US3617979A

US3617979A - Linear motion potentiometer with gears and rack

Info

Publication number: US3617979A
Application number: US77921A
Authority: US
Inventors: Harold L Purdy
Original assignee: Stackpole Carbon Co
Current assignee: Stackpole Carbon Co
Priority date: 1970-10-05
Filing date: 1970-10-05
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02

Abstract

An elongated case is provided in one of its sidewalls with a longitudinal slot, through which extends slidable means movable lengthwise of the slot. A bridging contact inside the case is carried by the The slideable means also means in engagement with resistance and collector elements. The slideable means also carry a large gear that rotates a pinion. An exposed manually rotatable small gear meshes with the large gear and is likewise carried by the slidable means. Rack teeth extend along the case and engage the pinion so that when the small gear is turned by hand the slidable means will be moved lengthwise of the case to adjust the potentiometer.

Description

United States Patent St. Marys, Pa.

Appl. No. Filed Patented Assignee LINEAR MOTION POTENTIOMETER WITH GEARS AND RACK 13 Claims, 7 Drawing Figs.

74/422 Int. Cl 1101c 9/02 Field of Search. 338/176,

References Cited UNITED STATES PATENTS 5/1905 Rupley Primary Examiner- Lewis 11. Myers Assistant Examiner-D. A. Tone Attorney-Brown, Murray, Flick & Peckham ABSTRACT: An elongated case is provided in one of its sidewalls with a longitudinal slot, through which extends slidable means movable lengthwise of the slot. A bridging contact inside the case is carried by the The slideable means also means in engagement with resistance and collector elements. The slideable means also carry a large gear that rotates a pinion. An exposed manually rotatable small gear meshes with the large gear and is likewise carried by the slidable means. Rack teeth extend along the case and engage the pinion so that when the small gear is turned by hand the slidable means will be moved lengthwise of the case to adjust the potentiometer.

PATENTEUNUVZ ISYI 3,617,979

SHEET 2 BF 3 //VVE/VTOR. meow L. PURDY ATTORNEYS.

LINEAR MOTION POTENTIOMETER WITH GEARS AND RACK It is among the objects of this invention to provide a linear motion potentiometer which is suitable for both coarse and fine tuning, which utilizes gears and a rack for fine tuning, which includes a wide thumb gear that requires only a narrow panel slot, which permits the use of various knobs and thumb gears to suit different customers, and which has a snaptogether assembly.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which FIG. 1 is a plan view;

FIG. 2 is a side view;

FIG. 3 is an end view;

FIG. 4 is an enlarged fragmentary cross section taken on the line IV-IV ofFIG. 2;

FIG. 5 is an enlarged cross section taken on the line V-V of FIG. 2;

FIG. 6 is an enlarged fragmentary longitudinal section taken on the line VI-VI of FIG. I; and

FIG. 7 is a horizontal section taken on the line VII-VII of FIG. 6.

Referring to FIGS. 1 to 5 of the drawings, the long rectangular case 1 of a variable resistor, such as a potentiometer, is provided along one of its sidewalls with a central slot 2 extending lengthwise of the case for nearly its full length. For the purpose of this description, the slotted wall will be called the top wall. Slidably mounted in the slot for movement lengthwise of the case is a slide 3 that has laterally opening grooves 4 (FIGS. 4 and 5) in its opposite sides receiving the sidewalls of the case slot to hold and guide the slide.

Inside the case a metal collector strip 6 and an electrical resistance strip 7 are mounted against its opposite sides in parallel relation to each other. The collector strip is provided with an integral terminal 8 that extends through the bottom of the case, and each end of the resistance strip is connected to another terminal 9 likewise extending out of the case. The slide 3 has a portion extending between these two strips, from which it is spaced. This portion of the slide may be a post 10 that extends part way across the collector and resistance strips. Encircling this post is a wire coil II, the convolutions of which are tilted relative to the post and firmly engage the strips beside the coil for good electrical engagement. The coil forms a bridging contact.

