Biomedical Engineering Reference
In-Depth Information
FIGURE 3-75
DLR/HIT prosthetic
hand based on
miniature electric
motors. (Courtesy
MicroMo.)
conveys sensed data back to field-programmable gate array (FPGA) based controllers.
Presently these are on a plug-in peripheral component interconnect (PCI) card integrated
in a standard personal computer (PC), but it the future it will be possible to integrate all
of the processing into the hand.
The complexity of this prosthetic hand has its price with each finger requiring several
separately controllable actuators. In this case, there are 12 16 mm diameter Faulhaber
analog Hall sensor-controlled brushless DC motors per hand. These are commercially
available, high-performance motors. They can be connected with gear systems of the
same diameter to form a single integrated unit. The motors produce an output power of
11 W and a maximum continuous torque of up to 2.6 mNm without gearing. However, for
this application the motor's no-load speed of 29,900 rpm is reduced to 188 rpm through all-
metal planetary gearheads with a ratio of 159:1. These simultaneously increase the torque
to a maximum value of 450 mNm. Hall sensors provide rotor position to the controller
and deliver the requisite feedback information with a resolution of at least eight bits. The
Hall sensors and motor form a compact 31 g unit with a length of only 28 mm and an
outer diameter of 16 mm.
3.7.3 Pneumatic Artificial Muscles
The Shadow Hand is the closest robot hand to the human hand available. It provides 24
movements, allowing a direct mapping from a human hand to the prosthesis. In addition,
it has integrated sensing and position control, allowing precise computer control.
The hand contains an integrated bank of 40 air muscles for actuation, some of which
are visible in Figure 3-76. The muscles are compliant, which allows the hand to be used
FIGURE 3-76
The
Shadow Hand in
action. (Courtesy
Shadow Robot
Company
http://www.
shadowrobot.com/,
with permission.)
