Body powered prosthetics

Force and Excursions Needed to Actuate a Number of Standard Body-Powered Prosthetic... 

Third, this fitting highlights the severity of the control interface problem when faced with amputations at this level. Everything is used—conventional harness control and biomechanical switches, using the chin, are extensively used in the control of the body-powered prosthetic components. These same chin motions are used to control externally powered components through the use of electromechanical switches and linear transducers. 

Comparison Study of the Transradial Prosthetics and Body Powered Prosthetics... 

Keywords— Transradial prosthetics, body powered prosthetics, pressure distribution. 

Functional prosthetics hand can be classified into two part body powered prosthetics (used tension cable) and externally powered prosthetics (electrically powered). Body... 

Fig. 2 and 3 compares the pressure waveform curves distributed with the use of body powered prosthetics with... 

The body powered prosthetics proven that it give a pressure to the person that worn it because of the socket and the weight of the prosthetics itself. While, for the transradial prosthetics shows that the socket was well comfortable be worn by the amputee. At the same time the pressure that occurs was because of the bones Ifacture instead of the socket design and the weight of the transradail prosthetics. 

FIGURE 42.2 Cable-driven body-powered arm prosthesis. (Courtesy of Mountain Orthotic and Prosthetic Services, Lake Placid, NY, USA.)... 

Current electric powered prosthetic elbows can attain about 12.2 N-m (9 ftdbf) of live-lift (lift by the elbows own motor mechanism) at speeds of about 2 rad/s (Boston Elbow III, Liberating Technology, Inc., Mass.). Body-powered eltows are limited by the speed and strength of the user and the efficiency of the linkage used to connect the user and e component. Humeral rotation for elbow components, with the exception of the RIMJET body-powered humeral rotator (RIMJET, Fla.), is achieved with manually positioned friction joints or turntables. The only shoulder joints available are also passive, manually-positioned units that use friction or a lock to hold their position. 

FIGURE 32.4 Photograph of how a Bowden cable is set up for use as the control cable of a transhumeral (above-the-elbow) body-powered prosthesis. The housing acts as a guide or channel for the control cable, which transmits forces developed by a harnessed body part, in this case the contralateral shoulder, to the prosthesis. Retainers on the housing fasten it to the prosthesis and serve as reaction points in the transmission of force by the cable Photograph courtesy of Mr. C. Heck-athorne of the Northwestern University Prosthetics Research Laboratory.)... 

The basic configuration of Bowden cables in prostheses has changed little over the intervening years and is stiU in use today. In fact, if prehensile function is the primary goal of the prosthetic fitting, the device of choice for most persons with amputations is a body-powered, Bowden-cable-operated prosthesis with a split hook-shaped terminal device. This is in spite of all the technological advances in electronics, computers, and dc motor technology that have occurred since the end of World War H. 

Backlocks are also found in some prosthetic elbows (Boston Elbow 111, LTI Otto Bock Body-Powered Elbow) as a means of holding elbow position in the absence of a drive torque. This ability allows users to park their prosthetic arm at any desired position and then remove (decouple) themselves from the arm s control. 

Physiologically correct feedback, beyond drat provided by vision, is essential if low mental loading or coordinated subconscious control of multifunctional prostheses is to be achieved (Pig. 32.33). When prosthetic aim technology moved to externally powered systems, the control modalities shifted, with the exception of Simpson (1974) and a few others, from the position-based cable control of the body-powered systems to open-loop velocity control techniques (such as myoelectric and switch control). That is, prosthetic technology shifted away from cable inputs, which provide sensory... 

Fryer, C. M. (1992). Harnessing and Controls for Body-Powered Devices, Chapter 6B. In Atlas of Limb Prosthetics, Surgical, Prosthetic, and Rehabilitation Principles, 2d ed. Bowker, J. H., and Michael, J. W., (eds.), Mosby-Year Book, Inc., St. Louis, Mo., pp. 133-151. 

Since then, prosthetic arm continues to evolve with variety of concept. For instance a Myoelectric prosthesis that uses electromyography signals or potentials from voluntarily contracted muscles to control the movements of the prosthesis arms. Here, a residual neuro-muscular system of the human body to control the functions of an electric powered prosthetic hand, wrist or elbow [2],... 

In position control the position of the prosthetic joint is proportional to the input amount/intensity. The input amount/intensity might be the position of another physiological joint or a force level. If the position of another joint is used as the input then the system is known as a position actuated, position servomechanism. If the amount of force applied by some body part is the input, then the system is a force actuated, position servomechanism. An example is die power steering of a car. Here, the position of the steering wheel is related directly (proportional) to the position of the front wheels. Such a system is an example of a position follower (the position of the wheels follows the position of the steering wheel) or a position servomechanism. 

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