Touch screen detection apparatus

• US 20030132922A1
• Filed: 01/14/2003
• Published: 07/17/2003
• Est. Priority Date: 01/17/2002
• Status: Abandoned Application

• Current Assignee: Harald Philipp
• Original Assignee: Harald Philipp
• Inventors: Philipp, Harald
• Application Number:
  US10/341,948
• Publication Number:
  US 20030132922A1
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/04186 Touch location disambiguation
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners

Abstract

Capacitive touch screens are subject to a ‘handshadow’ error associated with the undesired proximity detection of a portion of a relatively large object (such as a hand) comprising or associated with a smaller pointing portion or object (such as finger tip), where the smaller pointing portion is closer to a touch sensing surface than is the rest of the object. A history profile of data derived from the screen both just prior to, and just after the touch is detected can be processed to compensate for the handshadow effect and to determine a corrected touch position value based on regression techniques or other forms of predictive mathematics. In addition to accurately determining positions where a screen is touched, these approaches can also determine a screen location corresponding to a position of closest approach of a pointing object. A system for providing the handshadow-compensated measurements may comprise a memory for storing a temporal sequence of touch screen records and a computer for executing several algorithms.

Claims

1. ) A method for determining coordinates of a point of closest approach of a pointing portion of an object to a capacitive touch screen, the pointing portion closer to the screen than the rest of the object, the method comprising the sequentially executed steps of:

a) acquiring a time sequence of sets of touch screen signals from which respective coordinates can be calculated, the sequence comprising a currently acquired set and at least one other set, each of the sets having a respective magnitude associated therewith;

b) storing the at least one other set of signals in a memory;

c) determining if the magnitude associated with the currently acquired set of signals is at least a selected amount greater than the magnitude associated with any set of signals stored in the memory;

d) if so, continuing to acquire additional sets of signals in the time sequence thereof;

e) if not, determining that the pointing portion of the object has attained the position of closest approach and then calculating, from the currently acquired set of signals and at least one other of the sets of signal, the coordinates of the position of closest approach.

2. ) The method of claim 1 wherein, in step d), when each additional set of signals is acquired, the immediately previously acquired set of signals is stored in the memory.

3. ) The method of claim 1 wherein the calculation in step e) comprises a regression analysis.

4. ) The method of claim 1 wherein the calculation in step e) comprises an extrapolation

5. ) A system for correcting a set of measured coordinates of a point of closest approach of a pointing portion of an object to a capacitive touch screen, the pointing portion of the object closer to the screen than the rest of the object, the system comprising:

circuitry for generating, from a plurality of outputs from the touch screen, a corresponding plurality of records, each record representative of a respective set of uncorrected coordinates of the object and of a respective distance of approach of the object;

a memory for storing a temporal sequence of the records;

a first algorithm for comparing the respective distances of approach associated with two or more of the records to thereby select the record having a distance of closest approach associated therewith;

a second algorithm for calculating, from the respective uncorrected set of coordinates associated with the record having the distance of closest approach and from at least one other record stored in the memory, a correction that, when applied to the uncorrected coordinates associated with the record having the distance of closest approach, yields the set of corrected coordinates; and

a computer for executing at least the first and second algorithms and for supplying the set of corrected coordinates as an output.

6. ) The system of claim 5 wherein the circuitry for generating the plurality of records comprises signal filtering means.

7. ) The system of claim 5 wherein the circuitry for generating the plurality of records comprises XY location determination circuitry and amplitude determination circuitry.

8. ) The system of claim 5 wherein the first algorithm comprises steps for determining if the magnitude associated with a currently acquired set of signals is at least a selected amount greater than the magnitude associated with any other set of signals stored in the memory.

9. ) The system of claim 5 wherein the second algorithm comprises a regression analysis.

10. ) Apparatus for determining a set of coordinates of a point of closest approach of a pointing portion of an object to a capacitive touch screen, the pointing portion of the object closer to the screen than the rest of the object, the apparatus comprising:

signal acquisition circuitry for receiving a temporal sequence of sets of analog signals from the capacitive touch screen and for supplying as an output a corresponding temporal sequence of sets of digital signals, each of the sets of digital signals having a respective magnitude associated therewith;

a memory for receiving the temporal sequence of sets of digital signals and for storing at least one of the sets of digital signals;

detection determination logic means having the temporal sequence of sets of digital signals as an input, the detection determination logic providing a trigger signal as an output when the magnitude associated with one of the sets of digital signals is not at least a selected amount greater than the magnitude associated with the immediately previous set of digital signals in the temporal sequence thereof;

signal processing means having respective inputs from the memory and from the detection determination logic means, the signal processing means acting responsive to the trigger signal to calculate, from the set of digital signals that is not at least a selected amount greater than the magnitude associated with the immediately previous set of digital signals, and from at least one other set of digital signals stored in the memory, the coordinates of the point of closest approach.

11. ) The apparatus of claim 10 wherein a microcontroller comprises the detection determination logic means and the signal processing means.

12. ) The apparatus of claim 10 wherein the detection determination logic means and the signal processing means comprise respective hardwired logic computation circuits.

13. ) The apparatus of claim 10 wherein an analog computer comprises the detection determination logic means and the signal processing means.