Textile based sensing system for leg motion monitoring

In recent years, electronic products have become integrated with textile products with the production of chips having small size, being cheap and needing low energy need. Thanks to research in the field of textile, e-textile was born from the electrical response of textile product to the physical environments. With the multidisciplinary studies carried out in the fields of electronics, computers, control, and textiles, these electronic textiles are now being transformed into products used by consumers. It is possible to see electronic textiles in different fields such as sports training, robotics, health imaging, body motion analysis, etc. The textile based sensors have four different types: resistive, capacitive, optical and solar. Capacitive and resistive sensors can be used in motion capture systems. Resistive sensors have disadvantages such as low linearity, drift problem and high response time, whereas capacitive sensors have good features such as high linearity, low response time and high resolution. Although capacitive sensors have many advantages, noise is generated in the measurement due to the distance between the sensor and the measuring device. Motion capture systems, rely on three different techniques: optical, magnetic and mechanical. Optical motion detection systems operate according to the principle of extracting the skeletal structure of humans by using image processing methods. However, this system has many disadvantages such as the ability to measure in a specific area and require high processing cost in the calculation units. Magnetic motion capture systems are based on the principle of finding joint angles by magnetic sensors placed on the body. Unlike optical motion capture systems, these systems do not require a specific area of operation and high processing cost. However, these systems are affected by objects such as metals and circuits that will create an electromagnetic effect since these systems use magnetic sensors. In mechanical systems, joint angles are determined by sensors placed on the joints. These systems are not affected by the magnetic field and are not required to be used in a specific area. Since the sensor data is equal to the joint data, there is no calculation load. However, special clothing equipped with sensors should be used in such motion capture systems. The cost of this special clothing is the biggest drawback of such motion capture systems. This thesis deals with increasing the measurement quality by reducing the noise due to distance in the measurement of textile based capacitive sensors, creating a prototype with integration to textiles, and developing a motion monitoring system that will receive and store data from the prototype. This thesis focuses on the problem of noise in the measurement results due to the distance which is the biggest problem of capacitive sensors. This makes it possible to make use of the advantage of the capacitive sensors. The electrical system consists of textile based capacitive sensors, microcontrollers, bus, a transmitter, a mobile phone, and a battery. Microcontrollers are placed closest to the sensor. Thus, the noise caused by the distance is minimized. The microcontrollers are connected to the transmitter via bus. The transmitter transmits both requests and power to microcontrollers via the bus. The microcontroller measures and transmits them to the transmitter via the same line. Since the I2C connection is used in the system, the four-wire bus is created for the power and data line. The transmitter transmits the received data to the mobile phone via a Bluetooth connection. The entire system is fed with the battery connected to the transmitter. An Android application has been developed to receive data over a mobile device. The application shows the data to the user and sends them to the server. The server saves the data to the database and also sends it to other web clients instantly. With the prepared web front end, the measurement results are displayed instantaneously. In addition, historical measurement data is displayed on the web front end. Data communication between the web service, phone and web clients is made by socket programming to be fast and instantaneous. The sensor used in the system is a textile based flexible capacitive sensor. This sensor consists of two conductive fabrics and the dielectric material. The sensor acts as a parallel plate capacitor. The increase in the length of the sensor increases the electrode area of the sensor. This change also increases the capacitance of the sensor. In the textile integration of the design, the sensor is placed on the knee using the knee bracket. The microcontrollers are also located near the sensor and connected to the sensor. The bus to be established between the transmitters and the microcontrollers is made of conductive yarns. These conductive yarns are sewn on the fabric strip. In this way, the prototype will be tested under similar conditions to the commercial product to be prepared in the future. In the experiments with the prototype, the test object walks first, then stops, and finally makes a squatting motion. During walking, all characteristics of phases of gait can be extracted from the measurement data. The theoretical and practical results are similar when compared. At the same time, when the signals from both knees are compared, there is a phase difference between the signals parallel to the walking. In the motionless phase, there is no change in the signals. During the squatting motion, both signals move simultaneously, and there is no phase difference between them. When all stages are examined, it is verified the system successfully performs the lower limb motion capturing. The contribution of thesis is that we minimized the noise generated in the measurement results due to the distance which is the biggest problem of capacitive sensors. In addition, a system was prepared to collect data from users and send end-to-end data. Since the system is designed with low-priced materials, it will be suitable to be commercialized. In following studies, a follow-up system for patients in the health care domain, physiotherapy applications, and sports applications etc. can be developed. This thesis will also contribute to science as it opens new fields of study.