US3930133A

US3930133A - Limit switch assembly

Info

Publication number: US3930133A
Application number: US517471A
Authority: US
Inventors: Harry E Sulzer
Original assignee: Quaker City Gear Works Inc
Current assignee: Quaker City Gear Works Inc
Priority date: 1974-10-24
Filing date: 1974-10-24
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30
Also published as: JPS5165369A

Abstract

A limit switch assembly is disclosed in this application and includes a slider member adapted to slide with axial movement of an input shaft and having at least one adjustable cam member carried thereon for cooperation with a pivoted actuator member located adjacent to and normally spaced from an electrical switch connected in a control circuit. In operation, movement of the input shaft causes corresponding movement of the slider and cam members. When the input shaft moves to its limit position, the cam member pivots the actuator member into engagement with the switch member thereby actuating the control circuit. By adjusting the cam member, the spacing between the actuator member and the switch member is adjusted whereby the limit position of the input shaft is also adjusted.

Description

United States Patent 1 Sulzer [451 Dec. 30, 1975 1 LIMIT SWITCH ASSEMBLY [75] Inventor: Harry E. Sulzer, Warminster, Pa.

[22] Filed: Oct. 24, 1974 [21] App]. No.: 517,471

[52] U.S. Cl 200/47; 310/68 B; 318/475 [51] Int. Cl. H01H 3/16 [58] Field of Search 200/47, 153 LA, 153 LB;

Primary ExaminerRobert K. Schaefer Assistant Examiner-M. Ginsburg Attorney, Agent, or Firm-John W. Logan, Esq.

[5 7] ABSTRACT A limit switch assembly is disclosed in this application and includes a slider member adapted to slide with axial movement of an input shaft and having at least one adjustable cam member carried thereon for cooperation with a pivoted actuator member located adjacent to and normally spaced from an electrical switch connected in a control circuit. In operation, movement of the input shaft causes corresponding movement of the slider and cam members. When the input shaft moves to its limit position, the cam member pivots the actuator member into engagement with the switch member thereby actuating the control circuit. By adjusting the cam member, the spacing between the actuator member and the switch member is adjusted whereby the limit position of the input shaft is also adjusted.

16 Claims, 5 Drawing Figures U.S. Patent Dec. 30, 1975 LIMIT SWITCH ASSEMBLY This invention relates to limit switch assemblies for limiting axial movement of an input shaft, particularly a rotary drive shaft movable axially in accordance with torque developed therein. I

Various mechanical devices include a movable shaft or similar member movable axially to a limited extent and which require that when the'shaft has moved to its limit position, a signal, usually a stop signal to stop the movement of the shaft, should be provided. for example, a rotary drive shaft is usually driven by a motor developing a torque which is applied to an output device through the drive shaft. During application of the torque, axial thrust is developed in the shaft causing it to move in the axial direction. Of course, the movement of the shaft is proportional to the torque applied through the shaft so that a limit switch assembly sensing movement of the shaft can be used to develop a signal to stop the application of the torque when the movement of the shaft corresponds to or slightly exceeds the maximum allowable torque which can be delivered to the output device or by the motor.

Certain known limit switch assemblies usable in applications of the type noted above include arrangements for adjusting the limit position at which the signal is developed. These known limit switch assemblies, however, generally require the use of tools and, in some arrangements, the disassembly of portions of the switch assembly to make the adjustment. Obviously, situations can arise, particularly in the environment in which the devices are used, wherein the tools are not available and/or wherein the available time is limited. In those situations, adjustment of the switch assemblies is impractical and may be impossible.

Further, known limit switch assemblies that include adjusting arrangements are operative to allow adjustments whereby the maximum allowable movement of the shaft can be exceeded. Thus, a mistake on the part of the operator making the adjustment could result in damage to the shaft or its associated input and/or output devices. In the example noted above wherein the limit switch assembly is utilized to limit the torque which can be applied to the shaft, such a mistake could result in damage to a relatively expensive gear arrange ment used in conjunction with the shaft or in damage to the equipment being driven by the apparatus.

Accordingly, it is an object of this invention to provide a limit switch assembly that allows for the easy adjustment of the limits of travel of an axially movable shaft.

It is another object of this invention to provide a limit switch assembly that cannot be adjusted to allow movement of the shaft beyond its maximum design limits or beyond a predetermined set limit.

It is still another object of this invention to provide a limit switch assembly that is particularly adapted for use in limiting the torque which can be developed in a rotary drive shaft.