It is a feature of this invention that the bridging contact not only can be moved along the case as rapidly as desired, but also can be moved extremely slowly to obtain fine adjustment of the electrical resistance controlled by this potentiometer. Accordingly, a gear and rack arrangement is used that provides a high gear ratio that causes the contact to be moved a very short distance when the gears are turned a much greater distance. For this purpose the top of the slide 3 is provided with a central notch 13 as shown in FIG. 2, in which fits a central tongue 14 on the bottom of a gear carrier 15. As shown in FIG. 7, the ends of the tongue are tapered to fit tightly in tapered recesses 16 in the end walls of the notch when the tongue is pressed down into the notch, thereby holding the carrier and slide firmly together in a simple manner. The carrier has a central vertical slot 17 through it that is aligned with the slot 2 in the case. At opposite sides of the carrier slot the top of the carrier is provided with downwardly tapered recesses 18 that terminate at the bottom in vertical openings with semicircular lower walls, as shown in FIG. 6. Rotatably seated in these openings are the hubs 19 (FIG. 5) of a large gear 20 disposed in carrier slot 17 and projecting from its top and bottom. The top of the slide is provided with a concave recess 21 receiving the lower part of the gear.

The top of the gear meshes with the bottom of a much smaller, but thicker, gear 23 disposed in a vertical opening 24 through a knob 25 above the carrier. The hubs 26 (FIG. 5) of the small gear are rotatably mounted in the upper ends of upwardly extending slots 27 in the sidewalls of the knob opening. As shown in FIGS. 4 and 6, the opposite ends of the knob are provided with downwardly extending legs 28 that fit in vertical slots 29 in the ends of the carrier. To hold the two pieces together, the knob has integral downwardly tapered portions 30 at the inner sides of its legs, and lateral notches 31 at the upper ends of these portions. When the knob legs are pressed down in carrier slots 29, the tapered portions are forced down between tiny lugs 32 on the sidewalls of the carrier slots until these lugs snap into the notches to lock the knob and carrier together, with the two gears in mesh.

The small gear extends above the knob so that it can be turned by thumb or finger to rotate the large gear in the carrier. This rotates small pinions 34 integral with the outer ends of the hubs of the large gear. The pinions project from the opposite sides of the carrier. Each of the pinions meshes with a line of rack teeth extending lengthwise of the case. The rack teeth may be formed and attached to the case in any desired way. Preferably, however, they are part of a bracket 35 that is attached to the case. Such a bracket has parallel ends fitting over the ends of the case and connected by a long body parallel to the case but spaced outwardly from its slotted wall. The bracket may be metal and provided with parallel side flanges 36, between some of which the ends of the case fit. To lock the bracket in place, each of its ends is provided with a spring tongue 37 that snaps into a notch 38 in the adjoining end of the case, and with a pair of tongues 39 bent inwardly over the slotted wall of the case. The free ends of the brackets may project below the bottom of the case and be formed as tabs 40 for insertion in a panel or printed circuit board to hold the potentiometer in place. The bracket can be used for holding the two halves of the case together.

The long body of the bracket has a longitudinal slot 42 in it opposite the case slot. The bracket slot is formed by slitting the bracket lengthwise and then bending the sides of the slit inwardly parallel to the body flanges to form spaced-parallel sidewalls 43 for the slot as shown in FIGS. 4 and 5. The inner or lower edges of these walls are cut to provide rows of rack teeth 44 meshing with the two pinions below them. Of course, if desired, one pinion and one row of rack teeth could be omitted. The gear carrier extends through the bracket slot, and the main bodyof the knob and the entire small gear are located outside of the bracket.

This potentiometer can be adjusted in the usual way by simply moving the knob back and forth along the case. The gears will simply spin as the pinions are turned by the racks. On the other hand, fine adjustments can be made by turning the thumb gear. The fine tuning ratio is basically the ratio of the large gear pitch circumference to the pinion pitch circumference, so the larger the former relatively to the latter, the shorter the distance the pinions will move along the racks for any given degree of rotation of the large gear. The bridging contact can thus be moved an extremely short distance without any difficulty. The end teeth of the racks are cut away to allow the pinions to slip if the knob is moved too close to either end of the bracket. This slippage will prevent breakage of gear or pinion teeth.

