US2790052A - Precision resistance devices - Google Patents

Description

A rii 23, 1957 R. w. ARMSTRONG PRECISION mzszsmucs DEVICES 2 Sheets-Sheet 1 Filed Aug. 16, 1954 INVENTOR.

ROBERT W. ARMSTRONG f ATTORNEY April 23, 1957 R. w. ARMSTRONG 90,052

PRECISION RESISTANCE DEVICES Filed Aug. 16, 1954 2 Sheets-Sheet 2 INVENTOR ROBERT W. ARMSTRONG ATTORNEY United States Patent PRECISION RESISTANCE DEVICES Robert W. Armstrong, Mound, Minn., assignonto Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application August 16, 1954, Serial No. 450,017

6 Claims. (Cl. 201-62) This invention in general pertains to precision resistance devices and more specifically to precision potentiometers.

Prior art potentiometers comprise generally a supporting member with resistance means and collector means attached thereto together with wiper means adapted to contact both the collector means and the resistance means. These prior art devices may be of the rotary type or of the linear type according to the application and in general, all of the prior art potentiometers have a common shortcoming which is that the contact pressure between the wiper member and the resistance means and the collector means does not stay constant as the resistance device is subjected to a wide range of temperature changes. One of the reasons for the change in contact pressure for temperature variations is the fact that there generally is a difference between the coefiicient of thermal expansion of the support means and the resistance means. Since the ends of the resistance means generally are fixed with respect to the support means, the different rates of thermal expansion cause the resistance means to become distorted to the extent that the contact pressure of the wiper means thereon is changed. This change in contact pressure in turn causes a change in the resistance value reflected into the circuit in which the resistance device is a component with the accompanying error in the over-all system. In very sensitive applications this change of resistance due to a varying wiper pressure is very undesirable inasmuch as it destroys the accuracy of the system and it is the intent of this invention to overcome this problem by providing a means of maintaining constant wiper pressure.

An object of this invention is to provide a rugged, compact precision variable resistance device wherein means are provided to maintain a uniform contact pressure of the wiper means upon the resistance means and/or collector means for wide variations in temperature of the resistance device so that no change in resistance due to varying contact pressure is encountered. Certain novel aspects of this invention lie in the constructional details while other of the advantages of the invention lie in the selection of certain materials as will be pointed out with greater particularity in the detailed discussion of the device below.

Other objects of the invention will be set forth more fully in and become apparent from a reading of the following specification and appended claims, in conjunction with the accompanying drawing in which:

Figure l is a plan view in cross section of a precision potentiometer embodying the teachings of my invention;

Figure 2 is a side elevational view, partly in section, of the potentiometer shown in Figure 1;

Figure 3 is a transverse cross-sectional view of the device shown in Figure 1 taken along section line 33 of Figure 1;

Figure 4 is a transverse cross-sectional view, on an enlarged scale, of one of the main support members used in the potentiometer;

2,190,052 Patented Apr. 23, 1957 ice Figure 5 is a plan view of the device shown in Figure 1 with the housing member removed;

Figure 6 is a side elevational view of the device shown in Figure 5; and

Figure 7 is a transverse cross-sectional view of the subassembly as shown in Figures 5 and 6 as viewed along section lines 7-7 of Figure 5.

A housing member 10 having a hollow cylindrical tube-like configuration is made out of a suitable rigid material such as aluminum. A pair of generally semicylindrical hollow support members 16 and 18 are adapted to be positioned within housing member 10. Support members 16 and 18 are preferably identically shaped and are made out of a plastic insulative material such as nylon. The nylon material suggested for members 16 and 18 is desirable because of an inherent slipperincss quality. Obviously, other materials having the properties mentioned to the extent necessary for the particular application may be used.

Support members 16 and 18 are adapted to be assembled in abutting interlocking relationship. To this end support members 16 and 18 are fitted with cooperating tongue and groove projections and recesses 20 and 22 respectively along their common radial surfaces (see Figure 4). Support members 16 and 18 when thus assembled provide a rigid subassembly and have a common outer surface generally conformable to the inner surface of housing member 10. A plurality of longitudinal recesses 2d are provided in the outer surfaces of support members 16 and 18 so that when the assembled support members are inserted into the housing 10, longitudinal recesses or slots are formed between the inner surface of the housing member 1t) and the support members 16 and 18, the utility of these longitudinal slots to become clear in the description below.

