US3676822A

US3676822A - Modular potentiometer

Info

Publication number: US3676822A
Application number: US132463A
Authority: US
Inventors: James E Slagg; Grant W Nelson; Jerry T Moffitt; Joseph A Balint
Original assignee: Allen Bradley Co LLC
Current assignee: Allen Bradley Co LLC
Priority date: 1971-04-08
Filing date: 1971-04-08
Publication date: 1972-07-11
Anticipated expiration: 1989-07-11
Also published as: BE781817A; CA934021A; IT957264B; GB1386114A; FR2132636A1; FR2132636B1; DE2213814A1; GB1386115A; CH578779A5; DE2265148A1; NL7204752A

Abstract

A potentiometer module, containing circular resistance and collector paths with a sliding control bridging between the paths, is combined with other similar modules in side by side, stacked relation to form one of a possible assortment of multiple potentiometer controls. The modules are fastened together by four stack bolts extending through them and screwed at one end into a face plate formed on the back of a threaded bushing. The face plate and bushing are at one end of the stacked modules, and a shaft inserted through the bushing controls all modules simultaneously. Several alternative arrangements of the modules are shown, and in one, for example, two concentric shafts each control selected modules. Each potentiometer module has a rectangular case containing a rotor with a movable contact. A collector ring is disposed axially to one side of the movable contact and a resistance track deposited on a base is disposed to the other side of the movable contact. The rotor passes completely through the module and has an opening through it to allow passage of shafts connected to other modules.

Description

I United States Patent 1 2 Slagg et a]. [4 1 July 11, 1972 [54] MODULAR POTENTIOMETER 2,706,760 4/1955 Mucher ..338/174 X [72] Inventors: James E. Slagg, South Milwaukee; Grant get W. Nelson, Milwaukee; Jerry T. Mofiitt, 2431749 12/1947 G 132 x Cudahy; Joseph A. Baum, wauwatosa, a rant of 2,758,182 8/1956 Mucher ..338/131 [73] Assignee: Allen-Bradley Company Primary Examiner-Lewis l-l. Myers Assistant Examiner-D. A. Tone [22] Ffled' April 1971 Attorney-Barry E. Sammons and Arthur H. Seidel [21] App1.No.: 132,463

[57] ABSTRACT [52] US. Cl ..338/132, 338/128, 338/ l34, A potentiometer module, containing circular resistance and 174 collector paths with a sliding control bridging between the [5 l Int. Cl ..H0lc 9/02 paths is combined with other similar modules in side by side,

of Search l 34, tacked relation to fo -n1 one of a assortment of multi- 333/129 130, 133 ple potentiometer controls. The modules are fastened together by four stack bolts extending through them and [56] References Cited screwed at one end into a face plate formed on the back of a threaded bushing. The face plate and bushing are at one end UNITED STATES PATENTS of the stacked modules, and a shaft inserted through the bush- 1,466,293 8/1923 Brooks ..338/132 ing controls all modules simultaneously. Several alternative 1,613,606 1 1 927 Flammer ...338/132 arrangements of the modules are shown, and in one, for exam- 2,059,712 1 1/ 1936 Schellenger ...200/153 ple, two concentric shafts each control selected modules. 2,720,572 10/ 1955 Moore ..338/90 Each potentiometer module has a rectangular case containing 2,676,226 4/ l 954 Mucher l 3 l a rotor with a movable contact; A collector ring is disposed ax- 2,125,954 8/ 1938 Richt -m l 32 ially to one side of the movable contact and a resistance track 2,852,644 5 Elliott 338/174 deposited on a base is disposed to the other side of the mova- |,415,534 1922 Donle ble contact. The rotor passes completely through the module Arisman et al and has an opening through it to allow passage of hafts con. 3,01 l Mair nected to other modules 2,863,972 12/1958 Barton 2,257,979 10/ 1 941 Rubinstein ..64/4 24 Claims, 9 Drawing Figures Patented July 11, 1972 5 Sheets-Sheet l INVE NTORS JAMES E. SLAGG GRANT W- NELSON JERRY T. MOF'FITT JOSEPH A. BA LINT ATTRNEY Patented July 11, 1972 5 Sheets-Sheet 2 INVENTORS JAMES E. SLAGG GRANT W. NELSON ATTORNEY Patented July 11, 1972 5 Sheets-Sheet s INVE NTORS JAMES E. SLAGG GRANT W. NELSON JERRY T- MOFFlTT JOSEPH A.BAL|NT ATTORNEY Patented July 11, 1972 3,676,822

5 Sheets-Sheet 4 INVENTORS JAMES E. SLAGG GRANT W. NELSON JERRY T. MOFFITT JOSEPH .BALINT ATTORNEY Patented July 11, 1972 5 Sheets-Sheet 5 INVENTORS JAMES E.SLAGG GRANT W.NELSON JERRY T. MOFFITT JOSEPH A.BALlNT c ATTORNEY MODULAR POTENTIOMETER BACKGROUND OF THE INVENTION The present invention relates to variable resistors, or potentiometers, having a circular resistance track and a shaft which rotates a conductive brush around the resistance track to vary the resistance between the brush and the ends of the track.

