Advanced Control of Upper-Limb Prostheses with  Time-Synchronized Distributed Wireless Electrodes

Li, Jianan

Etd

Advanced Control of Upper-Limb Prostheses with Time-Synchronized Distributed Wireless Electrodes

Öffentlich Deposited

The human hand is the most powerful tool for human beings to sense and manipulate the world about them. The loss of one or both hands significantly impairs these abilities. Upper-limb prostheses help reproduce absent hand function. The electromyogram (EMG) generated by remnant muscle tissue is used as the control source in myoelectric prostheses. This thesis first describes a method for rapid calibration of hand-wrist EMG-force, as a basis for myoelectric prosthesis control, with performance evaluated via virtual real-time testing. Second, aspects of a distributed wireless electrode system are described. Such a system is needed to replace socket-based wired electrodes which do not fit into evolving osseointegrated prosthetics. Rather, electrodes need instead be placed inside of a liner without a wired connection to the prosthesis. The first part of the thesis studied a real-time rapid prosthesis calibration method based on hand-wrist EMG-force modeling, evaluated using both able-bodied and limb-absent subjects. Both 1-DoF (degree of freedom) and 2-DoF simultaneous, independent and proportional (SIP) control tasks were tested with three main control methods: conventional 2-site control (“sequential” mode switching via co-contraction) using 2 electrodes, intuitive 2-DoF SIP control (using EMG-force from muscles that typically activate the relevant DoFs), and mapping 2-DoF SIP control (using EMG-force from muscles that typically do not activate the relevant DoFs). The number of electrodes (6 or 12) was also tested for the 2-DoF SIP controllers. Performance on dynamic virtual target tracking tasks in 2-DoFs and a fixed virtual target stability task were evaluated. For all subjects, both 2-DoF SIP controllers with 6 optimally-sited electrodes had statistically better target matching performance than sequential control in number of matches (average of 4–7 vs. 2 matches, p< 0.001) and throughput (average of 0.75–1.25 vs. 0.4 bits/s, p< 0.001), but not overshoot rate and path efficiency. There were no statistical differences between 6 and 12 optimally-sited electrodes for both 2-DoF SIP controllers. The second part of the thesis investigated two aspects of wireless electrodes: power consumption when transmitting using a Bluetooth Low Energy (BLE) microcontroller and clock synchronization methods in distributed BLE systems. Using a Texas Instruments (TI) BLE microcontroller, power consumption was measured in different condition combinations. Results found that with the built-in ADC (which consumed 0.8–0.9 mA), total power consumption ranged from 0.9–3.0 mA, which satisfies the requirements of daily usage when powered by a coin cell battery. We additionally developed a low latency, BLE-based time synchronization algorithm and data alignment method. The method was implemented on two BLE platforms (TI, Nordic) to demonstrate the portability of the algorithm. We found time synchronization errors between two independent peripheral nodes of, on average, 69 ± 71 μs with 0.56 ms 90th percentile error for a TI platform and 477 ± 490 μs with 1.21 ms 90th percentile error for a Nordic platform. Total end-to-end latency was less than three connection intervals (i.e., <30 ms for Nordic, <45 ms for TI).

Creator