US2513415A - Rheostat switch - Google Patents

Description

July 4, 1950 M. J. LARSEN ETAL RHEOSTAT SWITCH Filed Nov. 20, 1948 Patented July 4, 1950 UNITED `STATES PATENT OFFICE RHEOSTAT SWITCH Merwin J'. Larsen, Villa Park, and James A. Kochi, Evanston,'Ill., assignors, by mesne assignments, to Central Commercial Industries, Inc., Chicago, Ill., a corporation of Delaware Application November 20, 1948, Serial No. 61,160

9 Claims. l

This invention relates to electric switches and has particular reference to switches for use with keying circuits adapted to be interposed in an electrical network between an audio signal supply source and the power amplifier of a signal translatingA device,

The primary object of the invention is the provision of a variable resistive switch, the operation of which, in response to depression of a playing-key, suppresses what has come to be called key thump caused by the sudden surge of signal voltage when close circuiting a source of tone signal voltage with the input circuit of the power amplier of the signal translating device.

A further object of the invention is the pro-- vision of a simple, inexpensive electric switch which is sturdy and dependable in operation and will function to vary the effective resistance in a signal transmission circuit as a function of the velocity of a control key.

A still further object of the invention is the provision of a noiseless, positively acting switch.

Other objects of the invention will manifestly appear from the following description and accompanying drawings, in which:

Figure l is a View partly in side elevation and partly in section of the switch and coactive control key;

Figure 2 is a view in rear elevation thereof;

Figure 3 is a section on line 3-3 fof Figure 1;

Figure 4 is a View in elevation of the resistive strip before application of the metallic coating to the respective ends thereof;

Figure 5 is a View similar to Figure 4 of the strip showing the metallic coating applied thereto;

Figure 6 is a section on lines '6 6 o'f Figure 4, and y Figure 7 is a perspective view of themetallic clip.

Figure 8 is a view in :perspective of a portion of the vertical member of the switch.

In carrying the `invention into practice, use is made of a channel member 5 of any suitable well known material such as hard wood, aluminum, Bakelite, or the like. Secured at 6 between the opposite side flanges 5 of member and disposed at right angles to said member, is a member 'I of electrical insulating material, the same formed at its lower end with a foot 8 confined between said side iianges 5v bythe aforementioned means 6.

Placed iiatwisey against the front face of member 'I is la. flat strip I0 of suitable well known electrical vinsulating material: such` as Bakelite.

2 The front face of said strip has parallel, laterally spaced apart lanes or tracks I I, i2 and I3,

each consisting of a resistive coating compound such as carbon, or other well known resistive coating, such that each lane or track is (in the present example) of the same predetermined high resistance between points A and B. The lower terminal of each of said lanes merges into a low resistive coating of carbon or other well known resistive coating indicated at I5, forming the signal voltage output end of the strip for transmission of signal voltage to the input circuit of a power amplifier from a source oi signal voltage common only to the high resistive lane with which the particular low resistive coating I 5 is electrically coactive. The opposite ends of said lanes merge into `a carbon coating I5 which is common to all of said lanes.

Carbon, or other well known resistive coating may be painted or sprayed upon the strip Ill by any well known method and when dried either by air or heat treatment, the low resistive coat- Ving I4 at the upper ends of lanes Il, I2 and I3 and common to all thereof, will preferably have applied thereto a metallic conductive paint I6 providing a common grounding connection to be hereinafter more fully described. The low resistive coating I5 at the lower end of each separate lane II, I2 and I3 is similarly coated with conductive paint I6. These conductive coatings may consist of any well known metallic paint which, when applied and properly set, insure hard surfaces at the respective ends of said lanes, which said surfaces merge into said lanes so as to form therewith one perfectly smooth continuous surface which lies in a single plane.

At the upper end of the vertical portion 'I of rthe switch are terminal lugs Il, there being one thereof for each separate high resistive lane Il, I2 or I3. As these lugs are identical both in form and purpose, a description of one will suilice for all. In Figure l, each separate lug Il' will connect with the output lead I9 of a tone signal Supply source 29 such as a vacuum tube oscil- -lator or any well known generator or" a wave form of signal voltage of predetermined irequency. Only one lug I'I is shown connected to a-signal supply source. Assuming that the switch is used with a musical instrument employing octave couplers, one of said lugs will connect vwith a tone frequency generator producing signal voltage, the frequency of which corresponds with Aan eight foot pipe tone whereas the others of said lugs respectively connect with tone signal sources providing tone signals corresponding to 4 and 16 ft. tones. Soldered at 2I to said lug is one terminal of a coil spring 2l a providing a resilient conductive lead between said source of Signal voltage and the short arm 22 of a contactor 23, to which short arm the other terminal of said coil spring is soldered as at 24.