Typically, the shaft is inserted through a bushing which is adapted for attachment to a control panel or other mounting surface. A case attached to the back of the bushing contains a circular resistance track disposed around and concentric with the axis of the shaft. A conductive collector is also disposed around the axis of the shaft and in the same plane as the resistance track. A conductive brush connected to the end of the shaft bridges the gap between the resistance track and collector and moves around the track when the shaft is rotated. As in the patent to Dehn et al., US. Pat. No. 2,868,931 titled Variable Resistance Control," the collector may be annular shaped, having a hole through its center through which the shaft may pass.

By extending the shaft through the collector and back surface of the case, other specially adapted cases also containing resistance and collector elements can be coupled to the back of the first potentiometer section. The shaft extends through the first potentiometer section to control the second potentiometer section.

Prior potentiometers are very inflexible. The first potentiometer section is an integral part of the shaft and bushing and subsequent potentiometer sections must be specially adapted to attach to its back. Multiple section potentiometers are generally assembled in the factory and require the customer to order and stock each type of control he needs. The variety of control types needed by a customer can be quite large, including not only a variety of special physical configurations such as vernier controls and concentric shaft arrangements with differing numbers of potentiometer sections and shaft shapes, but also a wide range of electrical values for each potentiometer section.

Another limitation on present controls is their depth, or axial length. With multiple section potentiometers the maintenance of proper alignment between the rotors of each section becomes more difficult as the number of sections is increased. Misalignment causes excess wear on the coupling mechanism between sections and makes fine adjustment of the resistance setting of the control difficult. As more potentiometer sections are combined one on back of the other, the increased leverage and the inadequate means presently used to attach them together add to the likelihood of misalignment. Typically, the potentiometer section to be attached has a series of tabs protruding from its front surface which tabs snap around the case of the potentiometer section to which it is attached. Particularly when more than two sections are combined, the control becomes very susceptible to damage from bumping and consequent misalignment during assembly of the equipment.

Another problem encountered when combining potentiometer sections, is the necessary increase in their diameter required to accommodate the shaft passing completely through potentiometer sections. The diameter of the annular shaped collector in prior devices is increased to allow for the shaft opening through it, and consequently the diameter of the surrounding resistance track must be relatively large to provide sufficient insulation between the concentric resistance track and collector. As a result, combining potentiometer sections into single controls has resulted in either an increase in their size or cost of manufacture.

SUMMARY OF THE INVENTION The present invention comprises a potentiometer module connectable to a bushing and shaft and connectable to other similar potentiometer modules to form a multiple section control. The modules are securely fastened together by a plurality of stack bolts inserted through them and into the bushing. The

potentiometer module includes a case having a rotor carrying a movable contact, a resistance track axially disposed to one side of the movable contact and in electrical contact with the movable contact, and a collector axially disposed to the other side of the movable contact and in electrical contact therewith. The rotor communicates with both the front and back surface of the potentiometer module for coupling to a shaft or other potentiometer module.

A general object of the invention is to provide a universal potentiometer module which can be combined with other modules to form a multiple section control. The module can be connected directly tothe bushing or mounted on the back surface of another module.

Another object of the invention is to provide a potentiometer module which can be securely fastened to other modules. The modules are structurally similar and have stack bolt openings passing completely through them from front to back. When combined to form a control, therefore, the openings are aligned to receive stack bolts which pass completely through the modules and securely fasten them to the bushing. Assembly is easy and rotor alignment is maintained regardless of the number of potentiometer modules used.

Another object of the invention is to provide a potentiometer module which is a universal building block for customerbuilt controls. Modules of difiering resistance value and taper can be stocked by customers along with bushings, shafts, stack bolts, switches and other functional modules. Any number and order of modules can be combined to provide the desired control. The hardware used is essentially identical for each control with the exception of the stack bolt length. Thus maximum flexibility is obtained with a minimum available stock.

