GB2279511A

GB2279511A - Lampholder

Info

Publication number: GB2279511A
Application number: GB9412490A
Authority: GB
Inventors: Malcolm Thomas Harrison
Original assignee: Seapart Ltd
Current assignee: Seapart Ltd
Priority date: 1993-06-22
Filing date: 1994-06-22
Publication date: 1995-01-04
Anticipated expiration: 2014-06-22
Also published as: GB2279511B; GB9312842D0; GB9412490D0

Abstract

A safety lampholder for a bayonet bulb comprises a housing 10 having J slots (11) to receive bayonet pins of an inserted bulb. Resilient bulb engaging contacts (57) are biased outwardly of the housing (11) and have ramp formations (59) at their respective free ends. Axially movable and rotatable shutter means (20) for selectively obstructing access to the contacts (57) is arranged so that insertion of a bulb displaces the shutter means (20) and contacts (57) (initially against their bias) between a first inoperative position in which the shutter means (20) obstructs the contacts (57) and the contacts (57) are offset from shutter apertures and a second operative position in which the free ends of the contacts (37) extend through the apertures in the shutter means to bear against an inserted bulb (80). Removal of a bulb rotates the shutter means (20) to drive the contacts (57) inwardly of the housing (10) to the first inoperative position by interengagement of the shutter means (20) with the ramp formations (59). An optional torsion spring (40) rotationally biases the shutter means (20) to the first inoperative position. <IMAGE>

Description

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

French Patent No. 2403665 discloses a so-called shuttered lampholder in which a shutter is interposed between contacts connected to a power supply and a bulb receiving socket. In use, when a bulb is inserted into the socket, the shutter is rotated by the bulb. This moves apertures in the shutter into alignment with telescopic spring loaded contacts supported by the lampholder. The contacts spring through the apertures in the shutter to engage pad electrodes on the end of the inserted bulb.

However, it has been found that, with the above shutter arrangement, the spring loaded contacts can become embedded in the bulb pad electrodes. This results in the contacts passing through the apertures in the shutter to such an extent that they lock the shutter against rotation. Thus, this prevents bulb removal.

Furthermore, even in the absence of a bulb, it is still possible for a wire, nail or the like to be inserted through the apertures in the shutter by, for example, an inquisitive child. If an inquisitive child should move the shutter to its open position, the spring loaded contacts would spring through the apertures in the shutter, locking the shutter against rotation with no bulb present. Thus, the lampholder may then be left in a highly dangerous condition.

The present invention seeks to provide an improved shuttered safety lampholder in which, in particular, the bulb engaging contacts do not lock the shutter against rotation when no bulb is present in the lampholder. The invention also aims to provide a lampholder in which apertures in the shutter are covered when a bulb is not present in the holder. The invention also seeks to provide a lampholder arranged to move a shutter which will automatically assume its closed position if a bulb is not present.

Accordingly, in a broad aspect the present invention provides a safety lampholder for a bayonet bulb, the lampholder comprising a housing defining slots, suitably of J type, at one end thereof to receive bayonet pins of an inserted bulb, resilient bulb engaging contacts for electrical connection to a power source to supply electricity to the bulb being arranged within the housing and biased outwardly thereof, the contacts having ramp formations at their respective free ends, axially movable and rotatable shutter means being located within the housing for selectively obstructing access to the contacts and arranged so as to be actuable upon rotation of a bulb, the shutter means being arranged such that insertion of a bulb actuates displacement of the shutter means and contacts against the bias of the contacts between a first inoperative position in which the shutter means obstructs the contacts and the contacts are offset from the shutter apertures, and a second operative position, when the bulb is fully inserted, in which the free ends of the contacts extend through the apertures in the shutter means to bear against an inserted bulb, and removal of a bulb actuates rotation of the shutter means which is effective to drive the contacts inwardly of the housing and against the bias of the contacts to the first inoperative position by interengagement of the shutter means with ramp formations on the contacts. In this way, the ramp formations on the contacts co-operate with the shutter means to displace the contacts when the shutter is rotated upon bulb removal. As a result the contacts are unlikely to lock the shutter against rotation to leave the contacts exposed, which is a problem with prior proposals.

Typically the end of the housing remote from the slots is closed by a terminal block which is fixed in relation to the housing and supports resilient flex engaging terminals. Suitably, the bulb engaging contacts comprise cylinders of an electrically conductive material, the cylinders being of generally arcuate form in cross-section, having a first dimension greater than a second dimension. In this regard the second dimension may correspond to the standard diameter for typical cylindrical contacts. Conveniently the cylinders have enlarged heads for retaining the cylinders in the housing. Typically, such contacts would be arranged with their respective first dimensions circumferentially spaced about the axis of rotation of the shutter means.

