US3413589A - Lead screw operated potentiometer - Google Patents

Description

NOV. 26, 1968 s GREENE 3,413,589

LEAD SCREW OPERATED POTENTIOMETER Filed sept. v, 1965 .o .ai ,7

United States Patent G 3,413,589 LEAD SCREW OPERATED POTENTIOMETER Sanford I. Greene, Wantagh, N.Y., assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Filed Sept. 7, 1965, Ser. No. 485,357 2 Claims. (Cl. 338-180) ABSTRACT F THE DISCLOSURE A lead screw operated potentiometer comprises a housing having a longitudinal cavity with the side walls forming guide surfaces. In the cavity are disposed an elongated resistance element, a longitudinally movable carriage carrying a resilient contact Ushaped in cross-section, and a lead screw. The lead screw engages complementary threads or grooves in the carriage extending only for 180 or less. As the lead screw is rotated, it exerts a downward camming action on the carriage, biasing the contact into engagement with the resistance element. In the event it is attempted to drive the carriage beyond its limit of travel, the lead screw cams the carriage out of engagement with its threads against the resilience of the contact element, thereby constituting an automatic overload release clutch.

Background of the invention This invention relates to lead screw operated potentiometers and particularly to such potentiometers of the type in which a resilient contact element serves both to bias its carriage into engagement with the leadA screw and to act as an overload release clutch.

There have heretofore been marketed and proposed numerous lead screw potentiometer mechanisms. In general, these have comprised some form of carriage positively engaging the lead screw for axial movement upon its rotation and a resilient contact element supported by such carriage for engaging a resistance element disposed parallel to the lead screw. Due to the positive engagement of the contact carriage and the lead screw, the device is subject to damaging in the event longitudinal movement of the contact carriage is jammed or obstructed, for example' by an attempt to move it beyond its limit of travel.

It is an object of the invention, therefore, to provide a new and improved lead screw operated potentiometer which obviates the above-mentioned disadvantage of prior devices of this type.

It is another object of the invention to provide a new and improved lead screw operated potentiometer in which the contact carriage is biased into engagement with the lead screw by the contact element so that it serves as an overload release clutch.

Summary of the invention In accordance with the invention, there is provided a lead screw operated potentiometer comprising a housing member for containing the operative elements of the potentiometer and including two opposed parallel guide surfaces having opposed longitudinal guide slots, a lead screw rotatably mounted within the housing parallel to its guide surfaces and including a portion accessible from the exterior of the housing for rotating the same, a resistance element supported in the housing parallel to the lead screw, a resilient sliding contact engaging the resistance element and having lateral extensions riding in the guide slots of the parallel guide surfaces, and a carriage for the contact having longitudinal and transverse sliding engagements with the parallel guide surfaces and having a plurality of transverse grooves complementary to substan- 3,413,589 Patented Nov. 26, 1968 ACe tial portions of the threads of the lead screw and engaging the same over a substantial arc not greater than -facing the resistance element, whereby the resilient contact serves to bias the carriage into engagement with the lead screw and to permit disengagement therefrom if it is attempted to drive the carriage beyond its limit of travel, thus forming an zautomatic overload release clutch. The term potentiometer is used herein and in the appended claims in accordance with its ordinary trade usage, referring to a resistance element with a sliding contact.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, while its scope will be pointed out in the appended claims.

Referring now to the drawing:

FIG. 1 is a longitudinal view, partly in section, of a lead screw operated potentiometer embodying the invention, the sectionalized portions being taken along the linel 1-1 of FIG. 2;

FIG. 2 is a cross-sectional view of the potentiometer of FIG. 1 along the line 2 2; while FIG. 3 is an exploded perspective view, partly broken away, of the contact assembly of the potentiometers of FIGS. 1 and 2.

Referring now more particularly to FIGS. 1 and 2 of the drawing, there is represented a lead screw operated potentiometer embodying the invention comprising a housing member 10 for containing the operative elements of the potentiometer and including two opposed parallel guide surfaces 10a, 10b having opposed longitudinal guide slots 10c and 10d formed therein. A lead screw 11 is rotatably mounted in the housing member 10 as in sleeve bearings 12 and 13. As shown in FIG. 2, the lead screw is disposed parallel to the guide surfaces 10a, 10b and includes a portion 11a, such as an extension of the root diameter of the lead screw, provided with a screwdriver slot accessible from the exterior of the housing for rotating the lead screw.

The potentiometer of the invention further comprisen an elongated resistance element 14, shown in the form of a wire-wound element, supported in the housing member 10 parallel to the lead screw. The potentiometer further includes an elongated contact element 15, shown in the form of a conductive rod, supported in the housing parallel to the resistance element 14.

The potentiometer further comprises a resilient sliding contact element 16 including a pair of extending resilient arms 16a and 16b, the arm 16a engaging the resistance element 14 and the arm 16b engaging the contact element 15. The element 16, with its arms 16a and 16b, has a U-shaped cross-section, as indicated. The contact element 16 also has lateral extensions 16e and 16d which ride iu the guide slots 10c and 10d, respectively. The main portion of the contact element 16 is provided with a pair of holes 16e and 161 for a purpose described hereinafter.

