A Novel Cooling System for Soft Wearable Robotic Devices

Researchers at Western University have developed a novel cooling apparatus for TCAs that is designed for soh wearable robotics

W-22-033

Background

Each year, approximately 62,000 Canadians and 795,000 Americans suffer a stroke. After suffering a stroke, it is recommended that patients receive a minimum of 45 minutes of rehabilitation therapy five days per week, which creates high demands on physiotherapists. High quantities of rehabilitation are essential, as it has been shown that increasing the amount of time spent completing physiotherapy exercises improves the ability of the patient to complete activities of daily living. One method of increasing access to rehabilitation is to create inexpensive, portable, wearable robotic systems that individuals can use at home and outside the clinic to complete physiotherapy exercises. It has been found that robotic therapy can provide the same benefits as conventional physiotherapy and that upper limb functions improved when robotic therapy was completed in addition to traditional therapy. Robotic therapy has many advantages such as progress tracking, real-time feedback, and reducing therapist workloads. However, these robotic devices are not standard due to their high cost and limited portability, which stems partly from using electric motors as the primary actuator. One method to reduce the cost and increase the portability of wearable robotic devices is to use alternative actuators, such as artificial muscles.

Artificial muscles have additional advantages of being biomimetic and compliant, reducing the risk of injury to the user. One promising type of artificial muscle available are twisted coil actuators (TCAs). TCAs are a promising actuator for wearable robotic devices due to their inherent compliance, low profile, easy and inexpensive fabrication method, and linear actuation. These artificial muscles are created by super-coiling silver-coated nylon thread, and they can carry loads up to 80 MPa. They will contract up to 21% when electrically heated and extend upon cooling. Unfortunately, their low bandwidth with passive cooling limits their effectiveness in devices designed for rehabilitation purposes. To increase the potential for TCAs to be used in wearable robotic devices, their cooling time needs to be decreased.

Technology Overview

Researchers at Western University have developed a novel cooling apparatus for TCAs that is specifically designed for soft wearable robotic devices. The cooling apparatus consists of a flexible fabric channel made from nylon pack cloth. The fabric channel is lightweight and could be sewn onto other garments for assembly into a soft robotic device. The TCA is placed in the channel, and a miniature air pump is used to blow air through it to enable active cooling. In the initial experimental evaluations, the performance of the TCA improved as the channel dimensions increased, with the combination of a 10 mm width and an 8 mm height resulting in the best balance between cooling time, heating time, and stroke. This channel was utilized in follow-up experiments to determine the impact of the cooling apparatus on TCA performance. In comparison to passive cooling without a channel, the channel and miniature air pump reduced the TCA cooling time by 42%. This work demonstrates that fabric cooling channels are a viable option for cooling thermally actuated artificial muscles within a soft wearable device.

Benefits

TCAs provide a much more appropriate method of actuation for wearable devices over the traditional electric motors, which are large, heavy and stiff in comparison.
Incorporating the channel and air pump decreases the TCA cooling time by 42% in comparison to passive cooling.

TCAs are a promising actuator for wearable robotic devices due to their inherent compliance, low profile, easy and inexpensive fabrication method, and linear actuation in comparison to shape memory alloys and pneumatic artificial muscles.

The channel material, nylon, is commercially available on large scales.

Applications

• Soh wearable robotics: This cooling apparatus for TCAs could be applied in many different soft robotic systems such as health (rehabilitation, motion assistance, motion control); sports (guided training); gaming (to provide haptic feedback) and space (to prevent muscle atrophy).

Opportunity

• Licensing
• Partnerships
• Collaborative Research

Patents

• Provisional filed August 2022.

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