Reflective Piano Keyboard Scanner with Optical Crosstalk Compensation
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Solution Overview
Problem
Existing systems for measuring key displacement and velocity on musical instruments, such as pianos, are often complex, costly, and require invasive installations, with issues like uniformity of response, crosstalk, and non-linearity affecting accuracy and usability.
Innovation Solution
A reflective scanning system using low-cost opto-electronic sensors with independent microprocessors that sample key positions nearly 1000 times per second, compensating for ambient light and crosstalk, and employing linearization algorithms to provide accurate MIDI velocity data without mechanical adjustments or attachments to the keys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If mechanical switch structures are used to detect key displacement, then the system is simple in structure, but the response uniformity is poor and key touch is affected
Solution Approach 1:
The patent replaces mechanical switch structures with optical sensing systems. Specifically, it uses optical interrupters with paddles mounted under keyboard keys to measure continuous key position, eliminating mechanical contact while maintaining structural simplicity. The optical system provides non-contact measurement that does not affect key touch characteristics.
Solution Approach 2:
The patent introduces optical intermediaries (light beams and optical sensors) to detect key displacement. The optical interrupters act as mediators between the key movement and the detection system, providing uniform response without direct mechanical contact with the keys.
2Measurement precision
If opto-electronic switches with two optical LED sensors per key are used, then continuous linear position sensing is achieved, but the installation becomes elaborate and delicate
Solution Approach 1:
The patent merges the sensing function into a single optical interrupter unit per key rather than using two separate LED sensors. The optical interrupter combines the light source and detector in one integrated component, simplifying installation while maintaining continuous position sensing capability.
Solution Approach 2:
The optical interrupter serves multiple functions simultaneously: it detects key position, measures displacement, and provides continuous linear position sensing all through a single component, eliminating the need for elaborate installation of multiple separate sensors.
3Device complexity
If stationary optical sensors with optical fibers are used adjacent to moving key paddles, then the number of displacement speed electrical signal converting elements is reduced, but space requirements are limited
Solution Approach 1:
The patent nests the optical sensing components within the existing keyboard structure. The optical interrupters are mounted under the keys, utilizing the existing space in the keyboard assembly rather than requiring additional external space for sensor positioning.
4Measurement precision
If AC voltages of equal amplitude but opposite phase are impressed on two electrodes for position sensing, then continuous position data is obtained, but the circuitry becomes complex and costly
Solution Approach 1:
The patent replaces complex electrical circuitry with optical sensing. Instead of using AC voltages and electrode systems, the invention uses optical interrupters that detect key position through light interruption, eliminating the need for complex phase-controlled electrical circuits while maintaining continuous position measurement capability.
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 system achieves high accuracy in key position and velocity measurement, reducing errors from ambient light and crosstalk, and is unobtrusive, cost-effective, and adaptable to various keyboard instruments, ensuring accurate data transmission and minimal installation requirements.
Implementation Method 1
A reflective scanning system using low-cost opto-electronic sensors
Implementation Method 2
opto-electronic sensors with independent microprocessors that sample key positions
Data Source
AI summary
A scanner for a keyboard device having a reflective surface for each key has a sensor associated with each key that includes an LED and a photo-transistor. The LED is turned ON for a first measurement, followed by a second measurement with the LED turned off, and a subtraction of the second measurement from the first yields an illumination value for a key x. The LEDs and associated photo-transistors are sequentially enabled in groups of n, thereby eliminating optical interference. Each key x has associated correction parameters of LinRest(x) associated with illumination value with the key in the rest (up) position, LinDown(x) associated with illumination value with the key in the down position, TrebErr(x) associated with the reflectivity effect of one adjacent key(x+1), and BassErr(x) associated with the reflectivity effect of another adjacent key(x−1). By reading a single illumination value in combination with these correction parameters, the key position may be accurately extracted and the effect of ambient light and surrounding key interference removed.