ulate recovery is imperative. However, before at-
tempting to produce methods that can provide effec-
tive therapy, consideration needs to be given to assess-
ing the level of hand impairment. Methods of mea-
suring the range of motion of the hand may result in a
means of quantifying impairment, monitoring patient
recovery and possibly diagnosing both neurological
and hand-specific disorders. Hart and Tepper (2001)
determined, through a questionnaire completed by pa-
tients with hand impairments, that patients who had
undergone rehabilitative therapy perceived improve-
ments in their functional abilities and health. By us-
ing a method of quantifying the range of motion of
the hand, the data recorded can possibly validate any
improvements observed in therapy.
Measuring the ROM of the hand has predomi-
nantly been achieved by using a goniometer. These
methods have been used in several studies (Bain et al.,
2015; Hayashi et al., 2014; Hume et al., 1990) to de-
termine the static ROM of patients performing activi-
ties of daily living (ADL). The accuracy and reliabil-
ity of the device are dependent on the patient’s ability
to hold a gesture, with minimal movements. In ad-
dition to this dependency, repeatedly measuring each
joint of each finger during activities or gestures, is te-
dious and time-consuming. This can affect the pa-
tient’s performance. Thus, a more efficient method of
measuring the ROM that addressed these areas was
developed.
2 MATERIALS AND METHODS
The current study was divided into three segments:
(1) flexible sensor analysis, (2) development of the
prototype, and (3) candidate testing.
2.1 Flexible Sensor Analysis
Before developing a prototype of the device, it was
necessary to analyse the flexible sensor. The analysis
entailed the configuration of the flexible sensors and
multiple tests conducted to verify the application of
the sensors. Apart from the sensor signal drift and
the limitations, tests aimed to replicate the anatomical
variations of the finger joints of a human hand, were
included.
Flex sensors (Sparkfun Electronics, Colorado,
USA), were chosen due to their availability and cost.
Alternative sensors such as potentiometers, can be
used as they can be configured in a similar manner.
However, the difficulty arises when aligning the rota-
tion of the sensor in conjunction to the rotation of a
finger joint. Furthermore, designing and implement-
ing this system brings further complications when
considering the different hand sizes of patients.
The sensors are based on polymer ink and conduc-
tive particles. As the sensor is bent or flexed, the con-
ductive particles move further away, increasing the
path distance the applied current must travel through,
thereby increasing the resistance. By recording the
resistance at different angles of flexibility or bending,
a correlation can be made against the range of motion.
Oess et al. (2012) had sampled multiple flexible
sensors with respect to signal drift, comparing differ-
ences based on both type and sensor length. The re-
sults displayed a relation between signal drift and sen-
sor length, with an increased length leading towards
a decreased signal drift. In addition, the minimum
signal deviations were observed from the sensors that
had gone through a polyester over-lamination process.
This suggests that a cover medium may result in lower
variations of the signal. The current study is heav-
ily influenced over the availability of resources and
therefore confined to the use of locally sourced, sin-
gle branded and sized flexible sensors.
Apart from the comments made by Oess et al.
(2012), the sensor datasheet highlighted that the base
of the sensor should be supported, and no bending
should occur near the output pin of the sensors. In the
current study a 3D printed base was used to secure the
ends of the sensors.
The flexible sensors were used along the joints of
the fingers. Before any prototype was developed, con-
sideration had to be given to the anatomical variation
in hand sizes and shapes. As discussed, the sensors
output resistances based on the extent at which they
are bent. The greater the bend, the higher the resis-
tance. These resistances will be used to map angles
that represent the rotation of the joint. It was thus
necessary to determine the resistance fluctuations ob-
served from these sensors.The basic configured cir-
cuit consisted of an Arduino Uno, one flexible sensor,
a single bread board and a 100 kΩ resistor. Only the
flexible sensor was changed within the circuit when
testing for repeatability.
2.1.1 Signal Stability
The flexible sensors were configured with a resis-
tor to replicate a voltage divider. This allowed the
analog pins of the selected microcontroller to read
a variable voltage. It was also necessary to deter-
mine whether the straight resistances of various flex-
ible sensors were similar, had minimal signal fluctu-
ations and are around 30 000 Ω, as indicated by the
manufacturer. To ensure that the readings of the sen-
sors remain undisturbed by any movements, a simple
rig was created to keep the sensor in a straight posi-
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