GB2253098A - Lampholder with safety switching - Google Patents

Abstract

A bayonet lampholder comprises a hollow body (1) which provides a bayonet socket and houses a rotatable member (2) which supports bulb contact terminals. The rotatable member is housed with the body such that insertion of a bayonet bulb rotates the body. The lampholder may be provided with a transverse switch bar (4) which in one position, the operative position, effects electrical contact between the bulb contact terminals and power supply terminals also housed within the body, and in a second position, the inoperative position, such electrical contact is broken. The switch bar and rotatable member define inter-engaging formations (Figs. 3, 5) whereby rotation of the rotatable member from a second (Fig. 5) to the first (Fig. 3) position resulting from the removal of a bulb from the lampholder causes a switch bar to be moved to the "off" position. The switch bar and the rotatable member define further locking formations which prevent the switch bar from being moved from the inoperative to the operative position until a bulb is again inserted into the socket and the rotatable member is rotated from the first to a second position. In another form (not shown), which may or may not have a switch bar, the rotatable member is arranged such that there can be no electrical contact between the bulb contacts and the power supply terminals when the rotatable member is in its first position. The contact terminals extend through the rotatable member and are axially movable between first and second Positions. Coil springs are provided to balance the bulb contact terminals into the first position. Insertion of a bayonet bulb into the lampholder socket depresses the bulb contacts from the first to the second position. The contact terminals provide locking means, whereby when they are in their first position the rotatable member cannot be rotated from its first to its second position. Thus electrical contact cannot be effected between the bulb contact terminals and the power supply terminals unless a bulb is inserted into the lampholder. <IMAGE>

Description

LAMPHOLDER The present invention relates to a safety lampholder for receiving a bayonet bulb.

With the most commonly available form of this type of lampholder, removing the bulb from the holder leaves the contact terminals exposed. Unless care is taken to isolate the lampholder from the supply when removing a bulb these contacts may be left live presenting an obvious danger to anyone changing a bulb or to inquisitive children.

There have been various proposed structures for safetv lampholders in which contact with the power supply terminals is prevented when a bulb is not in position. Examples of such safety lampholders are described in British Patent No. GB-2-207 819 and British Patent Specification No.GB-2-207 818.

British Patent No.GB-2-207 819 describes a safety lampholder in which the terminal contacts that are intended to bear against an inserted bulb are supported by a carrier rotatably mounted within the body of the lampholder. The contact terminals are in the form of spring strips and extend through the carrier. Power supply terminals are supported by the body such that they define a surface facing the contact carrier. The contact carrier is rotatable with respect to the lampholder body and the power supply terminals between an inoperative position, in which the contact terminals are spaced apart from the supply terminals, and an operative position in which there is electrical contact between the two sets of terminals.The contact carrier supports a sleeve that defines two slots that correspond with the axial portion of the usual "L" shaped slots provided in the lampholder body to receive the pins of a bayonet type bulb. The slots in the carrier sleeve are positioned so that when they are aligned with the slots on the body the carrier is in the inoperative position.

The arrangement is such that as a bulb is inserted into the lampholder the sleeve and contact carrier are forced to rotate with the bulb from the inoperative to the operative position, and vice versa. Thus when a bulb is removed from the lampholder the contact terminals are automatically isolated from the supply terminals. In addition the carrier and lampholder body are adapted so that when the bulb is removed and the carrier is in the inoperative position the carrier and lampholder body are resiliently engaged, tending to resist rotation of the carrier thereby providing a locking mechanism for the carrier.

The rotational force required to rotate the carrier therefore prevents the carrier being moved accidentally or by childrens inquisitive fingers. The carrier may alternatively be arranged so that axial movement as well as rotational movement is required to move it to the operative position thereby providing a more secure carrier locking mechanism.

Patent specification No. GB-2-207 818 describes a safety lampholder which has a switchbar housed transversely in the body cf the lampholder, situated between the contact terminals and the power supply terminals. The switchbar carries bridging contacts and is switchable between a position in which the bridging contacts effect an electrical contact between the two sets of terminals and a position in which such contact is broken. With these type of lampholders it is particularly difficult to be certain that the contact terminals are isolated from the supply when a bulb is not in position. Patent Specification No. GB-2-207 818 describes a switching lampholder structure for which it is not possible to remove a bulb unless the switchbar has first been manually moved to a position in which the contact terminals are isolated from the power supply terminals.A disc supporting a depending shutter element is rotatably mounted within the body of the lampholder between the switchbar and the contact terminals, such that the contact terminals extend through arcuate slots in the disc and abut the underside of the switchbar. The shutter elements. define axial slots which are aligned with the slots in the lampholder body when there is no bulb present. The arrangement is such that the shutter elements, and therefore the disc, rotate as a bulb is inserted or removed. The switchbar is movable between an operative position in which there is electrical contact between the contact terminals and the bridging contacts, and an inoperative position in which such contact is broken.The disc carries at its periphery an upstanding peg that engages with a slot defined in the underside of the switch bar when there is no bulb present and the switchbar is in the inoperative position, thereby preventing movement of the switchbar to the operative position. Inserting a bulb rotates the disc, disengaging the peg from the slot, and leaving the switchbar free to be moved between positions. In this position the peg now abuts the side of the switchbar so that the disc cannot be rotated back, and therefore the bulb cannot be removed, unless the switchbar is first moved to the inoperative position. To prevent accidental rotation of the disc when a bulb is not present a locking means is provided whereby axial movement of the disc is required to free it for rotation.

The above structure has the disadvantage that the switchbar must be manually returned to the inoperative position before a bulb can be removed. It is not desirable to lock a bulb in a lampholder.

In addition, the requirement of the locking means that the disc must be capable of moving axially increases the minimum axial length of the lampholder rendering it unsuitable for some applications.

It is an object of the present invention to provide a safety lampholder that obviates or mitigates these disadvantages.

