US2918643A

US2918643A - Variable resistors

Info

Publication number: US2918643A
Application number: US596571A
Authority: US
Inventors: Rattray George
Original assignee: George Rattray & Co Inc
Current assignee: George Rattray & Co Inc
Priority date: 1956-07-09
Filing date: 1956-07-09
Publication date: 1959-12-22
Anticipated expiration: 1976-12-22

Description

INVENTOR. Gearqe Raff/0y A 1 TORNEK? CS Patent- 1 1. ARIABLE RESISTORS George o a, N.Y., assignor to George Rat tray & CO-', Inc., Richmond Hill, N.Y., a corporation of New York T a pl c tion July '9, 1956, Serial No. 596,571

11 Claims. (Cl. ass-9s provide a variable resistor with fixed preset taps.

1 It is 'a further object of the present invention to pro- 'vide a movable contact arm operating in conjunction with the fixed taps to produce definite controlled resistance variations with respect to a number of preset taps.

It is still a further object of this invention to provide an improved arrangement for interconnecting the movable contact arm with the resistance arm.

It is yet a further object to provide a potentiometer with precision set taps which is simple and inexpensive to manufacture.

Other and further objects of the present invention will be com'eapparent by reference to the following description taken in conjunction with the accompanying drawings wherein? I i Fig. 1 is a side elevation partly in section of the invention; I

Fig. 2 is an end view of the invention;

1 ,Fig, 3 is a diagrammatic view of the resistance element and contact arms as shown in Fig. 2;

i Fig.4 is enlarged sectional view of a portion of Fig. 1 and v, ,Fig. Sis a sectional view showing a modification of the deviceas set forth in Fig.4

,QReferringpto the, drawings, there is shown in Fig. 1, a 'pOtentiometer unit generally indicated at 6. This potentiometer unit is shown connected to a second potentiometer unit gmerally indicated at 8 by means of at; clampin ring 9. For purposes of this description, -1'.eference.will;be made only to the potentiometer unit generally indicated at 6, it being understood that other pot'entiometers are of similar construction and operate in "ganged relationship.

The potentiometer unit 6 has a generally cylindrical housing 11. This housing is made from any suitable :rnaterial and has a side wall 12 and a bottom wall 14.

This side wall .12 has formed about its outer portion, a

- ,.cut-.out 16 at its lower extremity and a raised flanged portion 18' at its upper extremity. The cut-out 16 and the flange 18 are so formed that when the potentiometer units are ganged together, one on top of the other as shown in'Fig. .l, the flanged portion 18 of the lower potentiometer unit will peripherally engage the cut-out portion 16 of the potentiometer unit being placed thereon.

1 5V Two. external grooves 20 peripherally I surround the 'housing 11, one slightly above the cut-out16 and the other slightly below the flanged portion 18. These two grooves 20' are so adapted that when two potentiometer units are engaged by means of the cut-out 16 and the flange 18, a clamping ring will be placed in one of the grooves 20 and in the corresponding groove of the other potentiometer in such a manner so as to keep the potentiometers in a tight and firm engagement.

The bottom wall 14 of housing 11 has an opening extending therethrough adapted to receive two

conventional bearings

24 and 26 which are retained within an upstanding bearing support member 28.

This bearing support member peripherally surrounds these bearings and shaft 30 extending therethrough for free rotation. The shaft 30 extends below the bottom wall 14 of housing 11 and has aflixed at its lower extremity the coupling assembly for each potentiometer unit with successive units. This assembly is generally indicated at 32, Fig. 1.

The upstanding bearing support member has an externally formed seating ridge 34. A tap disc 36 is mounted on this seating ridge 34 and supports about its outer circumference, a plurality of taps 38, 38a, 38b, Fig. 2. The outer and upper extremity of the tap disc 36 is tapered, Fig. 4, so that when the tap 38 is inserted in the tap disc 36, the tap 38 tilts generally outwardly for purposes to be hereinafter described.

The tap disc further supports a contact ring 40 which .is mounted into the ridge 42 of the tap disc 36. A contact arm supporting block 44 is mounted on shaft 30 at its upper extremity. A series of insulated washers 46 supports this block from contact with the bearing 26. The block is held in place on shaft 30 by a screw 48 passing through bifurcated clamping ends 50. Extending from the block 44 are two

contact arms

52 and 54. These two contact arms are insulated from the block 44 by insulating material 56. However, these contact arms are freely conductive to each other although insulated from the block itself. On the extremity of each of the contact arms, are

contact terminals

58 and 60, respectively.

