US 3757063 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
United States Patent 11 1 Hart et al. 1 1 Sept. 4, 1973  OUTPUT TAPPING UNIT FOR USE WITH 3,551,617 12 1970 Seelbach zoo 51.07 ELECTRIC DISTRIBUTION TRACKS 3,639,709 2/1972 Hart et al.... 200/51 R 3,611,252 10/1971 Fremont 339 21 R Inventors: Derek James Hart; Robert Davis; 3,339,038 8/1967 Jorgensen et al. 200 50 B Wilhelm Henry Valentine Sanhen, all of London, England Assignee: Thorn Lighting Limited, London,
England Filed: Aug. 3, 1972 Appl. No.: 277,753
Foreign Application Priority Data Oct. 18, I971 Great Britain 48,426/71 Primary Examiner-David Smith, Jr. AttorneyRobert F. O'Connell  ABSTRACT An electrical fitting enabling power to be tapped from an electric distribution trunking has movable contacts carried by rockers which move, following a scissor action, to set the contacts to on and off positions. The fitting has a rotatable clamp to allow the fitting to be secured to the trunking and has an interlocking arrangement effective between the clamp and the rockers to ensure:
1. that the clamp cannot be released when the contacts are set to their on positions; and
2. that the contacts are prevented from being set to their onpositions when the clamp is released.
10 Claims, 4 Drawing Figures PATENTEU SEP M973 SHEET 1 OF 2 PATENTEU E 41975 3.757. 063
sum 2 BF 2 OUTPUT TAPPING UNIT FOR USE WITH ELECTRIC DISTRIBUTION TRACKS The present invention relates to output tapping unit for use with electric distribution tracks. The tapping unit enables electric power to be drawn from the track for supply to appliances such as electric tools and lamps. The tapping unit is particularly, but not exclusively, suitable for use with a track such as is described and claimed in our U.I(. Patent Specification.
According to the present invention, there is provided an output tapping unit for use with electric distribution tracks having bare, spaced-apart track conductors, the unit comprising a housing containing clamping means for releasable engagement with the track to clamp the unit thereto, a switch assembly including a pair of contacts which are movable between on and off positions, the contacts being able to contact the track conductors in the on position, and movable interlocking means arranged to coact between the switch assembly and the clamping member such that, with the unit clamped to the track and with its contacts in the on position, the interlocking means prevent release of the clamping means from the track and thereby displacement of the unit therefrom.
Preferably, the interlocking means are also arranged to prevent the contacts being switched to their on position when the clamping means is released.
In a preferred embodiment, the switch assembly consists of a pair of pivoted rocker elements, each carrying one of the contacts, whose movements are controlled, conveniently simultaneously, by a cam which is operable from outside the housing. It is preferred to bias the rocker elements towards the off position, for example by a generally U-shaped leaf spring bearing against the rocker elements. The clamping means in the preferred embodiment is a rotatably-mounted member having ears which can be projected out of the housing to engage the track for clamping the unit thereto, and which can be withdrawn into the housing to release the unit from the track.
The interlocking means preferably comprise a cam, which is rotatable with the clamping means, and a camfollower which is movable towards and away from the switch assembly in response to releasing and clamping rotations respectively of the clamping member. Rotation of the clamping member in the releasing direction is prevented by arranging that the cam-follower can abut the switch assembly while this is in the on position, thereby arresting the cam-follower and hence preventingrotation of the cam and the clamping means. It is preferred that the cam-follower is in the form of a U- shaped yoke whose arms are able to embrace the switch assembly inthe off position thereof when the clamping means is released, so as to make it impossible for the switch assembly to adopt the on position.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
FIG. 1 is an illustration of the tapping unit and an electrical distribution track,
FIG. 2 illustrates the unit, partly broken away, to show electrical contact structure within the unit,
FIG. 3 is a cross-section of the unit illustrating the position of its parts when attached to the track, and
FIG. 4 is a cross-section, similar to FIG. 3, but showing the position of the parts when the unit is released from the track.
