Variable Resistor

Abstract

A variable resistor in which a resistive strip is mounted on a base, a threaded member is mounted on the base adjacent and parallel to the resistive strip, and a sliding contact element is wound about, and received within, the threads of the threaded member, a part of the element being in constant electrical engagement with the resistive strip. The free ends of the sliding contact element extend from the threaded member and engage the base on opposite sides thereof. Rotation of the threaded member urges a free end against the base, thereby relaxing the winding sufficiently for the contact to be moved along the threaded member within the threads.

Description

The present invention relates to a variable resistor capable of extremely fine adjustment, usable as such or as a potentiometer.

Variable resistors are well known in the art. In a common form, a resistive wire is wrapped around a core, and a contact is moved along the length of the core making electrical contact with the individual coils of the wire. This form is rather difficult of precise adjustment, since resistance is a function of the length of wire, and adjustments in the quantum of resistance are limited to those increments which correspond to the length of an individual coil of wire. Devices in this form are not readily adaptable to the highly sophisticated circuits in use today which require small increments of adjustment.

In another form, a contact is moved along a resistive strip or element making contact with an infinite number of points along the surface of the strip. While precise adjustments of resistance are possible with such a device, they are often cumbersome and complicated of assembly, as there must be sufficient structure to (1) maintain the contact in electrical engagement with the resistive strip, and (2) to move the contact along the strip with a high degree of precision.

The present invention provides a variable resistor which is capable of extremely precise adjustment, and which has a structural simplicity which reliably maintains electrical contact, and affords ease of manipulation. As such, the present invention is highly adaptable for use in sophisticated devices such as television tuning assemblies, and in general any device which requires precision, simplicity, reliability, and miniaturization.

It is a prime object of the present invention to provide a variable resistance assembly which is capable of precise adjustment of the quantum of resistance.

It is another object of the present invention to provide a variable resistance assembly the structural simplicity of which makes it readily adapted for use with sophisticated electromechanical devices.

It is a further object of the present invention to provide a variable resistance assembly which is useful in devices in which miniaturization is required.

It is yet another object of the present invention to provide a variable resistance assembly which is inexpensive and reliable in operation.

The present invention provides a resistive element or strip mounted on a base. A threaded member is mounted adjacent and parallel to the resistive strip, and has a sliding contact wound about, and closely received within, the threads. The free ends of the sliding contact extend toward the resistive strip and contact the base on opposite sides thereof. A part of the winding of the sliding contact extends between the threaded member and the resistive strip. As the threaded member is rotated, depending upon the direction of rotation, one or another of the free ends act upon the base and relax the winding sufficiently for the contact to be readily moved along the threaded member within the threads. A first end of the threaded member is retained in the base; the second end of the threaded member is received in a slot in the base, and terminates in a beveled collar. A spring is placed over the beveled collar and urges the threaded member toward the resistive strip, which urging is opposed only by the contact engaging the base. The axial position of the threaded member must be precisely maintained, and this is accomplished by the interaction of the spring and the bevel on the threaded member collar.

To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to a variable resistor as defined in the appended claims and as described in the specification taken together with the accompanying drawings wherein:

FIG. 1 is a partially cross sectioned elevational view of a variable resistor of the present invention; and

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1.

Referring to FIG. 1, a preferred embodiment of the present invention is illustrated, generally designated by the numeral 10. A base 12 is closely received in a recess 14 in the drum 16 (shown best in FIG. 2) and extends out therefrom. A retaining washer 18 is inserted in the recess 19 in the drum 16, which washer retains the base 12 in the recess 14, preventing motion of that base relative to the drum 16. A resistive means in the form of a strip 20 is mounted on, secured to, and supported along its length by the base 12. One end of that resistive strip extends over the retaining washer 18, and the other end 22 is received in an opening 24 in an upstanding part 26 of the drum 16.