A sleeve 62 frictionally fits inside of the housing 11 resting against the side walls 16 and on the bottom wall 14. This frictional fitting sleeve has an interior seating ridge 64 formed at its upper extremity and an interior seating ridge 66 at its lower extremity. In the seating ridge 66 is mounted resistance element 68 fitting in friction tight engagement against the sleeve 62.

A terminal board 69 is affixed by means of a series of screws or other suitable conventional arrangements to the outer circumference of the housing 11. This terminal board 69 has a plurality of terminal contacts indicated at 72, 74, and 76, Fig. 2.

Referring to Fig. 1, it will be noted that the terminals above described are positioned in two tiers or rows on the terminal board. This invention need not be restricted to this particular showing as the arrangement on the terminal board is a matter of expediency and choice rather than an embodiment of this invention.

By means of a suitable wire, tap 38 is connected to one of these terminal contacts. Contact ring 40 is likewise connected to one of the terminal contacts. By the use of a plurality of terminal contacts, a plurality of taps 38, 38a, 38b, only three are shown, are connected by suitable leads to the

terminal contacts

72, 74, 76, 'only three shown, so that each tap is connected to a terminal contact.

The coupling assembly 32 includes a clamping block made of suitable metal or other material to which is soldered or welded a leaf spring 82. This clamping block is afiixed to the shaft 30 at its extension below lower wall 14 of housing 11, in the same manner as is the contact arm supporting block 44 hereinabove de- 3 scribed. It therefore follows that a rotation of the shaft will impart identical rotation to both the contact arm supporting block 44 and the clamping block 80. A suitable insulating washer 85 and insulating bearing 84 are provided to insulate the clamping block 80 from bearing 24 and shaft 30 respectively. 8

The leaf spring 82 is generally V-shaped, bent downward slightly from the clamping block and has a punched out opening in the apex of the V. This cut-out or punched out portion has upturned flanges 88 so adapted that they will engage the knob of pin 90 which is mounted on the contact arm supporting block 44 hereinabove described.

Referring to Fig. 1, it will be seen that when two potentiometer units are ganged together, the pin 90 mounted on the contact arm supporting block 44 of one potentiometer unit will protrude through the downwardly extending spring 82 of the clamping block of the other potentiometer unit. In this way the knob 90 will be engaged by the flanges 88 and will firmly position the two potentiometers so that the rotation of the shaft of one potentiometer will transmit an equal rotation to similar shafts of the ganged series of otentiometers.

The clamping blocks 80 and the contact arm supporting block 44 of all potentiometers are adjustable relative to each other by the respective screws 48 and 48'.

Taps 38, 38a and 38b are so positioned on the tap disc 36 that they are in a slightly inclined or tilted position. This angular displacement is accomplished by tapering the outer edge of the tap disc 36 and inserting the tap 38 on this tapered surface. In this manner, the taps are always in the same engagement with resistance element 68 regardless of whether or not the taps themselves rotate in their position.

As may be seen in Fig. 4, the tap 38 in contact with resistance element 68 bends against this resistance element forming pressure thereagainst. Rotation of tap 38 will in no way afiect the contact between the tap 38 and resistance element 68. This is important to eliminate the possible annoying variations in resistances during potentiometer use which would be caused should the position of the taps relative to the resistance elements, be subject to change whenever the taps become slightly loosened during extensive use.

By the use of taps 38 as shown, a plurality of taps may be provided in one potentiometer. Taps 38 can be placed as close together as of an inch without impairing their general operating efficiency. Further, additional taps may be easily added to the potentiometer unit after it has been fully assembled.

The modification illustrated in Fig. shows tap 100 set in the tap disc 36' in a generally vertical position. Resistance element 104, instead of being wound around an elongated card as shown at 68, Fig. 1 or Fig. 4, is wound around a tubular card. The same principle is true, however, as should the tap 100, Fig. 5, rotate about its vertical axis, its point of contact with tubular resistor 104 would not change.

The parts hereinabove described are simply assembled into the potentiometer unit. It is pointed out that. there is absent the usual screws, springs and wires and. other conventional connecting devices so often necessary to hold potentiometers in a fixed position. In order that the original relationship of the resistances of the potentiometers be maintained, the tap disc must be accurately centered with regard to either the center point of the casing or the outside diameter of the casing. This is necessary in order that correct relative values of re-- sistances in successive potentiometers shall be maintained. by this centering about a geometric axis.

