US2468344A

US2468344A - Electrical displacement-resistance contact member and method of manufacture thereof

Info

Publication number: US2468344A
Application number: US558720A
Authority: US
Inventors: Harold C Pasini; George M Heckel
Original assignee: Fairchild Camera and Instrument Corp
Current assignee: Fairchild Semiconductor Corp
Priority date: 1944-10-14
Filing date: 1944-10-14
Publication date: 1949-04-26
Anticipated expiration: 1966-04-26

Description

April 1949. H. c. PAs|Nl m-AL 2,463,344

ELECTRICAL DISPLACEMENT-RESISTANCE CONTACT MEMBER AND METHOD OF MANUFACTURE THEREOF Filed Oct. 14. 1944 2 Sheets-Sheet 1 PERCENT RESISZ'HNCE PERCENT LENGTH.

April26, 1949- H. c. PASlNl ETAL 2,468,344

ELECTRICAL DISPLACEMENT-RESISTANCE CONTACT MEMBER AND METHOD OF MANUFACTURE THEREOF 2 Sheets-Sheet 2 Filed Oct. 14, 1944 SERVO- AMPLIFIER UNIT INVENTORS.

Patented Apr. 26,1949

asses ELECTRICAL DISPLACEMENT-RESISTANCE CONTACT MEMBER MANUFACTURE THEREOF AND METHOD OF Harold C. Pasini, Fair Lawn, N. 1., and George M. Heckel, Elmhurst, N. 1., assignors to Fairchild Camera and Instrument Corporation, a corporation of Delaware Application October 14, 1944, Serial No. 558,720

6 Claims. (Cl. 201-62) This invention relates to electrical contacts ror resistors and to the method of their manufac-' ture and, while it is of general application, it is particularly useful in a system for winding precision resistors including circuit means for continuously comparing the resistor being wound with a variable portion of a reference resistor, together with means for controlling the winding of the precision resistor by such circuit means, and the invention will be described as embodied in such a system.

In various electrical systems it is frequently desirable to procure, in response to a given displacement of an element, a resistance value which is continuously variable in accordance with an accurately predetermined displacement-resistance characteristic over the extent of such displacement. In general this presents a problem, even when a linear displacement-resistance characteristic is desired, as resistors with accurate linear displacement-resistance characteristics often are not economically feasible. In installations in which non-linear displacement-resistance characteristics are desired, the problem is more difficult and in general requires some nonlinear driving mechanism, such as a mechanical cam, interposed between the movable elements and the adjustable resistor. Not only is the accurate construction of such a mechanical cam costly but in some cases the steepness of the required displacement-resistance characteristic involves excessive cam pressure angles which limit the sensitivity and accuracy of the system of which the cam forms a part.

It is an object of the invention, therefore, to provide a new and improved electrical contact for resistors by means of which any desired displacement-resistance characteristic may be obtained, at the same time obviating the limitation of the prior art arrangements for procuring similar results.

It is another object of the invention to provide a new and improved electrical contact for resistors by means of which any desired displacement-resistance characteristic may be obtained and one which is simple and economical in construction and accurate and sensitive in operation.

It is a further object of the invention to provide a new method of manufacture of electrical contacts for resistors of the type described.

-- In accordance with the invention, an electri- K cal contact for a resistor having a predetermined pended claims.

relief portionhas a configuration related to the displacement-resistance characteristic of the resistor. By the term linear-developed surface" as used herein and in the appended claims is meant a regular surface developed by a given line moving around or along a given generating path, well known examples being plane surfaces and circular cylindrical surfaces.

Further in accordance with the invention, the method of manufacturing a displacement-resistance contact member of the type described from a sheet of conductive material comprises producing on one surface of said sheet a graph of the desired displacement resistance characteristic, disposing a wire along said graph, and rolling the sheet and wire to cause the wire to emboss a relief portion on the opposite surface of the sheet. V

Further in accordance with the invention, an electrical contact member of the type described is embodied in a system for winding precision resistors including circuit means for continuously comparing the resistor being wound with a variable portion of an elongated reference resistor and means for controlling the winding of the precision resistor by such circuit means, the electrical contact member being provided for including a variable portion of the reference resistor in the circuit means.

v For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings the ap-' while its scope will be pointed out in Referring now to the drawings, Fig. 1 is a graph illustrating a type of displacement-resistance characteristic which may be desired; Fig. 2 is a top view of an electrical contact member to which the characteristic of Fig. 1 is transposed; Fig. 3 is a circuit diagram, partly schematic, of a complete system for winding precision resistors with any desired displacement-resistance characteristic and embodying the electrical contact of the invention; while Figs. 4a and 4b are side and end views, respectively, of a modified form of electrical contact member involving a rotational rather than a translatory displacement.

