US3657689A

US3657689A - Variable low noise electrical resistor with plural variable resistors connected in series

Info

Publication number: US3657689A
Application number: US75638A
Authority: US
Inventors: Harry B Casey; Carl E Clark
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1970-09-25
Filing date: 1970-09-25
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18

Abstract

A rheostat which includes a hollow housing having a pair of rotors rotatably mounted therein, and a resistance path on each of the rotors. One of the resistance paths provides relatively large incremental changes in resistance value over a wide range of resistance values, and the other resistance path provides small incremental changes in resistance value over a range equal to each increment of the resistance value of the one resistance path. The resistance paths are connected in series and terminals, which extend from the housing, are electrically connected to the resistance paths. By rotating the rotors, any desired resistance value over a wide range of values can be obtained. In one form of the rheostat, a separate shaft is provided to rotate each rotor. In another form of the rheostat, a single shaft drives both rotors.

Description

United States Patent Casey et al.

[54] VARIABLE LOW NOISE ELECTRICAL RESISTOR WITH PLURAL VARIABLE RESISTORS CONNECTED IN SERIES [72] Inventors: Harry B. Casey, Willow Grove, Pa.; Carl E. Clark, St. Petersburg, Fla.

[73] Assignee: TRW, Inc., Cleveland, Ohio [22] Filed: Sept. 25, 1970 [21] Appl. No.: 75,638

[56] References Cited UNITED STATES PATENTS 2,972,123 2/1961 Blom ..338/122X 3,027,551 3/1962 Laurin ..338/l50UX FOREIGN PATENTS OR APPLICATIONS 844,757 5/1952 Germany ..338/123 115] 3,657,689 [45] Apr. 18, 1972 Primary Examiner-Lewis H. Myers Assistant Examiner-Gerald P. Tolin Attorney-Jacob Trachtman [57] ABSTRACT A rheostat which includes a hollow housing having a pair of rotors rotatably mounted therein, and a resistance path on each of the rotors. One of the resistance paths provides relatively large incremental changes in resistance value over a wide range of resistance values, and the other resistance path provides small incremental changes in resistance value over a range equal to each increment of the resistance value of the one resistance path. The resistance paths are connected in series and terminals, which extend from the housing, are electrically connected to the resistance paths. By rotating the rotors, any desired resistance value over a wide range of values can be obtained. In one form of the rheostat, a separate shaft is provided to rotate each rotor. In another form of the rheostat, a

single shaft drives both rotors.

19 Claims, 13 Drawing Figures Patentd April 1a, 1972 3,657,689

4 Sheets-Sheet 1 2 FIG. 2 0 96d Es 15% 1 ll l? I a /4 74/ 98 a,

INVENTO/PS HARRY 8. CASE) v CARLECLARK ATTORNEY Patented April 18, 1972 3,657,689

4 Sheets-Sheet z 4 M 88 2 uvvavrons HARRY amuse-y CARL s. cum/r 9.2

ATTORNEY VARIABLE LOW NOISE ELECTRICAL RESISTOR WITH PLURAL VARIABLE RESISTORS CONNECTED IN SERIES The present invention relates to a variable electrical resistor, and, more particularly, to a miniature rheostat which will accurately provide any desired resistance value over a wide range of resistance values.

Rheostat type variable resistors in general comprise a path of resistance material having a terminal at one end and a movable contact engaging the resistance material path and having a terminal connected thereto. The contact is movable along the resistance material path to vary the resistance value between the terminals. The resistance path can be either a wire of a metal or metal alloy wound on a substrate, or a film of aresistance material coated on the surface of a substrate. The resistance wires generally have asmall resistance value per unit length of the wire so that the movement of the contact along the wire will provide small increments of change of the resistance of the rheostat. Although this permits the achievement of very accurate resistance values, the wire type resistance path has the disadvantage that it requires a very long path to achieve high resistance values. Thus, rheostats using wire resistance paths must be relatively large to achieve high resistance values.

Film type resistance paths can have a large resistance value per unit length so that high resistance values can be achieved with a relatively short length path. Thus, rheostats having film type resistance path can achieve high resistance values yet can be made small in size. However, they have the disadvantage that they do not permit the achieving of a desired resistance value with the accuracy that can be achieved with a wire resistance path because of the'large resistance value per unit length and also provide high contact resistance and contact noise. Therefore, it would be desirable to have a rheostat which combines the advantages of both the wire and the film types of rheostats, i.e. small size, achievement of high resistance values and low contact resistance and low noise, and small incremental changes for achieving accurate resistance values.

' It is therefore an object of the present invention to provide a novel rheostat with low contact resistance and low noise.

It is another object of the present invention to provide a novel rheostat which will provide accurate resistance values over a wide range of resistance values.

It is still another object of the present invention to provide a rheostat which will provide accurate resistance values over a wide range of resistance values and which is small in size.

It is a further object of the present invention to provide a miniaturized rheostat which will provide accurate resistance values over a wide range of resistance values and which uses film type resistance paths.

It is still a further object of the present invention to provide a miniaturized rheostat having two separate film type resistance paths, one of the paths providing relatively large incremental variations in resistancevalue over a wide range of resistance values, and the other path providingsmall incremental changes in resistance values over a small range of resistance values.

These objects are achieved by a rheostat which includes a hollow housing having a pair of rotors rotatably mounted therein and being rotatable from outside the housing. A resistance path is on each of the rotors with one of the resistance paths providing relatively large incremental changes in resistance value over a wide range of resistance values using highly conductive contact pads, and the other resistance path providing small incremental changes over a small range of low resistance values engaged by a slidable contact. A pair of contacts are mounted in the housing with each contact having a terminal projecting fromthe housing and each contact being electrically connected to a separate one of the resistance paths. The resistance paths are electrically connected together so that rotation of one of the rotors provides large incremental changes in the resistance value between the terminals and in the resistance value so as to achieve a rough and fine adjustment of the resistance value of the rheostat.

