US2872553A - Mechanical stop for potentiometers - Google Patents

Description

Feb. 3, 1959 HATHELD 2,872,553

MECHANICAL STOP FOR POTENTIOMETERS Filed Sept. 19, 1955 BY M 29 igfy I INVENTOR:

United States Patent MECHANICAL STOP FOR POTENTIOMETERS Lester N. Hatfield, Flushing, N. Y., assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Application September 19, 1955, Serial No. 535,195 1 Claim. (Cl. 201-48) This invention relates to electrical resistors such as potentiometers, and more particularly to mechanical stop arrangements for potentiometers.

The use of precision potentiometers of all types has become very widespread in many different classes of electronic equipment, with the result that much effort has been expended to reduce the cost of precision potentiometers by mass production methods. Since various applications often require potentiometers which have rotary wiper contacts travelling through different total arcs, although otherwise similar in construction, it is desirable to be able to use the same mass-produced resistance element in all such devices, the regulation of the travel are being set as desired for each potentiometer. It is hence a principal object of this invention to provide a mechanical stop arrangement for potentiometers that will permit the use of the same type of resistive element for potentiometers requiring different arcs of travel of the wiper or contact element.

In the conventional rotary potentiometer, the mechanical stop utilized usually consists of a radial pin secured to the wiper or contact shaft, and a stop pin located on an inner portion of the potentiometer front plate, rear plate, or housing. Thus the total are of travel is controlled by the diameter of the radial pin and the diameter of the fixed stop pin and its radial location from the center of the shaft. When the total angle of the arc approaches 360, the diameter of both pins must necessarily be decreased, assuming a fixed radial location. Such a reduction in the pin size will result in a reduction of the amount of torque that can be applied to the wiper or contact shaft without rendering the stop ineffective. It is hence another object of this invention to provide a potentiometer stop that is capable of use where the total are of travel approaches or even exceeds 360, and can be subjected to large torque values without rendering the stop ineffective, or injuring the same.

It is another object of this invention to provide a potentiometer stop arrangement that will permit the use of the same potentiometer for different arcs of wiper contact travel merely by changing a single easily accessible element.

Still another object of this invention is to provide a potentiometer stop mechanism which includes an interchangeable floating plate to determine the arc of travel of the contact element with high accuracy and precision.

The above as well as other objects and advantages of V the invention will be more readily understood from the following detailed drawings, in which Fig. 1 is an explodedperspective view of one embodiment of the stop mechanism.

Fig. 2 is a vertical cross sectional view of the device in Fig. 1, except that all the elements are shown in their actual operating relationship.

Fig. 3 is a perspective view of a modified form of floating plate that may be used in the mechanism illustrated in Fig. 1.

2,872,553 Patented Feb. 3, 1959 Fig. 4 is a plan view of the floating plate illustrated in Fig. 3.

Fig. 5 is a perspective view, partially broken away, of a further modification of the floating plate of Fig. 1.

Fig. 6 is a view similar to Fig. 1 showing a modified arrangement.

Fig. 7 is a schematic side elevation of a further modification.

Referring to Figs. 1 and 2, reference numeral 10 desig nates a front area bearing plate provided with a circular opening 12 for an actuator or contact shaft 14. Mounted on the end of the actuator shaft 14 is a wiper or contact blade 16 having a hub 18. The Wiper blade 16 is secured to the shaft 14 by means of a press fit on the hub 18 by set screws or by any other suitable means.

Front plate It) will normally constitute the front plate of a cylindrical potentiometer casing within which the resistance element, wiper arm 16 and other parts will be mounted. Since the present invention is not concerned with the resistor element itself, or the casing, these parts are shown diagrammatically, the resistor being indicated at R and the casing at C in Fig. 1.

Situated below the wiper blade 16 and also rigidly mounted on the shaft 14 is a circular shaft stop plate 20 provided with a center hole to pass the shaft 14. The underside of the shaft stop plate 20 is provided with an arcuate slot 22 of rectangular cross section. For the purpose of engagement with a stop member to be described in more detail below, there is provided a slender bar, pin or strut 24 bridging the arcuate groove 22 on one side only of the shaft stop plate 20; i. e., at a single radial location in the groove.