The rearwardly projecting portion 'la of vertical guide slots 25, there being a separate slot for each individual contactor 23. These slots are horizontally aligned with their coactive resistive lanes I I, l2 and I3 on strip IU. The contactors are each thereof mounted for pivotal motion about a center 26 on an insulating block 21 secured to the back end of a lever arm 28, pivoted for vertical motion at 2S to the forward end of member 5.

Each contactor has a long arm Sil received in a coactive guide slot in portion 'la of inember 'I and, as shown, the free end of said arm has an effective upset portion 30d presenting a smooth curved surface for effective electrical coaction with the resistive coating cf a respective one of the aforementioned lanes.

A metallic clip 3l is secured at 32 to member 'I and is formed with parallel springy portions 33 which are rmly pressed against the conductive coating I6 of the respective lanes il, I2 and I3 as shown at Figure 1. Said clip is connected to ground 34.

The springs 21a function to maintain a yielding, yet free sliding connection between the portion 30a of a respective contacter and its coactive resistive material on strip- Ill, and to urge lever arm 28 to the position shown at Figure 1. The forward end of the lever arm is provided with an adjusting screw 34' which is coactive with the back end of a vertically tiltable playingkey 35 such as the elongated key of a piano, organ or other musical instrument in which the key can pivot about a horizontal axis. When- `the playing-key is in the position shown at rFigure 1, screw 34 rests upon a strip of felt 34a,

at the bac-k end of the key and when pressure is applied to the forward end of the key, motion is ktransferred to the contactors 23 simultaneously moving them ofi' of the low resistive common Vground I8 and progressively onto their high resistive coatings II, I2 and I3, the value of the resistance lowering progressively as the oontactors approach their low resistive output terminals I6. Each low resistive output coating has firmly connected thereto a terminal lead 35 adapted to be connected to the input circuit of the power amplier of a sound translating device.

Emphasis is placed upon the'structural features of the switch and the forms and shapes of the component elements to the end that smoothness in action is assured and whereby variations in the resistance is made without any break in' 'the continuity of the movable Contact element of the switch during motion of said contactor rectilinearly. By mounting the contactors 23 as shown and described herein, only a negligible degrees of pressure of the effective contact porytions 30a is required 'for a good electrical contact between same and the resistive coating of the insulating strip I0. By proper hardening of the coating materials I6 and I5 and the resistive lcoatings which smoothly merge thereinto and by establishing and maintaining only a very minimum amount of pressure between same and said effective contact portions 30a, to which may be added use of German silver or its equivalent `and of suitable gauge, the resistive surfaces are kept clean and the switch is perfectly noiseless over very long periods of time. In practice. we nd that by these niceties, rubbing engagement of the portions 30al of contactors 30 can be continued for a great number of operations without fear of any metal being transferred onto the resistive lanes from said portions 30a.

In order to cushion the action of the lever 28, said lever is preferably provided with a strip of felt 28a adapted to come against the under side of the foot of the member 1 when the lever 28 is returned to an olf position of the switch. While it is preferred to coat the low resistive common ground end I4 of strip l0 with a metallic paint and similarly to apply metallic coatings I6 to the opposite ends of the lanes Il, I2 and I3, `we do not wish, however, to be limited in this respect as tests have been shown that very satisfactory results are had simply by the low resistance ycarbon coatings when used alone. By heat treatment of strip I0 after application of the carbon thereto, the resistive surface thus formed becomes exceedingly hard and is relatively permanent. The contactors 23 give excellent results when made from German silver of suitable gauge. With the resistive surface characterized as aforementioned a positively acting switch is produced which is smooth in action, noiseless and sturdy. The high resistive zone in each of the individual rectilinear lanes may be of different resistance for different purposes but lwhen used as a high impedance switch, said zone will preferably have' a resistance of approximately 50,000 ohms, such that when the contactor leaves the grounded terminus I and enters and proceeds in a direction longitudinally of the intermediate high resistive zone and toward terminus I6', the change in resistance will at no time be by `jumps but to the contrary will progressively lower as the contacter approaches said terminus IS.The reversal of this operation occurs during return motion of the contactor in the direction of and back onto the common grounding terminus.

