US3906176A

US3906176A - Tamperproof switch

Info

Publication number: US3906176A
Authority: US
Inventors: Ernest Reinhold Carlson
Original assignee: Harvey Hubbell Inc
Current assignee: Hubbell Inc
Priority date: 1974-08-02
Filing date: 1974-08-02
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16
Also published as: CA1019369A

Abstract

A tamperproof switch in which the tamperproof feature includes a blocking element biased to a blocking or locking position behind blocking lugs of the switch housing. The blocking element and lugs cooperate to prevent movement of a pivotal switch actuator until the blocking element is depressed to a position beyond the blocking lugs. This is readily accomplished with a special two tine key which engages the blocking element on both sides of the post along which it can move. The key and actuator are so arranged that insertion of the key to depress the blocking element moves the key to a position in which it is connected with the actuator so the actuator can be pivoted by the key to change the operating state of the switch. Tipping the blocking element by attempting to depress it with an unauthorized object causes it to lock on the post.

Description

United States Patent 11 1 Carlson l TAMPERPROOF SWITCH Ernest Reinhold Carlson, Fairfield, Conn.

[75] Inventor:

[73] Assignee: Harvey Hubbell, Incorporated,

Bridgeport, Conn.

[22] Filed: Aug. 2, 1974 [21] App]. No.1 494,319

Primary ExaminerHerman Hohauser Attorney, Agent, or-Firm -lerry M. Presson 4 1 Sept. 16, 1975 l 1571 ABSTRACT A tamperproof switch in which the tamperproof feature includes a blocking element biased to a blocking or locking position behind blocking lugs of the switch housing. The blocking element and lugs cooperate to prevent movement of a pivotal switch actuator until the blocking element is depressed to a position beyond the blocking lugs. This is readily accomplished with a special two tine key which engages the blocking element on both sides of the post along which it can move. The key and actuator are so arranged that insertion of the key to depress the blocking element moves the key to a position in which it is connected with the actuator so the actuator can be pivoted by the key to change the operating state of the switch. Tipping the blocking element by attempting to depress it with an unauthorized object causes it to lock on the post.

6 Claims, 8 Drawing Figures TAMPERPROOF SWITCH This invention relates to key opera-ted switches known in the art as tamper-proof" switches. More particularly, the invention relates to a tamper proof operating mechanism for an electric switch which requires a standard two-prong key for its operation.

Tamper proof switches of various types are well known. Characteristic of such switches is a recessed actuator which prevents manipulation of the switch without some tool, usually a special key which is designed to operate any one of a number of such switches. Typical of such switches is a key guide with a slot through which the key is inserted to couple it to the actuator. so that the actuator can be moved as the key is moved along the slot, to change the operating condition of the switch. Prior attempts to provide a tamper resistent switch have resulted in constructions where the key is of a tortuous or irregular shape, and when inserted, the key aligns with a similarly shaped passage way in the key guide. In another known construction, the key is simply a two-prong key which engages in a recess in the switch actuator to provide the necessary coupling to move or toggle the actuator. These recess and slot arrangements, while reasonably effective to prevent unauthorized operation of the switch, have not been exceedingly difficult to defeat by using a stiff wire or a narrow strip of metal.

Correspondingly, an object of the present invention is to provide a new and improved tamper proof switch adapted to be operated only by a special key, preferably of the two-prong type. and in which the tamper proof arrangement positively prevents unauthorized operation by such devices as nails, wires, screwdrivers, knives, and the like.

Another object of the invention is to provide a tamper proof operating mechanism for an electric switch which requires the use of a rigid key with two prongs in order to disable a blocking or locking device associated with the actuator and which positively prevents switching movement of the actuator unless the authorized key is used.

An additional object is a tamper proof switch with a blocking element biased toward an actuator locking position by a spring of sufficient strength that a rigid two-prong key is required to depress the blocking element to a disabled position where the actuator is coupled to the key and can be moved to cause the switching action.

An additional object is a unique switch assembly including a blocking element so arranged in conjunction with the switch housing that depressing one side only of the blocking element causes the blocking element to lock in its blocking position with the result that unauthorized actuation of the switch is effectively prevented.