The foregoing and other objects of the invention will become more apparent as the following detailed description of the invention is read in conjunction with the drawings, in which:

FIG. 1 is a perspective view of one embodiment of the rheostat of the present invention.

FIG. 2 is a top view of the rheostat with the top section of the housing removed.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3.

FIG. 5 is a sectional view taken along line 5-5 of FIG. 3.

FIG. 6 is a perspective view of the rotors and contacts of the rheostat.

FIG. 7 is a plan view of one surface of one of the rotors.

FIG. 8 is a perspective view of another embodiment of the rheostat of the present invention.

FIG. 9 is a back plan view of the rheostat of FIG. 8 with the back of the housing removed.

FIG. 10 is a front plan view of the rheostat of FIG. 8 with the front section of the housing removed.

FIG. 11 is a sectional view taken along line 11-11 of FIG. 10.

FIG. 12 is a sectional view taken along line 12-12 of FIG. 10.

FIG. 13 is a perspective view of the resistance paths and contacts of the rheostat of FIG. 8.

Like reference numerals designate likeparts throughout the several views.

Referring initially to FIGS. 1-7, one embodiment of the rheostat of the present invention is generally designated as 10. Rheostat 10 comprises a hollow, rectangular housing 12 of an electrical insulating material, such as a plastic, having mating lower and

upper sections

14 and 16 respectively. The lower housing section 14 has a pair of spaced, parallel

semicylindrical recesses

18 and 20 extending completely across the upper surface of its front wall from the inner surface to the outer surface of the front wall. The

recesses

18 and 20 have enlarged diameter portions 18a and 20a respectively adjacent the inner surface of the front wall. A notch 22 is provided in the upper surface of the front wall of the lower housing section 1 4 between the recess 18 and the adjacent side wall of the lower housing section (see FIG. 5). The notch 22 extends part way across the front wall from the inner surface thereof. A hole 24 extends through the front wall of the lower housing section 14 from the notch 22 to the bottom surface of the lower housing section. A pair of spaced, parallel

semicylindrical recesses

26 and 28 are provided in the upper surface of the back wall of the lower housing section 14 and are in alignment with the

recesses

18 and 20 respectively. The

recesses

26 and 28 extend part way across the back wall from the inner surface thereof. A notch 30 is provided in the upper surface of the back wall of the lower housing section 14 between the recess 28 and the adjacent side wall of the lower housing section (see FIG. 4). The notch 30 extends part way across the back wall from the inner surface thereof. A hole 32 extends through the back wall of the lower housing section 14 from the notch 30 to the bottom surface of the lower housing section. A stop lug 34 projects upwardly from the bottom of the enlarged diameter portion 18a of the recess 18 (see FIG. 3). A stop lug 35 projects upwardly from the bottom of the lower housing section 14 adjacent the back wall of the lower housing section 14 and in longitudinal alignment with the

recesses

20 and 28.

The upper housing section 16 has a pair of spaced, parallel,

semicylindrical recesses

36 and 38 in the bottom surface of its front wall, and a pair of spaced, parallel, semicylindrical recesses 40 and 42 in the bottom surface of its back wall (see FIGS. 4 and 5). The

recesses

36 and 38 are of the same size as and are positioned to mate with the

recesses

18 and 20 respectively in the lower housing section 14. The

recesses

36 and 38 have enlarged diameter portions 360 and 380 which mate with rotation of the other rotor provides small incremental changes the enlarged diameter portions 18a and 20a of the

recesses

18 and 20. The recesses 40 and 42 in the back wall of the upper housing section 16 are of the same size as and are positioned to mate with the

recesses

26 and 28 respectively in the back wall of the lower housing section 14.

A pair of rotor shafts 44 and 46 are rotatably mounted in ,the housing 12 in spaced parallel relation. The back end of the shaft 44 is seated and rotatably supported in the mating recesses 26 and 40 in the back walls of the housing sections, and the front end of the shaft 44 extends through and is rotatably supported in the mating recesses 18 and 36 in the front walls of the housing sections. The back end of the shaft 46 is seated and rotatably supported in the mating recesses 28 and 42 in the back walls of the housing sections, and the front end of the shaft 46 extends through and is rotatably supported in the mating recesses and 38 in the front walls of the housing sections. Enlarged heads 48 and 50 are provided on the front ends of the shafts 44 and 46 respectively, and are outside of the housing 12 so as to permit rotation of the shafts. The heads 48 and 50 have

slots

52 and 54 respectively extending across their front surfaces. The

slots

52 and 54 are adapted to receive a screw driver or the like tool for rotating the shafts.

Annular flanges

56 and 58 extend radially outwardly from the shafts 44 and 46 respectively adjacent their front ends. The flange 56 fits in the mating enlarged diameter portions 180 and 36a of the

recesses

18 and 36 to prevent longitudinal movement of the shaft 44. The flange 58 fits in the mating enlarged diameter portions 20a and 38a of the

recesses

20 and 38 to prevent longitudinal movement of the shaft 46. The

Rotor 66 has a stop lug 84 projecting radially from its peripheral edge. The stop lug 84 is adapted to engage the stop lug 35 of the housing 12 to limit the degree of rotation of the rotor 66 (see FIG. 3). A second resistance path 86 is provided on the back surface of the rotor 66 (see FIG. 7). The resistance path 86 has spaced ends with one of the ends being positioned adjacent a side of the stop lug 84. The resistance path 86 is a resistance material coated on the back surface of the rotor 66. A termination film 88 of an electrically conductive material is coated on the rotor 66. The termination film 88 extends from the end of the resistance path which is adjacent the side of the stop lug 84 over the peripheral edge of the rotor 66 onto the front surface of the rotor.