Between the shaft stop plate 20 and the front plate 10 there is situated a floating plate 26. The floating plate 26 may be in the form of a thin metal disc having a center opening for receiving the shaft 14, the center opening being sufliciently large to permit the plate 26 to rotate freely about the shaft 14, and its position along the shaft 14 determined in relation to pin 24 and pin 32 by means of spacers or other securing devices. The floating plate 26 is provided near its periphery with stop pins 28 and 29 which project toward the shaft stop plate 20 and which, when the parts are assembled in operative relationship, enter the arcuate slot 22 in order to engage pin or strut 24 upon relative rotation between the shaft stop plate 22'} and the floating plate 26. Also situated near the periphery of the floating plate 26 and extending in the direction of the front plate 10 is a third stop pin 30. The relative angular placement of stop pins 28, 29 and 30 is determined by the maximum extent of are it is desired to move the wiper or contact blade 16.

As has been said, the stop pins 28 and 29 are meant to engage the pin or strut 24 bridging the arcuate slot 22. The depending stop pin 30 is mounted for cooperation and contact with a further stop pin or lug 32 mounted fixedly upon the front area bearing support 10.

The assembly and operative relationship of the parts is clearly disclosed in Figs. 1 and 2. The floating plate 26 is so positioned that upon rotation of same stop pin 30 will engage stop pin or lug 32. The relative positioning of floating plate 26 and shaft stop plate 20 is such that stop pins 28 and 29 enter the arcuate slot 22 and engage pin or strut 24 upon relative rotation of the plates 20 and 26. As may be seen in Fig. 1, pin or strut 24 is free to traverse the angle 31 upon such relative rotation. The shaft stop plate 20 is secured to the actuator shaft 14 and of course is so positioned that the arcuate slot 22 faces the front plate 10. It will be understood that the shaft 14 is mounted for rotational movement upont front plate 10, and that positioning washers or spacing means may be included between the elements of the assembly, if desired.

The operation of-themechanism is simple and straightforward. When the actuator shaft 14 and shaft stop plate are rotated in a counter-clockwise direction (as viewed in Fig. 1), strut 24 engages pin 28 and thereby causes floating plate 26 to rotate in a counter-clockwise direction until pin 36 strikes pin or stud 32. The shaft 14 is then at one limit of its travel. When the shaft 14 is rotated in the other or clockwise direction (as viewed in Fig. 1), plate 20 rotates with respect to floating plate 26 until strut 24 engages pin 29, the relative rotation between the two plates equalling the angle 31 between the pins 23 and 29 (approximately 60 as shown in Fig. 1). Upon the engagement of strut 24 with pin 29, the floating plate 26 is rotated until pin 30 engages pin or stud 32 as a result of clockwise rotation, the shaft 14 then being at the other limit of its travel. It will be seen that the relative rotation between floating plate 26 and front plate 10 amounts to 360 less the lateral thickness of the pins 30 and 32. As stated above, the relative rotation between floating plate 26 and shaft stop plate 2% equals the angle 31 between pins 28 and 29. It thus becomes apparent that the shaft 1 is allowed to rotate through an angle greater than 360, namely the summation of the relative rotational displacements between the plates 2! and 26 and plates 26 and 10.

A greater rotational displacement between the shaft 14 and front plate 10 may be achieved with the structure of Fig. l by merely repositioning the floating plate 26 so that the strut 24 traverses the complementary portion of the periphery of plate 26, that is, the larger angle between the pins 28 and 29, instead of the smaller angle 31. If the pins 28 and 29 are placed closer together, with strut 24 positioned so as to traverse the larger angle between same, the obvious result is that of greater rotational displacement. The limit of such alteration is reached when the two pins 28 and 29 coincide, that is, when there is but one such pin on the upper face of floating plate 26. In this limiting position, the maximum rotation of shaft 14 Withrespect to front plate 10 is almost 720.

If an even greater displacement is desired, as may be in certain servo applications, additional floating plates may be included in the assembly in such manner that each of the plurality of floating plates is in operative (pinengaging) connection with an adjoining plate, thereby affording approximately 720 of additional displacement per plate.

Within the limits of variation afforded by each floating plate that may be utilized, the precise degree of rotation allowed may be set by the angular displacement between the stop pins of such plate. Adjustment of the relative angular positioning of stop pins may be accomplished by the use of movable stop pins or alternatively, and more desirably from the standpoint of practicability, such adjustment may be accomplished by the replacement of a given floating plate by another floating plate of similar functional characteristic but whose stop pins are positioned at a different relative angular displacement. In this manner, changes in the maximum permissible rotation of the potentiometer shaft may be accomplished by merely interchanging floating plates.

