US3646290A

US3646290A - Microswitch with pivotal microcontact actuator

Info

Publication number: US3646290A
Application number: US39746A
Authority: US
Inventors: Wilhelm Peter Borgmann
Original assignee: WP Borgmann KG
Current assignee: WP Borgmann KG
Priority date: 1969-05-23
Filing date: 1970-05-22
Publication date: 1972-02-29
Anticipated expiration: 1989-02-28
Also published as: JPS5031628B1; DE6920813U

Abstract

A microswitch having a microcontact operated by an actuating lever pivotally mounted to engage an overcenter snap-type switch arm which carries the movable contacts of the switch. A drive shaft extends through a nonlubrication requiring plastic bearing mounted in the casing and is rotated by an operating arm fixed to the drive shaft high-voltage pivotally between motion limiting stops on the outside of the casing. A cam connected to the inner end of the drive shaft engages one end of the actuating lever to pivot the lever against the overcenter snap arm to cause the contacts to switch. The elements of the switch are mounted in a two part casing held together by rivets and having electrical connecting lugs molded or otherwise embedded in the insulating material of the casing. The casing is enlarged at strategic places and the components are so arranged that the danger of flashing and tracking is substantially eliminated even when the switch is used for high voltage operation.

Description

United tates Patent Borgmann 1 1 Feb. 29, 1972 [54] MKCROSWITCH WlTH PIVOTAL 3,069,916 12/1962 Watson ..200/67 D UX MKCROCONTACT ACTUATOR 3,097,274 9/1963 Mamiya et al.. ..200/67 D UX 3,392,253 7/1968 Adams et a1. ..29/625 [72] Inventor: Wilhelm Peter Borgmann, Overath, Germany Primary ExaminerDavid Smith, J r. [73] Assignee: W. P. Borgmann KG, Kreuzfahrerstr. 14, -Y* Smith Overath, Germany [57] ABSTRACT [22] Filed: May 22, 1970 A microswitch having a microcontact operated by an actuat- [211 Appl' No; 39,746 ing lever pivotally mounted to engage an overcenter snap-type switch arm which carries the movable contacts of the switch. 30] Foreign A li fi priority m A drive shaft extends through a nonlubrication requiring plastic bearing mounted in the casing and is rotated by an May 1969 Germany 69 20 8135 operating arm fixed to the drive shaft high-voltage pivotally between motion limiting stops on the outside of the casing. A "200/67 cam connected to the inner end of the drive shaft engages one end of the actuating lever to pivot the lever against the over- [58] Field of Search 200/67 67 gs/g2; center snap arm to cause the contacts to switch. The elements of the switch are mounted in a two part casing held together by rivets and having electrical connecting lugs molded or [56] References Cited otherwise embedded in the insulating material of the casing. UNITED STATES PATENTS The casing is enlarged at strategic places and the components are so arranged that the danger of flashing and tracking is sub- 2,788,402 4/1957 lglehart et al ..200/47 smmially eliminated even when the Switch is used f high 2,805,299 9/1957 Cherry, Jr "200/67 B UX voltage operation 2,897,308 7/1959 Fergus ....200/67 D UX 3,001 ,041 9/1961 Wilson ..200/67 B UX 19 Claims, 4 Drawing Figures Patented Feb. 29, 1972 4 Sheets-Sheet 1 RWM, mm! M0 4 V 9/. mam W P M 5&0 M W J NOE 8 83 4 Sheets-Sheet 3 Patented Feb. 29, 1972 4 Sheets-Sheet 4 wm m m MICROSWITCII WITH PIVOTAL MICROCONTACT ACTUATOR This invention relates to a microswitch having a pivotal or rotary actuator for its microcontact. More specifically, the microswitch includes an overcenter snap type contact arm which is movable between two contact making positions by a pivotally mounted lever within the switch casing. The lever is engaged by a cam on the inner end of a drive shaft which extends through the switch casing. An operating arm is secured to the outer end of the drive shaft and is arranged for movement along an outside wall of the casing between a pair of stops formed integrally with the casing. The casing or housing is of the two part type held together by rivets, and connecting lugs are molded or otherwise embedded in the insulating material of the casing to facilitate making electrical connections to the microswitch.