Still another object of the invention is to provide a potentiometer module having a rotor which extends completely through the module, but does not necessitate an increase in case size. By removing the collector from the plane of the resistance track to a plane on the opposite side of the movable contact, a relatively large opening can be provided for the rotor without increasing the outside diameter of the resistance track. The movable contact is thus disposed axially between the resistance track and the collector. The contact pressure necessary to maintain electrical connection is obtained by biasing the movable contact against both the resistance track and the collector. The forces thus generated are substantially equal and opposite so that no moments are applied to the rotor.

The foregoing and other objects and advantages of the invention will appear from the following description. In the description reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration and not of limitation a preferred embodiment of the invention. Such embodiment does not represent the full scope of the invention. But rather the invention may be employed in many different embodiments, and reference is made to the claims herein for interpreting the breadth of the inventron.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded isometric view of a dual section control incorporating the potentiometer module of the present invention,

FIG. 2 is a view in elevation of the control in FIG. 1 with the first potentiometer module in cross section taken along the shaft axis and with parts of the second potentiometer module cut away,

FIG. 3 is an exploded isometric view of a potentiometer module,

FIG. 4 is a plan view of the base which forms a part of the potentiometer module,

FIG. 5 is a front plan view of the potentiometer module,

FIG. 6 is a view in elevation of a single section concentric shaft control with switch,

FIG. 7 is an exploded isometric view of a single section concentric shaft vernier control,

FIG. 8 is a view in cross section of a reduction gear module which forms part of the control shown in FIG. 7, and

FIG. 9 is a view in cross section with parts in the round taken along the shaft axis of a dual section concentric shaft control incorporating the potentiometer module of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, a cylindrical bushing l threaded along its outside surface includes a square face plate 2 formed at its back end perpendicular to the central axis of the bushing 1. The bushing 1 also includes a circular mounting surface 3 which extends forward from the front surface of the face plate 2, completely around the bushing 1. The bushing 1 is typically inserted through a hole in a control panel (not shown in the drawings) and the mounting surface 3 is drawn tightly against the back surface of the control panel by tightening a nut around the bushing 1 (not shown) against the front surface of the control panel. Four threaded stack bolt holes 4 are formed through the face plate 2, each located near one of its comers. A circular recess 5 is formed in the back surface of the face plate 2 concentric with a shaft opening 6 which extends completely through the bushing 1, along and concentric with its central axis.

A square locating plate 7 having a large central opening is mounted against the back surface of the face plate 2. The locating plate 7 also has four stack bolt holes 8, one located near each corner and in alignment with the stack bolt holes 4 in the face plate 2. A locating lug 9 is formed midway along one edge of the locating plate 7. The locating lug 9 extends axially forward, past the face plate 2 and midway along the length of the bushing 1. When mounted on a control panel, the locating lug 9 is inserted through a hole or slot in the panel to properly orient the control and prevent it from rotating.

A shaft 10 with a molded plastic female coupler 11 connected to its back end, extends forward through the shaft opening 6. The outer rim of the female coupler 11 has a diameter larger than that of the shaft opening 6, and its forward edge seats in the recess 5 formed in the back of the face plate 2. The female coupler 11 is annular shaped having a central opening into which a base key 13 and two wing keys 14 extend radially. The wing keys 14 are spaced slightly apart and located directly opposite the base key 13 on the inside surface of the coupler 11. A portion of the female coupler 11 clears the rear surface of the face plate 2 and a limit tab 12 is formed on the outer rim of this portion. The limit tab 12 extends radially outward and is free to revolve with the shaft 10.

Fastened to the back side of the locating plate 7 is a first potentiometer module 15. Referring to FIG. 3, the module 15 includes three basic components, a rectangular shaped case 16, a rotor 17 and a base 18. A front plan view of the base 18 is shown in FIG. 4 and a front plan view of the module 15 is shown in FIG. 5. The case 16 is formed from molded plastic or metal and has a square cross section with sides aligned with the sides of the face plate 2 and locating plate 7. Four stack bolt holes 19 pass completely through the case 16 from front to back, and align with the stack bolt holes 8 in the locating plate 7. A shaft opening 20 is formed through the center of the case 16 from front to back, and a deep circular recess is formed in the back surface of the case 16 to form a compartment 21. The diameter of the compartment 21 is less than the width of the case 16 and rectangular slots are cut in the top and bottom sides of the case 16 through to the compartment 21. A shallow circular recess 22 is formed on the front surface of the case 16, concentric with the shaft opening 20. As shown best in FIGS. 2 and 5, an annular-shaped wall 22 is thus formed and separates the front recess 22 from the compartment 21. When assembled, the coupler 11 including the limit tab 12, fits into the front recess 22 against the wall 22'. A stop is formed and extends upward from the bottom of the front recess 22 and forward from the wall 22 to prevent complete rotation of the shaft 10 by engagement with the limit tab 12.

nun

As shown in FIGS. 2 and 3, a metallic collector ring 23 is located in the compartment 21 attached to the back side of the wall 22'. The collector ring is annular shaped, having an outside diameter less than that of the compartment 21 and an inside diameter larger than the shaft opening 20. A collector terminal 24 extends from the collector ring 23 downward through the bottom side of the case 16.