According to a first aspect of the present invention there is provided a safety lampholder for receiving a bayonet bulb, the lampholder comprising a hollow body defining slots at one end thereof, each of the slots having two mutually inclined limbs along which the bayonet pins of a bulb slide during insertion and removal of the bulb, a rotatable member mounted within the body and rotatable with respect to the body between first and second positions, the rotatable member extending to the body slots and defining slots for engagement with the pins of an inserted bulb, the body slots and rotatable member slots being arranged such that insertion of a bulb causes the rotatable member to rotate from its first to its second position and removal of a bulb causes the rotatable member to rotate from its second to its first position, power supply terminals supported by the body and defining surfaces facing the rotatable member, two contact terminals supported within the body such that they extend through the rotatable member so as to be exposed on opposite sides thereof, a transverse bar slidably mounted within the body between the rotatable member and the power supply terminals such that when the rotatable member is in its said first position the transverse bar is immoveable in a first inoperative position but when the rotatable member is in its said second position the transverse bar is movable between the first inoperative position and a second operative position, and a pair of bridging contacts carried by the transverse bar such that when the transverse bar is in the operative position the bridging contacts effect an electrical contact between the contact terminals and the power supply terminals, said contact being broken when the transverse bar is in the inoperative position, wherein the rotatable member and the transverse bar are adapted to provide a return means whereby rotation of the rotatable member from its second to its first position causes the transverse bar to move from its operative to its inoperative position.

Preferably the return means comprises inter-engaging f - supported by the said rotatable member and the said * sverse bar.

Preferably the formation supported by the rotatable member comprises an upstanding peg positioned at the periphery of the rotating member.

Preferably the formation supported by the transverse bar comprises a protrusion extending laterally therefrom.

Alternatively the formation supported by the transverse bar comprises an angled surface defined on the underside of the transverse bar.

Preferably the rotatable member supports a second formation which engages with a corresponding second formation supported by the transverse bar when the transverse bar is in the inoperative position and the rotatable member is in its said first position, thereby preventing the transverse bar from being moved into the operative position.

Preferably the contact terminals are electrically connected to the bridging contacts via flexible conducting members which members may comprise coil springs.

Preferably the contact terminals are moveable axially along the body between first and second positions, biasing means are provided to bias the contact terminals towards the first position, movement of the contact terminals to the second position resulting from the axial insertion of a bulb into the body, and the contact terminals providing locking means such that when the contact terminals are in their first position the rotatable member is prevented from rotation but when the contact terminals are in their second position the rotatable member is free to rotate between its two positions.

Preferably the biasing means are coil springs.

The contact terminals may be supported by the said rotatable member and the locking means may be provided by the interengagement of the contact terminals with formations supported on the inner surface of the said hollow body.

Preferably the contact terminals comprise a strip of metal bent into a generally "U" shape with a laterally extending portion that engages the said formations on the inner surface of the body.

Preferably means are provided to bias the rotatable member towards the first position when there is no bulb present in the lampholder.

According to a second aspect of the present invention there is provided a safety lampholder for receiving a bayonet bulb2 the lampholder comprising a hollow body defining slots at one end thereof, each of the slots having an axial limb open to the said one end and a circumferential limb along which the bayonet pins of a bulb slide during insertion and removal of the bulb, a rotatable member mounted within the body and rotatable with respect to the body between first and second positions, the rotatable member extending to the body slots and defining slots for engagement with the pins of an inserted bulb, the body slots and rotatable member slots being arranged such that insertion of a bulb causes the rotatable member to rotate from its first to its second position and removal of a bulb causes the rotatable member to rotate from its second to its first position, power supply terminals supported by the body and defining surfaces facing the rotatable member, and two contact terminals supported within the housing such that they extend through the rotatable member so as to be exposed on opposite sides thereof, such that when the rotatable member is in its first position the power supply terminals are isolated from the contact terminals but when the rotatable member is in its second position there is electrical contact between the two sets of terminals, wherein the contact terminals are moveable axially along the body between first and second positions, and biasing means are provided to bias the contact terminals towards the first position, movement of the contact terminals to the second position resulting from the axial insertion of a bulb into the body, and the contact terminals providing locking means such that when the contact terminals are in their first position the rotatable member is prevented from rotation but when the contact terminals are in their second position the rotatable member is free to rotate between its two positions.

Preferably the biasing means comprise coil springs.

Preferably the contact terminals are supported by the said rotatable member and the locking means is provided by the inter engagement of the contact terminals with locking formations supported on the inner surface of the said hollow body.

Preferably the contact terminals comprise a strip of metal bent into a generally "U" shape with a laterally extending portion that engages the said locking formations on the inner surface of the body.

Alternatively the contact terminals may be supported by a supporting member housed within the body and extend through slots defined by the rotatable member, and the locking means may be provided by the interengagement of the contact terminals with formations supported by the said rotatable member.

The contact terminals may comprise a strip of metal formed into a "U" shape with laterally extending end portions and the said formations on the rotatable member may comprise upstanding wall portions partially bordering the said slots defined by the rotatable member and defining a gap between the said wall portions to receive the said laterally extending end portions of the contact terminals.

Alternatively the contact terminals may be in the form of metal cylinders provided with an enlarged head and the said formations on the rotatable member comprise substantially keyhole shaped slots defining a large diameter end and a small diameter end thereof, the said large diameter end being dimensioned to receive the enlarged head of the contact terminals and the said small diameter end being dimensioned to receive the cylindrical portion of the contact terminals.

The lampholder may be provided with an elongate member supported longitudinally within the body such that it cannot rotate with respect to the body and the locking means may be provided by the interengagement of the contact terminals with formations supported by the elongate member.

The said locking formations may comprise radially extending protrusions and the contacts may be supported by the rotatable member such that they rotate therewith.

Preferably the contacts are provided with radially outwardly extending flanges that abut with the said protrusions on the elongate member thereby providing the said locking means.

The rotatable member may define formations that engage with the contacts preventing rotation thereof with respect to the said rotatable member.

Preferably the rotatable member supports bridging contacts, said bridging contacts being electrically connected to the contact terminals, wherein when the rotatable member is in its second position the bridging contacts are in electrical contact with the power supply terminals and when the rotatable member is in its first position the bridging contacts are electrically isolated from the power supply terminals.

Preferalby the bridging contacts are electrically connected to the contact terminals by flexible conducting elements which may be in the form of coil springs.

The said coil springs may also provide the biasing means.

Preferably when the rotatable member is in its first position the bridging contacts bear against the body and when the rotatable member is in its second postion the bridging contacts bear against the said surfaces defined by the power supply terminals.

Preferably an anti-tracking mechanism is provided to prevent a conductive path being formed between the power supply terminals and the location of the bridging contacts with the rotatable member in any position other than its second position.