Pivotally operated microswitches of this type are used, for example, as microswitches in machine controls, and due to their compact construction and their high capacity to withstand stresses, are quite versatile. Requirements to be complied with regarding contact rating and switch voltages have increased considerably in recent years. In addition, requirements for resistance to tracking and flashover have also increased considerably. Resistance to flashover depends primarily on the air distance between conductive elements carrying voltage at different potential, while tracking re' sistance depends on the distance along the surface of the insulating material separating conductive elements at different potential. The various ratings of such switches for switching high voltages are specified by standards in various countries and also by international standards. Manufacturers of microcontacts are faced with the difficulty of having to comply with standardized requirements in a setup calling for small space. There must be met the additional requirement of a robust construction ensuring many switching cycles, and of a simple assembly and easily adjustable initially, so even with mass production manufacture and assembly, there are no sig nificant variations in the switching characteristics of such microswitches.

In pivotally operated microswitches, a mechanical movement turns a drive shaft which pivots a lever via an operating cam on the drive shaft. The lever acts on an overcenter snaptype spring contact arm thereby moving the arm from its stable position in which the arm engages one contact, to its overcenter snap position in which the arm engages an opposed contact. Connections are made to the fixed contacts as well as to the movable contact arm by connecting lugs projecting from the switch housing. The wires for such connections may be secured to the lugs either mechanically or by soldering. In prior art microswitches, the connecting lugs are always secured by two through rivets at the base portion of the hous- Numerous problems are caused by the bearings in which the drive shaft rotates, since it is not feasible to either adjust the microswitch or to lubricate the microswitch after it is installed. Therefore, the construction of such microswitches must be such as to ensure substantially constant switch operating characteristics and high reliability and safety. In addition, it is a distinct advantage to be able to precisely adjust the snap over or actuating point of the contact arm during manufacture without danger of subsequent changes which could affect the operating characteristics of the switch. The known microcontacts do not always meet perfectly with these requirements, and, above all, they do not comply with the requirements regarding fiashover stability and resistance to tracking. Therefore, it is an object of the invention to provide a rotationmicrocontact of improved quality compared to the known contacts from the electric and mechanical viewpoint, and which is suitable for mass production due to its construction and its easy adjustability.

In accordance with this invention, this object is attained by providing a microswitch having a drive shaft pivotable in a self-lubricating type plastic bearing firmly fitted in the case, the drive shaft carrying a bushing provided with a control cam,

and in which a lever pivotable on a second shaft fixed against rotation to the case is pivoted by the control cam to operate the contact arm to its overcenter snap position so the switch is operated.

The drive shaft of this construction has excellent stability. In addition, the construction is such that the control cam carrying bushing can be first firmly fitted on the shaft but can be ad justed angularly by application of sufficient torque to turn the bushing relative to the shaft. This arrangement permits precise setting of the angular position of the cam on the shaft and consequently, permits setting the angular position of the shaft at which the switch operates. While the drive shaft is pivotable in a bearing inserted in the housing, the shaft for the lever is secured against rotation and serves as a pivot shaft for the lever when driven by the control cam. Hence, only those parts of the microswitch which are essential to the operation of the switch, namely, the drive shaft-cam assembly, the lever and the overcenter snap arm are movable during operation of the switch. All the other parts of the microswitch are rigidly secured to the housing.

In the preferred embodiment, the housing includes a base plate which carries the operating elements of the switch. The baseplate has thickened and reinforced portions at the mountings for both the drive shaft and the shaft on which the operating lever pivots. Mounted on the base are all the operating elements of the switch as well as the lugs for effecting electrical connection to the switch. Advantageously, those portions of the base other than at the reinforced portions which support the drive shaft and pivot shaft for the lever, are of reduced thickness thereby providing additional space within the housing and maintaining material costs at a minimum.

The movable contact or spring arm advantageously includes two parallel webs connected at their ends with an integral connecting piece. The movable contacts are secured to the connecting piece and the over center snap spring extends longitudinally between the webs. The over center snap spring is connected at one end to the connecting piece and at the other end to a rigidly supported operating spring. By virtue of the bowed or scroll shape of the over center spring, movement of the operating spring to the over center position by engagement with the lever causes the contact arm to snap over center.

