The key to resistive touch screen in the material technology. Commonly used transparent conductive coating materials are:
① ITO, indium oxide, weak conductor, the characteristics of when the thickness drops to 1800 e (e = 10-10 meters) will suddenly become transparent, light transmission rate of 80%, and then thin down the transmittance rate fell to 300 ? thickness and rose to 80%. ITO is the main material for all resistive and capacitive technology touch screen touch screen are used. ITO is the main material used in all resistive and capacitive touch screen technology, in fact, the resistive and capacitive technology touch screen work surface is ITO coating.
② nickel gold coating, five-wire resistive touch screen of the outer conductive layer is the use of ductile nickel gold coating material, the outer conductive layer due to frequent touch, the use of ductile nickel gold material is designed to extend the life of the material, but the process cost is relatively high. Nickel-gold conductive layer, although good ductility, but only as a transparent conductor, not suitable as a resistive touch screen work surface, because of its high conductivity, and metal is not easy to do the thickness is very uniform, should not be used as a voltage distribution layer, can only be used as a probe layer.
1, five-wire resistance touch screen:
Five-wire resistance technology touch screen of the grass-roots level of the two directions of the voltage field through the precision resistance network are added to the conductive surface of the glass, we can simply understand that the two directions of the voltage field time-sharing added to the same work surface, and the outer layer of nickel-gold conductive layer is only used only as a pure conductor, there is a touch time-sharing detection of the inner layer ITO Contact X and Y axis voltage value method to measure the position of the touch point. Five-wire resistance touch screen inner ITO need four leads, the outer layer only as a conductor only one, the touch screen lead line **** there are five.
Five-wire resistive touch screen of another proprietary technology is through the precision of the resistance network to correct the inner layer of ITO linearity problems: due to the conductive coating may be uneven thickness and uneven distribution of voltage.
Resistive screen performance characteristics:
① They are all a completely isolated from the outside world of the working environment, not afraid of dust, water vapor and oil
② can be touched with any object, can be used to write and draw, which is their greater advantage
③ Resistive touch-screen precision depends only on the accuracy of the A/D conversion, so they can all be easily reached 4096*4096? Comparatively speaking, the five-wire resistor is superior to the four-wire resistor in guaranteeing the resolution accuracy, but the cost is expensive, so the selling price is very high.
Five-wire resistive touch screen improvements:
First of all, the five-wire resistive touch screen A-side is a conductive glass rather than conductive coating, the conductive glass process makes the A-side of the life has been greatly improved, and can improve the light transmission rate.
Secondly, the five-wire resistive touch screen puts the task of the working surface are given to the long life of the A-side, while the B-side is only used as a conductor, and the use of good ductility, low resistivity nickel-gold transparent conductive layer, so the B-side of the life of the great improvement.
The other proprietary technology of the five-wire resistive touch screen is to correct the linearity of the A-surface by means of a precise resistive network: due to the inevitable possibility of uneven thickness and uneven distribution of the voltage field caused by the process engineering, the precise resistive network flows through the majority of the current during the working time, and therefore compensates for the possible linear distortion of the working surface.
The five-wire resistive touch screen is currently the best resistive technology touch screen, the most suitable for military, medical, industrial control field use.
2, four-wire resistive touch screen
Touch screen attached to the surface of the display, and the display is used in conjunction with the display, if you can measure the touch point on the screen coordinates of the position of the display screen can be based on the corresponding coordinates of the point of the display content or symbols to be aware of the intention of the touch. The resistive touch screen is used more in embedded systems. Resistive touch screen is a 4-layer transparent composite film screen, as shown in Figure 2, the bottom is glass or plexiglass composed of the grass-roots level, the top is a layer of the outer surface after hardening treatment and thus smooth and scratch-resistant plastic layer, in the middle of the two layers of metal conductive layer, respectively, above the grass-roots level and the inner surface of the plastic layer in the conductive layer between the two there are a number of small transparent isolation points to separate them. When the finger touch screen, the two conductive layers in the touch point of contact. The two metal conductive layer of the touch screen is the two working surfaces of the touch screen, at each end of each working surface is coated with a silver gel, known as a pair of electrodes on the working surface, if the electrode pair in a working surface of the voltage applied to the working surface will form a uniform and continuous parallel voltage distribution. As shown in Figure 1, when a definite voltage is applied to the electrode pair in the X direction and no voltage is applied to the electrode pair in the Y direction, the voltage value at the contact can be reflected in the Y+ (or Y-) electrode in the X parallel voltage field, and the X coordinate value of the contact can be known by measuring the voltage magnitude of the Y+ electrode to ground. Similarly, when 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.
Four-wire resistance touch screen defects:
The B-side of the resistive touch screen is often touched, four-wire resistive touch screen B-side of the ITO, we know that the ITO is a very thin oxide metal, in the process of use, will soon produce small cracks, and cracks, once produced, the original flow of current through the place is forced to go around the cracks, the uniform distribution of the voltage and then be destroyed, the touch screen has damage. Destruction of the touch screen on the damage, manifested as cracks at the point is not allowed. As the cracks intensify and increase, the touch screen will slowly fail, so the service life is not long is the main problem of the four-wire resistive touch screen