Preferably, the first dimension of a cylinder decreases along a length of the cylinder towards the free end of a contact to define the ramp formation. In this regard, in preferred embodiments a ramp formation comprises an inclined slope. The length of the slope is selected so that, in the operative position, the contacts protrude through the shutter to a sufficient extent to provide an effective electrical connection to the bulb.

In some preferred embodiments means are provided for supporting the free ends of the contacts clear of the shutter means when the lampholder is in the first inoperative position. In this regard such supporting means may comprise surface formations within the housing.

In some preferred embodiments the surface formations are associated with a terminal block in the lampholder.

In some embodiments of the present invention recesses may be provided in the internal surface of the shutter means, alongside the apertures in the shutter means. The recesses are typically arranged to accommodate the free ends of the contacts when the lampholder is in the first inoperative position, or perhaps when the shutter means are displaced upon axial insertion of a bulb. In this way the interengagement of the contacts and shutter may inhibit inadvertent rotation of the shutter means. As regards, the apertured shutter means, preferably each aperture in the shutter means has a wall of ramp form arranged for interengagement with a ramp formation of a contact. In this way, interengagement of the shutter means and contacts may assist in driving the contacts inwardly of the housing.

Preferably the apertures in the shutter means are of generally arcuate form, arranged so as to be diametrically opposed with respect to the axis of rotation of the shutter means.

In preferred embodiments the contacts are arranged within the housing so that, when the lampholder is in the second operative position, the ramp formations at the free ends of the contacts do not extend completely through the apertures in the shutter. This is to assist in driving the contacts back behind the shutter upon bulb removal. In most preferred embodiments means are provided for rotationally biasing the shutter means to the closed position. This is preferred for safety reasons. Preferred biasing means comprise springs, particularly a torsion spring.

In many embodiments of the present invention surface formations are provided on the shutter means and are arranged to engage surface formations in the housing so as to limit the extent of rotational displacement of the shutter means.

In particularly preferred embodiments of the present invention locking means are provided to inhibit rotation of the shutter means, and the locking means are arranged to be releasable upon axial insertion of a bulb into the lampholder. In some embodiments the locking means are arranged to be releasable upon axial displacement of the shutter means upon insertion of a bulb. Example locking means comprise an apertured member located within the housing and arranged to be axially movable with respect to the housing, with the shutter means being rotatable with respect to the apertured member between a closed position in which apertures in the shutter and member are obstructed and an open position in which they are aligned. Suitably the axial movable member is arranged between the bulb engaging contacts and the shutter means.

Conveniently the apertures in the axially movable member are of a shape matching the cross-section of the contacts.

In preferred embodiments which employ an axially movable member, surface formations are conveniently provided on the axially movable member for limiting the extent of rotational movement of the shutter means.

Preferably the axially movable member has surface formations arranged to engage in apertures in the shutter means so as to limit the extent of rotation of the shutter means with respect to the axially movable member.

Most preferably the surface formations on the axially movable member are arranged to extend into apertures in the shutter means so as to shield the contacts from the apertures in the shutter means when the lampholder is in the first inoperative position.

In particularly preferred embodiments of the present invention, the axially movable member is biassed outwardly of the housing and stop means are provided in the housing to limit the extent of outward movement of the member. In such embodiments, preferably the biassing means for the axially movable member are arranged to rotationally bias the shutter to the first inoperative position. Preferably the biassing means and axially movable member are arranged such that only rotational forces are applied to the shutter means. Suitably the shutter means are arranged to be engaged by a bulb. In other embodiments rotatable means may be provided for engaging a bulb to drive rotation of the shutter means.

Suitably the rotatable means are arranged to engage the shutter means after axial insertion of a bulb.

