Patent Publication Number: US-7723597-B1

Title: 3-dimensional musical keyboard

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     SEQUENCE LISTING OR PROGRAM 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field 
     The invention relates generally to a musical keyboard apparatus for controlling electronic sound, and specifically to those keyboards whose keys may be actuated both up-and-down and in-and-out. 
     2. Defined Terms 
     Positions and movements of keyboard elements are described from the point-of-view of a player facing the instrument. 
     The axis in which the plurality of keys is arrayed left and right is termed the x-axis, and motion in that axis is termed lateral, or side-to-side; the axis is which the long axes of the keys lie towards and away from the player is termed the y-axis, and motion in that axis is termed longitudinal, or in-and-out; and the axis in which the keys move up-and-down is termed the z-axis, and motion in that axis is termed vertical, or up-and-down. 
     Key movement in the z-axis is termed ‘depression’, or ‘key dip’, and key movement in the y-axis is termed ‘displacement’. 
     A key is said to be in its ‘at-rest’ position when it is fully up in the z-axis, or undepressed, and centrally located in the y-axis, or undisplaced; and in an ‘active position’ when it is not at-rest. 
     The term ‘unguided’ refers to the state of a key that has been depressed, whether or not displaced, and released. 
     The term ‘key space’ refers to the locus of all positions in the vertical plane in which the long axis of a key lies to which the key may be moved. 
     Of the two key forms, ‘upper-rank’ keys are analogous to those commonly called ‘black keys’ in conventional claviers, and lower-rank&#39; keys are analogous to those commonly called ‘white keys’ in conventional claviers. 
     3. Prior Art 
     Tone producing means and control means in acoustic instruments are tightly bound to each other. A drumhead, for example, may be struck by hand, or with a stick—a distinction with a difference—but not so much you wouldn&#39;t know it was a drum. 
     Control means for electronic sound, on the other hand, may be entirely separate from tone producing means. Drum sounds can be played via keyboards, though, as is well understood by those skilled in the art, without the control of actually drumming. 
     Almost a century of effort since the Telharmonium (U.S. Pat. No. 580,035 (1897), Cahill) first made the sounds of electrical circuits audible has gone toward devising control means as expressive as those of acoustic instruments. The Telharmonium utilized multiple keyboards having position sensitivity in the z-axis to expand expression, but the instrument weighed several hundred tons and cost millions of dollars to fabricate. 
     Less inherently expensive but still very limited was the keyboard of Maurice Martenot (U.S. Pat. No. 2,562,471 (1948), Martenot). This patent teaches a platform, displaceable in the x or y-axis direction, on which all keys are mounted. The platform&#39;s excursion is directed at effects that can be controlled with short motion, like vibrato, but is not useful for control of higher resolution sonic events like pitch bending. Further, Martenot recognizes that the platform, when unguided, will continue to oscillate as a function of its mass and springing, eventually losing energy. Such oscillation is inherently distracting to the player, all the more so if it has a hearable result. Martenot&#39;s solution, balancing mass and spring force so that the platform has a natural frequency higher than that of an effect like vibrato, attempts to hide the problem of damping, and can only work for low frequency sonic events. 
     One known way to expand the expressive capability of an electronic keyboard controller is to recognize individual key-based playing gestures made in the direction of the longitudinal axis of the keys, in-and-out, in the y-axis. 
     Robert Moog described at the International Computer Music Conference in 1982 a ‘multiple-touch-sensitive keyboard’, later completed with help from one of us (DeRocco). The key surfaces of its otherwise conventional organ/synthesizer style keyboard were circuit boards that continuously recognized finger location. In one of its playing modes, absolute location of the initial contact in the y-axis was treated as a starting point for modulation, and in another, location relative to a ‘first touch’, that is, a note-on condition following a note-off condition, was recognized. Whichever the mode, however, player perception and control was principally mediated through skin sensation rather than via the more discriminating flexors and extensors of the hand. 
     The same ergonomic limitation applies to the more contemporary instrument taught in U.S. Pat. No. 6,703,552 (2004), Haken. The instrument is an uninterrupted planar surface (a membrane keyboard) with very sophisticated processing to extract player intent; but it, too, like Moog&#39;s keyboard, does not use the hand&#39;s more complex sensing and control capabilities. 