Finally, it is an object of this invention to provide a limit switch assembly that is simple, economical, rugged and easy to use.

These and'other objects of this invention are accomplished by providing a limit switch assembly including slider means movable with an input shaft member whose axial movement is to be limited. Carried on the slider means for movement therewith is cam means operatively engaged with actuator means for adjustably spacing the distance between the actuator means and switch means connected in a circuit. In certain positions of the slider means, the cam means spaces the actuator means from the switch means and in one position of the slider means, corresponding to the limit of movement of the input shaft member, the cam means moves the actuator means into engagement with the switch means and actuates the circuit whereby an appropriate signal may be developed. The initial spacing, that is, the spacing before any movement of the shaft, between the actuator means and the switch means is adjustable by the cam means so that the limits of move ment of the shaft can be adjusted.

Preferably, theswitch assembly includes another set of cam means, actuator means and switch means, one set being operative to limit movement of the shaft in one direction and the other being operative to limit movement of the shaft in another direction. Further, the cam means is rotatable to vary the initial spacing between the actuator means and the switch means and is readily locked in any position or unlocked for movement from any position by easily manipulated locking means without the use of tools. The cam means further includes a cam member having a high point and a low point and is arranged so that the high point is operative to initially space theactuator means and the switch means a distance corresponding to the maximum allowable design displacement of the shaft and so that the low point is operative to allow the actuator means to engage the switch means so that no displacement of the shaft can occur.

For a better understanding of the invention, reference is made to the following description of a preferred embodiment, taken in conjunction with the figures of the accompanying drawing, in which:

FIG. 1 is a side view partially in section of a limit switch assembly in accordance with this invention operatively associated with an input shaft assembly;

FIG. 2 is a plan view of a portion of the limit switch assembly illustrated in FIG. 1 and taken generally along line 2-2 thereof;

FIG. 3 is an end view of the limit switch assembly illustrated in FIG. 1 and taken generally along line 3-3 thereof; I

FIG. 4 is a view generally similar to FIG. 2 of the limit switch assemblyillustrated in FIG. 1, but with portions thereof shown in section; and

FIG. 5 is a sectional view of a portion of the limit switch assembly taken generally along line 5-5 of FIG. 4.

Referring to FIG. 1 of the drawing, there is illustrated an embodiment of the invention particularly adapted for use as a torque limiting switch assembly, it being obvious, as noted above, that the movement of a shaft member in various other mechanical devices could be limited by an assembly in accordance with this invention. Accordingly, there is illustrated an input shaft assembly 10 operatively associated with a limit switch assembly 12, the latter including a slider assembly 14 operatively associated with input shaft assembly 10 and on which is carried a pair of

cam assemblies

16, 16, each operatively associated with an

actuator assembly

18, 18 for

actuating switch assemblies

20, 20 and signaling circuits in which they are connected. As will be made clearer hereinafter, each cam means 16 is movable with slider means 14 and, accordingly, input shaft assembly 10 to limit the movement of the shaft assembly through its associated actuator assembly 18 and switch assembly 20.

Still referring to FIG. 1 of the drawing, input shaft assembly includes an input shaft 22 formed with a worm 24 intermediate its ends and driven by a motor 26 through suitable gears 28 and 30 for changing the speed of the shaft relative to the speed of the motor.

Operatively engaged with worm 24 is an output wormwheel 32 which transmits power from motor 26 to an output device (not shown). It should be noted, at this point, that motor 26 may be of any suitable type including an electrical control circuit for controlling its operation and that output wormwheel 32 may be connected to any suitable output device.

Still referring to FIG. 1, at one end input shaft 22 is rotatably mounted in a suitable bearing assembly 36 carried on a frame member 34 which may be the wall of a housing for the input shaft assembly. At its other end, input shaft 22 includes an enlarged cylindrical portion 38 rotatably mounted in a suitable bearing assembly 39 carried on a frame member 41 which may be part of the above-noted housing. Cylindrical portion 38 is formed with a bore 40 in which is received a shaft 42 extending from slider assembly 14 of limit switch assembly 12. Suitable bearing assemblies 44 and 46 are mounted between bore 40 and shaft 42, are spaced apart by a radially extending flange 48 formed on a shaft 42 and are secured in place by a retaining ring 50 so that relative axial movement of the shafts is precluded. When motor 26 is operative, shaft 22 is driven about

bearing assemblies

36 and 39 and also about bearing assemblies 44 and 46 and torque is applied to output wormwheel 32. As torque is developed in shaft 22, axial thrust is also developed which causes some axial movement of the shaft, the direction of which is dependent, of course, on the rotational direction of the shaft. If the torque developed by motor 26 exceeds a certain limit, the thrust in shaft 22 will cause its movement beyond a certain corresponding limit position which is sensed by limiting switch assembly 12 to actuate one of the signaling circuits and shut off motor 26.