Embodiments of the present invention will now be described further, by way of example, with reference to the accompanying drawings in which: Figs. 1 to 3 are cross-sectional views of an assembled lampholder according to a first embodiment, Fig. 1 illustrates the position of the components prior to bulb insertion, Fig. 2 after axial insertion of a bulb and Fig. 3 when the bulb has been fully inserted; Fig. 4 is an enlarged perspective view of part of the lampholder of Fig. 1; Fig. 5 is an enlarged plan view of part of the lampholder of Fig. 1; Figs. 6 & 7 show lampholder parts corresponding to those of Figs. 4 and 5 for a second embodiment; Figs. 8A to 8C show enlarged cross-sectional views of the lampholder of Fig. 1; Figs. 9 to 11 are cross-sectional views of a third embodiment: Figs. 12 to 14 are cross-sectional-views of a fourth embodiment after various stages of bulb insertion; Fig. 15 is a cross-sectional view of a fifth embodiment; Fig. 16 is a cross-sectional view of a sixth embodiment; Fig. 17 is a cross-sectional view of a seventh embodiment; Figs. 18A to C show enlarged cross-sectional views of part of a lampholder according to an eighth embodiment; and Figs. 19A and B show enlarged cross-sectional views of part of a lampholder according to a ninth embodiment.

Referring now to Figs. 1 to 8, there is illustrated a shuttered lampholder according to a first embodiment comprising a hollow, generally cylindrical, housing 10 which can receive the cap of a bayonet type bulb. The housing 10 is open at one end and provided with "J" slots 11 to receive the respective bayonet pins of a bulb. As is well known for such lampholders, the so-called J slots have an axial limb and a circumferential limb. The housing 10 is also typically provided with a screw thread 15 to retain a shade locking ring. A cover (not illustrated) would in use be secured to the lampholder housing 10 so as to cover its terminals whilst providing an entry port for a power supply flex.

The end of the housing opposite the open bulb receiving end is closed by a terminal block 50. This is secured in fixed relation to the housing 10 and supports a pair of resilient terminal contacts 54. The contacts 54 each comprise a flex engaging terminal block 55, a bulb engaging contact 57 and a bridging spring 56. The terminal contacts 54 extend through the terminal block 50 so as to be accessible on opposite sides thereof. Each contact 57 is generally cylindrical having a flared end 58 located on a step 52 in a bore 51 in the terminal block 50. At their free ends 59A the contacts have ramp formations 59, discussed in more detail below. Limbs 60 are also defined on and depend from the periphery of the inner surface of the terminal block 50.

Support means 17 in the form of an annular lip is provided in the housing for an axially movable and rotatable apertured shutter means 20. The shutter 20, which locates in the open bulb receiving end of the housing 10, is provided with an annular skirt 21 which extends to the open end of the housing to rest on support means 17. The skirt 21 is provided with a pair of axial slots 22 which, in use, align with the axial portion 12 of the "J" slots 11.

A pair of spaced elongate generally arcuate, apertures 23 are defined in the internal surface of the shutter 20. Each aperture has an inclined wall 23A.

Recesses 29 are provided in the internal surface of the shutter 20, alongside each aperture 23. The details of the shutter are shown more clearly in Figs. 4 and 5. A raised boss 25 also extends generally centrally from the inner surface of said shutter 20. A hollow portion of the boss 25 is arranged to house a torsion spring 40, the ends 41 and 41A of the spring 40 extending through an opening 27 in the boss wall 25. Projections 26 render the spring 40 captive within the boss 25. A pair of raised surfaces or stops 28 are also defined on the inner surface of the shutter 20, to limit the extent of rotational movement of the shutter 20, as discussed in more detail below.

Fig. 5 also shows a contact 57 in more detail. The contact 57 is of generally arcuate form in cross-section, having a first dimension (shown as width) greater than a second dimension (shown as depth). In use the contacts 57 are arranged with their respective first dimension circumferentially spaced about the axis of rotation of the shutter means 20. The width of the contact decreases towards its free end 59A to define an angled face or ramp formations 59. Provision of such ramp formations 59 is an important feature of the present invention, in enabling effective withdrawal of the contacts 57 back behind the shutter means 20 upon bulb removal, as discussed in more detail below.

An axially movable-member 30 locates in the housing 10 in a gap defined between the terminal block 50 and shutter 20. The member 30 is provided with a pair of spaced apertures 31. The apertures 31 are of generally curved oval shape, as shown in Fig. 5. The member 30 also has a central aperture 32. A pair of upstanding limbs 35 defined on the periphery of member 30 are arranged so that, in use, they are engaged by the terminal block 50 to prevent relative rotation.

A cutaway portion 33 in the axially movable member 30 accommodates the legs 41 and 41A of the spring 40, as described above. This is shown in Fig. 5. The spring 40 secures the axially movable member 30 to the shutter 20.

