GB2169683A - Gearing for a multiple turn variable resistor - Google Patents

Abstract

A worm gear-actuated variable resistance device comprises a worm gear (8) for providing relative movement between a resistance element (22) and a resistance contact (16), the worm gear having a circumferential portion of its teeth removed to form a blank area (8b) thereon, a worm screw (4) having threads (4a) for engaging the teeth (8a) of the worm gear whereby rotation of the worm screw causes rotation of the worm gear. A groove (14) disposed in a housing (2) is open towards the worm gear, both ends of the groove being in the form of vertical walls (14a, 14b). The worm gear includes a resilient finger- like projection (10) having a stop (12) on the end thereof. When the worm gear (8) reaches either end of its rotation, the stop (12) abuts one of the ends (14a, 14b) of the groove and resulting resilient deformation of the projection (10) tends to bias the worm gear in the opposite rotational direction to enable the teeth to re-engage the worm screw when rotation of the latter is reversed. <IMAGE>

Description

SPECIFICATION Clutch means for multiple turn variable resistor This invention relates to the field or variable resistance devices, more particularly to clutch means for worn gear actuated multiple turn resistors.

In some of the prior art devices (U.S. patent 3,242,452 patented March, 1966 A. A. Grunwald etal), a contact supporting member is rotatably mounted in the housing and is provided with teeth and a toothless section on its periphery. There is also a U-shaped slot provided in one side of the toothless section, the teeth being arranged to engage the screwthread on a lead screw so that the rotation of the lead screw will rotate the contact supporting member. A resilient means disposed in the U-shaped slot of the toothless section comprises a U-shaped spray having two legs and a bight section with the legs extending outwardly from the member and in position to engage the thread on the lead screw as the member is rotated.

A stop means is also arranged to limit the rotation of the member in either direction when one of the legs of the U-shaped spring engages the thread of the lead screw, the portion intermediate the legs of the U-shaped slot forming a stop member for limiting flexture of the legs of the spring toward each other from unflexed position.

Another prior art is described in U.S. Patent 3,768,325 dated Oct 30, 1973 in which a ratcheting mechanism for use in a worm gear actuated potentiometer which utilizes a worm gear having a circumferential portion of the teeth thereof removed, i.e. a blank area, a worm screw having a threads for engaging the teeth of the worm gear, and a ratcheting structure including a stop member and a resilient member. One of the two ratcheting structure members is attached to a housing or other unmovable structure and the other is attached to the worm gear at locations such that the resilient member will engage the stop member whenever the threads of the worm screw engage a tooth of the worm gear adjacent the blank area so as to provide ratcheting.

While such structures of prior arts have their own merit to overcome the disadvantages of typical clutch mechanism they have also disadvantage in that they require a separate stop mechanism in addition to ratcheting mechanism or clutch means which brings forth complexities in the structure thereof, the ratcheting mechanism or clutch means is somewhat unreliable and unpredictable practically after repeated usage, due to the use of strip shaped resilient members; and the device may be difficult and expensive to manufacture.

The present invention consists in a clutch for a variable resistance device having a worm gear rotation of which provides relative movment between an electrical contact and a resistance element of the device, said worm gear having peripheral teeth around a part of its circumference for engagement with a worm screw to provide said rotation and the remainder of its circumference being without such teeth, wherein said clutch further comprises a resilient finger with a stop projecting into a channel whereby rotation of the worm gear causes relative movement of the stop along the channel and wherein, when the worm gear is rotated in one direction until it runs out of teeth with which to engage, thereby preventing further rotation of the worm gear, said stop abuts one end of the channel and is resiliently deformed whereby it tends to bias the worm gear in the opposite rotational direction to enable the teeth to re-engage the worm gear when rotation of the latter is reversed.

In place of the separate resilient ratcheting member as found in a prior art, the clutch of the invention has a finger-like resilient projection which preferably cooperates with an arcuate groove disposed underneath the housing.

The above mentioned objects may be satisfies in the present invention in which the clutch means includes a worm gear having a portion of the teeth cut away to form a blank area, a finger-like resilient projection member extending in and along an elongated groove disposed in a rotor gear and a stopper attached or arranged integrally on the top end of the finger, which is protruding upwardly into an arcuated groove disposed underneath a housing.

The arrangement is such that when the tooth adjacent the blank area on the worm gear disengages the teeth or threads of the worm screw, the rotation of the worm gear is stopped whenever the stop arranged on the resilient finger-like projection slides to touch one end wall of the arcuate groove disposed in the housing and biases this tooth back toward the threads to permit the worm screw thread to engage the teeth of worm gear if the direction of rotation of the worm screw is reversed.

