E-Health Telecommunication Systems and Networks, 2013, 2, 65-71
Published Online December 2013 (http://www.scirp.org/journal/etsn)
Open Access ETSN
Biomechanical Signals Human-Computer Interface for
Severe Motor Disabilities
Albano Carrera, Alonso A. Alonso, Ramón de la Rosa, Javier M. Aguiar
Laboratory of Electronics and Bioengineering, Department of Signal Theory, Communications and Telematics Engineering, Higher
Technical School of Telecommunications Engineering, Universidad de Valladolid, Valladolid, Spain
Email: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com
Received July 31, 2013; revised August 30, 2013; accepted September 20, 2013
Copyright © 2013 Albano Carrera et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
A system that allows computer interaction by disabled people with very low mobility and who cannot use th e standard
procedure based on keyboard and mouse is presented. The development device uses the patient’s voluntary biome-
chanical signals, specifically, winks—which constitute an ability that gen erally remains in this k ind of patients—, as in-
terface to control the computer. A prototype based on robust and low-cost elements has been built and its performance
has been validated through real trials by 16 u sers without previous training. The system can be optimized after a learn-
ing period in order to be adapted to every user. Also, good results were obtained in a subjective satisfaction su rvey that
was completed by the users after carrying out the test trials.
Keywords: Man-Machine Systems; Electronics; Medical Rehabilitation; Independent Livin g; Biomedical Engineering
The present paper is placed in the Rehabilitation Tech-
nologies (RT) field, in particular in the human-machine
interfaces’ development and its application to different
systems with the aim of improving the quality of life and
the personal autonomy of the disabled. Specifically, this
work deals with the implementation of a human-com-
puter interface for severe motor disabilities and those
who cannot use the standard ways to control a computer,
mouse and keyboard, due to their disability.
Currently, there are several papers focused on the field
of RT and on the development of adapted interfaces for
the interaction with different devices. These interfaces
should meet a set of requirements, which can be found in
the related scientific literature, to ensure the best per-
formance . Due to the great diversity of interfaces that
can be developed, a preliminary study of adaptation to
the application of interest is necessary. Thus, a revision
of the related scientific literature has been carried out,
and different kinds of interfaces have been found: voice
recognition , video camera-based systems , bio-
electric signals, such as the electromyogram (EMG) or
the electrooculogram (EOG), while performing voluntary
movements , electroencephalogram (EEG) signals ,
residual movement detection withou t utilising bioelectric
signals , inertial sensors  and autonomous interac-
tion after activation . Previous analysis carried out by
the research group  advises and justifies the use of
interfaces based on residual voluntary movement detec-
tion without utilizing bioelectric signals for the tasks of
command detection generated by users with severe motor
Focusing our attention on this kind of human-machine
interfaces, the residual voluntary movement detection
without utilizing b ioelectric signals, a few projects based
on the registration of different gestures or corporal move-
ments can be found: movements of the head , winks
combined with movements of the head , movements
of the tongue , sniffing  and posture changes .
Among the above mentioned options, wink detection has
been considered the most adequate because this ability
prevails in most of the severe motor disability cases and
it is the gesture that interferes less with the normal daily
activity of the subject.
The interfaces mentioned above have been utilised for
the control of RT systems, such as electric wheelchairs
[1,14], surveillance systems  and, also, personal com-
puters . In this paper, the interfaces employed to con-
trol personal computers are of special interest and there
are articles that refer to interfaces that use movements of
A. CARRERA ET AL.
the head , movements of the tongue , inertial sen-
sors , image recognition systems that detect move-
ments of the head , eyes  or body movements ,
bioelectrical signals, such as EMG [18,19], and move-
ments of the head combined with winks . The afore-
mentioned paper presents a system that employs two
different remaining abilities: one of them is the move-
ment of the head to control the mouse. This ability, gen-
erally, does not prevail in severely disabled patients and,
notwithstanding, its use constitutes a greater impediment
for a simultaneous daily activity, while the patient is us-
ing the computer.
This paper presents a computer control system, by
means of a human-machine interface based on residual
movements that do not require bioelectric signals. In or-
der to improve the discussion, this paper has been di-
vided into different sections. The following one presents
the aims set in the research work. Section three intro-
duces the implemented material for the parts of the sys-
tem: interface, processing system and computer. Section
four presents the results and, finally, Section five presents
the conclusions we arrived at, after the development,
implementation and trials performed with the system.
The main objective of the device presented in this paper
is the design and implementation of an augmentative
communication system that would allow a computer
control for severe motor disabilities. Essentially, this
control consists in the handling of the mouse and the
keyboard by means of an adapted human-machine inter-
face, although the system includes additional functions
that have been optimised, such as the adapted wheelchair
driving training or the domotic control.
The human-machine interface to control the system is
based on the detection of user-simple gestures, without
utilising bioelectric signals. Thus, biomechanical signals
would be used to command the device and, specifically,
detecting the user’s voluntary winks.