Referring now to the'drawings, there is represented an electrical contact member for deriving from a reference resistor in response to a given displacement a continuously variable resistance value having a predetermined displacement-resistance characteristic, as represented by a continuously variable portion of the reference resistor, together with a system for winding precision resistors in which such electrical cam is utilized. It is assumed that it is desired to obtain a displacement-resistance characteristic of a predetermined shape. This characteristic is first plotted on appropriate coordinate paper, as represented in Fig. l, in which the abscissas represent the percentage of. length of the resistor, that is, of the given displacement, and the ordinates represent the percentage of maximum resistance. The characteristic of Fig. 1 is then reproduced on a conductive metallic member or template having a linear developed surface, such as the plane surface of member 9 of Fig. 2. The characteristic of Fig. 1 may be transferred to the template of Fig. 2 by photo-engraving, or like photographic process, by manually depositing a fine and uniform ridge of conductive material thereon, by embossing, or by any other equivalent process. Preferably the member 9 is a thin sheet or a thick foil of conductive material such as aluminum and the desired characteristic is transferred to one surface thereof by tracing the curve of Fig. 1 thereon with carbon paper. Thereafter a fine wire, for example No. 18 gauge, is disposed along the traced characteristic and, adhesively retained in place, as by an adhesive tape. This sheet is then run through a pair of rollers, the roller engaging the wire side of the member 9 being rigid and the other being semiresilient, such as hard rubber, so that the wire indents or embosses a relief portion on the opposite surface of. the member I. In anyevent, there is developed on member 9 a relief portion 9a, preferably lineal as illustrated, which has a configuration which is a reproduction of the characteristic of Fig. 1.

The member 3 of Fig. 2 can then be utilized in a system for winding precision resistors such as represented in Fig. 3, which is of the same general type as described and claimed in the copending application of Henry E. Hale, entitled Method of and apparatus for winding precision resistors and resistors formed thereby, Serial No. 514,894, filed December 20, 1943. This system includes circuit means for continuously comparing the resistor being wound with a variable portion of an elongated reference resistor and means for controlling the winding of the precision resistor by such circuit means. Specifically, the system of Fig. 3 comprises a winding mechanism consisting of a pair of holders l and H supported in bearings I2 and i 3, respectively, adapted resiliently to hold an elongated resistor card ll of insulation material, the holder il being biased into engagement with the card I4 by means of a spring 15. A manually operable knob I8 is provided for initiating a few turns on the card I. The winding mechanism also includes means for winding resistance wire on the card I to form a resistor R and consisting of a feed-wire holder I! in which is mounted a spool l8 carrying a supply of resistance wire IS, the wire being passed through a guide and tensioning element 20 constituting an extension of the holder H. The wire after passing through the element 20 is fed to the resistor card 14 in a. conventional manner to form a resistor thereon. The card It is adapted to be rotated at constant speed by means of a suitable motor 2i and reduction gearing 22. Electrical connections are made to the resistor R during winding by means of a sliding contact 20a attached to guide 20 and bearing on the wire I! as it is fed to card H and a brush Ila bearing on the conductive holder l i which is connected to a terminal Ha on card I or to any other suitable connection to the starting point of the winding forming the final resistor R.

The winding apparatus also includes an advancing means for producing relative transverse movement between the resistor card I4 and the feed-wire holder l1 during rotation of the card I to form a resistor thereon. This advancing means comprises a feed screw 23 engaging a threaded portion lla of the holder 11 and driven by a follow-up motor 24 through reduction gearing 25. The feed screw 23 is Journalled in supports 28, 26 which also hold a guide rod 21 engaging an extension Nb of the holder I! to maintain steady transverse movement of the holder II.