Before describing the output tapping unit in more detail, a brief description of the electrical distribution track will be given for clarity. The track 10 comprises an elongate member made, for example, from an extrusion of a plastics material such as P.V.C. The extrusion 11 has a base 12 and sides l3, 14 extending perpendicularly from the longitudinal edges thereof. The sides 13, 14 include housings in which track-conductor strips 15, 16 are carried. The track-conductors 15, 16 are accessible from the inner region of the track 10 by way of slots or recesses in the extrusion 11 which are inclined towards the base 12. A further track-conductor 18 is supported in the base 12 of the extrusion 11, and is used to provide an earth line. The sides 13, 14 additionally include flanges 22, 23 forming ledges to which the tapping unit and other accessories can be clamped. The flanges 22, 23 are located on the inner surfaces of the sides 13, 14 remote from the base 12 and include downwardly-open grooves 24, 25 which, like the flanges 22, 23, extend longitudinally along the track 10. A mating external covering track 29 may surround the track 10 and engage the grooves 24, 25 as shown in FIG. 1. It will readily be appreciated from FIG. 1 that the track 10 is asymmetrical in cross-section, about a central plane parallel to the sides 13, 14. In particular, the base 12 has a longitudinally extending groove 26 located adjacent one side 13. The base 12 further includes a surface 27 which is inclined towards the trackconductor 18 from the side 14.
The output tapping unit 30 has a housing 31 within which a movable contact structure and a clamping arrangement are mounted.
The movable contact structure is shown most clearly in FIG. 2 in which 32, 33 are a pair of movable contacts for making'and breaking contact with the track conductors 15, 16, and thus constitute a form of switch. The contacts have screw-clamp connector terminals 34, 35 of the captive-nut type associated therewith, to which cable leads from an appliance can be connected. The contacts 32, 33 can be moved from the position shown in the FIG. 2 to project out of the housing 31. In such an open position, which is shown in FIG. 3 the contacts 32, 33 can abut track-conductors l5, 16 carried by the track 10, and hence this constitutes a switch-on condition of the tapping unit.
Movement of the contacts 32, 33 is controlled by means ofa cam assembly acting on rocker elements 37, 38 which carrying the contacts 32, 33. The rocker elements 37, 38 operate in a manner generally similar to a pair of scissors, and are mounted in the housing 31 on a pivot 40 carried by a side wall 41 of the housing. It will be appreciated that when the lower portions 42 of the rocker elements 37, 38 are moved apart, then the contacts 32, 33 also are. moved apart into their outer, switch-on position. A substantially U-shaped leaf spring- 43 is disposed about the lower portions 42 of the rocker elements and serves to bias these portions inwardly towards one another, viz. to the switch-off condition of the tapping unit 30. I
The cam assembly consists of an elliptical cam 44 which is mounted on the side wall 41 between the lower portions 42 of the rocker elements 3.7, 38. The cam 44 is fast with a shaft which extends through the side wall 41, the shaft terminating in an enlarged head portion 45. The head portion 45 is provided with apertures so that control cords can be attached thereto for convenient control of the cam 44 when the track is mounted oer-head. The cam can be retained on the shaft by known means, which for example cound consist of a circlip or retaining nut. When the shaft and cam 44 are rotated through approximately 90 from their position shown in FIG. 2, the lower portions 42 are moved apart against the bias of the leaf spring 43 and corresponding movement of the contacts 32, 33 into the outer or switch-on position therefore results. When the cam 44 is rotated in this way for switch-on it is held in this position by engaging two complementary grooves 47 formed in the lower portions 52.
The tapping unit 30 includes a third contact (not shown) for making electrical connection with the earth-line conductor 18 of the track 10. The third contact consists of an upwardly-bowed metallic strip which is mounted on the top face of the housing 31. An earth lead from an appliance can be wired into a bush or terminal attached, within the housing 31, to the metallic strip.
A clamping member for securing the tapping unit 30 to the track 10 is illustrated in FIGS. 1, 3 and 4. The clamping member is a one-piece moulding consisting of a clamping element 56, a substantially eliptical cam portion 57, a knurled disc portion 58 and a shaft portion, visible in FIG. 1, between the element 56 and the cam portion 57, the shaft portion being rotatably mounted within the housing 31. The bottom face of the housing 31 has an opening for a cable from an appliance, the cable conveniently being led through a bore 60 extending wholly through the clamping member to the connector terminals 34, 35.
The clamping element 56 includes a pair of opposed ears 61 which can be projected out of the housing 31 and withdrawn into the housing upon appropriate rotations of the clamping member. In FIGS. 1 and 4, the ears 61 are shown withdrawn into the housing, and in FIG. 3, the ears 61 project out of the housing 31 through slots 62 in opposite faces of the housing 31. Rotation of the clamping member is obtained by manipulation of the knurled disc portion 58, the knurled periphery of which projects out of the housing 31 through slots 63 in opposite faces of the housing 31.
