Evaluation of a smartphone platform as a wireless interface between tongue drive system and electric-powered wheelchairs

Abstract

Tongue drive system (TDS) is a new wireless assistive technology (AT) for the mobility impaired population. It provides users with the ability to drive powered wheelchairs (PWC) and access computers using their unconstrained tongue motion. Migration of the TDS processing unit and user interface platform from a bulky personal computer to a smartphone (iPhone) has significantly facilitated its usage by turning it into a true wireless and wearable AT. After implementation of the necessary interfacing hardware and software to allow the smartphone to act as a bridge between the TDS and PWC, the wheelchair navigation performance and associated learning was evaluated in nine able-bodied subjects in five sessions over a 5-week period. Subjects wore magnetic tongue studs over the duration of the study and drove the PWC in an obstacle course with their tongue using three different navigation strategies; namely unlatched, latched, and semiproportional. Qualitative aspects of using the TDS-iPhone-PWC interface were also evaluated via a five-point Likert scale questionnaire. Subjects showed more than 20% improvement in the overall completion time between the first and second sessions, and maintained a modest improvement of ∼9% per session over the following three sessions.

Figures

Fig. 1

TDS–iPhone–PWC operating diagram: TDS headset communicates with a PC through a wireless USB dongle during calibration and training steps. For normal operation, the training results are wirelessly transferred from the PC to the iPhone via the TDS–iPhone–PWC interface, through which the iPhone also receives magnetic sensor raw data from the TDS headset.

Fig. 2

Connecting TDS to PWC via iPhone: (a) standard PWC controller for a Pride Q6000 PWC, known as the Enhanced Display, was connected to the TDS–iPhone–PWC interface via its DB-9 connector. (b) All the necessary components to drive the PWC, including a head-operated emergency stop switch, mounted on the PWC headrest, as a safety measure. (c) Utilized connections at the bottom of the Enhanced Display.

Fig. 3

TDS–iPhone–PWC hardware components consisting of (a) TDS headset, (b) wireless control unit, (c) wireless USB transceiver dongle, (d) a pair of magnetic sensor modules on each side of the headset supported by a pair of goosenecks for positioning, (e) magnetic tongue barbell, (f) TDS–iPhone–PWC interface, and (g) hardwired data transfer cable for iPhone.

Fig. 4

TDS–iPhone–PWC interface block diagram.

Fig. 5

(a) Recommended TDS command positions in the mouth for four directional commands and the tongue resting position as the neutral command. (b) A sample set of training results displayed in the 3-D virtual PCA space.

Fig. 6

iPhone apps created for the TDS–iPhone–PWC interface platform and its evaluation: (a) main TDS screen, (b) folder selection to enter the location and subject information, (c) training and calibration data transfer from PC to iPhone, (d) unlatched mode screen, (e) latched mode screen, (f) semi proportional mode screen, and (g) recalibration and retraining screen for the semiproportional mode.

Fig. 7

Flowchart of the TDS–iPhone–PWC interface applications running on the iPhone.

Fig. 8

(a) Subject wearing the TDS headset and driving the Q6000 PWC, while receiving visual feedback on the TDS–iPhone–PWC interface mounted on the left armrest. (b) Floor plan of the ~50 m obstacle course including the driving trajectory.

Fig. 9

(a) Front and side views of a subject's tongue before piercing, (b) right after tongue piercing with the standard stainless steel barbell, (c) day-3 postpiercing with some tongue swelling, and (d) following exchange in week 4 with the magnetic tongue barbell made of titanium.

Fig. 10

Volumetric measurement of nine subjects' (four males and five females) oral cavities over 4 weeks using the oral plethysmography method to study the tongue swelling.

Fig. 11

TDS–PWC measurement results over five sessions in 5 weeks: (a) completion time; (b) number of navigation errors (collisions, and out of track researcher-issued emergency stops); (c) number of researcher-issued emergency stops per session.

Fig. 12

Summary of the results for six questions related to the TDS–PWC navigation, which were asked from subjects at the end of each session.