US3037397A

US3037397A - Adjustable limit stop

Info

Publication number: US3037397A
Application number: US151969A
Authority: US
Inventors: Alton K Allen; Norman C Zatsky
Original assignee: Reeves Instrument Corp
Current assignee: Reeves Instrument Corp
Priority date: 1961-11-13
Filing date: 1961-11-13
Publication date: 1962-06-05
Anticipated expiration: 1979-06-05

Description

June 5, 1962 A. K. ALLEN ET AL ADJUSTABLE LIMIT STOP Filed NOV. 13, 1961 lie. 1

Ma; E2359? 25 I IIIIHIHIIIII: :Illlllllllllllll IIHIIIHII IN V EN TORS Y K Z M m M m United States Patent York Filed Nov. 13, 1961, Ser. No. 151,969 12 Claims. (Cl. 74424.8)

This invention relates tolimit stops and in particular to miniature adjustable limit stops.

Limit stops are frequenly used in servomechanisms to limit the angular travel of shafts, such as the shafts of motors, potentiometers, angular transducers and related devices. These limit stops serve the purpose of preventing damage to these devices by stopping the rotation of the shafts before they reach the end of their travel.

In the design of servomechanisms which are to include a limit stop,.it has been difiicult to readily determine in advance and to set the angular position at which a rotatable shaftshould be brought to a stop. Because of this difi'iculty, it has been the practice to manually adjust the. stop positions of the limit stop after the servomechanism has been assembled. The conventional limit stops found in the prior art are not easily adjusted after installation within a servomechanism. The present invention overcomes this problem by providing an improved limit stop whose limits may be readily adjusted after installation into a servomechanism assembly.

A principal object of this invention is to provide a limit stop whose limits may be easily, adjusted over a wide range.

Another object of the invention is to provide a simple and inexpensive adjustable limit stop whose limits may be adjusted Without disturbing or removing the limit stop from its servomechanism assembly.

A further object of the invention is to provide an adjustable limit stop whose limits may be adjusted by a single adjusting tool.

These and other objects and advantages will become apparent from a study of the following detailed description together with the drawing in which the same reference numerals refer to the same or similar parts, and wherein,

FIG. 1 is a sectional view of the improved adjustable limit stop of the invention as viewed from the side,

FIG. 2 is a sectional view of an alternative embodiment of the invention,

FIG. 3 is a perspective view of the threaded and grooved member forming an integral part of the limit stops of FIGS. 1 and 2, and

FIG. 4 is a perspective view of the threaded spur gear which is an integral part of the limit stops of FIGS. 1 and 2.

Referring to FIG, 1, there isshown a preferred embodiment of the adjustable limit stop having a hollow cylindrical housing or case .11 situated between a first end piece 12 and a second end piece 13. A first bearing assembly 14 is situated within a central opening 15 in end piece 112, and a second bearing assembly 16 is situated within a centrally recessed hole 17 in end piece 13. The first and

second bearing assemblies

14 and 16 are coaxially aligned and support shaft 18 for rotation about a central axis.

A threaded portion 19 of shaft 18 is situated within 7 3,037,397 Patented June 5, 196 2.

FIG. 4- illustrates in perspective spur gear 20 with its.

threaded bore 21.

The teeth 22 of the spur gear are meshed with the teeth 23 of a pinion shaft 24. Pinion shaft 24 is pro vided with

cylindricalends

25 and 26 mounted within the first and

second end pieces

12 and 13, respectively, for rotating the pinion shaft above an axis parallel with the axis of threaded shaft 18. The end 26 of the pinion shaft 24 extends substantially through hole 27 in end piece 13 and is provided with a hexagon shaped hole 28 for receiving a standard wrench for rotating the pinion shaft. A hexagon head cap screw 29 cooperates with a coordinate clamp mounted within end piece 13 for rigidly locking the, angular position of the pinion shaft 24. Other suitable means may be employed for locking the angular position of pinion shaft 24 without departing from the invention.

A member 30 having a threaded bore 31 is carried by the threaded portion 19 of shaft 18. A perspective view of member 30 with threaded bore 31 is illustrated in FIG. 3. 0ne end of member 30 is provided with a U-shaped groove 32 which straddles a cylindrical guiding rod 33 extending parallel to threaded shaft 18. The guiding rod 33 is afiixed between end pieces 12 and '13 by machine screws 34 and 34'. Rod 33 serves the dual purpose of guiding member 30 as it is driven along the threaded portion 19 by rotation of shaft 18 and holding the limit stop together by maintaining the

end pieces

12 and 13 firmly against the ends of the hollow cylindrical housing 11. Another identical rod not shown is placed opposite rod 33 for symmetrically holding the

end pieces

12 and 13 against the cylindrical housing. The guiding rod 33 while guiding member 30 also prevents its rotation. The invention is not limited to the U-shaped groove 32 in member 30 straddling rod 33 and other suitable means may be employed to guide member 30 and to prevent its rotation as shaft 18 is revolved without departing from the invention.

