Multiplexed Resonant Key Sensors for Polyphonic Aftertouch
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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, especially when aiming for polyphonic aftertouch functionality.
Innovation Solution
A sensing system utilizing passive and active resonant circuits with multiplexing and temperature compensation, allowing for accurate and reliable key position and velocity detection without mechanical contact, enabling polyphonic aftertouch and robust performance across a large number of keys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If mechanical switches are used to sense key position, then a simple and inexpensive sensing mechanism is achieved, but connection jitter and mechanical wear limit detection speed and reliability
Solution Approach 1:
The patent replaces mechanical switches with capacitive sensing circuits that detect key position through changes in capacitance. This eliminates mechanical contact, thereby removing connection jitter and mechanical wear while maintaining simple manufacturing. The capacitive sensor uses a detection circuit to measure capacitance changes between keys and a reference plane, providing reliable and fast detection without mechanical components.
2Reliability
If optical sensors are used for key position detection, then mechanical wear is eliminated, but the system becomes sensitive to contamination and shock
Solution Approach 1:
The patent uses capacitive sensing instead of optical sensing to detect key position. The capacitive sensor measures changes in capacitance caused by key displacement, providing contactless detection that eliminates mechanical wear. Unlike optical sensors, capacitive sensors are not sensitive to contamination or shock, as they use electrical field detection rather than light paths or delicate optical components.
3Reliability
If magnetic sensors with permanent magnets are used for each key, then mechanical wear is eliminated, but the system becomes expensive and sensitive to interference
Solution Approach 1:
The patent replaces magnetic sensors with capacitive sensing circuits that detect key position through capacitance changes. This eliminates the need for permanent magnets and magnetic sensors on each key, significantly reducing cost and complexity. The capacitive system is also less sensitive to external interference, as it measures electrical field changes rather than magnetic fields that can be affected by external sources.
4Measurement precision
If a separate pressure sensor is used for each key to enable polyphonic aftertouch, then independent pressure detection is achieved, but the system becomes expensive
Solution Approach 1:
The patent uses a single capacitive sensing circuit to perform multiple functions: detecting key position and measuring pressure for polyphonic aftertouch. The detection circuit measures capacitance changes that indicate both key displacement and applied pressure, eliminating the need for separate pressure sensors on each key. This multi-functional approach enables polyphonic aftertouch at a fraction of the cost of using individual pressure sensors for each key.
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 cost-effective key sensing with reduced interference and mechanical wear, enabling high-speed key detection and polyphonic aftertouch capabilities, maintaining performance over time and resisting contamination and interference.
Implementation Method 1
Each key sensor comprises a passive resonant circuit, for example for mounting on a moving part of a key, and an active resonant circuit, for example for mounting in a reference position. In implementations the passive resonant circuit has a resonant frequency and the active resonant circuit is configured to excite the passive resonant circuit at the resonant frequency.
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.