Optical Force Sensor for Stylus Without Axial Displacement
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Solution Overview
Problem
Conventional stylus devices with force measurement mechanisms create an unnatural experience due to axial displacement, failing to mimic the use of pens and pencils, which respond to varying forces by adjusting thickness and heaviness.
Innovation Solution
A force sensing mechanism using a light emitting device and a compressible light reflecting optic with two reflective layers, where the light transmissive layer's compression affects the reflected light's amplitude, allowing force measurement without discernable displacement, enabling differential control based on applied force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spring or mechanical device is used to measure force applied to the stylus tip, then force measurement capability is achieved, but axial displacement occurs resulting in an unnatural experience
Solution Approach 1:
The patent replaces the mechanical spring-based force measurement system with an optical sensing system. A light source emits light toward a reflective surface, and a photodetector measures the reflected light intensity. The force applied to the stylus tip changes the optical path or reflection characteristics, allowing force measurement without mechanical displacement. This substitution eliminates the unnatural axial displacement while preserving force measurement capability.
2Adaptability or versatility
If a force measurement device is added to the stylus, then differential control based on force is enabled, but the device complexity increases
Solution Approach 1:
The patent merges the force measurement function with the existing stylus structure by integrating the optical sensing components directly into the stylus body. The light source and photodetector are positioned within the stylus, and the reflective surface is incorporated into the tip assembly. This integration allows force measurement and differential control without adding separate, complex mechanical measurement devices to the stylus structure.
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 provides a natural stylus input experience by measuring force applied to the stylus tip without noticeable displacement, allowing for varying line widths and other control features based on force, enhancing user interaction with touch-sensitive devices.
Implementation Method 1
a compressible layer of light-transmissive material disposed between a first reflective layer and a second reflective layer, the second reflective layer being more reflective than the first reflective layer
Implementation Method 2
detecting reflected light at a light detector of the light emitting device as a result of the direction of the emitted light to the light reflecting optic, the reflected light based on a combination of light reflected from the first reflective layer and light reflected from the second reflective layer
Data Source
AI summary
Examples are provided for measuring force applied to a device, such as a stylus tip. An example stylus includes a stylus body, a stylus tip, and the stylus tip including a light emitting device and a compressible light reflecting optic, the light emitting device comprising a light emitter and a light detector, and the compressible light reflecting optic comprising a first reflective layer configured to (i) allow a first portion of light from the light emitting device to pass and (ii) to reflect a second portion of light from the light emitting device, and a second reflective layer, more reflective than the first reflective layer, configured to reflect light from the light emitting device, the first layer being spaced from the second layer by a light-transmissive material. A force exerted on the stylus tip is measurable based at least on a parameter of light received at the light detector.