An insulated wire 90 electrically connects the resistance path 80 and the resistance path 86 in series. One end of the wire 90 is soldered to the termination film 82 at the back surface of the rotor 64, and the other end of the wire is soldered to the termination film 88 at the front surface of the rotor 66. The wire 90 extends one turn around each of the shafts 44 and 46. Thus, one end of the resistance path 80 is electrically connected to an end of the resistance path 86. A detent spring member 92 is mounted on the bottom of the lower housing section 14 and extends longitudinally along and under the shaft 44. The detent spring member 92 is bent upwardly to the edge of the rotor 64 to providea lug 94 which extends into the notches 75 in the rotor 64.

A pair of

contact members

96 and 98 are mounted in the housing 12. The

contact members

96 and 98 are metal strips shafts 44 and 46 have square portions 60 and 62 respectively having

top sections

96a and 98a respectively, arcuate arms which are within the housing 12. The square portion 60 of the shaft 44 is adjacent the front wall of the housing, and the square portion 62 of the shaft 46 is adjacent the back wall of the housing. A stop lug 63 projects from the shaft 44 within the enlarged diameter portions 180 and 36a of the

recesses

18 and 36, and is adapted to engage the stop lug 34 to limit the degree of rotation of the shaft 44. A separate seal ring, not shown, may be provided around each shaft 44 and 46 between the shafts and the front walls of the

housing sections

14 and 16.

- Rotors 64 and 66 are mounted on the shaft 44 and 46 respectively within the housing 12. The rotors 64 and 66 are each a flat, circular disk of an electrical insulating material, preferably a material which will withstand high temperatures, such as a ceramic. The rotors 64 and 66 have

square holes

68 and 70 respectively through the centers thereof which receive the square portions 60 and 62 of the shafts 44 and 46 so that the rotors will rotate with the shafts. Snap rings 72 and 74 extend around the shafts 44 and 46 respectively adjacent the rotors 64 and 66 to hold the rotors on the shafts.

Rotor 64 has a plurality of notches 75 in its peripheral edge which are uniformly spaced around the edge of the rotor (see FIGS. 3 and 6). A plurality of spaced contact pads 76 of an electrically conductive material are coated on the front surface of the rotor 64 adjacent the peripheral edge of the rotor. The contact pads 76 are arranged along a circular path with each contact pad being in radial alignment with a separate one of the notches 75 in the rotor. The number of the contact pads is equal to the number of the notches 75. A separate connecting strip 78 of an electrically conductive material extends radially inwardly along the front surface of the rotor 64 from each of the contact pads 76. An annular resistance path 80 is on the front surface of the rotor 64 and extends over the inner ends of the connecting strips 78. The resistance path 80 has spaced ends which are at a pair of adjacent connecting strips 780 and 78b (see FIG. 6). The resistance path 80 is a film of a resistance material, such as a metal, mixture of metals, metal alloy, or particles of an electrically conductive material embedded in a matrix of glass or plastic, coated on the surface of the rotor. A termination film 82 of an electrically conductive material is coated on the rotor 64 and extends fromthe contact pad 760 at the end of the connecting strip 78a across the notch adjacent the contact pad 76a and onto the back surface of the rotor 64.

96b and 98b extending from one end of the top sections, a plurality of

parallel fingers

96c and 980 on the ends of the arms 96b and 98b, and

terminals

96d and 98d extending from the other ends of the top sections. The contact member 96 is mounted on the front wall of the lower housing section 14 with the top section 96a being seated in the notch 22 and the terminal 96d extending through the hole '24 and projecting beyond the bottom of the housing 12. The arm 96b of the contact member 96 extends downwardly along the front surface of the rotor 64 with the fingers 96c slidably engaging the front surface of the rotor at a point directly over the detent spring member 92. The fingers 96c engage the surface of the rotor 64 at the circular path of the contact pads 76 so that the fingers engage the contact pads 76 as the rotor 64 rotates. The contact member 98 is mounted on the backwall of the lower housing section 14 with the top section 98a being seated in the notch 30 and the terminal 98d extending through the hole 32 and projecting beyond the bottom of the housing 12. The arm 98b of the contact number 98 extends downwardly along the back surface of the rotor 66 and the fingers 98c slidably engage the resistance path 86.

The terminal 96d is electrically connected to the resistance path by the contact pads 76 and their connecting strips 78. As the shaft 44 is rotated, the contact fingers 96c engage different ones of the contact pads 76 so as to change the position along the resistance path to which the terminal 96d is connected. As the shaft'44 is rotated, the detent spring lug 94 snaps out of and into the notches 75 in the rotor 64 so as to indicate when the contact fingers 960 are engaging a contact pad 76. The terminal 98d is electrically connected to the resistance path 86 by the contact fingers 98c. As the shaft 46 is rotated, the terminal 98d is connected to different points along the resistance path 86.

The terminal 96d is electrically connected to the terminal 98d through the contact 96, resistance path 80, connecting wire 90, resistance path 86 and contact 98. The resistance value measured between the

terminals

96d and 98d is the resistance value of the portion of the resistance path 80 between the contact pad 76 engaged by the contact fingers 96c and the contact pad 76a plus the resistance value of the portion of the resistance path 86 between the contact fingers 98c and the termination film 88. By rotating one or both of the shaft 44 and 46, the resistance value measured between the

terminals

96d and 98d is varied. The resistance path 80 is of a resistance material having a relatively high resistivity so that the resistance of each incremental length of the resistance path 80 between adjacent connecting strips 78 is relatively high. The resistance path 86 is of a resistance material having a lower resistivity and is selected such that the total resistance of the resistance path 86 is equal to the resistance value of each incremental length of the resistance path 80. For example, if each incremental length of the resistance path 80 is of a resistance value of 100 ohms, and the resistance path 80 has nine increments, the total resistance value of the resistance path 80 would be 900 ohms. The resistance path 86 would then be made to have a total resistance value of 100 ohms.