The threaded portion 19 of shaft 18 is provided with a first stop pin 35 mounted in-the threaded portion 19 adjacent the first ball bearing assembly 14, and a second stop pin 36 mounted in the threaded portion 19 adjacent the second ball bearing assembly 16. Stop pin 35 projectsradially from threaded portion 19 by an amount suflicient to engage a third stop pin 37 carried by member 30. Stop pin 37 extends parallel to shaft 18 and projects from each side of member Why a distance greater than the spacing between adjacent threads of the threaded portion 19. Similarly, stop pin 36 projects radially from threaded portion 19 by an amount suflicient to engage a fourth stop pin 38 carried by spur gear 20. Stop pin- 38' extends through and projects from each side of spur gear 20 in a similar manner to pin 37. The adjacent ends of the '

stoppins

37 and 38 project toward each other from the surfaces of member 30 and spur gear 20, respectively, in order to engage each other and prevent the spur gear 20 from binding upon threaded portion 19 which wouldhave resulted if the spacing between spur gear 20'and member 30, during adjustment, were reduced sufiiciently to allow the surface of the spur gear 20'to abut against theadjacent surface of member 30.

Stop pin 35 in threaded portion 19 is located at afixed distance from the end of shaft 18 and is set at a par- 3 ticular angular position in the threaded portion 19 relative to the threads in order to insure that it will overlap stop pin 37 by an amount slightly less than the spacing between adjacent threads of the threaded portion when these two

stop pins

35 and 37 are driven into engagement by rotation of shaft 18. Similarly, stop pin 36 is located at a fixed distance from stop pin 35 and is set at a particular angular position in the threaded portion 19 relative to the threads so that it will overlap stop pin 38 by an amount slightly less than the spacing between adjacent threads of the threaded portion when these two pins are driven into engagement. While stop pin 35 projects upward and stop pin 36 projects downward in FIG. 1, it should be appreciated that the invention is not dependent upon these particular settings of the angular positions of the

pins

35 and 36.

In the operation of the limit stop of FIG. 1, a clockwise rotation of shaft 18 will, for example, cause both the threaded member 30 and the spur gear 20 to be driven together along threaded portion 19 toward end piece 12. Member 30 and spur gear 20 do not rotate as they travel along threaded portion 19 and the spacing between them remains fixed. Stop pin 35 revolves with shaft 18 and stop pin37 travels along with member 30 until the two are brought into engagement. When this condition is met, shaft 18 can no longer be revolved relative to the limit stop assembly in a clockwise direction and this angular position of shaft 18 represents the first of the two limit stops.

However, it is possible to rotate simultaneously the shaft 18 along with the entire limit stop assembly about the axis of the shaft. A circular flange 39 integral with end piece 12 is provided for mounting the limit stop in the conventional servo mount to enable both shaft 18 and the limit stop assembly to be angularly rotated within its mount before the limit stop assembly is permanently locked to the mount. This angular positioning may be done even though shaft 18 carries a gear engaged with the shaft of the motor, potentiometer, angular transducer or other related device whose shaft is to be stopped.

After the first limit has been properly set and the limit stop rigidly locked in its servo mount, the shaft 18 may be rotated in a counter-clockwise direction. Both the threaded member 30 and the spur gear 20 will now be driven together along the threaded portion 19 toward end piece 13. Stop pin 36 which revolves with shaft 18 will be stopped when it engages the stop pin 38 carried by spur gear 20. The angular position of shaft 18 at which

stop pins

36 and 38 become engaged to establish the second limit is determined by the position of spur gear 20 relative to the threaded member 30. It is possible, therefore, to adjust the second limit for shaft 18, in accordance with the invention, by adjusting the relative position of spur gear 20 with respect to threaded member 30. This is achieved by rotation of spur gear 20 about threaded portion 19 by means of the pinion shaft 24.

A hexagon shaped adjusting tool inserted in the head of cap screw 29 releases the coordinate clamp upon the cylindrical end 26 of pinion shaft 24 and permits the pinion shaft 24 to be rotated. The same hexagon shaped tool is inserted in the hexagon hole 28 and pinion shaft 24 is rotated to rotate spur gear 20 through the teeth 22 and 23 until the spur gear is properly positioned on threaded portion 19. In the event that the desired second limit for shaft 18 is required before stop pin 36 has become engaged with stop pin 38, then the pinion shaft 24 is rotated in a direction to cause spur gear 20 to approach end piece 13 until these two stop pins 36 and' 38 are engaged. When the second limit has been properly set, the adjusting tool locks end 26 of pinion shaft 24 by tightening cap screw 29. It will be observed that the spacing between spur gear 20 and threaded member 30 remains fixed when the pinion shaft 24 is locked.