Limiting switch assembly 12 includes a housing formed by a pair of

end plates

52 and 54 secured in spaced apart relationship by suitable fasteners such as stripper bolts 56 and is secured to frame member 41 in axial and radial alignmentv with shaft 22 by suitable fasteners 60 extending through end plate 52 and housing 41. Each

end plate

52 and 54 includes a central opening 55 through which shaft 42 extends. Completing the housing for limit switch assembly 12 are

side plates

62,62 which are secured to

end plates

52 and 54 by suitable fasteners 64. Spaced from each side plate 62 and extending parallel thereto is a coverplate 66 which is secured to the side plate by suitable fastener assemblies 68 which include spacer sleeves or other suitable spacer means.

Located within the central cavity defined by the housing is the slider assembly 14 which, in addition to shaft 42, includes a slider plate 70 slidably mounted on the smooth shank portions of stripper bolts 56. In the preferred embodiment, slider plate 70 has openings 71 through which stripper bolts 56 extend. A central opening 72 formed through slider plate 70 receives shaft 42 and the shaft is secured to the plate by a key arrangement 74 and retaining ring arrangement 76 to preclude relative rotary and axial movement, respectively, of the shaft and the plate. A disc spring assembly 78 bears between one face of slider plate 70 and the interior face of end plate 52 and a second disc spring assembly 80 bears against the opposite face of the slider plate and the interior face of end plate 54. Acting together the spring assemblies exert a centering force locating slider plate in the interior of the housing when no external load is acting on the slider plate. However, when input shaft 22 moves axially and, in turn, causes movement of shaft 42, the slider plate 70 is movable against the spring assemblies.

As noted previously there are two sets of cam, actuator and switch assemblies associated with the slider assembly and it is now noted that each set is the same except that one is a mirror-image of the other so that one set is operative to limit movement of shaft 22 in one direction and the other is operative to limit movement of the shaft in the other direction. Accordingly, like reference numerals will be used in the following description for like parts of the two sets.

Each cam assembly 16 includes a pin 82 extending from the side of slider plate 70 through a suitable elongated opening 84 in side plate 62, and in opening 85 in cover plate 66 to a point adjacent the outer surface of the cover plate. Each pin 82 carries a locking pin 86 extending transverse to the longitudinal axis thereof for a purpose which will be explained hereinafter. Rotatably carried on each pin 82 is a sleeve 88 formed at one end with a series of notches 90 and at the other end with radially projecting disc member 92. Intermediate the ends of each sleeve 88 is a cam 94 in the shape of a circular member eccentrically formed on the sleeve. Thus, each cam 94 has a point of minimum projection from sleeve 88 or low point 87 and a point of maximum projection from sleeve 88 or high point 89 spaced from the low point by 180 along the circumference of the cam. At its free end, each pin member 82 is threaded and cooperates with a nut member 96 including an enlarged bearing surface 98 which may be in the form of a flange on the nut or a washer and which retains a spring washer 100 in engagement with disc member 92 for exerting force on sleeve 88. If nut member 96 is tightened sufficiently, spring washer 100 retains the roots of notches 90 in engagement with locking pin 86 and precludes rotation of sleeve member 88 and cam 94 about pin member 82. By merely loosening nut member 96, which can normally be done by hand without the use of any tools, the force exerted by disc spring 100 can be reduced so that sleeve member 88 and cam 94 may be rotated to other desired positions.

As noted previously, each actuator assembly 18 is located adjacent a cam assembly 16 and, more particularly, each actuator assembly is mounted adjacent one of the cams 94 and includes a bellcrank 102 having a first leg 104 adjacent its associated cam member and a second leg 106 extending at a generally right angle thereto adjacent its associated switch assembly 20. At the intersection of each of the

leg members

104 and 106, each bellcrank 102 is pivoted on a pin member 108 extending from side plate 62. Each

leg member

104 and 106 is formed with a threaded opening in which is carried suitable adjusting screws 110 and 112, respectively. A suitable lock nut 114 may be associated with each adjusting screw 112 to secure the adjusting screw in a desired position. Biasing each bellcrank 102 to a first position out of engagement with its associated switch assembly 20 is a spring 116 connected at one end to a pin member 118 carried by side plate 62 and at its other end to a portion of leg 106. In the first position, switch assemblies 20 have not been actuated so that the circuits in which are connected are inoperative; however, when either cam 94 pivots its associated bellcrank 102 a sufficient distance, the associated adjusting screw 1 12 is in a second position bearing against a plunger 120 extending from its associated switch assembly 20, the circuit in which it is connected is activated and a signal is developed which in the embodiment disclosed herein would stop motor 26.