Preferably means are provided to bias the rotatable member towards the first position when there is no bulb present in the lampholder.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which : Fig.l is a perspective view of an exploded lampholder according to a first embodiment of the present invention; Fig.2 is a perspective view of part of the lampholder of Fig.1; Figs. 3, 4 and 5 are sectional views of the assembled lampholder of Fig.l showing respectively the arrangement before insertion of a bulb, after insertion of a bulb and with the switchbar in the inoperative position and after the insertion of a bulb and with the switchbar in the operative position; Figs. 6 and 7 are sectional views of the body of the lampholder of Fig. 1; Figs. 8 and 9 are perspective views of the switchbar of the lampholder of Fig. 1; Fig. 10 shows an alternative switchbar for use in the lampholder of Figs. 1-5;; Fig.ll is a perspective view of the contact carrier of the lampholder of Fig. 1; Fig. 12 is a sectional view of a lampholder body of a second embodiment of the invention; Fig. 13 is a plan view of the body shown in Fig.12; Fig. 14 is a perspective view of a modified contact carrier for use in the Fig. 12 embodiment of the invention; Figs. 15 and 16 respectively show the relative positions of the contact terminals, the body, the contact carrier and the switchbar of the Fig. 12 embodiment of the invention before and after the insertion of a bulb; Fig. 17 is a perspective view of a contact terminal shown in Figs. 15 and 16; Fig.18 is a perspective view of a contact carrier for incorporation in a non-switchable third embodiment of the invention;; Figs. 19 and 20 respectively show the relative positions of the components of the Fig. 18 embodiment of the invention before and after the insertion of a bulb; Fig.21 is a perspective view of an exploded lampholder according to a fourth embodiment of the invention incorporating a spring loaded return mechanism; Figs. 22-24 are sectional views of the assembled lampholder of Fig. 21 showing respectively the arrangements of the components before the insertion of a bulb, after the insertion of bulb and with the switchbar in the inoperative position, and after the insertion of a bulb and with the switchbar in the operative position; Fig. 25 is a sectional view the body of a lampholder according to a fifth embodiment of the invention; Fig. 26 is a plan view of the lampholder body of Fig. 25;; Figs. 27-29 show respectively the arrangement of the components of the Fig. 25 embodiment of the invention before insertion of a bulb, after the insertion of a bulb with the switchbar in the inoperative position, and after the insertion of a bulb with the switchbar in the operative position; Fig. 30 is a perspective view of a contact carrier incorporated in the Fig. 25 embodiment of the invention; Fig. 31 is a perspective view of a contact terminal shown in Figs. 27-29; Fig. 32 is a perspective view of a bridging contact shown in Figs. 27-29; Fig. 33 is a perspective view of a modification of the contact carrier of Fig. 30; Figs. 34-36 correspond to Figs. 27-29 but incorporating the contact carrier of Fig. 33 in conjunction with modified contact terminals;; Fig. 37 is a perspective view of a further modified contact carrier for use in conjunction with a modified terminal block; Figs. 38 and 39 correspond to Figs. 34 and 36 but with a modified terminal block and modified bridging contacts to provide an antitracking mechanism; Figs. 40 and 41 correspond to Figs. 27 and 29 but incorporating the anti-tracking mechanism of Figs. 38 and 39; Figs. 42-44 illustrate a modification of the embodiment shown in Figs. 37 to 41 incorporating a carrier return mechanism; Figs. 45-47 are sectional views of a further embodiment of the invention which allows the use of a metal lampholder body showing respectively the arrangement of the components before the insertion of a bulb, after insertion of a bulb with the switchbar in the inoperative position, and after insertion of a bulb with the switchbar in the operative position;; Figs. 48 and 49 are cross-sectional views perpendicular to the views of Figs. 45 and 47; Fig. 50 is a plan view of the contact carrier incorporated in the lampholder of Figs. 45-49; Fig. 51 is a view similar to that of Fig. 50 but with the contact terminals in position; Fig. 52 is a perspective view of the connecting pin of the embodiment of Figs.45-49; Figs. 53 and 54 are plan views of the terminal block of the lampholder of Figs 45-49; Figs. 55 and 56 are plan views of the switchbar of Pigs. 45-49; Fig. 57 is a side elevation of the switchbar of Figs. 55 and 56 with the bridging contacts in position; Fig. 58 is a sectional view of a non-switchable version of the lampholder of Figs. 45-49 incorporating an anti-tracking mechanism; Fig. 59 is a cross-sectional view of Fig. 58 with the body removed; Fig. 60 shows Fig. 58 with the terminal block and connecting pin removed;; Fig. 61 is a sectional view of the lampholder body of Fig. 60; Figs. 62 and 63 are plan views of the terminal block shown in Figs. 58 and 59; Fig. 64 is a sectional view of the contact carrier of Figs. 58 60 showing the contact terminal and bridging contacts in position; Fig. 65 is a cross-sectional view of Fig. 64; Fig. 66 shows the carrier of Fig. 65 with the contacts removed; Fig. 67 is a perspective view of an alternative contact carrier for the lampholder of Figs. 1-5; Fig. 68 is a perspective view of a switchbar to be used in conjunction with the contact carrier of Fig. 67; Figs. 69-71 show the components of a non-switched lampholder, based on the structure shown in Figs. 37-41; Figs. 72-94 show the components of a further non-switched lampholder structure according to the present invention; ; Figs. 95-112 show the modified components of a non-switched lampholder sructure based on the structure of Figs. 69-91; and Figs. 113-125 show the components of a switched lampholder structure based on the non-switched lampholder of Figs. 110-123.

Referring to figures 1-9, the illustrated lampholder comprises a hollow cylindrical body 1, adapted to house a contact terminal carrier 2, a power supply terminal support block 3 and a transverse switchbar 4.

The body 1 defines a socket 5 at one end and is provided with "L" shaped slots 6 to receive the bayonets of a bayonet bulb (not shown) inserted into the socket 5. The external surface of the body 1 is formed with a plain circumferential band 7 intermediate its ends, above and below which the body 1 is provided with screw threads 8 and 9. The lower screw thread 8 is provided to receive a threaded retainer ring of a lamp shade (not shown) and the upper screw thread 9 is provided to receive a lampholder cap (not shown). The end of the body 1 opposite the socket 5 defines two diametrically opposite slots 10. The inner surface of the body 1 is contoured to define circumferential support ledges 11, and axial abutment surfaces 12, 13 and 14. The inner surface of the body 1 is further provided with circumferential flanges 15.

