The most profound technological change affecting touch screen performance is the transfer from resistive to capacitive touch screen technology. According to market forecaster iSuppli, by 2011, nearly 25% of touch-screen phones will be transferred from resistive to capacitive touch screens. The various benefits brought by capacitive touch screen technology will prompt the market to grow rapidly.
In the conventional resistive touch panel, when the finger or the stylus is sensed, the top flexible transparent material is pressed down to contact the underlying conductive material layer; and the projected capacitive screen has no movable parts. In fact, the projected capacitive sensing hardware consists of a top layer of glass, followed by X and Y axis components, and an indium tin oxide (ITO) insulating layer overlying the glass substrate. Some sensor suppliers will make a single-layer sensor with embedded X and Y-axis sensors and small bridge components in a single layer of ITO. When a finger or other conductive object is close to the screen, it will be generated between the sensor and the finger. A capacitor. This capacitance is quite small compared to the system, but it can be measured using a variety of techniques.
One technique is to use TrueTouch components, including quickly changing the capacitance and using a bleeder to measure the discharge time. This all-glass touch surface gives the user a smooth and smooth feel. End-product manufacturers also prefer glass screens because glass materials give end products a line of aesthetically pleasing industrial design and provide superior capacitive signals for measuring touch. Finally, it is important not only to consider the appearance of the touch panel, but also to understand its mode of operation. In order to design a touch screen product with excellent performance, the following parameters must be noted.
Accuracy : Accuracy can be defined as the maximum positioning error in a predefined touch screen area, in units of the linear distance between the actual position of the finger and the measurement position. When measuring accuracy, an analog or mechanical finger is used. Place your finger in an exact position on the panel and compare the actual position of the finger to the measured position. Accuracy is very important, and the user wants the system to accurately find the finger position. One of the most frustrating drawbacks of resistive touch screens is their low accuracy and the gradual decrease in accuracy over time. The precision of capacitive touch screens creates many new applications, such as virtual keyboards and handwriting recognition without the stylus. Figure 1 shows an incomplete touch panel data showing that the finger position has a wandering phenomenon, but actually the simulated finger is moving in a straight line.
Figure 1 shows an inaccuracy or error in touch panel tracking.
Finger Spacing : Finger spacing is defined as the shortest distance between the center points of two fingers on the screen when the touch screen controller measures the position of two fingers. The finger spacing measurement method (Fig. 2) is to place two analog or mechanical fingers on the panel and then gradually pull the distance between the two fingers until the system detects that the two fingers are one finger. Some touch screen vendors' finger spacing is the edge-to-edge distance, and some are the distance between the center points. The 10 mm finger spacing of a 10 mm mechanical finger indicates that multiple fingers touch the screen, or the distance between the fingers is 10 mm, depending on the specifications of the touch controller. Without good finger spacing, you can't design a multi-touch solution. Finger spacing is especially important for emulated keyboards because the spacing of the fingers on the screen is typically very short when using a simulated keyboard.
Figure 2 Measuring finger spacing
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