In a preferred embodiment the plastic self lubricating bearing has an enlarged flange which engages the outside of the housing. This arrangement prevents shifting of the bearing due to forces such as eccentric forces acting on the drive shaft which extends through the bearing. By virtue of the construction of the drive shaft, including a collar which engages the bearing flange, even axial pressure exerted on the drive shaft will not cause displacement of the bearing or the drive shaft to any meaningful extent so far as the operation of the switch is concerned. Hence, reliable operation is assured even under adverse conditions. Within the scope of the invention, for a rotation-microcontact of the mentioned type, the connecting lugs are cast into the plastic case, and they are provided with contact plates at their ends projecting into the inner case. By avoiding the customary metal rivets for the assembly of the connecting lugs,.'there is not only achieved a simpler preparation of the switch, but also a higher flashover stability and a higher resistance to tracking. At their ends projecting into the case, the connecting lugs carry the fixed contact plates for the switch, against which the contact plates of the operating lamella come to a rest. Therefore, the current paths are mostly cast in the plastic, thus avoiding detrimental electric side-effects. According to the invention, there are further provided with a rotation-microcontact cylindrical projections at the case embracing the rivets. This will ensure a sleevelike enclosure of the rivets being thus completely insulated against the switch inside.

The cylindrical projections of the base and cover through which the hollow rivets extend partly intermesh or interengage to increase the length of the tracking paths.

Numerous other features, objects, and advantages of the invention will become apparent with reference to the accompanying drawings which form a part of the specification and in which:

FIG. 1 is a top plan view of the microswitch with portions of the cover removed;

FIG. 2 is a sectional view taken along line II-ll of FIG. I, and showing portions of the cover;

FIG. 3 is a rear view in elevation showing the microswitch as seen from the side from switch the connecting lugs. extend; and

FIG. 4 is a bottom plan view of the microswitch.

Referring now to the drawings, and particularly to FIGS. 1 and 2, the case or housing of the microswitch includes a base or baseplate l and a box-shaped cover 11. The cover and base are connected together by hollow rivets 12 and 13 extending through openings in diagonally opposed corners of the assembly with the rivets parallel to each other. Cover 11 includes integral tubular cylinders 14 and 15 which extend inwardiy toward base 10. Base has corresponding integrally formed hollow cylindrical projections 16 which also extend inwardly toward the cover. By virtue of this arrangement where the respective tubular cylinders 14 and of the cover and the cylindrical projections 16 of the base embrace the respective hollow rivets 12 and 13, the rivets are completely insulated relative to the interior of the case and in addition, by virtue of the overlapping and interfitting of the cylinders and projections, as shown at FIG. 2 for cylinder 14 and projection 16, a high resistance to electrical tracking is realized between the rivets and the components within the casing.

Connecting lugs 17-19 are provided for connecting the microswitch to the wires of the circuit to be controlled. These connecting lugs are advantageously cast into the base when the plastic base 10 is formed. To ensure that the connecting lugs are firmly retained by the base, openings are provided in the portions of the lugs that extend through the base so material such as the material 20 (FIG. I) will flow through these openings when the base is formed to secure the connecting lugs to the base against movement.

Alternatively, connecting lugs 17-19 can be secured to the base by ultrasonically deforming or welding the plastic material of the base around the lugs. In the case where the connecting lugs are welded into the base, the base is provided with plastic rivets at the regions 20 and the connecting lugs 17-19 are slipped over the rivets so the lugs are aligned as shown at FIG. 1. Then, the rivets or projections are deformed ultrasonically in such a manner to ensure that the surface area of each lug within the base is completely covered with plastic insulating material.

With reference to FIG. 1, it will be seen that connecting lug 19 has a plate-shaped end portion 21 which is bent to extend perpendicularly from the body portion of this lug. The assembly including movable contact arm 24 and spring-operating arm 22 has a leaf spring clip 60 at one end to receive the plate 21 and securely clamp the arms both mechanically and electrically to the clamping plate. As shown at FIG. 2, springoperating arm 22 is engaged at one end by a bowed or scroll spring of 180 circumferential extent. The other side of spring 23 engages a transverse or connecting portion of the movable contact arm 24 to which the movable contact plates or

contacts

25 and 26 are secured. Operating arm 22 and scroll spring 23 may be formed from resilient or elastic plastic material of good electrically insulating characteristics. These elements may be formed integrally with each other to simplify manufacture and assembly and when so formed from plastic material, the insulating characteristics of the switch are improved because of the additional insulation provided by the plastic of these elements. The movable contact arm or blade 24 is connected to the operating arm 22 at the region of clamping plate 21, for example, by the spring clip 60, Of course, movable contact arm 24 which carries the movable contacts is of a resilient electrically conducting metal such as phosphor bronze and the spring clip 60 provides a good electrical connection between contact arm 24 and clamping plate 21.

