Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Electrical and Computer Engineering

Collaborative Specialization

Musculoskeletal Health Research

Supervisor

Trejos, Ana Luisa

Abstract

Twisted coiled actuators (TCAs) are biomimetic and inexpensive artificial muscles. To enable their integration into soft robotics, a novel cooling apparatus was designed, consisting of a fabric channel to house the TCA and a miniature air pump for forced convection. The channel was designed to be lightweight, flexible, and easy to integrate into a soft wearable robotic device. The effect that the channel dimensions had on TCA performance (cooling time, heating time, and stroke) was investigated by testing combinations of three widths (6, 8, and 10 mm) and three heights (4, 6, and 8 mm). In general, as the channel dimensions increased, the cooling time and heating time decreased, however the stroke was unaffected (provided that the channel height was above 4 mm). The largest channel, 10 mm width and 8 mm height, resulted in the best combination of cooling time, heating time, and stroke, and thus it was used in a secondary experiment to compare the performance of the TCA with and without the cooling apparatus. When compared to passive cooling without a channel, the cooling apparatus resulted in a 42% decrease in cooling time (21.71 ± 1.24 s vs. 12.54 ± 2.31 s), 9% increase in the heating time (3.46 ± 0.71 s vs. 3.76 ± 0.71 s), and a 28% decrease in stroke (5.40 ± 0.44 mm vs. 3.89 ± 0.77 mm). This work demonstrates that fabric cooling channels are a viable option for cooling TCAs. Future work can continue to improve the channel design and investigate alternative means of air flow to further improve the performance of the TCA.

Summary for Lay Audience

Wearable devices have the potential to improve the quality of life for many individuals, either as assistive devices or as rehabilitation aids. These devices are not commonplace, as they are often heavy, bulky and expensive, which is due in part to the technology being used to make the devices move (actuators). Twisted Coiled Actuators (TCAs), a type of artificial muscle made from nylon thread, are a promising alternative as they are lightweight, slim, and inexpensive. They contract upon heating and extend upon cooling. Unfortunately, their natural cooling rate is too slow for many applications in healthcare and rehabilitation. Therefore, a new cooling method was developed. It consists of a fabric channel to house the TCA and a miniature air pump to circulate air through the channel. This system has been explicitly designed for soft wearable robotics, as it was designed to be lightweight, low-profile, and flexible, to help with user comfort. Additionally, since the channel is made from fabric, it can easily be sewn onto other materials for assembly into a robotic device. The effect of channel size on TCA performance was evaluated by testing nine channel sizes, which were combinations of three widths (6, 8, and 10 mm) and three heights (4, 6, and 8 mm). TCA performance was evaluated by comparing the cooling time, heating time, and stroke of TCAs in each channel size. In general, the cooling and heating times of the TCA decreased as the channel size increase, however, there was no change in the stroke, provided that the height was above 4 mm. The channel with a 10 mm width and 8 mm height had the best combination of heating time, cooling time, and stroke. Using this channel, a second experiment was completed to compare TCA performance with and without the cooling system. With the cooling system, the average TCA cooling time decreased by approximately 42%, however there was a 9% increase in heating time and a 28% decrease in stroke. This work shows that fabric cooling channels a promising way to improve the cooling time of TCAs.

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