Chapter 2. Prehension

410 Appendices
Sears et al., 1989). Without feedback, other than visual and auditory
feedback, they are hard to use when the hand obscures the object from
view. The hook, in contrast, does not interfere visually as much as an
artificial hand does. In the Millstein et al. (1986) study, disadvantages
for the cable-operated hand were its difficulty to operate,
awkwardness, its heavy weight, lack of durability, and a weak grip.
It was rated good as a cosmetic nonactive prosthesis.
Commercially available active mechanical hands are seen in see
Table D.2. In some of these, only three fingers are active. The thumb,
as VF1, acts against the index and middle fingers, which in turn work
in tandem as VF2. The fingers and thumb come together in pad
opposition in all of these devices. The passive ring and little fingers
add minimally in prehension. All four fingers can be used as a VF3
in a hook grasp to carry a bag. An example of a mechanical hand is the
Dorrance hand, which is a voluntary opening hand consisting of a
thumb and index and middle fingers with adjustable closing force.
The ring and little fingers don’t move.
Another example is the APRL voluntary closing hand (Hosmer
Dorrance Corporation). Similar to the Dorrance Hand, it also has a
moveable thumb and two fingers, with two passive fingers. The
thumb can be pre-positioned in one of two positions, thus permitting
the handling of a wide variety of objects. Being a voluntary closing
device, it is self-locking in any position.
The NYU Number 1 Child-sized Mechanical Hand, for children
ages 2-7, has two fingers and a thumb that articulate at the
metacarpophalangeal joints. The nonfunctional ring and fifth fingers
are passively mobile, and it uses a voluntary-opening four-bar linkage
mechanism for adjusting the opening size. The fingers lock in a
closed position, but an emergency override releases the clutch when
necessary.
D.2.4 Commercially available electrical hands
Electric hands have a thumb and two fingers. The ring and fifth
finger are created by an inner glove which covers and protects the
mechanical parts. They use a variety of control methods, as seen in
Table D.3, to activate the two fingers and thumb, opening and closing
with one degree of freedom. Table D.3 displays a list of commercial
hands, categorized into the same categories as in Table 1. The thumb,
as VF1, acts against the index and middle fingers, which in turn work
in tandem as a VF2. The fingers and thumb come together in pad
opposition in all of these devices. The ring and fifth act in a limited