## 3 Experiments and Results
### Guideline for Fabricating Pressure Sensors for Individual Applications
#### 3.2.2 Experimental Participant Information
In the conversion movement from a standing to a sitting position, the pressure change increases to \(0\%\) or more at the upper part of the front and rear parts and \(+50\%\) or more at the lower part of the rear parts. In the case of the sensors in the position of the biceps femoris, the pressure value generated due to the pressing of the lower part in the seated state is different. Therefore, two positions of the biceps femoris exceed the threshold setting. Table 6 summarizes the internal pressure change patterns of the socket to set a threshold based on the results of the pressure changes according to the six movements presented in Figure 14. In the standing position, all four sensors begin their initial state at \(0\%\), and when converted to flat locomotion, they are \(-100\%\), \(100\%\), \(-100\%\), and \(50\%\) in order from the front to the rear. When converting to the stair climbing movement, the results are \(-100\%\), \(100\%\), not set, and \(0\%\), and when converting to the stair descending movement, the value shows a \(100\%\) rise at all four positions. Conversion from standing to sitting presents values of \(-100\%\), \(100\%\), \(50\%\), and \(0\%\), and for conversion from sitting to standing, the value changes from \(-50\%\) to \(0\%\), not set, \(50\%\), and \(0\%\). It is possible to detect the movement of the lower limb to be switched by setting a threshold value based on the suggested pressure change characteristics. It was confirmed that the pressure change patterns according to each lower limb movement measured through the application of the fabricated sensor were similar to the expected pressure changes according to the six lower limb movements presented in Section 3. In the experimental results, there is a position at which different pressure changes are determined depending on the subject, even though the same behavior is verified. It is difficult to set a clear threshold at the lower part of the biceps femoris in flat locomotion and stair climbing movements and the lower part of the rectus femoris in the conversion from sitting to standing movements. This is caused by a difference in the structure of the transfemoral prosthesis socket for each subject. In addition, it is estimated that the difference occurs due to the variations in the subjects' physical structure, posture, and habits of performing movements. For this reason, when setting the scale of the pressure change at each sensor position to the critical value, only the common occurrence conditions are verified and defined. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Pressure Change of** & **Pressure Change of** & **Pressure Change of** & **Pressure Change of** & **Pressure Change of** \\  & **Sensor 4 [\%]** & **Sensor 3 [\%]** & **Sensor 2 [\%]** & **Sensor 1 [\%]** & \\  & **(Upper of Biceps** & **(Lower of Biceps** & **(Lower of Rectus Femoris)** & **(Upper of Rectus Femoris)** & **(Upper of Femoris)** & \\ \hlineThrough these experiments, the possibility of measuring pressure changes according to the lower limb movement of the flexible pressure sensor system based on the Velostat film proposed in this study was confirmed. It was verified that accurate classification was possible according to each movement by addressing the problems of not detecting pressure changes and the saturation of existing pressure sensors. In addition, the possibility of classifying the movement intention was determined by confirming the patterns of pressure changes according to six intentional movements. There was a point at which the time required for a pressure change for each subject was different, but this could be addressed according to the degree of movement learning of the user. The Velostat-film-based sensor proposed in this study is able to set a relatively clear threshold by solving the problems of not detecting pressure changes and the saturation of existing capacitive sensors.