As shown in FIGS. 2 and 3, the rotor 17 includes a hollow sleeve 26 of molded plastic which fits snugly in the case shaft opening 20. Both ends of the sleeve 26 are identical. The front end of the sleeve 26 fits snugly into the female coupler 11. As shown in FIG. 5, it has a narrow notch which forms a base keyway 32 and a wider notch directly opposite which forms a wing keyway 33. The

keyways

32 and 33 receive the keys l3 and 14 of the female coupler 11. A plastic flange 27 is formed midway between the sleeve ends and partway around its circumference. A movable contact assembly 28 is firmly attached to the front face of the flange 27 by sonic welding a pair of plastic rivets 27. The movable contact assembly 28 includes a metallic wiper ring 29 which completely encircles the sleeve 26 and is deformed to bend axially backward. A conductive button 30 is attached to the wiper ring 29 at a point directly opposite its attachment to the flange 27. Also included is a contact ring 31 attached to the front face of the wiper ring 29 at the flange 27. It wraps substantially around the sleeve 26 and has two contact ends which are deformed to bend axially forward. This deformation creates a spring force acting to press the contact ends of the wiper ring 29 against the collector ring 23 when the sleeve 26 is inserted into the shaft opening 20.

As shown in FIGS. 2-4, the module base 18 is formed of molded plastic and has an annular-shaped body 34 which fits within the compartment 21 of the case 16. A recess 35 is formed in the back surface of the body 34 concentric to its central opening. A rectangular cap 36 is formed on the top edge of the body 34, and a rectangular pedestal 37 is formed on its lower edge directly opposite the cap 36. The cap 36 and pedestal 37 tightly engage the case 16 and provide means of anchoring electrical terminals connected to a resistance track 38 deposited in the front surface of the body 34. The track 38 comprises a layer of conducting material in the form of metals and metal oxides dispersed within a glass matrix. The track 38 extends around the front surface and terminates above the pedestal 37. Each of the two ends of the resistance track 38 are electrically and mechanically connected to one of the two terminals 39. The terminals 39 extend through the pedestal 37 out the bottom side of the module 15.

When assembled, the rotor 17 is inserted first into the case compartment 21 followed by the base 18 which is retained by hot staking portions of the plastic case 16 against the back surface of the base 18. A housing containing the collector 23, rotor 17 and resistance track 38 is thus formed. The front end of the sleeve 26 protrudes through the shaft opening 20 and is substantially flush with the front surface of the module 15. The back end of the rotor sleeve 26 protrudes through the opening in the base 18 and is substantially flush with the back surface of the module 15. The length of the rotor sleeve 26 is not crucial to the inventionit is necessary only that the rotor 17 communicate with both the front and back surface of the module 15 in order that it may be coupled to adjacent modules, stacked either in front or back of the module 15. The movable contact 28 is located axially between the resistance track 38 and the collector ring 23. The permanent deformation of the wiper ring 29 spring biases the button 30 against the resistance track 38 insuring good electrical contact. Likewise, the permanent deformation of the contact spring 31 spring biases its contact ends against the collector ring 23. The button 30 of the wiper ring 29 is circumferentially aligned between the contact ends of the contact spring 31. The moments generated by the contact bias forces are equal and opposite and therefore generate no net moment, or transverse torque on the rotor 17.

All of the potentiometer modules referred to subsequently herein are structurally similar to the module described above. To more clearly describe the various controls which can be built with the potentiometer module of the present invention, however, the modules are given different reference numbers. For example, in the dual section control shown in FIGS. 1 and 2, a second potentiometer module 40 is fastened to the back surface of the first module 15. A link 41 having identical female coupling connections at each end is disposed between the

modules

15 and 40 to connect their rotors 17. The link 41 fits snugly in the recess on the back surface of the first module 15 and in the recess 22 formed on the front surface of the second module 40.

