Resonant Keyboard Key Sensing for Polyphonic Aftertouch
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Solution Overview
Problem
Musical keyboards face limitations with mechanical switches due to key bounce, reliability issues, and high costs, while alternative sensing methods like optical, magnetic, and capacitive sensors suffer from interference, contamination, and high costs, especially when implementing polyphonic aftertouch systems.
Innovation Solution
A sensing system utilizing passive and active resonant circuits with multiplexing and temperature compensation, allowing for efficient detection of key position and velocity, and enabling polyphonic aftertouch with reduced interference and cost, using coils with opposite windings and a multiplexing system to manage sensor addressing and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical switches are used to sense key position, then the system is simple and reliable for basic note-on/note-off detection, but the system suffers from key bounce, mechanical wear, and inability to detect polyphonic aftertouch
Solution Approach 1:
The patent replaces mechanical switches with capacitive sensors that detect key position through electrical capacitance changes. This substitution eliminates mechanical wear and key bounce while enabling polyphonic aftertouch detection through independent capacitive measurement for each key.
Solution Approach 2:
The capacitive sensor system serves multiple functions: it detects note-on/note-off events, measures key position, and enables polyphonic aftertouch detection. A single capacitive sensing mechanism handles all these functions without requiring separate mechanical components for each capability.
2Measurement precision
If a separate pressure sensor is used for each key to enable polyphonic aftertouch, then the system achieves accurate polyphonic aftertouch detection, but the system becomes expensive
Solution Approach 1:
The same capacitive sensing circuitry used for key position detection is also employed for pressure/aftertouch detection. This multi-functional approach allows polyphonic aftertouch capability without requiring separate dedicated pressure sensors for each key, thereby reducing system cost.
Solution Approach 2:
The patent combines key position sensing and pressure detection into a single capacitive sensing system. By merging these functions into one sensor type and signal processing pathway, the system achieves polyphonic aftertouch capability while avoiding the cost of separate sensor arrays.
3Reliability
If optical sensors are used for key position sensing, then the system avoids mechanical wear and key bounce, but the system becomes vulnerable to contamination and requires delicate optical elements that are sensitive to shock and vibration
Solution Approach 1:
The patent replaces optical sensing with capacitive sensing, which uses electrical field detection instead of optical paths. This substitution eliminates vulnerability to contamination, shock, and vibration that affect optical elements, while maintaining contactless key position detection.
4Reliability
If magnetic sensors with permanent magnets are used for each key, then the system achieves reliable key position detection, but the system becomes expensive and sensitive to external magnetic field interference
Solution Approach 1:
The patent replaces magnetic sensing with capacitive sensing, substituting electrical field detection for magnetic field detection. This eliminates sensitivity to external magnetic field interference and removes the need for permanent magnets, while maintaining reliable key position detection.
5Reliability
If inductive coil sensors are used for key detection, then the system avoids mechanical wear, but the system becomes slow and affected by metal jewellery and casework
Solution Approach 1:
The patent replaces inductive coil sensing with capacitive sensing, which uses electrical capacitance changes rather than inductive coupling. This substitution increases detection speed and eliminates interference from metal objects like jewellery and casework, while maintaining contactless operation.
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 reliable, fast, and cost-effective key sensing with reduced interference, enabling accurate detection of key position and velocity, and supporting polyphonic aftertouch, with the ability to operate at high speeds and maintain stability across varying temperatures.
Implementation Method 1
Each key sensor may comprise 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.
Implementation Method 2
resonant circuit-based sensors
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~5
AI summary
A sensing system and method for detecting a position and/or velocity of keys on a keyboard. The keyboard is provided with a set of sensors, each sensor comprising a passive resonant circuit for mounting on a moving part of a key and an active resonant circuit for mounting in a reference position. One or more coils of the active resonant circuits have windings in opposite senses to reduce interference between sensors of adjacent keys. The passive resonant circuit has a resonant frequency and the active resonant circuit excites the passive resonant circuit at the resonant frequency. Each sensor has a detector to detect variations of a resonant signal in the active resonant circuit with relative position of the active and passive resonant circuits to detect a position and/or velocity of the key.