US3007126A - Rotary potentiometers - Google Patents

Description

Oct. 31, 1961 A. w. FRASER ET AI. 3,007,126

ROTARY POTENTIOMETERS Filed Jan. 13, 1959 2 Sheets-Sheet 1 @55 M LOO/V1. Jk

Oct. 31, 1961 A. w. FRASER ET AL 3,007,126

ROTARY POTENTIOMETERS Filed Jan. 13, 1959 2 Sheets-Sheet 2 A32 5 Fl 6. 9 INVENTORS United States Patent 3,007,126 RQTARY POTENTIQMETERS Alton W. Fraser, Van Nuys, Joseph M. Looney, Jr., Tarzana, and Robert M. Martin, Van Nuys, Caliii, assignors to Technology Instrument Corporation of Acton,

a corporation of Massachusetts Filed Jan. 13, 1959, Ser. No. 786,480 14 Claims. (Cl. 338172) This invention relates to rotary potentiometers and more particularly to (1) improved stop means for limiting rotation of the slider element and (2) means operated by the stop means for actuating switches associated with the potentiometer.

The growing emphasis on miniaturization resulting from the need to reduce the bulk and weight of airborne electronic equipment has necessitated the development of small precision potentiometers that are capable of withstanding sudden shock, have fine resolution, will not fail or become unreliable under continuous use, and can be linked with other electrical or electronic components to form a small compact package.

Unfortunately, the more compact a rotary potentiorneter, the more troublesome it becomes to achieve a construction that permits full resolution without sacrifice of strength, accuracy, or range of output. For the purposes of this specification, full resolution occurs when the slider is capable of scanning the resistance element from one end to the other. Since the output range is proportional to the length of the resistance element, it is desirable to employ as long a resistance as possible. In a rotary potentiometer, this necessitates having the resistance element encompass almost a full circle. Theoretically, of course, the angle covered by the resistance element may be as much as 359 59' 59", the sole requirement being that the resistance stop short of a full circle. In practice, it is very difiicult to achieve full resolution of resistances exceeding 340 in precision otentiometers of relatively small size as, for example, a potentiometer contained in a cylindrical case whose outside diameter is less than one inch. This is due to the difiiculty in providing stops which will allow the slider or contact arm to fully scan the resistance and still prevent it from cov ering a full 360. The stops must be sturdy enough to prevent the slider from exceeding the limits of the resistance; but sturdy stops of necessity are of appreciable size. Heretofore, in otentiometers smaller than one inch in diameter, stops of desired strength have been so large as to limit rotation of the slider arm by as much as 20 degrees.

Accordingly, one of the primary objects of this invention is to provide a rotary potentiometer having novel stop mechanism which permits the contact arm to rotate through an angle up to approximately 359 (or greater if desired, as in the case of a 360 winding with taps at O, 90, 180, and 270 such as is used in a phase shifter) but which also is sufiiciently sturdy to last for the life of the potentiometer.

In practice, it is often necessary to combine a potentiometer and two snap-action switches in such a way that one switch is operated when the contact arm reaches one end of its operating stroke and the other switch is operated when the contact arm reaches the other end of its operating stroke. This is advantageous where it is desired to automatically reverse connections to an electrical or electronic component each time the contact arm reaches one end of its stroke. Heretofore, it has been difiicult to combine the potentiometer and two switches as a single package without sacrificing precision control, range, or compactness. Accordingly, another object of the present invention is to combine a rotary potentiometer employing novel stop mechanism and two snapaction switches in such a manner that the snap-action switches are supported and operated by the potentiometer.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a first form of potentiometer embodying the present invention;

FIG. 2 is a vertical or longitudinal section of the potentiometer of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;

FIG. 3a is an enlargement of a portion of FIG. 3;

FIG. 4 is a cross-sectional view taken along line 44 of FIG. 2;

FIG. 5 is a perspective view of a second form of potentiometer embodying the present invention;

FIG. 6 is a vertical or longitudinal section of the potentiometer of FIG. 5;

FIG. 7 is a plan view of the same potentiometer;

FIG. 8 is a plan view of the same potentiometer with the switches and switch-actuating member removed; and

FIG. 9 is a plan view of the slider assembly.