       FIG. 1   a  is a side elevational view of the prior art of U.S. Pat. No. 3,818,114 (1974), Okamoto, showing a digitally operable electronic organ key with limited 3-dimensional capability. A key  110  is supported by a leaf spring  111  “resilient enough to permit each . . . [key] . . . to move back and forth in the lengthwise direction of each said key”. Such motion is limited by interference between the ‘white’ key (as shown in the drawing) and a ‘black’ key (not shown). At the front end of the key, a member  112  supports a stop  113  at its upper end, which stop is “somewhat loosely received in a housing of any suitable shape formed on the underside of the key  110 , in such a manner that the angle of swing of the key  110  is thereby delimited.” That is, the stop is only directed at and suitable for z-axis motion. Thus Okamoto shows a digitally operable electronic organ key with limited 3-dimensional capability. Its longitudinal, or y-axis, motion is very short, of necessity, as there is little space between the front of black keys and ‘L-shaped’ portions of adjacent white keys. Short key travel is suitable only for sonically low resolution musical features, like tremolo. Significantly greater travel in the y-axis would be needed to control higher resolution sonic events, like pitch. Also, Okamoto makes no provision for frictionless guidance at the front of the key; increased friction under the natural lateral loads in playing, having no sonic purpose, only distract the player. Okamoto speaks specifically of the restraint at the front of the key as “somewhat loosely received in a housing of any suitable shape formed on the underside of the key, in such a manner that the angle of swing of the key is thereby delimited.” The structure is directed only at z-axis motion and does not adequately support y-axis motion suited to control high resolution musical events. Finally, Okamoto makes no provision for physically signaling a key&#39;s center position in the y-axis. 
       FIG. 1   b  is a side elevation, partly sectionalized, view of the prior art of U.S. Pat. No. 4,068,552 (1978), Allen, showing an electronic key mechanism with extended 3-dimensional capability. The pin  115 , which makes sliding contact with the inside of slot  116 , is subject to binding if torsion is exerted on the key  114  through lateral loading, which is a natural component of playing. At the rear of the key, a pivoting mount is comprised of a yoke  117  to which the key  114  is pivotally pinned. The yoke  117  is then attached to a leaf spring  118 . These joints are is a source of instability and play in the mechanism, require a complexity of parts, and the need for adjustment. While Allen describes an electronic key mechanism with extended key displacement range through the use of cantilevered, or undercut, ‘black keys’, the pin mechanism used to control lateral loads is susceptible to cocking and binding in its associated slot; no means is provided for damping the longitudinal oscillations of an unguided key; and the rear key mount requires a bearing in its upper aspect, at the expense of play which may be amplified over the length of the key, and shows a complexity of parts needing assembly and adjustment, and hampering long term reliability. 
       FIG. 1   c  is an exploded view of the prior art of U.S. Pat. No. 4,498,365 (1985), Tripp et al., showing a pressure and longitudinal sensor coupled to a longitudinally displaceable key with extended 3-dimensional capability and center signaling. A rocker assembly  119  establishes a central detent for longitudinal key motion through a complexity of elements, including slots  120  and  121  in a rocker body  122  and a key  123 , respectively. Rocker body  122  is pinned at one of its ends to a leaf spring  124  through holes  125  and  126  and attached at its other end by a coil spring  127  to a pin  128 . A perpendicularly extending pin  129 , inserts into a slot  130  in key  123 , acts as a key travel limit and supplies lateral key motion restraint at the front of the key. A second rocker assembly  131  requires that pins  132  and  133 , “mutually parallel and non-skewed”, be assembled at one end into bearing holes  134  of key  123  and, at the other end, into hole  135  and its mate (not shown) in a bracket  136 . The rocker assembly, which provides a central detent for longitudinal key motion, comes at the expense of a complexity of elements and of assembly and disassembly when pinning the rocker body both to the leaf spring at one end and the key at the other. No provision is made to damp both the z and y-axis components of unguided longitudinal key motion beyond the damping internal to the key/springs themselves. There is no means to resist substantially without play and friction lateral loads at the front of the key as longitudinal key guidance is supplied by a pin oriented perpendicularly in a slot, which is thus subject to cocking and binding. Lastly, a second rocker assembly at the rear of the key is complex to manufacture and assemble as well as a source of looseness in the keys and error in their mutual alignment. 
     Lastly, none of the prior art addresses how the mass of a key and the spring and player forces acting on it must be organized for player control simultaneously in the z and y axes, adding articulation to the sound. 
     SUMMARY 
     In accordance with the embodiment disclosed herein, an improved 3-dimensional musical keyboard apparatus is described to support more facile control of musical sound. It comprises a plurality of planar, longitudinally extending keys mounted for both downward depression and longitudinal displacement; spring components to return an unguided key to its at-rest position; means to limit the extent of key motion; sensing means to detect key position at any point in its range of motion; and electronic digital signal processor means responsive to key position signals and productive of musical control information. Additionally, it comprises a single line of contact structure for restraining keys from lateral motion; differential damping for the vertical and horizontal components of key motion; simplified means for signaling key center position in the displacement axis; and support for musical articulation in the direction of key displacement when a key is moving upward from a depressed position. 
    