Contacts

25 and 26 are movable between a first position in which contact 25 engages the contact plate or contact 27 and a second position in which the contact 26 engages a second stationary contact plate or contact 28 in opposed relation to contact 27. FIG. I shows the movable contact arm 24 in its stable position in which movable contact 25 engages stationary contact 27. It will be observed with reference to FIG. I that contact 27 is formed on a portion of lug 17 that extends perpendicularly from the body portion of the lug. Stationary contact 28 is formed on a portion of lug 18 which similarly extends at right angles to the body portion of lug 18, which body portion is embedded in the insulating material of base 10.

As shown at FIG. 2, base 10 has a thickened reinforced portion 30 formed on the wall of the base and which projects inwardly toward cover 11. Mounted in an opening in this reinforced portion 30 of the base is a cylindrical bearing 31 in the form of a bushing having a flanged end 32. Flanged end 32 provides a shoulder in abutting relation to the outwardly facing surface of a shallow recess in the outside surface of the base. Bearing 31 is formed from a plastic material with selflubricating properties so the bearing is self-lubricating.

A drive shaft 33 extends through the bore of bushing 31. A reduced diameter portion 34 of drive shaft 33, which portion is located within bearing 31, reduces friction between the bearing and the shaft by virtue of the decrease in the surface area of contact between these elements. At the outer end of shaft 33 is a flange 35, and outwardly of the flange is a mova ble lever or actuating arm 36 which is fixed to the drive shaft. Advantageously. drive shaft 33 has a flange 35 and actuating arm 36 integrally formed therewith so the entire drive shaft assembly is ofone piece construction. preferably of an insulating plastic material. Such one piece construction facilitates manufacture and assembly of the switch.

As shown at FIGS. 2 and 4, a rounded stop projection 37, integrally formed with base 10 extends from the outside of the base in the same direction as a projecting wall portion 61. Projection 37 provides a rounded stop face 370 which limits movement of actuating arm 36 in a counterclockwise direction as viewed at FIG. 4. A side face 61a of wall portion 61 forms a stop which limits movement of actuating arm 36 in a clockwise direction. As shown at FIGS. 3 and 4, the wall portion 61 projects outwardly and also includes an elongated rectangular tip 62 which extends generally between rivet 12 and lug 19. Tip 62 further increases the tracking path between rivet 12 and lug 19 in addition to providing a shield against flashover between the lug and the rivet.

As is apparent with reference to the drawings, actuating arm 36 is relatively thin and flat and has

side edges

33a and 340 respectively which diverge slightly relative to each other in a direction away from shaft 33. Side edge 34a engages stop face 61a to limit pivotal movement of actuating arm 36 in a clockwise direction as viewed at FIG. 4 whereas side edge 33a engages the rounded or cylindrical surface 371; to limit movement of arm 36 in a counterclockwise direction. Since the extent of pivotal movement of actuating arm 36 is limited, the extent of angular displacement of shaft 33 to which the arm is fixed is correspondingly limited.

Secured to the inner end of shaft 33 is a bushing 38. Bushing 38 includes a hollow arm 39 which extends in a direction generally perpendicularly to the axis of shaft 33. Projecting from the arm is a cylindrical control cam 40 which is parallel with shaft 33 and extends toward cover 11. At the region of connection between bushing 38 and shaft 33, shaft 33 is provided with a reduced diameter portion 41 to reduce friction between the bushing and the shaft so the angular position of the bushing and its control cam 40 relative to the shaft can be adjusted after the bushing is force fitted onto the end of the shaft. By virtue of this arrangement, actuating arm 36 can be properly angularly oriented and bushing 38 can be properly angularly adjusted relative to the shaft 33 after the bushing is fitted onto the shaft. Of course, the friction forces between bushing 38 and shaft 33 are sufficiently great that the angular position of the bushing will not change relative to the shaft as a result of the forces exerted when the shaft is rotated by moving actuating arm 36 to operate the microswitch.

Within the bounds of the reinforced portion 30 of the base, a blind bore is formed which opens into the casing and a shaft 42 is force fitted into the opening against movement. As shown at FIG. 2, shaft 41 has its axis parallel to but spaced from the axis of drive shaft 33. Formed on the free end of shaft 42 is an enlarged head or flange 43. Mounted on shaft 42 for pivotal movement about the shaft is a lever 44. To reduce fric tion between lever 44 and shaft 42, shaft 42 is provided with a reduced diameter portion 45 which decreases the surface contact area between the bore of the hub 46 of the lever and the outside surface of shaft 42. As shown at FIG. 2, hub 46 is elongated in the direction of the axis of shaft 42 and has only slight end clearance between the face of reinforced portion 30 and the flange 43 of the shaft 42.