The shutter 20 is free to rotate against the force of the spring 40 between its open and closed position, described in more detail below. A wall section 27A on the shutter is engaged by the leg 41A of the spring 40. The leg 41 of spring 40 is anchored in the member 30 so that the leg 41A biases the shutter 20 rotationally relative to the member 30 to a closed position, in which the pair of apertures 23 in the shutter 20 are non-aligned with the pair of apertures 31 in the member 30. Projections 36 depend from the outer surface of the member 30 to locate in the apertures 23 in the shutter. These projections 36 act as cover means and may also provide stop means, as discussed in more detail below in relation to Fig. 8.

The bulb engaging contacts 57 are shown in more detail in the cross-section views of Fig. 8. Prior to bulb insertion, each bulb engaging contact 57 is supported by its flared end 58 locating on a step 52 in bore 51 in terminal block 50. The contacts 57 are arranged with their respective free ends 59A positioned just clear of or within recesses 29 which are defined in the inner surface of the shutter 20. The recesses 29 are located adjacent the apertures 23 which are closable by the member 30 (Fig. 8A).

In this example flex terminals 55 are provided with a screw thread 53 by means of which they are secured in the terminal block 50. Bridging springs 56 provide an acceptable resilient electrical connection between the contacts 57 and flex terminals 55.

Fig. 8B illustrates the position of the components, with the exception of the spring 40, after axial insertion of a bulb. The contacts 57 are depressed inwards of the housing 10 by the shutter 20 (suitably by 5.5 mm as required by I.E.C. standards). The flared ends 58 of contacts 57 are raised off steps 52 and the springs 56 become further loaded. Fig. 8C shows the position of the components after the bulb has rotated the shutter 20 relative to the housing 10 and member 30 from a closed to an open position. Here, the free ends 59A of the contacts 57 are raised out of the holding recesses 29.

The contacts 57, via their angled faces or ramp formations 59, extend through the apertures 23 in the shutter 20 to bear against the pad electrodes 80 of an inserted bulb.

The extent to which the contacts 57 are allowed to protrude through apertures 23 is determined by the stop members 28 or 36. The angled face or ramp formation 59 of a contact 57 is selected to be of a length such that, when the contact 57 is at maximum projection, the trailing end of the angled face 59 is at least on a level with the inner surface of the shutter 20. Thus, it will be impossible for the contacts 57 to lock the shutter 20 against rotation relative to the housing 10, whether or not a bulb is present in the lampholder. It can also be appreciated that, in the absence of a bulb, the illustrated lampholder components will automatically assume their first "shuttered" position and that the proposed lampholder cannot be left in an "unshuttered" position when no bulb is present.

It should also be noted that the proposed lampholder may be modified to omit the torsion spring 40 and thus the auto return facility. In such an arrangement, prior to bulb insertion, the ends 59A of the contacts 57 would be engaged in and loaded against the holding recesses 29 in the shutter 20. This biases shutter 20 outwards of the housing 10 and against support means 17. Recesses 29 provide resistance to rotation of the shutter 20 relative to the housing 10 and member 30.

Figs. 6 and 7 illustrate an alternative means of securing a shutter 20' a member 30', namely by snapengagement. A central peg 45' is defined on the inner surface of the shutter 20' and provided with an annular protrusion. The peg 45' is then a force fit into a stepped aperture 32A' in the member 30' although the shutter remains free to rotate relative to the member 30' between its two positions. The leg 41A' of the loaded spring 40' engages stop 28A', biasing the shutter 20' to its closed position. The other leg 41' of the spring 40' is anchored in a slot 37' in the member 30' and provides that, as the shutter 20' is rotated by the bulb on insertion from its open to its closed position, the stop 28A' moves the loaded spring leg 41A'. In this way the shutter 20' is biased to its closed position. Annular protrusions 26' may retain the spring 40' captive in the axially movable member 30'.

In use, with the lampholder of Figs. 1 to 5 and 8 assembled and with no bulb present, the lampholder components assume the position illustrated in Figs. 1, 5 and 8A. The axial slots 22 of shutter 20 are aligned with the axial portion 12 of the "J" slots 11. The contacts 57 are located behind the shutter 20 which is biased to its closed position by the torsion spring 40, in which position the elongated apertures 23 in the shutter 20 are non-aligned with the apertures 31 in the member 30. The member 30 also covers the apertures 23 in the shutter 20. The shutter is supported on the support means of ledge 17.

Insertion of a bulb is done in two stages, an axial state and a rotational stage. As a bulb is inserted axially into the lampholder, the bayonet pins engage in the aligned slots 12 and 22 and the pad electrodes 80 on the end of the bulb engage the outer surface of the shutter 20. This moves the shutter 20 and thereby the member 30 inwards of the housing 10. As this happens the shutter 20 depresses the loaded contacts 57 via their ends 59A until the bayonet pins have moved to the full extent of the axial portion 12 of the "J" slots 11. The lampholder components assume the position illustrated in Figs. 2 and 8B after this axial stage of bulb insertion.