In operation, as motor 26 drives input shaft 22 through gears 28 and 30, worm 24 drives wormwheel 32 and the applied torque is operative to develop axial thrust in the input shaft which causes axial movement of the shaft in one direction or the other depending on the direction in which the shaft is rotated. Axial movement of shaft 22 is dependent on the axial thrust therein which is, in turn, dependent on the torque developed therein so that the axial movement of the shaft is proportional to the torque output of motor 26. As shaft 22 moves in the axial direction, its movement is transmitted to shaft 42 which causes movement of slider member 70 and

cam assemblies

16, 16. As

cam assemblies

16, 16 move, one cam 94 moves against adjacent adjusting screw 110 pivoting its associated bell crank 102 about pin 108 and moving the associated adjusting screw 112 closer to plunger 120. The other cam 94 is moved away from its associated adjusting screw 110 so that the associated spring 116 retains the associated bell crank 102 in its first position. Eventually, when sufficient torque is developed by motor 26, the one cam member has pivoted its associated bell crank 102 to the second position wherein adjusting screw 112 bears on plunger 120 actuating switch assembly 20 so that the circuit in which it is connected develops a stop signal shutting off the motor. By adjusting the

cams

94, 94, the appropriate spacing between each adjusting screw 112 and its associated plunger 120 can be selected so that the stop signal is developed when the motor is developing the maximum torque allowable for the application in which the limit switch assembly is being used.

To initially adjust limit switch assembly 12, nut members 96 are loosened and cams 94 are rotated until high points 89 bear on their associated adjusting screws 1 10. Then, adjusting screws 112 are adjusted so that they bear on their associated plungers 120 and just close switch assemblies 20. Adjusting screws 112 are now locked in position by lock nuts 114. Rotation of

cams

94, 94 to any other position allows bell crank 102 to pivot about pins 108 and moves legs 106 away from plungers 120 and, accordingly, adjusting screws 112 are moved to their first positions spaced from the plungers. When the appropriate points on cams 94 bear on adjusting screws 1 l0, nut members 96 are tightened to urge notches 90 into' locking pins 86 and lock the cams in place. For further adjustments, nut members 96 can be loosened and the cams rotated to a new position and locked in place by tightening the nut members.

The appropriate setting of cams 94 may be readily determined by providing suitable indicia on the outer surface of disc member 92 which is correlated with the maximum allowable torque which can be applied to shaft 22. Thus, the low point of the cam would correspond to 100% of the allowable torque applied to shaft 22 and the high point on cam 94 would correspond to a zero setting wherein no torque would be applied to the shaft. By graduating the indicia around the 180 arcuate distance between high point 89 and low point 87 of cams 94, according to percentage points, the

correct setting of the cams can be determined, Thus, if the maximum allowable torque which can be applied to shaft 22 is divided into the desired torque limit which should be applied in the particular application of switch assembly 12, the desird torque limit can be expressed as a percentage of maximum torque and the cams can be adjusted until the indicia indicates that the setting corresponds to the determined percentage. Thus, the cams can never be adjusted to allow an output greater than that is, greater than the maximum allowable torque which can be applied.

It should be noted, that cam assemblies 16 and their associated actuating assemblies 18 and switch assemblies 20 have been illustrated as extending from opposite sides of slider plate 70, but that the noted assemblies could be so constructed and arranged that each extends from the same side of the slider plate. In certain embodiments of the invention the latter arrangement may be preferred since it facilitates access to the cam assemblies. The arrangement illustrated in the drawing has been specifically disclosed since it facilitates an understanding of the invention by allowing for greater clarity in the drawing. Also, it should be noted that while two cam assemblies 16, actuating assemblies 18 and switch assemblies 20 have been described, certain applications may require that only one limit be established so that only one cam assembly, actuating assembly and switch assembly need be provided.

