Browsing by Author "Williams, T. Walley, III"

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    A COMPENSATING SHOULDER JOINT TO ASSIST THE SHORT TRANSHUMERAL AMPUTEE
    (2008) Williams, T. Walley, III
    The typical problem patient has a transhumeral amputation 30 to 60 mm below the axilla. No matter how well the socket is made, the moment arm in the socket is too little to sustain the four foot-pound torque of a typical advanced prosthesis when working out in front. Matters get worse if the prosthetic terminal device carries a load. A prosthesis that solves this problem must compensate for the gravitational torque generated by the prosthesis itself so that all user generated torque can be used to position the prosthesis and to support the terminal device load
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    ADAPTING THE BOSTON DIGITAL ARM TO ACCEPT FIVE INDEPENDENT INPUTS FROM TMR AMPUTEES
    (2008) Williams, T. Walley, III
    In conventional myoelectric control, muscles are assigned to control functions differing from those controlled in the intact limb. In 1984 a bilateral amputee was fitted with four myoelectric inputs around the shoulder. These were to be used in pairs to independently control operation of the gripper and elbow flexion-extension. Since none of the muscles were doing their original assignment, a program was set up to train the user on the system. After many sessions, the amputee and trainer agreed that simultaneous control was never going to work. The control system was reconfigured, and the user mastered controlling one device at a time sequentially with the two best control sites. Twenty years later people are again trying to control several devices simultaneously, but with a difference. Now, with targeted muscle reinnervation (TMR) each muscle is being used to control the same function as in the intact limb.
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    Casting To Make A Frame Socket For Use With FSR Pressure Pads
    (1997) Williams, T. Walley, III
    A technique is described to cast for a frame socket to be used with Force Sensing Resistors (FSR's) The technique produces the largest number of control sites and ensures that at each site all forces on the FSRs are normal not shear. Key elements of the technique are prior identification of the control sites, casting the 'immobile frame' first and the use of multiple splints to locate up to five sites with respect to the immobile frame.
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    Clinical Application Of Roll-On Sleeves For Myoelectrically Controlled Transradial And Transhumeral Prosthese
    (1999) Daly, Wayne; Williams, T. Walley, III
    Three transhumeral and five transradial prostheses have been successfully fit to patients using electrodes installed in roll-on sleeves. New metal electrodes and wiring have been developed and tested along with techniques for installing electrodes so that the sleeves are not damaged. It is now possible to fabricate a system where the sleeve lasts for one year. The roll-on sleeve is a superior way to achieve suspension, especially with patients who change weight.
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    ELECTRIC UNLOCK FOR LTI LOCKING SHOULDER JOINT
    (2008) Williams, T. Walley, III
    At the 2002 MEC, LTI introduced the improved Collier Shoulder Joint which was still being shown at the 2005 MEC. In 2006, the Collier design was replaced by a completely new joint with greatly improved durability. The original joint had an option of adding on an electric unlocking mechanism that was slow and noisy. A year later in the summer of 2007 an electric unlock was made available for the new joint. This paper will discuss the design features of this new shoulder joint and the kit that can convert it to a joint that is locked and unlocked by an electric actuator.
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    Improved Compensation Of Gravitational Torque At The Shoulder
    (1997) Williams, T. Walley, III
    A simple analysis of prosthetic shoulders reveals that they are mainly used to position the orientation of the elbow in relatively few fixed positions. For some tasks the elbow needs to be positioned forward of the shoulder (Forward flexion). For desk and table tasks the preferred positions are both forward and out (flexion and abduction). For a few tasks straight out angles are appropriate (abduction). What all of these positions have in common is the need to compensate for the gravitational load of the prosthesis as the angle with respect to the vertical is increased. The paper on the Z-axis shoulder joint shows that by first moving away from the vertical in the abduction direction one need only provide one strong locking joint to take care of the gravitational load. However, the amputee still requires considerable effort to move the arm out, and the lock mechanism must be made stronger to accommodate the load. These two problems can be addressed by compensating for all or part of the gravitational load.