Rotating the bulb causes the shutter 20 to rotate with it, against the force of the spring 40, from its closed to its open position, aligning the shutter apertures 23 with the respective member apertures 31.

This action simultaneously causes the ends 59A of the contacts 57 to be raised out of the holding recesses 29 and to slide via their angled faces or ramp formations 59 outwards of the housing 10, through the apertures 23, to bear against their respective pad electrodes of the inserted bulb. The lampholder components assume the position shown in Figs. 3 and 8C when a bulb is fully inserted.

As the shutter 20 is rotated on removal of a bulb, from its open back to its closed position, angled faces 23A of the shutter apertures 23 engage respective angled faces 59 of the contacts 57. This moves the contacts 57 inwards of the housing 10 and back through the apertures 23 in the shutter 20. The apertures 23 are covered or shielded by the movable member 30.

As the bulb is removed axially from the lampholder, the loaded contacts 57 move the shutter 20 outwards of the housing 10 until their flared ends 58 are arrested by the steps 52. The loaded torsion spring ensures that the shutter 20 is firmly biased to its closed position and the lampholder components reassume the position shown in Figs. 1, 5 and 8A. In this position the live terminal contacts 54 are inaccessible and not visible behind the shutter 20.

Referring now to Figs. 9 to 11, a modified version of the present invention is shown in which a compression spring 81 is arranged to act between a terminal block 150 and shutter 120 to bias the shutter 120 to its closed position. An elongate boss 70 extends from the inner surface of the shutter 120. The boss 70 has a hollow portion which houses one end of spring 81. The other end of the spring 81 locates within a stepped bore 75 in the terminal block 150. A pair of diametrically opposed bearing surfaces 73 are defined on and extend from the outer surface of the boss 70 and in use respectively engage a pair of ramp formations 74 defined on the wall of the bore 75 in the terminal block 150. Engagement of the bearing surfaces 73 and ramps 74 provide means to bias the shutter 120 to its closed position in the absence of a bulb.

Prior to bulb insertion the bearing surfaces 73 are located at the foot of the ramps 74 (see Fig. 9). After axial insertion of a bulb each bearing surface 73 is positioned above but to one side of a respective ramp 74 (see Fig. 10). As the shutter 120 is rotated from its closed to its open position, the bearing surfaces 73 are positioned at the top of the ramps 74 (see Fig. 11). In this position, if a bulb is not present in the lampholder, the combined forces of the springs 156 and 81 will move the shutter 120 outwards of the housing 110, the bearing surfaces 73 will engage the ramps 74 which, in conjunction with the angled surfaces 159 of the contacts 157, will rotate the shutter from its open back to its closed position. The bearing surfaces 73, when each located in their first position at the foot of a ramp 74, will provide means to lock the shutter 120 in its closed position against rotation until it has first been moved axially inwards of the housing 110. The annular protrusions 72 defined externally on the boss 70 are means by which the member 130 is secured to the shutter 120 to prevent relative axial movement. All other aspects of this embodiment are identical to those of Figs. 1 to 3.

Turning now to Figs. 12 to 14, there is illustrated a further alternative embodiment of the present invention. The principle of operation of this embodiment is almost identical to those of the previous embodiments.

However, in this arrangement, an additional rotatable component 90 is provided as a means of rotating a modified shutter 220 between its closed and open positions. In this case, the modified shutter does not have an annular skirt which extends to the housing "J" slots or slots to engage the bayonet pins of the bulb.

As in the previous embodiments, the shutter 220 and axial member 230 are secured together against relative axial movement and the shutter 220 is rotatable relative to the member 230. A torsion spring 240 is arranged to act between the shutter 220 and member 230, to bias the shutter rotationally relative to the member 230 and to its closed position. The shutter 220 and member 230 are movable inwardly of the housing 210 by the bulb on axial insertion.

The additional rotatable component 90 is in the form of a cylindrical body part of hollow section and it provides a pair of diametrically opposed limbs 91. The rotatable member 90 locates in the housing 210 beneath the terminal block 250. Its limbs 91 extend to the housing "J" slots 11 and are provided with slots 92 for engagement with the bayonet pins of an inserted bulb, the slots 92 aligning with the axial portion 12 of the J2 slots 11. The rotatable member 90 cannot move axially with respect to the housing 10 but is engaged by the shutter 220 and provides that, as the rotatable member 90 is rotated by the bulb on insertion, it rotates the shutter 220 with it from its closed to its open position.