If the shaft 44 is rotated to place the contact fingers 960 on the contact pad 76a, and the shaft 46 is rotated to place the contact fingers 98c at the termination film 88, the resistance value between the

terminals

96d and 98d would be zero. By rotating the shaft 46 so as to move the contact fingers 98c along the resistance path 86, the resistance value measured between the tenninals 96d and 98d would vary in small increments from zero to 100 ohms. If the shaft 44 is rotated to place the contact fingers 960 on the contact pad 76 next adjacent the contact pad 76a, rotation of the shaft 46 would vary the resistance value between the

terminals

96d and 98d in small increments between 100 ohms and 200 ohms. As the shaft 44 is rotated to move the contact fingers 96c consecutively from one contact pad 76 to the next, the resistance value of the rheostat increases by 100 ohms. Rotation of the shaft 46 moves the contact fingers 98c along the resistance path 86 so as to vary the resistance value of the rheostat 10 in small increments between the incremental change provided by the resistance path 80. Thus, rotation of the shaft 44 provides a coarse setting of the resistance value of the rheostat 10, and rotation of the shaft 46 provides a fine setting of the resistance value. The resistance path 80 provides incremental changes of resistance value over a wide range of resistance values, and the resistance path 86 provides small incremental changes over a narrow range of values, the range of each incremental change of the resistance path 80. This provides a rheostat 10 which provides small incremental changes in resistance value over a wide range of values so as to permit the accurate adjustment of the rheostat 10 to any desired resistance value over the wide range of values. In addition, since the rheostat 10 uses film type resistance paths, the rheostat can be made small in size and still provide the wide range of resistance values.

Referring to FIGS. 8-13 inclusive, another embodiment of the rheostat of the present invention is generally designated as 100. The rheostat 100 comprises a hollow rectangular housing 102 of an electrical insulating material, such as a plastic, having mating front and

back sections

104 and 106. The front sec tion 104 has a circular hole 108 through its front wall at one side of the center of the front wall, and a circular bearing hub 110 (see FIG. 11) projecting from the inner surface of the front wall at the other side of the center of the front wall. The back section 106 has a hub 112 (See FIG. 12) projecting from the inner surface of its back wall in alignment with the hole 108 in the front section 104. The hub 112 has a groove 114 extending diagonally thereacross (see FIG. 10).

A rotor 116, which is a flat, circular disk of an electrical insulating material, is within the housing 102 between the hole 108 in the front section 104 and the hub 112 on the back section 106. A rotor shaft 118 is either secured to or integral with the center of the front surface of the rotor 116. The shaft 118 extends through and is rotatably supported in the hole 108 in the front housing section 104. A slot 120 extends across the front end of the shaft and is adapted to receive a screw driver or like tool to rotate the shaft. A sealing ring may be provided around the rotor shaft 118 between the shaft and the front wall of the housing so as to seal the hole 108. The hub 112engages the back surface of the rotor 116 to hold the rotor in position with the shaft extending through the hole 108. A drive lug 122 extends radially outwardly from the shaft 118 (see FIG. 10) within the housing 102 and adjacent the front surface of the rotor 116. An annular resistance path 124 having spaced ends is coated on the back surface of the rotor l 16 (see FIGS. 9 and 13) and extends around the peripheral edge of the back surface. The resistance path 124 may be of any type of resistance material. A circular contact path 126 is on the center of the back surface'of the rotor 116 within the resistance path 124 and is electrically connected to one end of the resistance path by a termination strip 128. The contact path 126 and termination strip 128 are films of an electrically conductive material coated on the surface of the rotor 116.

A second rotor 130, which is a flat, circular disk of an electricalinsulating material, is within the housing 102 adjacent the bearing hub 110. A hub shaft 132 is secured to or integral with the front surface of the rotor 130. The hub shafi 132 has a circular hole 134 (see FIG. 10) in its front end which receives the bearing hub so that the hub shaft 132 and the rotor are rotatably supported on the bearing hub 110. The rotor 130 has a plurality of circumferentially spaced notches 136 in its peripheral edge. The rotor 130 also has a circumferentially elongated groove 138 in its peripheral edge in the space between two of the notches 136. The rotor 130 overlaps a portion of the front surface of the rotor 116 to the extend that the drive lug 122 on the shaft 118 extends into one of the notches 136 in the rotor 130 (see FIG. 10). The outer surface of the hub shaft 132 is serrated by a plurality of V-shaped grooves 140. The bottom of each of the grooves 140 is in radial alignment with a separate one of the grooves 136 in the rotor 130 (see FIG. 10). A V-shaped spring member 141 is compressed between the hub shaft 132 and the side wall of the front housing section 104 with the apex of the spring member fitting in a groove 140 in the hub shaft (see FIG. 10).

