Keyboard Resonant Sensor Layout 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 expenses, especially when implementing polyphonic aftertouch systems.
Innovation Solution
A sensing system utilizing passive and active resonant circuits with multiplexing and temperature compensation, where each key sensor comprises a passive resonant circuit mounted on a moving part and an active resonant circuit in a fixed position, driven by an RF signal, allowing for simultaneous detection of key position and velocity with reduced interference and high reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical switches are used for key detection, 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 sensing circuits that detect key position through changes in capacitance. This substitution eliminates mechanical wear and key bounce while enabling continuous position detection for polyphonic aftertouch. Each key has an associated capacitive sensor that measures capacitance changes as the key moves, providing both note-on/note-off detection and continuous pressure information.
Solution Approach 2:
The capacitive sensing system serves multiple functions: it detects note-on events, note-off events, and continuous key pressure for polyphonic aftertouch all through a single sensing mechanism. The same capacitive sensor that detects key activation also measures the continuous position and pressure applied to each key, eliminating the need for separate mechanical switches and pressure sensors.
2Measurement precision
If a separate pressure sensor is used for each key to enable polyphonic aftertouch, then the system achieves accurate individual key pressure detection, but the system becomes expensive
Solution Approach 1:
The same capacitive sensor used for key detection also serves as the pressure sensor. By measuring capacitance changes continuously, the system extracts both activation information and pressure information from a single sensor element per key, eliminating the need for separate pressure sensing components and reducing overall system cost.
Solution Approach 2:
The capacitive sensor uses the key structure itself and the musician's finger as part of the sensing mechanism. The finger acts as one plate of a capacitor while the key structure serves as the other plate, eliminating the need for additional dedicated pressure sensing elements. The system leverages the natural electrical properties of the interaction between finger and key.
3Speed
If optical sensors are used for key position detection, then the system achieves fast response, but the system becomes vulnerable to contamination and requires cleaning or recalibration
Solution Approach 1:
The patent replaces optical sensing with capacitive sensing that uses electrical fields rather than light. This substitution eliminates the need for optical paths, lenses, and light sources that are susceptible to contamination. The capacitive sensor detects key position through electrical field changes caused by the movement of conductive keys, which are not affected by dust, dirt, or environmental contamination in the same way optical systems are.
4Reliability
If magnetic sensors with permanent magnets are used for key detection, then the system achieves contactless sensing, but the system becomes sensitive to external magnetic field interference and temperature changes
Solution Approach 1:
The patent replaces magnetic sensing with capacitive sensing that uses electrical fields rather than magnetic fields. This substitution eliminates sensitivity to external magnetic field interference, temperature-induced magnetic property changes, and hysteresis effects. The capacitive sensor detects key position through changes in electrical capacitance caused by the movement of conductive keys, which are not affected by magnetic interference or temperature variations in the same way magnetic sensors are.
5Productivity
If time-interleaved multiplexing is used with mechanical switches to support large numbers of keys, then the system can handle 21-88 keys, but the detection speed is limited by switch bounce and connection jitter
Solution Approach 1:
The patent replaces mechanical switches with capacitive sensors that provide continuous analog signals rather than discrete on/off states. This substitution eliminates switch bounce and connection jitter, allowing for much faster detection rates. The system can detect key position changes at rates exceeding 1000 Hz per key while supporting 88 keys through time-interleaved multiplexing, because the capacitive sensors provide smooth, noise-free signals that can be accurately sampled at high rates without the mechanical limitations of switch-based systems.
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 detection, enabling polyphonic aftertouch and robust performance against contamination and interference, with the ability to determine key position continuously and respond quickly to key movements, suitable for large keyboards.
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. 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
The active resonant circuit is configured to excite the passive resonant circuit at the resonant frequency... a detector to detect a level of RF signal from a driven key sensor
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~5
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. At least the active resonant circuit, and optionally also the passive resonant circuit, comprises one or more coils with windings in opposite senses. A sensor driver drives the active resonant circuit with an RF drive signal at the resonant frequency, 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. The combination of coils with opposite sense windings and multiplexed sensor addressing facilitates the use of multiple sensors in close proximity.