    
     
       DRAWINGS 
       Figures 
         FIG. 1   a  is a side elevational view of the prior art of U.S. Pat. No. 3,818,114 (1974), Okamoto, showing a digitally operable electronic organ key with limited 3-dimensional capability 
         FIG. 1   b  is a side elevation, partly sectionalized, view of the prior art of U.S. Pat. No. 4,068,552 (1978), Allen, showing an electronic key mechanism with extended 3-dimensional capability. 
         FIG. 1   c  is an exploded view of the prior art of U.S. Pat. No. 4,498,365 (1985), Tripp et al., showing a pressure and longitudinal sensor coupled to a longitudinally displaceable key with extended 3-dimensional capability and center signaling. 
         FIG. 2   a  is a side, elevational view of the present embodiment. 
         FIG. 2   b  is a side, elevational view of a second key form of the present embodiment. 
         FIG. 3   a  is a perspective view of the two key forms of the present embodiment in their at-rest positions. 
         FIG. 3   b  is a perspective view of the two key forms of the present embodiment with lower rank key  211  depressed. 
         FIG. 3   c  is a perspective view of the two key forms of the present embodiment with upper rank key  211   a  depressed and displaced. 
         FIG. 4   a  is a side, elevational view of area  204  in  FIG. 2   a  of the present embodiment, showing y-axis spring  223  in an undeflected state. 
         FIG. 4   b  is a side, elevational view of area  204  in  FIG. 2   a  of the present embodiment, showing y-axis spring  223  in a deflected state. 
         FIG. 4   c  is a block diagram of the present embodiment showing the relationship between the sensors and the electronic processor, including the output of the electronic processor. 
         FIG. 5   a  is a perspective view, from the side and above and partially sectioned, of area  205  in  FIG. 2   a  of the present embodiment. 
         FIG. 5   b  is a front elevational view of pin  229  in slot  510  in guide plate  230  taken at section line  5   b - 5   b  in  FIG. 5   a.    
         FIG. 5   c  is a front elevational view of pin  130  in slot  131  in key  123  taken at section line  5   c - 5   c  in the prior art of  FIG. 1   c.    
         FIG. 6   a  enlarges for clarity area  206  in  FIG. 2   a  of the present embodiment, showing the relationship of key  211  and rocker  215  when the key is centered in the y-axis. 
         FIG. 6   b  enlarges for clarity area  206  in  FIG. 2  of the present embodiment, showing the increased separation of key  211  and rocker  215  during initial displacement. 
     