The accurate positioning of the taps on the tap disc can initially be made to set up the desired relative re sistances between the respective taps. The resistance is known for the linear distance of resistance wire wound around the card forming the resistance element. The

4 linear distance is converted to an angular measurement and the taps then accurately positioned on the tap disc. When this is done, because of the preset relative positions of the taps with regard to each other, the resistances at other terminals at the same time will be known, useable and definite.

It is therefore possible, by presetting these taps with relation to each other, to provide a potentiometer in which desired proportional resistances will be provided at respective tap terminals.- In this manner, most accurate resistances can be initially gained and successfully maintained. Terminal connections can also be made to additional resistor 106 to provide other than the linear resistance variation provided for by the potentiometer alone.

It is to be understood that the invention is not to be limited to the drawings or the specification hereinbefore given, but what I desire to cover and protect by Letters Patent is claimed as follows:

I claim:

1. A variable resistor comprising a housing, a resistor element mounted in said housing, rotatable shaft means mounted in said housing arranged to sweep over said resistor element in touching contact therewith, first terminal means on the outside of said housing connected to said shaft means, a tap disc member in said housing adjacent said resistor element having a plurality of small diameter holes drilled therethrough adjacent the outer edge thereof, second terminal means on the outside of said housing, and a tap contact member comprising a pin which is inserted through each of said holes and connected at one end and on one side of said disc to said second terminal means and having its opposite end extending into contact with said resistor element.

2. In a variable resistor according to claim 1, wherein said resistor element is cylindrical and said tap disc member is substantially flat.

3. In a variable resistor according to claim 1, wherein said resistor element is a thin walled ring and said tap disc is provided with a beveled upper outer face through which said taps extend into contact with said resistor element.

4. In a variable resistor comprising a cylindrical housing, a resistor element mounted within said housing adjacent the inner cylindrical wall, a shaft rotatably mounted in the central portion of said housing, a contact ring spaced from said resistor element, a first terminal member on the outside of said housing connected to said contact ring, a contact member afiixed to said shaft for rotation therewith having portions which sweep over each of said resistor element and said contact ring for electrical contact therewith, and a plurality of second terminal members on the outside of said housing, the improvement comprising a tap disc member of insulating material positioned in said housing between said resistance element and said inner contact ring, said tap disc member having a plurality of small diameter holes drilled therethrough adjacent the outer edge thereof and located at predetermined angularly spaced positions, and a tap contact member comprising a pin which is inserted through each of said holes and connected at one end and on one side of said disc to a respective terminal memher and having its opposite end on the. other side of said disc extending into contact with said resistor element.

5. In a variable resistor according to claim 4, including means connected to an end of said shaft on the outside of said housing for connecting said shaft to a cylinder shaft of a similar resistor element, and wherein said cylindrical housing is recessed at each end whereby a similar element may be nested in the open end of said element and each of said shafts may be connected for simultaneous movement.

6. In a variable resistor according to claim 4, wherein said housing inner cylindrical wall is formed of two different internal diameter portions forming a ridge upon which said resistor element is positioned.

of potentiometers each of said potentiometers including 10 a housing having a bottom wall and a side wall, a freely rotatable shaft extending through and below said bottom wall, a contact arm supporting block mounted within said housing, coupling means adapted to join said potentiometers, one to another, independent of said shaft, said 1 coupling means including an upstanding pin mounted on said contact supporting block, a knob at the upper extremity of said pin, a clamping block mounted outside said housing on said shaft at the opposite extremity of said shaft from said contact arm supporting block, an insulating bearing mounted on said shaft adapted to insulate said clamping block from said shaft, a leaf spring, having its extremity bent downwardly, mounted on said clamping block and raised flanges formed by a cut-out portion in said downwardly bent extremity of said leaf spring, said flanges being adapted to engage the knob of the pin mounted on said contact arm supporting block.

10. A variable resistor as in claim 9, including a clamp ring, grooves in the outer wall of said housing adapted to receive said clamp ring, a cut out ridge peripherally surrounding one extremity of the side wall of said housing and a flanged portion at the opposite extremity of said side wall of said housing.

1 1. A variable resistor assembly as in claim 9 wherein said leaf spring is V-shaped.

References Cited in the file of this patent UNITED STATES PATENTS 1,926,206 Lodge Sept. 12, 1933 2,125,954 Richter Aug. 9, 1938 2,619,570 Takats Nov. 25, 1952 2,748,230 Burgess May 29, 1956 FOREIGN PATENTS 473,508 Great Britain Oct. 14, 1937