Referring now to FIGS. 1-5, the first form of the invention comprises three cylindrical casing sections 2, 4, and 6 provided at their adjacent ends with peripheral grooves 8 which function as seats for split rings 10'. The latter, when tightened by screws 12, function to clamp the sections together as a unit. The topmost section 2 has an end wall 14 provided at its center with a tapped opening in which is screwed a bearing sleeve 16. Sleeve 16 surrounds and rotatably supports a shaft 18. Shaft 18 extends through a top end wall 20' formed in casing section 4, and its bottom end is journaled in a bearing sleeve 22 secured in a bottom end wall 24 formed in casing section 6.

Secured to the bottom end of bearing sleeve 16 by means of a non-conductive ring 26 is an annular conductive ring 28. Attached to shaft 18 is a rotor 30* of the split-ring type. A screw 32 functions to frictionally secure the rotor to the shaft. Rotor 30 has a curved spn'ng member 34 provided at each end with rounded contact head 36 which rides on conductive ring 28. Also attached to rotor 30 is a leaf spring contact member 40 which slidably engages a resistance element 42 that is attached to the inside surface of easing section 2. The ends 44 and 46 of resistance element 42 are secured by wire leads (not shown) to the terminals 48 and 50 respectively of a terminal block 52 attached to the outside of easing section 2. The third terminal 54 of the same block is attached by a wire lead 56 to conductive ring 28. Rotor 39 functions to prevent upward relative movement of shaft 18. A split-retaining ring 58 attached to shaft 18 and seated in the upper end of bearing sleeve 16 prevents relative axial movement of the shaft in a downward direction.

Also mounted on shaft 13 but in rotatable relation thereto is a rotatable stop member 61 having a short radial extension 62 which is bent to form 21 depending extension 64. Stop member 69 is held in slidable engagement with the top Wall 20 of casing section 4 by means of a rotor 66. Rotor as is of the split-ring type and is held tightly on shaft 13 by means of screw 68. Rotor 66 has a frusto-conical extension 70. Cooperating with stop member 69 are two spaced depending stop pins 74 and 76 screwed to the to; end wall 20 of easing section 4. Pins 74 and 76 are long enough to be engaged by radial extension 62 of the movable stop member 60 but not so long as to int rfere with extension 76 of rotor 66. It is to be noted that the radial extension 62 is located between pins 74 and 76 and can be moved through an arcuate path equal in length to the are between said pins less the are occupied by the width of said extension 62.

Mounted in opposed slots in the side wall of casing section 6 are two snap-action switches A and B. These switches are of the type having spring-biased actuating buttons, the buttons 80 and 82 of switches A and B respectively being shown in dotted lines in PEG. 3a. As illustrated, switches A and B have three terminals. One terminal 84 is the common terminal. The second terminal 36 is the normally open terminal. The third terminal 88 is the normally closed terminal.

Finger 64 extends down into casing section 6 far enough to be engageable with switch buttons 36 and 32. As seen in FIG. 3a, the buttons 80 and 82 are spaced from each other by an angle slightly less than the angle between stop pins 74 and 76. Thus, finger 64 will engage button 86 of switch A just before it engages stop pin 74 and will engage button 82 of switch 8 just before it engages stop pin 76.

Rotors 3i and 66 and resistance element 42 are so oriented that when finger 64 engages button 80, slider 46 will be at the end 44 of resistance element 42; and when finger 64- engages button 82, slider to will be at the opposite end 46 of the resistance element. Assuming then that switches A and B are reversing switches connected to external circuitry to which is applied the output signal picked off by slider 36, switch A will be actuated when the signal is smallest-pr vice versa, depending on how the input signal is applied to resistance element The stop elements automatically determine the length of the operating stroke of slider 46.

Assuming that stop member 60 is in the position shown in FIG. 3, rotor 66 can be rotated clockwise but not counterclockwise. When rotor 66 is rotated clockwise, its extension 70 will pass first under pin 76 and then under pin 74. As it passes under pin 74, it will engage finger and cause stop member 60 to rotate in the same direction until it is stopped by pin 76. This in turn stops rotor 66 but leaves it free to rotate counterclockwise to engage and drive stop element 60 back to its original position. In eflect, stop element 60 provides a limited amount of lost motion, enabling shaft 18 to be rotated through an angle not otherwise permissible except by the use of relatively small and, therefore, relatively weak stop elements. Yet, the illustrated construction is quite sturdy and dependable. Moreover, should it be desired to increase the size of pins 74 and 76, the same angle of movement for rotors 66 and 30 can be achieved by placing the pins further apart.

