Page 210 - Handbook of Biomechatronics

Upper-Limb Prosthetic Devices 207

The mechanical design for a five fingered, 20 DoF dexterous hand pat-
terned after human anatomy and actuated by SMA wires strands of 150μmin
diameter, was presented. Two experimental prototypes of a finger were
developed, one fabricated by traditional means and another fabricated by
rapid prototyping techniques, showing promise for use in prosthetic hands
(De Laurentis and Mavroidis, 2002).

1.5.5 MEMS
Microelectromechanical systems (MEMSs) refer to the technology of
microscopic devices, particularly those which include moving parts.
MEMSs are fabricated using modified semiconductor device fabrication
technologies, including molding, plating, wet and dry etching, electro
discharge machining, and other similar technologies.
The most common application of MEMS is sensors, such as accelerom-
eters, inertial measurement units (IMUs), magnetic field sensors, micro-
phones, pressure sensors, biosensors (bio-MEMS), and more. MEMS are
used in large quantities in modern cars, propelling their proliferation in other
areas, including upper-limb prostheses. Here, the MEMSs are mostly used as
posture sensors and force/tactile sensors.
The development and preliminary experimental analysis of a soft com-
pliant tactile microsensor with minimum thickness of 2mm was presented in
3
Beccai et al. (2008). A high shear sensitive 1.4mm triaxial force microsensor
was embedded in a soft, compliant, and flexible packaging. The performance
of the sensor was evaluated by static calibration, maximum load tests, noise
and dynamic tests, and by focusing on slippage experiments. The experi-
ments showed that the tactile sensor is sufficiently robust for application
in artificial hands while sensitive enough for slip event detection.
A tactile sensor designed to measure shear forces for use in robotic and
prosthetic hands, where haptic feedback or ability to detect shear forces asso-
ciated with slip are critical is described and characterized (Tiwana et al.,
2011). The sensor employs the principle of differential capacitance to mea-
sure the mechanical deflection of the sensor and can be easily mass produced.
Sensors with a full-scale displacement range of 0.525mm were produced
and the differential capacitance was measured. Shear force transduction was
characterized over the range of 0–4N. A maximum standard deviation of
1.35e 15F was measured across the characterized full-scale sensor range
of 4N. The sensor output was found to be approximately linear.
A triaxial force sensor was developed with a MEMS as its core compo-
nent (Sieber et al., 2008). This device allows measuring forces the range of
0–3N for normal and 50mN for tangential forces with a resolution of