A plurality of recesses are provided on the inner surfaces of support members 16 and 18. Each of support members 16 and 1% has a pair of recesses 26 on the inner surface thereof, one recess 26 adjacent to each of the common abutting radial surfaces with the recesses 26 being so shaped such that overhanging or undercut portions 28 are defined. When support members 16 and 18 are assembled in interlocking relationship, the recesses 26 of the individual support members cooperate to form a. pair of common recesses therebetween. Resistance means are adapted to be positioned in said pair of common recesses defined by recesses 26, the resistance means comprising a pair of separate resistance elements, each comprising a bobbin or support member 30 having resistance wire 32 wound thereupon. As will be observed in Figure 3, the cross-sectional configuration of the bobbin members 30 with resistance wire 32 thereupon is generally conformable to the common recesses defined by the individual recesses 26 of the support members 16 r and 18. The resistance Wire 32 is placed upon bobbin members 30 and insulated therefrom using conventional winding techniques as a preliminary step in the assembly of the devices. The resistance elements are then assembled with support members 16 and 18 by being placed in the recesses 2d of one of the support members and the other support member being then placed in abutting interlocking relationship with the first supporting member. The subassembly may then be inserted into the housing 10. lt will be noted that when support members 16 and 18 are assembled with the resistance means that the overhanging portions 28 thereof serve to hold or clamp the resistance elements with respect to the assembled support members 16 and 18 and preclude relative transverse motion therebetween. However, while transverse motion between support members 16 and 18 and the resistance means is precluded it will be appreciated that the inherent slipperiness quality of the nylon we ges support members will allow a slight amount of relative longitudinal movement between themselves and the resistance elements. Thus, upon wide variations in the ambient temperature to which the resistance device is subjected, slight longitudinal movement between the resistance means and the support means 16 and 13 will occur without any transverse movement. The elimination of the transverse movement allows the pressure of the wiper means to be described below on the resistance wire 32 to remain constant over wide temperature changes and thus eliminates the introduction of any errors into the system of which the resistance device is a component.

E ach of the support members 16 and 18 has on the inner surface thereof a U-shaped recess 40 symmetrically positioned and having straight side portions and a curved bight portion with a further recess 42 centrally rioned in the bight portion. A collector strip M is adapted to be disposed ineach recess 42. A movable wiper carrying rod 46, adapted to be longitudinally displaced by condition responsive means (not shown), is supported for reciprocation by a journal bearing 48 positioned within the right end of housing as viewed in Figure A washer 50 of a suitable resilient material such as neoprene rubber is positioned about shaft 46 adjacent to the outer axial end of bearing member 455. Washer 50 has, as shown, a rounded inner periphery as well as a rounded outer periphery and is proportional so as to lit snugly between shaft 46 and housing as well as to snugly embrace shaft 46. The rounded inner periphery of washer prevents the washer from pumping any oil that might be present on the exposed part of shaft 46 inside to contaminate the resistance device. Washer 50, in addition to providing an oil seal, serves as an expansion absorber between the housing It and the internal parts of the resistance device. 52 disposed in a suitable recess 54 in the housing 10 serves as a retainer for bearing 48 and gasket St). A washer member 56 of an insulative material is disposed between the inner axial end of bearing member 48'and one end of the assembled interlocking support members 16 and 18 as is shown in Figure l. Washer 56 prevents journal bearing 48 from shorting out the resistance means within housing 10. A ball end connector 58 is secured to the outer end of rod member 46 so as to provide a means of connecting rod 46 to condition responsive means (not shown).