The second form of the invention is shown in FIGS. -9 and comprises a casing or housing 1%. Casing 1'56 has a bottom end wall 162 provided with a. central opening 194 and a sleeve 106 formed coaxially with said opening. Secured in opening 164 and sleeve 1436 is a pair of ball bearing members, each consisting of an outer race 163 and an inner race 116. A shaft 112 extends through and is secured to the inner races 11%.

Frictionally seated on the upper end of sleeve 1% is a cap 114 formed of insulating material. The upper surface 116 of cap 114 is flat and embedded therein are three arcuate conductive strips 118, 120, and 122. Extending in the cap from its bottom end and secured to these conductive strips are wire leads 124, 126, and 128. Theseleads extend through a common opening in the casing and are connected to separate ones of the terminals 130 of a terminal board 132 which is attached to the outer side of the casing.

Secured to the inner surface of casing 100 are three separate wire- wound resistance elements 134, 136, and 138. Leads 140 and 142 are attached to the opposite ends of resistor 134 leads 144 and 146 are attached to the opposite ends of resistor 136; and leads 148 and 150 are attached to the opposite ends of resistor 136. These leads also pass through the wall of casing 166" and are also attached to separate terminals 13%).

Attached to shaft 112 in spaced relation to cap 114 is a circular disk 156 constructed of non-conductive material. Secured to the underside or" disk 156 by means of rivets 158 are three equiangulariy spaced conductive contact members 16%, 162, and 164. Tl'iese contact members are constructed of resilient material and include downwardly inclined portions 166 provided with hemispherical contacts 168 that engage the conductive strips on cap 114. The contacts 163 of members 16-0, 162, and 16% contact conductive strips 113, 121 122 respectively. Also attached to each contact member is a pair of spring wire sliders 17%. Sliders 173 extend tangentially of disk 156 and are bent at their free ends to form rounded portions 172 that lightly engage the resistance elements. Sliders 17% of members 166, 162, and i6 3 slidably contact resistance elements 134, 136, and respectively.

Shaft 112 also carries a radially extending pin 174 which is spaced vertically from disk 156. Pin 174- cooperates with a movable stop member which extends across the casing. Stop member 176 has a relatively large central opening 177 through which extends shaft 112. One end 178 of stop member 176 is pivotally secured by a screw 13% to a flat end surface 182 formed by a cavity in the top end edge of the casing. The opposite end of stop member 176 is located in a second cavity also formed in the top end edge 186. Cavity 1556 defines a flat surface 191 on which rests the free end 183 of the stop member. Cavities 18 and are diametrically oppcsed. Casing 166 also has two tapped cores 192- and iint which are axially aligned along a chord of the circle defined by the casing. Set screws 196 and 198 are crewed into these holes. The free end 188 of stop member 176 extends between set screws 1% and 198. The spacing between these set screws determines the angular distance through which stop member 176 may be pivoted. This spacing may be varied by advancing or retracting the screws. However, stop member 176 cannot be pivoted beyond. the limits determined by the difference in diameter of shaft 112 and central opening 177.

Stop member 176 has depending flanges 2% and 292 at its opposite edges. These edges depend far enough to be engaged by pin 1'74 when shaft 112 is rotated. Engagement of pin 174 with these flanges causes pivotal movement of the stop member, the latter pivoting to the extent permitted by set screws 1% and 198.

Casing also has two diametrically opposed slots 206 and 208 formed in its top end. These slots accommodate snap-action switches A and B. Tapped holes 210 are provided for screws 212 which function to secure the switches to the casing. Switches A and B are like the switches shown in the embodiment of FIGS. 1-4, having spring-biased actuating buttons 214 and 216 respectively. Switch A is actuated when button 214 is engaged by flange 290 and switch B is actuated when button 216 is engaged by flange 202.

The several elements are oriented so that switch A is actuated when sliders 1'70 approach the ends of the resistance elements to which are attached leads 140, 144, and 143. Switch B is actuated when sliders approach the opposite ends of the resistance elements to which are attached leads 142, 146, and 150. In practice, set screws 196 and 193 may be set to prevent flanges 200 and 262 from actuating the switches or may be set to stop movement of stop member 176 just as or just after the flanges contact switch buttons 214 and 216. Set screws 196 and 198 act to limit the operating stroke of sliders 170 by limiting the distance through which stop member 176 may be pivoted. Thus, set screws 196 and 198 determine the maximum and minimum values of the voltages picked off by sliders 170.

