Optical Touch Control With Orthogonal Modulation
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Solution Overview
Problem
Optical touch systems face interference issues due to the limited range of usable frequencies for amplitude modulation, leading to prolonged scanning times and reduced accuracy in detecting touch events and mechanical control device status.
Innovation Solution
Implementing a modulation scheme where multiple optical emitters are driven with orthogonal modulation functions, allowing simultaneous emission and correlation of energy received by detectors to distinguish between emitter signals and reduce interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amplitude modulation with fixed frequency is used, then interference from external sources increases, but changing frequency range is limited by detector response times
Solution Approach 1:
The patent changes the modulation parameter from fixed frequency amplitude modulation to time-varying intensity patterns with characteristic transitions. Each emitter uses a unique temporal pattern that includes specific rise and fall times, allowing detectors to distinguish between different emitters based on their temporal signatures rather than frequency separation.
Solution Approach 2:
The system employs periodic scanning sequences where emitters are activated in predetermined patterns. The scanning sequence repeats over time with each emitter having a unique activation pattern, creating periodic temporal signatures that can be correlated at the detector to identify signal sources and filter interference.
2Productivity
If sequential beam scanning is used, then scanning time is prolonged, but simultaneous emission from multiple emitters causes signal interference
Solution Approach 1:
The patent merges multiple emitter operations by allowing simultaneous emission from multiple emitters. Instead of sequential scanning, multiple emitters operate concurrently with unique temporal patterns, and the detector combines these signals through correlation processing to resolve individual contributions.
Solution Approach 2:
The system uses correlation processing as a feedback mechanism where detector outputs are correlated with predetermined emitter patterns. This correlation process provides feedback information that enables the system to distinguish between simultaneous emitter signals and filter out interference, maintaining signal resolution despite parallel operations.
3Productivity
If multiple emitters operate simultaneously, then scanning efficiency improves, but distinguishing between emitter signals becomes more difficult
Solution Approach 1:
The patent applies preliminary action by establishing unique temporal patterns for each emitter before operation begins. These predetermined patterns serve as reference signatures that simplify the detection process, as detectors can correlate incoming signals against these known patterns to easily differentiate between simultaneous emitter sources.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach accelerates the scanning process, enhances accuracy by minimizing interference, and improves signal resolution through noise averaging, while maintaining efficient power usage and reduced peak current demand.
Implementation Method 1
a plurality of optical emitters and a plurality of 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
Implementation Method 2
The touch sensitive area may be an optically transparent planar waveguide through which the beams pass by total internal reflection
Implementation Method 3
An object such as a finger or a stylus coming into contact with the transparent waveguide will have a higher refractive index than the air normally surrounding the waveguide. The increase in refractive index will disrupt total internal reflection of light energy at the interface between the waveguide and the touching object
Implementation Method 4
This modulating signal can be applied to an emitter by using it to modulate the current flowing through the emitter, which is usually be a current controlled device such as an LED
Data Source
AI summary
An optical control system is described, which employs a series of optical emitters and detectors arranged about a touch area. The emitters are driven by a series of functions, and the system is operable to correlate the signals received at the detectors with the functions to determine the amount of energy received by the detectors from each of the emitters. This system means that all or many emitters can be modulated simultaneously, so the scanning process is accelerated. Also, the energy estimates arrived at by correlation with the functions are largely unaffected by external interference signals as well by each other. An additional benefit of the present invention is that the correlation processing makes use of many detector samples and tends to yield results which have higher resolution than the sample values themselves, due to the averaging of noise over the sample set.