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    Low Level Response Of Bock And Steeper Electrodes
    (1999) Wallace, Craig; Williams, T. Walley, III; Taneja, Nathan
    For many years myoelectric fittings have been limited by the need for signals of at least 2011V when using convenient in-socket myoelectrode-amplifiers. With the introduction of the Bloorview-MacMillan MyoMicro technology, the controller is able to further amplify the patient myosignal. To evaluate the Bock 13E125 and Steeper Electrodes for providing suitable signals for control in the region below 20uV, both electrodes were tested at each gain setting. The Bock electrode gives the best signals in the 1 to 5uV range while the Steeper electrode is less sensitive. With suitable downstream amplification, both electrodes will provide proportional control with signals of 0-10uV.
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    New Clinically-Useful Control Strategies Made Possible By The Varigrip II Multi-Device Controller
    (1999) Wallace, Craig; Williams, T. Walley, III
    The VariGrip II Controller can operate up to three variable speed motors. For inputs it uses two, three, or four variable voltages and one on-off switch. This makes a large number of control strategies available, but not all are clinically useful. To date the most popular controls have used two myoelectrodes to control two or three devices. The controller has been used with the two VASI elbows and the Hosmer and Boston elbows to solve clinical problems that were heretofore intractable. The system also permits proportional control of two-motor devices such as the Bock 2000 hands, the Steeper Gripper, and the Centri UltraLite hand. We will discuss a number of the strategies that have proven clinically useful.
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    SMALL, LIGHT-WEIGHT, BUILT-IN BATTERIES OFFER MORE ENERGY AND IMPROVED COSMESIS
    (2008) Williams, T. Walley, III
    One might think that with over a hundred Li-Polymer cells on the market, one could find just the right cell for every application, but this is far from the case. Most cells are made in Asia by companies that only sell in large quantities. Dimensions are driven by the size and shape that is appropriate for 3.6V hand held devices. For these devices thin and flat are paramount, while the linear dimensions are driven by the size of the device and are usually too wide for a prosthesis. Figure 1 shows four cells that have proven usable in prosthetics. Left to right, the first cell is a mere 200 mAh, but is really small. The second, 250 mAh, is the smallest rectangle that will mount crosswise at the end of a child prosthesis. Unfortunately, it has been discontinued by the manufacturer. The third cell, 450 mAh, is slim in two dimensions so it fits well with one cell each on side of a wrist. The 750 mAh cell on the right is good for a full day’s operation of an adult transradial prosthesis. Cells must be selected for their electrical characteristics as well as for size. For instance, many of lithium ion cells have a high internal resistance limiting the current that can be drawn. Recent changes in the chemistry of some of the lithium polymer cells have opened up new high current applications. To move an elbow or shoulder with weight in the gripping device requires substantial current even when extra cells are added to increase voltage. With battery operation every component must be as efficient as possible and this includes the batteries.
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    Strategies For Controlling Several Powered Devices
    (1995) Williams, T. Walley, III
    When it is not possible to control two devices independently, mode selection schemes are used to shift one good control source like two good myoelectric sites so that two or duet devices can be controlled. The Boston Elbow II, the Utah Artificial Arm and, Otto Bock 2-Channel and 4-Channel controls all use simple mode selection. Selection schemes may be operated by the signals themselves or by external switches. They may revert to a default state, to a ready state or they may cycle through states. Liberty Technology VariGrip circuits permit practitioners to apply mode selection to devices from many manufacturers of wrists, elbows and hands
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    The Z-Axis Shoulder Joint - A New Concept
    (1997) Williams, T. Walley, III
    It is difficult for a shoulder amputee to do anything while sitting at a desk or table with the elbow tucked in against the side. For useful work the elbow needs to move forward 30-45 degrees and out 30-45 degrees to a position of function. These moves require a well designed shoulder joint. Conventional friction joints are constrained to move about an abduction axis followed by a forward flexion axis with both motions against gravity. An ideal shoulder moves 'out' away from vertical and then locks. It then swings forward or back around the vertical Z axis with no gravitational constraint. Such a joint places the forearm in a convenient location for useful work.
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    Working With VASI Push Switches
    (1997) Williams, T. Walley, III
    Two single acting VAST push switches or the VASI operate a hand, elbow, or other device in dual-action push-a-little, push-a-lot switch will two directions. These switches are very reliable, but pose a number of problems that must be understood before one attempts to use them.