Watch Crown Rotor Reflective Coating for Optical Input Detection
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Solution Overview
Problem
Existing wearable electronic devices face challenges in accurately detecting rotational and translational inputs due to non-uniform optical reflectance and manufacturing tolerances, which affect the precision and accuracy of optical sensing systems.
Innovation Solution
A crown for wearable electronic devices featuring a rotor with a recessed reflective coating made of titanium dioxide, ensuring uniform thickness and reflectance, coupled with an optical sensing system using self-mixing laser interferometry to determine rotational inputs, and a shaft assembly that translates and rotates to detect both types of inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reflective coating is applied to detect rotational input, then the optical sensing system can detect rotation, but non-uniform thickness and manufacturing tolerances cause non-uniform optical reflectance which reduces detection accuracy
Solution Approach 1:
The rotor surface is segmented into multiple discrete reflective elements (reflective markers or patterns) rather than using a continuous coating. This segmentation allows each element to be precisely positioned and sized, compensating for coating non-uniformity and manufacturing tolerances while maintaining accurate rotational detection through optical tracking of these discrete features.
Solution Approach 2:
Instead of requiring uniform reflectance across the entire rotor surface, the invention applies reflective properties locally at specific detection points or zones. The optical sensing system is configured to detect reflections from these specific localized areas, making the system insensitive to non-uniformities in other regions of the rotor.
2Manufacturing precision
If the recess depth is increased to accommodate the reflective coating, then the coating can have uniform thickness, but the manufacturing complexity increases
Solution Approach 1:
The invention uses discrete reflective markers or patterns that can be applied as overlays or stickers onto the rotor surface, rather than requiring permanent recesses molded into the rotor. This copying approach allows the reflective elements to be precisely positioned and removed or replaced without complex manufacturing processes, achieving uniform reflectance without complex recess structures.
3Adaptability or versatility
If the crown is configured to receive both rotational and translational inputs, then the device functionality is enhanced, but the sensing system complexity increases
Solution Approach 1:
The optical sensing system is designed with multi-functionality to detect both rotational and translational movements of the crown using the same reflective coating and optical components. By tracking changes in the reflected light pattern, the system can distinguish between rotational input (change in angular position) and translational input (change in linear position), enabling a single sensing system to handle multiple input types without requiring separate sensing mechanisms.
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
The solution enhances the accuracy and precision of input detection, improving user experience by maintaining high signal-to-noise ratio and power efficiency, while accommodating manufacturing tolerances and ensuring consistent tactile feedback.
Implementation Method 1
a coating positioned in the recess and configured to reflect at least a portion of light incident on the coating
Implementation Method 2
the optical sensing system may determine a speed and a direction of the rotational input using self-mixing laser interferometry
Data Source
AI summary
An electronic watch may include a housing and a crown configured to receive a rotational input. The crown may include a knob external to the housing, a rotor coupled to the knob and configured to rotate in response to the rotational input, the rotor defining a recess extending about a circumference of the rotor, and a coating positioned in the recess and configured to reflect at least a portion of light incident on the coating. The electronic watch may further include an optical sensing system configured to detect the rotational input using the reflected portion of the light.