An annular resistance path 142 having spaced ends is on the back surface of the rotor 130 and extends around the rotor adjacent the periphery thereof (see FIG. 9). The resistance path 142 is of any desired resistance material coated on the back surface of the rotor 130. The ends of the resistance path 142 are positioned in alignment with the notches 136a and 1361; which are at opposite ends of the groove 138. A- circular contact path 144 is on the center of the back surface of the rotor 130 and is electrically connected to one end 1420 of the resistance path 142 by a tennination strip 146 which extends over the end 1420 of the resistance path (see FIGS. 9 and 13). The contact path 144 and the termination strip 146 are films of an electrically conductive material. A plurality of circumferentially spaced contact pads 148 are provided on the back surface of the rotor 130 in the space between the resistance path 142 and the contact path 144. Each of the contact pads 148 is electrically connected to the resistance path 142 by a connecting strip 150 which extends radially from the contact pad over the resistance path. Each connecting strip 150 is tapered in width with its narrowest end being at it respective contact pad 148. The narrow end of the connecting strip is narrower than the width of the contact pad. Each contact pad 148 and its respective connecting strip 150 is in radial alignment with a separate one of the notches 136 in the edge of the rotor 130 so that the contact pads 148 are electrically connected to circumferentially spaced points along the resistance path 142. Thus one of the contact pads 148 is electrically connected to the end 142b of the resistance path 142. The contact pads 148 and the connecting strips 150 are films of an electrically conductive metal coated on the surface of the rotor 130.

A pair of

metal strip contacts

152 and 154 are within the housing 102 between the

rotors

116 and 130 and the back housing section 106. Each of the

contacts

152 and 154 is bent over at its upper end to provide a contact arm 152a and 154a respectively extending toward the

rotors

116 and 130. Each of the contact arms 152a and 1540 has a pair of contact fingers l52b and 154b respectively on its end. Terminals 152C and 154C extend downwardly from the bottom ends of the

contacts

152 and 154 respectively. The contact 152 is seated in the groove 114 in the hub 112 on the back housing section 106 with the contact fingers 152b slidably engaging the contact path 126 on the rotor 116. The terminal 152c extends through a notch 156 in the bottom of the back housing section 106 and projects beyond the bottom of the housing 102. The contact 154 is seated behind the rotor 130 with the contact fingers 15412 slidably engaging the contact path 144. The terminal l54c extends through a notch 158 in the bottom of the back section 106 and projects beyond the bottom of the housing A flat, metal connecting strip 160 extends along and is seated in a groove 162 in the bottom of the front housing section 104 (see FIGS. 9, 11 and 12). A pair of connecting

arms

164 and 166 are integral with and extend upwardly from the connecting strip 160. Each of the connecting

arms

164 and 166 has a plurality of fingers 164a and 166a respectively on its upper end. The fingers 164a slidably engage the resistance path 124 on the rotor 116, and the fingers 166a slidably engage the contact pads 148 and connecting strips 150 on the rotor 130. Thus, the connecting strip 160 and its

arms

164 and 166 electrically connect the

resistance paths

124 and 142 so as to electrically connect the terminal 152s to the terminal 1540 through the resistance paths.

The resistance path 142 on the rotor 130 is of a resistance material having a relatively high resistivity so that the resistance of each incremental length of the resistance path 142 between adjacent connecting strips 150 is relatively high. By rotating the rotor 130, the connecting arm fingers 166a slide over the rotor from one set of contact pad 148 and connecting strip 150 to the next set so that the resistance value between the terminal 154C and the connecting arm 166 varies in relatively large incremental steps. The resistance path 124 on the rotor 116 is of a resistance material having a low resistivity such that the resistance value of the entire length of the resistance path 124 is equal to the resistance value of each incremental step of the resistance path 142 on the rotor 130. Since the connecting arm fingers 164a directly contact the resistance path 124, as the rotor 116 is rotated, the resistance value between the terminal 152a and the connecting arm 164 varies in very small increments. Thus, rotation of the rotor 130 provides large incremental changes in resistance value over a large range of resistance values, and rotation of the rotor 116 provides small incremental changes over a resistance range equal to each incremental change of the resistance path 142 on the rotor 130. Since the resistance value between the terminals 152s and 1546 is equal to the resistance value between the terminal 152a and the connecting arm 164 plus the resistance value between the terminal'154c and the connecting arm 166, rotation of the two

rotors

116 and 130 can provide any desired resistance value over a wide range of resistance values.

The rotor 116 is rotated by rotating the shaft 118. When the rotor 116 is rotated so that the connecting arm fingers 164a are at either end of the resistance path 124, the drive lug 122 on the shaft 118 extends into a notch 136 in the edge of the rotor 130 (see FIG. 10. Further rotation of the shaft 118 in the same direction causes the drive lug 122 to rotate the rotor 130 until the drive lug moves out of the notch 136. This rotates the rotor 130 a circumferential distance equal to the distance between the notches 130. Since the contact pads 148 are in radial alignment with the notches 130, each such rotation of the rotor 130 moves the connecting arm fingers 166a from one contact pad 148 and its related connecting strip 150 to the next. Thus, each time that the rotor 116 is rotated so that the connecting arm fingers 164a pass across the space between the ends of the resistance path 124, the rotor 130 is rotated a distance to move the contact arm fingers 166a from one contact pad 148 to the next so as to change the resistance value between the terminals 152s and 1540 by one incremental change of the resistance path 142. If the rotor 116 is rotated to move the connecting arm fingers 164a from its high resistance end to its low end, the rotor 130 is rotated to decrease the resistance value provided by the resistance path 142 and vice versa. Thus, the single shaft 118 rotates both

rotors

116 and 130 so that the rotor 130 is rotated in incremental steps to provide incremental changes in resistance value over a wide range of resistance values and the rotor 116 is rotated to provide small incremental changes in resistance value over the range of each incremental change provided by the resistance path 142 on the rotor 130.