A square back plate 42 covers the back surface of the second module 40, and four stack bolt holes 43, each located near one corner, are formed in the back plate 42. Four stack bolts 44 having threaded ends are inserted through the back plate 42, the second module 40, the first module 15, the locating plate 7, and into the face plate 2. The surface of the back plate 42 is recessed adjacent each of its comers to countersink the stack bolt heads. By using stack bolts 44 of appropriate length, the second potentiometer module can be removed to form a single section control, or other modules can beadded. Regardless of the number of potentiometer modules, the stack bolts 44 can be tightened to form a rigid structure virtually impervious to forces tending to misalign the modules. Threaded stack bolts 44 are shown herein and provide for easy disassembly of the control, however, metal or plastic rivets can also be used when cost reduction is a more important factor and as used herein, the term stack bolt is intended to include rivets and other similar fastening devices which are inserted through openings in parts to clamp them together.

The potentiometer module is a building block which can be used to form numerous types of controls. For example, as shown in FIG. 9, a double section, concentric shaft control is formed with a first potentiometer module 45 and a second potentiometer module 46. The bushing 1, face plate 2, and back plate 42 are identical to those in the double section control described above. The shaft, however, is divided into an outer shaft 47 and a concentric inner shaft 48. Attached to the back end of the outer shaft 47 is a female coupler 49, identical to the coupler 11 described above. The outer shaft 47 engages and drives the rotor 17 of the first potentiometer module 45. The inner shaft 48, on the other hand, extends through the outer shaft 47, its coupler 49, and the first potentiometer module 45. A female coupler 50 is formed on the back end of the inner shaft 48 to engage and drive the rotor 17 of the second potentiometer 46. Because the sections of the control are driven separately, a square spacer 51 having four aligned stack bolt holes (not shown in the drawing) is inserted between the first and

second modules

45 and 46 to separate their rotors and provide space for the female coupler 50. Four stack bolts 52 are inserted through the back plate 42, the second module 46, the spacer 51, the first module 45, the locating plate 7 and into the face plate 2. Because of the added spacer 51, the stack bolts 52 are slightly longer than those used with the conventional double section control described above. Of course, additional modules can be added to the con trol and driven by either the outer shaft 47 or inner shaft 48. For example, additional potentiometer modules can be stacked directly behind the first module 45 with links 41 used to couple their rotors 17. Alternatively or additionally, potentiometer modules can be stacked behind and coupled to the rotor 17 of the second module 46.

As shown in FIG. 6, the concentric shaft arrangement is also useful to separately drive a first potentiometer module 53 and a switch 54. The switch section 54 can be either rotary or push-pull, the only constraint on its design being the placement of four stack bolt holes in alignment with the holes in the potentiometer module 53. A spacer 51 is inserted between the module 53 and the switch module 54 although it may also be formed as an integral part of the switch module 54. The outer shaft 47 drives the rotor 17 of the potentiometer module 53 as in the concentric shaft arrangement described above, and the inner shaft 48 is attached to the switch section 54 by a suitable coupling means (not shown in the drawing). Additional modules can be added and driven by either shaft 47 or shaft 48.

As shown in FIGS. 7 and 8, the potentiometer modules can also be used to form a vernier control. A potentiometer module 55 and a reduction gear module 56 are combined with a bushing 1, face plate 2, locating plate 7, and back plate 42 identical to those described above. The reduction gear module 56 has a square cross section and contains four stack bolt holes 62 aligned with the stack bolt holes in the face plate 2 and locating plate 7. The reduction gear module 56 is attached to the back surface of the locating plate 7 and is driven by an outer shaft 57 which extends through the bushing 1, faceplate 2, locating plate 7 'and a central opening in a front cover 59 of the module 56. A first sun gear 58 is attached to the back end of the outer shaft 57 and a circular retainer flange 60 is formed around the outer shaft 57 immediately forward of the sun gear 58 to retain the shaft 57 to the front cover 59.

As shown in FIG. 8, located within the reduction gear module 56 is a gear train connecting the sun gear 58 to a female coupler 61, rotatably attached to the back surface of the module 56. The interior of the module 56 is circular in cross section and has a gear rack 71 around its entire circumference. The first sun gear 58 engages and drives a pair of first planet gears 72 which engage and revolve around the gear rack 71 when the outer shaft 57 is rotated. The first planet gears 72 are each rotatably attached to the front surface of a circular flange 73 on a second sun gear 74. The second sun gear 74 engages and drives a pair of second planet gears 75 which engage and revolve around the gear rack 71. The second planet gears 75 are each rotatably attached to the front surface of a flange 76 which is formed as an integral part of a drive shaft 77. The drive shaft 77 extends out through an opening in the back surface of the reduction gear module 56 and attaches to a circular pedestal 63, upon the back surface of which the female coupler 61 is integrally formed. Thus the gear train links the outer shaft 57 to the female coupler 61 to drive the latter at a substantially reduced rate of rotation.