The thumb gear is made wide and comfortable to turn, and yet the large gear and the legs of the knob require only a narrow slot in a panel having the toothed bracket on one side and the knob on the other. Various knobs and thumb gears can be used to suit customer requirements because the knobs are so easily snapped onto the carriers.

According to the provisions of the patent statutes, 1 have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

Iclaim:

I. A linear motion potentiometer comprising an elongated case provided in one of its sidewalls with a longitudinal slot, resistance and collector elements disposed in the case lengthwise thereof, slidable means extending through said slot and movable lengthwise thereof, a bridging contact inside the case carried by said means in engagement with said elements,

a large gear carried by said slidable means with its axis transverse to said slot, a pinion coaxial with the gear and rotatable thereby, a manually rotatable exposed small gear carried by said slidable means and meshing with the large gear, and a line of rack teeth extending along the case and engaged by said pinion, whereby when the small gear is turned said slidable means will be moved lengthwise of the case.

2. A linear motion potentiometer according to claim 1, including a pair of said pinions, the pinions being on opposite sides of said gear and rigidly connected therewith, and a line of rack teeth engaged by the second pinion.

3. A linear motion potentiometer according to claim 1, in which the axis of the large gear is outside the case, and the large gear projects into the case slot.

4. A linear motion potentiometer according to claim l, in which said slidable means are provided with openings containing said gears, and said small gear is located at the edge of the large gear farthest from the case and projects from said slidable means.

5. A linear motion potentiometer according to claim 1, in which said rack teeth are formed on a bracket attached to said case.

6. A linear motion potentiometer according to claim 5, in which said pinion is located between said rack teeth and case.

7. A linear motion potentiometer according to claim 5, in which said bracket has ends fitting over the ends of the case, and tongues extending inwardly from the bracket ends, the case having recesses in its ends receiving said tongues to lock the bracket on the case.

8. A linear motion potentiometer according to claim I, in which a bracket is attached to said case and has a portion extending along the slotted side of the case but spaced therefrom, said bracket portion is provided with a slot parallel to the case slot, said gear projects out through the bracket slot, said rack teeth are formed on the bracket along a side of the bracket slot and project inwardly toward the case, and said pinion is located between said teeth and case.

9. A linear motion potentiometer according to claim 8, including a second line of rack teeth formed on the bracket at the side of its slot opposite the first-mentioned teeth, and a second pinion engaging the second line of teeth and coaxial with said gear.

10. A linear motion potentiometer according to claim 1, in which said slidable means include a knob outside the case provided with an opening therethrough, said small gear being rotatably mounted in said opening and projecting outwardly therefrom.

11. A linear motion potentiometer according to claim 1, in which said slidable means include a slide engaging said slotted case wall and supporting said contact, a carrier connected to the slide and supporting said large gear and pinion, and knob connected to the carrier and supporting said small gear.

12. A linear motion potentiometer according to claim 11, in which said slide and carrier and knob are connected together by friction and snap action means.

13. A linear motion potentiometer according to claim 11, in which said knob is spaced from the carrier by thin legs.

Claims

1. A linear motion potentiometer comprising an elongated case provided in one of its sidewalls with a longitudinal slot, resistance and collector elements disposed in the case lengthwise thereof, slidable means extending through said slot and movable lengthwise thereof, a bridging contact inside the case carried by said means in engagement with said elements, a large gear carried by said slidable means with its axis transverse to said slot, a pinion coaxial with the gear and rotatable thereby, a manually rotatable exposed small gear carried by said slidable means and meshing with the large gear, and a line of rack teeth extending along the case and engaged by said pinion, whereby when the small gear is turned said slidable means will be moved lengthwise of the case.

8. A linear motion potentiometer according to claim l, in which a bracket is attached to said case and has a portion extending along the slotted side of the case but spaced therefrom, said bracket portion is provided with a slot parallel to the case slot, said gear projects out through the bracket slot, said rack teeth are formed on the bracket along a side of the bracket slot and project inwardly toward the case, and said pinion is located between said teeth and case.