Keyboard sensor systems and methods

Abstract

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.

1 . A sensing system comprising a set of sensors for a keyboard of a keyboard instrument,
 wherein the keyboard has a plurality of keys;   wherein each sensor of the set of sensors comprises a passive resonant circuit for mounting on a moving part of a key and an active resonant circuit for mounting in a reference position, the passive resonant circuit having a resonant frequency, the active resonant circuit exciting the passive resonant circuit at the resonant frequency, each sensor of the set of sensors further having a detector to detect a variation of a resonant signal in the active resonant circuit corresponding to a variation of a relative position of the active and passive resonant circuits to detect a position and/or velocity of the key; and   wherein the set of sensors comprises sensors having two or more different resonant frequencies arranged such that sensors having the same resonant frequency are non-adjacent.   
     
     
         2 . The sensing system as claimed in  claim 1 , wherein the active resonant circuit comprises one or more coils with windings in opposite senses, wherein the windings in opposite senses are configured to generate magnetic fields in opposite senses to cancel one another. 
     
     
         3 . The sensing system as claimed in  claim 1 , wherein the active resonant circuit comprises a pair of laterally adjacent pancake coils. 
     
     
         4 . The sensing system as claimed in  claim 1 , further comprising a temperature-compensation system to temperature-compensate a detected resonant signal in the active resonant circuit, wherein the temperature-compensation system is configured to apply an off-resonance drive signal to at least one of the active resonant circuits, to measure a level of the off-resonance drive signal from the at least one detector, and to compensate a detected level of the resonant signal responsive to the level of the off-resonance drive signal. 
     
     
         5 . The sensing system as claimed in  claim 1 , wherein each sensor of the set of sensors further comprises a deformable element configured to limit motion of one or both of the passive resonant circuit and the active resonant circuit for pressure sensing. 
     
     
         6 . A polyphonic aftertouch keyboard comprising the sensing system of  claim 1 , each key of the plurality of keys having a deformable end-stop, such that an after-touch position corresponds to movement of a key beyond an end-stop position defined by the deformable end-stop, wherein identification of the aftertouch position for the key enables polyphonic aftertouch. 
     
     
         7 . The sensing system as claimed in  claim 1 , wherein sensors having a first resonant frequency are interleaved with sensors having a second, different resonant frequency. 
     
     
         8 . The sensing system as claimed in  claim 1 , further comprising a multiplexing system and/or controller configured to control selection of sensors of the set of sensors such that adjacent keyboard sensors are selected at different times. 
     
     
         9 . The sensing system as claimed in  claim 8 , wherein the multiplexing system and/or controller is further configured to damp the active resonant circuits of unselected sensors. 
     
     
         10 . The sensing system as claimed in  claim 8 , wherein the multiplexing system and/or controller is configured to perform time division multiplex operation of the sensors, wherein each resonant frequency defines a group of sensors having the resonant frequency, wherein the time division multiplexing defines a plurality of n time slots, and wherein successive keyboard sensors of each group are allocated successive time slots. 
     
     
         11 . The sensing system as claimed in  claim 10 , wherein the multiplexing system and/or controller is configured to multiplex an RF drive signal used to drive active resonant circuits of the set of sensors such that one of the sensors is driven in each of a set of time slots. 
     
     
         12 . The sensing system as claimed in  claim 11 , further comprising a temperature-compensation system configured to temperature-compensate a level of a resonant signal, in a first active resonant circuit of a first sensor, that is detected by a first detector of the first sensor,
 wherein the temperature-compensation system is configured to apply an off-resonance drive signal to the first active resonant circuit, to measure a level of the off-resonance drive signal from the first detector, and to compensate the detected level of the resonant signal responsive to the level of the off-resonance drive signal, and   wherein the temperature-compensation system is configured to apply the off-resonance drive signal during an additional time slot to the set of time slots.   
     
     
         13 . The sensing system as claimed in  claim 10 , wherein there are N resonant frequencies and N groups of sensors, wherein sensors of the groups of sensors are interleaved on the keyboard. 
     
     
         14 . The sensing system as claimed in  claim 13 , wherein the multiplexing system and/or controller is configured such that keyboard sensors in the same group and activated in the same time slot have (n×N)- 1  sensors between them. 
     
     
         15 . The sensing system as claimed in  claim 1 , further comprising a processor configured to process the variation of the resonant signal in the active resonant circuit of each sensor to determine the motion of each key of the keyboard over a succession of time intervals as a depressed key moves between released and depressed positions, wherein the motion of each key comprises a position and a velocity of the key as the key moves between released and depressed positions. 
     
     
         16 . The sensing system as claimed in  claim 15 , wherein the processor is configured to process the variation of the resonant signal in the active resonant circuit of each sensor to determine the velocity of a key, as the key moves between depressed and released positions, from changes in position of the key determined at successive time intervals, wherein the changes are filtered dependent upon key velocity. 
     
     
         17 . The sensing system as claimed in  claim 1 , further comprising a processor configured to process the variation of the resonant signal to determine a key press and key release event for each key. 
     
     
         18 . The sensing system as claimed in  claim 15 , wherein the processor is further configured to distinguish between at least three different key positions, a first, note-off position, a second, note-on position, and a third, aftertouch position, wherein the aftertouch position is beyond the note-on position and corresponds to additional pressure applied to the key after depression. 
     
     
         19 . A method of sensing the positions of a plurality of keys of a keyboard instrument, the method comprising:
 providing each key with a 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, the passive resonant circuit having a resonant frequency, the active resonant circuit exciting the passive resonant circuit at the resonant frequency, each sensor further having a detector to detect variation 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; and   arranging the sensors to operate at two or more different resonant frequencies arranged such that keyboard sensors having the same resonant frequency are non-adjacent; and/or   reducing interference between sensors by configuring one or more coils of at least the active resonant circuits to have windings in opposite senses.   
     
     
         20 . The method as claimed in  claim 19 , further comprising providing polyphonic aftertouch by distinguishing between at least three different key positions, a first, note-off position, a second, note-on position, and a third, aftertouch position, wherein the aftertouch position is beyond the note-on position and corresponds to additional pressure applied to the key after depression and movement of a key beyond an end-stop position.