US3781501A

US3781501A - Single pole electric switch with contacts convertible from normally open to normally closed and vice versa

Info

Publication number: US3781501A
Application number: US00313844A
Authority: US
Inventors: G Borghetti
Original assignee: Telemeccanica Elettrica
Current assignee: Telemeccanica Elettrica
Priority date: 1971-12-22
Filing date: 1972-12-11
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25
Also published as: FR2164592A1; FR2164592B1; IT940796B

Abstract

An electric switch having fixed contacts on a housing and having an invertible bar slidable therein, the bar carrying a contact bridging arm with contacts engageable with the fixed contacts, a contact pressure applying spring acting between the bar and the arm and a return spring acting between the bar and an abutting element mounted off-center on an invertible and removable lid for the housing. In one position of the bar and lid, the contacts are normally open and in the inverted position thereof, the contacts are normally closed, the contact position being indicated by symbols alternately exposed depending on the lid position.

Description

United States Patent [191 11] 3,781,501 Borghetti Dec. 25, 1973 [54] SINGLE POLE ELECTRIC SWITCH WITH 3,437,773 4/1969 Koertge 200/166 BC CO C CONVERTIBLE FROM 3,253,092 5/1966 Landow 200/166 BC X 2,811,617 10/1957 Townsend ZOO/166 BC ggggl gfkzb sfgiz slzggf 2,545,986 3/l95l Basnett 200/165 [75] Inventor: Giuseppe Borghetti, Turin, Italy Primary Examiner Robert Schaefer [73] Assignee: Telemeccanica Elettrica Officine I Assistant Exa" linerwmiam Smith 'Meccaniche Riunite S.p.A., Milan, Brooks et Italy [22] Filed: Dec. 11, 1972 [57] ABSTRACT [21] 313844 An electric switch having fixed contacts on a housing and having an invertible bar slidable therein, the bar [30] F i Application priority Data carrying a contact bridging arm with contacts engage- D e c 22 1971 Italy 32766 A /71 able with the fixed contacts, a contact pressure applying spring acting between the bar and the arm and a [52] CL U zoo/166 BC ZOO/165 return spring acting between the bar and an abutting [51] Int. Cl. 1101b l/34 element mounted off-center on an invertible and [58] Field of Search [6 BC movable lid for the housing. In one position of the bar 335/l32' and lid, the contacts are normally open and in the inverted position thereof, the contacts are normally [56] References Cited closed, the contact position being indicated by sym- UNITED STATES PATENTS bols alternately exposed depending on the lid position.

3,505,625 4/1970 Nielsen et al 200/166 BC X 8 Claims, 5 Drawing Figures (Ya a PATENTED BEBE 5 I975 SHEET 1 OF 2 SINGLE POLE ELECTRIC SWITCH WITH CONTACTS CONVERTIBLE FROM NORMALLY OPEN TO NORMALLY CLOSED AND VICE VERSA This invention relates to a single pole electric switch which can easily and quickly be converted from a switch with normally open contacts to a switch with normally closed contacts or vice versa.

Switches of the type to which the invention relates are often demanded by the users both because the associated circuit can be modified by converting its own electric condition and because it is convenient, for example, to have a stored stock of switches which can be used as required, as normally open or normally closed contact switches. In fact, if the stored stock comprises switches of the type in which the contacts are always normally closed and others of the type in which the contacts are always normally open, double inventory problems are involved. Also, the stock of one of the two types of switches may be depleted in the course of time, and the switches of the other type cannot be used to supply the demand. In the latter event, the user is then compelled to await, after a further order, the receipt of a new stock, with a consequent loss of time and, usually, he cannot utilize switches of the other type.

On the other hand, if switches of the convertible contact type are available in the stock, the user can, if necessary, convert the switch to the type suitable for the required use, and at the same time, he can be sure to utilize the whole stored stock.

Switches of the above described type are already known in the art. In general, they comprise an operating bar or plunger slidable on guides, either by manual actuation or by the action of a machine part with which the switch is associated, a bridging arm carrying movable contact members and being secured to the operating bar and two cylindrical or helical springs, the first of which will be hereinafter called overrun spring and the second return spring."

The second, or return, spring opposes the movement imparted to the operating bar, whereas the first, or overrun, spring has a double function, namely that of ensuring, when the movable contact members engage the fixed contact members, a pressure sufficient to establish a good electric contact, and when the device is normally closed, prevention of the opening of the contact members for accidental causes, such as, for example, vibrations which may cause small movements of the operating bar. In the prior art, the conversion from one condition of the contact members to the other is carried out in various ways. By way of example, reference is made to the switch described in the British Pat. No. 784,777.