An alternative form of floating plate is illustrated in Figs. 3 and 4. In this embodiment, the floating plate 34 is provided with stop members 36, 33, 4t and 42 in the form of tabs which have beenstamped or punched from the disc itself. This type of construction is simple and may be produced economicallyby a metal stamping process or the like, and thus the limits of angular movement in production items may be readily controlled as to accuracy without-tedious and expensive manual adjustment. The stopmembers 36 and 38 are adapted to cooperate with pin or strut 24 in a manner similar to the relation between-the stop pins 28 and 2? and said strut, and stop members 40 and 42 cooperate with stop pin 32 in a manner similar to that described in connection with stop pins 30 and '32. It will be understood that the ,stop

members 36 and 38 define the limits of travel ofpin or strut 24 with respect to floating plate 34, and stop members 40 and 42 similarly define the limits of travel of floating plate 34 with respect to stop pin 32. As in the case of the previously described embodiment, additional relative rotational displacement may be had between shaft stop plate 2}) and front plate 16 by the inclusion of additional floating plates in the assembly. Conversely, this displacement may be restricted by placing closer together the stop members 36 and'38 or the stop members 40 and 42, or both.

As will be obvious to those skilled in the art, the primary reason for the inclusion of a pair of stop members of the stamped tab type in place of the single stop pins of Figs. 1 and 2 is due to the fact that the stamped tabs offer but one positive'and accurately defined active surface. In order to obtain accuracy of operation, it is therefore necessary in this latter embodiment to provide a pair of oppositely directed stop members on both sides of the floating plate 34.

Fig. 5 shows a further modification of the floating plate of Fig. l, which modification is similar to that of Figs. 3 and 4 except that the stop member 46 of the floating plate 44 in Fig. 5 is struck up in such ganner as to present an accurately positioned stopping surface on either side of the stop member. in the use of a floating plate of this type the strut 24 of the shaft stop plate 26 engages either side of stop member 46 in a positive fashion, similar to the action of the stop pins 23 and 29 of Fig. 1. Thus it is not necessary to provide pairs of stop members as needed in the modification of Figs. 3 and 4, since there are no longer any cam-like surfaces which may be presented to the cooperating strut 2 5. Obviously, this type of struck-up tab or stop member may equally well be used in cooperation with the stop pin or lug 32 of Fig. 1.

Fig. 6 of the drawings shows a further modification in which the plate 2% is replaced by a simple radial pin 24 secured directly to shaft 14 as by being pressed into a suitable radial hole in the shaft. Obviously, such a pin 24 could equally well be secured to a sleeve or bushing which is in turn fastened to the shaft 14 as by set screws or the like. In Fig. 6, only the parts of Fig. l necessary to show this modification are included, as it will be understood that the casing and resistor element will occupy the same relative positions as in the former figure.

it will also be obvious to those skilled in the art that while Fig. 1 shows the pin 2 and floating plate 26 arranged between the wiper arm 16 and the bearing plate or cover it), it is equally feasible to arrange the pin 24 and plate 26 between the wiper arm and the casing C. In this case, as shown schematically in Fig. 7, the stop element 32' would be secured to the underside of the end of easing C, rather than to the cover plate iii.

While the invention has been described herein in connection with certain preferred embodiments and procedures, it is to be understood that these are given by way of illustration and example and that the invention itself is not limited thereto except insofar as required by the scope of the appended claim.

What is claimed is:

In a potentiometer of the type having an arcuate resistive element for contact by a wiper arm, the combination comprising a front bearing support having an opening therethrough, an actuator shaft positioned for rotation within said opening, a wiper arm mounted on said actuator shaft, a shaft stop plate between said wiper arm and said front bearing support, said shaft stop plate mounted on said actuator shaft for rotation with said shaft, 21 floating plate between said shaft stop plate and said front bearing support, said floating plate loosely mounted on said actuator shaft to permit free rotation of said shaft with respect thereto and having a pair of 5 6 spaced independent stop elements projecting from one References Cited in the file of this patent fi f F 2 21 igs? and adsiligla 2 g: UNETED STATES PATENTS en pro1ec1n re 18 o ace, an sop m m i on said stop plate and said front bearing support for co- 01,710 g fi g g acting respectively with the stop elements projecting 5 2156'O67 i i 3 from the opposite faces of said disc. 2591650 W1 lams FOREIGN PATENTS

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