The contact carrier 2 comprises a disc 16 supporting an upstanding peripheral wall 17 and depending arms 18. The arms 18 define axial slots 19 at the ends thereof. The disc 16 is provided with two diametrically opposed square shaped apertures 20 situated between the arms 18. The apertures 20 are bordered by upstanding wall sections 21 which form channels for contact terminals 22. The contact carrier 2 is further provided at its periphery with an abutment 23 and an upstanding peg 24.

The contact carrier 2 is housed within the body 1 with the bottom edges of the arms 18 supported by the support ledges 11.

Rotation of the contact carrier 2 within the body 1 is limited in one circumferential direction by the abutment of the arms 18 with the abutment surfaces 12. In this first position the slots i9 are aligned with the axial portion of the "L" slots 6. Rotation of the carrier 2 in the other circumferential direction is limited by the abutment of the arms 18 with the abutment surfaces 13, in this second position the arms 19 are aligned with the indent at the end of the circumferential portion of the "L" slots 6.

The contact terminals 22 are generally "U" shaped and are seated within the channels in the contact carrier 2 defined by the wall sections 21 such that they extend through the apertures 20. The contact terminals 22 have laterally extending ears 25 which are supported within cutaways 26 in the wall 17 so that they extend radially from the carrier 2. The location of the contact terminals 22 within the carrier 2 is such that when the carrier 2 is in the above mentioned first position and no bulb is present in the socket 5 then the contact terminals 22 abut against the abutment surfaces 14 defined on the inner surface of the body 1.

The terminal block 3 comprises a disc 27 which supports a depending leg 28 and projections 29. The upper surface of the disc 27 supports formations 30 that house power supply terminals 31 which extend through the disc 27 defining surfaces on the underside thereof.

The underside of the disc 27 further supports protrusions 32 and stops 33.

The terminal block 3 is located within the upper end of the body 1 with the leg 28 supported by the peripheral wall 17 of the carrier 2. Axial movement of the terminal block 3 within the body 1 is restrained by the flanges 15 which bear against the upper surface of the disc 27. Rotational movement of the terminal block 3 relative to the body 1 is prevented by the location of the projections 29 within the slots 10 in the body 1.

The switchbar 4 comprises a central portion 34 and longitudinally extending end portions 35. The central portion 34 defines two laterally spaced apertures 36 adapted to receive square sectioned "U" shaped bridging contacts 37. The upper surface of the central portion 34 supports a formation 38 having two longitudinally spaced abutments 39. The underside of the switchbar 4 supports a depending abutment 40 and a protrusion 41 extends from one side of the central portion 34.

The switchbar 4 is housed transversely within the body 1 between the contact carrier 2 and the terminal block 3 with the end portions 35 extending through the slots 10.

A pair of helical springs 42 are located between the switchbar 4 and the contact carrier 2 such that one end of each is supported within the "U" shaped contact terminals 22 and the other end is supported within the "U" shaped bridging contacts 37. The springs 42 provide a good flexible electrical connection between the two pairs of contacts 22 and 37.

The action of the springs 42 on the bridging contacts 37 is transferred to the switchbar 4 causing the protrusions 39 on its upper surface to bear against the underside of the terminal block 3.

Transverse movement of the switchbar 4 within the body 1 is limited by the engagement of the abutments 39 with the stops 33 on the underside of the terminal block 3 to movement between two positions, an operative position wherein the bridging contacts 37 are brought to bear against the surfaces defined by the power supply terminals 31 on the underside of the terminal block 3, and an inoperative position wherein there is no such contact. As the switchbar 4 is moved between these two positions abutments 39 ride over the protrusions 32 on the underside of the terminal block 3 which present some resistance to the movement. Thus the two pairs of protrusions 32 and 39, and the stops 33 form a detent mechanism positively locating the switchbar 4 in each of its two positions.

In use, and before the insertion of a bulb, the lampholder components are arranged as shown in Fig. 3. The switchbar 4 is in the inoperative position in which there is no electrical contact between the power supply terminals 31 and the contact terminals 22. The contact carrier 2 is in its above described first position with the arm slots 19 aligned with the axial portions of the "L" slots 6. In this position the abutment 23 on the carrier 2 is aligned with the depending abutment 40 on the switchbar 4. Thus the switchbar cannot be moved to the operative position until the contact carrier 2 is rotated so that the abutment 23 is moved out of alignment with the abutment 40. As described above this rotation of the carrier is prevented by the abutment of the ears 25 of the contact terminals 22 with the abutment surfaces 14 defined on the inner surface of the body 1.

Fig.2 shows the arrangement of the components after a bulb (not shown) has been inserted into the socket 5. The insertion of a bulb into the socket 5 is in two stages, a first stage in which the bayonets of the bulb (not shown) travel along the axial portion of the "L" slots 6 and a second stage in which the bulb is rotated within the socket 5, the bayonets travelling along the circumferential portions of the "L" slots 6 and finally coming to rest in the indents provided.

During the first stage of the bulbs insertion the contact terminals 22 are depressed by the bulb against the action of the springs 42 so that the ears 25 of the contact terminals 22 are raised above the shoulders of the abutment surfaces 14 leaving the contact carrier 2 free to rotate within the body 1.

At the completion of this first stage of the bulbs insertion its bayonets are located within the slots 19 so that the arms 18 and therefore the contact carrier 2 are rotated with the bulb during the second stage of its insertion. With the bulb fully inserted the contact carrier 2 assumes its above described second position. The abutment 23 on the carrier 2 is therefore moved from the path of the depending abutment 40 of the switchbar 4 so that the switchbar 4 can now be freely moved between its two positions.

The arrangement of the components after a bulb has been fully inserted into the socket 5 and the switchbar 4 has been moved to the operative position is shown in Fig. 3. The bridging contacts 37 have been brought into contact with the power supply terminals 31 so that an electrical connection is made between the power supply terminals 31 and the contact terminals 22 via the springs 42. The action of the springs 42 on the contact terminals 22 also ensure that good electrical contact is maintained between the contact terminals 22 and the contact pads on the bulb (not shown).