As shown at FIGS. 1 and 2, lever 44 has an integral arm 47 which extends perpendicularly relative to the axis of hub 46. Arm 44 is formed on the portion of the hub closely adjacent flange 43. The arm 47 is of sufficient length to overlap control cam 40 so the arm is engaged by and moved by the control cam when shaft 33 is rotated. Extending from the side of hub 46 opposite the arm 47 is a second arm 48 also integral with the hub.

Arms

47 and 48 lie in essentially parallel planes as shown at FIG. 2. Arm 48 has a transversely extending tip 49 which engages operating arm 22 with line contact. As shown at FIG. 2, tip 49 engages operating arm 22 at the longitudinal center of the arm. With

lever arms

47 and 48 in parallel planes, as previously mentioned, the distance a (FIG. 2) from the centerline of arm 47 to the center of engagement of arm 48 with operating arm 22 is the same as the distance b from the center of contact of arm 48 to the end of hub 46. This centered arrangement avoids excessive stresses on the shaft 42, which it must be remembered is of relatively small diameter because of the small size of the components in a microswitch.

Reinforcing

webs

50 and 51 integrally connect arm 48 with hub 46. In addition, there is a reinforcing web 52 which extends from hub 46 to the inner end of arm 47. An additional reinforcing web 53 extends from the side of the reinforced thickened portion 30 of the base to the inside surface of the wall of the base. It will be observed with reference to FIGS. 1 and 2 that each of the reinforcing webs is generally rectangular in section, and hence, these reinforcing webs not only strengthen the various portions of the switch assembly to which they are connected, but also increase the tracking paths along the surfaces of the reinforced components of the assembly.

As previously explained, movable contact arm or blade 24 is firmly clamped to plate 21. As shown at FIG. 2, this contact arm is generally U-shaped and includes

legs

54 and 55 integral with the end portion of the arm. As shown at FIG. 2, the distance between the

legs

54 and 55 is sufficient to ensure free movement of operating arm 22 and the bowed or scroll spring 23.

OPERATION After all the operating components of the switch are mounted on the base, but before cover 11 is secured to the base to enclose the components, the position of operating cam 40 is angularly adjusted on shaft 33 so that when actuating arm 36 is in the position of FIG. 4 contact arm 24 and operating arm 22 are in the idle or stable position of FIG. 1. with reference to FIG. 4, it will be seen that in this position of the actuating arm 36, edge 33a engages stop face 37a. In this position of the contact arm 24 and operating arm 22, contact 25 engages contact 27.

To operate the switch, actuating arm 36 is moved in a clockwise direction from the position of FIG. 4 and toward stop surface 61a. During such movement of actuating arm 36 shaft 33 is rotated and correspondingly, operating cam 40 turns and acts on arm 47 of lever 44. This causes the lever to pivot in a counterclockwise direction as viewed at FIG. 1, so

tip 49 is pressed against operating arm 22. Tip 49 forces arm 22 upwardly at the line of engagement with tip 49 until the assembly including operating arm 22 and spring 23 reach an overcenter position relative to movable contact arm 24, whereupon contact arm 24 is forced downwardly by the action of spring 23. This causes contact 26 to engage contact 28 so a circuit is completed from lug 18 to lug 19 via contact arm 24 and the contacts 26 and 28. When lever 36 is released, the force from spring-operating arm 22 pivots lever 49 clockwise as viewed at FIG. I, thereby turning shaft 33 clockwise via the engagement of arm 47 with operating cam 40, and correspondingly, actuating arm 36 is moved back to the position of FIG. 4 in which edge 33a engages stop face 37a.

After initial assembly, in the event that operating arm 22 does not cause contact arm 24 to snap overcenter to switch the contact when lever 36 is moved against stop projection 61, the angular position of operating cam 40 can be readily adjusted before the cover is secured to the base, in the manner previously described, by applying sufficient torque to bushing 38 to rotate the bushing relative to the shaft 33, so operating cam 40 is in the proper angular position to cause the contacts to switch within the limits of movement of actuating arm 36. Even though bushing 38 can be adjusted on shaft 33 by applying sufficient torque to the bushing, the frictional engagement between the bushing and shaft is such that there is no relative rotation between the shaft and bushing during operation of the switch. Hence, bushing 38 and cam portion 40 remain in the same relative angular positions to which they are initially set by such adjustment. Cover II is of course secured to the base after bushing 38 is properly adjusted on shaft 33.

