Dual sensor touchscreen utilizing projective-capacitive and force touch sensors

• US 6,492,979 B1
• Filed: 09/07/1999
• Issued: 12/10/2002
• Est. Priority Date: 09/07/1999
• Status: Expired due to Term

• Current Assignee: Elo Touch Solutions, Inc.
• Original Assignee: Elo Touchsystems Incorporated (Elo Touch Solutions, Inc.)
• Inventors: Kent, Joel, Wilson, Geoffrey D.
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): ZAMANI, ALI A
• Application Number:
  US09/391,352
• Time in Patent Office: 1,190 Days
• Field of Search: 345/173, 345/179, 345/156, 345/174, 345/178, 178/18.03, 178/18.05, 178/18.01, 178/18.9, 178/18.09, 338/68
• US Class Current: 345/173
• CPC Class Codes: G06F 2203/04106 Multi-sensing digitiser, i.e. digitiser using at least two different sensing technologies simultaneously or alternatively, e.g. for detecting pen and finger, for saving power or for improving position detection
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: G06F 3/0447 Position sensing using the local deformation of sensor cells

Abstract

A method and apparatus for discriminating against false touches in a touchscreen system is provided. The system is designed to confirm a touch registered by one touch sensor with another touch sensor, preferably of a different sensor type, prior to acting upon the touch (i.e., sending touch coordinates to the operating system). If the touch registered by the first touch sensor is not confirmed by the second touch sensor, the touch is invalidated. Thus the strengths of one type of sensor are used to overcome the deficiencies of another type of sensor. This system is particularly well suited to meet the demands of an outdoor or semi-outdoor application. In one embodiment, one or more force sensors are used as the false touch sensor and a projective-capacitive sensor is used as the position coordinate determining sensor. In another embodiment, a projective-capacitive sensor is used as the false touch sensor. As the projective-capacitive sensor is only being used to provide touch confirmation, in this embodiment very few electrodes are required as well as minimal channel electronics. In another embodiment, both touch sensors are capable of providing accurate touch coordinates. In this configuration the system preferably determines which of the sensors is more likely to provide accurate information based on the circumstances.

Claims

1. A touchscreen system, comprising:

at least one force sensor coupled to a touchscreen of said touchscreen system, said force sensor monitoring a force component associated with a touch of said touchscreen;

a projective-capacitive sensor system coupled to said touchscreen; and

a processor coupled to said at least one force sensor and said projective-capacitive sensor system, wherein said processor calculates a set of position coordinates associated with said touch when said force component is greater than a force threshold, said set of position coordinates determined by said projective-capacitive sensor system.

2. The touchscreen system of claim 1, wherein said processor sets said force threshold.

3. The touchscreen system of claim 1, wherein said processor increases said force threshold when said projective-capacitive sensor system does not register said touch substantially simultaneously wit h said at least one force sensor.

4. The touchscreen system of claim 1, further comprising a discriminator coupled to said at least one force sensor, wherein said discriminator determines if said force component exceeds said force threshold.

5. A touchscreen system, comprising:

a plurality of force sensors coupled to a touchscreen of said touchscreen system;

at least on e electrode coupled to said touchscreen;

a projective-capacitive sensor system coupled to said at least one electrode, wherein said at least one electrode is insufficient to determine a set of position coordinates associated with a touch of said touchscreen; and

a processor coupled to said plurality of force sensors and said projective-capacitive sensor system, wherein said processor calculates said set of position coordinates when said plurality of force sensors and said projective-capacitive sensor system substantially simultaneously detect s aid touch, wherein said set of position coordinates is determined by said plurality of force sensors.

6. The touchscreen system of claim 5, wherein said at least one electrode is formed along a single axis of said touchscreen.

7. A touchscreen system, comprising:

a plurality of force sensors coupled to a touchscreen of said touchscreen system;

a plurality of electrodes coupled to said touchscreen, wherein a first portion of said plurality of electrodes are formed along a first axis and a second portion of said plurality of electrodes are formed along a second axis;

a projective-capacitive sensor system coupled to said plurality of electrodes; and

a processor coupled to said plurality of force sensors and said projective-capacitive sensor system, wherein said processor calculates said set of position coordinates when said plurality of force sensors and said projective-capacitive sensor system substantially simultaneously detect a touch of said touchscreen.

8. The touchscreen system of claim 7, wherein said first axis is substantially orthogonal to said second axis.

9. The touchscreen system of claim 7, wherein said set of position coordinates is registered by said plurality of force sensors.

10. The touchscreen system of claim 7, wherein said set of position coordinates is registered by said projective-capacitive sensor system.

11. A method of operating a touchscreen system, comprising the steps of:

detecting a force applied to a touchscreen of said touchscreen system with at least one force sensor, wherein said detected force corresponds to a touch of said touchscreen;

confirming said touch of said touchscreen detected by said at least one force sensor with a projective-capacitive sensor;

generating a set of position coordinates corresponding to said touch; and

transmitting said set of position coordinates to a touchscreen operating system.

12. The method of claim 11, further comprising the step of returning said touchscreen system to a stand-by mode if a negative response to said confirming step is received from said projective-capacitive sensor.

13. The method of claim 11, further comprising the step of setting an untouch threshold for said projective-capacitive sensor.

14. The method of claim 13, wherein said untouch threshold is a percentage of an initial projective-capacitive signal amplitude determined when said touch was first detected by said force sensor.

15. The method of claim 13, further comprising the step of comparing a projective-capacitive signal amplitude corresponding to said touch to said untouch threshold, wherein said set of position coordinates corresponds to a second touch location associated with said projective-capacitive signal amplitude falling below said untouch threshold.

16. The method of claim 13, further comprising the steps of comparing a projective-capacitive signal amplitude corresponding to said touch to said untouch threshold, and generating a second set of position coordinates corresponding to a second touch location associated with said projective-capacitive signal amplitude falling below said untouch threshold.

17. The method of claim 15, further comprising the steps of generating an untouch message when said projective-capacitive signal amplitude falls below said untouch threshold and transmitting said untouch message to said touchscreen operating system.

18. The method of claim 11, wherein said set of position coordinates is generated by said at least one force sensor.

19. The method of claim 11, wherein said set of position coordinates is generated by said projective-capacitive sensor.

20. The method of claim 11, further comprising the step of setting a force sensor threshold if a negative response to said confirming step is received from said projective-capacitive sensor.

21. The method of claim 20, wherein said force sensor threshold is a force amplitude.

22. The method of claim 20, wherein said force sensor threshold is a frequency spectrum.

23. The method of claim 20, wherein said force sensor threshold setting step comprises applying a frequency filter to said detected force.

24. The method of claim 11, further comprising the steps of:

comparing a first touch position determined by said at least one force sensor with a second touch position determined by said projective-capacitive sensor; and

returning said touchscreen system to a stand-by mode if an offset between said first and second touch positions is greater than a predetermined offset threshold.

25. The method of claim 11, further comprising the steps of:

determining a background mechanical noise level; and

comparing said background mechanical noise level with a noise threshold, wherein said set of position coordinates is generated by said at least one force sensor if said background mechanical noise level is less than said noise threshold, and wherein said set of position coordinates is generated by said projective-capacitive sensor if said background mechanical noise level is greater than said noise threshold.

26. The method of claim 11, further comprising the step of determining if said touchscreen system is operating in a drag mode, wherein said set of position coordinates is generated by said at least one force sensor if said touchscreen system is not operating in said drag mode, and wherein said set of position coordinates is generated by said projective-capacitive sensor if said touchscreen system is operating in said drag mode.