A methodology for dynamic calibration of inertial dynamometers for wheelchairs

Abstract

Every day, wheelchair users face countless obstacles that make their social inclusion a real challenge. In this way, it is important that assistive technologies be constantly developed and improved. An example is the dynamometer, which helps in training to characterize the performance of the wheelchair user. In this work, we present a methodology for the dynamic calibration of an inertial dynamometer for wheelchair users, which aims to assist in the rehabilitation and to enable them to perform day-to-day activities independently. The dynamometer is placed on a structure elevated in relation to the ground, at a known height. At the upper end, a wire is attached to the dynamometer cylinder and at the lower end, a known weight is used to enforce acceleration on the cylinder. The wheelchair is placed on top of the cylinder with known different weights corresponding to the user's weight for each repetition of the experiment. The wire is then wrapped around the cylinder and the object is dropped freely, rotating the cylinder. The measurement of the system acceleration is given by an encoder. Data collected in the tests enable to get the system inertial characteristics for each applied weight, allowing to set calibration curve and to evaluate the performance when the propulsion in the dynamometer is imposed by the wheelchair user.  This work describes the methodology proposed for calibrating the complete device allowing the quantification of measured values such as power, torque and speed imposed by the user. The calibration steps can be easily reproduced at a low cost and very good performance.