While a preferred embodiment of the microswitch of this invention has been shown and described in detail, it is to be understood that numerous changes can be made in this embodiment without departing from the scope of this invention as defined herein and in the appended claims.

I claim:

1. A microswitch comprising:

a. a casing including a base, and a cover secured to said base;

b. bearing means carried by said casing and having a shaftreceiving opening therein;

c. a drive shaft extending through said opening of said bearing means;

cl. a bushing within said casing and connected to said drive shaft for rotation with the shaft, said bushing including a control cam portion;

e. a contact arm within said casing, said contact arm being movable to a first position in engagement with a stationa ry contact in said casing, and a second position out of engagement with said stationary contact;

f. a second shaft secured to said base in spaced parallel relation to said drive shaft;

g. a lever mounted on said second shaft at a point intermediate the ends of the lever and adapted for pivotal movement around said shaft and including a first portion at one end of said lever engaging said cam portion of the bushing, and a second portion at the opposite end of said lever engaging said contact arm to move said contact arm from one of said positions to the other; and

h. operating means to rotate said drive shaft.

2. A microswitch according to claim 1 wherein said bearing means takes the form of a bushing with a cylindrical body and an enlarged head, said bushing including a bearing portion formed from a self lubricating plastic material;

said base has an opening therethrough to receive said bushing; and

said bushing extends into said opening with said enlarged head engaging an exterior surface of the base.

3. A microswitch according to claim 1 wherein said microswitch further includes operating means outside said casing to rotate said drive shaft, and

limiting means on said casing to limit angular displacement of said drive shaft in response to movement of said operating means. 4. A microswitch according to claim 3 wherein said operating means is an arm outside said casing and closely adjacent a wall of the casing; and said limiting means includes a first stop in the path of movement of said arm, and a second stop spaced from the first stop and in the path of movement of said arm. 5. A microswitch according to claim I wherein said lever is formed from a plastic-insulating material and includes a first arm integral with a tub, a second arm integral with a hub, and reinforcing web means extending between said arms and said hub; said reinforcing web means increasing the electrical tracking path along the surfaces of said lever. 6. A microswitch according to claim 1 wherein said base has an enlarged reinforced thickened wall portion;

and reinforcing web means integral with said base and wall portion and providing an increased surface path to resist electrical tracking in the region of said web portions. 7. A microswitch according to claim 1 wherein said contact arm assembly includes a generally U-shaped thin flat arm having side legs and a connecting portion at the ends of the legs, contact means at the U-shaped connecting portion of said arm, an operating spring arm extending between the legs of said contact arm, and a bowed spring connected between said connecting portion of the contact arm and an end of said operating arm. 8. A microswitch according to claim 7 wherein said operating arm and contact arm are connected to a common electrically conducting plate; said contact arm is formed form spring material with good electrically conducting characteristics; and said operating arm and bowed spring are integrally formed from resilient plastic material with good electrically insulating characteristics. 9. A microswitch according to claim 1 wherein a plurality of electrical connecting lugs extend through and are embedded in the material of the base; said connecting lugs having integral contact plates at the ends thereof within said casing; one of said connecting lugs having said contact arm secured thereto; and another of said contact lugs providing said stationary contact in said casing. 10. A microswitch according to claim 1 wherein said base includes first and second hollow cylindrical projections at opposite sides of the base respectively, said projections extending toward said cover; said cover includes first and second tubular projections extending toward said base, said tubular projections overlapping said respective cylindrical projections; and rivets extending respectively through said first cylindrical projection and first tubular projection, and through said second cylindrical projection and second tubular projection, and securing said cover to said base; said overlapping tubular and cylindrical projections increasing the electrical tracking paths between the respective rivets and the electrical components within said casing. 11. A microswitch according to claim 1 which includes an adjusting means whereby the switching movement of the contact arm may be precisely positioned relative to the desired angular position of said drive shaft.

12. A microswitch according to claim 11 wherein said adjusting means is comprised of a friction type coupling between said bushing and said drive shaft so that the bushing is prevented from rotating on said drive shaft during normal use of the microswitch and is capable of being rotataoiy adjusted relative to each other in response to a force greater than the normal resisting force of the lever and contact arm.

13. A microswitch according to claim 12 wherein the section of the drive shaft which is contiguous with the bushing and constitutes the friction connection is undercut a predetermined length whereby the friction in the connection between the bushing and drive shaft to a desired level whereby the rotational adjustment between the elements can be easily performed.