A further object is a unique blocking arrangement for a tamper proof switch where the tamper proof feature takes the simple form of a spring and a blocking element in the form of an aperturcd flat metal element having tabs which engage projecting blocking lugs of a switch housing part to prevent moving the actuator from one position to another until the locking element is depressed to a position beneath the blocking lugs of the housing with an authorized key.

The objects described above are realized by providing a spring urged blocking element within the switch actuating mechanism which cooperates with a portion of the switch housing to positively prevent movement of the actuator unless a special key is used to depress the blocking element below blocking lugs ofthe switch housing. The special key, in addition, effectively engages and couples with the actuator in such a manner that the actuator can easily be moved by the key to operate the switch, after the blocking element is depressed by inscrting the key.

Other objects, advantages, and features of the invention will be apparent from the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial view showing a switch, according to this invention. and a key which is used to operate the switch;

FIG. 2 is a view in section taken along line 2-2 of FIG. 1 and showing the switch actuator in one of its extreme positions in which the switch contacts are open;

FIG. 3 is a view corresponding to FIG. 2 and showing the switch actuator in its other extreme position in which the switch contacts are closed;

FIG. 4 is a pictorial view of a blocking element, according to the invention;

FIG. 5 is a partial view in section taken along line 55 of FIG. 2;

FIG. 6 is a view in section taken along line 6-6 of FIG. 2;

FIG. 7 is a view in section taken along line 7-7 of FIG. 6; and

FIG. 8 is a partial view corresponding to FIG. 2 and showing the use of the key to switch the actuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 shows a typical embodiment of a tamper proof switch assembly 10 according to the invention. Switch I0 comprises a housing or support including a base 12 with a cover 14, both formed from an insulating material. Cover 14 has a recess corresponding to the configuration of a body portion 16 of a mounting strap 18 of the type customarily used to secure the switch assembly 10 to a mounting box (not shown). Secured to mounting strap 18 and forming part of the housing is a key guide 20 of insulating material having a centrally located key receiving slot 22. Slot 22 is of a width to receive and guide a two prong end 24 of a switch operating key 26 which is positioned as shown at FIG. I, for insertion through the slot. The width of slot 22 is only slightly greater than the thickness of key 26.

Key 26 can have another bifurcated end 28 with rounded tines or prongs 30. The two prong end 24 having tines 32 with their respective outer edges 34 generally parallel is used to operate an AC tamperproof switch. At the other end of key 26, the tines 30 with rounded sides are for operation of a DC tamperproof switch.

While the switch described and shown herein is a typical embodiment of an AC tamperproof switch. it will be appreciated that the invention can readily be used with a DC type tamperproof switch, with minor modification, and without departing from the scope of this in vention.

As shown at FIG. 2, the body portion 16 of mounting strap 18 has an opening 36 immediately beneath key guide 20 which generally follows the outline of the guide but is slightly smaller than the guide. Guide presents an arcuately curved inside surface 38 along wall 39 in which slot 22 is formed. Surface 38 is bounded on each side by a side wall 40 having a pair of recesses 41 and 42 (FIGS. 2 and 3) which definea centrally located generally v-shaped blocking lug 44 which is integrally formed with key guide 20. The respective side walls 40 are in parallel planes on opposite sides of slot 32 (FIG. 6).

Mounted within housing 12, for pivotal movement about a predetermined axis extending transversely of the housing is a switch acutator 46. Actuator 46 is moveable between one extreme position in which

switch contacts

48 and 50 are closed, as shown at FIG. 3, and another extreme position in which a switch operating cam 52 of the actuator engages a leaf type moveable contact arm 54 of the moveable contact 48 to open the contacts, as shown at FIG. 2.