    
    
     DRAWINGS 
     Reference Numerals 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                  4a 
                 y-axis area, FIG. 2a 
                  5a 
                 guide area, FIG. 2a 
               
               
                   
                  6a 
                 rocker area, FIG. 2a 
                 110 
                 key 
               
               
                   
                 111 
                 support 
                 112 
                 member 
               
               
                   
                 113 
                 stop 
                 114 
                 key 
               
               
                   
                 115 
                 pin 
                 116 
                 slot 
               
               
                   
                 117 
                 yoke 
                 118 
                 spring 
               
               
                   
                 119 
                 rocker assembly 
                 120 
                 slot 
               
               
                   
                 121 
                 slot 
                 122 
                 rocker body 
               
               
                   
                 123 
                 key 
                 124 
                 spring 
               
               
                   
                 125 
                 hole 
                 126 
                 hole 
               
               
                   
                 127 
                 spring 
                 128 
                 pin 
               
               
                   
                 129 
                 pin 
                 130 
                 slot 
               
               
                   
                 131 
                 rocker assembly 
                 132 
                 pin 
               
               
                   
                 133 
                 pin 
                 134 
                 hole 
               
               
                   
                 135 
                 hole 
                 136 
                 bracket 
               
               
                   
                 210 
                 base structure 
                 211 
                 key 
               
               
                   
                 211a 
                 key 
                 212 
                 key body 
               
               
                   
                 212a 
                 key body 
                 213 
                 key top 
               
               
                   
                 213a 
                 key top 
                 214 
                 key surface 
               
               
                   
                 214a 
                 key surface 
                 215 
                 rocker 
               
               
                   
                 216 
                 recess 
                 217 
                 projection 
               
               
                   
                 218 
                 recess 
                 219 
                 projection 
               
               
                   
                 220 
                 spring 
                 221 
                 projection 
               
               
                   
                 222 
                 pivot point 
                 223 
                 spring 
               
               
                   
                 224 
                 projection 
                 225 
                 pivot point 
               
               
                   
                 226 
                 pivot point 
                 227 
                 sensor 
               
               
                   
                 228 
                 sensor 
                 229 
                 projection 
               
               
                   
                 230 
                 plate 
                 231 
                 projection 
               
               
                   
                 232 
                 bracket 
                 233 
                 cushion 
               
               
                   
                 234 
                 collar 
                 235 
                 cushion 
               
               
                   
                 236 
                 cushion 
                 237 
                 cushion 
               
               
                   
                 310 
                 relief 
                 311 
                 relief 
               
               
                   
                 410 
                 shape 
                 411 
                 shape 
               
               
                   
                 510 
                 slot 
                 511 
                 slot 
               
               
                   
                 512 
                 slot 
                 513 
                 surface 
               
               
                   
                 514 
                 interior 
                 515 
                 contact point 
               
               
                   
                 516 
                 contact point 
                 610 
                 end point 
               
               
                   
                 611 
                 end point 
                 612 
                 flat 
               
               
                   
                 613 
                 surface 
               
               
                   