Very severe motor disabilities preserve certain move-
ment abilities, that the patient can make use of. In most
cases, disabled people can make facial gestures: random
eye movements, blinks and winks. The fact that a system
based on voluntary winks, in which closing the eyelid is
not necessary, should allow the user of the system to
keep on utilising other residual abilities in order to inter-
act with the environment, such as sight, hearing or voice.
This means that a RT system which does not interfere
with the patient’s usual activities is the purpose of our
The global structure of the augmentative communication
system is very simple (Figure 1), as shown in the dia-
gram of the three different parts of the system. First of all,
the set of adapted interfaces developed for computer
control detecting voluntary winks. Secondly, the proc-
essing system in charge of discrimination orders by the
users. Finally, the functions of the computer where the
developed so ft ware runs.
3.1. Adapted Interface
The first part of the equipment is the adapted interface.
This interface, as explained above, is responsible for the
reception of the user’s voluntary winks. For the detection
of these biomechanical signals, the implementation of
different interfaces has been developed by the research
group . The function of the interface chosen is based
on the light reflexion or not, according to a user’s volun-
tary gesture. This task is carried out with a CNY70 de-
vice, which has a light emitter and an infrared phototran-
sistor. The led light emitted reflects on a surface and de-
pending on the nature of the surface the light will find a
reflection or not. In this case, a bicolour adhesive tape
(black and white) on the user’s orbicularis oculi muscle
skin, on the edge of the eye, is used to achieve a correct
performance (Figure 2). The adhesive tape moves when
a voluntary wink is performed, and the consequent move-
ment causes a colour change and, hence, a change on the
output of the device.
Figure 1. Augmentative communication system block diagram.
Open Access ETSN
A. CARRERA ET AL. 67
With the aim of getting the best comfort and user’s
adaptability, the wink detectors were implemented on
conventional glasses and mechanical adjusting elements
to improve the performance were included. The human-
machine interface final aspect is shown in Figure 3.
3.2. Processing System
As the system needs a low computational load, as it only
has two logic sensors with binary output, a microcon-
troller as process device was chosen. Specifically, an
Arduino hardware platform, which implements a micro-
controller and all the additional elements in a commercial
board, was utilised.
Starting with this process device and its free develop-
ment environment, a software algorithm for the detection
of all wink gestures was developed. The gestures to be
detected are: left wink, right wink, eyes closing wink,
consecutive left-right winks and consecutive right-left
winks, an array of possibilities.
The implemented program flowchart (Figure 4) em-
ploys the microcontroller interrupt functions in order to
get the best efficiency in command detection. In order to
avoid fake detections a duration wink timer threshold is
Figure 4 flowchart omits the implicit thresholds in the
detection functions. After the detection of one of the five
patterns defined by the winks combination, the corre-
sponding control command is sent to the computer.
These commands are shown at the bottom of the flow-
chart (“left”, “left + right”, “right + left”, “right” and
“both eyes” action blocks) on a generic form, and differ-
ent actions can be assigned depending on the application
or the system handled.
3.3. Computer. Augmentative Communication
The communication between the personal computer and
the wink detection adapted interface requires the imple-
mentation of specific software that will also be entrusted
the running of the task regarding the augmentative com-
As explained above, this software allows mouse and
keyboard control on a personal computer, it also includes
other modules such as the control of virtual adapted elec-
tric wheelchairs or domotics devices.
With the aim of getting a scalable design, the software
implementation has been made dividing it in different
modules. Thus, progressively, new modules can be added,
i.e., new system functionalities without the modification
Figure 2. Detail of the adhesive tape used for correct per-
formance of the light reflection sensors on the user’s skin.
Figure 3. Human-machine interface of biomechanical sig-
nals for the detection of voluntary winks.
Figure 4. Algorithm flowchart implemented for the Arduino processing system. This flowchart shows the recognition of the
ive basic wink patterns that corresponded to control commands. f
Open Access ETSN
A. CARRERA ET AL.
of the existing ones; additionally, a user database was
created to improve the user’s interaction and save the
The software mouse module controls the mouse on the
full interaction with the computer
ink, i.e., for the consecutive winks a
The keyboard module, whose control commands a
ule, allows a biomechanical
groups, the same as in a
personal configuration which can define for example, the
time between two consecutive winks.
3.3.1. Mouse Mo d ule
computer screen with a
as with a standard mouse. This means that a full move-
ment on the screen is possible and also the left and right
button clicks. Figure 5 shows the state diagram including
possible ope rations.
Figure 5 shows the winks with a letter code: L is left
wink and R is right w
milar codification is used: L + R corresponds to left and
right consecutive winks and R + L to right and left con-
secutive winks. For the movement states, vertical or
horizontal, once the cursor starts to move, it can be
stopped winking and any of the Figure 5 states will re-
main active. An always visible help window was created
to improve the user’s control of the application.
3.3.2. Keyboa r d Mod ul e re
similar to the mouse mod
signals virtual keyboard to be used by a disabled user.
The implemented keyboard is optimised in order; the
letters are ordered by a Spanish utilisation frequency,
where the point of maximum frequency is the keyboard
centre (Figure 6). The handling of the keyboard is simi-
lar to the state diagram shown in Figure 5 and the wink
codification, with the ex ception that in this case the right
clicks not exist. In order to facilitate the user interaction,
as in the case of the mouse module, a brief summary with
the possible actions is included.
