Due to the rapid development of plasma and LCD video technologies and the pursuit of high-end consumer goods, a large number of positioning technology and display technology combined with the emergence of large-scale smart touch screen products. One of the more cost-effective infrared positioning technology has been developed from the initial touch screen to the current large-scale smart touch screen, write, control screen, and touch, write, control the size range is increasingly large. Therefore, the key technical issues to be solved in the design of large-scale smart touch screens are construction, resolution, refresh rate, and structural design.
Large-Scale Smart Touch Screen Construction
Example: 4m long and 2m high electronic blackboard or whiteboard, we install every 5mm (the actual installation will be larger than 5mm) an infrared tube or receiver tube, where the infrared tube diameter is also 5mm. the length of the transmitting side and the receiving side are 6m, a total of 2,400 tubes, of which the upper side needs 800 transmitting tubes, the lower side needs 800 receiving tubes, the left side needs 400 transmitting tubes, and the right side needs 400 receiving tubes. The left side requires 400 transmitting tubes and the right side requires 400 receiving tubes. According to the test, it takes 0.2ms to scan a pair of tubes, and 160ms to scan the long side and the short side at the same time, with a refresh rate of 6.25 times per second for the long side and 80ms for the short side, with a refresh rate of 12.5 times per second. Even if the display area of the whiteboard is reduced to 1/4 of the above size, i.e., 2m long and 1m high, the refresh rate is only 1 time higher, which is difficult to meet the usage requirements. Generally, it is necessary to refresh 50 times per second to meet the requirements. Our 70 large-scale smart touch screen products can be designed to refresh more than 80 times per second.
Large-Scale Smart Touch Screen Resolution Design
Resolution is an important indicator of the large-scale smart touch screen and can affect positioning accuracy. For the example given above, the resolution of a typical infrared touch screen is 800 x 400, but, based on optical knowledge, the software is designed to subdivide the light particle reception density to precisely touch the occluded location, such as 4, 8, 16, etc. Here is a simple calculation method, when a touch point is detected, in which the light of three infrared tubes in the horizontal direction is blocked or partially blocked, in which the middle tube is completely blocked, the left tube is blocked 5/16, and the right tube is blocked 11/16, the touch center position is in the middle tube from left to right 11/16, and the touch width is exactly 2 times the width of the tube; the calculation method for the vertical direction is the same. The calculation is the same for the vertical direction. In fact, when a circle is divided horizontally into 16 equal parts, the area of the 16 parts is not exactly the same, with the area near the middle being larger and the area near the side being smaller. Therefore, the above method has to be corrected for this factor to achieve the exact position calculation.
The method provided in Chinese Patent No. ZL00818786.X can determine the position of a fixed touch point, but for a moving touch point, there is a delay from initial positioning to precise positioning, and the touch position has changed, so the meaning of precise positioning no longer exists. Draw a line through the touch screen at a rate of 1m per second. Even if the line is drawn at a slow speed of 0.25m per second, the touch point moves by 5 mm, which is equivalent to the distance between two infrared tubes, so it is not possible to perform precise operations such as touching and writing.
Large-Scale Smart Touch Screen Refresh Rate Design
The following is an example of the impact of a low refresh rate on the use of a large-scale smart touch screen, if you want to draw a small circle 10cm in diameter on the touch screen, assuming that 1 second to complete, if the refresh rate of 6 times per second, because only 6 touch points are collected, the computer can only draw a hexagon instead of a circle, the same, if the refresh rate of 12 times per second, the computer will only draw 12 sides. If the writing is to be completed, the handwriting will not be smooth, and the pen will be broken or even distorted. We designed the 70-in smart interactive touch screen product refresh rate that can reach more than 80 times per second. It writes beautifully, with smooth lines.
Large-Scale Smart Touch Screen Structural Design
The simple structure and processing are also important factors to be considered in our design and implementation. We did not adopt the approach of some manufacturers to install a light guide hole in front of the infrared tube, because such an approach can solve the interference problem mentioned above to some extent. However, during the production process, it is difficult to align the transmitter and receiver tubes with the light guide hole, and the light will be weakened by the blockage. More importantly, climate change and a long time after use, structural components and circuit board thermal expansion and contraction of different degrees, and aging deformation will further lead to light deviation from the right relationship, ultimately affecting the positioning performance. Some manufacturers of infrared touch screens have encountered problems such as inaccurate positioning and pen breakage or pen skipping. Since we designed the product using innovative technology to solve the interference problem, there is no need to design the structure of the light guide holes and other masking measures to fully ensure that the light emission channel, even if the transmitter module and receiver module alignment error of more than 1cm will not affect the light reception performance. For example, with the need for 2400 infrared tubes for a large touch screen, our design does not require each infrared tube alignment performance to be identical, we must tolerate a certain amount of infrared tube error and installation error, in fact, the infrared tube alignment center error is generally greater than 50, and the general alignment performance of good screening rate of only one-tenth, which will greatly increase the purchase cost of infrared tubes. When designing the program, it was suggested to add a spotting prism in front of each emitter tube, but the cost increased significantly and the production process was quite complicated.
Only by solving the above problem, can we develop large-scale smart touch screens well.