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION 
     Defined Terms 
     Positions and movements of keyboard elements are described from the point-of-view of a player facing the instrument. 
     The axis in which the plurality of keys is arrayed left and right is termed the x-axis, and motion in that axis is termed lateral, or side-to-side; the axis is which the long axes of the keys lie towards and away from the player is termed the y-axis, and motion in that axis is termed longitudinal, or in-and-out; and the axis in which the keys move up-and-down is termed the z-axis, and motion in that axis is termed vertical, or up-and-down. 
     Key movement in the z-axis is termed ‘depression’, or ‘key dip’, and key movement in the y-axis is termed ‘displacement’. 
     A key is said to be in its ‘at-rest’ position when it is fully up in the z-axis, or undepressed, and centrally located in the y-axis, or undisplaced; and in an ‘active position’ when it is not at-rest. 
     The term ‘unguided’ refers to the state of a key that has been depressed, whether or not displaced, and released. 
     The term ‘key space’ refers to the locus of all positions in the vertical plane in which the long axis of a key lies to which the key may be moved. 
     Of the two key forms, ‘upper-rank’ keys are analogous to those commonly termed ‘black keys’ in conventional claviers, and lower-rank&#39; keys are analogous to those commonly termed ‘white keys’ in conventional claviers. 
     Structure and Operation 
     FIGS.  2   a - 3   c    
       FIG. 2   a  is a side, elevational view of the present embodiment. It shows a base structure  210  on which is mounted a planar, longitudinally extending key  211  of the lower-rank, comprised of a key body  212  to which a key top  213  having an upwardly facing playing surface  214  is firmly affixed. Key  211  is supported toward its front by a rocker  215  located generally under playing surface  214  and having, at its bottom, a recess  216  that locates rocker  215  on a projection  217  from a flat spring  220 . At its top is a recess  218  into which an aligning projection  219  from key  211  extends without interference when key  211  is unguided and in its at-rest position. 
     Under the foregoing conditions, the two rocker recesses and their associated projections are aligned perpendicularly to base structure  210 . Rocker  215  has a partially truncated, curvilinear upper surface. A flat spring  220 , firmly affixed to an upward projection  221  from base structure  210  and rotatable at a pivot point  222 , supports and captures rocker  215 . The rear of key  211  is firmly affixed to the upper end of a flat spring  223  and the key is rotatable at pivot point  225 . At the other end of spring  223 , it is firmly affixed to an upward projection  224  from base structure  210  such that, when undeflected, it is perpendicular to base structure  210  and rotatable at pivot point  226 . 
     Two non-contact sensors  227  and  228  are located near, and aimed directly at, the broad dimension of flat springs  220  and  223 , respectively. At the front of key  211 , a horizontally disposed, cylindrical projection  229  passes through a zero-clearance, vertical slot in a plate  230 , then through vertical slots both having clearance in a projection  231  and a bracket  232 . Both plate  230  and bracket  232  are firmly affixed to, and may be integral with, projection  231 , which is generally perpendicular to base structure  210 . A cushion  233 , mounted on key projection  229 , is interposed between a collar  234  and bracket  232 , and a cushion  235 , similarly mounted, is interposed between the frontmost, vertical face of key  211  and plate  230 . 
     Finally, key  211  is limited in its movement upwards by a cushion  236 , retained between projection  231  and bracket  232 , and, at the bottom of its travel, by a cushion  237  supported by base structure  210 . 
       FIG. 2   b  is a side, elevational view of a second key form of the present embodiment. It shows a planar, longitudinally extending key  211   a  comprised of a key body  212   a  to which a key top  213   a  having an upwardly facing playing surface  214   a  is firmly affixed. 
       FIG. 3   a  is a perspective view of the two key forms of the present embodiment in their at-rest positions,  FIG. 3   b  is a perspective view of the two key forms of the present embodiment with lower-rank key  211  depressed, and  FIG. 3   c  is a perspective view of the two key forms of the present embodiment with upper-rank key  211   a  depressed and displaced. 
       FIG. 3   a  shows that lower-rank key top  213  extends closer to the player than does upper-rank key top  213   a , as is commonly the case in claviers. The two key forms may be arrayed as repeating groups of five upper-rank and seven lower-rank keys, commonly called ‘octaves’, or may be aggregated in other proportions and/or orders in comprising the intended plurality. 