The standard width of the playing-key of an organ or a pianois approximately one-half inch. As the herein disclosed switch organization is designed and constructed primarily for use with such keyboard musical instruments, an essential feature of our invention is the embodiment in a unitary structure of a'plurality of individual switches which are so formed and arranged as to enable the entire organization to be accommodated in a space not in excess of one-half inch. On `reference to Figure 2`of the accompanying drawings, it is noted that the organization occupies a' vertical position above playingkey 35, and that the width of the playing-key is slightly inexcess of the width of said organization. It is further noted that motion ofthe key is simultaneously transferred' to all contact elements While they are in'constant yielding engagement with their coactive resistivelanes, the distance of travel of all contactors being precisely the same.' This is necessary in order that the impedance in the separate output paths through said lanes shall be the same ineach thereof. yTo the best olf our knowledgeno one has ever before combined in a single 4resistive switch organizationaplurality vof individual switches lcapableiof being accommodated in so limited a space as allowed for their association with the playing-key of an'r organ or similar keyboard musical instrument! This is made possible by'our use of a. thin, stiif rectangular strip of insulating material, one side of which is coated with a hard resistive substance as herein set forth. This enables use of fine gauge contact wires such as 30, which wires are in parallel relation and only slightly spaced apart from each other laterally. Also by our use of a single strip of insulating material, all resistive lanes necessary for as many conductive paths can be readily insulated from each other by simply routing the material to a depth below the effective resistive coating substance after one face of the strip has been coated with the resistive substance.

What we claim as our invention is:

1. An electric switch organization for actuation by a yplaying key of a musical instrument comprising means having a plurality of parallel resistive lanes disposed in a common plane and each including a high resistive zone, a low resistive zone and grounding means common to said high resistive zones, a plurality of contactors coacting with the respective lanes and movable progressively from said common ground and longitudinally along said high resistive zones, and into and along said low resistive Zones, voltage output terminals for the respective low resistive zones, and means including voltage input terminals and expansible and contractable rnetallic conductors connecting said terminals with the respective contactors.

2. In an electric switch for varying the resistance in a signal transmissionpath and actuable by an elongated playing-key which has pivotal motion about a horizontal axis; insulating material having a longitudinal resistive surface; means by which said material is adapted to be mounted to dispose said resistive surface at right angles to the longitudinal center line of said key; and means including a playing-key actuated icontactor coactive with said resistive surface to vary the resistance in said path as a function of pivotal motion of said key.

3. In an electric switch for varying the resistance in a signal transmission path and actuable by an elongated playing-key which has pivotal motion about a horizontal axis; a thin planar strip of insulating material lcoated at one side with a resistive material providing a longitudinal resistive surface; means by which said strip is adapted to be :mounted to dispose said resistive surface at right angles to the longitudinal center line of said key; and means electrically coactive with said resistive surface in response to motion of said key for varying the resistance in said path.

4. In a variable resistive switch for use in a signal transmission path employing a control key which is tiltable about a horizontal axis; a strip of insulating material provided with a longitudinal resistive surface; a springy contactor in constant engagement "with said resistive surface and movable longitudinally thereof; and mounting means for said strip for disposing said resistive surface at right angles to the long axis of said key and including means coactive with said key for causing relative motion between said surface and said contactor with resultant progressive changes in the effective resistance in said path during pivotal motion of'said key.

5. As a new article of manufacture, a variable resistive switch organization comprising a flat rectangular strip of electrical insulating material having a plurality of laterally spaced apart, rectilinearly disposed, parallel continuous, resistive lanes at one side thereof, said lanes being electrically insulated from each other and adapted to be connected to respective signal transmission paths; means including a slidably mounted contacter for and in constant yielding engagement with each of said lanes; and an actuator common to said contactors for simultaneously sliding same along said lanes to vary the impedance in said paths.

6. As a new article of manufacture, a variable resistive switch organization comprising a flat rectangular strip of electrical insulating material having a plurality of laterally spaced apart rectilinear, continuous lanes at one side thereof, said lanes being electrically insulated from each other and adapted to be connected to respective signal transmission paths; means including a resilient contactor :for and in constant yielding electrical engagement with each of said lanes; and an actuator common to all of said contactors for causing relative rectilinear motion between said strip and said contactors for simultaneously varying the impedance in said paths by even increments.

7. A switch organization as set forth in claim 5 wherein the impedance value of the resistance in each of said lanes is the same.

8. A switch organization as set forth in claim 6 wherein the impedance value of the resistance of each of said lanes is the same.

9. The combination with a. playing key of a musical instrument, of a switch organization including means operated by said key and disposed perpendicular to a line drawn through the long axis thereof, said organization having a width not in excess of that of said key and including a vertically disposed, thin rectangular strip of insulating material secured flatwise against said means and adapted to be connected to a signal transmission path, and a springy contactor slidable rectilinearly on said strip and actuable by said playing-key to cause sliding motion of said contacter between the ends of said strip, said strip having a continuous resistive coating substance against the surface of which the contactor has constant yielding engagement.

MERWIN J. LARSEN. JAMES A. KOEHL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 432,894 Parrish July 22, 1890 2,135,809 Fruth Nov. 8, 1938 2,215,124 Kock et al. i Sept. 17, 1940 2,242,327 Rubinstein May 20, 1941 2,280,305 Schauer Apr. 21, 1942

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