When the rotor is not being rotated by the drive lug 122, it is prevented from accidental rotation by the spring 141 fitting in one of the notches in the hub shaft 132. When the rotor 130 is rotated by the drive lug 122, thespn'ng 141 snaps from one notch 140 to the next. When the rotor 130 is rotated to a position where the connecting arm fingers 166a contact the connecting strip at either end of the resistance path, the next complete rotation of the shaft 118 brings the drive lug 122 into the groove 138 in the rotor 130. Since the groove 138 is much wider than the width of the drive lug 122, further rotation of the shaft 118 will not cause any rotation of the rotor 130. Thus, the groove 138 acts as a clutch to prevent the connecting arm fingers 166a from being moved across the spaced between the ends of the resistance path 142. When the rotor 130 is rotated to shift the connecting arm fingers 166a from one contact pad 148 and its related connecting strip 150 to the finger the fingers at one side of the arm moves to the next contact pad or connecting strip before the finger at the other side of the arm leaves the one contact pad or connecting strip because of the tapered shape of the connecting strips. Thus, there is a smooth transition in the change of the resistance value without any breaks in the circuit through the rheostat.

The variable resistors 10 and 100 have their housing sections joined to each other and to the terminals extending.

therethrough by suitable bonding techniques.

The disclosed devices thus provide accurate resistance values over a wide range while being small in size. Also since the series contact resistances are a function of the resistances of the materials contacted, the variable resistors 10 and 100 by utilizing highly conductive pads for engagement by respective contact fingers, in series with respective low resistance paths (-86, 124) for slidable engagement by respective fingers (98, 164), maintain their total series contact resistances at low values. Because of such low contact resistance, the noise generated by the low resistor paths (86, 124) during their adjustment is also low. The resistors thus provide infinite resolution with low noise over a wide range of resistance adjustment.

It will, of course, be understood that the description and drawings, herein contained, are illustrative merely and that various modifications and changes may be made in the structures disclosed without departing from the spirit of the invention.

What is claimed is:

1. A variable resistor comprising a hollow housing;

a pair of rotors rotatably mounted in said housing;

means for rotating each of said rotors from outside of said housing;

a separate resistance path on each of said rotors, each of said resistance paths being a film of a resistance material coated on the rotor, the resistance path on oneof the rotors being of a high resistivity resistance material so as to provide large incremental changes in resistance along its length and the resistance path on the other rotor being of lower resistivity material so as to provide small incremental changes in resistance along its length,

the one rotor having the film of high resistivity resistance material has a plurality of circumferentially spaced contact pads of an electrically conductive material each electrically connected to the resistance path at spaced points along the resistance path so as to divide said resistance paths into incremental lengths of resistance;

a pair of contact within said housing, one of said contact slidably engaging the contact pads of said one rotor as the one rotor is rotated, and the other contact slidably engaging the resistance path on the other rotor and means electrically connecting said resistance paths to each other;

whereby said contact which slidably engaging the contact pads provides slow contact resistance and low noise when incremental resistance variations are made along the high resistivity film.

2. A variable resistor in accordance with claim 1 in which each of the rotors is a flat circular disk of an electrical insulating material and the resistance paths are annular with spaced ends and extend circumferentially around a flat surface of their respective rotors.

3. A variable resistor in accordance with claim 2 in which the one rotor has the plurality of circumferentially spaced contact pads of an electrically conductive material on the same surface as the resistance path and a separate connecting strip of an electrically conductive material extends from each of said contact pads to the resistance path, said connecting strips contacting said resistance path at uniformly spaced points along the resistance path so as to divide said resistance path into incremental lengths of uniform resistance.

4. A variable resistor in accordance with claim 3 in which the resistance value of the total length of the resistance path on the other rotor is substantially equal to the resistance value of each incremental length of the resistance path on the one rotor.

5. A variable resistor in accordance with claim 4 in which each of the contacts is a metal strip having an arm extending from one end, fingers on the end of the arm, and the terminal extending from the other end, the fingers of each of the contacts slidably engages a separate one of the rotors.

6. A variable resistor in accordance with claim 5 in which each of the rotors has on the same surface as the resistance path a contact path of an electrical conductive material and a termination strip of an electrically conductive material extending between the contact path and one end of the resistance path, and the fingers of each of the contacts engages a separate one of the contact paths.

7. A variable resistor in accordance with claim 8 in which the means electrically connecting the resistance paths comprises a connecting strip of an electrically conductive metal mounted in the housing and having a pair of arms extending therefrom with fingers on the ends of the arms, the fingers on one of the arms slidably engage the one rotor so as to contact the contact pads and connecting strips as the rotor is rotated, and the fingers on the other arm slidably engage the resistance path on the other rotor.

8. A variable resistor in accordance with claim 7 in which the means for rotating the rotors comprises a shaft secured to the other rotor and extending through a wall of the housing so as to be accessible from outside the housing, and drive means between the shaft and the one rotor so that the one rotor is rotated a circumferential distance equal to the circumferential length of each increment of the resistance path on the one rotor each time the shaft is rotated through a revolution.

9. A variable resistor comprising a hollow housing; a pair of rotors rotatably mounted in said housing; means for rotating each of said rotors from outside of said housing; a separate resistance path on each of said rotors, each of said resistance paths being a film of a resistance material coated on the rotor, the resistance path on one of the rotors being of a high resistivity resistance material so as to provide large incremental changes inresistance along its length and the resistance path on the other rotor being of lower resistivity material so as to provide small incremental changes in resistance along its length; a pair of contacts within said housing, each of said contacts having a terminal extending through and projecting beyond a wall of said housing; means electrically connecting each of said contacts to aseparate one of said resistance paths; and means electrically connecting said resistance paths to each other; each of the rotors being a flat circular disk of an electrical insulating material and the resistance paths being annular with spaced ends and extending circumferentially around a fiat surface of their respective rotors; the one rotor having a plurality of circumferentially spaced contact pads of an electrically conductive material on the same surface as the resistance path and a separate connecting strip of an electri cally conductive material extending from each of said contact pads to the resistance path, said connecting strips contacting said resistance path at uniformly spaced points along the resistance path so as to divide said resistance path into incremental lengths of unifomi resistance; the resistance value of the total length of the resistance path on the other rotor being substantially equal to the resistance value of each incremental length of the resistance path on the one rotor; each of the contacts being a metal strip having an arm extending from one end, fingers on the end of the arm, and the terminal extending from the other end, the fingers of each of the contacts slidably engaging a separate one of the rotors; the fingers of one of the contacts engaging the surface of the one rotor so as to contact the contact pads as the one rotor is rotated, and the fingers of the other contact slidably engaging the resistance path on the other rotor.

