Chapter 2. Prehension

Chapter 6 - During Contact 205
presented through analytic robotic models, muscles as actuators,
studies of pad opposition, and biomechanical studies of oppositions.
Finally, the issue of imparting motion through active manipulation,
using sensory information to monitor and guide motion is presented,
addressing analytic models and human studies.
6.1 Skin: An Organ Critical For Grasp
“The largest sense organ of the body, interposed between the
organism and its environment, skin must maintain that organism in a
constant state of awareness of all environmental changes” (Montagna
& Parakkal, 1974, p.157). In this sense, a constant state of
awareness of all environmental changes is likely a different level of
awareness from conscious awareness in the cognitive sense. Skin
serves as an organ for thermoregulation, protection (including
containment of body fluids and tissues) and sexual attraction; here we
restrict ourselves to skin’s fourth function as an organ for functional
contact, manipulation and adaptation with objects in the environment
(see Elden, 1971). For stably grasping, some of the relevant
characteristics of skin providing sensibility, force generation and
adhesion include: characteristics of epidermis, dermis and their
interface; papillary ridges; eccrine glands; sensory receptors; and their
innervation. We exclude lymph and blood vessels, recognizing that
local changes here might affect sensibility and force generation by
temperature changes, edema (swelling), or as yet undisclosed ways.
6.1.1 Skin structure and function: from fingerprints to
friction
Look at your fingerprints. Papillary ridges refer to the visible
ridges on the skin of the palm and fingers. The characteristic pattern
of ridges and sulci on the skin of the ventral aspect of the hand, called
dermatoglyphics, are found in the friction surfaces only of primates
and marsupials (Montagna & Parakkal, 1974). Also called sweat or
primary ridges, papillary ridges are composed of externally projecting
folds of stratum corneum (the outer layer of the epidermis of skin),
arranged in parallel whorls, arches or loops with distinct interunit
periodicity (Montagna & Parakkal, 1974; Quilliam, 1978). These
ridges, first visible in palmar and plantar surfaces of the digits of
13-week old fetuses, later extend over the entire volar (e.g., palmar)
surfaces of the hands and feet; the patterns remain unchanged, and the
width of the furrows increases at the same rate as the growth of the