Rotary Variable Resistor

The present invention relates to a rotary variable resistor. More particularly, it relates to a rotary variable resistor of the type wherein a resistance value can be varied by turning a holder for a slider in either its forward or reverse direction by means of a pair of levers mounted on a case.

FIG. 9 illustrates a known structure for turning a slider holder and, as shown, a slider holder 27 is rotated by a lever 28 movable vertically to engage tooth portions 27a of the slider holder in its downward stroke. In its inoperative state, the lever 28 must lie outside the turning range of the tooth portions 27a. Therefore, when the lever 28 is moved to turn the slider holder 27, it moves a distance l before engaging a tooth portion 27a, and this results in considerable play, and the moving stroke of the lever 28 becomes large. Another problem of such structure is that the pitch of the tooth portions 27a cannot be made small and thus the slider holder 27 cannot be turned through a small angle.

The present invention has been made to overcome the disadvantages described above, and has for its object to provide inexpensively a rotary variable resistor of the specified type whose operation is reliable, the stroke of the levers is small and which can turn a slider receiver through a small angle.

In order to accomplish the object, according to the present invention, a rotary variable resistor is provided with a case and two levers which are arranged on opposing sides of said case. Two cams are also provided and one end part of each cam is pivotally mounted on a respective lever. The cams are formed with an indent in a position close to the connection to the levers and edge portion of each cam extends inwardly of said case in such a manner that a cam keeper provided in said case abuts on said indent. A slider holder and a toothed wheel which are rotatably arranged in a central part of said case sliders adapted to engage arcuate resistors formed on an insulating base plate. The levers can be vertically moved to cause the edge portion of the corresponding cam to turn said toothed wheel and said slider holder and thus cause said sliders to slide on said arcuate resistors, whereby a resistance value of said variable resistor is varied.

All of FIGS. 1 to 8 show an embodiment of the present invention, in which:

FIG. 1 is a top view showing the interior of a rotary variable resistor,

FIG. 2 is a front view of the rotary variable resistor,

FIG. 3 is a plan view of the insulating base plate,

FIG. 4 is a bottom view of the slider holder,

FIG. 5 is a perspective view showing the slider,

FIG. 6 is a side sectional view of essential portions showing the state in which a light emitting diode is mounted on the slider holder,

FIGS. 7A to 7E are explanatory views for illustrating the operating states between the cam and the toothed wheel, and

FIG. 8 is a bottom view of the pointer frame, and

FIG. 9 is a view for illustrating the operating state of a prior-art rotary variable resistor.

Hereunder, the present invention will be described in detail with reference to the drawings.

Numeral 1 designates a box-shaped insulating case which is made of a synthetic resin. The insulating case 1 includes an upstanding side wall portion 1a, a lower wall portion 1b, and an upper wall portion 1d. An overhang portion 1c extends upwardly from the top of the lower wall portion 1b, and serves to hold a cover 13 to be mounted on the case 1. The case 1 includes two arms 1a' extending upwardly from opposite sides of the lower wall portion 1b. Between each arm 1a' and the adjacent side wall portion 1a are formed respective recesses 1e and 1e'. A respective elongate lever 2 having a generally square cross-section is disposed in each larger recess 1e, while a respective coiled spring 3 is disposed in each smaller recess 1e' . The fore end of each arm 1a' is provided with a cam keeper 1f extending outwardly toward the respective lever 2. The cam keepers 1f are cantilevered at the fore ends of the arms 1a', with the connection of the respective arm to the side of the lower bottom portion 1b serving as; the fulcrum.

The fore ends of the levers 2 received in the respective recesses 1e form operating portions which project out from the case 1. The rear end of each lever 2 is provided with a cylindrical portion 2b, which bears one end of the respective coiled springs 3. A stopper 2c formed on each respective lever 2 serves to control the swiveling of cams 4 to be described below. Each cam 4 is made of a single metal plate pivotally mounted at its upper end to a respective protuberance 2d formed on each lever 2. When the levers 2 are not pressed inwardly of the case, the upper end portion of each cam 4 is held in engagement with the respective cam keeper 1f of the arms 1a', and its lower end portion has its outward movement restrained by the stoppers 2c of the respective levers 2, as shown in FIG. 1. Tapered edge portions 4b of the cams 4 angle inwardly of the case form the levers 2. Numeral 5 indicates a slider holder which is made of an insulating synthetic resin. The slider holder 5 is unitarily formed with a disc-shaped spacer portion 6 which has a plurality of cam portions 6a formed along the lower part of its peripheral surface, and a toothed wheel portion 7 which overlies the spacer 6 and which is provided with a plurality of small tooth portions 7b at opposing peripheral surface portions. Symbol 5i represents a notch which is provided in the upper portion of the slider holder 4, and symbol 7a a bifurcated engaging portion which is provided at the upper part of the toothed wheel 7. A pointer frame 8 which receives a light emitting diode 9 therein is arranged in the notch 5i. Terminals 10 of the light emitting diode 9 are attached to the spacer 6.