Mounted adjacent and parallel the resistive strip 20 is an electrically conductive threaded member 28 which is capable of being connected to an external circuit. That threaded member has at one end thereof a collar 30, which is received in a countersunk hole 32 in a second upstanding part 34 of the drum 16. The other end of the threaded member 28 is received in a slot 36 in the part 26, and extends beyond that slot. A beveled collar 38 is mounted thereon, preferably rotatably. A spring 40 is resiliently downwardly active on the beveled collar 38 and bears against that collar and the part 26. The threaded member 28 is rotatable in the hold 32 and slot 36, and also preferably rotates in beveled collar 38.

A contact element generally designated 42 is wound around the threaded member 28. This contact consists of a resilient conductive wire winding 44 which is closely received within the threads. As seen best in FIG. 2, the winding 44 preferably is wound around the threaded member 28 for at least one complete turn. Electrical contact is made between the winding 44 and the resistive strip 20 by the part 46 which extends out beyond the threads of member 28 and is urged into strip 20 by the spring 40. The free ends 48a and 48b of the winding 44 extend down and contact the base 12 on opposite sides thereof. Rotation of the threaded member 28 causes the winding 44 to relax sufficiently to be driven along that threaded member by, and within, the threads thereof. For example, if the threaded member is rotated in a clockwise direction (when looking along the line 2--2 of FIG. 1), the free end 48b bears against the base 12. Since there is friction between the threads and the winding 44, that winding will tend to rotate along with the threaded member 28. Since the free end 48b bears against the base 12 at the same time, the winding 44 tends to expand by increasing the distance between the free ends 48a and 48b. This expansion relaxes the winding 44 about the threaded member 28 sufficiently for the threads to drive the winding 44 in one direction. Similarly, if the threaded member 28 is rotated in a counterclockwise direction, the free end 48a bears against the base 12, and the winding 44 is again relaxed allowing the threads to drive the winding 44 in the other direction. Upon termination of the rotation (in either clockwise or counterclockwise direction) of the threaded member 28, the winding 44 resiliently returns to its normally tightly wound position, in which the free ends 48a and 48b each contact the base 12 on opposite sides thereof.

The action of the spring 40 on the beveled collar 38 serves a twofold purpose: (1) it urges the threaded member 28 toward the resistive strip 20, which urging is resisted only by the bearing of the part 46 on the resistive strip 20, thus providing a constant electrical engagement between that part 46 and that resistive strip 20; and (2) it eliminates all longitudinal lost motion between the threaded member 28 and the drum 16, whereby the winding 44 will remain stationary on the resistive strip 20 until that threaded member is deliberately rotated.

To effect rotation of the threaded member 28, any suitable drive mechanism will suffice. For use in tuning assemblies and like devices, it is found convenient to attach a pinion 50 to the threaded member 28 near the collar 30. A gear 52 which is suitably connected to any external manual or automatic control (not shown), may be moved into driving engagement with the pinion 50, thereby rotating the threaded member 28. The rotational motion imparted to that threaded member is directly and easily converted into the translational motion of the winding 44 along that threaded member.

Referring to FIG. 2, three variable resistor assemblies are illustrated. The adaptability of the structure herein disclosed allows for any number of assemblies to be used as may be required by any apparatus. It is possible to assemble these variable resistor assemblies closely adjacent to each other without interference between the adjoining assemblies, since each assembly acts totally independent of all other surrounding assemblies. For devices such as television tuners, several resistor assemblies 10 can be arranged on the periphery of a drum 16. A stationary contact 54 can be connected to tuner circuitry (not shown, and which forms no part of the present invention), and extend laterally over the drum 16. Upon rotation of the drum 16, the individual resistor assemblies (corresponding to the several tuner stations) are positioned adjacent the stationary contact 54. That contact electrically engages the threaded member 28 of the adjacent assembly 10. Since there can be one assembly 10 for each tuning station, the resistance of each assembly 10 will remain fixed while the drum is rotated to other stations.

From the foregoing it will be appreciated that the variable resistance herein described provides a novel structure which can be utilized to great advantage in devices where very precise adjustments of resistance are necessary. Its compact construction makes it particularly useful in devices where a plurality of variable resistors are necessary.

