RESUMO
This article reports on an experiment that studied the critical angular clamping speeds for fasteners using the Design of Experiments (DOE) methodology and Analysis of Variance (ANOVA). The study aimed to investigate the stick-slip phenomenon, a critical factor limiting the angular speed. The stick-slip was measured using the stick-slip factor, which is defined as the ratio of stick-slip chattering amplitude to frequency. The investigation focused on the factors that affect the stick-slip factor, torque, and clamping force (preload): friction coefficient, clamping angular velocity, cathodic electrodeposition, and hardness of the bolthead bearing plate. Automated predictive algorithms can utilize the data collected from this study to prevent the occurrence of the stick-slip phenomenon in screw clamping processes.
RESUMO
Manual wheelchair propulsion is known to be inefficient and causes upper extremity pain, fatigue, and injury. Power-assisted wheelchairs can mitigate these effects through motors that reduce users' effort and load during propulsion. Among the different control strategies proposed to govern the user-wheelchair interaction, impedance control-based ones appear to be the most natural and effective. It can change the apparent dynamical properties of the wheelchair, particularly mass and friction, and automatically compensate for external disturbances such as terrain conditions. This study investigates the advantages and disadvantages of this control strategy employing predictive simulations of locomotion with power-assisted wheelchairs in different scenarios. The simulations are generated using a biomechanically realistic model of the upper extremities and their interaction with the power-assisted wheelchair by solving an optimal control problem. Investigated scenarios include steady-state locomotion vs. a transient maneuver starting from rest, movement on a ramp vs. a level surface, and different choices of reference model parameters. The results reveal that the investigated impedance control-based strategy can effectively reproduce the reference model and reduce the user's effort, with a more significant effect of inertia in the transient maneuver and of friction in steady-state locomotion. However, the simulations also show that imposing a first-order, linear reference model with constant parameters can produce disadvantageous locomotion patterns, particularly in the recovery phase, leading to unnecessary energy dissipation and consequent increase in energy consumption from the batteries. These observations indicate there is room for improvement, for instance, by exploring energy regeneration in the recovery phase or by switching reference model nature or parameters along the cycle. To the best of our knowledge, this is the first investigation of impedance control-based strategies for power-assisted wheelchairs using predictive simulations and a realistic, nonlinear model of the user-wheelchair system.