Preferred embodiments of the present invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with accompanying drawings in which: Figure 1 is a perspective view of a multiple turn variable resistor; Figure 2 is a cross sectional view of the variable resistor seen along the line ll-ll of Fig. 1; Figure 3 is an exploded isometric view partially in section showing the interior of the variable resistor with a housing and a rotor gear being taken away partially; Figure 4 is a plan view of a worm screw and a rotor gear with a housing partially cut away; Figure 5(A) is a plan view of a rotor gear equipped with a projection of finger-like resilient member, (B) is a side view of Fig. 5(A);; Figure 6(AJ is a plan view of rotor gear and a worm screw of another embodiment; Figure 6(B) is a side view of Fig. 6(A); Figure 7 is a plan view of housing showing an arcuate groove engraved therein; Figure 8 is a plan view of a base; Figure 9(AJ, (B), (CJ, (D) indicate an outline sketch of clutch machanism of a worm screw and a rotor gear.

As shown in Figs. 1,2 and 3, a worm screw 4 having the thread 4a engageable with the teeth 8a of rotor gear are arranged inside of a housing 2.

rotor gear 8 is formed or provided at its lower face with a shallow circular recess 15 and a deeper recess or pocket 17 which is trapezoidal in section.

Disposed in the pocket 17 and held captive is a helical spring wiper 18. The spring wiper 18 extends radially toward the collector element 24 and contacts the spring wiper and the collector 24 by spanning both of them.

The resistance element 22 is preferably a cermet material in the form of an annul with the ends thereof being connecting to strips of highly conductive termination material 24, 26, 26 and pin terminals 6a, Sb, Sc are connected to termination materials 24, 26, 26 respectively by a connectional means.

The rotor gear 8 is preferably formed of a plastics material.

In the housing 2 an arcuate groove 14 open toward the rotor gear 8 is disposed as shown in Fig. 7. Both ends of the groove are in the form of vertical walls 14a and 14b which will function to withhold a further shifting of the stopper 12 positioned on the top of the finger-like resilient projection 10, as will be explained hereinafter, when the finger-like resilient projection 10 is rotated along the housing groove 14 when the worm screw teeth 4a being in engagement with rotary gear thread 8a.

Fig. 5 further illustrates a plan view of the rotor gear 8 which has a plurality of teeth 8a regularly spaced about the circumference thereof with the exception of blank area 8b. A slit 9 disposed in the rotor gear 8 which is in the form of shoe head starts from the blank area 2b in the direction to plurality of thread 8a and return back toward the blank area 8b, thus forming a configuration of shoe head.

In and along the slit 9 a finger-like resilient projection 10 is disposed. To the top end of the projection 10 is fastened a stopper 12.

Fig. 6(A), (B) illustrate another embodiment of rotor gear 8 having different shape of slit 9' and a finger-like resilient projection 11 on which a stopper 13 is fixed. Except the configuration of the element, as the efficiency and the operation are the same as the preceding embodiment, the detail explanation is eliminated.

Fig. 8 illustrates a plan view of the base 20 on which is arranged arcuated resistance material 22 which is preferably of film materials.

Through terminal materials 26 and central terminal material 24, pin terminals 6a, 6b, Sc are electrically connected to the base 20.

Referring to Fig. 9(A), (B), (C), (D) the operation of the mechanism of the present invention will now be explained.

As shown in Fig. 9(A), when the worm screw 4 is rotated counterclockwise direction as shown by an arrow by applying a driver in the worm screw and the rotor gear 8 is also rotated in the direction as shown by an arrow, teeth 4a of the worm screw 4 and these of the rotor gear engage with each other in turn simultaneously with the rotation of the rotor gear 8, and the helical coil wiper 16 held firmly by the silicon rubber 18, both being arranged in the recess or pocket 17 of the rotor gear 8, slides along the arcuated resistance element 22 and reaches to the edge thereof. While the protruded stopper 12 of rotor gear 8 shifts therewith along the arcuate groove 14 defined in the housing 12 with the result that the stopper 12 is rotated to touch the side wall 14a of the groove 14 of the housing.The gear tooth 8a' located at the border between the blank area 8b is also engaged with one of the teeth 4a of the worm screw 4. And with further rotation of worm screw 4 in the same direction, as shown in Figs. (B) and (C) brings forth a further rotation of the worm gear 8 in an arrow direction with its edge tooth 8a' engaging with one of the worm screw teeth 4a, whereby the finger-like resilient projection 10 equipped with the stopper 12 thereon is shifted together with the rotor gear 8 in the same direction as shown by an arrow. Eventuaily the stopper 12 is shifted to touch onto the end wall 14a of arcuated groove 14 and the finger-like resilient projection 10 is warped or deformed as shown in Fig. 9(B) touching against the wall 14a by dint of the force exerted by the rotor screw 4 and the rotor gear 8.

