3D Force Measurements and the Application in Handwriting Recognition

Three-dimensional (3D) force sensor refers to a sensor that can measure forces in three directions at the same time. Because of its rich force measurement information, it is widely used and researched. The working principle of the flexible three-dimensional force sensor is to convert the external force into the change of the internal parameters of the sensor, and obtain the force components in the x, y, and z directions through analytical formulas. According to the different working principles, it can be divided into Four types are capacitive sensors, piezoresistive sensors, piezoelectric sensors and electromagnetic sensors. This paper studies a new type of flexible capacitive three-dimensional force sensor, which can detect horizontal force while detecting vertical pressure. The sensor is composed of 4 capacitors, using the symmetry analysis of the sensor to obtain the positive pressure in the vertical direction and the tangential force in the horizontal direction. In order to verify the practicability of the sensor, this article has realized the application of the sensor in handwriting recognition by establishing a fast capacitance array measurement system and a software system with a GUI interface in Matlab. Experimental results show that the system has a measurement error within 0.1 %, a sensitivity of 1 V/pF, and a minimum resolution of 3 fF. It can be seen that the measurement system can meet the requirements of three-dimensional force detection sensors.