This module incorporates different keyboards in order
to include specific functionality
andard keyboard that includes special keys. Thus, the
left keys in Fig ure 6 keyboard: “Num/Esp”, “Bloq. May”,
Figure 6. Virtual keyboard aspect with the letters ordered
according to their Spanish utilisation frequency.
“Shift”, “Funciones” and “´”, give access to specific key
the use of
numbers and special characters. Once the required
to the lower case letter keyboard (Figure 6).
e software returns to Figure 6 keyboard.
different operations. configuration module where in-
d his/her skill regarding the system
Num/Esp keyboard. This keyboard allows
key has been clicked, the software returns automati-
Capital letter keyboard. The access to this k eyboard is
done by “Bloq. May” key or by “Shift” with one
touch only, and it can includ e capital letters.
Functions keyboard. This keyboard is for spec
functions and it allows the performing of actions that
normally are done with a keyboard and require the
combination of different keys, such as cop
cut, tab, window change, select and displacement ar-
Acute accent keyboard. This keyboard allows the use
of written accent vowels both capital and lower case
letters, it can be accessed by the “´” key and after the
Therefore, this keyboard module allows to write and
use the standard keyboard facilities in any application by
means of an adapted human-computer interface.
3.3. Other Modules
Additionally to the two modules presented above, mouse
and keyboard, another two have been included th
The first module is a
terface operation and interaction trials can be performed
(Figure 7). In this way, a user can verify if the orders are
correctly detected an
ill be shown in a configuration window.
The second one is an adapted wheelchair training ap-
plication, which allows for trials to be carried out with a
virtual wheelchair that simulates the movements of an
adapted wheelchair in a specific environment (
ke this, the wheelchair can move forwards, backwards
or turn either left or right. With this module both training
and improving of the adapted wheelchair driving tasks
are expected and also the study of a possible purchase of
a real wheelchair.
Figure 5. Function state diagram for the implemented
Open Access ETSN
A. CARRERA ET AL. 69
Figure 7. Aspect of the configuration and trial module.
Figure 8. Aspect of the adapted wheelchair simulation
module. In the picture, one of the implemented environ-
es into account both the prevailing
as voluntary winks, in severely motor dis-
and control subjects. In most cases of in-
rning the adapted interface
age time to access and click
e of the system
es to use a computer has been
subjects assessment for different para-
Also, another module, still in progress, has been in-
cluded and it would allow tasks automation in a domotic
The assessment of the augmentative communication sys-
tem developed tak
terest this assumption is true, and the handling of this
kind of gestural actions can be even much highly devel-
oped by some patients due to a compensation for other
lost abilities. Therefore, trials were carried out on 16
healthy subjects, without the handicaps involving a loss
of the validity of the results.
For these trials a specific protocol was designed. This
protocol consists in the writing of a preset phrase and
clocking the time taken to complete it. Then the control
subject does a survey conce
ed. Specifically, the writing trial is to complete two
spanish phrases: “Hola mundo. Esto es una prueba.”.
This text, in spite of being very simple, involves clicking
on 33 different keys (letters, capital letters, spaces and
punctuation), so it is very appropriate to test the user-
friendliness of the system.
The trials evaluate objective results such as the time to
each subject to write the phrases, without any previous
training. The average time to write the text was 8 minutes
and 42 seconds. The aver
ch key was 15.8 seconds. Certainly, if the subjects
train with the system and the interface, the handling of
the equipment would improve, due to learning and fa-
miliarisation. This learning is reflected on some subjects.
The number of voluntary winks needed to complete
the preset phrases was 363, taking into account clicking
and column and row choices. The number of winks can
be increased if errors are produced when the user is
oosing the key or movement. In addition, as the num-
ber of gestures is high, the use of the system may cause
fatigue; this effect can be supplemented with training or
the incorporation of technical steps for writing improve-
ment such as a prediction dictionary.
As explained previously, th e subjects filled in a surv ey
where they assessed various parameters of the wink de-
tection interface. The evaluation scale employed from 0,
the worst score, to 5, the best (Table 1
The results obtained in the survey reflect user’s satis-
faction with the system. Control subjects greatly appr eci-
ated the convenience and the easy use of the interface
and the orders code. In the specific cas
lay, a slightly lower rating was given because orders
that require two consecutive winks for execution accu-
mulated delay. This problem can be solved through train-
ing and customised software to shorten waiting times to
include a second wink.
An augmentative communication system that allows for
severe motor disabiliti
Table 1. Control
meters of the voluntary winks detection interface.
Parameter Average score (0 to 5)
Interface comfort 4.06
Easy handling 4.56
Order code 4.44
Test usefulness 4.00
Open Access ETSN
A. CARRERA ET AL.
im d. An interface adapted to detect residual
untovements, eye winks, has beeveloped and
the system uses these signals, after thcessing, to
ce and a virtual keyboard carry out all
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