SPAD Optical Encoders for Compact Rotational and Translational Input
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Solution Overview
Problem
Conventional mechanical user input systems in compact electronic devices face challenges with resolution and responsiveness due to size constraints, and modern solutions like capacitive sensors lack haptic feedback.
Innovation Solution
An input component with a movable member featuring a spatially-varying pattern, illuminated by a light source and detected by a two-dimensional array of single-photon avalanche diodes (SPADs) in Geiger mode, which processes reflected light to determine rotation and translation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional mechanical input systems are used in compact electronic devices, then haptic feedback and tactile response are provided, but resolution and responsiveness deteriorate due to size constraints
Solution Approach 1:
The patent replaces conventional mechanical encoders and analog sensing systems with a photonic detection system using SPADs. The mechanical rotation/translation of the input member is converted to optical pattern movement, which is then detected by the SPAD array, eliminating the need for bulky mechanical components while achieving superior resolution
Solution Approach 2:
The patent transitions from one-dimensional mechanical sensing to two-dimensional optical pattern detection using an array of SPADs. The spatially-varying pattern on the input member creates a two-dimensional optical signature that provides richer information for determining both rotational and translational movements, significantly improving detection resolution
2Measurement precision
If conventional mechanical input systems are used, then high detection resolution is achieved, but device complexity and component count increase
Solution Approach 1:
The patent eliminates complex mechanical encoder disks, read heads, and analog-to-digital conversion circuits by replacing the entire mechanical sensing system with a photonic detection system. The SPAD array directly outputs digital signals when photons are detected, simplifying the overall circuit architecture
Solution Approach 2:
The patent creates an optical copy of the mechanical movement through the spatially-varying pattern on the input member. This pattern acts as an optical encoder that replicates the mechanical position information in the light reflection, which is then detected by the SPADs, eliminating the need for physical encoders
3Volume of moving object
If modern capacitive sensors are used instead of mechanical input systems, then device size is reduced, but haptic feedback capability is lost
Solution Approach 1:
The patent creates a hybrid input system that combines the compact form factor of electronic sensors with the haptic feedback capability of mechanical systems. The movable input member provides tactile and haptic feedback to the user, while the SPAD-based optical detection system provides precise digital measurement, achieving both goals simultaneously
Solution Approach 2:
The spatially-varying pattern on the input member acts as an intermediary that bridges the mechanical domain and the optical domain. It converts mechanical movement into an optical pattern that can be detected by the SPADs, enabling the system to provide both haptic feedback through the mechanical interface and precise digital measurement through optical detection
4Productivity
If conventional optical encoders are used, then rotational and translational detection is achieved, but frame rate and responsiveness are limited
Solution Approach 1:
The patent changes the detection parameter from mechanical position to photon arrival time. The SPADs operate in Geiger mode to detect individual photons and measure their arrival times with picosecond precision, enabling both high frame rates and high detection resolution simultaneously through time-correlated single photon counting
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
Provides improved movement and rotation detection resolution with reduced size, simplified circuitry, and higher frame rates, while eliminating the need for analog-to-digital conversion and offering haptic feedback.
Implementation Method 1
an array of single-photon avalanche diodes (SPADs) configured to operate in Geiger mode... positioned to receive the reflected light
Implementation Method 2
a light-emitting element oriented to emit light toward the pattern, which is then reflected as reflected light patterned in a manner based on the spatially-varying pattern
Data Source
AI summary
An input component for an electronic device configured to detect rotational and/or translational movement of a surface. In an implementation, the input component includes a movable input member with a shaft with a pattern disposed on its surface. A light-emitting element is positioned to direct light towards this pattern, a portion of which is thereafter reflected back. An imaging system is situated to capture the reflected light. The imaging system includes an array of single-photon avalanche diodes (SPADs) operating in Geiger mode. This array is coupled with a counter circuit, which increments one or more values based on the SPAD array output. These values and corresponding SPAD locations within the array can be correlated to the spatial phase of the reflected light, which in turn can be converted to rotational or axial displacement of the movable input member.