If the bulb is rotated to remove it from the socket 5 the contact carrier 2 will again rotate with it returning to its first position. The peg 24 on the contact carrier 2 will now be brought to bear against the protrusion 41 of the switchbar 4 so that rotation of the contact carrier 2 back to its first position forces the switchbar 4 into the inoperative position. As the bulb is then removed axially from the socket 5 the contact terminals 22 will return to their original position, extending into the socket 5, under the action of the springs 42. Thus all the components of the lampholder reassume the position shown in Fig. 3 with the contact terminals 2 safely isolated from the power supply terminals 31 and the switchbar 4 prevented from movement to the operative position until a bulb is again inserted into the socket 5.

An alternative transverse bar to that shown in Figs. 8 and 9 that can be incorporated in the above described structure to provide a non-switchable lampholder is illustrated in Fig. 10. The end portions 35 are shortened so that they only just extend into the slots 10 to locate the bar 4 in position within the body 1. The protrusion 41 defines a recess 41a that engages with the peg 24 on the carrier 2 such that the bar 4 is moved from the inoperative to the operative position as a bulb is inserted in addition to returning to the inoperative position as a bulb is removed.

Figs. 12 to 17 show a second embodiment of the invention in which the body 1, the carrier 2 and the contact terminals 22 have been modified to provide an alternative locking mechanism for the carrier 2. The same reference numerals will be used to identify features common to all embodiments. The modified body 1 is provided with a support member 43 and the internal abutment surfaces 14 have been omitted, otherwise the body 1 is unchanged from that of the first embodiment described above.

The support member 43 comprises a disc 44 joined at its periphery to the internal wall of the body 1. The periphery of the disc 44 is formed with two diametrically opposite arcuate cutaways 45 such that arcuate slots 46 are defined between the periphery of the disc 44 and the internal surface of the body 1. The disc 44 supports two diametrically opposite cylindrical bosses 47, positioned between the arcuate slots 46, which define square shaped apertures 48 that extend through the disc 44. The arcuate slots 46 are dimensioned to receive the arms 18 of the carrier 2 and allow rotation of the carrier 2 between its above described two positions.

The modified carrier 2 defines arcuate slots 49 partially bordered by upstanding walls 50 and 51. The carrier 2 is housed within the body 1 with the arms 18 extending through the arcuate slots 46 and supported by the support ledges 11. The position of the arcuate slots 49 in the carrier 2 are such that they align with the apertures 48 in the support member and remain aligned as the carrier 2 is rotated between its two positions.

Modified contact terminals 22 are received within the apertures 48 and slots 49 such that they extend into the socket 5, being supported by ears 52 which extend laterally from the contact terminals 52, beyond the edges of the slots 49.

The arrangement is such that when the carrier 2 is in its first position, with the arm slots 19 aligned with the axial portion of the "L" slots 6, and prior to the insertion of a bulb into the socket 5, then the ears 52 of the contact terminals seat within a gap defined between the walls 50 and 51. This arrangement is illustrated in Fig. 15.

In this position the ears 52 abut against the edges of the walls 50 and 51 thereby preventing the carrier 2 from being rotated with respect to the body 1.

If a bulb is inserted into the socket 5 the contact terminals 22 are depressed against the force of the springs 42 so that the ears 52 are raised above the tops of the walls 50 and 51. The carrier 2 is then free to rotate into its second position as the bulb is rotated for the second stage of its insertion. This arrangement is illustrated in Fig. 16.

Apart from the above described locking mechanism the second embodiment of the invention functions in the same manner as the first embodiment.

Fig.s 18 to 20 illustrate further modified components of the above embodiment to provide a third, non-switched, embodiment of the invention. A modified carrier 2 is provided with formations 53 which are adapted to support bridging terminals 54. The bridging terminals 54 have a rounded upper surface that bears against the underside of a modified terminal block 3 under the action of the springs 42. The carrier locking mechanism is the same as that described above for the second embodiment. Rotation of the carrier from its first to its second position moves the bridging contacts into electrical contact with the power supply terminals, and vice-versa. The underside of the terminal block 3 supports a protrusion 55 which offers resistance to the movement of the bridging contacts 54 thus providing a detent mechanism to positively locate the bridging contacts 54 into each of its two positions.

Repeated movement of the bridging contacts 54 across the undersurface of the terminal block 3 between its two positions may result in the deposit of a faint "track" of metal between the two positions. This could result in electrical connection between the power supply terminals 31 and the contact terminals with the carrier 2 in its first position and without a bulb present in the socket 5.

This is an obviously dangerous situation, defeating the purpose of the safety lampholder. To prevent this from happening the protrusion 55 on the undersurface of the terminal block 3 is split longitudinally forming a gap at its crest. This results in a break in any "track" that may form and thus provides an anti-tracking mechanism.

A fourth embodiment of the invention incorporating a spring return mechanism is illustrated in Figs 21 to 24. A modified carrier 2 is supports an upright cylindrical housing 56 for a coil spring 5;.

Each end of the coil spring 57 extends laterally therefrom defining an upper leg 58 and a lower leg 59. The upper leg 58 is fised within a suitably adapted formation on the underside of a modified terminal block 3 which is itself fixed within the body 1. The lower leg 59 extends through a groove 60 defined by an upright formation 61 supported by the carrier 2 such that it protrudes radially from the carrier 2. A pin 62 is housed within a hole 63 which extends through the formation 61 to the underside of the carrier 2 such that the leg 59 rests on the head of the pin 62.

With the components assembled and the carrier in its first position prior to insertion of a bulb, the leg 59 of the spring engages abutments 64 on the inner surface of the body 1 preventing rotation of the carrier 2. Inserting a bulb into the socket 5 depresses the pin 62 which raises the leg 59 so that it disengages from the body 1 leaving the carrier free to rotate with the bulb against the action of the spring 57. The location of the bayonets of the bulb in the indentations in the "L" slots 6 prevents the spring 57 from returning the carrier to its first position until the bulb is manually removed.

The spring return mechanism provides additional resistance to accidental rotation of the carrier and in the event that the locking mechanism is inadvertently released and the carrier rotated without a bulb in the socket, the mechanism will return it to the safe first position.

A further embodiment of the invention incorporating a modification of the above described locking mechanism is illustrated in Figs. 25 to 30. The carrier 2 is provided with slots 65 each defined by two intersecting circular apertures, one having a larger diameter than the other, defining small and large ends of each slot. Contact terminals 66 are in the form of hollow cylinders with an enlarged head 67 and closed at the opposite end. The apertures 48 defined by the support member 43 have a circular profile to accommodate the cylindrical contact terminals 66 and are countersunk to provide a seating for the enlarged heads 67 of the terminals 66.