As the rotatable member 90 is rotated on bulb removal it moves the shutter 220 from its open back to its closed position. Preferably, the shutter 220 is arranged so that it does not engage the rotatable member 90 until it has first been moved substantially inwards of the housing 210 on axial insertion. Alternatively, the shutter 220 may be engaged by the rotatable member at all times.

Projections 235 are provided on the axial member 230 to engage in vertical channels 216 defined in the housing wall thereby to prevent relative rotation. Prior to bulb insertion the projections 235 locate on support ledges 218 in the housing wall. The ledges 218 are the means by which the shutter/axial member assembly is retained in the housing 210. All other aspects of this embodiment are comparable to those of the embodiment of Figs. 1 to 8.

In use, when the lampholder of Figs. 12 to 14 is assembled and with no bulb present, the components assume the position illustrated in Fig. 12. The slots 92 are aligned with the axial portion 12 of the "J" slots 11.

The contacts 257 are located behind the shutter 20 which is biased to its closed position by the torsion spring 240. In this position, the apertures 223 in the shutter 220 are non-aligned with the pair of apertures 231 in the member 230. The member 230 is covering apertures 223 and the shutter is supported on the ledges 218. Insertion of a bulb is done in two stages, an axial stage and a rotational stage. As a bulb is inserted axially into the lampholder the bayonet pins engage in the aligned slots 12 and 92 and the pad electrodes 80 on the end of the bulb engage the outer surface of the shutter 220 moving the shutter 220 and thereby the member 230 inwards of the housing 210. The shutter 220 depresses the loaded terminal contacts 257 via their ends 59A until the bayonet pins- have travelled to the end of the axial portion 12 of the "J" slots 11 and the shutter 220 has engaged the wall portion 93 of the rotatable member 90.

The lampholder components assume the position shown in Fig. 13 after this axial stage of bulb insertion.

Rotating the bulb causes the rotatable member 90 to rotate with it which also causes the shutter 220 to rotate against the force of the spring 240 from its closed to its open position in which the respective pairs of apertures 223 and 231 are aligned. The loaded contacts 257 are also moved out of the holding recesses 229 such that they slide via their angled faces 259 outwards of the housing 210 to extend through the apertures 223. The free ends 259A of the contacts 257 bear against the pad electrodes 80 of the inserted bulb.

The lampholder components assume the position illustrated in Fig. 14 when a bulb has been fully inserted.

As the rotatable member 90 is rotated on removal of a bulb, it moves the shutter 220 with it from its open back to its closed position. Angled walls of apertures 223 engage the respective angled portions 259 of the contacts 257, to move contacts 257 inwards of the housing 210, back through the apertures 223 so as to be relocated behind the shutter 220. The pairs of apertures 223 and 231 become non-aligned, with apertures 223 being covered by the member 230. As the bulb is removed axially from the housing 210, the loaded contacts 257 move the shutter and member 230 outwardly of the housing 210, disengaging the shutter 220 from the rotatable member 90. The flared ends 258 of the contact 257 are arrested by the steps 252 and the lampholder components assume the position shown in Fig. 12. In this position the loaded torsion spring 240 is firmly biasing the shutter 220 to its closed position and the live terminal contacts 254 are inaccessible and visible behind the shutter 220.

Further modifications to the example lampholders are illustrated in the accompanying drawings. Fig. 15 shows an example lampholder in a first, inoperative position.

The lampholder comprises a housing 310 which accommodates a terminal block 350, an axially movable member 330 and a rotatable shutter 320. In this embodiment the terminal block 350 is provided with two depending limbs 315 having channel sections 325 terminating in hook formations 305.

Corresponding hook formations 303 are provided on the axially movable member 330. Interengagement of hook formations 303 in channel section 325 permits axial displacement of the member 330 and interengagement of the hook formations 305, 303 retains the axially movable member 330 in engagement with the terminal block.

Constructing the terminal block in this way is an alternative to providing channels or guideways for the axially movable member in the internal wall of the lampholder housing.

The embodiment of Fig. 15 also differs from previous embodiments in that the shutter 320 is mounted on a screw member 345, which screw member 345 is free to rotate within a bore 330' in the axially movable member 330 and a bore 350' in the terminal block. A spring 340 is located between the terminal block 350 and axially movable member 330. The spring 340 biases the member 330 axially outwardly of the housing 310 and provides a rotational bias for the screw member 345 and shutter 320.