The sun gears 58 and 74 and the drive shaft 77 each have central openings through them to accommodate an inner, concentric shaft 66 which extends completely through the outer shaft 57, the reduction gear module 56, and the potentiometer module 55.

In the preferred embodiment the female coupler 61 and the circular pedestal 63 extend out the back surface of the reduction gear module 56, and as a consequence, a square spacer 64 having a large central opening to accommodate the pedestal 63 is inserted between the reduction gear module 56 and the potentiometer module 55. The female coupler 61 directly engages and drives the front end of the rotor 17 in the potentiometer module 55. The spacer 64 need not be a separate item, but instead may be formed as an integral part of the gear reduction module 56.

Formed on the back end of the inner shaft 66 is a plastic coupler 67 having two wing keys 68 and a base key 69. The coupler 67 mates with and drives the back end of the rotor 17 in the potentiometer module 55. A back plate 42 covers the back surface of the module 55 and four stack bolts 70 tightly fasten the components of the vernier control to the face plate 2.

By rotating the inner shaft 66, the rotor 17 of the potentiometer module 55 is controlled directly, whereas rotation of the outer shaft 57 controls the rotor 17 at a substantially reduced rate through the gear reduction module 56. Other potentiometer modules can be added and controlled in like fashion by inserting them between the spacer 64 and the potentiometer module 55 and coupling their rotors 17 together with links 41. Also, more concentric shafts can be added and coupled to selected potentiometer modules.

It is apparent that by using identical potentiometer modules with a minimal amount of hardware, a large number of different controls can be built. Because parts are kept to a shaft even when large numbers of modules are combined and subjected to external bending forces. Finally, displacing the collector ring axially to the side of the movable contact opposite the resistance track allows passage of two or more concentric rotatable members through the center opening in a resistance track of minimal outside diameter and substantially reduces the moment forces on the rotors, which forces make fine control settings difficult and cause excessive wear of the couplers between modules.

We claim:

1. A potentiometer module the combination comprising:

a case having a front and back surface;

a rotor connected to said case to rotate about an axis, said rotor having a movable contact;

a collector connected to said case and disposed axially to one side of said movable contact and in electrical contact therewith; and

a resistance track connected to said case and disposed axially to the other side of said movable contact and in electrical contact therewith;

wherein said rotor includes a sleeve having ends which communicate with the front and back surfaces of said case and said collector and resistance track are disposed around said sleeve.

2. A potentiometer module as recited in claim 1, wherein said sleeve has identical coupling means at its ends.

3. The potentiometer module as recited in claim 1, wherein said movable contact comprises:

a wiper which is spring biased against said resistance track by a force acting axially in one direction; and

a contact ring which is spring biased against said collector by a force acting axially in the opposite direction.

4. The potentiometer module as recited in claim I, wherein said resistance track is formed on an annular-shaped base disposed around said rotor sleeve and connected to said case.

5. A control the combination comprising:

a bushing adapted to attach to a control panel;

a shaft extending through said bushing;

a coupler connected to the back end ofsaid shaft;

a first potentiometer module having front and back surfaces, said first module including a rotor which communicates with the front surface of said first module to connect with said coupler and which extends through said first module to communicate with its back surface;

a second potentiometer module having front and back surfaces, said second module including a rotor which communicates with the front surface of said second module to connect with the rotor of said first module and which extends through said second module to communicate with its back surface; and

a plurality of stack bolts each passing completely through said first and second modules to fasten them to the bushing.

6. A control as recited in claim 5, wherein said first and second potentiometer modules are structurally identical, each rotor having a sleeve which communicates with the front and back surfaces of the module and a movable contact, each module also having a collector disposed around said rotor sleeve and axially to one side of said movable contact to make electrical contact therewith and a resistance track disposed around said rotor sleeve and axially to the other side of said movable contact to make electrical contact therewith.

7. A control the combination comprising: a bushing adapted to attach to a control panel and having a shaft opening extending through it from front to back; a face plate disposed around the opening at the back end of the bushing and perpendicular to the central axis of the shaft opening;

a first potentiometer module fastened to the face plate, said first module having a rotor in alignment with the shaft opening axis, which rotor extends completely through the first module and has a central concentric opening completely through it;

an outer shaft rotatably retained within said shaft opening and connected to the rotor of said first module, said shaft having a central concentric opening;

a second potentiometer module structurally identical to the first potentiometer module and connected to the first potentiometer module, said second module having a rotor aligned with the rotor of said first potentiometer module; and

an inner shaft rotatably retained within and passing through the openings in the outer shaft and the rotor of the first module to connect with the rotor of the second module.

