Fishing Line Based Twisted and Coiled Polymer (TCP) Muscles and Thermoelectric Coolers for Improved Frequency of Actuation




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The combination of muscles, bones, cartilage, and ligaments that are essential for mobility can result in different configurations of a musculoskeletal system design. The most used actuators for robotic movement are tendon driven systems using DC-motor-based. Besides DC motors, pneumatic artificial muscles are of interest for biologically inspired musculoskeletal systems due to pneumatic muscles’ similarity to natural muscles in terms of length-load curves, their compliance, rapid contraction, and the high power/weight ratio. Actuators such as the electric motors and pneumatic artificial muscles used in robotics have their own drawbacks. Although electric motors are energy efficient actuators, they require complex transmission systems, resulting in limitations in terms of size and space. Above all, electric motors do not fit in the bio-inspired design approach. On the other hand, pneumatic artificial muscles require a compressor to force a gas into the actuators to create a pressure difference between the inside and the ambient environment for actuation. This makes pneumatic artificial muscles bulky in an overall system. We investigate twisted and coiled polymer (TCP) artificial muscles for actuation of limb movements using fishing line and a resistive heater nichrome (TCPFL NR). The actuation by these muscles is due to their contraction and expansion while exposed to different temperatures. TCP muscles have been deeply researched in the University of Texas at Dallas and have been implemented on multiple robotic arms. One of the major drawbacks observed after using these muscles is the time it takes to move back to its initial length after actuation. Hence a method of cooling is required to increase the rate of cooling such that the muscles take shorter time to get back to their initial length. This thesis proposes the use of Peltier cooling mechanism that should be employed during the contraction and extension of TCP muscles. The addition of a Peltier module decreases the time it takes for the muscle to expand back to its original length. Currently, for a typical TCP muscle of diameter 3 mm, the muscles are only subjected to natural convection for cooling and takes about 40 seconds to cool down for 10 seconds actuation stimuli. Due to this, the robotic fingers, attached to the TCP muscles, also take 40 seconds to retract back to their initial length. Current research focuses on the improvement of TCP muscles as actuators for use in robots. The primary area of improvement would be the actuation frequency of the artificial muscles to ensure realistic applications of TCPFL.



Engineering, Mechanical