US2714145A - Under keyboard switch - Google Patents

Description

July 26, 1955 M. J. LARSEN UNDER KEYBOARD SWITCH 3 Sheets-Sheet l Filed May 21, 1952 INVENTOR. MERWIN J. LARSEN ATTORNEY July 26, 1955 J LARSEN 2,714,145

UNDER KEYBOARD SWITCH Filed May 21, 1952 3 Sheets-Sheet 2 FIG 4 'i' Q 6 22 3o 29 MIA T INVENTOR.

MERWIN J. LARSEN ATTORNEY July 26, 1955 LARSEN 2,714,145

UNDER KEYBOARD SWITCH Filed May 21, 1952 3 Sheets-Sheet 3 N x m o o ma E (f k 0 N PHHHIIMIII I- INVENTOR. [\JIERWI N J. LARSEN ATTORNEY United tree unuan KEYBGARD swircn Merwin J. Larsen, Gainesville, Fla, assignor to eutral Commercial industries, Inc, Cook County, Ill, a poration of Belaware Application May 21, 1952, Serial No. 289,141 1,

1 Claim. (Cl. Mic -453) This invention relates to electric switches and has par ticular reference to improvements upon the form of switch disclosed in United States Letters Patent to A. F. Evett, No. 2,573,895, issued November 6, 1951.

The herein disclosed invention is primarily formed, constructed and adapted for use with a keyboard musical instrument of the class and for the purpose set forth in United States Letters Patent No. 2,250,065 wherein electrical generators of audio tone signals are adapted to be selectively conducted to an electroacoustical translating system for activation of the latter and production of audible sounds when playing said keyboard.

The principal object of the invention is the provision of a simple, inexpensive and exceedingly compact organization or assembly of substantially similar electric switches that can be applied as a unitary structure to a piano inside the case thereof and underneath the keyboard to dispose the individual switches relative to respective playingkeys thereof for actuation of the switches from off conditions when the keys are raised to on conditions of said switches when the keys are lowered as when playing said keyboard.

Attempts heretofore made to adapt electric switches to the keys of a keyboard from underneath the latter and inside the case of a piano have proved unsuccessful and impractical for a number of reasons, notwithstanding the exercise of good judgment and great care when adjusting the individual switches to respective keys. Electric switches for use as herein proposed are characterized by coactive electrical contact elements. The playing-keys of the keyboard of a piano are tensioned by springs that I tend to rock the keys in a direction which urges their front ends to playing positions. Devices are generally coactive with the keys for adjusting the tension of said springs in order that said front ends of the keys can be leveled and placed under such tension that allows the keys to be played when pressure of from two to four ounces is applied thereto. It has been discovered that variables in adjustment of the above named parts occur from time to time as a more or less natural consequence and that as a direct result thereof the front ends of the 55 keys seek lower positions than originally intended and that and due thereto, the contact elements of the switches engage each other to the extent that the circuits in which they are connected are either partially or completely closed. This causes unwanted sounds to be produced which interfere materially with satisfactory playing the instrument.

An important object of my invention is the provision of an organization of similar electric switches, the key operated contactor of which automatically assumes a form and condition during initial application of the key a to the mounting on which it has detachable connection and is free to rock vertically as to render the switch self compensatory once the contactor has assumed a change in its form as provided for during initial application of 70 the key as aforestated.

A further object resides in the general form and con- (J: struction of an organization of electric switches that enables said org. .ization to be attached as a unitary structure to conventional p ts of a piano, such as the mounting for the keyboard.

Other objects and advantages of the invention will be a parent upon reference to the following description and th carrying drawings, wherein:

l -e l is a sectional perspective view of a portion of the case of a piano showing my impoved organization of electric switches attached to the keyboard mounting of the piano;

Figure 2 is a fragmentary view in top plan of the 'eybor d mounting snowing two of the switches in posiactuatron of respective keys, said keys being d for the sake of clearness; e 3 is a sect onal perspective view of a portion of said switch organization showing the parts on an enlarged scale and illu ing the mode of attachment of the organization to ortion of the keyboard mounting;

Figure 4 is a schematic transverse section through the organization and a portion of the keyboard mounting illustrating a playing-key in a position of initial application to said mounting;

Figure 5 is a view similar to Figure 4 showing the key depressed to a position which is coactive With the switch actuator to change the an le of its effective key operated brz h;

Figure 6 is a view similar to Figure 5, showing the contactor at rest against a fixed surface and the branch 28 bent to its final form;

Figure 7 is a view similar to Figure 6 with the key raised or in a playing position as distinguished from a completely depressed position of the key as shown in said Figure 6, and

Figure 8 is a transverse section of a conventional keyboard mounting and an associated key.