In the switch described in British Pat. No. 784,777, the conversion from normally open contacts to normally closed contacts is effected by rotating through 180 both the operating bar and the springs. When, in such switch the contacts are normally open, its operation is the following: the operating bar, pushed by an operator or by a machine part, overcomes gradually the resistance of the return spring and, as soon as the movable contact members on the bridging arm abut the fixed contact members, the overrun spring is compressed, applying the correct pressure to the contacts.

When in such prior art switch the contact members are normally closed, the movement of the operating bar presses both the return spring and the over-run spring and, since the bridging arm carrying the movable contact members is contained between the two springs, the contacts will quickly open. It has been found that such operation is objectionable in a switch of this kind in the second operating condition, namely when the contact members are normally closed. In fact, if for accidental reasons, such as, for example, vibrations, the operating bar is actuated, the contact members open immediately. ln such switch, the undesired displacement of the operating bar can give rise to irregular working conditions in a machine, for example, unnecessary interruptions of the working cycle, false alarms, temporary opening of a safety circuit, etc.

A further disadvantage present in the switch described in the above-mentioned British Patent, as well as in other analogous devices, lies in the fact that for the conversion from normally open contacts to normally closed contacts it is necessary to rotate by the housing of the switch itself. It will be understood by those skilled in the art that in such case, it is necessary to carry out assembling and disassembling operations which involve the use of tools, for example, to unscrew the screws connecting the switch housing to the structure of a machine or to a wall. It will also be understood that said assembling and disassembling operations must often be effected in difficult conditions, the switches being associated with others and being, therefore, located in spaces which are narrow or at least, making access to the switch difficult.

-A further disadvantage common both to the switch described in the British Patent and to other analogous switches resides in the fact that, when the operating bar is rotated by 180, the springs and the bridging arm carrying the movable contact members, because of the manner in which they are assembled, are likely to be dropped or misplaced, so that the conversion becomes long and troublesome.

The present invention has as one object the providing of a switch which is reliable in any working conditions and which is constructed so that difficult assembling and disassembling operations are avoided in the conversion of the condition of the contacts from normally open to normally closed or vice versa.

Accordingly, the object of the present invention is to provide a single pole, electric switch of the type which can be converted from normally open to normally closed contacts by rotating a movable assembly through 180 with respect to a fixed assembly, said fixed assembly comprising a housing, a lid, and fixed contact members, and said movable assembly comprising an operating bar slidable in said housing, said operating bar carrying a bridging arm with movable contact members, a first over-run spring and a second return spring for moving said bar. The switch of the invention is characterized by an abutting element which is fixed in position with respect to the housing when the switch is in operating condition and which can be arranged in two different positions, depending on whether the contacts are normally open or normally closed. The second, or return, spring is compressed between said abutting element and said movable assembly.

The present invention will be better understood from the following detailed description of the presently preferred embodiment thereof which illustrates, by way of example, the principles of the invention, which description should be considered in conjunction with the accompanying drawings, in which:

FIG. 1 is an end, exterior view of the switch with the contacts normally open;

FIG. 2 is a front elevation, cross sectional view of the embodiment in FIG. 1 and is taken along the line lIII indicated in FIG. 1;

FIG. 3 is a longitudinal, sectional view of the embodiment in FIG. 2and is taken along the line IIIIII indicated in FIG. 2;

FIG. 4 is a fragmentary, longitudinal sectional view of the embodiment in FIG. 2 and is taken along the line IVIV indicated in FIG. 2; and

FIG. 5 is a front elevation, cross sectional view, similar to FIG. 2, but showing the parts in their positions when the contacts are normally closed.

As mentioned hereinbefore, the electric switch of the present invention is provided with a single pole contact which can be normally open or normally closed. The switch comprises a fixed assembly and a movable assembly. The latter must be rotated through 180 to carry out the change from one condition of the contacts to the other.

The fixed assembly comprises a housing 1, a lid 2, and fixed

contact members

3, 4 having double-faced, fixed contacts. Both thehousing 1 and the lid 2 may be of a thermoplastic material, such as, for example, a polycarbonate.

The'movable assembly comprises an operating bar 4, a bridging arm 6 carrying movable contact members 6a and 6b, a first spring 7 called an over-run spring, a second spring 8 called a return spring, and an abutting element 9 (see FIGS. 1, 2 and 3).

The abutting element 9 is stationary and can be arranged in two different positions, depending on whether the contacts are normally open or normally closed, FIGS. 2-4 showing the position when the contacts are normally open and FIG. 5, showing its position when the contacts are normally closed.

