Ambulatory Estimation of Center of Mass Displacement During Walking

Abstract

The center of mass (CoM) and the center of pressure (CoP) are two variables that are crucial in assessing energy expenditure and stability of human walking. The purpose of this study is to estimate the CoM displacement continuously using an ambulatory measurement system. The measurement system consists of instrumented shoes with 6 DOF force/moment sensors beneath the heels and the forefeet. Moreover, two inertial sensors are rigidly attached to the force/moment sensors for the estimation of position and orientation. The estimation of CoM displacement is achieved by fusing low-pass filtered CoP data with high-pass filtered double integrated CoM acceleration, both estimated using the instrumented shoes. Optimal cutoff frequencies for the low-pass and high-pass filters appeared to be 0.2 Hz for the horizontal direction and 0.5 Hz for the vertical direction. The CoM estimation using this ambulatory measurement system was compared to CoM estimation using an optical reference system based on the segmental kinematics method. The rms difference of each component of the CoM displacement averaged over a hundred trials obtained from seven stroke patients was ( 0.020 +/-0.007 ) m (mean +/- standard deviation) for the forward x-direction, ( 0.013 +/-0.005) m for the lateral y-direction, and ( 0.007 +/-0.001) m for the upward z-direction. Based on the results presented in this study, it is concluded that the instrumented shoe concept allows accurate and continuous estimation of CoM displacement under ambulatory conditions.

COM motion estimation of a biped robot based on kinodynamics and torque equilibrium

“…Equation (14) is utilized in a different form in several works [13][14][15]20,21,23] by interposing ZMP as…”

“…For quasi-static motions, this is directly available to estimate COM motion. [20,21] For faster motions, Brodie et al [22] and Schepers et al [23] proposed a complementary filter that combines the dynamics of COM for high-frequency domain with low-passfiltered ZMP. It still has an uncertainty in the height of COM.…”

“…[9,10,[16][17][18][19][20][21][22][23] The most commonly used method in those fields is to compute it from the forward kinematics and the mass property based on its mathematical definition. [9][10][11][12][13]16,17,19] However, it is always a problem how to acquire the mass property of an individual robot or human subject.…”

“…[13][14][15] It coincides with the ground projection of COM in quasi-static motions, so that it is offset-free in horizontal direction. [20][21][22][23] The problem of this idea is that it has an uncertainty in the height of COM. The goal of this paper is to propose an accurate COM motion estimation technique for a biped robot.…”

Subject-Specific Center of Mass Estimation for In-Home Rehabilitation – Kinect-Wii Board vs. Vicon-Force Plate

“…Human static stability while standing is dependent on the relative position of the ground projection of the center of mass (CoM) to the support polygon described by the subject's feet. The most common methods for CoM estimation require either knowledge of the subject's pose, or measurement of his center of pressure (CoP) [2], [3]. In both cases high-end equipment is required.…”