Abstract
Modern assistive devices are very sophisticated systems with multiple degrees of freedom. However, an effective and user-friendly control of these systems is still an open problem since conventional human-machine interfaces (HMI) cannot easily accommodate the system’s complexity. In HMIs, the user is responsible for generating unique patterns of command signals directly triggering the device functions. This approach can be difficult to implement when there are many functions (necessitating many command patterns) and/or the user has a considerable impairment (limited number of available signal sources). In this study, we propose a novel concept for a general-purpose HMI where the controller and the user communicate bidirectionally to select the desired function. The system first presents possible choices to the user via electro-tactile stimulation; the user then acknowledges the desired choice by generating a single command signal. Therefore, the proposed approach simplifies the user communication interface (one signal to generate), decoding (one signal to recognize), and allows selecting from a number of options. To demonstrate the new concept the method was used in one particular application, namely, to implement the control of all the relevant functions in a state of the art commercial prosthetic hand without using any myoelectric channels. We performed experiments in healthy subjects and with one amputee to test the feasibility of the novel approach. The results showed that the performance of the novel HMI concept was comparable or, for some outcome measures, better than the classic myoelectric interfaces. The presented approach has a general applicability and the obtained results point out that it could be used to operate various assistive systems (e.g., prosthesis vs. wheelchair), or it could be integrated into other control schemes (e.g., myoelectric control, brain-machine interfaces) in order to improve the usability of existing low-bandwidth HMIs.
Highlights
An ideal human-machine interface (HMI) should allow a consistent, intuitive and simple control of a multi-function system with minimal user training
We have demonstrated a proof of concept of a novel HMI system (EMI) that can increase the effective number of functions a user can control without concomitantly increasing the number of command signals he/she needs to generate
The HMI have a general applicability and the current study demonstrated how it could be used for controlling a multi-grasp prosthetic hand in a closed-loop manner
Summary
An ideal human-machine interface (HMI) should allow a consistent, intuitive and simple control of a multi-function system with minimal user training. It should integrate a feedback channel informing the user about the state of the device, thereby closing the control loop. For example, can implement more than 10 grip types [6,7], while some arm prostheses [8] replicate closely the full kinematic chain of the human arm (e.g., 18 out of 22 DoFs) These designs demonstrate that various technological challenges (size, power, many DoFs) are being successfully overcome, but the user-friendly control of these complex devices still remains an open problem
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