Abstract:
A limit switch comprising a switch enclosure, a snap action switch, and an operating head. An actuator slidably mounted in the operating head is provided with a wing which prevents the rotation of the actuator.

Description:
BRIEF SUMMARY OF INVENTION 
     This invention relates to an actuating means in a limit switch which is usually used to control various kinds of machine tools. 
     In some types of actuators in which the top portion has directivity, such as a roller type and bevel type, it is required that the actuator be kept from rotating from a set direction to meet a dog correctly. In a prior art limit switch, an actuator is provided with a flange portion having two sides cut to engage with a slot for preventing a rotation of the actuator. The flange portion is made in one body with the actuator by machining, therefore, the flange portion can not be made large enough, and the machining is expensive. 
     Accordingly, an object of the invention is to provide a limit switch having an improved actuator which is prevented from rotating. 
     Another object of the invention is to provide an improved actuator which is strong to resist shock imparted by a dog. 
     An additional object of the invention is to provide an improved actuator which can be manufactured easily and cheaply. 
     These and other advantages are obtained through the provision of an actuator having a wing on its bottom part, which is guided by guides for preventing a rotation of the actuator. In a particularly preferred form of the invention, two rod shaped guides are provided in the operating head for guiding the wing, and two return springs are further provided around the rod shaped guides for urging the actuator upwardly through the wing. 
     The nature of the invention, including the foregoing and the other objects and novel features, will be more fully appreciated from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an improved limit switch; 
     FIG. 2 is a sectional view taken along line A--A in FIG. 1; and, 
     FIG. 3 is a exploded view of an operating head shown in FIG. 1. 
     FIG. 4 is a perspective view of a roller actuator which may be used in lieu of the wedge shaped actuator shown in FIGS. 1-3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings FIG. 1 through FIG. 3, a limit switch embodying the present invention comprises a switch enclosure 20, a snap action switch 21, and an operating head 22. 
     The snap action switch 20 is mounted in the switch enclosure 20 which is made of Aluminum alloy. The operating head 22 is mounted on a upper surface of the switch enclosure 20 for actuating the snap action switch 21. The switch enclosure 20 has flange portions 40 in which holes 37 are bored for mounting screws, and has a threaded bore 39 to receive a wire conduit. A hole 23 is formed at the center of the operating head 22. A dust seal 24 and a retaining ring 25 are inserted in a upper portion 23a of the hole 23. Beside the hole 23, rod shaped guides 26 having threaded bores 26a are formed in parallel with the hole 23. An actuator 27 having a wedge shaped top portion (FIGS. 1-3) or having a roller on the top (FIG. 4) is slidablly inserted in the hole 23. The actuator 27 has a wing 30 calked or welded on the bottom of the actuator 27 so that the actuator 27 is urged upwardly by springs 32 that are placed around the guides 26. In a hole drilled in the bottom of the actuator 27, a plunger 29 is arranged with an actuator spring 28 urging the plunger 29 downwardly. The wing 30 forms a retainer for the plunger 29 which has a first stepped portion 29a for seating on a edge of a slot 30a formed on the wing 30. The, the wing 30 has two holes 31 at opposite ends of wing 30 in which the rod shaped guides 26 are slidably fitted. 
     A plate 33 screwed up on the bottom of the guides 26 holds the return springs 32. One end of the plunger 29 projects downwardly through a center hole 33a of a plate 33 to actuate the snap action switch 21. The plate 33 also forms a stopper for the plunger 29 by a second stepped portion 29b meeting with the periphery of the hole 33a when the actuator is pressed down to excess. 
     When a dog (not shown) moves in contact with the actuator 27, the actuator 27 pushes down the plunger 29 through the actuator spring 28. One end of the plunger 29 pushes down a button 21a of the snap action switch 21 through a oil seal 35. If the actuator 27 is pushed down to excess, the plunger 29 is stopped by the plate 33. The excessive motion of the actuator 27 is absorbed by the actuator spring 28 for protecting the snap action switch 21. 
     As shown in the above, a limit switch embodying the present invention has an actuator which is kept from rotating for secure operation. The limit switch is strong resisting shocks imparted by a dog, is easy to manufacture, and is of low cost. 
     Although a particular embodiment of the invention has been described in detail with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment disclosed and that various changes and modifications may be readily effected by one skilled in the art without departing from the spirit or scope of the invention which is defined solely by the appended claims.