The second limit for shaft 18 with respect to its first limit may be adjusted over a very wide range, from a fraction of a revolution of shaft 18 to a large number of revolutions, depending upon the physical length of the limit stop. The adjustment of the limits is not restricted to complete turns of shaft 18. Only a single adjusting tool for insertion in cap screw 29 and hole 28 is required for setting the second limit.

It is believed apparent that the limit stop of FIG. 1 may be modified by interchanging the member 30 with the spur gear 20 on threaded portion 19 without departing from the scope of the invention. With this modification, the stop pin 38 of spur gear 20 would be translated toward end piece 12 and would engage stop pin 35. The first limit of shaft 18 would, accordingly, be adjusted by setting the pinion shaft 24. The second limit would be reached when the stop pin 37 of member 30 translated toward end piece 13 and so as to engage stop pin 36.

The stop pins 35 and 36 may, of course, be resiliently mounted in threaded shaft 18 to absorb shock and prevent damage to the limit stop without departing from the invention. Similarly, stop pins 37 and 38 may be resiliently mounted in threaded member 30 and spur gear 20, respectively. If desired, the stop pins 35--38 may be made of suitable resilient material to absorb shock.

The invention is not restricted to the particular angular disposition of pinion shaft 24 and guiding rod 33 about the axis of threaded shaft 18 shown in FIG. 1. While pinion shaft 24 and guiding rod 33 are diametrically disposed about threaded shaft 18 in the illustration, it is apparent that the guiding rod 33 could be disposed closely adjacent to the pinion shaft 24 without disturbing the principle of operation of the limit stop.

FIG. 2 illustrates an alternative embodiment of the invention in which the necessity for a guiding rod has been eliminated. In this embodiment, the pinion shaft 24 serves the dual purpose of guiding both member 30 and spur gear 20. The U-shaped groove 32 of member 30 straddles the pinion shaft 24 which guides the member 30 and prevents its rotation. The operation and adjustment of the limit stop of FIG. 2 is identical with the limit stop of FIG. 1. The cylindrical housing 11 is made an integral part of the end piece 13 and the end piece 12 is secured to housing 11 by machine screws 40.

Since many changes could be made in the construction of the above described limit stops and many widely different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illus trative and not in a limiting sense.

What is claimed is:

1. An adjustable limit stop comprising in combination:

(a) hollow cylindrical housing means,

(b) first and second end pieces mounted in the ends of said hollow cylindrical housing means,

(0) first and second bearing means centrally mounted in said first and second end pieces, respectively, and being aligned with the axis of said hollow cylindrical housing means,

(d) a threaded shaft situated within and coaxially aligned with said hollow cylindrical housing means and mounted for rotation within said bearing means.

(2) a spur gear having a centrally threaded bore situated on said threaded shaft.

(f) a longitudinally extending pinion shaft rotatably mounted within said cylindrical housing means between said first and second end pieces, said pinion shaft extending parallel with and displaced from the longitudinal axis of said cylindrical housing means, said spur gear being in mesh with said pinion shaft and being adapted for travelling along said threaded shaft as said threaded shaft is rotated,

(g) a threaded member situated on said threaded shaft.

(h) a longitudinally extending guiding rod situated within said cylindrical housing means and aflixed between said first and second end pieces, said guiding rod extending parallel with and displaced. from the longitudinal axis of said cylindrical housing means,

(i) said threaded member situated on said' threaded shaft havingagroovedportionstraddling said guidingrodand being adapted for travelling along said threaded shartas"saia'nrreadea shaft is rotated,

(j) adjusting irieansaflixedto saifd'pinion shaft for rotating said pifiion' shaft and said spur gear to adjust the spacing between said spur gear and said threaded member, and

(k) means for locking the angular position of said pinion shaft to hold the relative spacing between said spur gear and said threaded member fixed as said threaded shaft is rotated.

2. The adjustable limit stop as defined by claim 1 further comprising:

(a) first and second stop pin means affixed to said threaded shaft adjacent said first and second bearing means, respectively, said first and second stop pin means extending radially from the surface of said threaded shaft, and

(b) third and fourth stop pin means affixed to said spur gear and said threaded member, respectively, said third and fourth stop pin means extending parallel to and displaced from said threaded shaft.

