Resonant Keyboard Key Sensing for Fast Polyphonic Aftertouch
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Solution Overview
Problem
Existing musical keyboard sensing systems face limitations such as mechanical switch bounce, reliability issues, and high costs due to the need for multiple sensors, and are prone to interference and contamination, which affect accuracy and longevity.
Innovation Solution
A resonant circuit-based sensing system with passive and active resonant circuits, where the active circuit excites the passive circuit at a specific frequency, using shared detectors to sense key position and velocity, and employing coils with opposite windings to reduce interference, allowing for polyphonic aftertouch detection without the need for multiple sensors per key.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical switches are used to sense key position, then key position detection is achieved, but switch bounce and mechanical wear occur limiting detection speed and reliability
Solution Approach 1:
The patent replaces mechanical switches with a resonant circuit-based sensing system. The system uses an active resonant circuit to excite a passive resonant circuit attached to the key, and detects changes in resonant frequency and amplitude to determine key position. This eliminates mechanical contact points, thereby eliminating switch bounce and mechanical wear while maintaining high detection speed and reliability.
Solution Approach 2:
The patent utilizes resonant vibration principles by employing circuits that oscillate at specific resonant frequencies. The active resonant circuit drives the passive resonant circuit into resonance, and the system detects key position through changes in the resonant characteristics. This vibration-based approach provides contactless sensing with high speed and reliability.
2Measurement precision
If multiple pressure sensors are used for polyphonic aftertouch, then individual key pressure detection is achieved, but system cost increases significantly
Solution Approach 1:
The patent makes the resonant circuit system multi-functional by enabling it to detect both key position and key pressure using the same hardware components. By analyzing the resonant frequency and amplitude characteristics of the passive resonant circuit, the system can distinguish between different key states including pressed, released, and aftertouch conditions, eliminating the need for separate pressure sensors for each key.
Solution Approach 2:
The patent detects pressure changes by monitoring variations in resonant parameters (frequency and amplitude) of the existing resonant circuits rather than requiring additional sensors. When additional pressure is applied to a key during the aftertouch phase, it causes measurable changes in the resonant characteristics that the system can detect and interpret as pressure information.
3Speed
If optical sensors are used for position sensing, then detection speed is improved, but susceptibility to contamination and shock increases
Solution Approach 1:
The patent replaces optical sensing components with electrical resonant circuit components. Instead of using optical elements like shades or films that are vulnerable to contamination and shock, the system uses electrically conductive resonant circuits that are sealed and protected within the keyboard structure, providing robust long-term reliability while maintaining high detection speed.
4Measurement precision
If magnetic sensors with permanent magnets are used, then position sensing is achieved, but sensitivity to external interference and temperature increases
Solution Approach 1:
The patent replaces magnetic sensing systems with electrical resonant circuit-based sensing. This substitution eliminates the permanent magnets and magnetic sensors that are vulnerable to external magnetic fields, ferrous metal interference, and temperature changes. The resonant circuit system uses electrical properties that are inherently more stable and less susceptible to environmental interference.
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 reliable, fast, and accurate key position and velocity sensing, enabling polyphonic aftertouch capabilities while being cost-effective and resistant to contamination and interference, with the ability to detect key movements at high speeds and maintain performance over time.
Implementation Method 1
the passive resonant circuit has a resonant frequency and the active resonant circuit excites the passive resonant circuit at the resonant frequency
Implementation Method 2
Each sensor may further comprise a detector, which may be shared between multiple sensors, to detect variation of a resonant signal in the active resonant circuit with relative position of the active and passive resonant circuits
Data Source
AI summary
A sensing system for a keyboard. Each key sensor comprises passive and active resonant circuits. The passive resonant circuit has a resonant frequency and the active resonant circuit excites the passive resonant circuit at the resonant frequency. A sensor driver drives the active resonant circuit with an RF drive signal, a multiplexing system multiplexes the drive signal such that simultaneously driven key sensors are separated by at least (k−1) keys, and a detector detects a level of RF signal from a driven key sensor for sensing a position and/or velocity of a key.