A wiper array is secured to the inner end of rod 46 which is relieved as at 64 so as to define a head 65. The array comprises a pair of insulative members 60 and 62 fastened about head 65 of rod member 46 by suitable rivet means 66. Members 60 and 62 are also preferably made out of a plastic material such as nylon. The wiper array also comprises two wiper subassemblies and 72 which are electrically insulated from one another. Each subassembly 70 and 72 includes an L-shaped electrio-ally conductive support bracket 74, the long ends of which are embedded in suitable recesses between insulative members 60 and 62 and the short ends of which extend toward one another but do not touch and are maintained in spaced relationship by an insulative spacer 76 asis shown in Figure 1. Each L-shaped bracket 74 has a first pair of wipers 7 8 electrically connected thereto by suitable'means such as soldering which wipers 78 are adapted to engage collector strips 44 and a second pair of wiper members 80 also electrically connected thereto and: extending normal to wipers 78 and being adapted to engage the resistance means 32 on the bobbin members 30 Thus, in the embodiment of the precision resistance device shown, two independent potentiometers are provided, each potentiometer comprising a resistance winding 32 on a bobbin 30 and a collector strip 44 with electric continuity/being, established between the resistance winding 31nd the collector strip 44 by the cooperating 8 0 and 78, While two independent potentionieters or. variable resistors are'shown', it will be ap- A snap ring washer prcciated that the scope of the invention includes arrangements wherein only one of the common recesses between the individual recesses 26 in support members 16 and i8 is used to position resistive means as well as other arrangements wherein resistive means are disposed in both of the common recesses as shown herein, but are connected in series or parallel relationship instead of being electrically independent. The insulative members 60 and 62 when secured to the inner end of rod 46 have a cross-sectional configuration generally conforming to the space defined by the straight side portions and curved bight portion of recess 46 (see Figure 3). Thus rod 46 is supported not only by hearing member 48 but also to a lesser extent by members 60 and 62 coacting with support members 16 and 18. Further, the insulative n. nbcrs 6i and 62 have recess means cooperating with the head portion 65 on rod member 46 so that relative rotation between rod 46 and the insulative members 60 and 62 is allowed although relative longitudinal motion therebetween is precluded. Thus, any longitudinal displacement of rod 46 by the condition responsive means will. result in a positive displacement of the wiper means 78 and 80 with respect to the collector strips 44 and the resistive means 32, but any relative rota on between the rod 46 and the housing 10 will not imp 1y change to the relationship of the wipers and the .r tor means 32. The in'iportance of this arrangement "ny rotative torques imparted. to shaft 46 tlu'ougii vib on or too sional stresses within the base upon which the housing it; and/or condition responsive means are mounted are not imparted to the wiper arrays so as to vary the contact pressure thereof on the resistance wire 32 and thus impart an error into the system of which he resistance device is a component.

Referring to Figures 5, 6 and 7. it will be noted that recesses 24 in the outer surfaces of support members 16 and 18 are used to provide a means for connecting external connection means to the ends of the resistance wire 32 on bobbins 30 as well as center taps to the resistance wire 32 when and where desired. A plurality of connection leads 86, individually insulated and having a common outer covering 88 are brought into the resistance device through a terminal box 90. As viewed in Figure 1, terminal box 90 is positioned against the left end of the assembled and interlocked support members 16 and 18. A resilient disc 91 is positioned between terminal box. 90 and support members 16 and 18 and serves as additional expansion absorption means similar to washer 50.

A ball end connector 93 for connecting the resistance device to a base, not shown, has its shank portion positioned against the outer face of terminal box 90 and is retained in position by a snap ring 92 disposed in a suitable recess 94. Snap ring 92 thus cooperates with snap ring 52 in holding the internal components of the resistance device in assembled relationship.

Terminal box 90 comprises an outer recessed cuplike member 96 and an inner recessed cup-like member 98, said cup- like members 96 and 98 being disposed with their recessed sides in abutting relationship so as to define a void space therebetween and both of members having a peripheral aperture which combine to define a. common aperture 100 through which extend the leads 86 covered with the common wrapping 88. A notch 101 in housing 10 registers with aperture 1%. Further, the inner cup member 98 has apertures 102 therein registering with, the ends of recesses 24 on the outer surfaces of support members 16 and 18 so that the individual lead wires 86 may be led out through apertures 162 and through suitable apertures, not shown, in resilient disc 91 and be disposed in said recesses. At the point at which it is desired to connect lead wires 86 to the resistance wire 32 on the bobbins 30, a suitable aperture or notch 104 is provided in support members 16 and 18 (see Figure 7). Adjacent to said notches 104 in the support members 16 and 18 are recesses 106 into which are placed and secured thereto by suitable means such as an adhesive the ends of spring contact members 108 which have free ends 110 extending through the apertures or notches 104 and bear against the resistance wire 32 on the bobbin members 30. The individual leads 86 are connected to the spring contact members 188 at 112 by suitable means such as soldering and thus are effectively connected to the resistance wire 32 on the bobbins 30. If desired, only one lead 86 may be placed in each of the recesses 24 or more than one lead may be so placed according to the particular application and size of wire and the recesses 24 (see Figure 7 Where a single lead 86 is disposed in each of three of the recesses 24 while two connection leads 86 are disposed in the remaining recess 24). Where there is only one wire in each recess 24 and where it is desired to have a connection to both ends of the resistance winding, one of the connection leads 86 initially disposed in a recess 24 spaced from the recess 24 adjacent to the resistance means is brought to the correct point by means of a circumferential recess 114 joining the two adjacent longitudinal recesses 24. The leads 86 connected to the collector strips 44 pass through suitable apertures 116 in the inner cup member 98 of the terminal box 90 and are fastened to the collector strips 44 by suitable means such as soldering as at 118.