Numeral 11 indicates a leaf spring member which is held between the opposing arns 1a' in proximity to the lower wall portion 1b of the case 1. A projection 11a which is provided substantially in the middle of the spring member 11 is removably engaged with the cam portion of the spacer 6 to give the slider holder 5 a proper torque and to control the stop position of the slider holder 5. Numeral 12 denotes a plurality of optical guide members such as glass fibers held to in the upper overhang 1d of the case 1 at predetermined intervals. The lower end faces of the optical guide members 12 are arranged in an arcuate pattern around the top of the slider holder 5, while the upper end faces thereof are aligned in a parallel arrangment along the top end of the overhand 1d, as shown in FIG. 2. Numeral 13 indicates an insulating cover which closes the open surface of the case 1, and numeral 14 an insulating base plate which closes the other open surface of the case 1. The cover 13 and the insulating base plate 14 are mounted on the case 1 by, for example, welding a plurality of small projections 1g and 1h provided in the case top portion 1d. The lower end of the cover 13 is held by the overhang 1c of the bottom portion 1b of the case 1.

The insulating base plate 14 is specifically shown in FIG. 3. Around a central shaft hole 14a, there are disposed a pair of arcuate resistors 15 which are concentric with the shaft hole and each of which has its end parts connected to terminals 18 by leads 15a and 15b, respectively. A pair of arcuate and concentric leads 16 and 17 are spaced inwards radially of each resistor 15. The leads 16 and 17 are connected respectively to corresponding terminals 18. The resistors 15 and the leads 16 close thereto form a variable resistance circuit. Further, the pair of inner leads 17 form a circuit for supplying current to the light emitting diode 9.

Referring now to the plan view of FIG. 4, a pair of sliders 19 and 20 which are adapted to come into sliding contact with the resistor 15 and the leads 16 and 17 of the insulating base plate 14 are mounted on the rear surface 5b of the slider holder 5.

Symbol 5c represents a supporting shaft which is carried in the shaft hole 14a of the base plate 14. Symbol 5d represents a columnar protrusion for mounting the pointer frame 8 receiving the light emitting diode 9 therein. As shown in FIG. 8, wherein the pointer frame 8 is seen from a side on which the light emitting diode is inserted, symbol 8a denotes a cavity for receiving the light emitting diode 9, symbol 8b a hole for transmitting the light of the light emitting diode 9, and symbol 8c a pair of engaging arms each having a engaging hook 8d at its fore end which are shaped so as to snap over the engaging portion 5e of the protrusion 5d. In mounting the pointer frame 8 on the slider holder 5, the cavity 8a of the frame 8 is placed over the light emitting diode 9 held on the slider holder 5 in advance, and the pointer frame 8 is engaged by a snap fit with the engaging portion 5e of the columnar protrusion 5d in a manner to spread out the engaging arms 8c. Then, the leg portion 8e of the pointer frame 8 is fitted with the bifurcate engaging portion 7a of the toothed wheel 7 as shown in FIG. 1.