The underneath of each ear, as viewed in FIG. 1, has an inclined or ramped surface 64, the presence of which is to obtain a smoothly. increasing clamping force when the clamping member is rotated.
Clamping of the tapping unit 30 to the track 10 is accomplished as follows. The clamping member is first checked, and if necessary manipulated such that the cars 61 are withdrawn into the housing 31. The housing 31 is then inserted into the track 10 from below; it will be noted that, by virtue of projections 65 and an inclined surface 66 in its top face, the housing 31 is similarly asymmetrical as the track 10. Thus, in order to fit within the track, the housing 31 must be appropriately oriented relative to the track, in order that its projections 65 can enter the groove 26 in the track 10. The similar asymmetry of the housing 31 and the track 10 ensure that electrical power supplied to an appliance through the track 10 and tapping unit 30 is of the correct polarity. Having correctly inserted the housing 31 into the track 10, the clamping member is then rotated anticlockwise as seen in FIG. 4, through approximately 90, by manipulating the disc portion 58. This rotation causes the ears 61 of the clamping element 56 to emerge from the housing 31 into contact with the ledges formed by flanges 22, 23 of the track 10. After the cars 61 have initially made contact with the said ledges, continued rotation of the clamping member to the position shown in FIG. 3 causes the ramped surfaces 64 to ride over the said ledges, producing an increasing clamping force urging the housing 31 firmly against the base 12 of the track 10. This ensures good electrical contact between the third, earth-line contact of the tapping unit 30 and the conductor 18 of the track 10.
Movable interlocking means are provided to ensure that the tapping unit 30 cannot be unclamped and released from the track 10 whilst the contacts 32, 33 are engaging the track conductors 15, 16 in the switch-on position. The interlocking means are also arranged to make it impossible to move the contacts 32, 33 from the switch-off position into engagement with the track conductors 15, 16 unless the housing 31 is already clamped to the track 10. The interlocking means consist of a cam-follower to which coacts with the elliptical cam portion 57 of the clamping member.
The cam follower 70 is in the form of a U-shaped yoke, whose arms 71 extend towards the movable contact structure. The arms 71 are received in grooves, not shown for clarity, in the opposed inner walls of the housing 31 so that the cam-follower is guided for reciprocable movement towards and away from the movable contact structure. Remote from the tips of the arms 71, the yoke 70 has an upstanding portion 72 in the middle of which is formed a depression 73. The depression 73 forms a seating for a swelling 74 on the elliptical cam portion 57, the swelling lying on the minor axis of the cam portion 57. The cam follower 70 is biased against the cam portion 57 by a compression spring 75.
The operation of the interlocking means will now be described with reference to the positions of the parts shown in FIG. 3. In FIG. 3, the housing 31 is clamped to the track 10 with the ears 61 of the clamping element 56 in engagement with the said ledges of the track 10. In this position of the clamping member, the major axis of the cam portion 57 lies transverse to the length of the track, and the swelling 74 lies in the depression 73 of the cam follower 70. The cam follower is in its extreme left-hand position. Whilst in this position, the movable contact structure can be actuated at will to move the contacts 32, 33 from their switch-on to switch-off positions and vice versa. When the contacts 32, 33 are in their switch-on position as illustrated, it is impossible to rotate the clamping member sufficiently to unclamp and release the housing 31 from the track 10. An initial small rotation of the clamping member causes its cam portion 57 to advance the camfollower 70 slightly towards the contact structure The tips of the arms 71 then abut the edge of the U-shaped leaf spring 43 and movement of the cam-follower 70 is halted. The cam follower 70 in turn blocks the cam portion 57, preventing further rotation of the clamping member.