10. A variable resistor in accordance with claim 9 in which the means electrically connecting the resistance paths comprises a wire electrically connected at one end to one end of one of the resistance paths and at its other end to one end of the other resistance path.

11. A variable resistor in accordance with claim 10 in which the means for rotating each of the rotors comprises a separate shaft rotatably supported on the housing and projecting through a wall of the housing so as to be accessible from outside the housing.

12. A variable resistor in accordance with claim 11 in which the one rotor has a plurality of circumferentially spaced notches in its outer edge, each of said notches being in radial alignment with a separate one of the contact pads on the one rotor, and a detent spring member is mounted in the housing and extends into one of the notches in theone rotor, said detent spring member being adapted to move out of and into the notches as the one rotor is rotated.

13. A variable resistor in accordance with claim 12 in which the housing is rectangular having front, back, top, bottom and side walls, the shafts extend in spaced parallel relation between and are supported on the front and back walls and project through the front wall of the of the housing, and each of the rotors is mounted on a separate one of the shafts.

14. A variable resistor in accordance with claim 13 in which the resistance path on the one rotor is on the front surface of the one rotor, the one contact is mounted on the front wall of the housing with its terminal extending downwardly through the front wall and projecting beyond the bottom wall of the housing, the resistance path on the other rotor is on the back surface of the rotor and the other contact is mounted on the back wall with its terminal extending downwardly through the back wall and projecting beyond the bottom wall of the housmg.

15. A variable resistor in accordance with claim 11 including stop means for limiting the rotation of each of the rotors to the circumferential length of the resistance path on the rotor.

16. A variable resistor comprising a hollow housing; a pair of rotors rotatably mounted in said housing; means for rotating each of said rotors from outside of said housing; a separate resistance path on each of said rotors, each of said resistance paths being a film of a resistance material coated on the rotor, the resistance path on one of the rotors being of a high resistivity resistance material so as to provide large incremental changes in resistance along its length and the resistance path on the other rotor being of lower resistivity material so as to provide small incremental changes in resistance along its length; a pair of contacts within said housing, each of said contacts having a terminal extending through and projecting beyond a wall of said housing; means electrically connecting each of said contacts to a separate one of said resistance path; and means electrically connecting said resistance path to each other; each of the rotors being a fiat circular disk of an electrical insulating material and the resistance paths being annular with spaced ends and extending circumferentially around a flat surface of their respective rotors; the one rotor having a plurality of circumferentially spaced contact pads of an electrically conductive material on the same surface as the resistance path and a separate connecting strip of an electrically conductive material extending from each of said contact pads to the resistance path, said connecting strips contacting said resistance path at uniformly spaced points along the resistance path so as to divide said resistance path into incremental lengths of uniform resistance; the resistance value of the total length of the resistance path on the other rotor being substantially equal to the resistance value of each incremental length of the resistance path on the one rotor; each of the contacts being a metal strip having an arm extending from one end, fingers on the end of the arm, and the terminal extending from the other end, the fingers of each of the contacts slidably engaging a separate one of the rotors; each of the rotors having one the same surface as the resistance path a contact path of an electrical conductive material and a termination strip of an electrically conductive material extending between the contact path and one end of the resistance path, and the fingers of each of the contacts engaging a separate one of the contact paths; the means electrically connecting the resistance paths comprising a connecting strip of an electrically conductive metal mounted in the housing and having a pair of arms extending therefrom with fingers on the ends of the arms, the fingers on one of the arms slidably engaging the one rotor so as to contact the contact pads and connecting strips as the rotor is rotated, and the fingers on the other arm slidably engaging the resistance path on the other rotor; the means for rotating the rotors comprising a shaft secured to the other rotor and extending through a wall of the housing so as to be accessible from outside the housing, and drive means between the shaft and the one rotor so that the one rotor is rotated a circumferential distance equal to the circumferential length of each increment of the resistance path on the one rotor each time the shaft is rotated through a revolution; the drive means between the shaft and the rotor comprising a plurality of circumferentially spaced notches in the edge of the one rotor, each of said notches being in radial alignment with a separate one of the contact pads on the one rotor, and a drive lug extending radially from the shaft, said drive lug fitting into and driving the one rotor during a portion of each revolution of rotation of the shaft.

17. A variable resistor in accordance with claim 16 in which the one rotor has a circumferentially elongated groove in its edge extending along the space between the ends of the resistance path on the one rotor and between the notches at the ends of the resistance path.

18. A variable resistor in accordance with claim 17 including a hub shaft secured to the one rotor and a bearing hub on the same wall of the housing that the shaft extends through, said bearing hub rotatably supporting the hub shaft so that the rotors rotate about spaced parallel axes.

19. A variable resistor in accordance with claim 18 in which the hub shaft has a plurality of circumferentially spaced notches in its outer surface with the bottom of each notch being in radial alignment with a contact pad on the one rotor, and a spring member fits in a notch in the hub shaft and is adapted to move from one notch to the next as the hub shaft is rotated.