It is believed to be apparent that by placing bores 192 and 194 in a different position and by changing the length of pin 174, it is possible to increase the angle through which the stop member 176 may be pivoted. Similarly, the switches A and B may be omitted without disturbing the function of limiting the stroke of shaft 112 and sliders 120 which is performed by the cooperative association of pin 174, stop member 176, and set screws 196 and 198.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. Therefore, it is to be understood that the in vention is not limited in its application to the details of construction and arrangement of parts specifically described or illustrated, and that within the scope of the appended claims, it may be practiced otherwise than as specifically described or illustrated.

I claim:

1. In a rotary potentiometer comprising a rotatable shaft, a resistance element arranged in concentric spaced relation to said shaft, a contact element slidably engaging said resistance element, and means connecting said shaft and contact element whereby said contact element will rotate with said shaft, a movable member movably mounted in a plane extending transversely of said shaft, a radially extending arm attached to said shaft, first means on said movable member positioned to be engaged by said arm when said arm is rotated clockwise, whereby said movable member will be moved in a first direction by said arm, second means on said movable member poistioned to be engaged by said arm when said arm is rotated a predetermined amount counterclockwise away from said first means, whereby said movable means will be moved in a second direction by said arm, third means limiting movement of said movable member in said first direction, and fourth means limiting movement of said movable member in said second direction.

2. The combination of claim 1 wherein said movable member is mounted for rotational movement.

3. The combination of claim 1 wherein said movable member is rotatably connected to said shaft.

4. The combination of claim 1 wherein said third and fourth means are adjustable to vary the extent of movement of said movable member.

5. The combination of claim 1 further including first and second switches, means supporting said first switch in position to be engaged and operated by said movable member as it moves in said first direction, and means supporting said second switch in position to be engaged and operated by said movable member as it moves in said second direction.

6. The combination of claim 1 further including a casing surrounding and supporting said resistance element, a bearing member attached to said casing and supporting said shaft, and first and second switches carried by said casing, said first switch having an actuating member positioned to be engaged and operated by said movable member as said movable member moves in said first direction, said second switch having an actuating member positioned to be engaged and operated by said movable member as it moves in said second direction.

7. In a rotary potentiometer comprising a circularly arranged resistance element, a casing surrounding and supporting said resistance element, a shaft, means rotatably supporting said shaft in said casing, an electrical contact member slidably engaging said resistance element, and means for moving said contact member along said resistance element as said shaft is rotated, the improvement comprising an arm on said shaft, a stop element pivotally connected to said casing, said stop element extending across the interior of said casing in a position to be engaged and pivoted by said arm as said shaft is rotated, first stop means for limiting pivotal movement of said stop element in a first direction, and second stop means spaced from said first stop means for limiting pivotal movement of said stop element in a second direction opposite to said first direction.

8. In a rotary potentiometer comprising a circularly arranged resistance element, a casing surrounding and supporting said resistance element, a shaft, means rotatably supporting said shaft in said casing, an electrical contact member slidably engaging said resistance element, and means for moving said contact member along said resistance element as said shaft is rotated, the improvement comprising an arm on said shaft, a stop element rotatably mounted on said shaft, said stop element com prising a disk having a depending finger positioned to be engaged and moved by said arm as said shaft is rotated, and first and second fixed stop means spaced from each other and disposed so as to be engageable directly only by said finger when said shaft is rotated.

9. In a rotary potentiometer comprising a circularly arranged resistance element, a casing surrounding and supporting said resistance element, a shaft, means rotatably supporting said shaft in said casing, an electrical contact member slidably engaging said resistance element, and means for moving said contact member along said resistance element as said shaft is rotated, the improvement comprising an arm on said shaft, a stop element having one end pivotally connected to said casing, said stop element extending laterally across the interior of said casing in a position to be engaged and pivoted by said arm as said shaft is rotated, first stop means attached to said casing in position to be engaged by and block the opposite end of said stop element on pivotal movement of said stop element in a first direction, and second stop means attached to said casing in position to be engaged by and block said opposite end of said stop'element on pivotal movement of said stop element in a second direction opposite to said first direction.

