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Research Papers

# A Portable and Automated Postural Perturbation System for Balance Assessment, Training, and Neuromuscular System Identification

[+] Author and Article Information
Albert H. Vette1

Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, ON, M5S 3G9, Canada; Toronto Rehabilitation Institute, Lyndhurst Centre, 520 Sutherland Drive, Toronto, ON, M4G 3V9, Canadaa.vette@utoronto.ca

Egor Sanin

Toronto Rehabilitation Institute, Lyndhurst Centre, 520 Sutherland Drive, Toronto, ON, M4G 3V9, Canada; Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, ON, M5S 3G8, Canadaegor.sanin@utoronto.ca

Abdulkadir Bulsen

Toronto Rehabilitation Institute, Lyndhurst Centre, 520 Sutherland Drive, Toronto, ON, M4G 3V9, Canadabulsen.abdul@torontorehab.on.ca

Alan Morris

Toronto Rehabilitation Institute, Lyndhurst Centre, 520 Sutherland Drive, Toronto, ON, M4G 3V9, Canadaalan.morris@utoronto.ca

Kei Masani

Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario, M5S 3G9, Canada; Toronto Rehabilitation Institute, Lyndhurst Centre, 520 Sutherland Drive, Toronto, ON, M4G 3V9, Canadak.masani@utoronto.ca

Milos R. Popovic

Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario, M5S 3G9, Canada; Toronto Rehabilitation Institute, Lyndhurst Centre, 520 Sutherland Drive, Toronto, ON, M4G 3V9, Canadamilos.popovic@utoronto.ca

1

Corresponding author.

J. Med. Devices 2(4), 041007 (Nov 25, 2008) (9 pages) doi:10.1115/1.3026558 History: Received February 29, 2008; Revised October 16, 2008; Published November 25, 2008

## Abstract

To date, a postural perturbation system capable of generating position-, velocity-, and force-controlled perturbations while being portable and suitable for use during various postural scenarios does not exist. Therefore, the purpose of the present study was to design, develop, and test a portable and automated postural perturbation system (PAPPS) that can be used to measure and train postural reactions during sitting, standing, and treadmill walking. The core component of the PAPPS was a linear actuator that provides horizontal perturbations. The actuator could generate arbitrary displacement, velocity, or force perturbations as a function of time. In addition, the PAPPS was able to measure the actuator’s displacement, velocity, and load, which could be used to study postural perturbation responses. The height at which the PAPPS was delivering the perturbations could be easily adjusted to allow for different subject/patient anthropometrics and a wide range of postural scenarios such as sitting, standing, and treadmill walking. The PAPPS generated a peak displacement of $0.6m$, a peak velocity of $0.5m∕s$, and a peak force of $600N$, which is more than sufficient to elicit high intensity postural perturbations. Multiple and nested safety circuits have been implemented into the PAPPS to ensure the safety of the subjects/patients during experiments and/or training. To evaluate the accuracy and repeatability of the PAPPS during position-, velocity-, and force-controlled perturbations, experiments were conducted using sinusoidal, impulse, and ramp profiles as a function of time. Highly sensitive displacement and force sensors that were external to the PAPPS were used to determine the accuracy and repeatability of the proposed device. In addition, a case study was performed to demonstrate the performance of the PAPPS during pseudorandom sinusoidal perturbations that were applied to a healthy individual during sitting. The accuracy and repeatability tests suggest that the PAPPS can generate reliable and high-precision displacement, velocity, and force perturbations. Potential applications of this system include, but are not limited to (1) studies of postural response to various perturbation types and profiles in diverse subject populations during sitting, standing, and treadmill walking, and (2) training of postural balance in diverse patient populations during sitting, standing, and treadmill walking.

###### FIGURES IN THIS ARTICLE
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Copyright © 2008 by American Society of Mechanical Engineers
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## Figures

Figure 1

Diagram of the PAPPS hardware configuration. The actuator was controlled using a custom software interface developed in LabVIEW, a Xenus digital servo amplifier, and a Xenus edge filter.

Figure 2

Graphical user interface for controlling the PAPPS. After having selected the desired perturbation unit (actuators 1–8), the user could choose from different perturbation types and profiles. In addition, any arbitrary profile using a single column text file could be uploaded. During the perturbations, the measured position and velocity, the current commands to the servo amplifier, and the measured force were recorded for all active actuators and could be monitored (one actuator at a time).

Figure 3

Schematic, photograph and potential daisy chain configuration of the PAPPS (actuator and frame). The frame had a height of 65in.(165.10cm), a length of 36.75in.(93.35cm), and a width of 29in.(73.66cm). It was kept stationary during actual perturbations using friction: a wooden platform (10) was fixed onto the frame base and a large mass (∼60kg) was placed on top of it.

Figure 4

Sinusoidal displacement perturbations with amplitudes and frequencies listed in Table 1. The bold gray lines mark the desired position and the thin black lines mark the actual position of the actuator. (a) and (c) show the internal measurements and (b) and (d) show the external measurements.

Figure 5

Gaussian and ramp displacement perturbations with amplitudes, variances, and rise times described in Table 1. The bold gray lines mark the desired position and the thin black lines mark the actual position of the actuator. The left subplots (a) show the internal measurements and the right subplots (b) show the external measurements.

Figure 6

Sinusoidal velocity perturbations with amplitudes and frequencies listed in Table 1. The bold gray lines mark the desired velocity and the thin black lines mark the actual velocity of the actuator. (a) and (c) show the internal measurements and (b) and (d) show the external measurements.

Figure 7

Gaussian and ramp velocity perturbations with amplitudes, variances, and rise times described in Table 1. The bold gray lines mark the desired velocity and the thin black lines mark the actual velocity of the actuator. The left subplots (a) show the internal measurements and the right subplots (b) show the external measurements.

Figure 8

Force perturbations with amplitudes, frequencies, variances, and rise times listed in Table 1. The bold gray lines mark the desired force and the thin black lines mark the measured force on the system. (a), (b), and (c) show the sinusoidal, the Gaussian, and the ramp perturbations, respectively.

Figure 9

Actuator displacement (top row), average load cell force (second row), average trunk acceleration (third row), average ES-L3 activity (fourth row), and raw ES-L3 activity (bottom row) during pseudorandom sinusoidal displacement perturbations. The dotted lines mark instants in time at which the advance of trunk acceleration and ES-L3 activity with respect to actuator position and force can be easily seen.

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