Actuator 46 has an over-center toggle action as a result of a helically wound compression spring 55. The lower end of spring 55 extends over a cylindrical projection 56 on bottom wall 58 and seats on edges 57 which flank the projection of the housing. The upper end of the spring seats on a washer 59 on a cylindrical inner tip 60 of actuator 46. The edges 57 permit the lower end of the spring to pivot, and edges 61 which flank tip 60 permit washer 59 and the upper end of the spring to pivot. Compression spring 55 provides a toggle action which urges actuator 46 toward one or the other of its two extreme positions in which the switch contacts are either open or closed.

Mounted within the housing on supports 62, and 64, integral with the housing, are

cushion buttons

66 and 68 respectively. These buttons are dimensioned and positioned to be engaged by

stop surfaces

70 and 72 respectively of the actuator to cushion the actuator at each extreme end of its movement and thereby make the switch operation essentially silent.

Acutator 46 has

arcuate cars

76 and 78 at each side of a centrally located post 80.

Ears

76 and 78 are each arcuately curved and are closely adjacent the curved inner surface 38 of guide 20. The cars have a width slightly less than the distance between the side walls 40 of key guide 20. As a result of these clearances, the actuator can pivot between its extreme positions.

At the inner end of post 80 is an annular recess 82 (FIGS. 2 and 3) which provides a seat for a helical compression spring 84. Seated on the upper endof spring 84 is a blocking element 86 mounted on post 80 and having a central opening 88 through which post 80 extends. Blocking element 86 has a body 89 of generally rectangular exterior configuration. (FIGS. 4,5 and 6) and has locking tabs or stops 90 and 92 of a width less than the body at its opposite sides and which project in a direction transverse to the direction of movement of actuator 46. The locking

tabs

90 and 92 project beyond the sides of the actuator and into either recesses 41 or recesses 42 depending on the position of the actuator. Opening 88 is formed by coining the metal of locking bar 86 to form a collar 94 projecting toward recess 82 and which presents a sharp inside corner 96. The diameter of opening 88 is only very slightly greater than the diameter of post 80. Locking

tabs

90 and 92 each have a width which is slightly less than the width of

recesses

41 and 42. This dimensioning enables

tabs

92 and 90 to seat in the respective recesses against either surfaces 98 or surfaces 100 of blocking lugs 44, depending on the position of the acutator.

As is shown at FIGS. 5 and 6, the distance between the outer edges l02o'ftabs 90 and 92 is slightly less than the distance between the" inside surfaces 103 of either recesses 4 1 or 42. In addition, the distance between

edges

104 and 106 of the body of blocking element 86 locking bar is slightly less than the distance between the inner surfaces of the walls 40 of the key guide 20. Correspo ndinglyQwhen locking bar 86 is depressed (FIG. 8) so its outer or upper surface 108 is below the inner end of blocking lug 44, actuator 46 can beswitched fromone position to another.

'Such depressing of blocking element 86 against the action of spring 84 requires that blocking element 86 be engaged simultaneously at two locations 109 and 110 (FIG. 5) on opposite sides of post 80 in a plane perpendicular to post 80. Blocking element 86 is readily depressed by using end 24 of key 26. With the key inserted through slot 20 (FIG. 8) and blocking element 86 depressed to a position beneathblocking lug 44, movement of the key along the slot causes the actuator 46 to switch from one of its extreme positions to the other. The edges 34 of end 24 of the key engage against the side surfaces 111 and 112 respectively of

cars

76 and 78 to connect the key to the actuator and permit movement of the actuator against the action of the compression toggle spring 55 which holds the actuator in either of its extreme positions. 7

Unauthorized operation of the switch is effectively thwarted by the blocking element 86 and the blocking lugs 44. Any attempt to operate the switch for example by using an unauthorized object suchas a nail or screwdriver which engages only one side of blocking element 86 will cause the blocking element to tip or tilt (as shown in dotted lines at FIG. 3) with respect tolpost 80, and the sharp inner edge 96 of the blocking element will then grip or dig into the insulating material of post 80. Correspondingly, it is impossible to depress locking element 86 to a position beneath blocking lug 44 without simultaneously engaging the blocking element on both sides of post 80. Compression spring 84 is of sufficient strength that thin wire or other material which can readily bebent to, for example, a hair pin shape so both sides of blocking. element 86' can be simultancously engaged, will have insufficient strength to depress the blocking elernent without bending.

