A control-oriented dynamic model for sit-to-stand motion with fixed support

Abstract

Establishing a validated dynamic model for human daily life movements is a crucial step in designing assistive devices for people with disabilities. Sit-to-stand motion with fixed support is a frequent task in daily life, and in order to provide assistive devices for such task, a validated dynamic model is required. The main contribution of this paper is to present a multi-body dynamic model of sit-to-stand motion with fixed support and to validate the model with experimental results from human joint tracking and force sensors on the support. Dynamic equations governing the body motion during sitto-stand are derived using a multi-body model interconnected to the fixed support through handling muscle force. It is hypothesized that sit-to-stand motion is performed by optimized support force and control effort by the subject. In this regard, the human body attempt for sit-to-stand motion is distributed among various joints such that an energy-based cost function is optimized, and at the same time, the choice of biomechanical actuation is prioritized through adjusting various weighting coefficients in the objective function. The limitations on joint torques and the hand force are included as inequality constraints in the optimization problem. The developed multi-body dynamic model is evaluated through comparison between the computed support force (theoretical) and the measured force (experimental) obtained from a fixed support equipped with three-axis force sensors. The proposed dynamic model uses the visual data that are recorded to track the skeleton configuration of the subjects as the desired trajectory to follow by the controller. A set of experimental data from five healthy subjects is obtained, and the results show acceptable agreement between simulation and experimental results. The results suggest energy-based optimization solution can be considered as a valid approach is multi-body dynamic modelling of sit-to-stand task.

Modeling and control of the linear actuator for the lower limb rehabilitation device

“…Applying the Lagrange equation with q i = θ i as the rotation angle at the joints, and Q i as the torque at the joint axes, the dynamic equations at the following stages are obtained 30,31 :…”

“…The total kinetic and potential energy of the model is calculated as follows: Substitute K 1 , K 2 , K 3 and P 1 , P 2 , P 3 from equations (12), (16), (20), (13), (17), (21) into (22): Applying the Lagrange equation with q i = θ i as the rotation angle at the joints, and Q i as the torque at the joint axes, the dynamic equations at the following stages are obtained 30,31 : The dynamic equations of each joint, written in matrix form as follows: Equation (25) can be expressed in the following general form: where…”

A Bond Graph Model for the Estimation of Torque Requirements at the Knee Joint During Sit-to-Stand and Stand-to-Sit Motions

“…This work focuses on the modeling of SiTSt and StTSi motions for the development of a knee assistance device for elderly people. Different models of SiTSt motion have been developed by various researchers which are either based on the experimental acquisition of data by optoelectronic systems, force plates, etc., or optimization of cost functions subjected to some kinematic constraints or energy-based formulations [3]. In comparison with the SiTSt motion, fewer studies have been carried out for StTSi motion.…”