Research & Presentations
Liner With Embedded Electrodes for MyoelectricControlled Prostheses By Matthew Wernke, PhD; Cody Doddroe; Alexander Albury, CPO; Michael Haynes, MS; and Luke Beery
Background Achieving robust control of a myoelectric prosthesis utilizing skin surface electrodes is highly dependent on acquiring noise-free surface electromyography (sEMG) signals. Acquiring noise-free signals is complicated by the variety of positions and loading conditions experienced by the prosthesis in use, which can further degrade signal quality.1-6 The traditional approach to myoelectric socket interfaces is to embed the electrodes into the wall of the socket. In this design, the metal dome electrodes can separate from the skin due to translation of the socket, presenting significant challenges to the goal of collecting high-quality sEMG signals.7-10 These movements typically lead to inconsistent or varying signals that greatly diminish control.7 To address the challenges associated with incorporating electrodes directly into the socket, several attempts have been made to incorporate a gel liner into myoelectric socket interfaces.11-15 These attempts involved retroactive changes to the liner and therefore reduced the mechanical durability of the assembly and complicated the donning process. More recently, the Shirley Ryan AbilityLab (formerly the Rehabilitation Institute of Chicago) developed a gel liner with integrated electrodes for use with a pattern recognition system
such as Coapt Complete Control. Preliminary testing showed that the system maintained electrical signal quality after eight weeks of at-home use (although electrical resistance did increase) and was preferred by the test participants over their existing systems. Further development of the system was performed by the authors. Mechanical testing to evaluate the performance of the new myoliner over the expected lifetime is warranted. Further, the ability to don the liner in a consistent orientation and place the electrodes within the liner system accurately should be investigated to explore possibilities of the liner system to work with two-site control systems. The purpose here is to investigate these areas.
Methods Two sets of experiments were conducted to evaluate the myoliner. The first set focused on the mechanical durability of the myoliner using both ultimate strength and fatigue testing. The second set focused on the accuracy of electrode placement. Mechanical Durability
Both an ultimate strength test and a fatigue strength test were conducted on a tension-compression machine (Figure 1). The ultimate strength test was used to
Figure 1
Tension-compression machine used to mechanically test the myoliner.
verify the myoliner could withstand a predetermined axial tension force. The predetermined axial tension force was chosen to be 200 pounds. This force was selected with the consideration that the weight limit of most myoelectric upper-limb components being around 50 pounds and increasing that by a safety
O&P News | March 2018
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