At Fi ure 3 of the drawings is a strip of Bakelite ill on which is mounted an individual switch of my improved organization of similar switches. At Figure l the individual switches are disposed in a horizontal series or row with the switches longitucinally spaced apart from each other, such that there will be a switch for and coactive with each playing-key of a conventional keyboard.

The switch shown at Figure 3 and the switches shown at Figures 1, 2 and 4 to 7, are identical in every respect and a description of one thereof will smiles for all and enable their structural features to be identified by like reference numerals. l2 and 33 arc vertically spaced apart bus-bars supported by blocks 34 of insulating material secured to the upper face of said strip 19. A key operated actuator 15 comprising a flat strip of metal is tiltably mounted on said strip and, as shown, said actu ator includes a tantially rectilinear flat portion 16 of suitable len th ha. at one of its ends a depending lug 17 which is rreely received in a slot 24 in said strip Ell so that said contactor can tilt vertically. The other end of said portion 1% is formed with lower and upper angularly related branches 2% and which are joined to each other by a curved portion Said portion 16 passes through the space between said bus-bars 1 and 13 and same is provided with a longitudinally extending slot 22 for a purpose to be described later.

Secured to strip ll is a terminal clip 25. A coil retractile spring 26 has one of its ends fixed to said clip and its other end attached to a lug 23 which is upset from said portion 16. By connecting the spring to said clip 25 and to said lug 23 in the manner shown, the spring is free to be flexed laterally and its fiexure compensated 22 as will be appreciated upon reference of the drawings. The spring tends always for by said slot to Figures 4 to 7 to tilt the actuator in an upward direction in order that its normal coactive relationship to an associated playingkey will be maintained. It is noted that said spring passes through the space between said bus-bars l2 and i3 and that it functions both as an electrical conductor and as a resilient means tending to tilt the actuator as aforementioned. The clip 25 is adapted to be connected in circuit with a signal supply so that when the key is depressed, signal current will be conducted through an electrical network in response to actuation of a paying-key. Bus-bar 12 is connected to ground G. The spacing between busbars 12 and 13 is such that by vertical motion of said actuator, first downwardly and then upwardly, the spring alternately makes and breaks electrical contact therewith, such that when an associated playing-key is in a playing or rained position the signal supply sou ce :Rkl be connected to ground via said bus-bar 12, whereas the key is depressed or lowered as when played, the s supply source will be coactive with bus-bar is, cli latter can be connected to any well known electroacoustical translating system for conversion of signal current into audible sound.

Said actuator 15 is formed of metal having a low degree of resiliency. Dead soft steel of about 10,006 inch gauge has been found entirely suitable for the purpose of the invention. Its width may be approximately or inch and the length of the portion i6 from lug ii to the bend 21 is about one and a half in J63. The length or the branch 2-0 is approximately nine-sixteenths of an inch. It is not intended that the actuator shall be confined tr: the specific proportions above stated. Tne diameter or the coil spring is about of an inch and the width of the slot 22 is about of an inch. Reference w ll be made herein to the terms relatively ductile, slightly resilient and low degree of resiliency when describing the properties of the metal from which the key operated actuator is formed. These terms shall be construed to mean that the portion 16 is of sufficient strength to resist flexure under tension of said spring that when the branch of said actuator is bent from an initial angle to'a permanent angle, it will yield only very s htly under any key pressure imposed thereon. At no time Vigil 1 yield to an extent that the spring 2n Wlll move on of the grounding bus-bar and onto the signal output bus-bar merely by the weight of the key.

Now, and with particular reference to Figure 4 of the drawings, it is noted that branch of the key operated actuator 16 occupies an initial or non-permanent angle, such that when K is being applied to its guide and fulcrum pins 27 and 28, said branch 2 will have its extreme tree end disposed at an elevation which is higher than a substantially horizontal playing position of the key and thus in a position where it will be pressed against by the key when depressing same a first time. Upon further downward motion of the key, b .nch T9 of the actuator 15 is advanced against an insulating surface 29 upon a rigid metal plate 39. This squashes branch 7 with a resultant change in its angular relation to said by this manent means. said branch 2% is changed from a no er angle relative to branch f9 as shown at Figure 4 to a permanent or set angle relative thereto as shown at Figures 6 and '7, in the latter of which the playing-key IS in a normal substantially horizontal position.