Actuator 46 has trunions mounted for pivotal movement in cooperating bearing

halves

122, 124 in cover 14 and base 12 respectively, as shown in FIGS. 6 and 7. After the switch is assembled, the action of toggle spring 54 is to urge the actuator toward cover 14 so the trunions of the actuator are forced against the generally semicircualr bearing half recesses 122 of the cover. Inward movement of the actuator toward rear wall 58 of the housing is prevented by the bearing surfaces 124of the base 12.

ing the corners at these edges to engage the surfaces of the. wings tofurther resist depressing the locking bar with an unauthorized object. I

By virtue ,ofthis arrangement where the width of slot 22 is slightly less-than the diameter of post 80, flat objccts such as a screwdriver are blocked against insertion by the tip of post 80. Unauthorized operation using a tube or pipe is also prevented by virtueof this dimensioning where the post has a diameter greater'thah the width of slot 22. However, since post 80 has a'uriiform diameter along a substantial portion of its length; including that portion along which the blockingelement 86 can move. and since key 26 can be used to depress the blocking element without tilting or tipping, the switch can easily be operated by one having an authorized key. The extent of inward movement of the blocking element against the action of spring 84 is limited by engagement of the bottom surface 131 of the blocking element with a shoulder 133 surrounding recess 82 (FIG. 8).

In view of the foregoing, it is apparent that a tamperproof lock switch, constructed in accordance with this invention, effectively defies tampering with unauthorized objects, and can be operated only by an authorized key of the type shown at FIG. 1. While the typical preferred embodiment described herein is for a switch of the AC type, adapted to be operated with end 24 of key 26, it is, of course, apparent, that by changing the configuration of post 80 and the space between

cars

76 and 78, the tamperproof features of this switch can be adapted to a DC switch requiring the key configuration of end 28 of key 26.

An additional advantageous feature of the switch of this invention is that upon movement of the actuator 46 to either of its extreme positions, spring 86 exerts an outwardly directed force which tends to eject the key from the switch. This outwardly directed force simplifies and assures removal of the key from the switch after it has been switched from one position to the other. By virtue of the sharp or narrow tip on blocking lug 44 and the offset location of projection 56 at rear wall 58 which retains the lower end of toggle action spring 55, the switch has no stable center position and will always move to one of extreme positions of H65. 2 or 3 whenever the key is removed. This occurs depending on the position of the actuator, either as a result of the off center toggle action of spring 55 or as a result of the action of spring 84 which forces the

tabs

90 and 92 of the blocking element into

recesses

41 or 42.

While a typical preferred embodiment of a tamperproof switch according to this invention has been shown and described in detail, it is apparent that changes can be made without departing from the scope of this invention, as set forth herein and as defined in the amended claims.

I claim:

1. A tamper proof key operated electric switch comprising a housing;

a switch mechanism carried by the housing, said switch mechanism including an actuator moveable along a predetermined path to a first position in which the switch is in one condition of operation, and a second position in which the switch is in another condition of operation;

said switch mechanism including key receiving means to receive a key for moving the actuator to said positions;

blocking means in the housing;

a blocking element within the housing and moveable withrespect to the actuator to a blockingposition in which the blocking element I cooperates with the blocking means to prevent 5 I movement of the actuator, and

a released position in which the actuator can be moved from one of its positions to the other; spring means for urging said blocking element toward its blocking position; said blocking element having surface means positioned for engagement by. a key inserted in said key receiving means for moving said blocking element to said released position so that said actuator can be moved to said positions upon insertion of the key. 2. A tamper proof switch according to claim 1 wherein said blocking means includes a pair of blocking lugs at opposite sides of said actuator; and said blocking element includes a pair of tabs which in said blocking position of the blocking element, cooperate with said lugs to prevent movement of the actuator. 3. A tamper proof switch according to claim 1 which further includes means mounting said actuator for pivotal movement;

