User:TalkaboutIt84/sandbox

Background:

The human hand is one of the most versatile tools on Earth, especially when it is manipulating a manmade tool. It can support hundreds of pounds in tension or compression. The hand can conform to the shape of objects and surround them. Individual fingers can be used for pinching, spreading, and fine pointing tasks. The fingerprints increase the friction of the fingers and prevent objects from easily slipping from the hands. In addition to being an amazing mechanical tool, the human hand is a social instrument. People greet one another by shaking hands or waving to a neighbor. Many people actively move their hands as a means of accentuating spoken statements, shaping the overall nuance of their communication. Hands are used to reach out and connect with others and the environment. They are used to flirt, to comfort, and to insult. Integral to the hand, the wrist and forearm act as the sole means of translating force from the hand to the upper arm. The wrist varies the angle of the hand, positioning it for other fine and gross motor tasks. Similarly, the bones of the forearm can twist around each other, which causes the hand to flip over. A hand’s efficacy would dramatically decrease if it didn’t have these supporting structures to modify its position. Losing a hand can profoundly disadvantage an amputee and severely affect their quality of life. Myoelectric prosthetic hands have been developed in an attempt to simulate all the capabilities of the human hand, but even these sophisticated prostheses are incapable of replicating the versatility and reliability of a biological hand. A wide variety of prosthetic terminal devices attempt to replicate the breadth of functions that a healthy human hand produces.

Categories: Several categories of terminal devices have been developed for task specific operations. These categories include: wrist, aesthetic, hook, gripper, kitchen, hygiene, sports, gardening, carpentry/mechanics, and music (2).

Wrists

Prosthetic wrists critically affect the successful use of prosthetic terminal devices. Some devices have built in wrists, while the majority do not. The wrist is often a set of mechanical linkages that can be manually positioned and locked by the patient’s intact hand or by bumping the prosthesis into the desired orientation. Once the wrist position is reached, a locking mechanism is engaged to hold the wrist in that orientation. One such wrist that was developed by and amputee has over 20,000 possible orientations (6).

Aesthetic

Some amputees are highly concerned about the aesthetics of their prosthesis, but they still desire to have a functional prosthesis. Bearing that in mind, a variety of “lifelike” prosthetic hands have come to the market. These hands have an anatomical appearance and are available in various skin tones (4). They typically have the ability to instigate a thumb and pointer finger grasping through the use of a body powered system. Body powered systems consist of a set of shoulder harnesses and cables. Users can shrug and contract their shoulders and in turn pull on the cables attached to the shoulder harness. These cables then operate the end effectors.

Hook

Hooks are by far the oldest and most versatile prosthetic terminal devices. They are capable of lifting and pushing large loads, and their pointed tip is capable of fine movements within a confined space. Many hooks open analogous to a pointer and middle finger. These hooks come in normally-open and normally-closed configurations. Varying numbers of rubber bands are used to simulate muscle force in the hooks. The majority of hook systems are body powered.

Gripper

Grip prehensors are similar to hooks, but they have a locking bar that closes the hook, forming a loop. This allows the terminal device to completely encircle an object such as a baseball bat or a shopping bag handle (4). Departing from the standard humanoid hand, Kaylene Kau has developed a prosthetic tentacle that allows an amputee to completely encircle an object with their prosthesis (1). Similarly, a robotic wrist/hand unit has been designed that effectively uses a drill chuck as a terminal device. The user can select a tool they would like to use and tighten the chuck around it (5).

Kitchen

A wide assortment of terminal devices are available for use in the kitchen. They are designed for food preparation and eating. Examples include forks, knives, sporks, brisket slicers, and knife sharpeners (2).

Hygiene

Hygienic products are also available including devices such as toothbrushes, razors and hairbrushes.

Sports

Sports terminal devices are the most varied category. They emulate properties of the natural hand such as, hand conformity, grip strength and frictional characteristics of the hand. They frequently exploit energy storing and frictional properties of elastic materials. These terminal devices are used for weight lifting, martial arts, basket ball, pool, climbing and swimming, just to name a few (4).

Gardening

Gardeners also have options. Gardening hand tools such as spades, cultivators and limb saws are available (2).

Carpentry/Mechanics A plethora of hand tools exist for carpentry and mechanical work. Some examples are screwdrivers, saws, hammers, pliers, and wrenches (2).

Music

Several terminal devices have been developed specifically for musicians. Some prostheses help violinists grasp and position the bow. One device enables guitar players to use a pic while playing a guitar (2). Another device, designed at Georgia Tech, provides a robotic drumming assist (3).

Sources: 1) http://boingboing.net/2013/05/23/prosthetic-tentacle.html

2) http://n-abler.org/Mechanic%20Tools/Box%20End%20Wrench%20Sets.htm

3) http://www.news.gatech.edu/2014/03/05/robotic-prosthesis-turns-drummer-three-armed-cyborg

4) http://www.trsprosthetics.com/

5) http://www.tuvie.com/prosthetic-limb-aids-the-remaining-good-hand-on-various-activities/

6) https://www.youtube.com/watch?v=5tsrO9qZ7P0&list=UUKuELlosMTJEoDVdn2bHiVQ