US2492429A - Electric translating device - Google Patents

Description

Dec. 27, 1949 R. s. Jol-IN 2,492,429

ELECTRIC TRANSLATING DEVICE Filed Aug. 17, 1945 Patented Dec. 27, 1949 ELECTRIC TRANSLATING DEVICE Robert S. John, Waukegan, Ill., assigner to Pianstielil Chemical Company, a corporation of Illinois Application August 17, 1945, Serial No. 610,975

14 Claims.

This invention relates to a translating device and particularly to a 'method of making a translating device for translating mechanical variations into electrical variations, and the product prepared thereby.

One object of this invention is to provide an improved translating device made of a flexible material and having a, coating forming an electrical path with the resistance being varied by strain. Another object is to provide an improved method of making such a translating device so that the resulting product will give uniform results over a Wide range of frequencies. Still another object is to provide a simple, efficient, and rapid method of producing such a translating device so that any desired characteristics may be given thereto. Other objects will be apparent from the detail description given hereinafter.

The particular translating device described herein is a phonograph pick-up of the same general nature as those shown in the Kenneth J. Germeshausen Patents No. 2,329,526, 2,373,676, and 2,380,514, but it will be understood that the processes here disclosed are applicable to translating devices in any field where a mechanical movement is to be translated into an electrical variation.

In practicing this invention I provide a flexible base member having at least one surface of a flexible insulating material with this base member being intended to be subjected to mechanical variation. A coating of finely divided particulate material suspended in a solvent for the flexible insulating surface is applied to this surface. The particulate material used is one that is capable of forming a layer whose electrical resistance is varied by strain. This coating is dried, and then a final coating of flexible insulating material is applied over the strain-sensitive coating.

The base member may be made of a flexible insulating material throughout, and this is preferably a synthetic elastomer having a low modulus of elasticity, such as polystyrene, polymerized methyl methacrylate, or the like. The strainsensitive material is preferably very finely divided graphite, such as that made in an electric furnace, and this graphite is applied by suspending it in a solvent for the synthetic elastomer. Where the elastomer is polystyrene carbon tetrachloride is an excellent solvent, as it softens the polystyrene so that the graphite will be held thereon, but evaporates so rapidly that there is no undue penetration and substantially no swelling action on the polystyrene. Other solvents for polystyrene include toluene, ethyl benzene, ethyl on spring-mounted drying apparatus.

acetate, turpentine, dioxane, gasoline, ethylene chloride, Cellosolve acetate, and paradichlorobenzene. For any given synthetic elastomer a solvent should be chosen that softens the elastomer sufflclently to form an adhesive surface upon which the graphite may be deposited, but should also have a low boiling point so that the solvent will readily evaporate before penetrating very deeply into the elastomer.

In making the strain-sensitive coating of graphite on polystyrene, a suspension of graphite in 2 to 3 times its volume of carbon tetrachloride is prepared. The polystyrene surface is then dipped in this suspension and allowed to dry quietly at preferably not more than '70 F. for at least an hour, and preferably for as much as 24 hours, in an atmosphere having low humidity. not over 30% and preferably between 10% and 20%. The extra drop that clings to the dipped coating should not be wiped off, but should be evenly distributed, such as by holding the polystyrene with the coating in a horizontal position. and slowly rotating it under conditions where it is substantially entirely free from vibration, as

One dipping will produce a very opaque coating of rather high resistance. If the resistance is to be brought down to a lower predetermined value successive clippings are made in the same solution, with each coating dried thoroughly before the next is applied. My preferred method provides a coating having desired resistance characteristics with freedom from noise in operation.

Aifter the strain-sensitive coating has been made, the desired circuit is scribed out and the plastic with the graphite coating is then dipped in a fairly thin lacquer solution and dried. This gives an overall covering of flexible insulating material. One lacquer that has been used is made by the Zapon Brevolite Corporation, and is known as XL-44 Lacquer. 'I'he active ingredient is elemi, a natural resin. The lacquer to be used should be one that is flexible and that will not cause distortion of the plastic base member. Lacquers other than that mentioned have these properties and may be used.