Said abutting element 9, in each of said two positions, engages an end of the return spring 8. In the embodiment illustrated by way'of example, the abutting element 9 is secured to and extends from the lid 2 (see FIG. 4) and is changed in position with the lid 2 when the latter is rotated by 180 in the changing from the condition of normally open contacts to that of normally closed contacts or vice versa. Although it is preferred that the abutting element 9 be movable with the lid 2, it will be apparent to those skilled in the art that the abutting element 9 need not be secured to the lid 2 and may, instead, be mounted on another part of the switch and be movable between the two positions described. Hereinafter said element 9 will not be described as a part of the lid 2 but as an abutting element 9.

The operating bar 5 is slidable in the housing 1, in the manner described hereinafter, and is provided with two windows 10 and 11 (FIG. 3). The window 10 is provided with two

centering seats

12 and 13 for the ends of the return spring 8, and the window 11 is provided with one centering seat 14 for the over-run spring 7. The latter, in the case of normally open contacts(see FIG. 2), has one end engaging the bridging arm 6 which carries the movable contact members 6a and 6b and the arm 6 is pressed against a surface 15 at one end of the window 11. The operating bar 5 also has seats or

guides

35 and 36 in the form of cut-outs for assuring the correct insertion of the lid 2 in the housing 1 (see FIG. 3).

Referring now to the details of the fixed assembly, it will be noted that the housing 1, besides being provided with the seats or

apertures

16 and 17 intended to receive the means for securing the lid 2 (hereinafter described), has

cavities

18 and 19 for the

fixed contact members

3 and 4, which extend into

openings

20 and 21 to allow the necessary connections, e.g., with electric wires. Moreover, the housing 1 is provided with

portions forming guides

22, 23 for guiding the sliding of the operating bar 5 and with a stop surface 24 (see FIG. 3.).

The operating bar 5 has at one end a protuberance 25 and a supporting or stop engaging surface 27 and, at the other end, a protuberance 26 and a supporting or stop engaging surface 28.

When the switch is in the rest or non-operated position, and the contact members are normally open, said supporting surface 27 contacts the stop surface 24 of the housing 1, whereas when the switch is in the rest or nonoperating position and the contact members are normally closed, the supporting surface 28 comes into contact with the stop surface 24.

With respect to the means 29 and 30 (FIGS. 2 and 3) for securing the lid 2, they are of elastic type. Each of said

means

29 and 30 is provided with two teeth, such as the

teeth

31 and 32 shaped in a particular manner. As the lid 2 is progressively inserted in the housing 1, the

teeth

31 and 32 are kept in close proximity to each other. After having reached the end of the narrow passage leading to the seat 16, the

teeth

31 and 32 flare out, causing the securing of the lid 2 to the housing 1. Further, the lid 2 is provided with a positioning tooth 37 (see FIG. 3) which will be received in the positioning cut-out 35 when the switch is in the condition of normally open contacts or will be received in the positioning cut-out 36'when the switch is in the condition of normally closed contacts.

The operation of the switch will now be considered with reference at first to the embodiment illustrated in FIGS. 1-4, namely, to a switch having normally open contacts. Under these conditions, the operating bar 5 (see FIG. 3) has its supporting surface 27 in contact with the stop surface 24 of the housing 1 because the return spring 8 is compressed between the abutting element 9 and the end surface of window 10, the spring 8, at one end, surrounding the centering seat 13. The actuation of the switch and closing of the contacts occurs when an operator or a machine part modifies this rest condition by exerting a force on the protuberance 26 of the operating bar 5, which is pushed upward and guided by the

guides

22 and 23. When this occurs, the return spring 8 is compressed, one of its ends surrounding the centering seat 13 situated on the operating bar 5 now being moved and the other end pressing against the abutting element 9, which is stationary. The overrun spring 7 remains in its initial condition until the operating bar 5, on account of its motion, brings the contacts 6a and 6 b of the bridging arm 6 into contact with the fixed

contact members

3 and 4. At this point, the over-run spring 7 behaves like the return spring 8, the spring 7 having one end surrounding the centering seat 14 situated on the operating bar 5 and the other end engaging the bridging arm 6 carrying the movable contact members 6a and 6b which now engage the fixed

contact members

3 and 4.

During the compression of the over-run spring 7, the surface of the window 11 moves away from the bridging arm 6 which carries the movable contacts members 6a and 6b. When the force exerted on the operating bar 5 is discontinued the return spring 8 and the over-run spring 7 expand, but the

contact members

6a, 6b, 3 and 4 do not separate immediately because, owing to the return movement of the operating bar 5, the surface 15 of the window 1 1 does not come into immediate contact with the bridging arm 6. When this does take place, the over-run spring 7 is already in its fully extended position, whereas the return spring 8, expanding further, brings the operating bar 5 into the position shown in FIG. 2 which corresponds to that of a switch with normally open contacts.