14. A microswitch comprising:

a. a casing including a base formed from plastic material having good electrical insulating characteristics and a cover formed from plastic material having good electrical insulating characteristics, and secured to said base;

b. bearing means secured by said base and having a shaft receiving opening therein;

. a drive shaft having electrical insulating material extending through said opening of said bearing means;

d. an actuating arm secured to said drive shaft and disposed outside said casing along a wall of said base;

. a bushing within said casing and connected to said drive shaft for rotation with the shaft in response to movement of said actuating arm, said bushing including a control cam portion;

. an overcenter snap-type contact arm within said casing, said arm being movable to a first position in engagement with a first stationary contact within said casing, and a second position in engagement with a second stationary contact within said casing and in opposed relation to said first contact;

. a second shaft secured to said base in spaced parallel relation to said drive shaft;

a lever within said casing mounted on said second shaft at a point intermediate the ends of the lever and adapted for pivotal movement around said shaft and including a first arm portion at one end of said lever engaging said control cam, and a second arm portion at the opposite end of said lever engaging said movable contact arm;

. said second arm portion engaging said contact arm to urge same to its overcenter snap position in response to operation of said actuating arm; and

j. stop means on said casing to limit the extent of movement of said actuating arm in at least one direction to correspondingly limit the extent of angular movement of said shaft in said at least one direction.

15. A microswitch according to claim 14 wherein connecting lugs extend into said casing through the material of said base;

one of said connecting lugs includes a movable contact arm support portion; and

spring clip means secure said movable contact arm to said contact arm support portion of said lug,

16. A microswitch according to claim 14 wherein said stop means is an integral abutment formed on said base;

said cover is secured to said base by hollow rivets extending through diagonally opposed corners of said cover and base;

electrical connecting lugs project from a side of said base generally in a plane perpendicular to the axes of said rivets; and

said integral abutment on said base includes a projecting portion thereof between one of said rivets and an adjacent connecting lug, said projecting portion increasing the electrical tracking path between said adjacent lug and said one rivet.

17. A microswitch according to claim 14 wherein said first and second arm portions of said lever extend generally diametrically relative to a hub portion of said lever;

said cam portion of said bushing engages said first arm on one side thereof; and

said second arm engages said movable contact arm on the same side thereof as the side of said first arm engaged by said cam.

18. A microswitch according to claim 14 wherein said connecting lugs are permanently molded into and secured solely by the material of said casing.

19. A microswitch according to claim 14 which includes an

Claims

1. A microswitch comprising: a. a casing including a base, and a cover secured to said base; b. bearing means carried by said casing and having a shaftreceiving opening therein; c. a drive shaft extending through said opening of said bearing means; d. a bushing within said casing and connected to said drive shaft for rotation with the shaft, said bushing including a control cam portion; e. a contact arm within said casing, said contact arm being movable to a first position in engagement with a stationary contact in said casing, and a second position out of engagement with said stationary contact; f. a second shaft secured to said base in spaced parallel relation to said drive shaft; g. a lever mounted on said second shaft at a point intermediate the ends of the lever and adapted for pivotal movement around said shaft and including a first portion at one end of said lever engaging said cam portion of the bushing, and a second portion at the opposite end of said lever engaging said contact arm to move said contact arm from one of said positions to the other; and h. operating means to rotate said drive shaft.

2. A microswitch according to claim 1 wherein said bearing means takes the form of a bushing with a cylindrical body and an enlarged head, said bushing including a bearing portion formed from a self lubricating plastic material; said base has an opening therethrough to receive said bushing; and said bushing extends into said opening with said enlarged head engaging an exterior surface of the base.

3. A microswitch according to claim 1 wherein said microswitch further includes operating means outside said casing to rotate said drive shaft, and limiting means on said casing to limit angular displacement of said drive shaft in response to movement of said operating means.

4. A microswitch according to claim 3 wherein said operating means is an arm outside said casing and closely adjacent a wall of the casing; and said limiting means includes a first stop in the path of movement of said arm, and a second stop spaced from the first stop and in the path of movement of said arm.

5. A microswitch according to claim 1 wherein said lever is formed from a plastic-insulating material and includes a first arm integral with a tub, a second arm integral with a hub, and reinforcing web means extending between said arms and said hub; said reinforcing web means increasing the electrical tracking path along the surfaces of said lever.

6. A microswitch according to claim 1 wherein said base has an enlarged reinforced thickened wall portion; and reinforcing web means integral with said base and wall portion and providing an increased surface path to resist electrical tracking in the region of said web portions.

