With the improvement of the degree of social automation, the human-computer interaction capability urgently needs a big change, and it is developing in a more convenient and more intuitive direction. The laser treatment machine mainly uses the physical properties of the laser to act on the human body, and produces a chemical reaction of the body to achieve the purpose of treating diseases. As a precision instrument, the laser treatment machine requires precise control and strict requirements for dustproof, anti-static and moisture-proof. The laser treatment machine input device adopts touch screen control, which is based on the above requirements and is also considered from the perspective of user-friendly operation and intuitive interface. The touch screen application combines the display of data with the input of data, simplifying the entire device.

1 touch screen principle

The touch screen is attached to the surface of the display for use with the display. The analog electrical signal is generated by touch, and the coordinates of the touched point are calculated by the microprocessor after being converted into a digital signal, thereby obtaining the operator's intention and executing. The touch screen can be divided into five categories according to its technical principle: vector pressure sensing type, resistive type, capacitive type, infrared type and surface acoustic wave type, wherein the resistive touch screen is used more in practical applications. The resistive touch screen consists of 4 layers of transparent thin film, the bottom layer is the base layer made of glass or plexiglass, and the top is a layer of plastic layer which is hardened and smoothed to prevent scratching, and is attached to the inner surface of the upper and lower layers. It is a metal conductive layer (OTI, indium oxide), which is insulated by fine transparent isolation points. When the finger touches the screen, the two conductive layers are in contact at the touch point.

The two metal conductive layers of the touch screen are used to measure the coordinates of the X-axis and Y-axis directions, respectively. The conductive layer used for the X coordinate measurement draws two electrodes from the left and right ends, denoted as X+ and X-. The conductive layer used for the Y coordinate measurement leads two electrodes from the upper and lower ends, denoted as Y+ and Y-. This is the lead structure of the four-wire resistive touch screen. When a voltage is applied across a pair of electrodes, a uniform continuous voltage distribution is formed across the conductive layer. If a certain voltage is applied to the pair of electrodes in the X direction, and no voltage is applied to the pair of electrodes in the Y direction, the voltage at the contact can be reflected on the Y+ (or Y-) electrode in the X parallel voltage field. By measuring the voltage of the Y+ electrode to ground, the X coordinate value of the contact can be known. Similarly, when a voltage is applied to the Y electrode pair and no voltage is applied to the X electrode pair, the Y coordinate of the contact can be known by measuring the voltage of the X+ electrode. The measurement principle is shown in Figure 1.

Figure 1 Four-wire touch screen measurement principle

The five-wire touch screen is different from the four-wire type. The main difference is that the five-wire touch screen draws out the four ends of one of the conductive layers as four electrodes, and the other conductive layer only outputs the voltages in the X and Y directions as the measured conductors. The measurement is alternated in the X and Y directions. Apply voltage.

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