Design and Modeling of a Textile Pressure Sensor for Sitting Posture Classification Journal Article

Journal Article: Design and Modeling of a Textile Pressure Sensor for Sitting Posture Classification

Summary

It is important to note, from the onset, that the relevance of analyzing siting posture cannot be overstated in healthcare and biomedical realms. For this reason, there is need to develop posture monitoring systems that are not only confortable, but also economical and more efficient. Towards this end, Meyer, Arnrich, Schumm, and Troster suggest a textile pressure sensor designed to not only monitor but also measure a person’s body pressure distribution. In this case, the authors point out that “electrodes built with conductive textiles are arranged on both sides of a compressible spacer, forming a variable capacitor.”

Over time, various techniques have been utilized in an attempt to gauge siting posture. Some of the said techniques include, but they are not limited to, using radiographs for spinal curve examination, sitting state video analysis, etc. Others include the utilization of specialized chair pressure sensors. All these approaches have had a weakness or two – with the most prominent weaknesses being prohibitive cost of acquisition, complexities of use, etc. It is important to note that the utilization of textiles in this case is a welcome step in the right direction. This is more so the case given that as the authors point out, sensors of this kind are not only washable, but also lightweight, and confortable.

The textile pressure sensor adopts a dynamic design that is made up of two parts. These, as the authors point out, are the textile sensor array and the measurement electronics. Towards this end, textile wires are utilized in the routing of electrical signals which are linked and moored to the devices adapted for communication as well as measurement. While the textile sensor is made up of a three key components, i.e. a compressible spacer and two electrodes effectively creating a variable capacitor; it should be noted that with regard to the measurement electronics, “the capacitance to digital converter AD7745 from Analog Devices is used to measure the capacitance of the sensor elements.” In reference to the textile sensor, the induced pressure causes the thickness of the compressible spacer to vary. On the other hand, the other component of the textile sensor i.e. two electrodes, as the authors point out, “are arranged on one side of the spacer as an array, while the other side consists of one common electrode, forming the capacitors between each electrode and the common electrode.”

In seeking to appraise as well as assess the sensor system’s quality, the authors of this particular piece conduct a sitting postures classification experiment. In total, 16 sitting postures are classified. In this particular undertaking, the authors make use two sensor systems, i.e. the textile sensor system and a pressure mat that is commercially available. For reference purposes, the latter is placed below the former. The authors point out that the textile sensor’s pressure distribution is not in any way affected by the placement of the reference sensor. On this front, the authors further note that “the two sensor systems have been synchronized so that only the frames of the reference systems are used with a timely corresponding frame of the textile sensor system.” The kind of chair used in the experiment is height-adjustable, meaning that regardless of the height of the subject, both of their feet can touch the ground while sitting on the chair. The authors conducted an evaluation of the following sitting postures in the experiment: “seated upright (1), leaning right (2), left (3), forward (4), back (5), left leg crossed over the right (6), right over left (7), once seated upright and once leaning back (8) and (9), once while the knees are touching and once with the ankle rested on the leg (10)–(13), slouching (14), sitting on the leading edge (15), and slouched down (16).” A total of nine subjects participated in this particular undertaking. The authors concluded that the rate of recognition was 59% and 82% without, and with back sensor respectively. It should be noted that the reading I highlight herein is inclusive of hysteresis compensation. On the other hand, the reference system recorded a recognition rate of 56% and 84% without, and with back sensor respectively.

The textile pressure sensor is a welcome addition to sitting posture monitors and could, as a matter of fact, prove to be a better alternative to systems available at present. Various studies have clearly indicated that an inappropriate sitting posture could be injurious to a person’s health. Textile pressure sensors would have wider application than just the monitoring of sitting posture for health purposes. Thanks to the utilization of textile, and as the authors of this particular article point out, “clothing is worn almost anytime and is an ideal substrate for mounting sensors with direct contact to the body.” This effectively means that sensors of this nature could be utilized in sports and occupational training as well. However, it is important to note that there are various concerns that ought to be addressed on this front for the textile pressure to be not only more efficient, but also viable as far as its medical application is concerned. For instance, for sensing purposes, textiles, as the authors observe, do not provide optimal utility in comparison to some other materials. This, in the author’s own words, is largely because “hysteresis provoked by compressed or stretched material influences the measurement of pressure or stretch sensors.” The authors suggest a possible solution to this concern, i.e. via textile comportment modeling. The said modeling, which the authors clearly highlight in the fourth section of the paper, helps in the further enhancement of the sensor system’s accuracy.

The spacer’s permittivity is yet another concern that ought to be highlighted especially given that the same could change over time. It is important to note that this permittivity does influence the capacitance measurement. For this reason, the said permittivity changes which do not reflect changes in pressure could negatively impact capacitance measurement. In the words of the authors, “such alternations could occur due to aging and changes in the material of the spacer, humidity, or temperature.” With that in mind, there is need to further examine and evaluate these parameters and their influence upon capacitance measurement and how adverse or undesired influences could be curtailed or minimized. Addressing the said concerns would be a welcome move especially given that at the present time, the classification accuracy of the textile pressure sensor and that of related work is comparable - effectively making the latter as viable as the commercial system utilized for reference purposes. The relevance of this article is not, therefore, in question.