Claims

1. A variable resistor comprising a hollow housing; a pair of rotors rotatably mounted in said housing; means for rotating each of said rotors from outside of said housing; a separate resistance path on each of said rotors, each of said resistance paths being a film of a resistance material coated on the rotor, the resistance path on one of the rotors being of a high resistivity resistance material so as to provide large incremental changes in resistance along its length and the resistance path on the other rotor being of lower resistivity material so as to provide small incremental changes in resistance along its length; the one rotor having the film of high resistivity resistance material has a plurality of circumferentially spaced contact pads of an electrically conductive material each electrically connected to the resistance path at spaced points along the resistance path so as to divide said resistance paths into incremental lengths of resistance; a pair of contact within said housing, one of said contact slidably engaging the contact pads of said one rotor as the one rotor is rotated, and the other contact slidably engaging the resistance path on the other rotor and means electrically connecting said resistance paths to each other; whereby said contact which slidably engaging the contact pads provides low contact resistance and low noise when incremental resistance variations are made along the high resistivity film.

9. A variable resistor comprising a hollow housing; a pair of rotors rotatably mounted in said housing; means for rotating each of said rotors from outside of said housing; a separate resistance path on each of said rotors, each of said resistance paths being a film of a resistance material coated on the rotor, the resistance path on one of the rotors being of a high resistivity resistance material so as to provide large incremental changes in resistance along its length and the resistance path on the other rotor being of lower resistivity material so as to provide small incremental changes in resistance along its length; a pair of contacts within said housing, each of said contacts having a terminal extending through and projecting beyond a wall of said housing; means electrically connecting each of said contacts to a separate one of said resistance paths; and means electrically connecting said resistance paths to each other; each of the rotors being a flat circular disk of an electrical insulating material and the resistance paths being annular with spaced ends and extending circumferentially around a flat surface of their respective rotors; the one rotor having a plurality of circumferentially spaced contact pads of an electrically conductive material on the same surface as the resistance path and a separate connecting strip of an electrically conductive material extending from each of said contact pads to the resistance path, said connecting strips contacting said resistance path at uniformly spaced points along the resistance path so as to divide said resistance path into incremental lengths of uniform resistance; the resistance value of the total length of the resistance path on the other rotor being substantially equal to the resistance value of each incremental length of the resistance path on the one rotor; each of the contacts being a metal strip having an arm extending from one end, fingers on the end of the arm, and the terminal extending from the other end, the fingers of each of the contacts slidably engaging a separate one of the rotors; the fingers of one of the contacts engaging the surface of the one rotor so as to contact the contact pads as the one rotor is rotated, and the fingers of the other contact slidably engaging the resistance path on the other rotor.

12. A variable resistor in accordance with claim 11 in which the one rotor has a plurality of circumferentially spaced notches in its outer edge, each of said notches being in radial alignment with a separate one of the contact pads on the one rotor, and a detent spring member is mounted in the housing and extends into one of the notches in the one rotor, said detent spring member being adapted to move out of and into the notches as the one rotor is rotated.

14. A variable resistor in accordance with claim 13 in which the resistance path on the one rotor is on the front surface of the one rotor, the one contact is mounted on the front wall of the housing with its terminal extending downwardly through the front wall and projecting beyond the bottom wall of the housing, the resistance path on the other rotor is on the back surface of the rotor and the other contact is mounted on the back wall with its terminal extending downwardly through the back wall and projecting beyond the bottom wall of the housing.

16. A variable resistor comprising a hollow housing; a pair of rotors rotatably mounted in said housing; means for rotating each of said rotors from outside of said housing; a separate resistance path on each of said rotors, each of said resistance paths being a film of a resistance material coated on the rotor, the resistance path on one of the rotors being of a high resistivity resistanCe material so as to provide large incremental changes in resistance along its length and the resistance path on the other rotor being of lower resistivity material so as to provide small incremental changes in resistance along its length; a pair of contacts within said housing, each of said contacts having a terminal extending through and projecting beyond a wall of said housing; means electrically connecting each of said contacts to a separate one of said resistance path; and means electrically connecting said resistance path to each other; each of the rotors being a flat circular disk of an electrical insulating material and the resistance paths being annular with spaced ends and extending circumferentially around a flat surface of their respective rotors; the one rotor having a plurality of circumferentially spaced contact pads of an electrically conductive material on the same surface as the resistance path and a separate connecting strip of an electrically conductive material extending from each of said contact pads to the resistance path, said connecting strips contacting said resistance path at uniformly spaced points along the resistance path so as to divide said resistance path into incremental lengths of uniform resistance; the resistance value of the total length of the resistance path on the other rotor being substantially equal to the resistance value of each incremental length of the resistance path on the one rotor; each of the contacts being a metal strip having an arm extending from one end, fingers on the end of the arm, and the terminal extending from the other end, the fingers of each of the contacts slidably engaging a separate one of the rotors; each of the rotors having one the same surface as the resistance path a contact path of an electrical conductive material and a termination strip of an electrically conductive material extending between the contact path and one end of the resistance path, and the fingers of each of the contacts engaging a separate one of the contact paths; the means electrically connecting the resistance paths comprising a connecting strip of an electrically conductive metal mounted in the housing and having a pair of arms extending therefrom with fingers on the ends of the arms, the fingers on one of the arms slidably engaging the one rotor so as to contact the contact pads and connecting strips as the rotor is rotated, and the fingers on the other arm slidably engaging the resistance path on the other rotor; the means for rotating the rotors comprising a shaft secured to the other rotor and extending through a wall of the housing so as to be accessible from outside the housing, and drive means between the shaft and the one rotor so that the one rotor is rotated a circumferential distance equal to the circumferential length of each increment of the resistance path on the one rotor each time the shaft is rotated through a revolution; the drive means between the shaft and the rotor comprising a plurality of circumferentially spaced notches in the edge of the one rotor, each of said notches being in radial alignment with a separate one of the contact pads on the one rotor, and a drive lug extending radially from the shaft, said drive lug fitting into and driving the one rotor during a portion of each revolution of rotation of the shaft.