Take the X-axis transmitting transducer in the lower right corner as an example. The transmitting transducer converts the electrical signal sent by the controller through the touch screen cable into sound wave energy and transmits it to the left surface, and then is controlled by a set of precision reflection stripes under the glass plate. The sound wave energy is reflected into an upward uniform plane to transfer. The sound wave energy passes through the surface of the screen, and then is gathered by the upper reflection fringe into a rightwardly propagating sound wave to the X-axis receiving transducer. The receiving transducer changes the returned surface acoustic wave energy For electrical signals.
When the transmitting transducer emits a narrow pulse, the sound wave energy reaches the receiving transducer through different paths. The sound wave energy arrives at the earliest by going to the far right, and arrives at the latest by going to the far left. The sound wave energy that arrives early and arrives late is superimposed into one. Wider waveform signal. It is not difficult to see that the received signal is a collection of all the acoustic energy returned through different long and short paths in the axis direction. They travel the same distance on the y axis, but on the x axis, the farthest one travels twice as much as the nearest one. The maximum distance on the x-axis. Therefore, the time axis of this waveform signal reflects the position before each original waveform is superimposed, which is the X-axis coordinate.
When there is no touch, the waveform of the received signal is exactly the same as the reference waveform. When a finger or other object that can absorb or block sound wave energy touches the screen, the sound wave energy going up on the X axis through the finger part is partially absorbed, reflecting that there is an attenuation gap in the received waveform, that is, the waveform at a certain moment. The receiving waveform attenuates a notch corresponding to the signal at the part blocked by the finger. The controller analyzes the attenuation of the received signal and determines the X coordinate from the position of the notch. After that, the F axis uses the same process to determine the y coordinate of the touch point. In addition to the x and y coordinates that the general touch screen can respond to, the surface acoustic wave touch screen also responds to the third axis Z coordinate, that is, it can sense the magnitude of the user's touch pressure. The principle is calculated from the attenuation at the attenuation of the received signal. Once the three axes are determined, the controller transmits them to the host.
The controller detects the touch by comparing the received signal with the reference waveform under untouched conditions. This process allows the controller to ignore impurities such as dust and scratches. The controller continues to detect and eliminate the impurity pollution factors. When a "touch" lasts for about 3 seconds, the controller will make a judgment and eliminate the impurity factor.
In this case, a new reference waveform is required to effectively ignore the impurities and restore the normal operation of the touch screen. If the impurities are removed, the controller will repeat the new reference waveform request procedure again.