     As may be seen in  FIG. 3   b , upper-rank key body  212   a  has a relief  310  in its forward aspect, to avoid interference between the key forms when they are not in their at-rest positions, in this case when lower-rank key  211  is depressed. 
       FIG. 3   c  shows that upper-rank key top  213   a  has a relief  311  in its forward aspect to avoid interference with that portion of lower-rank key top  213  lying in its longitudinal plane. The shapes of the keys, and, in particular, those of the key tops, may vary, as do those of conventional claviers, for example, without affecting their function. Other than the foregoing differences, there are no material differences in the structure and operation of the keys, and the structure and operation of any one key is representative of the structure and operation of all. 
     Referring again to  FIG. 2   a , base structure  210  is flat, where horizontal, to aid in aligning the key playing surfaces in their respective planes, and is rigid overall to maintain key alignment under the stresses of key actuation. It is preferably constructed from material that is both light and has a high stiffness-to-weight ratio, for example aluminum honeycomb panel or aluminum composite material. Key  211  is resiliently mounted to base structure  210  so that when unguided it comes to rest substantially centered in the y-axis direction and fully up in the z-axis direction. Its stability in the y-axis when at-rest is a function of the restoring forces of y-axis flat spring  223  and z-axis flat spring  220  and of the width of the truncation (or “flat”) on rocker  215 . More detail is provided in the discussion of  FIGS. 6   a - b , below. 
     Key  211  may be guided to any position in the plane in which its long axis lies, limited only by contact with stop cushions  233 ,  235 ,  236 , and  237 , whose exact positions may be adjusted for player preference in a variety of common ways including shims and hinged mounts. Cushions  233 ,  235  and  237  serve to absorb energy generally normal to their broad aspects and may be usefully made of piano felts, while cushion  236  may engage the projection  229  as key  211  moves in both the z and y-axis directions and may be usefully made of a skinned elastomeric foam, regarding which more detail may be found in  FIG. 5   a  and its detailed description. 
     Key  211  is preferably of sufficient length to minimize: (a) diminishing playing leverage as the key is actuated increasingly closer to pivot point  225 , and (b), the angle to which the playing surface  214  inclines from the horizontal when the key  211  is depressed. At a chosen length, key  211  must be stiff enough so as not to be affected by spurious inputs from unintended motion and/or lateral key-to-key contact. At a chosen length and stiffness, it must be light enough that the inertia imparted to it through impulse inputs in the z-axis and/or the y-axis is generally not greater than the restoring forces in those directions, insuring continuous control. To accomplish the foregoing, key  211  may be advantageously made of a composite material, for example, glass or carbon-fiber/epoxy, and key guide projection  229 , preferably cylindrical in cross-section, may be made integrally with key body  212 , or separately, using drill rod or the like. Z-axis flat spring  220  is preferably made of high-carbon, fully tempered spring steel; it flexes in simple bending at z-axis pivot point  222  whenever key  211  is depressed and for all measures of key displacement, urging key  211  upward to engagement with stop cushion  236   
     Key surface  214  and its analog, key surface  214   a  depicted in  FIG. 2   b , are preferably made of an elastomer of medium durometer whereby longitudinal motion control may be abetted through the conformity of the surface material under finger pressure; at the same time, the elastomer, silicone rubber, for example, should also have no palpable ‘stickiness’ when in contact with human skin, to insure unconstrained release of the keys when desired. 
     FIGS.  4   a - 4   c    
       FIGS. 4   a  and  4   b  detail the operation of y-axis flat spring  223 , which functions as a support, a pivot, and a resilient force.  FIG. 4   a  is a side, elevational view of area  4   a  in  FIG. 2   a , showing y-axis spring  223  in an undeflected state, supporting key  211  in the key&#39;s at-rest position.  FIG. 4   b  is a side, elevational view of area  4  in  FIG. 2   a , showing y-axis spring  223  in a deflected state, subsequent to key  211  having been both depressed and displaced. 
     Key depression is accommodated in a frictionless and substantially resistance-less way at y-axis upper pivot point  225 . If y-axis flat spring  223  is made of AISI 1095 high-carbon, fully tempered spring steel feeler gauge stock, for example, it will flex at that point without fatiguing. Longitudinal force on key  211  causes y-axis flat spring  223  to bend rearward frictionlessly and within its elastic limit at a pivot point  226 ; as a result, the spring adopts a characteristic double-bighted shape  410  and  411 , generating more force for a given measure of key displacement than it would were it to bend as a simple cantilever over the same measure of displacement. 
