairs based on two common CCI formulations: Rudolph et al. (2000) (CCI1) and Falconer and Winter (1985) (CCI2). CCI1 measures antagonist muscle activation relative to not only total activation of agonist plus antagonist muscles but also agonist muscle activation, while CCI2 measures antagonist muscle activation relative to only total muscle activation. We computed the correlation between these two CCIs and model-based estimates of sagittal plane joint stiffness for the hip, knee, and ankle of both legs. Although we observed moderate to strong correlations between some CCI formulations and corresponding joint stiffness, these associations were highly dependent on the methodological choices made for CCI computation. Specifically, we found that: (1) CCI1 was generally more correlated with joint stiffness than was CCI2, (2) CCI calculation using EMG signals with calibrated electromechanical delay generally yielded the best correlations with joint stiffness, and (3) choice of antagonist muscle pairs significantly influenced CCI correlation with joint stiffness. By providing guidance on how methodological choices influence CCI correlation with joint stiffness trends, this study may facilitate a simpler alternate approach for studying joint stiffness during human movement.

A geometric framework for the estimation of joint stiffness of the human wrist.

Estimating joint stiffness is of paramount importance for studying human motor control and for clinical assessment of neurological diseases. Usually stiffness estimation is performed using cumbersome instrumentations (e.g. robots), and by approximating robot joint angles and torques to the human ones. This paper proposes a methodology and an experimental setup to measure wrist joint stiffness in unstructured environments, with the twofold aim of: 1) providing a geometric framework in order to derive angular displacements and torques at the wrist Flexion/Extension (FE) and Radial/Ulnar Deviation (RUD) axes of rotation, using a subject specific kinematic model; 2) suggesting an experimental setup made of two portable sensors for motion tracking and one load cell, to allow for measurements in out-of-the-lab scenarios. We tested our method on a hardware mockup of wrist kinematics, providing a ground truth for estimated angles and torques at FE and RUD joints. The experimental validation showed average absolute errors in FE and RUD angles of 0.005 rad and 0.0167 rad respectively, and an average error of FE and RUD torques of 0.006 Nm and 0.003 Nm.

SEISMIC VULNERABILITY OF FLAT PLATE COLUMN JOINT WITH OUT SLAB SHEAR REINFORCEMENT

During an earthquake, a brittle punching failure can arise in flat plate-column connections due to poor transfer capacity of shearing forces and unbalanced moments. To increase the shear capacity of the slab, various types of shear reinforcement can be used in the slab around the connection. The aim of the project is to study the response of slab column connections containing without slab shear reinforcement when subjected to combined gravity and cyclic lateral loading. At first a calibration model was developed to simulate the tested flat plate-column joint using finite element analysis program MASA. This model was used to predict the load displacement behaviour. The predicted behaviour was compared with the observed behaviour as reported by James Lee & Ian Robertson (Ref.4). The comparison showed that the model predicts the load level excellently but significantly over estimates the stiffness of the joint compared to that observed by James Lee & Ian Robertson. Since the present study is to compare the relative behaviour of slab-column joints provided without slab shear reinforcement, the error in the estimation of joint stiffness will not alter the comparative conclusions drawn. Thus, the developed model was validated for application to various types of column slab connection behaviour.

1P1-G10 粗いEMG情報を用いて関節剛性を表現するマスタースレーブシステムの提案

In this paper, we propose a method, how to estimate the joint stiffness by using the posture of human body and surface EMG. In general, direct measurement of the joint stiffness is difficult due to the inner information. We used human posture and coarse quantization EMG information for estimation. As the result, the rough estimation of joint stiffness can be achieved by posture and strength of the surface EMG.

Estimation of Joint Stiffness Using Instantaneous Loads via an Electromyogram and Application to a Master–Slave System with an Artificial Muscle Manipulator

Master–slave systems and human-assisted systems in which robots can work together with humans have been widely developed. Such systems are necessary to communicate human intentions to a robot. Therefore, it is important for these systems to be able to estimate human joint characteristics such as torque, position and stiffness. In this context, we focus on the myoelectric (ME) potential. In many previous studies, an electric motor has been used as an actuator, and the torque and position are estimated from the ME potential. However, the joint stiffness of humans has not been studied extensively. In this study, we propose a method to estimate the stiffness of the human elbow by using antagonistic muscles when an instantaneous load is applied. Furthermore, we apply our method to a 1-d.o.f. manipulator with an artificial muscle. In the case of eccentric contraction, it has been shown that the stiffness of a joint can be estimated solely by an electromyogram of the triceps. Then, the stiffness and angle control of the artificial muscle manipulator that used it as the slave side is proposed. Furthermore, the estimated joint stiffness is set as a desired value for joint stiffness control of the artificial muscle manipulator. Experimental results of stiffness control indicate that the angle and the stiffness of the 1-d.o.f. artificial muscle manipulator can be adequately controlled for a master–slave system. Safer remote control systems can be developed by using this system.