In order to impart to the resistor R, formed as described, a displacement-resistance characteristic which is an accurate reproduction of that of Fig. 1 and of the relief portion 9a of member 0, the system comprises means including the electrical contact of the invention for continuously comparing the resistance value of the resistor R during the winding operation with that of a corresponding varlable portion of a reference standard resistor. Specifically, a reference standard resistor 30 is mounted in a yoke ll, including guide ways Ila sliding on a pair of guides 32 supported in a frame II. The yoke II also includes a threaded nut I I b engaging a threaded rod 34 comprising an extension of a shaft 34a iournalled in the frame 33. The frame II is disposed to slide the reference resistor 10 over the member 3 maintaining a continuous contact between the resistor in and the relief portion 9a of the member 9, the frame 3| and its operating mechanism thus comprising means for producing relative translatory motion between the member 8 and the resistor 30.

The system of Fig. 3 also includes a pair of output terminals comprising the terminal lb connected to the relief portion 8a of the meml, which connection, in case of homogeneous metallic construction, may constitute a connection to any point of the member 9, and the terminal I lc connected to an adjustable contact Ild engaging a conductive portion of the frame 3! in electrical connection with a fixed point on the reference resistor 30, preferably the end or zero point of the resistor. The portion of the resistor wound on the card H at any moment is compared with the portion of the reference resistor 30 included between terminals lb and tie by means of an electrical bridge including as two adjacent arms the corresponding portions of the reference resistor 30 and the resistor R and as the other two arms resistor elements II and 36 of predetermined relative resistance values, the bridge being connected to compare such portions of resistors l4 and 30 by electrically balancing them against each other in the bridge circuit. To this end, one secondary winding 31 of a supply transformer II is connected across one diagonal of the bridge circuit described, while the other diagonal of the bridge circuit is connected to the input circuit of a servoarnplifier unit 3!. The power supply circuit of the amplifier unit I. is energized from a secondary winding ll of the supply transformer II, while the output circuit of the amplifier 3! is connected to energize the follow-up motor 24 which produces a relative transverse movement between the wire-feed apparatus and the resistor card ll.

In order to effect movement of the resistor ll over the relief portion la of the member 9, corresponding to the given range of displacement of the yoke 3|, for selecting a continuously varithe bride circuit.

\ and de-energization of the several circuits of the apparatus tov start and stop the winding operation. If desired, suitable automatic stopping devices well known in the art may be included automatically to stop the system upon the completion of winding of any resistor R.

Referring now to the operation of the system of Fig. 3 described above, it will be assumed that theresistor card I4 is placed in the holder and a few turns wound thereon by means of the menually actuated knob it until the wire reaches the terminal No or other equivalent connection to the starting point of the winding. It is assumed that, at this point, the adjustable yoke ii is at the extreme left-hand limit of its movement, in which position all of the resistor 30 is cutout of Assuming that at this point there is a small amount of resistance, which may be inherent circuit resistance with or without an added resistance element approximately to balance the bridge circuit under these conditions and which is represented by dotted-line resistor R in circuit with the reference resistor 30, the bridge circuit comprising elements R, R0, 35, 36 is slightly unbalanced. The unbalance voltage is applied to the amplifier 39, is amplified therein, and applied to the follow-up motor 24, initiatinz transverse movement of the feed-wire holder I! to start the formation of the resistor R on the card l4. At the same time the follow-up motor through the

gearing

25, 42, 43 actuates the threaded rod 34 to advance the yoke 3|, which is effective to move the reference resistor 30 over the relief portion 9a of the conductive member I to include continuously increasing portions of the resistor 80 in the bridge circuit.

When the apparatus described has reached a state of equilibrium, there will be a substantially constant difference in resistance between the portion of the reference resistor 30 included in the bridge circuit and the portion of the resistor wound on card I, this difference being only the small amount required to maintain the unbalance of the bridge circuit sufficient to actuate the follow-up motor 24 for advancing the feed-wire holder l1 relative to the resistor card I. Since the card I4 is rotated at constant speed by motor II to wind a given number of turns per unit of time, while the wire-feed holder l1 and the yoke Ii are advanced synchronously but at a variable speed by motor 24 to maintain the bridge circuit in balance, the amount of resistance wire wound on the card l4 per unit of transverse movement of the feed-wire holder I1 is varied to control the displacement-resistance characteristic of the resistor R. The gearing 25 is preferably one of a number of interchangeable gearings to provide a different range of rates of advance of the holder H for each wire size used, the rate within each range being controlled as described. This arrangement causes the system to operate with a minimum unbalance signal and maximum accuracy.