8. The control as recited in claim 7 wherein a plurality of stack bolts extend through aligned openings in the first and second potentiometer modules to connect said modules to the face plate, wherein said aligned openings are substantially parallel to the axis of rotation of said rotors.

9. The control as recited in claim 8 wherein the module rotors each include a movable contact connected to a sleeve and each module includes a collector disposed around said sleeve and axially to one side of said movable contact and -a resistance track disposed around said sleeve and axially to the other side of said movable contact.

10. A control the combination comprising:

a bushing adapted to attach to a control panel or the like and having a shaft opening extending through it from front to back;

a face plate disposed around the opening at the back end of the bushing and perpendicular to the central axis of the shaft opening;

a gear reduction module fastened to the face plate, said gear reduction module including a gear train with an output which rotates at a reduced rate of rotation with respect to a rotatable input;

an outer shaft rotatably retained within said shaft opening and connected to rotate said gear train input, said outer shaft having a central concentric opening;

a first potentiometer module fastened to said gear reduction module, said first module having a rotor in alignment with the shaft opening axis and coupled to said gear train output, which rotor extends completely through the first potentiometer module and has a central concentric opening completely through it; and

an inner shaft rotatably retained within and passing through the outer shaft and reduction gear module to connect with the rotor of the first potentiometer module.

11. The control as recited in claim 10, wherein a plurality of stack bolts extend through aligned openings in the gear reduction module and first potentiometer module to connect said modules to the face plate, and wherein said aligned openings are substantially parallel to the axis of rotation of said rotor.

12. The control as recited in claim 10, wherein the potentiometer module rotor includes a movable contact connected to a sleeve and the potentiometer module includes a collector disposed around said sleeve and axially to one side of said movable contact and in electrical contact therewith, and a resistance track disposed around said sleeve and axially to the other side of said movable contact and in electrical contact therewith.

13. The control as recited in claim 10, wherein said gear train includes a first sun gear connected to said outer shaft, a first planet gear set connected to revolve around said first sun gear when the outer shaft is rotated to rotate said gear train output.

14. The control as recited in claim 13, wherein a second sun gear is connected for rotation by said first planet gears, and a second set of planet gears connect to revolve around said second sun gear when it is rotated to rotate said gear train output.

15. The control as recited in claim 14, wherein there is a central opening through said first and second sun gears through which said inner shaft passes.

16. In a variable resistance module the combination comprising:

a housing having front and back walls with a compartment therebetween and also having central openings in the walls communicating with the compartment;

an electrical resistance track on the inside of one of said walls facing into the compartment;

an electrical collector on the inside of the other of said walls and also facing into the compartment, whereby said resistance track and collector are spaced from one another in facing relation;

a rotor within said compartment journaled in said central openings for turning motion; and

contact means in said compartment mounted by said rotor for rotation therewith that has a first sliding contact in engagement with said resistance track and a second sliding contact in engagement with said electrical collector.

17. A variable resistance module as in claim 16 in which said resistance track and electrical collector are circular and located concentric with the axis of rotation of said rotor; and

wherein said sliding contacts are spring biased in opposite axial directions.

18. A variable resistance module as in claim 17 wherein said sliding contacts are circumferentially aligned to minimize transverse torque on the rotor.

19. A variable resistance module as in claim 16 having in combination therewith a bushing at the front of the module;

a rotatable control shaft in said bushing; and

a detachable coupling connection between the rear end of said shaft and said rotor.

20. The structure of claim 19 in combination with a second module like the first module, said second module being attached to the rear of the first module, and there being a detachable coupling connection between the rotors of the modules.

21. The structure of claim 19 in combination with a second module like the first module, said second module being attached to the rear of the first module, the rotors and control shaft are hollow, a second inner shaft extends through said hollow rotors and control shaft, and there being a coupling connection between the rotor of said second module and said second inner shaft.

22. A control formed by connecting together a plurality of physically identical potentiometer modules, each module including:

a case having a front and a back wall spaced to define a compartment between the walls;

a collector connected to said case and located within said compartment;

a resistance track connected to said case and located within said compartment; and

a rotor rotatably attached to said case and communicating through openings in the front and back walls thereof to couple with the rotors of adjacent potentiometer modules.

23. The control as recited in claim 22, wherein an opening is formed through each rotor, and the rotors of adjacent modules are coupled by means of a link which has an opening that aligns with the openings in the coupled rotors.

24. The control as recited in claim 22 in which a face plate is attached to the front wall of one potentiometer module and a shaft journaled in a bushing formed on said face plate couples with the rotor of said one potentiometer module.

