Automatic Electromechanical Perturbator for Postural Control Analysis Based on Model Predictive Control

Abstract

Objective clinical analyses are required to evaluate balance control performance. To this outcome, it is relevant to study experimental protocols and to develop devices that can provide reliable information about the ability of a subject to maintain balance. Whereas most of the applications available in the literature and on the market involve shifting and tilting of the base of support, the system presented in this paper is based on the direct application of an impulsive (short-lasting) force by means of an electromechanical device (named automatic perturbator). The control of such stimulation is rather complex since it requires high dynamics and accuracy. Moreover, the occurrence of several non-linearities, mainly related to the human–machine interaction, signals the necessity for robust control in order to achieve the essential repeatability and reliability. A linear electric motor, in combination with Model Predictive Control, was used to develop an automatic perturbator prototype. A test bench, supported by model simulations, was developed to test the architecture of the perturbation device. The performance of the control logic has been optimized by iterative tuning of the controller parameters, and the resulting behavior of the automatic perturbator is presented.

Contact force regulation in physical human-machine interaction based on model predictive control

“…10, continuous red line). The HIL's FID and TAE of the most accurate force profile obtained in Pacheco et al [37] are about [−15; 24]%, compared to this paper in which they are about [−0.56; 12]%. In the latter, the apparent high value of TAE is mainly due to the non-instantaneous falling edge of the perturbations.…”

“…• Hardware-in-the-loop (HIL), in which a dedicated test bench, presented in [37] and depicted in Fig. 4, is employed to assess the performance of the perturbation device in a controlled environment.…”

“…The achieved HIL results can be compared to the force profile (rectangular wave of 50 N, 250 ms) obtained with the previous version of the control logic based on a hybrid force/speed control architecture tested in HIL [37]. As highlighted in Fig.…”

“…Therefore, by reducing the duration, the FID increases from 0.19% (150 ms) to −1.3% (100 ms) to 5.2% (50 ms), while TAE increases from 15% (150 ms) to 19% (100 ms) to 31% (50 ms). However, maintaining the same optimized tuning parameters avoids the large overshoot highlighted in the short-lasting force profile in Pacheco et al [37], which could be unsafe for the patient.…”

“…The system consists of an electric actuator and a hybrid force/speed control architecture. Previous MIL and HIL tests highlighted the adequate dynamic performance of the perturbation device, with some limitations in the accuracy of impulse and force profile tracking [37]. The switching behavior of the proposed control logic led to an undesired delay between human-device contact and the actual control of the force signal.…”