While but a single embodiment of the present invention is here disclosed, it will be appreciated that many variations may be made in the details thereof, without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. In a variable resistor comprising a base and resistive means on said base, a contact assembly which comprises a threaded member rotatably mounted relative to said base adjacent and parallel to said resistive means, a conductive contact element wound about said threaded member and a part of which is closely received within said threads, a part of said element extending from said threaded member and slidably engaging said resistive means and making electrical connection therewith, and means for connecting said contact element to an external circuit, whereby rotation of said threaded member moves said contact element along said threaded member, thereby sliding along said resistive means, in which said contact element is wound about said threaded member for at least one complete turn, is resilient, normally tends to wind itself tightly around said threaded member, and has free ends which engage said base, whereby upon rotation of said threaded member one or another of said ends, depending upon the direction of rotation, acting upon said base, relaxes the winding

2. In the variable resistor of claim 1, means operatively connected to said threaded member for urging it downwardly toward said resistive means, thereby to urge said extending part of said contact element against said

3. In the variable resistor of claim 1, resilient means operatively connected to said threaded member for urging it downwardly toward said resistive means, thereby to urge said extending part of said contact

4. The variable resistor of claim 1, in which said threaded member comprises a beveled part, and resilient means acting on said part urging said threaded member axially, thereby to remove lost motion of said

5. The variable resistor of claim 1, in which said threaded member is electrically conductive and comprises said external circuit connecting

6. The variable resistor of claim 1 in which said free ends of said contact

7. In the variable resistor of claim 6, means operatively connected to said threaded member for urging it downwardly toward said resistive means, thereby to urge said extending part of said contact element against said

8. In the variable resistor of claim 1, resilient means operatively connected to said threaded member for urging it downwardly toward said resistive means, thereby to urge said extending part of said contact

9. The variable resistor of claim 1, in which said threaded member comprises a beveled part, and resilient means acting on said part urging said threaded member axially, thereby to remove lost motion of said

10. The variable resistor of claim 6, in which said threaded member is electrically conductive and comprises said external circuit connecting

11. In a variable resistor comprising a base and resistive means on said base, a contact assembly which comprises a threaded member rotatably mounted relative to said base adjacent and parallel to said resistive means, a conductive contact element wound about said threaded member and a part of which is closely received within said threads, a part of said element extending from said threaded member and slidably engaging said resistive means and making electrical connection therewith, and means for connecting said contact element to an external circuit, whereby rotation of said threaded member moves said contact element along said threaded member, thereby sliding along said resistive means, and means operatively connected to said threaded member for urging it downwardly toward said resistive means, thereby to urge said extending part of said contact

12. The variable resistor of claim 11, in which said contact element is

13. The variable resistor of claim 12, in which said downward-urging means

14. In a variable resistor comprising a base and resistive means on said base, a contact assembly which comprises a threaded member rotatably mounted relative to said base adjacent and parallel to said resistive means, a conductive contact element wound about said threaded member and a part of which is closely received within said threads, a part of said element extending from said threaded member and slidably engaging said resistive means and making electrical connection therewith, and means for connecting said contact element to an external circuit, whereby rotation of said threaded member moves said contact element along said threaded member, thereby sliding along said resistive means, and resilient means operatively connected to said threaded member for urging it downwardly toward the said resistive means, thereby to urge said extending part of

15. In a variable resistor comprising a base and resistive means on said base, a contact assembly which comprises a threaded member rotatably mounted relative to said base adjacent and parallel to said resistive means, a conductive contact element wound about said threaded member and a part of which is closely received within said threads, a part of said element extending from said threaded member and slidably engaging said resistive means and making electrical connection therewith, and means for connecting said contact element to an external circuit, whereby rotation of said threaded member moves said contact element along said threaded member, thereby sliding along said resistive means, in which said threaded member comprises a beveled part, and resilient means acting on said part urging said threaded member axially, thereby to remove lost motion of said

16. The variable resistor of claim 15, in which said contact element is wound about said threaded member for at least one complete turn.