Evaluation of EMG, force and joystick as control interfaces for active arm supports (Epidemiologic Perspectives & Innovations)

Background: The performance capabilities and limitations of control interfaces for the operation of activemovement-assistive devices remain unclear. Selecting an optimal interface for an application requiresa thorough understanding of the performance of multiple control interfaces. Methods: In this study the performance of EMG-, force- and joystick-based control interfaces were assessedin healthy volunteers with a screen-based one-dimensional position-tracking task. The participantshad to track a target that was moving according to a multisine signal with a bandwidth of 3 Hz.The velocity of the cursor was proportional to the interface signal. The performance of the controlinterfaces were evaluated in terms of tracking error, gain margin crossover frequency, informationtransmission rate and effort. Results: None of the evaluated interfaces was superior in all four performance descriptors. The EMG-basedinterface was superior in tracking error and gain margin crossover frequency compared to the forceandthe joystick-based interfaces. The force-based interface provided higher information transmissionrate and lower effort than the EMG-based interface. The joystick-based interface did not present anysignificant difference with the force-based interface for any of the four performance descriptors. Wefound that significant differences in terms of tracking error and information transmission rate werepresent beyond 0.9 and 1.4 Hz respectively. Conclusions: Despite the fact that the EMG-based interface is far from the natural way of interacting with the environment,while the force-based interface is closer, the EMG-based interface presented very similar andfor some descriptors even a better performance than the force-based interface for frequencies below1.4 Hz. The classical joystick presented a similar performance to the force-based interface and holdsthe advantage of being a well established interface for the control of many assistive devices. Fromthese findings we concluded that all the control interfaces considered in this study can be regarded asa candidate interface for the control of an active arm support.