       FIG. 4   c  is a block diagram showing the relationship between the sensors and the electronic processor, including the output of the electronic processor. Z-axis sensor  227  is preferably an optical reflective object sensor or other non-contact transducer; it detects all possible positions of flat spring  220 , which spring is used as an analog for the z-axis position of key  211 . Y-axis sensor  228  is preferably an optical reflective object sensor or other non-contact transducer; it detects all possible positions of flat spring  223 , which spring is used as an analog for the y-axis position of key  211 . 
     For the purpose of identifying musical intent, key positions are recognized everywhere in the key space, and information about their velocities is derived as well. The microprocessor unit converts sensor information into electronic music control information, as, for example, MIDI (Musical Instrument Digital Interface) data or other music control language forms, for the purpose of controlling sound devices external to the present embodiment. Additionally, the microprocessor unit may control analog output, again for the purpose of controlling external sound devices. 
     FIGS.  5   a - 5   c    
       FIG. 5   a  is a perspective view, from the side and above and partially sectioned, of area  5   a  in  FIG. 2   a . Key guide projection  229  fits without play in a slot  510  in guide plate  230 , and passes with clearance through a slot  511  in control rail projection  231  and through a slot  512  in push stop bracket  232 . Lateral (x-axis) playing loads are resisted by guide plate  230 , which is preferably made of a material having a low coefficient of friction, for example PTFE. 
       FIG. 5   b  is a front elevational view of pin  229  in slot  510  in guide plate  230  taken at section line  5   b - 5   b  in  FIG. 5   a . Lateral force on key  211  (not shown) causes key projection  229  to rotate in slot  510  in guide plate  230 ; the circle and tangent line geometry assures a single line of contact for any degree and/or direction of rotation, and thus consistent and low friction. 
       FIG. 5   c  is a front elevational view of pin  130  in slot  131  in key  123  taken at section line  5   c - 5   c  in prior art  FIG. 1   c . A lateral force, indicated by the arrow, on key  123  causes its slot  131  to bind on pin  130  at contact points  515  and  516 . The structure and operation of the present embodiment as detailed in  FIG. 5   b  is a distinct advantage, as increased friction from lateral loading, having no controllable musical result, is a distraction to the player. 
     Referring again to  FIG. 5   a , cushion  236  acts to diminish the horizontal (y-axis) component of key motion through frictional contact at its surface  513  with key guide projection  229 . That friction is increased force proportionally with the vertical component of key motion because stop cushion  236  transiently conforms to the shape of key guide projection  229 . The vertical component of unguided key motion is dissipated as heat in the interior  514  of cushion  236 , which may be advantageously made of a so-called ‘skinned elastomer’, for example a closed cell urethane foam sold under the trademark Poron by Rogers Corporation, Woodstock, Conn. It is critical that key  211  (not shown), when displaced and released from player control, both return to its center position in the y-axis, that is, that it not be overdamped, and that it do so with little, if any, distracting oscillation, that is, that it not be underdamped. This may be accomplished by varying the durometer and/or the surface of cushion  236 , in which case the key/spring system approaches the ideal condition, critical damping. 
     FIGS.  6   a - 6   b    
       FIG. 6   a  enlarges for clarity area  6   a  in  FIG. 2   a  of the present embodiment, showing the relationship of key  211  and rocker  215  when the key is centered in the y-axis. Key  211  rests at least on end points  610  and  611  of flat  612 , the truncated section of rocker  215 &#39;s circumferential surface  613 , establishing a first, and minimum, extent of separation between key  211  and flat spring  220 , as shown in  FIG. 2   a.    
       FIG. 6   b  enlarges for clarity area  6  in  FIG. 2  of the present embodiment, showing a second, increased extent of separation of key  211  and rocker  215  during initial key displacement. The separation between key  211  and flat spring  220 , determined by rocker  215 , thus also increases. 