10. In a rotary potentiometer comprising a circularly arranged resistance element, a casing surrounding and supporting said resistance element, a shaft, means rotatably supporting said shaft in said casing, an electrical contact member slidably engaging said resist-ance element, and means for moving said contact member along said resistance element as said shaft is rotated, the improvement comprising an arm on said shaft, a stop element having one end pivotally connected to said casing, said stop element extending laterally across the interior of said casing in a position to be engaged and pivoted by said arm as said shaft is rotated, first stop means attached to said casing for limiting pivotal movement of said stop element in a first direction, and second stop means attached to said casing and spaced from said first stop means for limiting pivotal movement of said stop element in a second direction opposite to said first direction, said first and second stop means being set screws which are accessible externally of said casing and are movable toward and away from each other whereby to adjust the spacing therebetween.

11. In a rotary potentiometer comprising a circularly arranged resistance element, a casing surrounding and supporting said resistance element, a shaft, means rotatably supporting said shaft in said casing, an electrical contact member slidably engaging said resistance element, and means for moving said contact member along said resistance element as said shaft is rotated, the improvement comprising an arm on said shaft, a stop element pivotally connected to said casing, said stop element extending across the interior of said casing in a position to be engaged and pivoted by said armas said shaft is rotated, first stop means for limiting pivotal movement of said stop element in a first direction, second stop means spaced from said first stop means for limiting pivotal movement of said stop element in a second direction opposite to said first direction, two switches attached to said casing, first means on said stop element for actuating one switch when said stop element is pivoted in said first direction, and second means on said stop element for actuating the other switch when said stop element is pivoted in said second direction.

12. In a rotary potentiometer comprising a circularly arranged resistance element, a casing surrounding and supporting said resistance element, a shaft, means rotatably supporting said shaft in said casing, an electrical contact member slida-bly engaging said resistance element, and means for moving said contact member along said resistance element as said shaft is rotated, the improvement comprising an arm on said shaft, a stop element pivotally connected to said casing, said stop element contained Wholly Within said casing and extending across the interior of said casing in a position to be engaged and pivoted by said arm as said shaft is rotated, first stop means for limiting pivotal movement of said stop element in a first direction, and second stop means spaced from said first stop means for limiting pivotal movement of said stop element in a second direction opposite to said first direction, said stop element having an opening through which said shaft extends, said opening being suificiently large to permit said stop element to be pivoted between the limits determined by said first and second stop means.

13. In a rotary potentiometer comprising a circularly arranged resistance element, a casing surrounding and supporting said resistance element, a shaft, means rotatably supporting said shaft in said casing, an electrical contact member slidably engaging said resistance element, and means for moving said contact member along said resistance element as said shaft is rotated, the improvement comprising an arm on said shaft, a stop element rotatably mounted on said shaft between said arm and an end wall of said casing, said stop element comprising a disk having a depending finger positioned to be engaged and moved by said arm as said shaft is rotated, and first and second stop pins anchored in said end wall, said stop pins spaced from each other and disposed so as to be engageable directly only by said finger when said shaft is rotated.

14. In a rotary potentiometer comprising a circularly arranged resistance element, a casing surrounding and supporting said resistance element, a shaft, means rotatably supporting said shaft in said casing, an electrical contact member slidably engaging said resistance element, and means for moving said contact member along said resistance element as said shaft is rotated, the improvement comprising an arm on said shaft, a stop element rotatably mounted on said shaft, said stop element comprising a. disk having a depending finger positioned to be engaged and moved by said arm as said shaft is rotated, first and second fixed stop means spaced from each other and disposed so as to be engageab le directly only by said finger when said shaft is rotated, a pair of switches supported by said casing, one of said switches disposed so as to be actuated by said finger when said stop element is rotated in one direction by said arm, and the other of said switches disposed so as to be actuated by said finger when said stop element is rotated in the opposite direction by said arm.

References Cited in the file of this patent UNITED STATES PATENTS 611,185 Richardson et al Sept. 20, 1898 1,376,841 Tirrill May 3, 1921 1,804,243 Bond May 5, 1931 1,909,664 Douglas May 16, 1933 2,177,482 Hall Oct. 24, 1939 2,616,013 Greenlee Oct. 28, 1952

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