As best shown in FIG. 4, the slider 19 for the variable resistor is made of a single resilient metal plate and has a plurality of branched contactor pieces 19a and 19b. It is caulked to the rear surface 5b of the slider holder 5 by protrusions 5f. One of the contactor pieces 19a comes into sliding contact with the resistor 15 of the insulating base plate 14, and the other contactor piece 19b contacts the lead 16, thereby to vary the resistance value of the variable resistor. As shown in FIG. 5, the other slider 20 is constructed of a mounting portion 20b which is provided with a caulking hole 20e for the protrusion 5g of the slider holder 5, a plurality of contactor pieces 20a which extend downwardly from the mounting portion in a curved manner, a pair of engaging pieces 20c and 20c' which extend upwardly from the mounting portion, and a contact plate 20d which extends from one engaging piece 20c horizontally and has a generally sinuous shape. As shown in FIG. 6, the engaging piece 20c and the contact plate 20d are loaded in a square recess 5h formed in the rear surface 5b of the slider holder 5, and the sinuous contact plate 20d lies in resilient contact with the terminal 10 of the light emitting diode 9 within the recess 5h. Accordingly, the contactor pieces 20a of the slider 20 come into sliding contact with the lead 17 of the insulating base plate 14, whereby the contact plate 20d and the pair of terminals 10 of the light emitting diode 9 are electrically conducted. In accordance with the turning of the slider holder 5, the light emitting diode 9 and the pointer frame 8 receiving it therein turn in the same direction. When the pointer frame 8 successively comes into opposition to the lower ends of each optical guide members 12 shown in FIG. 1, the light of the light emitting diode transmitted through the hole 8b of the upper surface of the pointer frame 8 is propagated to the upper end part of the respective guide members 12 and can be seen at the top portion 1d of the case 1.

The present invention is constructed as described above. Now, the operation will be described with reference to FIGS. 7A to 7E. FIG. 7A corresponds to the state of FIG. 1. When, in this state, the operating portion 2a of the lever 2 is pressed inwardly of the case 1, the cam 4 pivots in the direction of the arrow about the fulcrum 2d under the action of the cam keeper 1f, as illustrated in FIG. 7B. That is, an indent 4a of the cam 4 moves along the side surface of the cam keeper 1f, and the edge portion 4b of the cam 4 moves leftwardly to come into engagement with a tooth portion 7b of the toothed wheel 7 as shown in the figure. When, in this state, the lever 2 is further depressed, the edge portion 4b of the cam 4 is moved downwardly so as to turn the toothed wheel 7 in the direction of the arrow (FIG. 7C), and the slider holder 5 moves along with the toothed wheel 7 one step.

At this time, simultaneously with the turning of the toothed wheel 7, the cam portion 6a of the spacer 6 fitting within the projection 11a moves past the projection 11a of the spring member 11. Thus, tactility is afforded.

When, under this state, the depression of the lever 2 is released, the toothed wheel 7 stops in the state in which it has turned a predetermined angle as shown in FIG. 7D. The cam 4 and the lever 2 are restored to their initial positions by the resilience of the coiled spring 3, and the cam 4 abuts against the stopper 2c.

By successively moving either of the levers 2 up and down in this manner, the slider holder 5 can be rotated in accordance with the toothed wheel 7 and in the same direction as that of the latter, and the resistance value of the resistor 15 can be varied by the slider 19. Simultaneously, owing to the turning of the pointer frame 8 receiving the light emitting diode 9 therein, the adjustment position of the resistance value is indicated on the upper end face of the case 1 via the corresponding optical guide member 12 embedded in the overhang top portion 1d of the case 1.

When the slider 1a has reached the end position of the resistor 15, of the cam does not engage tooth portion 7b, but reaches the side part of the bifurcate engaging portion 7a of the toothed wheel 7, as shown in FIG. 7E. In this state, the toothed wheel 7 is prevented from turning any more in the same direction. When the other lever 2 is moved up and down, the slider holder 5 is turned counterclockwise on the basis of the same principle as stated before. By selectively operating the pair of levers 2, disposed on the opposing sides of the case 1, in this way, the slider holder 5 and the pointer frame 8 can be turned through predetermined angles clockwise and counterclockwise, and the resistance values of the pair of resistors 15 can be adjusted mutually and selectively. The adjustment positions of the resistance values are displayed on the upper end face of the case 1 by the single light emitting diode 9.

As set forth above, the rotary variable resistor of the present invention is so constructed that a pair of levers are arranged in a case, that one end part of a cam is pivotally mounted on the projection of each lever, and that in accordance with the movement of the lever, the cam comes into engagement with tooth portions of a toothed wheel so as to turn a slider holder. Therefore, the play are stroke of the lever can be made smaller than in the prior-art structure, and the moving stroke of the lever can be lessened. In addition, the slider holder can be turned through every small angles. The present invention can achieve such functional effects remarkably in practical use.