If the counterclockwise rotation of the worm screw 4 is thus continued, the engagement of the rotor gear teeth 4a with the border tooth 8a' of the worm screw 8 will finally be released and due to the repulsion force of the finger-like resilient projection 10 which is warped by touching against the vertical end wall 14a, the rotor gear 8 tends to be rotated in reverse direction as shown by dotted line in Fig. 7(C) thereby the rotation of the rotor gear 8 comes to a stop. Simultaneously the helical coil spring 16 stops sliding along the resistance element 22.

As shown in Fig. 9(D), whenever the worm screw 4 begins to be rotated clockwise, teeth 8a' of the rotor gear 8 continues to rotate anti-clockwise by engaging with teeth 4a of the worm screw until the stopper 12 disposed on the finger-like resilient projection 10 shifts anti-clockwise to finally push against the inner vertical wall 14b of the arcuated groove 14 to be stopped thereat.

Thus the helical coil wiper 16 is, as heretofore described, able to slide along forward or backward on the arcuated resistance element 22 in accordance with clockwise or anticlockwise rotation of the rotor gear 8 with the cooperation of worm screw.

The clutch means of this invention is simple in structure and efficiently designed such that the stopper disposed on the resilient fingerlike projection shifts along the arcuated groove defined in the housing and stops against end walls of the arcuated grooves by the operation of the rotor gear and the worm screw simultaneously the coil spring wiper slides along the resistance element to be stopped in accordance with the movement of the rotor gear and the worm screw both of them being simple in structure and inexpensive to manufacture.

Claims (9)

1. A clutch for a variable resistance device having a worm gear rotation of which provides relative movement between an electrical contact and a resistance element of the device, said worm gear having peripheral teeth around a part of its circumference for engagement with a worm screw to provide said rotation and the remainder of its circumference being without such teeth, wherein said clutch further comprises a resilient finger with a stop projecting into a channel whereby rotation of the worm gear causes relative movement of the stop along the channel and wherein, when the worm gear is rotated in one direction until it runs out of teeth with which to engage, thereby preventing further rotation of the worm gear, said stop abuts one end of the channel and is resiliently deformed whereby it tends to bias the worm gear in the opposite rotational direction to enable the teeth to reengage the worm gear when rotation of the latter is reversed.

2. A clutch according to claim 1, wherein the resilient finger and stop are carried by the worm gear and the channel is an arcuate channel formed in a housing a which the worm gear is mounted.

3. A clutch according to claim 2, wherein the worm gear is essentially disc-shaped and the resilient finger is formed integrally with the worm gear by cutting through a central portion of the disc, leaving a gap on either side of the disc to allow a degree of bending thereof in the plane of the disc.

4. A clutch according to claim 3, wherein the resilient finger has a curved configuration.

5. A clutch according to claim 3, wherein the resilient finger has a triangular configuration and points towards the non-toothed part of the periphery of the worm gear.

6. A clutch for a variable resistance device, substantially as herein described with reference to the accompanying drawings.

7. A clutch means for a worm gear-actuated variable resistance device having a worm gear for providing relative movement between element and a resistance contact, said worm gear having a circumferential portion of its teeth removed to form a blank area thereon and a worm screw having threads for engaging the teeth of the worm gear whereby rotation of said worm screw causes rotation of said worm gear when the worn1 screw threads engage the teeth of said worm gear, comprises: a clutch means comprised of a groove disposed in a housing and opened toward the rotor gear, both ends of the groove being in the form of vertical walls, a slit disposed in the rotor gear being in the form of shoe head the top of which is positioned toward the teeth of the rotor gear and a resilient projection of a finger-like configuration having a stopper on one end thereof being disposed in and along the slit.

8. A clutch means as is claimed in claim 7, wherein the slit is of square configuration, while the finger-like resilient projection having a stopper thereon is of a triangular configuration protruding in the slit toward the blank area.

9. A worm gear-actuated variable resistance device having a clutch according to any preceding claim.