3. An adjustable limit stop comprising in combination:

(a) first and second end pieces spaced apart,

(b) first and second bearing means mounted within said first and second end pieces, respectively,

() supporting means coupled to said first and second end pieces for coaxially aligning said bearing means and maintaining said end pieces in fixed relation to each other,

(d) a threaded shaft extending between said first and second end pieces and mounted for rotation within said bearing means,

(e) a spur gear having a centrally threaded bore situated on said threaded shaft,

(f) a pinion shaft rotatably supported between said first and second end pieces and extending parallel with said threaded shaft, the teeth of said pinion shaft being in mesh with the teeth of said spur gear,

(g) a threaded member situated on said threaded shaft, said threaded member having a grooved portion straddling said pinion shaft, said spur gear and said threaded member being guided along said pinion shaft and being driven along said threaded shaft as said threaded shaft is rotated,

(h) adjusting means provided on said pinion shaft for rotating said pinion shaft and said spur gear to adjust the spacing between said spur gear and said threaded member, and

(i) means for locking the angular position of said pinion shaft to hold the relative spacing between said spur gear and said threaded member fixed as said threaded shaft is rotated.

4. The adjustable limit stop as defined by claim 3 further comprising:

(b) third and fourth stop pin means afiixed to said spur gear and said threaded member, respectively, said third and fourth stop pin means extending parallel to and displaced from said threaded shaft.

5. An adjustable limit stop comprising in combination:

(a) first and second end pieces spaced apart,

(0) supporting means coupled to said first and second end pieces for coaxially aligning said bearing means and maintaining said end pieces in fixed relation to each other,

(d) a threaded shaft extending between said first and second end pieces and mounted for rotation within said bearing means, l

(1) a threaded member situated on said threaded shaft,

(g) means situated between said first-and secondend pieces and extending parallel to said threaded shaft for guiding said spur gear and said threaded member along said threaded shaft as said threaded shaft is rotated,

(h) said means including adjusting means for rotating said spur gear on said threaded shaft to adjust the spacing between said spur gear and said threaded member,

(i) means for locking said adjusting means to prevent rotation of said spur gear and to hold the relative spacing between said spur gear and said threaded member fixed as said threaded shaft is rotated,

(j) first and second stop pin means affixed to said threaded shaft adjacent said first and second bearing means, respectively, said first and second stop pin means extending radially from the surface of said threaded shaft, and

(k) third and fourth stop pin means afiixed to said spur gear and said threaded member, respectively, said third and fourth stop pin means extending parallel to and displaced from said threaded shaft.

6. An adjustable limit stop comprising in combination:

(a) first and second end pieces spaced apart,

(b) supporting means coupled to said first and second end pieces for maintaining said end pieces in fixed relation to each other,

(0) a threaded shaft extending between and mounted for rotation within said first and second end pieces,

(d) first and second threaded members situated on said threaded shaft,

(e) means extending parallel to said threaded shaft and mechanically intercoupled with said first and second threaded members for guiding said first and second threaded members and preventing their rotation as said threaded shaft is rotated,

(1) said means extending parallel to said threaded shaft including adjusting means for adjusting the spacing between said first and second threaded members, and

(g) locking means coupled to said adjusting means for locking said adjusting means and maintaining the spacing between said first and second threaded members fixed as said threaded shaft is rotated.

7. The adjustable limit stop as defined by claim 6 further comprising:

(a) first and second stop pin means afiixed to said threaded shaft adjacent said first and second end pieces, respectively, said first and second stop pin means extending radially from the surface of said threaded shaft, and

(b) third and fourth stop pin means afiixed to said first and second threaded members, respectively, said third and fourth stop pin means extending parallel to and displaced from said threaded shaft.

8. The adjustable limit stop as defined by claim 1 wherein said threaded shaft situated within and coaxially aligned with said hollow cylindrical housing means includes a non-threaded end portion extending through and projecting beyond said first end piece.

9. The adjustable limit stop as defined by claim 1 wherein said means for locking the angular position of said pinion shaft includes clamp means aflixed to said second end piece.

10. The adjustable limit stop as defined by claim 2 wherein said first and second stop pin means are rigidly attached to said threaded shaft at a fixed spacing therebetween.

11. The adjustable limit stop as defined by claim 5 portion straddling said means extending parallel to said wherein said means situated between said first and secreaded Shaftond end pieces and extending parallel to said threaded References Cited in the file of this patent shaft includes a pinion shaft and a longitudinally extend- UNITED STATES PATENTS ing guiding rod.

2,356,861 L k Au 29, 1944 T e adjustable llmlt StOP 21S defined by clalrn 6 1 74 ig Jagn' 7 1958 wh rein one Of said threaded members includes a grooved 2 37 925 Rowley et a] June 10 195