Biomedical Engineering Reference
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Fig. 2. From top left, clockwise: dynamic rotation, isometric rotation, finger tapping and hand
extension exercises on the proposed hand functional evaluation device
The Sensorized Aids. A precision multi-turn potentiometer, equipped with a 30mm
aluminium knob, has been used as dynamic rotation aid. The potentiometer (Vishay
534, 20k Ω , 2W) is able to perform 10 turns opposing a torque of 0.006 Nm. The re-
sistance varies linearly with the rotation of the knob so that it suffices to measure the
voltage on the wiper to detect the angular position at any instant. Due to the low oppos-
ing torque, the exercise can be considered without any load.
On the contrary, the isometric rotation aid is composed of a 5-lobe 50mm plastic
knob able to slightly turn on its own axis pulling along with it a T bar nut able to
press one of two thin-film force sensors (the low-cost Tekscan FlexiForce A201, max
110N), for clockwise and anticlockwise rotations. These sensors linearly vary their con-
ductance in response to the applied force. Being an isometric exercise, thanks to the
aforementioned design, the knob cannot spin.
The hand extension exercise is dynamic but it introduces a counter-resistance. It is
evaluated by means of an analogue draw wire position sensor (LX-PA-15 by TME)
mounted on a roller (CES30-88-ZZ by Rollon) free to move on a 40cm linear zinc
plated guide (TES30-1040 by Rollon): the wire coming out from the sensor is attached
to a second roller mounted on the same guide. The two rollers are attached to as many
L-shaped aluminium profiles actuated by the patient opening and closing his hand. The
sensor is characterized by a nominal wire rope tension of 3.9N, which must be over-
come by the patient in order to extend his hand.
Lastly, the finger tapping aid exploits a capacitive touch board. Compared to the one
presented in [9], the capacitive approach is still able to provide a detection of the touch
without any counter-resistance from the measuring device but also avoids any direct
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