Fig. 27 shows the arrangement of the components with the carrier 2 is in its first position and prior to the insertion of a bulb into the socket 5. The contact terminals 66 are seated within the support member 43 with the enlarged heads 67 occupying the large end of the slots 65. The diameter of the enlarged heads 67 is greater than that of the small end of the slots 65 and thus the carrier is prevented from rotation until a bulb is inserted into the socket 5 and the contacts 66 are depressed raising the enlarged heads 67 out of the slots 65 as shown in Fig.s 28 and 29. The contact terminals 66 are tapered around the base of the enlarged heads 67 and the large end of the slots 65 are countersunk, to aid relocation of the heads 67 within the slots 65 when the bulb is removed and the carrier is returned to its first position.

A slight variation of this locking mechanism in which the contact terminals 66 are supported by the carrier 2 as oppose to the support member 43 is illustrated in Figs. 33 to 36. Each of the enlarged heads 67 is formed with a radially extending external lip 68 which has a greater diameter than that of the large end of the slots 65 and thus supports the contact terminals 66 by its contact with the surface of the disc 44 of the carrier 2.

The above describe locking mechanisms can replace the locking mechanism of Figs. 18 to 20 to provide further non-switched embodiments of the invention, as illustrated in Figs. 37 to 41.

A modification to the embodiment of Figs. 37 to 41, incorporating a carrier return mechanism, is illustrated in Figs. 42 to 44. The carrier 2 is provided with upstanding tiangular formations adjacent the radialy inner and outer edges of the small diameter portion of each of the keyhole slots 65, the innermost formation being integral with the formations 53. Each of the triangular formations defines a ramp surface sloping downwards towards the large diameter portion of the respective keyhole slot 65. The arrangement is such that with the carrier 2 in the first position, as shown in Fig. 43, the lips 68 of the bulb engaging contacts 66 lie adjacent the bottom of the ramp surfaces. With the carrier 2 in the second position and the bulb contacts 66 depressed the lips 68 bear against the top of the ramp surfaces, as shown in Fig. 44.When in this position and without a bulb maintaining the contacts 66 depressed, the springs 42 force the contacts 66 downwards which rotates the carrier 2 into the first position as the lips 68 of the contacts 66 slide down the ramp surfaces. Thus in the event that the locking mechanism is defeated and the carrier 2 is rotated into the second postition without a bulb in place, the ramped formations provide a return mechanism to return the carrier 2 to the safe first position.

In each of the above described lampholder structures the various embodiments of the locking mechanism are based upon the inter engagement of the terminal contacts with the carrier 2 and the body 1. Further embodiments of the invention will now be described in which there is no contact between the terminal contacts and the lampholder body 1 thereby providing structures suitable for use with bodies formed from conducting materials, such as brass.

Referring to Figs. 42 to 51 the carrier 2 is provided with a raised portion 69 which has a shallow depression 70. A generally "S" shaped aperture 71 extends through the raised portion 69 to the underside of the carrier 2. The aperture 71 has a substantially "T" shaped cross-section such that it presents a larger opening to the underside of the carrier 2 than to the surface of the raised portion 69. The carrier is also provided with two diametrically opposite circular apertures 72 to receive contact terminals 73. The upper ends of the contact terminals 73 are provided with oval shaped flanges 74 to support them within the apertures 71. The flanges 74 seat within cutaways in carrier walls 75 thereby preventing the contacts 73 from rotating with respect to the carrier 2 within the apertures 72 The external surface of the carrier 2 is formed with 2 circumferential shoulder 76 adapted to support the terminal block 3.

The terminal block 3 supports a central boss 77 which defines a square sectioned aperture 78 which extends through to opposite surfaces of the terminal block 3. The terminal block 3 further supports a depending skirt 79 which is provided with slots 80 to receive the ends of the switchbar 4.

The carrier 2, terminal block 3 and switchbar 4 are connected together by a connecting pin 81 (Fig.49). The pin 81 comprises a base portion 82, a cylindrical portion 83, a square sectioned portion 84 and a screw threaded cylindrical portion 85. The cylindrical portion 83 supports diametrically opposed radially extending fins 86.

To assemble the components the pin 81 is first passed up through the aperture 71 in the carrier 2 so that the pins base 77 is received in the large opening of the aperture 71 in the underside of the carrier. The "S" shaped profile of the aperture 7i allows the fins 86 to pass therethrough. The square sectioned portion 84 of the pin 81 passes through an oblong aperture 87 in the switchbar 4 and is received within the square sectioned aperture 78 in the terminal block 3. The screw threaded portion 85 of the pin 81 extends from the aperture 78 and receives a nut 89 to complete the assembly.

The above assembly is then housed within a metallic body 1 being supported by the abutment of the lower edge of the terminal block skirt 79 with the upper rim of the body 1. The upper rim of the body 1 and the lower edge of the skirt 79 are provided with suitable formations (not shown ) to secure the terminal block 3 against rotation with respect to the body 1. A metallic cap (not shown) matching the body 1 can then be positioned around the terminal block 3 completing the lampholder structure.

In use and prior to the insertion of a bulb inter the socket 5 the components are arranged as shown in Figs.42 and 45 with the carrier 2 in its first position. The carrier 2 is locked in this position, being prevented from rotating with respect to the body 1 in one direction by the abutment of the flanges 74 with the fins 86 supported by the pin 81, and in the other direction by the abutment of the bottom edge of the fins 86 with the sides of the depression 70. The pin 81 is itself prevented from rotating with respect to the body 1 by the cooperation of its square sectioned portion 84 with the square sectioned aperture 71 in the terminal block 3.

Inserting a bulb into the socket 5 depresses the contact terminals 73 and raises the flanges 74 above the upper edge of the fins 86 leaving the carrier 2 free to rotate on the pin 81 as the bulb is rotated for complete insertion. If the bulb is removed from the socket 5 the contact terminals i3 will be returned to their original locking position under the action of the springs 42.

A non-switchable version of the above structure is illustrated in Figs. 55 to 62 in which the locking mechanism works in exactly the same way as described above. The structure shown in Fig.s 55 to 62 is provided with a alternative anti-tracking mechanism to that shown in Figs. 19 and 20. Modified bridging contacts 88 are formed with nipples 89 which define rounded shoulders 90 on the upper surfaces of the contacts 88. The undersurface of the terminal block is provided with a step 91 adjacent the exposed surface of each of the power supply terminals. As the bridging contacts 88 ride over these steps 91 the shoulders 90 ensure that there is a break in the contact between the nipples 89 and the undersurface of the terminal block 3 thereby forming a break in any track that may form on the undersurface of the terminal block 3.

