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VR Interfaces: Fluidhand Prosthetic Hand


Overview of Fluidhand Prosthetic Hand
Fluidhand is a product of the Orthopaedic University Hospital in Heidelberg, Germany. At this time, it is not yet being produced commercially, as the University hospital is still seeking a production partner. However, the intent is for commercial availability.

It has the distinction of being the first such prosthesis in which each finger moves separately, without being a separate prosthesis.

The hand has what the university hospital terms ?a natural range of grip configurations?. What this actually means is that the hand has been pre-programmed to grip in preset ways, in addition to the ways a person might ask it to grip. The fingers can squeeze together, to hold a credit card for example, as one of the presets. Another preset sees the hand become a fist, to either grip tightly or ask someone to back off.

The presets, like all other controls, are activated by a combination of neural signals from the nervous system directly, or myoelectric signals taken from the organic nerve fibres in the stump of the arm will control the prosthesis attachment's motors. Rather than have to decode each neural signal from the remaining arm nerves, the fluidhand is smart enough that when it detects certain muscle movements in the arm, it knows how the hand would naturally respond. This allows a greater range of motion than nerves alone, purely as we have yet to decode what all those signals are ? a subset only, is currently available.

Each finger not only moves in a prehensile manner, but also can lock in place, again at a command. This allows for example, the index finger to be locked in place such that it will not budge, and the hand to be moved to type with it on a keyboard. There is not enough independent flexibility or control to be able to type normally with the fluidhand.

The largest improvement fluidhand has over earlier prosthetics, is the grip. Unlike previous gripping hands, because the fingers do move independently, any object with an irregular surface can be gripped naturally. When one finger stops moving, as it has a tight grasp of the object, others do not. Each finger curls up separately, for the firmest grasp it can get on the item being held. If a lighter touch is needed, the hand will only grip hard enough to avoid slippage, allowing an egg to be held equally as well as a piece of wood.

All four fingers are prehensile in this manner, and so is the thumb. Each finger, whilst normal sized, manages to pack considerable electronics, and five motors into each digit, for a complete natural range of motion. The flexible drives are located directly in the movable finger joints and operate on the biological principle of the spider leg ? to flex the joints, elastic chambers are pumped up by miniature hydraulics. When a finger encounters resistance, an electrical signal is triggered, which pulses back into the hand, and into the person?s stump. It travels back up the appropriate nerve, delivering haptic feedback from that finger to the brain. One sensor per finger, and thumb. Nowhere near natural sensation levels, but enough to know you are gripping something, and the strength of the grip.

The thumb additionally serves as a preset activator. If it is moved into set positions by the user first, (before moving the fingers) the preset corresponding to that position will activate, and the fingers will move accordingly.

Weight wise, the hand will lift up to 20kg without causing damage to itself, or the attachment holding it to the person?s arm. Whether or not the person with the prosthetic hand can hold 20kg on that arm, is another story.

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