The clamping member can only be rotated to release the housing 31 from the track 10 when the contacts 32, 33 are in their switch-off position which is illustrated in FIGS. 1 and 4. In this position, the lower portion 42 of the rocker elements 37, 38 are in their innermost, switch-off positions with the limbs of the U-shaped leaf spring 43 in contact therewith. It is arranged that the gap between the arms 71 of the cam-follower 70 is greater than the distance between the immediately adjacent portions of the limbs of the spring 43 when the contacts 32, 33 are in their switch-off position. The cam-follower 70 is thus free to be advanced fully to the right to the position illustrated in FIG. 4. This freedom of movement of the cam-follower 70 allows the major axis of the cam-portion 57 to be aligned with the length of the track 10, and thus permits the rotation of the clamping member which releases the ears 61 of the clamping element 60 from the said ledges of the track It will be appreciated that, with the cam-follower 70 held in its fully advanced (FIG. 3) position corresponding to the released condition of the clamping member, it is impossible to operate the contact structure so as to move the contacts 32, 33 to their switch-on position. This is because the arms 71 of the cam-follower 70 embrace i.e. are located to either side of the leaf-spring 43 thereby preventing outward movement of its limbs and of the lower portions of the rocker elements 37, 38.
Rotation of the clamping member is restricted to approximately 90, between the extreme positions thereof illustrated in FIGS. 3 and 4. This is accomplished by means of a stopping element 75 in the form of a ledge formed, in this instance, on one surface of the knurled disc portion 58. The stopping element 75 possesses two stopping faces 75a and 75b which in turn are able to abut one or other of the inner walls of the housing 31 adjacent the slots 63 so as to limit rotation of the clamping member in an anticlockwise and a clockwise direction respectively.
1. An output tapping unit for use with electric distribution tracks having bare, spaced-apart track conductors, the unit comprising:
clamping means within said housing, said clamping means including a rotatably-mounted member having ears for releasably engaging ledges provided in an associated electric distribution track to clamp the unit thereto;
said rotatably-mounted member further including a cam portion; said housing being slotted to permit said ears to emerge from, and to retract into, said housing upon clamping and releasing rotation of said housing;
a switchable contact assembly within said housing,
said contact assembly including:
two contact elements mounted in said housing for switchable movement between on and off positions wherein said contact elements are able to make contact with the conductors and of a distribution track in their on position, and
movable interlocking means comprising a cam follower co-operable with said cam portion to effect reciprocable movement of said cam follower towards and away from said contact assembly to prevent release of said clamping means from said track when said contact elements are in their on positions.
2. A unit according to claim 1, wherein said contact assembly further includes a pair of pivoted rocker elements which carry said two contact elements, said rocker elements being operable to move said elements inwardly and outwardly to their off and on positions respectively.
3. A unit according to claim 2, wherein said rocker elements are mounted on a common pivot intermediate their ends, and said contact elements are carried on adjacent ends of said rocker elements, exteriorlyoperable rotatable camming means being provided to effect movement of said rocker elements, said camming means being located between said rocker elements on the opposite side of said common pivot from said contact elements.
4. A unit according to claim 1 wherein said rotatablymounted member has a disc portion whose periphery projects out of said slotted housing to enable said member to manipulated.
5. A unit according to claim 1, wherein said cam follower is retracted and spaced from said contact assembly when said clamping member is in its clamping position, said cam follower being capable of moving into abutment against said contact assembly in the on condition thereof when advanced by said cam portion during an initial releasing rotation of said clamping member thereby preventing further releasing rotation of said clamping member, said cam follower and contact assembly being adapted to permit free advancing movement of said cam follower when said contact assembly is in the off condition.
6. A unit according to claim 2, wherein said cam follower is a generally U-shaped yoke having two spaced fingers, the tips of which are located close'to the rocker elements of said contact assembly when said clamping member is in its clamping position, said yoke being movable by said cam portion towards said rocker elements in response to an initial releasing rotation of said clamping member and the fingertips of said yoke being located to abut against said rocker elements, when these are in their on positions, thereby to react against said cam portion and prevent further releasing rotation of said clamping member.
7. A unit according to claim 3, when the spacing between said fingers is sufficient to allow said fingers to clear said rocker elements when the latter are in their off positions, thereby permitting unimpeded advance movement of said yoke and providing corresponding freedom of rotation of said clamping member to its release position.
8. A unit according to claim 6, wherein while said fingers are fully advanced, corresponding to the release position of said clamping member, said fingers are located on either side of said rocker elements, thereby preventing operation of said rocker elements to set the contact elements to their on positions.
9. A unit according to claim 5, wherein said cam portion is of generally elliptical shape, its major axis lying across said housing when said clamping member is in its clamping position, said major axis being aligned along said housing with said cam follower fully advanced when said clamping member is moved to its releasing position.
10. A unit according to claim 9, wherein spring means are provided to bias said cam follower against said cam portion.