1. Field of the Invention
The present invention relates generally to touch detection and more specifically it relates to a touch detection system for detecting touches on a given surface.
2. Description of the Related Art
Touch detection has been in use for years. Typically, touch detection is comprised of products that determine the location of a touch based on resistive, capacitive, infrared, surface acoustic waves, force and bending waves. Those devices that utilize acoustic waves to determine the touch location are based on either by measuring the time of flight or by measuring the phase differences and/or characterizing the screen.
U.S. Pat. No. 6,922,642 teaches how to generate acoustic waves on a surface that is capable of transmitting acoustic waves. Furthermore, this patent teaches how to generate dispersion corrected convolution function, dispersion corrected correlation function and other phase equivalent functions to determine information related to contact on the surface. This approach does not characterize the screen in advance and uses real time signals to determine the touch location. Reflections from the substrate boundaries cause detection problems therefore certain materials that reduces these reflections are required on the edges of the screen.
U.S. Pat. No. 6,871,149 discloses how to use phase differences in detected signals to determine the touch location on a given surface. At least two pairs of transducers are required to detect acoustic waves generated on a surface. These signals are processed to determine the phase and then phase differences between these signals are used to determine the touch location.
WO 00/38104 World Patent Application teaches how to detect the position of a touch on a large surface. The application discusses how acoustic waves can be generated either by using a hard object or finger (either nail or skin of the finger) and then how these acoustic waves are analyzed to determine the touch location.
US Patent Application 2005/0083313 teaches how to detect the location of a touch by using phase information. During the characterization process, phase of the arriving signals for right and left channels are determined and then the differences between these phases are calculated and stored in a memory. When the surface is touched in real time application, phase differences between the right and the left channels are calculated and compared with the phase differences stored in the memory. This approach has two shortcomings. First, the entire screen has to be touched at several locations to characterize it. This requires additional time during manufacturing, and has a detrimental effect on productivity. Secondly, more memory is necessary, resulting in increased cost for producing larger screens.
US Patent Application 2005/02127777 teaches how to characterize a surface and store the characterized data in memory. Different techniques are disclosed including how to compare measured phase differences with stored phase differences to detect the touch location.
WO0148684 teaches how to detect acoustic waves on a given surface and how to use the measured data to construct a non-dispersive signal to determine the touch location.
U.S. Pat. No. 6,456,952 teaches how to characterize a touch screen to prevent drifting.
U.S. Pat. No. 6,977,646 discloses how to calibrate for a touch screen.
U.S. Pat. No. 5,751,276 teaches how to perform calibration on a touch screen and how to save those numbers in memory location to be used later.
U.S. Pat. No. 6,353,434 teaches how to perform calibration on a touch screen and how to store calibration data in a memory location to be used later.
U.S. Pat. No. 6,650,319 discloses complete mapping and screen characterization.
These prior art patents and patent applications reveal the fact that there are two distinct ways detecting touch location on a surface that is capable of propagating acoustic waves. The first approach is to use the real time signal and perform signal processing techniques on the signal to determine the touch location. The issue with this approach is the reflections from boundaries of the substrate and the manufacturing cost as a result of that. The second approach is to characterize the screen and store the characterization information in memory to be compared with the real time data to detect the touch location. This approach requires storage for many points on the screen.
In these respects, the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of easy calibration and detection of a touch on a given surface. The calibration of the screen is accomplished by touching either a single point or multiple points on the surface. This can be performed either at the factory during the manufacturing of the touch screen or by the end user before the touch screen is placed into service. The present invention provides a touch detection system that can calibrate the screen on a single touch and determines the location of the touch by using a simple algorithm to implement.
In these respects, the touch detection according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of detecting touches on a given surface that overcomes the shortcomings of the prior art.