During the displacement of the operating bar 5 in either direction, the positioning tooth 37 is always contained inside the positioning seat 35 of the operating bar itself.

Before describing the operation shown in FIG. 5, it will be explained how it is possible to carry out the change from normally open contacts (see FIG. 2) to normally closed contacts (see FIG. 5). In this connection it is to be taken into account that reference 33 (FIG. 1) indicates on the housing 1 the symbol of normally open contacts, and this helps to ascertain visually the electric condition of the switch.

To arrange the switch as shown in FIG. 5, the lid 2 is removed, if necessary with the aid of the slit 34 (see FIG. 1) between the lid 2 and the housing 1, and the operating bar 5 is removed from between the

guides

22 and 23. This operation is feasible since the abutting element 9 which, as stated above, serves to push the operating bar 5 against the stop surface 24 of the housing, is no longer present.

At this point, the operating bar 5 is rotated end-toend through l80 with respect to the position it had in the housing 1 (FIG. 2), thus causing the inversion of the

springs

7 and 8 and of the bridging arm 6 carrying the movable contact members 6a and 6b. The operatingbar 5 is introduced into the housing 1 in such a way that the protuberance 25 passes between the walls of the guide 23 and the protuberance 26 passes between the walls of the guide 22 of said housing. The lid 2 is then rotated end-to-end through 180 with respect to the position illustrated in FIG. 2 and is connected to the housing. 1 with the securing means 21 and 30, respectively on seats 16 and I7, and the positioning tooth 37 is inserted in the positioning seat 36 of the operating bar 5.

The abutting element 9 is located off-center with respect to the center of the lid 2, so that, when the lid 2 is inverted, the element 9 occupies a position different from that which it had when the contact members were normally open. In particular, when the lid 2 is inverted, the element 9 engages the opposite end of the return spring 8, which, in turn, transmits the received thrust to the operating bar 5 to thereby bring the supporting surface 28 into engagement with the stop surface 24 of the housing 1.

Under these conditions the operating bar 5, by reason of the abutting element 9, is pushed downward (FIG. 5') by the spring 8 in such a way that the bridging arm-6 carrying the movable contact members 6a and 6b is detached from the surface 15 of the window 11 and that the over-run spring 7 is compressed and thereby provides a good electric contact between the

fixed contact members

3 and 4 and the movable contact members 6a and 6b.

When the operator or a machine part applies force to the bar 5, the operating bar 5 is pushed upward in such a way that protuberances 26 and 25 slide respectively in

guides

22 and 23. As stated hereinbefore, the return spring 8 is previously compressed, having one end bearing against the operating bar 5 and the other end bearing against the abutting element 9, which is stationary.

During the first movement, the over-run spring 7 extends progressively, since one of its ends is in contact with the bridging arm 6 carrying the movable contact members 6a and 6b, which remains stationary, whereas the other end of the spring 7 is around the centering seat 14 on the operating bar 5 which is in motion. The opening of the contact members takes place only when, in consequence of the movement of the operating bar 5, the surface 15 of the window 11 comes into contact with the bridging arm 6 thereby causing separation of the contacts 6a and 6b from the fixed

contact members

3 and 4. When the force exerted on the operating bar 5 is discontinued, the return spring 8 again brings the switch to its initial position (FIG. 5), compressing the over-run spring 7 and establishing thereby a good electric contact. During the displacement of the operating bar 5 in either direction, the positioning tooth 37 of the lid 2 is always situated inside the positioning seat 36 of the operating bar 5 itself. The electric condition of the switch shown in FIG. 5 is visible on the end of the housing 1 by a normally closed contact symbol not shown but which is under the portion 35 of the lid 2 (FIG. 1). When the lid 2 is inverted, the normally open contact symbol appearing in zone 33 of the housing 1 (see FIG. 1) will be concealed by a lid portion similar to the portion 35, and the symbol for normally closed contacts will be exposed.

One of the advantages of the invention lies in the fact that the abutting element 9 permits the separation of the return spring 8 from the over-run spring 7, which ensures that, in the event of a small displacement of the operating bar 5, the movable contact members 6a and 6b remain pressed on the fixed

contact members

3 and 4.