An essential feature of the invention is the provision of an organization of switches for use under the playingkeys of a conventional piano keyboard, or the keyboard of an organ or other keyboard musical instrument. A keyboard of this type is usually mounted upon a base structure 31 which includes a longitud. all front strip 32 on which guide pins 27 are moun ed. At the back, said mounting is provided with a similar longitudinal strip or fulcrum bar 34 having the customary fulcrum pins The strip 32 and said fulcrum gether by transverse bars 23a. 32 and bar 34 accommodated bar 34 are connected to- The space between strip the aforementioned strip it),

and, as shown, said strip rests flatwise against the upper surface of said cross bars 28a. The metal plate is secured at 35 to the rear portion of said strip 32 in a manner to cause the underside of said strip to rest firmly on said bars 23a.

Upon referring to Figure l, the signal input lead wires to the respective springs 26 of the individual switches are shown at 37 and same are formed into a cable 38 h extends longitudinally of the switch organization. the foregoing description, it is only necessary that the keys a conventional keyboard be removed so as to expose the underlying key mounting from which the keys are readily separable. The key switch organization is then applied to the mounting and attached to the 32, all as clearly shown at Figures 4 to 7 of or. ,b. The switches are spaced apart from each other that for each playing key there is a switch indivlduar thereto and adapted to be operated by the key.

The process of reinserting the keys is then in order this is accomplished by individually inserting the keys o the instrument so that each key is operatively concted to a respective fulcrum pin 28. The forward end he key is then vertically aligned with a respective guide p 27. in this operation, the key will approximately occupy the position shown at Figure 4. Under the urge 5 spring 26, contactor 15 will be tilted in an upward irecticn and against the underside of the key. It will be orne it mind that at this instant the branch 24 of the tuator is at a non-permanent angle relative to branch 1. Fress is progressively applied against the key so as to the actuator downwardly against the normal urge of spring 26 until branch 19 comes substantially wise against the insulated face of the rigid metallic it is noted that at Figure 6 the key has been fully depressed and that branch 24) has been squashed or a non-permanent angle as shown at Figure 4 lent angle, such that when the angle has once i by the initial placement of the keys in an tstrunient it is never changed and is, therefore, capable of unite 'in coaction with the key at all times.

Hereto fore it has been impossible to properly correlate the actuator of an electric switch with a vertically tiltable key so that by means of identical switches, there will be no variables in. the time in which a circuit is made and it In the instant case, the springs 26 always urge the free ends of the branches 2% against the undersides of their respective playing keys. The gist of the invention lies the self-compensatory action of the actuator. By this is meant that when applying the keys to an instrument in the manner aforem ntioned the actuators will be operated upon by the keys and their portions 20 bent from the no ermanent angles shown at Figure 4 to the per- .nent an e shown at Figure 7.

When pressure is released from a key the latter is returned to its normal playing position under the tension of spring S. The branch 20 of the actuator maintains its fixed angle except possibly for some slight-degree of resiliency in the metal which causes it to bear very lightly against the underside of the key.

While I have referred to use hereinof dead soft steel of which the actuator 15 is constructed, this is by illustration only and it is to be understood that any well known equivalent material can be substituted therefor. The retractile spring 26 can also be made of any suitable wellknown material which is a good conductor of electricity to beryllium wire or copper wire has been found entirely satisfactory.

What 1 claim as my invention is:

A single pole, double throw electric switch comprising a mounting member of electrical insulating material'ha'ving a grounding element and a signal output element, said signal output element and said grounding element supported in vertical spaced-apart relation to each other, a contactor of springy material attached tosaid'mounting strip member and related to and coactive with said grounding E? coil spring, one end of which is secured to said mounting member and the other end thereof to the pressure-responsive means to normally urge said means against said grounding element, as and for the purpose set forth.

References Cited in the file of this patent UNlTED STATES PATENTS Nov. 6, 1951 Oct. 14, 1952 Evett Kitto

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