The potentiometer of the invention further comprises a carriage 17 for the contact element 16 and having a pair of protrusions 17a and 17b for detachably engaging the holes 16e, 16f, respectively, of the contact element 16. As shown more clearly in FIG. 3, the carriage 17 is of approximately U-shaped cross-section, the outer `arms of which have longitudinal sliding engagements with the guide surfaces 10a, 10b of the housing member 10. The carriage 17 has a plurality of transverse grooves or threads 17c in the base of the U, substantially complementary to and engaging substantial portions of the threads of the lead screw 11 over a substantial arc not greater than 180, and preferably approximately 180, on the side of the lead screw 11 facing the resistance element 14.

As shown more clearly in FIG. 1, the 4grooves or threads in the carriage 17 engage substantial portions of the threads of the lead screw 11 but not the entire threads as in an ordinary` threaded engagement. The potentiometer will also be provided with conventional external electrical terminals connected to the contact rod and to the terminals of the resistance element 14 (not shown). As shown, the carriage 17 is of insulation material but if it is permissible that the head 11a of lead screw 11 be at the potential of the sliding contact 16, the carriage 17 may be of a conductive metal and the lead screw 11 used as the electrical connection to the contact 16, in which case the contact rod 15 may be omitted. An enclosing cap 18 is secured to the end of the housing member 10 as by suitable screws 19 to retain the parts in their assembled positions.

It is `believed that the operation of the lead screw operated potentiometer of the invention will be apparent from the foregoing description. In brief, rotation of the lead screw 11 by its extension 11a causes the carriage 17 `and the contact element 16 to move longitudinally, varying the amount of the resistance between the contact 16a and the terminals of the resistance element 14 in a conventional manner. During this movement, the outer faces of the U-shaped carriage 17 slide along the guide surfaces 10a, 10b of the housing member. In FIG. l, the parts are shown with the carriage 17 and contact 16 at their extreme left-hand positions. If, now, it were attempted to move these elements still further to the left by further rotation of the lead screw 11, the camming action of the lead screw on the threads or grooves of the carriage 17 would force it downwardly against the bias of the extensions 16e and 16d of resilient contact element 16 which bear on the lower faces of the guide slots 10c and 10d, respectively, as shown in FIG. 2, disengaging the lead screw from the carriage 17. During this movement, the outer surfaces of the carriage 17 would slide vertically along the guide surfaces 10a, 10b, that is, transverse to the normal sliding movement.

The lead screw operated potentiometer described has a number of distinct advantages over prior devices of this type. The carriage 17 can be readily molded from a thermosetting resin since the threads 17c do not extend over 180 of arc so that the upper half of the threads are completely open. Further, the carriage 17 engages the lead screw with a plurality of threads over approximately 180 of arc, thereby reducing and distributing wear and assuring long life and reliability. This construction is to be contrasted with some prior designs in which a single wire or lbail on the carriage engages a single thread of the lead screw. The camming .action of the threads of the lead screw on the grooves of the carriage 17 is such as to assist in biasing the contacts 16a, 16h into engagement with the resistance element 14 and the contact 15, respectively, assuring positive electrical contacts. Moreover, as described above, the carriage 17 :and contact 50 element 16 serve as an overload release clutch, preventing damage to the device.

While there has been described what is, at present, considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein, without 4 departing from the invention, and it is, therefore, aime in the appended claim-s to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A lead screw operated potentiometer comprising:

a housing member for containing the operative elements of the potentiometer and including two opposed parallel guide surfaces having opposed longitudinal guide slots;

a lead screw rotatably mounted within said housing parallel to said surfaces and including a portion accessible from the exterior of said housing for rotating the same;

a resistance element supported in said housing parallel to said lead screw;

a resilient sliding contact engaging said resistance element and having lateral extentions riding in said guide slots;

and a carriage `for said contact having longitudinal and transverse sliding engagements with said surfaces and having `a plurality of transverse grooves complementary to substantial portions of the threads of said lead screw and engaging the same over a substantial arc not greater than 180 facing said resistance element;

whereby said resilient contact serves to bias said carriage into engagement with said lead screw.

2. A lead screw operated potentiometer comprising:

a housing member for containing the operative elements of the potentiometer and including two opposed parallel guide surfaces;

a lead screw rotatably mounted within said housing parallel to said surfaces and including a portion accessible from the exterior of said housing for rotating the same;

a resistance element supported in said housing parallel to said lead screw;

a resilient sliding contact engaging said resistance element and including a plurality of holes;

and a carriage including a plurality of protrusions detachably engaging said holes in said sliding contact to actuate the same, having longitudinal and transverse sliding engagements with said surfaces and having a plurality of transverse grooves complementary to substantial portions of the threads of said lead screw and engaging the same over a substantial arc not greater than facing said resistance element;

whereby said resilient contact serves to bias said carriage into engagement with said lead screw.

References Cited UNITED STATES PATENTS 2,926,324 2/1960 Barden et al. 338--180 3,187,289 6/1965 Rolwes 338--180 3,238,488 3/1966 Laugenbach et al. 338-180 RICHARD M. WOOD, Primary Examiner.

I. G. SMITH, Assistant Examiner.

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