and

means mounting said blocking element on said actuator for movement with the actuator; said blocking element presenting a pair of key engagable surfaces exposed with respect to said key receiving means to enable moving said blocking element to its released position upon insertion of a key. 4. A tamper proof switch according to claim 1 wherein said spring supports said blocking element for tilting movement with respect to the actuator; and cooperating means on said actuator and blocking element for locking said blocking element against movement to its released position upon tilting of the blocking element. 5. A tamper proof switch according to claim 1 wherein said blocking element includes surface means for engagement by a key at two spaced apart locations; said spring supports said blocking element for tilting movement; and means extending along the path of travel of the blocking element between its released and blocking positions to lock the blocking element against movement to its released position, in response to tilting of said blocking element. 6. A tamperproof key operated electric switch comprising housing means; switch contacts within the housing means; an actuator within the housing means mounted for pivotal movement to a first position in which the switch contacts are opened. and second position in which the switch contacts are closed; means defining a slot opening through the housing means for insertion of a key to operate the actuator; blocking means within the housing means;

moved from one of its positions to another;

spring means for urging said blocking element toward its blocking position;

said blocking element having surface means positioned for engagement at two locations by a key inserted through said slot for moving said blocking element to said released position; and

means on said actuator for connecting a key inserted through the slot to the actuator for movement therewith to pivot the actuator and switch the switch contacts.

Claims

1. A tamper proof key operated electric switch comprising a housing; a switch mechanism carried by the housing, said switch mechanism including an actuator moveable along a predetermined path to a first position in which the switch is in one condition of operation, and a second position in which the switch is in another condition of operation; said switch mechanism including key receiving means to receive a key for moving the actuator to said positions; blocking means in the housing; a blocking element within the housing and moveable with respect to the actuator to a blocking position in which the blocking element cooperates with the blocking means to prevent movement of the actuator, and a released position in which the actuator can be moved from one of its positions to the other; spring means for urging said blocking element toward its blocking position; said blocking element having surface means positioned for engagement by a key inserted in said key receiving means for moving said blocking element to said released position so that said actuator can be moved to said positions upon insertion of the key.

2. A tamper proof switch according to claim 1 wherein said blocking means includes a pair of blocking lugs at opposite sides of said actuator; and said blocking element includes a pair of tabs which in said blocking position of the blocking element, cooperate with said lugs to prevent movement of the actuator.

3. A tamper proof switch according to claim 1 which further includes means mounting said actuator for pivotal movement; and means mounting said blocking element on said actuator for movement with the actuator; said blocking element presenting a pair of key engagable surfaces exposed with respect to said key receiving means to enable moving said blocking element to its released position upon insertion of a key.

4. A tamper proof switch according to claim 1 wherein said spring supports said blocking element for tilting movement with respect to the actuator; and cooperating means on said actuator and blocking element for locking said blocking element against movement to its released position upon tilting of the blocking element.

5. A tamper proof switch according to claim 1 wherein said blocking element includes surface means for engagement by a key at two spaced apart locations; said spring supports said blocking element for tilting movement; and means extending along the path of travel of the blocking element between its released and blocking positions to lock the blocking element against movement to its released position, in response to tilting of said Blocking element.

6. A tamperproof key operated electric switch comprising housing means; switch contacts within the housing means; an actuator within the housing means mounted for pivotal movement to a first position in which the switch contacts are opened, and second position in which the switch contacts are closed; means defining a slot opening through the housing means for insertion of a key to operate the actuator; blocking means within the housing means; a blocking element; means on said actuator mounting said blocking element for pivotal movement with the actuator and for movement with respect to the actuator, in a direction generally radially of the direction of pivotal movement of the actuator; said blocking element being moveable in said radial direction to a blocking position in which the blocking element cooperates with the blocking means in the housing to prevent pivotal movement of the actuator, and; a released position in which the actuator can be moved from one of its positions to another; spring means for urging said blocking element toward its blocking position; said blocking element having surface means positioned for engagement at two locations by a key inserted through said slot for moving said blocking element to said released position; and means on said actuator for connecting a key inserted through the slot to the actuator for movement therewith to pivot the actuator and switch the switch contacts.