7. A microswitch according to claim 1 wherein said contact arm assembly includes a generally U-shaped thin flat arm having side legs and a connecting portion at the ends of the legs, contact means at the U-shaped connecting portion of said arm, an operating spring arm extending between the legs of said contact arm, and a bowed spring connected between said connecting portion of the contact arm and an end of said operating arm.

8. A microswitch according to claim 7 wherein said operating arm and contact arm are connected to a common electrically conducting plate; said contact arm is formed form spring material with good electrically conducting characteristics; and said operating arm and bowed spring are integrally formed from resilient plastic material with good electrically insulating characteristics.

9. A microswitch according to claim 1 wherein a plurality of electrical connecting lugs extend through and are embedded in the material of the base; said connecting lugs having integral contact plates at the ends thereof within said casing; one of said connecting lugs having said contact arm secured thereto; and another of said contact lugs providing said stationary contact in said casing.

10. A microswitch according to claim 1 wherein said base includes first and second hollow cylindrical projections at opposite sides of the base respectively, said projections extending toward said cover; said cover includes first and second tubular projections extending toward said base, said tubular projections overlapping said respective cylindrical projections; and rivets extending respectively through said first cylindrical projection and first tubular projection, and through said second cylindrical projection and second tubular projection, and securing said cover to said base; said overlapping tubular and cylindrical projections increasing the electrical tracking paths between the respective rivets and the electrical components within said casing.

11. A microswitch according to claim 1 which includes an adjusting means whereby the switching movement of the contact arm may be precisely positioned relative to the desired angular position of said drive shaft.

12. A microswitch according to claim 11 wherein said adjusting means is comprised of a friction type coupling between said bushing and said drive shaft so that the bushing is prevented from rotating on said drive shaft during normal use of the microswitch and is capable of being rotatably adjusted relative to each other in response to a force greater than the normal resisting force of the lever and contact arm.

14. A microswitch comprising: a. a casing including a base formed from plastic material having good electrical insulating characteristics and a cover formed from plastic material having good electrical insulating characteristics, and secured to said base; b. bearing means secured by said base and having a shaft-receiving opening therein; c. a drive shaft having electrical insulating material extending through said opening of said bearing means; d. an actuating arm secured to said drive shaft and disposed outside said casing along a wall of said base; e. a bushing within said casing and connected to said drive shaft for rotation with the shaft in response to movement of said actuating arm, said bushing including a control cam portion; f. an overcenter snap-type contact arm within said casing, said arm being movable to a first position in engagement with a first stationary contact within said casing, and a second position in engagement with a second stationary contact within said casing and in opposed relation to said first contact; g. a second shaft secured to said base in spaced parallel relation to said drive shaft; h. a lever within said casing mounted on said second shaft at a point intermediate the ends of the lever and adapted for pivotal movement around said shaft and including a first arm portion at one end of said lever engaging said control cam, and a second arm portion at the opposite end of said lever engaging said movable contact arm; i. said second arm portion engaging said contact arm to urge same to its overcenter snap position in response to operation of said actuating arm; and j. stop means on said casing to limit the extent of movement of said actuating arm in at least one direction to correspondingly limit the extent of angular movement of said shaft in said at least one direction.

15. A microswitch according to claim 14 wherein connecting lugs extend into said casing through the material of said base; one of said connecting lugs includes a movable contact arm support portion; and spring clip means secure said movable contact arm to said contact arm support portion of said lug.

16. A microswitch according to claim 14 wherein said stop means is an integral abutment formed on said base; said cover is secured to said base by hollow rivets extending through diagonally opposed corners of said cover and base; electrical connecting lugs project from a side of said base generally in a plane perpendicular to the axes of said rivets; and said integral abutment on said base includes a projecting portion thereof between one of said rivets and an adjacent connecting lug, said projecting portion increasing the electrical tracking path between said adjacent lug and said one rivet.

17. A microswitch according to claim 14 wherein said first and second arm portions of said lever extend generally diametrically relative to a hub portion of said lever; said cam portion of said bushing engages said first arm on one side thereof; and said second arm engages said movable contact arm on the same side thereof as the side of said first arm engaged by said cam.

19. A microswitch according to claim 14 which includes an adjustable connection means connecting said bushing to said drive shaft whereby said bushing will normally rotate with said shaft in response to movement of said actuating arm and said adjustable means permits the cam portion of the bushing to be angularly repositioned with the drive shaft to properly adjust the operation of the microswitch.