In view of the above, it can be seen that a limit switch assembly is disclosed which is usable for adjustably limiting movement of an input member wherein adjustments can easily be made without the use of tools. Further, it can be seen that a limit switch assembly has been disclosed wherein an adjustment to a limit greater than a maximum limit cannot inadvertently be made. Finally, it can be seen that each limit position can be adjusted independently so that limits at each end of the range can differ.

While in the foregoing there has been described a preferred embodiment of a limit switch in accordance with this invention, it should be obvious to one skilled in the art that various modifications can be made without departing from the true spirit and scope of the invention as recited in the appended claims.

I claim:

1. A limit switch assembly comprising slider means movable with axial movement of an input shaft, cam means carried bysaid slider means for movement therewith and actuator means located adjacent switch means and having a first position spaced from said switch means and a second position in engagement with said switch means, said cam means being engaged with said actuator means in said first and second positions thereof and being operatiave to move said actuator means from said first position to said second position when said slider means moves in one direction, whereby a limit signal is developed, said cam means further being adjustable whereby the spacing between said first and second positions of said actuator means is adjustable.

2. A limit switch assembly in accordance with claim 1 wherein said slider means includes a slider plate and spring means bearing on opposite sides thereof for locating said slider plate.

3. A limit switch assembly in accordance with claim 2 wherein said slider plate is connected to shaft means extending therefrom and adapted to be secured to said input shaft for movement therewith.

4. A limit switch assembly in accordancewith claim 3 wherein said shaft means includes a shaft secured to said slider plate at one end and formed with means for securing said shaft to said input shaft at its other end.

5. A limit switch assembly in accordance with claim 1 wherein said actuator means includes spring means for biasing said actuator means to said first position and for retaining said actuator means in said first position when said slider means moves in another direction.

6. A limit switch assembly in accordance with claim 1 wherein said cam means includes a cam member rotatably mounted on said slider means and including locking means for locking said cam member in a selected position.

7. A limit switch assembly in accordance with claim 6 wherein said locking means includes a plurality of notches formed on one side of said cam member which cooperate with pin means for locking said cam member in its selected position.

8. A limit switch assembly in accordance with claim 7 including spring means biasing said notches into engagement with said pin means.

9. A limit switch assembly in' accordance with claim 8 wherein said spring means includes a spring washer bearing on the other side of said cam member and adjustably retained therewith by a nut assembly.

"10. A limit switch assembly in accordance with claim 1 wherein said cam means includes a pin member fixed to said slider means and projecting therefrom, a cam member rotatably mounted on said pin member and formed with a plurality of notches on the side adjacent said slider means, said pin member having a locking pin carried thereon for cooperation with said notches to lock said cam member against rotation.

l l. A limit switch assembly in accordance with claim 10 including spring means bearing on another side of said cam member for biasing said notches into locking engagement with said locking pin, said spring means being adjustably retained against said cam member whereby the biasing force exerted by said spring means can be varied to allow rotation of said cam member or to lock said cam member.

12. A limit switch assembly in accordance with claim 11 wherein said spring means is adjustably retained by a nut assembly.

13. A limit switch assembly in accordance with claim 1 including second cam means carried by said slider means for movement therewith and second actuator means located adjacent second switch means, said second actuator means having a first position spaced from said second switch means and a second position in engagement with said second switch means, said second cam means being operatively engaged with said second actuator means for moving said second actuator means from said first position to said second position when said slider means moves in another direction, said second cam means further being adjustable whereby the spacing between said first and second positions of said second actuator means is adjustable.-

14. A limit switch assembly in accordance with claim 1 wherein said cam means includes an arcuate cam member eccentrically mounted for rotation about a pin member and having a high point and a low point, one of said points defining a spacing between said first and second positions corresponding to the maximum limit signal which can be developed.

15. A limit switch assembly including a housing member having a slider plate slideably carried therein, said slider plate being fixed to a slideable shaft member extending therefrom and adapted to be mounted to a rotary drive shaft for axial movement therewith, spring means bearing on opposite faces of said slider plate for exerting a force locating said slider plate in said housing member, cam means mounted on said slider plate for movement toward and away from actuator means mounted adjacent switch means, said actuator means having a first position spaced from said switch means and a second position in engagement with said switch means, said cam means including a cam member rotatably mounted about a pin member extending from said slider plate along an axis adjacent said actuator means, said cam member further being formed with a plurality of notches on a first side adjacent said slider plate and cooperating with a locking pin carried on said pin member for locking said cam member against rotation when one of said notches seats on said locking pin, spring means bearing on a second side of said cam member adjacent the free end of said pin member and being retained in engagement with said-second side by a nut assembly whereby the force exerted on said cam member can be varied to lock said cam member or allow rotation thereof, said actuator means including a pivoted arm member having one end adjacent said cam member and the other end adjacent said switch means, said arm member being biased to said first position, and being movable to said second position by said cam member when said slider plate moves in one direction, the spacing between said other end of said arm member and said switch means being adjustable by said cam member whereby the distance said slider plate and said drive shaft can move before said actuator means moves from said first position to said second position is also adjustable.

