Optical Control System With Feedback Control

• US 20110157095A1
• Filed: 08/07/2009
• Published: 06/30/2011
• Est. Priority Date: 08/07/2008
• Status: Active Grant

• Current Assignee: Beechrock Limited
• Original Assignee: Rapt Ip Limited
• Inventors: Drumm, Owen
• Granted Patent: US 8,426,799 B2
• Time in Patent Office: Days
• US Class Current: 345/175
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen

Abstract

An optical control system is described which provides for more efficient operation of an optical device. The system is operable to provide an integrated output from the detection system. Accordingly, by controlling the operating time of the detection system of the optical device it is possible to match the dynamic range of the integrated output to the operational input range of an ADC means to provide a digital output value, thereby minimising the quantisation noise of the ADC means.

Claims

1. An optical control system comprising:

a plurality of optical emitters and a detection system comprising a plurality of optical detectors, the optical emitters and the optical detectors defining therebetween an area of optical paths whereby the transmission of energy between an emitter and a detector may be modulated by an optical interaction occurring in the vicinity of said area, wherein the detection system is operable to provide an integrated output of one or more of said optical detectors over time;

switching means for controlling the operation of said detection system;

analogue to digital conversion (ADC) means for receiving and converting an output of said detection system to a digital value; and

a feedback mechanism for receiving said digital value from said ADC means and for controlling the switching means in response thereto, to thereby adjust the dynamic range of the integrated output relative to the operational input range of said ADC means.

2. An optical control system as claimed in claim 1, wherein the detection system comprises an integrator for receiving and integrating the output of one or more of said optical detectors over time, and wherein said switching means switching is operable to control the operation of said integrator and/or its associated detector(s).

3. An optical control system as claimed in claim 2, further comprising a compensation circuit for providing a compensation charge to said integrator before or during a period of operation of said integrator, whereby said compensation charge operates to compensate for a background signal which is received from said one or more of said optical detectors but which is not associated with the operation of said optical emitters.

4. An optical control system as claimed in claim 3, wherein said compensation charge is derived from a digital output value from the ADC means measured when the emitters transmitting energy received by said one or more detector(s) associated with said integrator are inactive.

5. An optical control system as claimed in claim 3, further comprising a controller for controlling the operation of said detection system and said ADC means to controllably discharge and charge the detection system and to convert the integrated output to digital form.

6. An optical control system as claimed in claim 5, wherein said detection system comprises a capacitor, and further comprising a sink to which said capacitor may be selectively connected under the control of said controller to controllably discharge said capacitor.

7. An optical control system as claimed in claim 6, wherein said controller operates to control said detection system and said ADC means by reconfiguring a connection between said capacitor, said ADC means, and said sink, to one of three states selected from (i) a charge state in which said capacitor is isolated from said sink;

(ii) a measurement state in which said capacitor is connected to said ADC means; and

(iii) a discharge state in which said capacitor is connected to said sink.

8. An optical control system as claimed in claim 7, wherein said ADC means is integrated into a device having an analogue input pin to which said capacitor is connected and which is reconfigurable under control of said controller to select one of said three states.

9. An optical control system as claimed in claim 7, wherein said controller is further operable to select a fourth state in which said capacitor is connected to said compensation circuit for providing a compensation charge to said capacitor.

10. An optical control system as claimed in claim 7, wherein said controller is further operable to select a fifth state in which said capacitor is isolated from both a charge path and a discharge path to provide a hold state.

11. An optical control system as claimed in claim 1, further comprising a drive circuit for one or more of said optical emitters, said drive circuit being operable to pulse said one or more of said emitters with a pulse period less than said operational time of said detection system.

12. An optical control system as claimed in claim 11, wherein said drive circuit further comprises means for controlling a duty cycle of said one or more emitters such that the detection system output is approximately proportional to the emitter duty cycle.

13. An optical control system as claimed in claim 12, further comprising means for determining a signal-to-noise ratio of said detection system output, and for controlling the emitter duty cycle to maintain said signal-to-noise ratio above a predetermined minimum value.

14. An optical control system as claimed in claim 11, wherein said emitter drive circuit is operable to control a plurality of said emitters and to ensure that the activations of said plurality of emitters are staggered in time such that the number of emitters active at any given instant is reduced.

15. An optical control system as claimed in claim 1, wherein said area of optical paths is positioned close to a touchable surface and wherein said optical interaction is the touching of said touchable surface.

16. An optical control system as claimed in claim 15, wherein the touchable surface is the surface of a sheet waveguide and the emitters and detectors are arranged at the edges of the waveguide such that light is transmitted into the waveguide by the emitters and received by the detectors along said multiple intersecting optical paths by total internal reflection within the waveguide, the material of the waveguide being selected such that the amount of light passing along said at least two optical paths is reduced by an optical interaction involving touching said surface of the waveguide to cause leakage of light from the waveguide.

17. An optical control system as claimed in claim 1, wherein said ADC means receives a plurality of multiplexed signals from a plurality of said detectors.

18. An optical control device as claimed in claim 1, wherein the switching means controlling the operational time of the detection system is adjustable as a function of the amplitude of signal detected by said detection system.

19. An optical control device as claimed in claim 1, further comprising a processor for controlling the operation of said ADC means to sample said detection system output during an integration time of said detection system, and to predict from said sampling a predicted final detection system output at the end of said integration time.

20. An optical control system as claimed in claim 19, wherein said processor is operable to determine whether said predicted final detection system output is likely to exceed an operational input limit of said ADC means, and if so, to reduce the integration time.

21. An optical control system as claimed in claim 20, wherein said processor performs an interpolation of said sampled detection system output to determine a saturation time at which said operational limit of said ADC means is likely to be exceeded, and sets said reduced integration time to a value less than or equal to said saturation time.

22. An optical control system as claimed in claim 19, wherein said processor is operable to determine whether said predicted final detection system output is likely to exceed an operational input limit of said ADC means, and if so, to supply said predicted final detection system output as an output in substitution for a saturated ADC output.

23. An optical control system as claimed in claim 1, wherein one or more of said optical detectors is configured with a relatively long response time, such that said one or more of said optical detectors acts as an integrator.

24. A method of operating an optical control system comprising the steps of:

transmitting energy from a plurality of optical emitters to a detection system comprising a plurality of optical detectors, said emitters and detectors defining therebetween an area of optical paths whereby the transmission of energy between an emitter and a detector may be modulated by an optical interaction occurring in the vicinity of said area, wherein said detection system is operable to provide an integrated output of one or more of said optical detectors over time;

controlling the time of operation of at least a portion of said detection system;

receiving an integrated output signal from said detection system and converting said integrated output signal to a digital value using an analog to digital converter (ADC) means;

controlling the switching means in response to said digital value, to thereby adjust the dynamic range of the detection system output relative to the operational input range of said ADC means.