How does the automatic wiper work?
The automatic wiper of automobile is an induction wiper. The basic principle is to control the wiper by an inductor. The two mainstream sensors currently widely used are optical sensors and capacitive sensors.
The first one is optical sensor. It is based on the principle of refraction of light. In the optical sensor there is a light emitting diode which emits a cone of light which passes through the front windshield. When there is no rain on the windshield and it is dry, almost all the light is reflected on an optical sensor. When it rains, there will be rain on the windshield, and some of the light will deviate. This will cause changes in the total amount of light received by the sensor, thus detecting the presence of rain. The larger area where the optical sensor can receive reflected light, the more detailed the information obtained. Optical sensors are very accurate and may even accurately determine the number of raindrops that fall on the area being sensed.
Capacitive sensor. Capacitive sensors are mainly designed using the great difference in dielectric constant between water and glass, in which the dielectric constant of water is 80 and the dielectric constant of glass is 2. It is a common practice to place two parallel plates of finger-like metal plates between the inner and outer layers of the windshield. A group of finger-like metal plates are staggered but do not touch other metal fingers. board. When the windshield is in a dry state, a dielectric is formed between the outer surface of the windshield and each set of finger metal plates.
When the windshield gets wet, the dielectric constant of the windshield changes differently depending on the amount of water that is in contact with the windshield. If the sensor is mounted on the surface of the windshield or close to the lower surface of the windshield, this is advantageous for the operation of the sensor, because such an installation enables the sensor to exert its optimum sensitivity. Disadvantageously, mounting the capacitive sensor on the outer surface of the windshield creates the same problems as the resistance sensor, and its metal plating is quickly scraped off the windshield under the long-term operation of the wiper.