A Cost-Effective Inertial Measurement System for Tracking Movement and Triggering Kinesthetic Feedback in Lower-Limb Prosthesis Users

Abstract

Advances in lower-limb prosthetic technologies have facilitated the restoration of ambulation; however, users of such technologies still experience reduced balance control, also due to the absence of proprioceptive feedback. Recent efforts have demonstrated the ability to restore kinesthetic feedback in upper-limb prosthesis applications; however, technical solutions to trigger the required muscle vibration and provide automated feedback have not been explored for lower-limb prostheses. The study's first objective was therefore to develop a feedback system capable of tracking lower-limb movement and automatically triggering a muscle vibrator to induce the kinesthetic illusion. The second objective was to investigate the developed system's ability to provide kinesthetic feedback in a case participant. A low-cost, wireless feedback system, incorporating two inertial measurement units to trigger a muscle vibrator, was developed and tested in an individual with limb loss above the knee. Our system had a maximum communication delay of 50 ms and showed good tracking of Gaussian and sinusoidal movement profiles for velocities below 180 degrees per second (error < 8 degrees), mimicking stepping and walking, respectively. We demonstrated in the case participant that the developed feedback system can successfully elicit the kinesthetic illusion. Our work contributes to the integration of sensory feedback in lower-limb prostheses, to increase their use and functionality.

Keywords: device development; kinematic feedback; kinesthetic feedback; kinesthetic illusion; lower-limb prostheses; sensory feedback; wearable sensor.

Figure 1

(A) The wireless inertial measurement unit-based system (WIbS) consisted of two of the following: an Arduino Pro Mini microcontroller (center), an inertial measurement unit (bottom right), a Bluetooth radio (top right), a lithium-ion battery, and a boost converter (left of the microcontroller). (B) An enclosure was manufactured for each sensor module to manage wires, improve ergonomics, and fixate the inertial measurement unit.

Figure 2

(A) The participant was shown his unattached prosthesis with the inertial measurement unit (IMU) modules attached proximally and distally of the knee joint. For each segment of the prosthesis, the orientation of the IMU module was calibrated as described in Section 2.1. The participant was informed that movement of the prosthesis, as detected by the wireless modules, was responsible for triggering the vibratory actuator. (B) The participant was unaware, however, that the robotic arm was used instead to provide motion measurements, triggering the vibration motor. The calibrated local coordinate frames and the global coordinate frame are shown within and below the figure, respectively.

Figure 3

The Gaussian profile results for the individual axes of the wireless inertial measurement unit-based system (WIbS), red lines, when compared to those of the commercial inertial measurement unit system (cIMU), blue lines, and the motion capture system, gray lines. The rows show results for individual axes, whereas the columns represent the tested velocities.

Figure 4

The sinusoidal profile results for the individual axes of the wireless inertial measurement unit-based system (WIbS), red lines, when compared to those of the commercial inertial measurement unit system (cIMU), blue lines, and the motion capture system, gray lines. The rows show results for individual axes, whereas the columns represent the tested velocities.

Figure 5

The experienced movement percepts of the participant, as demonstrated by the participant’s intact limb and captured via motion capture. The negative joint angle values (y-axis, in degrees) indicate knee flexion. Only 13 s are shown for the x-axis since the participant did not experience a change in illusion beyond that time frame. The black line is the average of the 16 successful trials, whereas the shaded area depicts the variation across trials (±1 standard deviation band). Note that the maximum standard deviation, within the terminal phase was approximately 6.5 degrees. The participant’s movement percepts can be generally described as an inverted sigmoidal curve.