While I have shown and described a specifice embodiment of this invention, further modifications and improvements will occur to those skilled in the art. I desire it to be understood, therefore, that this invention is not limited to the particular form shown and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.

What I claim is:

1. A resistance device of the class described comprising: a hollow housing member; a plurality of support members of a material characterized by having a slipperiness quality positioned in said housing member resilient means positioned in said housing member at the ends of said support members cooperating with said support members and said housing member, said support members having cooperating abutting surfaces, said resilient means acting to absorb expansion between said housing member and said support members; recess means on said abutting surfaces of said support members which define, when said support members are in abutting relationship, a common recess; resistance support means having a configuration substantially identical to said common recess defined by said support members; resistance means on said resistance support means, said resistance support means with said reistance means thereon being disposed in said common recess and said recess means being undercut such that transverse movement of said resistance support means with said resistance means thereon with respect to said hollow support members is precluded, said inherent slipperiness quality of said support members permitting relative longitudinal movement between said support members and said resistance support means with said resistance means thereon.

2. A variable resistance device of the class described comprising: a hollow housing member; a pair of hollow support members having inner and outer surfaces adapted when abutted against one another to have a common outer periphery generally identical to the inner periphery of said hollow housing member; recesses on said inner surfaces of said support members, selected ones of said inner recesses defining a common recess; resistance means disposed in said common recess; conductive means disposed on said inner surfaces; movable means journalled for longitudinal reciprocation by said pair of hollow support members and comprising conductive means in contact with said resistance means and said first named conductive means; apertures in said support members adjacent said resistance means; spring means secured to said support members and having free portions extending through said apertures and contacting said resistance means; and connection means connected to said spring means.

3. A variable resistance device of the class described comprising: a hollow housing member; a plurality of support members having inner and outer surfaces and adapted when assembled together to have a common outer surface generally conforming to the inner surface of said hollow housing member; recesses on said inner surfaces of said support members, selected ones of said recesses defining a common recess; resistance means disposed in said common recess; conductive means on said support members and condition responsive means slidably mounted between said support members and comprising conductive means in contact with said resistance means and said first named conductive means.

4. A variable resistance device of the class described comprising: a hollow housing member having an inner surface; a plurality of support members having inner and outer surfaces adapted when assembled to have a common inner surface and a common outer surface generally conforming to said inner surface of said hollow housing member; recesses on said outer surfaces of said support members; resistance means disposed between adjacent ones of said support members and adjacent to said common inner surface; conductive means disposed on said common inner surface; movable means adapted to be longitudinally reciprocated within said assembled support members and comprising conductive means in contact with said resistance means and said first named conductive means; apertures in said support member between said inner and said outer surfaces thereof and adjacent to said resistance means; contact means secured to said support members and having free portions extending through said apertures and contacting said resistance means; and connection means disposed in said recesses on said outer surfaces connected to said contact means.

5. A variable resistance device of the class described comprising: a hollow housing member having an inner surface; a plurality of support members of a material characterized by a slipperiness property, said support means having inner surfaces and outer surfaces and said support members being adapted when assembled to have a common outer surface generally conformable to the inner surface of said hollow housing member; recesses on said inner surfaces of said support members, selected ones of said inner recesses defining a common recess; resistance means disposed in said common recess; conductive mean disposed on said inner surfaces; and movable means positioned for longitudinal movement within said assembled support members and comprising conductive means in contact with said resistance means and said first named conductive means, said slipperiness property of said support members permitting relative longitudinal movement between said resistance means and said support members.

6. A resistance device of the class described comprising: a hollow cylindrical housing member, a plurality of support members of a material characterized by having a slipperiness quality snugly positioned in said housing member, resilient means positioned in said housing memher at the ends of said support members to absorb expansion between said support members and said housing memher, said support members having cooperating abutting surfaces and means which define, when said support members are in abutting assembled relationship, a common recess; and resistance means disposed in said common recess.

References Cited in the file of this patent UNITED STATES PATENTS 2,668,218 Searle Feb. 2, 1954- 2,687,463 Riley Aug. 24, 1954 FOREIGN PATENTS 495,836 I Canada Sept. 8, 1953

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