An alternative switchbar return and locking means is illustrated in Figs. 63 and 65. This locking means is designed for lampholder structures in which the switchbar must be moved axially relative to the lampholder body before it can be moved longitudinally. The carrier 2 supports diametrically opposed stepped abutments 92 having lower portions 93 and upper portions 94. The lower portions 93 are formed with an angled leading edge 95. The undersurface of the switchbar is provided with slots 96 each having an angled face 97 and a stop face 98.

In use, when a bulb is rotated to remove it from the lampholder the carrier 2 will rotate such that the lower portions 93 of the abutments 92 engage the angled faces 96 of the slots 97. Thus angular movement of the carrier 2 results in linear movement of the switchbar to its inoperative position. When the carrier is fully rotated to remove the bulb the upper portions 96 of the abutments 92 locate in front of the stop faces 97 of the slots 96 thereby preventing the switchbar 4 from being moved to the operative position. In addition the lower portions 93 of the abutments 92 abut the under surface of the switchbar 4, preventing it from being moved axially.

Figs. 66 to 68 show the components of another non-switched lampholder structure, based on the structure shown in Figs. 37 to 41.

In this modification the keyhole slots 65 are defined by the support member 43 as oppose to the carrier 2. The enlarged heads 67 of the terminals 66 have been axially extended to pass through the slots 65 and circular apertures 99 defined by the carrier 2. The terminal block 3 supports modified power supply terminals 100 and a hump 101 which together provide an anti-tracking mechanism.

Figures 69 to 91 show the various components of further nonswitched lampholder structure. As will be evident from the drawings, many of the structural details are the same or similar to those of previous embodiments. The only notable differences are detailed below.

Spring loaded contact terminals 102 are housed within a supporting structure 103 defined by the carrier 2. The supporting structure 103 has a central cylindrical channel 104 and two rectangular sectioned channels 105. The terminals 102 have square shaped flanges 106 that are received within the rectangular sectioned channels 105 thereby preventing the terminals 102 from rotating with respect to the carrier 2.

The terminal block 3 supports a central depending stem 107 which extends into the channel 104 and has abutment shoulders 108 that engage the contact flanges 106. The terminal block 3 further supports anti-tracking terminals 100. The carrier 2 cannot be rotated into the operative position unless a bulb is inserted into the lampholder to depress the contact terminals 102. This raises the contact flanges 106 above the abutment shoulders 108 hereby freeing the carrier 2 for rotation.

A variation of the above structure, in which the contact terminals 102 engage the lampholder body 1 instead of the terminal block 3, is illustrated in Figures 92 to 109 modification. The contact flanges 106 are rectangular shaped and extend radially from a modified carrier 2 so as to engage formations 109 formed on the inner surface of the body 1. Depression of the terminals 102 lifts the flanges 106 out of engagement with the body formations 109 thereby freeing the carrier 2 to rotate within the body 1.

The above described structres of Figs 66 to 109 may be modified to incorporate a return mechanism based on the same principle as that described with referance to Figs. 42 to 44. For instance, sloping ramp surfaces may be provided on the internal wall of the body 1, or on the central support structures 103, to bear against the upper lips/flanges of the bulb contact terminals, and perform the same function as the ramp surfaces shown in Figs. 42 to 44.

The above two non-switched lampholder structures have been designed to readily facilitate automated assembly.

A final switched lamp holder structure is illustrated in Figs. 110 to 122. This structure is based on the non-switched lampholder of Figs. 95 to 109 in that it incorporates spring loaded contact terminals 102 with rectangular flanges 106 that engage formations 109 defined on the internal surface of the body 1.

Claims (34)

1. A safety lampholder for receiving a bayonet bulb, the lamphoider comprising a hollow body defining slots at one end thereof, each of the slots having two mutually inclined limbs along which the bayonet pins of a bulb slide during insertion and removal of the bulb, a rotatable member mounted within the body and rotatable with respect to the body between first and second positions, the rotatable member extending to the body slots and defining slots for engagement with the pins of an inserted bulb, the body slots and rotatable member slots being arranged such that insertion of a bulb causes the rotatable member to rotate from its first to its second position and removal of a bulb causes the rotatable member to rotate from its second to its first position, power supply terminals supported by the body and defining surfaces facing the rotatable member, two contact terminals supported within the body such that they extend through the rotatable member so as to be exposed on opposite sides thereof, a transverse bar slidably mounted within the body between the rotatable member and the power supply terminals such that when the rotatable member is its said first position the transverse bar is immoveable in a first inoperative position but when the rotatable member is in its said second position the transverse bar is movable between the first inoperative position and a second operative position, and a pair of bridging contacts carried by the transverse bar such that when the transverse bar is in the operative position the bridging contacts effect an electrical contact between the contact terminals and the power supply terminals, said contact being broken when the transverse bar is in the inoperative position, wherein the rotatable member and the transverse bar are adapted to provide a return means whereby rotation of the rotatable member from its second to its first position causes the transverse bar to move from its operative to its inoperative position.

2. A lampholder according to claim 1, wherein the return means comprises inter-engaging formations supported by the rotatable member and the transverse bar.

3. A lampholder according to claim 2, wherein the formation supported by the rotatable member comprises an upstanding peg positioned at the periphery of the rotating member.

4. A lampholder according to claim 2 or 3, wherein the formation supported by the transverse bar comprises a protrusion extending laterally therefrom.

5. A lampholder according to claim 2 or 3, wherein the formation supported by the transverse bar comprises an angled surface defined on the underside thereof.

6. A lampholder according to any preceding claim, wherein the rotatable member supports a second formation which engages with a corresponding second formation supported by the transverse bar when the transverse bar is in the inoperative position and the rotatable member is in its said first position, thereby preventing the transverse bar from being moved into the operative position.

7. A lampholder according to any preceding claim, wherein the contact terminals are electrically connected to the bridging contacts via flexible conducting members.

