Wrist Touch Detection Using PPG Sensor Reflection
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Solution Overview
Problem
Wearable devices like smart watches face limitations in touch interaction due to their small screen size, which restricts the number of icons that can be displayed and limits functionality, and increasing the screen size is not desirable for fashion or wearability reasons.
Innovation Solution
The method involves using a photoplethysmography sensor to project light onto a user's wrist, isolating a stray-light component from the reflected light to generate a waterfall image, which represents the amplitudes of the light over time, and analyzing this image to detect touches and gestures, allowing for extended touch interaction areas without increasing hardware complexity or power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the screen size is increased to display more information and improve touch interaction, then the functionality and information display are improved, but the wearability and fashionability deteriorate
Solution Approach 1:
The patent extends the touch interaction area from the two-dimensional screen surface to the three-dimensional wrist surface by using the back of the wrist as an additional interaction zone. The optical sensor detects touches on the wrist skin adjacent to the device, effectively adding a new dimension for user interaction without increasing the physical screen area.
Solution Approach 2:
The existing optical sensor, originally designed for health monitoring functions, is repurposed to detect touch gestures on the wrist. This multi-functional use of the same hardware component enables extended touch interaction capability without adding separate dedicated touch sensors or increasing device complexity.
2Area of stationary object
If dedicated touch sensors are added to extend the touch area beyond the screen, then the touch interaction area is improved, but the device complexity and cost increase
Solution Approach 1:
The optical sensor serves dual purposes: its original health monitoring function and the new touch detection function. By reusing the existing sensor hardware and optical path, the system extends touch interaction capability without adding dedicated touch sensors, thereby avoiding increased device complexity and cost.
Solution Approach 2:
The optical sensor inherently captures light reflected from the wrist skin, and this existing capability is leveraged for touch detection. The system uses the sensor's natural light-receiving function to detect touch gestures, eliminating the need for separate touch sensing hardware and keeping the device simple.
3Adaptability or versatility
If additional touch sensors are added to enable gestures on adjacent skin areas, then the gesture recognition capability is improved, but the power consumption increases
Solution Approach 1:
The same optical sensor used for health monitoring is utilized for touch gesture detection. This approach avoids the power consumption penalty of adding dedicated touch sensors, as the existing sensor's power budget is already allocated for health tracking and can handle the additional touch detection function without significant additional power requirements.
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 solution enables more information to be displayed on the smart watch and changes user interaction methods, facilitating new applications without adding complexity, cost, or power consumption, by allowing touch interactions on the skin adjacent to the device.
Implementation Method 1
The method involves using a photoplethysmography sensor to project light onto a user's wrist, isolating a stray-light component from the reflected light
Data Source
AI summary
A sensor on a wearable device may be further configured as a sensor for detecting and recognizing a gesture to control the wearable device. For example, light detected by a photoplethysmography (PPG) sensor of a smart watch may include (i) light back reflected from underneath the smart watch and (ii) light back reflected from a touch to a wrist adjacent to the smart watch. The detected light may be filtered to isolate the light back reflected from the touch. A waterfall image that includes information about how the isolated light changes with time and amplitude may be generated and used to detect and recognize gestures performed on the wrist, such as a touch. This additional touch area may help to supplement a touch area provided by a display to control the smart watch.