When the polystyrene or other synthetic elastomer is successively dipped in the graphite suspension, each dipping should be made as rapidly as possible, so that some of the graphite put on in previous dippings is not washed off. The drying which follows each dipping should be done in a dust-free and dry atmosphere, free from drafts, and should be done at a temperature not substantially greater than F. The nal 3 dryin should be continued for at least 24 to 48 hoursas in this time the resistance drops to a final value and becomes quieter.

The translating device which is the subject of this invention has the flexible portion containing the graphite layer or other strain-sensitive material. and usually has another rigid portion that is not flexed. This rigid portion ordinarily carries binding posts or the like to which electrical leads may be fastened so as to complete the electrical circuit through the strain-sensitive coating. In the prior patents mentioned hereinabove this rigid portion was coated with a graphite layer to complete the circuit. The graphite layer, however, resisted ilow of electricity where such resistance was not needed. It has been discovered, however, that a superior translating device will be produced if the rigid portion of the device is coated with a layer of freely-conducting material which contacts the layer of strain-sensitive material in order to complete the electrical circuit. The conducting material preferably is an oxide-free suspension of metal in a solvent for the synthetic elastomer.

One of the best metals for making conductive coatings is commercially precipitated silver free of silver oxide and having substantially no particles larger than 200 mesh. This silver may be suspended in 2 or 3 times its volume of solvent and applied to the base member with a brush in the desired path. When the elastomer is polystyrene the solvent may be carbon tetrachloride. The coating of powdered metal should be thick enough to be opaque, usually not less than 0.001 inch.

One embodiment of this invention is shown in the accompanying drawings. Of the drawings Fig. 1 is a side elevation of a translating device made according to the method of this invention; and Fig. 2 is a plan view of this translating de- V1(':Ihe translating device I0 shown in the accompanying drawings comprises a rigid portion li adapted to be mounted on a tone arm o a phonograph or the like, and a beam I2 extending therefrom. At the end of the beam there is located a rigidly mounted needle or stylus I3 adapted to engage the grooves of a record. The beam I2 has a coating of graphite Il arranged in the form of a path extending from near the base II out toward the end of the beam I2 and back to the base. The beam II has two holes I5 and I6 by which the device may be mounted and which may also be used to provide electrical connections to the resistance path. From each of these holes there is provided a layer of silver Il with each layer connecting to one end of the graphite path. Thus a complete circuit is formed extending toward the end of the beam I2 that holds the needle I3.

In making the graphite layer I4 the beam I2 is immersed in a graphite suspension of electrically produced graphite in 2 or 3 times its volume of carbon tetrachloride. The beam is lmmersed in the suspension a plurality of times, with each immersion followed by complete drying for at least one hour, at a temperature not greater than 70 F. These successive immersions are continued until the overall resistance of the graphite layer is five to eight thousand ohms before scribing and 30,000 to 35,000 ohms after the circuit paths have been scribed thereon. This circuit path may be on one or more sides of the beam. The silver layer on the rigid portion II of the translating device is prepared by brushing 4 on a suspension of finely divided oxide-tree silver in carbon tetrachloride. The silver is brushed on in the desired path and a sumcient quantity is applied so that the silver layer will be at least 0.001 in. thick. The rigid portion is then dried for at least one hour at not more than 70 l".

After the silver and graphite layers have been applied these layers are covered with a solution of lacquer as described above. 'Ihe lacquer layer is then dried at a temperature not greater than 70 F. The graphite layer which prior to the lacquer coating had a resistance oi' 30,000 to 35.000 ohms, should now have a resistance o! 60,000 to 80.000 ohms.

The silver coatings may be lightly burnished before the lacquer is applied. as this improves the conductivity of the silver layers.

The solvent used in making the various suspensions employed in practicing this invention should be one which dissolves the iiexible material readily but has a rapid rate of evaporation so that the penetration of the solvent will be very slight. One of the best solvents for use with polystyrene base members is carbon tetrachloride, while acetone is an excellent solvent when polymerized methyl methacrylate is used to make the base member. The lacquer used should be one that is freely exible at all ordinary temperatures, and thatA has no distorting etiect on the base member.