The shutter 320 has axial slots 322 to receive the pins of a bayonet bulb which may drive rotation of the shutter 320. The contacts 357 may be released to extend through apertures in the shutter 320, in the same way as in previous embodiments. This embodiment is advantageous in that, whilst the axially movable member 330 is biassed outwardly of the housing 310 by spring 340 outward compression forces are not transferred to the shutter 320. This allows clearance for the shutter 320 to rotate freely with respect to the axially movable member 330 when engaged by a bulb.

Fig. 16 illustrates an alternative embodiment, in which the terminal block 450 and axially movably member 430 engage by way of matching hook formations. In this version the axially movable member 430 has a boss 435 for engaging a spring 440 which biases the axially movable member 430 outwardly of the housing 410 with respect to the terminal block 450. One end of the spring 440 is secured to shutter 420 and the other end secured to the terminal block 450. Again, this may be advantageous in that it permits the axially movable member 430 to be biassed outwardly of the housing 410 without transferring the compression forces to the shutter 420.

Fig. 17 illustrates a further alternative lampholder in which a rotatable shutter 520 carries a boss 525 which engages a spring 540 which provides a rotational bias for the shutter 520. The spring 540 also provides an axial bias for the axially movable member 530.

Fig. 18 illustrates part of an alternative apparatus in which a part of the shutter or rotatable member 620 which carries apertures 623 is located in the housing between a terminal block 650 and an axially movable member 630. In this embodiment, the shutter 620 would be provided with depending limbs (not illustrated) which would extend to the open end of the housing to engage the pins of an inserted bulb, and the axially movable member 630 would carry arcuate slots (not illustrated) which, in use, would receive the limbs from the shutter. The arcuate slots are of .an appropriate form to permit rotational movement of the shutter 620 and limbs with respect to the axially movable member 630.

In this embodiment the shutter 620 has depending surface formations 620A arranged to engage in respective apertures 631 in the axially movable member 630. In this way the formations 620A provide a shield for contacts 657 and a stop means for limiting the degree of relative rotation between the shutter 620 and axially movable member 630.

The shutter apertures 623 have a wall 623A of ramp form. The contacts 657 are of generally arcuate cross section and have opposed ramp formations, 659A and 659B, at their free ends. Provision of such opposed ramp formations is advantageous in that it assists raising of the contact 657 back behind the shutter 620 upon bulb removal. This is because both the shutter 620 and axially movable member 630 can engage a respective ramp formation to effect axial displacement of the contact 657.

Fig. 19 shows part of a further alternative lampholder, in which a shutter 720 is located in the housing (not illustrated) between terminal block 750 and axially movable member 730. In this embodiment, a contact 757 has a single-ramp formation 759. The shutter 720 has an aperture 723, wall of the aperture 23 providing a ramp formations 720A and 720B. The axially movable member has an aperture 731, a wall of the aperture having a ramp formation 731A matching that of the shutter 720A. The axially movable member 730 also has an upstanding surface formation 732 which, together with wall 720B of shutter aperture 723, defines a chamber for the free end of contact 757.

It will be appreciated that this embodiment is advantageous in that the axially movable member 730 and shutter 720 together provide an effective shield for the contact 757 when the lampholder is in an inoperative position.

Various other modifications may be made to the illustrated embodiments.

Claims

1. A safety lampholder for a bayonet bulb, comprising a housing defining slots at one end thereof to receive bayonet pins of an inserted bulb, resilient bulb engaging contacts for electrical connection to a power source to supply electricity to the bulb being arranged within the housing and biased outwardly thereof, the contacts having ramp formations at their respective free ends, axially movable and rotatable shutter means being located within the housing for selectively obstructing access to the contacts and arranged so as to be actuable upon rotation of a bulb, the shutter means being arranged such that insertion of a bulb actuates displacement of the shutter means and contacts against the bias of the contacts between a first inoperative position in which the shutter means obstruct the contacts and the contacts are offset from the shutter apertures, and a second operative position in which the free ends of the contacts extend through the apertures in the shutter means to bear against an inserted bulb, and removal of a bulb actuates rotation of the shutter means which is effective to drive the contacts inwardly of the housing and against the bias of the contacts to the first inoperative position by interengagement of the shutter means with ramp formations on the contacts.

2. A lampholder according to Claim 1 wherein the bulb engaging contacts comprise cylinders of an electrically conductive material, the cylinders being of generally arcuate form in cross-section, having a first dimension greater than a second dimension.

