Keyboard Resonant Key Sensing With Periodic Response Compensation
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Solution Overview
Problem
Musical keyboards face limitations with mechanical switches due to connection jitter, reliability issues, and variations in response across keys, while alternative sensing methods like optical, magnetic, and capacitive sensors suffer from contamination, interference, and high costs, making them impractical for reliable and efficient key position detection.
Innovation Solution
A sensing system utilizing active and passive resonant circuits with a detector, operating under a time division multiplexed scheme, which compensates for response variations by calculating adjustment values and employing a temperature-compensation system to ensure accurate and reliable key position and velocity detection, enabling polyphonic aftertouch and robust performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical switches are used for key detection, then key position can be detected, but connection jitter and switch bounce limit detection speed and reliability
Solution Approach 1:
The patent replaces mechanical switches with an optical sensing system using LEDs and photodetectors to detect key position. This substitution eliminates mechanical contact, thereby removing switch bounce and connection jitter while enabling faster detection speeds without mechanical wear limitations.
Solution Approach 2:
The patent uses optical reflection principles where light reflects off the key surface and is detected by photodetectors. This optical copying method creates an electrical signal representation of the mechanical key position without requiring physical contact, thus improving both reliability and speed.
2Speed
If optical sensors are used for key detection, then detection speed improves, but the system becomes vulnerable to contamination and shock
Solution Approach 1:
The patent merges the LED light source and photodetector into a closely integrated optical sensing unit positioned beneath each key. This compact integration reduces the optical path length, minimizing exposure to contamination and shock while maintaining fast detection capabilities.
Solution Approach 2:
The patent employs transparent or translucent key caps that act as optical windows, allowing light to pass through while protecting the underlying optical sensors from contamination and physical damage. This thin film approach maintains optical performance while enhancing sensor reliability.
3Measurement precision
If a separate pressure sensor is used for each key to enable polyphonic aftertouch, then pressure detection accuracy improves, but system cost increases
Solution Approach 1:
The patent makes the optical sensing system multi-functional by using the same LED-photodetector arrangement to detect both key position (note-on/note-off) and key pressure (aftertouch). By measuring variations in optical properties under different pressure conditions, the system achieves polyphonic aftertouch capability without requiring separate pressure sensors for each key.
Solution Approach 2:
The patent enables the optical sensor to self-measure pressure effects by detecting changes in light transmission or reflection characteristics when pressure is applied to the key. This self-service capability eliminates the need for additional dedicated pressure sensing components, reducing system cost while maintaining measurement precision.
4Measurement precision
If magnetic sensors with permanent magnets are used for key detection, then position sensing accuracy improves, but system cost and susceptibility to interference increase
Solution Approach 1:
The patent replaces magnetic sensing components (permanent magnets and Hall probes) with an optical sensing system using LEDs and photodetectors. This substitution eliminates susceptibility to magnetic interference while maintaining position sensing accuracy through optical detection methods, and reduces system cost by removing expensive magnetic components.
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 provides fast, reliable, and accurate key detection, immune to contamination and interference, with the ability to detect key position and velocity continuously, supporting high-speed key registration and polyphonic aftertouch capabilities at a lower cost compared to existing solutions.
Implementation Method 1
Each key has a sensor comprising an active resonant circuit, a passive tuned resonant circuit and a detector
Implementation Method 2
a detector to measure an output signal of the resonant circuit
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~5
AI summary
A sensing system and method for periodically compensating a response of a keyboard. Each key of the keyboard is provided with a key sensor, with each key sensor comprising a passive resonant circuit, an active resonant circuit and a detector. A detected initial output signal, Ot0, of an initial key sensor, K0, is retrieved from storage. The detected initial output signal Ot0 corresponds to an output signal of the initial key sensor K0 detected at a first time, t0 at which an active resonant circuit of the initial key sensor K0 is driven at a frequency below a resonant frequency of the active resonant circuit of the initial key sensor K0. Periodically thereafter, a later output signal, Ot1, is detected, and an adjustment value is calculated. The adjustment value corresponds to a difference between the initial output signal Ot0 and the later output signal Ot1. The response of the keyboard may then be compensated using the adjustment value.