Another advantage of the invention is that it is easy to change from one condition of the contacts to the other, both because the various elements constituting the movable assembly are all mounted on the bar 5 and are held thereon, and because it is unnecessary to rotate the fixed

contact members

3 and 4 thereby permitting the conversion by means of simple steps which do not require a long time.

A further advantage lies in the fact that it is not possible to insert the lid 2 in the housing 1 in an incorrect manner. In fact, looking at FIG. 3, the position of the normally open contacts, it can be noted that the position of the lid 2 cannot be different from that illustrated. Thus, if the lid 2 were rotated through approximately with respect to the position shown in FIG. 3, the positioning tooth 37 would come into contact with the edge 38 of the operating bar 5, preventing in this way the closure of the lid 2 on the housing 1. It is, therefore, ensured that the electric condition visible from the symbol appearing on the end of the housing 1 (in the example, that of zone 33 of FIG. 1) corresponds to the actual electrical condition of the contact members situated inside the housing and which are not visible.

Although a preferred embodiment of the present invention has been described and illustrated, it will be understood by those skilled in the art that various modifications may be made without departing from the principles of the invention.

What is claimed is:

1. An electric switch convertible from normally closed to normally open contacts and vice versa, said switch comprising a housing member having an opening permitting access to the interior thereof, a lid member for covering said opening, means for holding said members together, a pair of fixed contacts mounted in spaced relation on said housing member, a switch operating bar movably and detachably mounted on one of said members for movement between a normal position and an operated position, an abutting element mounted on one of said members, first spring means acting between said bar and said abutting element to urge said bar into its normal position, a bridging arm having contacts thereon and mounted on said bar for movement therewith and for movement with respect thereto from a first position to a second position, and second spring means acting between said bridging arm and said bar to urge said bridging arm into its first position, said abutting element and said bar being changeable from first positions in which the contacts on said bridging arm engage said fixed contacts in said normal position of said bar and are separated from said fixed contacts in said operated position of said bar to second positions in which the contacts on said bridging arm are separated from said fixed contacts in said normal position of said bar and engage said fixed contacts in said operated position of said bar.

2. A switch as set forth in claim 1, wherein in said first positions thereofisaid bridging arm and said abutting element are disposed at one side of said fixed contacts and in said second positions thereof, said bridging arm and said abutting element are disposed at the opposite side of said fixed contacts.

3. A switch as set forth in claim 2, wherein said abutting element is mounted in a fixed position on said lid 4. A switch as set forth in claim 3, wherein said bar has an aperture therein and said lid member has a'tooth which is receivable by said aperture when said bar and said lid member have predetermined, correct relative positions and which is engageable with said bar to prevent seali'ng of said lid member on said housing member in a different relative position of said lid member with respect to said bar.

5. A switch as set forth in claim 1, wherein said bar, said bridging arm and said first and second spring means are detachable as a unit from the member on which said bar is mounted.

6. A switch as set forth in claim 5, wherein said first and second spring means are mounted on said bar and said bar has retaining elements for holding said spring means and said arm thereon.

7. A switch as set forth in claim 1, wherein said means for holding said members together comprises an elastic, releasable hooking means secured to one of said members and a hooking means receiving and engaging seat forming part of the other of said members.

8. A switch as set forth in claim 1, wherein said lid member is receivable by said housing member in either of two positions of said lid member, wherein one of said members has a pair of electrical symbols thereon corresponding respectively to normally open and normally closed contacts and wherein the other of said'members has a portion which obscures oneof said symbol in one of said positions of said lid member and obscures the other of said symbols in the other of said positions of said lid member. 7

Claims

2. A switch as set forth in claim 1, wherein in said first positions thereof, said bridging arm and said abutting element are disposed at one side of said fixed contacts and in said second positions thereof, said bridging arm and said abutting element are disposed at the oppOsite side of said fixed contacts.

3. A switch as set forth in claim 2, wherein said abutting element is mounted in a fixed position on said lid member and said bar and said lid member are receivable by said housing member in either of two positions of said bar and said lid, one of said two positions being inverted with respect to the other thereof.

4. A switch as set forth in claim 3, wherein said bar has an aperture therein and said lid member has a tooth which is receivable by said aperture when said bar and said lid member have predetermined, correct relative positions and which is engageable with said bar to prevent sealing of said lid member on said housing member in a different relative position of said lid member with respect to said bar.

8. A switch as set forth in claim 1, wherein said lid member is receivable by said housing member in either of two positions of said lid member, wherein one of said members has a pair of electrical symbols thereon corresponding respectively to normally open and normally closed contacts and wherein the other of said members has a portion which obscures one of said symbol in one of said positions of said lid member and obscures the other of said symbols in the other of said positions of said lid member.