Ponieważ konsumenckie urządzenia komunikacji mobilnej coraz częściej przyjmują metody cyfrowe i integrują więcej funkcji, rozwój intuicyjnych i innowacyjnych rozwiązań interfejsu użytkownika (UI) stał się ważniejszy dla projektowania urządzeń. W ramach projektowania interfejsu użytkownika projektowane pojemnościowe ekrany dotykowe pomagają sprostać temu wyzwaniu.
To design a successful projected capacitive touch screen system, it is necessary to carefully consider the mechanical design, substrate selection and user interface of the device. In addition, at all stages of the design process, one must not forget the trade-off between cost and technology.
Different from resistive touch screen technology, projected capacitive touch screen is easier to handle finger movements, especially multi-touch user input. Resistive technology needs to rely on finger pressure to make electrical contact with multiple mechanical layers of the touch screen.
This method of operation will affect the fluency of finger sliding and the dexterity of gesture operations. In addition, the multilayer mechanical structure of the resistive touch screen is prone to early wear due to repeated use.
Several common multi-touch gestures implemented with the projection touch screen include finger pinching, zooming, two-finger sliding and rotating. They can process data, content and user parameters quickly and easily. Portable games and text/email applications can also take advantage of multi-touch technology. In a multi-finger touch process, the multi-touch APA (all-point addressable) mode can accurately determine the coordinate position pressed by each finger.
There is no need to press Shift to change the character set and then input the actual characters. Multi-touch can click Shift plus actual characters at the same time. Multi-touch methods are also widely used in GPS navigation. No need to enter the starting place and destination, APA can realize the choice of the target location on the screen, allowing people to reach the destination faster. Figure 1 demonstrates some of the possible scenarios for multi-touch operations.
Aby ocenić konstrukcję mechaniczną urządzenia, należy rozwiązać kilka kluczowych problemów:
1. Is the protective layer (touch surface) flat or curved?
It is generally recommended to install a capacitive touch screen on a flat touch surface. Curved surfaces add complexity. To achieve a robust capacitive touch design, the transparent touch sensor must be neatly clamped under the protective layer. Any air bubbles generated due to uneven pressing will reduce the touch performance and affect the aesthetics of the product.
The curved protective layer can only use PET (polyester) as the base of the touch sensor. The plastic sensor can be bent to adapt to the shape of the protective layer. If you must use a curved protective layer, from the perspective of reflection, it is recommended that the curvature does not exceed 45 degrees. The increase in curvature will increase the difficulty of the pressing process and may damage the ITO (Indium Tin Oxide) pattern, which may affect the yield.
It is cheaper to use pressure sensitive adhesive (PSA) to realize pressing, but it cannot be used for curved protective layer. To ensure better compression integrity, more expensive UV-curable adhesives may be used. UV adhesives are expensive, but they are easy to use, have a thin adhesive layer, and have very high optical quality (transparency greater than 95 percent ).
2. What is the edge width of the non-working area (opaque area) of the protective layer?
For touch screens with a size less than 4 inches (10 cm), the edge width of the touch screen should not be narrower than 10mm on the side of the tail wire of the touch sensor, and the sides adjacent to the tail wire should not be narrower than 3mm. This edge space is used to hide the non-transparent silver foil wire that links the transparent ITO pattern to the control circuit and hide the control circuit itself. For touch screens using glass substrates, the width of the edges may be narrower, but the above guidelines are still recommended. Figure 2 describes these guidelines.
3. Z jakiego materiału wykonano warstwę ochronną?
In the working area of the touch screen, conductive materials should not be used for the protective layer and any decorations.
Because the use of conductive materials will shield the electric field of the capacitive sensor and greatly reduce the sensing performance. The thickness of the protective layer should be 1mm or less.
4. What is the distance between the bottom surface of the protective layer and the liquid crystal display module (LCM)?
Due to the compact size of portable communication devices, the distance between the liquid crystal module (LCM) and the protective layer needs to be considered. There must be enough space to install the thin touch screen sensor. In addition, there must be a large enough air gap to prevent the touch sensor from electromagnetic interference from the LCM. It is recommended to leave a gap of at least 0.5mm between the touch sensor substrate and the LCM.
5. How to deal with electrostatic discharge (ESD)?
In order to prevent electrostatic discharge events from occurring on the touch surface, a low-impedance ground path must be set up throughout the entire device. A ground ring placed in the non-working boundary area of the protective layer should be used to protect the touch sensor.
The ground ring can be a simple metal foil. It must be ensured that there is a reliable connection between the ground ring and the system ground of the device.
After completing the mechanical evaluation, a suitable substrate must be selected for the touch screen.
