Page 207 - Handbook of Biomechatronics

204 Georgios A. Bertos and Evangelos G. Papadopoulos

the form of magnetic or optical encoders. When these are part of a position
control system, which regulates the position of a mechanical load precisely,
they are called servomotors.
To increase the acceleration, brushed micromotors are usually coreless, that
is, their windings are glued on a hollow rotor, while the stator carries the
permanent magnets. Current commutation is done using a commutator
and brushes, which are subject to wear. Brushless DC micromotors represent
an inversion of the dc brushed motor principle. Here, no brushes are needed,
the stator carries the windings, while the rotor carries the permanent mag-
nets. The rotor can be rotating inside the stator, or outside (outrunner
motor) for increased torque output, to the expense of higher moment of
inertia.
Three versions of a multifunction haptic device that can display touch,
pressure, vibration, shear force, and temperature to the skin of an upper
extremity amputee have been developed (Kim et al., 2010). For the devices,
a number of actuators, such as ultrasonic motors, and electromagnetic
motors, were considered. Although ultrasonic motors produced high torque
and need no reduction, they had poor frequency response and could not
achieve high accelerations for enough time. Therefore, DC brushed micro-
motors with appropriate gearboxes were selected providing better open-
loop frequency response, closed-loop force response, and tapping response
in constrained motion.
A 3D printed prosthetic hand for transmetacarpal amputees was devel-
oped (Mio et al., 2017). Due to the little space to fit actuators and their asso-
ciated electronics was actuated by DC micromotors. Four-bar linkage
mechanisms were used for the index, middle, ring, and little fingers flexion
movements, while a mechanism of cylindrical gears, and worm drive was
used for the thumb, all position controlled by local controllers.
A parallel prosthesis aiming to increased force, and reduced weight and
size was developed. The prosthesis has four DoF driven by four brushless
motors, weighs 1010g, and can lift 2kg, while the time for a total excursion
of the flexion of the elbow is about 2s (Escudero et al., 2002).
An overview of past and present artificial hands, developed in the frame-
work of research projects in prosthetics and humanoid robotics is available
(Controzzi et al., 2014). Most of them use DC micromotors in conjunction
with micromechanisms, for better matching the micromotor to its
mechanical load.
Ultrasonic motors. These are electric motors, which produce motion by
the mechanical vibration of the stator, placed against the rotor (for rotation)