Claims

1. A potentiometer module the combination comprising: a case having a front and back surface; a rotor connected to said case to rotate about an axis, said rotor having a movable contact; a collector connected to said case and disposed axially to one side of said movable contact and in electrical contact therewith; and a resistance track connected to said case and disposed axially to the other side of said movable contact and in electrical contact therewith; wherein said rotor includes a sleeve having ends which communicate with the front and back surfaces of said case and said collector and resistance track are disposed around said sleeve.

3. The potentiometer module as recited in claim 1, wherein said movable contact comprises: a wiper which is spring biased against said resistance track by a force acting axially in one direction; and a contact ring which is spring biased against said collector by a force acting axially in the opposite direction.

4. The potentiometer module as recited in claim 1, wherein said resistance track is formed on an annular-shaped base disposed around said rotor sleeve and connected to said case.

5. A control the combination comprising: a bushing adapted to attach to a control panel; a shaft extending through said bushing; a coupler connected to the back end of said shaft; a first potentiometer module having front and back surfaces, said first module including a rotor which communicates with the front surface of said first module to connect with said coupler and which extends through said first module to communicate with its back surface; a second potentiometer module having front and back surfaces, said second module including a rotor which communicates with the front surface of said second module to connect with the rotor of said first module and which extends through said second module to communicate with its back surface; and a plurality of stack bolts each passing completely through said first and second modules to fasten them to the bushing.

7. A control the combination comprising: a bushing adapted to attach to a control panel and having a shaft opening extending through it from front to back; a face plate disposed around the opening at the back end of the bushing and perpendicular to the central axis of the shaft opening; a first potentiometer module fastened to the face plate, said first module having a rotor in alignment with the shaft opening axis, which rotor extends completely through the first module and has a central concentric opening completely through it; an outer shaft rotatably retained within said shaft opening and connected to the rotor of said first module, said shaft having a central concentric opening; a second potentiometer module structurally identical to the first potentiometer module and connected to the first potentiometer module, said second module having a rotor aligned with the rotor of said first potentiometer module; and an inner shaft rotatably retained within and passing through the openings in the outer shaft and the rotor of the first module to connect with the rotor of the second module.

9. The control as recited in claim 8 wherein the module rotors each include a movable contact connected to a sleeve and each module includes a collector disposed around said sleeve and axially to one side of said movable contact and a resistance track disposed around said sleeve and axially to the other side of said movable contact.

10. A control the combination comprising: a bushing adapted to attach to a control panel or the like and having a shaft opening extending through it from front to back; a face plate disposed around the opening at the back end of the bushing and perpendicular to the central axis of the shaft opening; a gear reduction module fastened to the face plate, said gear reduction module including a gear train with an output which rotates at a reduced rate of rotation with respect to a rotatable input; an outer shaft rotatably retained within said shaft opening and connected to rotate said gear train input, said outer shaft having a central concentric opening; a first potentiometer module fastened to said gear reduction module, said first module having a rotor in alignment with the shaft opening axis and coupled to said gear train output, which rotor extends completely through the first potentiometer module and has a central concentric opening completely through it; and an inner shaft rotatably retained within and passing through the outer shaft and reduction gear module to connect with the rotor of the first potentiometer module.

16. In a variable resistance module the combination comprising: a housing having front and back walls with a compartment therebetween and also having central openings in the walls communicating with the compartment; an electrical resistance track on the inside of one of said walls facing into the compartment; an electrical collector on the inside of the other of said walls and also facing into the compartment, whereby said resistance track and collector are spaced from one another in facing relation; a rotor within said compartment journaled in said central openings for turning motion; and contact means in said compartment mounted by said rotor for rotation therewith that has a first sliding contact in engagement with said resistance track and a second sliding contact in engagement with said electrical collector.

17. A vaRiable resistance module as in claim 16 in which said resistance track and electrical collector are circular and located concentric with the axis of rotation of said rotor; and wherein said sliding contacts are spring biased in opposite axial directions.

19. A variable resistance module as in claim 16 having in combination therewith a bushing at the front of the module; a rotatable control shaft in said bushing; and a detachable coupling connection between the rear end of said shaft and said rotor.

22. A control formed by connecting together a plurality of physically identical potentiometer modules, each module including: a case having a front and a back wall spaced to define a compartment between the walls; a collector connected to said case and located within said compartment; a resistance track connected to said case and located within said compartment; and a rotor rotatably attached to said case and communicating through openings in the front and back walls thereof to couple with the rotors of adjacent potentiometer modules.