These lacquers, as well as the solvents for the various flexible materials that may be used in making the translating devices, and their uses are well understood by those skilled in the art.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. The method oi making a translating device for translating mechanical variations into electrical variations which comprises providing a ilexible base member having at least one surface of a flexible insulating material, said base member being one that is to be subjected to mechanical variation, applylng to said surface a coating oi a finely divided particulate material suspended in a solvent which acts as a solvent for the ilexible insulating surface with said particulate material being capable of forming a layer whose electrical resistance is varied by strain, ydrying the coating at a temperature not substantially above '70 F.. and applying over the coating a layer of flexible insulating material.

2. The method of claim 1 wherein the suspension is maintained at a temperature not substantially above 70 F.

3. The method of claim 1 wherein the ilexible insulating surface is a synthetic elastomer and the solvent is one that has a substantially nonswelling action on the ilexible insulating material and that has a rapid rate of evaporation.

4. The method of making a translating device for translating mechanical variations into electrical variations which comprises providing a ilexible base member having at least one surface of a synthetic elastomer, said base member being one that is to be subjected to mechanical variation, applying to said surface a coating of nely divided graphite suspended in a solvent which acts as a solvent for the elastomer while maintaining the suspension at a temperature not substantially above 70 F., said solvent being one that has a substantially non-swelling action on the elastomer and that has a rapid rate of evaporation, drying the coating at a temperature not substantially above 70 F. and at low humidity, ap-

plying over the coating a solution of a exible insulating material, and drying..

` 5. The method of claim 4 wherein the synthetic elastomer is polystyrene and the solvent is carbon tetrachloride.

6. The method of claim 4 wherein the solution of flexible insulating material is a lacquer that has substantially no effect on the dimensions of the synthetic elastomer. 7.. The method of making a translating device for translating mechanical variations into electrical variations which comprises providing a base member of polystyrene that is to be subjected to mechanical variation, applying to at least one surface of said base member a coating of finely divided graphite suspended -in carbon tetrachloride that is maintained at a temperature not substantially above 70 F., drying at a temperature not substantially above 70 F. and at low huI midity, applying over the coating a lacquer that has substantially no effect on the dimensions oi' the polystyrene, and drying.

-8. The method of claim 7 wherein the graphite is applied to the base member by a plurality of dipping operations with substantially complete drying of each coating before applying the next one, with the dipping operations being continued until there is a iinal resistance of 30,000 to 35,000 ohms, after scraping and scribing.

9. The method of making a translating device for translating mechanical variations into electrical variations which comprises providing a flexible base vmember having at least one surface of a ilexible insulating material, said base member v being one that isto be subjected to mechanical variation, applying to said surface a coating of a finely divided vparticulate, material suspended in a solvent which is a solvent for the ilexible insulating surface by successive applications of said suspension with each application followed by drying, said particulate material being capable of forming a layer whose electrical resistance is varied by strain, and applying over the final coating a layer ofilexible insulating material.

10. The method of claim 9 wherein each application is 'an immersion and is dried at a temperature not substantially above '10 F. for approximately 24 hours.

11. The method of claim 9 wherein the suspension is maintained at a temperature not substantially above 70 F., and each immersion is dried at a temperature not substantially above 70 F. for approximately 24 hours.

12. The method of making a translating device for translating mechanical variations into electrical variations which comprises providing a base member of polystyrene having one portion to be subjected to flexing and another portion to be held substantially rigid, coating the flexible portion with graphite suspended in carbon tetraoh1oride, drying, coating the rigid portion with a suspension of nely divided oxide-free silver in carbon tetrachloride with no particles of the silver being larger than 200 mesh,5 drying, said coatings overlapping at their adjacent edges to form a continuous electrical path, covering said coatings with a lacquer, and drying.

13. The method of claim 12 wherein the suspensions are maintained at a temperature not substantially above 70 F., and the coatings are dried at a temperature not substantially above 70 F.

14. The method of claim 4 wherein the solution of Vflexible insulating material causes the resistance of the coating of graphite to be substane tially doubled.

ROBERT s. JOHN.

REFERENCES curan The following references are of record in the file of this'patent:

UNITED STATES PATENTS 211,324 Great Britain Rb. 21,1924

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