     As rocker  215 , driven by the key  211 , rotates counter-clockwise, end point  610  on flat  612 , being in the first quadrant, rises. Thus a portion of playing force directed in the y-axis is converted to z-axis force, urging key  211  upward, providing both a signal of center and a point of stability. When key  211  is fully down (the condition where z-axis flat spring  220  is in firm contact with stop  237 ), downward force by the player causes a reaction force from the base structure  210 , at which point a player can choose, by varying playing pressure downwards, to make the center signal more or less palpable. 
     FIG.  2   a    
     Referencing again  FIG. 2   a , an important articulation in overall musical gesture may be applied when key  211  is moving upward in the z-axis by additionally displacing the key in the y-axis. To accomplish this, the downward force of key  211  and the restoring force exerted by spring  220  are chosen such that, when a player releases a fully depressed key while playing at tempos up to moderato (approximately 110 beats per minute), key  211  accelerates upward quickly enough to enable a player to continuously manipulate key position in the y-axis direction. By way of example, when key  211  is fully up in the z-axis direction, the restoring force of spring  220  must balance the static downward force of the key where it rest on rocker  215 , approximately 30 grams, plus an incremental value, typically 40-50 grams, to resist accidental key depression when a player&#39;s fingers are resting on, but not actuating, the keys. Thus, if the z-axis flat spring  220  has a working length of 7.9 cm, a width of 1.3 cm, and a thickness of 0.041 cm, and key  211  has a length of 40.6 cm, depressing the key 0.76 cm at its front, a typical distance, generates an additional upward (z-axis) restoring force from spring  220  of approximately 30 grams accelerating key  211  upward. 
     CONCLUSIONS, RAMIFICATIONS, AND SCOPE 
     According to the embodiment here presented, we have provided a more controllable and manufacturable dynamic 3-dimensional musical keyboard through improvements to key guidance, damping, centering, and dynamics. 
     The prior art of Okamoto has the following characteristics which hamper full realization of player control: key displacement so limited as to be unsuited for control of high resolution sonic events, key mounting is subject to both play and increasing friction under the lateral loads incidental to ordinary playing, and no provision is made for physically signaling a key&#39;s center position in the y-axis. 
     In the prior art of Allen, the pin mechanism used to control lateral loads is susceptible to cocking and binding in its associated slot, no means is provided for damping the longitudinal oscillations of an unguided key, and the rear key mount requires a bearing in its upper aspect, at the expense of play which may be amplified over the length of the key. Overall the teaching shows a complexity of parts needing assembly and adjustment, and hampering long term reliability. 
     Finally, in the prior art of Tripp et al., the rocker assembly comes at the expense of a complexity of elements and of assembly and disassembly when pinning the rocker body both to the leaf spring at one end and the key at the other. No provision is made to damp both the z and y-axis components of unguided longitudinal key motion beyond the damping internal to the springs themselves. There is no means to resist substantially without play and friction lateral loads at the front of the key as longitudinal key guidance is supplied by a pin oriented perpendicularly in a slot, which is thus subject to cocking and binding. Lastly, a second rocker assembly at the rear of the key is complex to manufacture and assemble as well as a source of looseness in the keys and error in their mutual alignment. 
     The embodiment disclosed herein overcomes each and all of the foregoing limitations through, one, a guidance system having the extreme low friction of single line contact between surfaces, two, an economical, single damper for both the horizontal and vertical components unguided key motion, three, a center signaling support that does not require attachment to the components it separates. 
     Finally, the prior art fails to recognize that control of key motion in the y-axis (in-and-out) direction is interrupted if the dynamics of the mechanism established by predetermined values of mass and spring force are not properly balanced. Without this control, full realization of artistic intent is not possible. 
     While the above description contains many specificities, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of the presently preferred embodiment thereof. Different materials, different sizes, different component shapes, for example, may be used without the result differing materially from what is taught here. 
     Thus the scope of the invention should be determined by the appended claims and their legal equivalents, and not by the examples given.