1'6. A limit switch assembly in accordance with claim 15 wherein said slider plate carries second cam means similar to the first cam means for movement toward and away from second actuator means similar to the first actuator means mounted adjacent second switch means similar to the first switch means whereby movement of said rotary drive shaft in one direction closes said first switch means and movement in the other direction closes said second switch means.

n n s;

Claims

1. A limit switch assembly comprising slider means movable with axial movement of an input shaft, cam means carried by said slider means for movement therewith and actuator means located adjacent switch means and having a first position spaced from said switch means and a second position in engagement with said switch means, said cam means being engaged with said actuator means in said first and second positions thereof and being operatiave to move said actuator means from said first position to said second position when said slider means moves in one direction, whereby a limit signal is developed, said cam means further being adjustable whereby the spacing between said first and second positions of said actuator means is adjustable.

4. A limit switch assembly in accordance with claim 3 wherein said shaft means includes a shaft secured to said slider plate at one end and formed with means for securing said shaft to said input shaft at its other end.

9. A limit switch assembly in accordance with claim 8 wherein said spring means includes a spring washer bearing on the other side of said cam member and adjustably retained therewith by a nut assembly.

10. A limit switch assembly in accordance with claim 1 wherein said cam means includes a pin member fixed to said slider means and projecting therefrom, a cam member rotatably mounted on said pin member and formed with a plurality of notches on the side adjacent said slider means, said pin member having a locking pin carried thereon for cooperation with said notcHes to lock said cam member against rotation.

11. A limit switch assembly in accordance with claim 10 including spring means bearing on another side of said cam member for biasing said notches into locking engagement with said locking pin, said spring means being adjustably retained against said cam member whereby the biasing force exerted by said spring means can be varied to allow rotation of said cam member or to lock said cam member.

13. A limit switch assembly in accordance with claim 1 including second cam means carried by said slider means for movement therewith and second actuator means located adjacent second switch means, said second actuator means having a first position spaced from said second switch means and a second position in engagement with said second switch means, said second cam means being operatively engaged with said second actuator means for moving said second actuator means from said first position to said second position when said slider means moves in another direction, said second cam means further being adjustable whereby the spacing between said first and second positions of said second actuator means is adjustable.

15. A limit switch assembly including a housing member having a slider plate slideably carried therein, said slider plate being fixed to a slideable shaft member extending therefrom and adapted to be mounted to a rotary drive shaft for axial movement therewith, spring means bearing on opposite faces of said slider plate for exerting a force locating said slider plate in said housing member, cam means mounted on said slider plate for movement toward and away from actuator means mounted adjacent switch means, said actuator means having a first position spaced from said switch means and a second position in engagement with said switch means, said cam means including a cam member rotatably mounted about a pin member extending from said slider plate along an axis adjacent said actuator means, said cam member further being formed with a plurality of notches on a first side adjacent said slider plate and cooperating with a locking pin carried on said pin member for locking said cam member against rotation when one of said notches seats on said locking pin, spring means bearing on a second side of said cam member adjacent the free end of said pin member and being retained in engagement with said second side by a nut assembly whereby the force exerted on said cam member can be varied to lock said cam member or allow rotation thereof, said actuator means including a pivoted arm member having one end adjacent said cam member and the other end adjacent said switch means, said arm member being biased to said first position, and being movable to said second position by said cam member when said slider plate moves in one direction, the spacing between said other end of said arm member and said switch means being adjustable by said cam member whereby the distance said slider plate and said drive shaft can move before said actuator means moves from said first position to said second position is also adjustable.

16. A limit switch assembly in accordance with claim 15 wherein said slider plate carries second cam means similar to the first cam means for movement toward and away from second actuator means similar to the first actuator means mounted adjacent second switch means similar to the first switch means whereby movement of said rotary drive shaft in one direction closes said first switch means and movement in the other direction closes said second switch means.