Basic Knowledge And Principles Of Touch Screens (2) ——Basic Principles And Characteristics Of Capacitive Touch Screens

In recent years, with the rise of smart phones and tablet computers, the capacitive touch screen market has developed rapidly, and the technology has been updated very rapidly, and the industry has shown a blowout development. One is that the size has not increased gradually, from a few inches to tens of inches, the function is getting stronger and stronger, waterproof, oil-proof, adapt to high and low temperature, from a single point to multiple points, currently supports up to 80 points of touch, this is The biggest difference with resistive touch, resistive touch intelligently realizes single-point touch. In addition, capacitive touch has better penetration performance and a wide range of applications. The appearance is simple and generous, which is very popular.

The basic technical principles and characteristics of capacitive touch: capacitive touch screen technology uses the current induction of the human body to work. The capacitive touch screen is a four-layer composite glass screen. The inner surface and the interlayer of the glass screen are each coated with a layer of ITO. The outermost layer is a thin layer of silica glass protective layer. The interlayer ITO coating is used as the working surface, and the four corners are led out Four electrodes, the inner layer of ITO is a shielding layer to ensure a good working environment. When a finger touches the metal layer, due to the electric field of the human body, a coupling capacitor is formed between the user and the surface of the touch screen. For high-frequency current, the capacitor is a direct conductor, so the finger draws a small current from the contact point. This current flows from the electrodes on the four corners of the touch screen, and the current flowing through these four electrodes is proportional to the distance from the finger to the four corners. The controller calculates the position of the touch point by accurately calculating the ratio of these four currents. .

Capacitive screens need to realize multi-touch by increasing the electrodes of mutual capacitance. Simply put, the screen is divided into blocks, and a set of mutual capacitance modules in each area work independently, so the capacitive screen can be independent The touch condition of each area is detected, and after processing, multi-touch is simply realized.

The advantages of capacitive touch screens are mainly reflected in the good sense of interaction of the man-machine interface. When the user touches the capacitive screen, due to the electric field of the human body, the user's finger and the working surface form a coupling capacitor. Because the working surface is connected to high-frequency signals, the finger absorbs one. A very small current flows from the electrodes on the four corners of the screen. In theory, the current flowing through the four electrodes is proportional to the distance from the finger tip to the four corners. The controller calculates the proportions of the four currents. , Get the location. It can reach 99% accuracy and has a response speed of less than 3ms.

The touch technology of the capacitive panel. The projected capacitive touch screen is to etch different ITO conductive circuit modules on two layers of ITO conductive glass coating. The etched patterns on the two modules are perpendicular to each other, and they can be regarded as sliders that continuously change in the X and Y directions. Since the X and Y structures are on different surfaces, a capacitor node is formed at the intersection. One slider can be used as a drive line, and the other slider can be used as a detection line. When the current flows through one wire in the drive line, if there is a signal of capacitance change from the outside, it will cause the change of the capacitance node on the other layer of wire. The change of the detected capacitance value can be measured by the electronic circuit connected to it, and then converted into a digital signal by the A/D controller for the computer to perform arithmetic processing to obtain the (X, Y) axis position, and then achieve the purpose of positioning.

The capacitive touch screen structure is composed of a four-layer composite screen: the outermost layer is a protective glass layer, followed by a conductive layer, the third layer is a non-conductive glass screen, and the fourth innermost layer is also a conductive layer. The innermost conductive layer is the shielding layer, which plays the role of shielding the internal electrical signals. The middle conductive layer is the key part of the entire touch screen. There are direct leads on the four corners or sides to detect the position of the touch point.

The specific working principle is as follows:

Capacitive touch has obvious advantages, mainly in the following seven aspects:

The first is high accuracy, up to 99% accuracy.

The second material has strong performance and reliability: completely scratch-resistant glass material (Mohs hardness 7H), not easy to be scratched and worn by sharp objects, and not affected by common pollution sources, such as water, fire, radiation, static electricity, dust or oil. It also has the eye protection function of goggles.

Third, three high sensitivity: less than two ounces of force can be sensed, and a quick response of less than 3ms. fourth

Fourth, high definition: three surface treatments (Polish, Etch, Industrial) are available. The MTBF of the SMT controller is greater than 572,600 hours (per MILHANDBOOK-217-F1).

Fifth, long service life, touch life: any point can withstand more than 50 million touches

Sixth, the stability is good, and the cursor does not drift after one calibration.

Seventh, the light transmittance is good, and the light transmittance can reach more than 90%.

Lihaojie is a high-tech enterprise that specializes in open displays, embedded displays, industrial touch displays, industrial computers, industrial liquid crystal display modules, and industrial control motherboards, which integrates R&D, design, manufacturing and sales to serve Industry 4.0. . Products mainly include: industrial touch screens, liquid crystal display modules, displays, industrial integrated machines and other industrial control products.