3. A lampholder according to Claim 2 wherein the cylinders have enlarged heads for retaining the contacts in the housing.

4. A lampholder according to Claim 2 or 3 wherein the contacts are arranged with their respective first dimensions circumferentially spaced about the axis of rotation of the shutter means.

5. A lampholder according to any one of claims 2 to 4 wherein the first dimension of a cylinder decreases along a length of the cylinder at the free end of a contact to define the ramp formation.

6. A lampholder according to Claim 5 wherein the ramp formation comprises an inclined slope.

7. A lampholder according to any one of claims 1 to 6 wherein means are provided for supporting the free ends of the contacts clear of the shutter means when the lampholder is in the first inoperative position.

8. A lampholder according to Claim 7 wherein means for supporting the contacts comprise surface formations within the housing.

9. A lampholder according to any one of claims 1 to 8 wherein recesses are provided in the shutter means alongside the apertures in the shutter means, the shutter means being arranged such that it is displaced inwardly of the housing upon axial insertion of a bulb so that the recesses accommodate the free ends of the contacts so as to inhibit rotation of the shutter means.

10. A lampholder according to any one of claims 1 to 6 wherein recesses are provided in the shutter means alongside the apertures in the shutter means, the recesses being arranged to accommodate the free ends of the contacts when the lampholder is in the first inoperative position, so as to prevent rotation of the shutter means in the absence of a bulb.

11. A lampholder according to any preceding claim wherein each aperture in the shutter means has a wall of ramp form arranged for interengagement with a ramp formation of a contact to assist in driving the contact inwardly of the housing.

12. A lampholder according to any preceding claim wherein the apertures in the shutter means are of arcuate form.

13. A lampholder according to any preceding claim wherein the contacts are arranged so that, in the second operative position, the ramp formations at the free ends of the contacts do not extend completely through the apertures in the shutter.

14. A lampholder according to any preceding claim wherein means are provided for rotationally biasing the shutter means to the closed position.

15. A lampholder according to Claim 14 wherein the biasing means comprises- a torsion spring.

16. A lampholder according to any preceding claim wherein surface formations are provided on the shutter means and are arranged to engage surface formations in the housing to limit the extent of rotation of the shutter means.

17. A lampholder according to any preceding claim wherein locking means are provided to inhibit rotation of the shutter means, the locking means being releasable upon axial insertion of a bulb into the lampholder.

18. A lampholder according to Claim 17 wherein the locking means are arranged to be releasable upon axial displacement of the shutter means by insertion of a bulb.

19. A lampholder according to Claim 15 wherein the locking means comprises an apertured member located within the housing and arranged to be axially movable with respect to the housing, the shutter means being rotatable with respect to the apertured member between a closed position in which apertures in the shutter and member are obstructed and an open position in which they are aligned.

20. A lampholder according to Claim 19 wherein the axially movable member is arranged between the bulb engaging contacts and the shutter means.

21. A lampholder according to any one of claims 1 to 20 wherein the apertures in the axially movable member are of a shape matching the cross-section of the contacts.

22. A lampholder according to any one of claims 19 to 21 wherein surface formations are provided on the axially movable member for limiting the extent of rotational movement of the shutter means.

23. A lampholder according to Claim 22 wherein the axially movable member has surface formations arranged to engage in apertures in the shutter means so as to limit the extent of rotation of the shutter means with respect to the axially movable member.

24. A lampholder according to Claim 23 wherein surface formations on the axially movable member are arranged to extend into apertures in the shutter means so as to shield the contacts from the apertures in the shutter means when the lampholder is in the first inoperative position.

25. A lampholder according to any one of claims 19 to 24 wherein the axially movable member is biassed outwardly of the housing and stop means are provided in the housing to limit the extent of outward movement of the member.

26. A lampholder according to Claim 25 wherein the biassing means for the axially movable member are arranged to rotationally bias the shutter means to the first inoperative position.

27. A lampholder according to Claim 26 arranged such that substantially only a rotational bias is applied to the shutter means.

28. A lampholder according to any preceding claim wherein the shutter means are arranged to be engagable by a bulb.

29. A lampholder according to any one of claims 1 to 26 wherein rotatable means are provided for engaging a bulb to drive rotation of the shutter means.

30. A lampholder according to Claim 29 wherein the rotatable means are arranged to engage the shutter means after axial insertion of a bulb.

31. A lampholder substantially as hereinbefore described with reference to and as illustrated in, any one of the accompanying drawings.