8. A lampholder according to claim 7, wherein the flexible conducting members comprise coil springs.

9. A lampholder according to any preceding claim, wherein the contact terminals are moveable axially along the body between first and second positions, biasing means are provided to bias the contact terminals towards the first position, movement of the contact terminals to the second position resulting from the axial insertion of a bulb into the body, and the contact terminals providing locking means such that when the contact terminals are in their first position the rotatable member is prevented from rotation but when the contact terminals are in their second position the rotatable member is free to rotate between its two positions.

10. A lampholder according to claim 9, wherein the biasing means comprise coil springs.

11. A lampholder according to claim 9 or 10, wherein the contact terminals are supported by the said rotatable member and the locking means is provided by the inter engagement of the contact terminals with locking formations supported on the inner surface of the said hollow body.

12. A lampholder according to claim 11, wherein the contact terminals comprise a strip of metal bent into a generally "U" shape with a laterally extending portion that engages the said locking formations on the inner surface of the body.

13. A lampholder according to claim 9 or 10, wherein the contact terminals are supported by a supporting member housed within the body and extend through slots defined by the rotatable member, and the locking means is provided by the interengagement of the contact terminals with locking formations supported by the said rotatable member.

14. A lampholder as claimed in claim 13, wherein the contact terminals comprise a strip of metal formed into a "U" shape with laterally extending end portions and the said locking formations on the rotatable member may comprise upstanding wall portions partially bordering the said slots defined by the rotatable member and defining a gap between the said wall portions to receive the said laterally extending end portions of the contact terminals.

15. A lampholder as claimed in claim 13, wherein the contact terminals comprise metal cylinders having an enlarged head, and the said formations on the rotatable member comprise substantially keyhole shaped slots defining a large diameter end and a small diameter end thereof, the said large diameter end being dimensioned to receive the enlarged head of the contact terminals and the said small diameter end being dimensioned to receive the cylindrical portion of the contact terminals.

16. A safety lampholder for receiving a bayonet bulb, the lamphoider comprising a hollow body defining slots at one end thereof, each of the slots having an axial limb open to the said one end and a circumferential limb along which the bayonet pins of a bulb slide during insertion and removal of the bulb, a rotatable member mounted within the body and rotatable with respect to the body between first and second positions, the rotatable member extending to the body slots and defining slots for engagement with the pins of an inserted bulb, the body slots and rotatable member slots being arranged such that insertion of a bulb causes the rotatable member to rotate from its first to its second position and removal of a bulb causes the rotatable member to rotate from its second to its first position, power supply terminals supported by the body and defining surfaces facing the rotatable member, and two contact terminals supported within the housing such that they extend through the rotatable member so as to be exposed on opposite sides thereof, such that when the rotatable member is in its first position the power supply terminals are isolated from the contact terminals but when the rotatable member is in its second position there is electrical contact between the two sets of terminals, wherein the contact terminals are moveable axially along the body between first and second positions, and biasing means are provided to bias the contact terminals towards the first position, movement of the contact terminals to the second position resulting from the axial insertion of a bulb into the body, and the contact terminals providing locking means such that when the contact terminals are in their first position the rotatable member is prevented from rotation but when the contact terminals are in their second position the rotatable member is free to rotate between its two positions.

17. A lampholder according to claim 16, wherein the biasing means comprise coil springs.

18. A lampholder according to claim 16 or 17, wherein the contact terminals are supported by the said rotatable member and the locking means is provided by the inter engagement of the contact terminals with locking formations supported on the inner surface of the said hollow body.

19. A lampholder according to claim 18, wherein the contact terminals comprise a strip of metal bent into a generally "U" shape with a laterally extending portion that engages the said locking formations.

20. A lampholder as claimed in claim 16 or 17, wherein the contact terminals are supported by a supporting member housed within the body and extend through slots defined by the rotatable member, and the locking means is provided by the interengagement of the contact terminals with locking formations supported by the said rotatable member.

21. A lampholder as claimed in claim 20, wherein the contact terminals comprise a strip of metal formed into a "U" shape with laterally extending end portions and the said locking formations on the rotatable member may comprise upstanding wall portions partially bordering the said slots defined by the rotatable member and defining a gap between the said wall portions to receive the said laterally extending end portions of the contact terminals.

22. A lampholder as claimed in claim 20, wherein the contact terminals comprise metal cylinders having an enlarged head, and the said formations on the rotatable member comprise substantially keyhole shaped slots defining a large diameter end and a small diameter end thereof, the said large diameter end being dimensioned to receive the enlarged head of the contact terminals and the said small diameter end being dimensioned to receive the cylindrical portion of the contact terminals.

23. A lampholder according to claim 16 or 17, comprising an elongate member suppbrted longitudinally within the body such that it cannot rotate with respect to the body, the locking means being provided by the interengagement of the contact terminals with locking formations supported by the elongate member.

24. A lampholder according to claim 23, wherein the locking formations comprise radially extending protrusions and the contact terminals are supported by the rotatable member such that they rotate therewith.

25. A lampholder according to claim 24, wherein the contact terminals are provided with radially outwardly extending flanges that abut with the said protrusions on the elongate member thereby providing the said locking means.

26. A lampholder according to any one of claims 23 to 25, wherein the rotatable member defines formations which engage with the contact terminals preventing rotation of the contact terminals with respect to the rotatable member.

27. A lampholder according to any one of claims 16 to 26, wherein the rotatable member supports bridging contacts, said bridging contacts being electrically connected to the contact terminals. wherein when the rotatable member is in its second position the bridging contacts are in electrical contact with the power supply terminals and when the rotatable member is in its first position the bridging contacts are electrically isolated from the power supply terminals.

28. A lampholder according to claim 27, wherein the bridging contacts are electrically connected to the contact terminals by flexible conducting elements.

29. A lampholder according to claim 28, wherein the flexible conducting elements comprise coil springs.

30. A lampholder according to claim 28, wherein the said coil springs provide the biasing means.

31. A lampholder according to any one of claims 27 to 30,wherein when the rotatable member is in its first position the bridging contacts bear against the body and when the rotatable member is in its second postion the bridging contacts bear against the said surfaces defined by the power supply terminals.

32. A lampholder according to claim 31, wherein an anti-tracking mechanism is provided to prevent a conductive path being formed between the power supply terminals and the location of the bridging contacts with the rotatable member in any position other than its second position.

33. A lampholder according to any preceding claim, wherein means are provided to bias the rotatable member towards the first position when there is no bulb present in the lampholder.

34. A safety lampholder, substantially as hereinbefore described, with referance to the accompanying drawings.