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(11) | EP 0 908 982 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Bayonet-fitting lamp bulb holder |
| (57) There is disclosed a bayonet-fitting bulb holder (11) having an apertured cover plate
(12) which is capable of axial and rotational movement in the bulb socket (13) and
which is so moved on insertion of a bulb (14) into the socket so as to align apertures
(15) with sprung contact pins (16) of the holder (11) to allow contact thereof with
the bulb terminals (17) when the bulb (14) is locked home in the bayonet fitting,
and which is moved in reverse on removal of the bulb (14) to conceal the contact pins
(16) beneath the cover plate (12). |
[0002] Conventional such holders have upstanding sprung contact pins within the socket. The contact pins are aligned, with respect to the bayonet channels in which the bayonet projections of the bulb base slide, so as to mate with the bulb contacts when the bulb is fully home and engaged in the terminal.
[0003] When no bulb is present, the pins are visible and extended under their spring loading into the socket where they can, such are the design and dimensions of the socket, k easily be contacted by an injudiciously-placed finger, leading to electrocution, if the pins are, or if one them is, live.
[0004] The obvious risk is tolerated only because
- there is a massive market for and correspondingly massive production of bayonet fitting bulbs and, it follows, lampholders, and manufacturers are reluctant to abandon this design because of the enormous cost of replacement, and
- nobody has yet come up with a safe bayonet-fitting lampholder.
[0005] This latter problem, and, hence, presumably, the former problem, is solved by the present invention.
[0006] The invention comprises a bayonet-fitting bulb holder having an apertured cover plate which is capable of axial and rotational movement in the bulb socket and which is so moved on insertion of a bulb into the socket so as to align apertures with sprung contact pins of the holder to allow contact thereof with the bulb terminals when the bulb is locked home in the bayonet fitting, and which is moved in reverse on removal of the bulb to conceal the contact pins beneath the cover plate.
[0007] It may be arranged that, when the bulb is absent, the cover plate is maintained at an initial forward position by the sprung pins.
[0008] The cover plate may have two generally circular apertures corresponding to the sprung pins, each aperture being relieved by a sloping section which acts as a cam surface when the bulb is turned in the bayonet fitting to release the bulb to initiate relative sliding of the plate over the tips of the sprung pins and their downward movement thereunder.
[0009] The cover plate may be rigid with a sleeve upstanding therefrom and lying just inside the inner surface of the cylindrical socket wall, (and of such thickness as not to interfere with the insertion of a bulb base) which has a recess at each side corresponding to the tracks of the bayonet fitting in which the projections from the bulb base engage.
[0010] Bayonet fitting bulb holders according to the invention look like and behave to all intents and purposes like conventional bulb holders, except that when no bulb is present, no live terminal can be exposed.
[0011] A bayonet-fitting bulb holder according to the invention will now be described with reference to the accompanying drawings, in which:-
- Figure 1
- is an axial section through the bulb holder with the bayonet track developed, with a bulb mounted;
- Figure 2
- is a section like Figure 1 in a configuration with no bulb mounted;
- Figure 3
- is a view on Arrows 3 of Figure 1; and
- Figure 4
- is a view on Arrows 4 of Figure 2.
[0012] The drawings illustrate a bayonet-fitting bulb holder 11 having an apertured cover plate 12 which is capable of axial and rotational movement in the bulb socket 13 and which is so moved on insertion of a bulb 14 (Figure 2) so as to align apertures 15 with sprung contact pins 16 of the holder 11 to allow contact thereof with the bulb terminals 17 when the bulb 14 is locked home in the bayonet fitting, and which is moved in reverse on removal of the bulb 14 to conceal the contact pins 16 beneath the cover plate 12.
[0013] The cover plate 12 is, when the bulb 14 is absent (Figure 1), maintained in an initial forward position by the sprung pins 16. It has two generally circular apertures 15 corresponding to the sprung pins 16, each aperture 15 being relieved by a sloping section 15a which acts as a cam surface when bulb 14 is turned in its bayonet fitting 11 to release the bulb 14 to initiate relative sliding of the plate 12 over the tips of the sprung pins 16 and their downward movement thereunder.
[0014] The cover plate 12 is rigid with a sleeve 12a (best seen in Figure 2) upstanding therefrom and lying just inside the inner surface of the cylindrical socket 13 (and of such thickness as not to interfere with the insertion of a bulb base - the socket 13 is always amply-proportional to receive the bulb base) which has a recess at each side corresponding to the tracks 18 of the bayonet fitting 11 in which the projections 14a from the bulb base engage.
[0015] A radially-inwardly directed step 19 on the socket 13 retains the cover plate 12 by limiting its movement outwardly of the socket 13.
[0017] The bayonet fitting 11 comprises bayonet pin 14a receiving slots 18 in the socket 13 which are inclined with respect to the axis "A" (so as essentially to be helical slots) terminating in an upturned retention section 22a whereby insertion of the bulb 14 demands an essentially screw thread action as compared with the conventional axial push followed by a rotation action.
1. A bayonet-fitting bulb holder having an apertured cover plate which is capable of
axial and rotational movement in the bulb socket and which is so moved on insertion
of a bulb into the socket so as to align apertures with sprung contact pins of the
holder to allow contact thereof with the bulb terminals when the bulb is locked home
in the bayonet fitting, and which is moved in reverse on removal of the bulb to conceal
the contact pins beneath the cover plate.
2. A bulb holder according to claim 1, in which the cover plate is, when no bulb is absent,
maintained in an initial forward position by the sprung pins.
3. A bulb holder according to claim 2, in which the cover plate has two generally circular
apertures corresponding to the sprung pins, each aperture being relieved by a sloping
section which acts as a cam surface when the bulb is turned in its bayonet fitting
to release the bulb to initiate relative sliding of the plate over the tips of the
sprung pins and their downward movement thereunder.
4. A bulb holder according to any one of claims 1 to 3, in which the cover plate is rigid
with a sleeve upstanding therefrom and lying just inside the inner surface of the
cylindrical socket wall (and of such thickness as not to interfere with the insertion
of a bulb base) which has a recess at each side corresponding to the tracks of the
bayonet fitting in which the projections from the bulb base engage.
5. A bulb holder according to any one of claims 1 to 4, having a retaining arrangement
limiting movement of the cover plate outwardly of the socket.
6. A bulb holder according to claim 5, in which the retaining arrangement comprises a
radially-inwardly directed step on the socket.
7. A bulb holder according to any one of claims 1 to 6, in which the cover plate is mounted
to a bulb-holder base by an axial mounting pin.
8. A bulb holder according to any one of claims 1 to 7, in which the bayonet fitting
comprises bayonet pin receiving slots in the socket which are inclined with respect
to the axis (so as essentially to be helical slots) terminating in an upturned retention
section whereby insertion of the bulb demands an essentially screw thread action as
compared with the conventional axial push followed by a rotation action.