1. Field of the Invention
The present disclosure relates to a method for detecting a touch, and more particularly, to a method for detecting a touch and a flat panel using the same in which both an upper threshold level and a lower threshold level are set to make more sensitive detection in a structure which uses infrared cameras positioned at least at three corners for receiving and emitting light and retro-reflecting plates for reflecting light from the infrared camera to the infrared camera again.
2. Discussion of the Related Art
In general, a touch screen is one of interface types between a user and an information and communication device which uses various kinds of displays. A touch screen is an input unit which enables the user to interact with the device as the user personally touches a screen with a hand or a pen.
The touch screen is a device which allows for a conversational and intuitive handling of the device, since it may be used by anyone by touching a button displayed on a display device with a finger. Because of these features, the touch screen is applied to many fields, such as issuing machines in banks and public agencies, various medical apparatuses, tour and major facility guidance devices and traffic guidance devices.
In the touch screen, various types are available, such as, but not limited to, a resistive type touch screen, a micro capacitive touch glass, an ultrasonic wave touch glass, an infrared type touch screen, and so on depending on methods of detection used.
The resistive type touch screen typically has two transparent conductive layers where a lower layer thereof is formed of glass or plastic coated with a conductive material and an upper layer thereof is formed of a film coated with a conductive material. The two layers are spaced by micro printed spacers and are electrically insulated. The resistive type touch screen is a device which involves a change of resistance at each of an upper plate (X-axis) and a lower plate (Y-axis) when the upper plate is touched with a hand or a touch pen in a state where a fixed voltage is applied to the two layers with the conductive material coated thereon. In this instance, a controller calculates an X (the upper plate) position and a Y (the lower plate) position by detecting changes in resistances and displays the positions on a monitor or inputs as data.
The micro capacitive touch glass has a transparent glass sensor coated with a thin conductive material. Therefore, an electrode pattern is precisely printed along a periphery of a conductive layer and a transparent vitreous protective film is placed closely on the thin conductive coating for protecting and enclosing the sensor. In the micro capacitive touch glass, a voltage is applied to a screen, and an electrode pattern forms a low voltage field on a touch sensor surface through the conductive layer. When a finger touches the screen, a micro current flows at a touch point. A current from each corner is proportional to a distance from the corner to the finger, and a touch screen controller calculates ratios of current flows to find a position at which the touch is made.
The ultrasonic wave touch glass is not affected by surface damage or wear at all in comparison to other products, which are formed of 100% vitreous material and a lifetime of the expensive touch screens instantly come to an end even by small surface damage or wear. A touch screen controller forwards a 5 MHz electric signal to a transducer to generate an ultrasonic wave, and the ultrasonic wave generated passes a surface of the touch screen by reflected rays. In the ultrasonic wave touch glass, if a user presses a surface of the touch screen, a portion of the ultrasonic wave passing through a pressed point is absorbed by the user, a signal thus lost is identified instantly by a controller through a received signal and a digital map, and based on this, coordinates of a point having a change of the signal presently are calculated. Such a series of steps are performed independently on X- and Y-axes.
The infrared type touch screen utilizes an attribute of the infrared ray in which the infrared ray cannot travel if the infrared ray comes to an obstacle since an infrared ray travels in a straight line. A portion having a pressure applied thereto cuts off the infrared rays in a transverse direction and a longitudinal direction, and X and Y coordinates of a cut off portion are read for sensing. An infrared ray light type touch screen identifies a touched position by detecting a cut off of an infrared ray scan light at a front of the touch screen. The infrared type touch screen has an infrared ray emitted from one side and received at an opposite side for both x and y axes to form a lattice of the infrared ray.
Though above types have different advantages, recently, the infrared type touch screen is drawing attention due to a minimized pressure required to be applied to the touch screen, and convenience of arrangement.
A related art infrared type touch screen will be described with reference to the attached drawings.
FIG. 1 illustrates a plan view showing a touch detecting method of a related art infrared type touch screen.
Referring to FIG. 1, the related art infrared type touch screen is provided with infrared sensors 5 mounted to adjacent two corners of the panel 10 and reflective plates 7 mounted to three sides of the panel 10.
A touch to the infrared type touch screen is detected as follows. That is, lights from infrared sensors 5 at opposite ends of the panel 10 are reflected, lights cut off at the time of the touch are sensed, and angles thereof are calculated, to perceive the touch.
However, the infrared type touch screen has a dead zone with a range greater than a certain angle between the infrared sensors 5 in which the detection is not possible, making accuracy of the touch poor at a particular region to require adjustment. In order to adjust for the dead zone, the infrared sensors are positioned outside the corners of the liquid crystal display panel to form the dead zone at an outer side of the liquid crystal panel. In this case, a touch screen greater than the liquid crystal panel is required, resulting in increase of a non-effective area which does not contribute to picture display, thereby making efficiency of the display device poor.
In general, the liquid crystal panel is separate from the touch screen. If it is intended to enable touch capabilities, additional work is required to assemble the respective components and apply coordinates to the touch screen suitable to the liquid crystal panel, and to secure the touch screen to a liquid crystal module.
In the related art touch screen, selection of accurate coordinates is difficult, and only one touch point may be perceived at a time. In other words, if two points on the touch screen are touched at the same time, the touch screen fails to perceive the touches, or perceives one of the touch points touched first, causing an error.
FIG. 2 illustrates a graph showing a touch sensing method in a related art touch screen, and FIG. 3 illustrates a simulation diagram showing a light quantity, threshold level of each pixel and a touch perception according to the above on a panel by using the method of FIG. 2.
Referring to FIG. 2, in the related art touch screen, if there is a part having a light quantity reduced in sensing a light quantity of each region, it is determined that the part is touched.
That is, if the sensed light quantity is greater than a predetermined touch perception threshold level, the sensed light quantity is determined that no touch is made, and if the sensed light quantity is smaller than the predetermined touch perception threshold level, the sensed light quantity is determined that the touch is made.
FIG. 3 illustrates a graph for comparing an actual light quantity of each region sensed with an infrared camera to a touch perception level of the regions.
In actual infrared cameras, differences of quantities of lights reflected at the retro-reflecting plates and returned to the infrared cameras occurs due to differences of distances from the infrared cameras and differences of incident angles on the retro-reflecting plates, causing an intrinsic light quantity difference between regions which is not a change of the light quantity resulting from an actual touch. FIG. 3 illustrates that the touch perception threshold levels varies with regions, taking the above into account.
In this case, light quantities smaller than the touch perception threshold level are sensed at about 250 pixels and 300 pixels, and these parts are determined to be touched.
However, the related art touch sensing method has the following problems.
In the related art touch sensing method according to the above, if a touch means of a reflective material, particularly, having a highly reflective surface such as a finger nail, metal or a mirror makes a touch, a reflected light greater than the threshold level is detected, causing an incorrect determination that no touch is made.
Moreover, in the related art touch detection, a touch perception detection threshold level of each region is set to be about 80% of a quantity of the light of the case where light is emitted from the infrared camera with no touch being made at the region, reaches the retro-reflecting plate and returns to the infrared camera. However, if a particular part is touched with a thin pen or the like, a fine change light quantity caused by the touch cannot be detected if the touch is determined by the about 80% or below of the un-touched light quantity due to the fine change.
The intrinsic difference of the light quantity reflected at the retro-reflecting plate caused by arrangement of the infrared cameras and incident angles on the retro-reflecting plates regardless of the touch is also liable to cause failure in detection of a change of the fine touch at a part having a small light quantity.