Analysis and Characterization of Embroidered Textile Strain Sensors for Use in Wearable Mechatronic Devices
Abstract
Stroke and musculoskeletal disorders affect hundreds of millions of people around the world. To aid in the recovery process of people affected by these conditions, the use of wearable mechatronic devices has been proposed during traditional rehabilitation therapies. However, factor such as rigidity, increased weight, and overall bulkiness have hindered the adoption of these devices in a clinical setting. Therefore, alternative solutions in the form of soft wearable mechatronic devices have been proposed recently. This is due to these devices being lightweight and comfortable, and compliant, which makes them easier to conform to the human body. To achieve such compliance, high emphasis has been placed on the development of soft sensing mechanisms, as they are in charge of collecting information from the device, the environment and user. Among these sensing mechanisms, force and motion sensors have been extensively studied, as they are the simplest to integrate in wearable mechatronic devices. However, the majority of these sensors have been developed using soft materials that are not breathable and can cause skin irritations due to the materials used to fabricate them. For these reasons, textile sensors have been proposed as an alternative. Among these textile solutions, embroidered sensors have shown great potential, as they are relatively simple to manufacture and have high scalability characteristics. Unfortunately, embroidered sensors have the disadvantage of not being stretchable, which is one of the many characteristics of motion and force sensors. To address these issues, this thesis focuses on the design, development, characterization, and performance assessment of embroidered textile strain sensors. To this end, a framework for the development of embroidered textile strain sensors was proposed. This framework included all the necessary steps to design and fabricate these sensors. To achieve the required stretchability of embroidered sensors, a set of customizable parameters were included within this framework. Then, following the guidelines of the proposed framework, a novel embroidered strain sensor was created using a honeycomb pattern. This pattern had two main purposes: a distribution of the axial forces across the walls of the honeycomb design to protect the conductive thread; and the addition of stretchiness to the embroidered sensor. Sensors created using this pattern were embroidered onto an elastic band and then attached to a strain compensation system to increase the stretchability of the sensor further. After 50 stretching cycles, sensors showed good linearity, an average gauge factor of 0.24, an average hysteresis of 36.85% and up to 55.56% working range. This demonstrated the ability of the embroidered sensor to work as a strain sensor, without showing signs of damage and without showing signs of deformation. Lastly, a series of embroidered sensors were fabricated using a Kirigami design. These sensors were created to measure forces under dynamic conditions. Before testing, these sensors were attached to a strain compensation mechanism, which in turn was attached to a force sensing device that served as ground truth for the data collected by the embroidered sensors. The embroidered sensors were tested under three different speed profiles: slow speed, medium speed, and high speed. On each speed profile, each sensor showed high linearity, a low hysteretic behaviour, and relatively good repeatability. These results established the capabilities of the embroidered strain sensors as force sensors that could be used inside soft wearable mechatronic devices.