The displacement-resistance characteristic of the resistor R is thus accurately predetermined by the characteristics of the reference standard ll and the electrical contact member. I and the reference resistor II. The configuration of the relief portion 8a of the member 0 is so proportioned in relation to the displacement-resistance characteristic of the reference resistor as to develop between the output terminals 9b, tie the desired predetermined resistance characteristic which is duplicatd in the resistor R. being wound. In case the reference resistor III has an accurately linear displacement-resistance characteristic, the configuration of the relief portion la will correspond exactly to the desired displacement resistance characteristic. However, in practice it will generally be more feasible to adopt a reference standard having a characteristic which may be either linear or non-linear but which preferably approximates that desired and then represent in Fig.1 and transfer to the member of Fig. 2 a measured calibration curve effective to convert the actual displacement-resistance characteristic of the reference resistor II to the desired displacement-resistance characteristic. In any event, the displacement-resistance characteristic of the resistor R will be substantially matched to the resistance characteristic appearing at the terminals 912, lie, which is determined by the electrical cam comprising the reference resistor 30 and the member 9. i

In Figs. 4a and 4b are represented a modified form of the electrical cam of the invention in which the conductive contact member having a linear-developed surface is, in this instance, a cylindrical conductive member 5|! having a lineal relief portion 50a formed thereon. The member 50 is mounted for rotation on a suitable shaft 5i supported in

bearings

52, 52 and includes an electrical connection 50b to a slip ring 53 having a cooperating brush 53a. The reference resistor 30 is held in suitable holders 54 and the mounting of the elements is such that, as the shaft 5| is rotated to produce relative rotation between the member 50 and the resistor 30, the relief portion 50a is biased into continuous contact with the reference resistor 30. The operation of the modification of Fig. 4a is in other respects similar to that described in connection with Fig. 3.

Thus, it is seen that by means of the electrical contact of the invention embodied in a resistor winding system, a resistor having a non-linear displacement-resistance characteristic of any desired taper or steepness may be readily formed without the disadvantages accompanying the use of a mechanical cam with a large pressure angle.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What is claimed as new is:

1. The method of manufacturing a displacement-resistance contact member of a sheet of conductive material which comprises, producin on one surface of said sheet a graph of the desired displacement-resistance characteristic, disposing a wire along said graph, and rolling said sheet and said wire to cause said wire to emboss a relief portion on the opposite surface of said sheet.

2. The method of manufacturing a displacement-resistance contact member of a. sheet of conductive material which comprises, plotting a graph of the desired displacement-resistance cam characteristic, transferring said graph to one surface of said sheet, disposing a wire along said transferred graph, and rolling said sheet and said wire to cause said wire to emboss a relief portion on the opposite surface of said sheet.

3. The method of manufacturin a displacement-resistance contact member of a sheet of conductive material which comprises, producing on one surface of said sheet a graph of the desired displacement resistance characteristic, disposing a wire along said graph, adhesively retaining said wire in place on said surface, and rolling said sheet and said wire to cause said wire to emboss a relief portion on the opposite surface of said sheet.

4. In a system for winding precision resistors including circuit means for continuously comparin the resistor being wound with a variable portion of an elongated reference resistor and means for controlling the windin of said precision resistor by said circuit means, an electricai contact member for including a variable portion of said reference resistor in said circuit means comprising, a member having an integral linear-developed surface and a conductive relief portion thereon, means for producing relative motion between said member and said reference resistor whiie maintaining contact between said relief portion and said resistor, and output terminals connected to said relief portion and to a fixed point on said reference resistor, the configuration of said relief portion being so proportioned in relation to the displacement-resistance characteristic of said reference resistor as to develop the desired displacement-resistance characteristic between said terminals.

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

UNITED STATE. PATENTS Number Name Date 2 3,320 Crooke Aug. 29, 1882 844,380 Marwich Feb. 19, 1907 1,102,483 Dolson July 7, 1914 1,940,102 Roberton Dec. 19. 1933 1,971,238 Silling Aug. 21, 1934 2,095,199 Speed Oct. 5, 1937 2,220,951 Borden Nov. 12, 1940 FOREIGN PATENTS Number Country Date 265,706 Great Britain Feb. 17, 1927