GB2269270A - Switched bayonet lampholder. - Google Patents

Abstract

A safety lampholder for bayonet pin lamps has a housing (10) in which a rotatable shutter (38) is mounted outside electrical contacts (44) which in a first position of the shutter (fig) 1A are shielded from contact with a counterpart by the shutter; the shutter is kept clear of the contacts in this position. The shutter being rotated by the insertion of a lamp into the holder so that in a final position fig 2A the contacts (44) protrude through apertures (42) in the shutter to contact the counterpart. The lampholder may have a stepped guideway (fig 5, not shown) for the bayonet pins of the counterpart. <IMAGE>

Description

SAFETY LAMPHOLDER The present invention relates to a safety lampholder of the type designed to receive a bayonet clamp.

Bayonet lampholders have a pair of contacts either as spring pins or as resilient flat leaf contacts. When the lamp is removed, unless the lampholder is switched off the holder is potentially dangerous to at least a child inserting a finger into the holder. For this reason there have been a number of proposals to make the holder safe.

Because of the restricted space within the holder there has been a tendency to mount the contacts so that when the lamp is removed they spring outwards and break contact with the power terminals. Such a holder is shown in French Patent specification FR-A-2045036, The problem with these kinds of holders is that there is little to indicate that the power connections are in fact broken. They can be confused with standard non-safety holders leading to dangerous handling of these. A safety holder with a clearly apparent safe indication is therefore required. In German AS 2651334 there is shown a different approach in which a shutter is rotated by insertion of the lamp so as to uncover sprung contacts which when the lamp is rotated through the J slots to the fully home position, protrude through apertures in the shutter to make contact with the lamp contacts.Whilst this simple arrangement is reasonably satisfactory as to safety, it is unsatisfactory because the holder contacts do not easily retract on lamp withdrawal because they press on the shutter.

Accordingly a safety bayonet lampholder according to the invention comprises a housing including a pair of electrical contacts with means to connect them to an electrical supply, the contacts being arranged to make contact with a lamp inserted in the holder, a rotatable shutter having a pair of apertures therein, the shutter in a first position before lamp insertion shielding the contacts, the shutter being rotated by lamp insertion to a final position in which the contacts protrude through the shutter apertures to contact the lamp, characterised in that in the first position mea-ns are provided so that the shutter is located so as to be clear of the contacts.

The means for locating the shutter clear of the contacts is preferably a spring which may also be used to return the shutter from the final position to first position.

The invention by ensuring the shutter is kept clear of the contacts enables the insertion of the lamp to easily rotate the shutter so that the contacts can then be moved relative to lamp for electrical engagement therewith, the contacts moving relatively through the shutter apertures.

Preferably the shutter has associated therewith, that is fixed to it or as a part of it, a sleeve which is slidable within the housing, the housing being provided with at least one bayonet pin guideway the sleeve being arranged to engage with a lamp bayonet pin to move the shutter relatively toward the contacts as guided by the guideway.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figures 1 to 4 are cross sections of a safety lamp holder according to the invention taken at I-I, II-II, III-III and IV-IV respectively in Figures 1A to Figures 4A respectively but with the bayonet pins of the lamp of Fig.

1B at AA, BB, CC and DD respectively.

Figures 1A to 4A are plan view of the holder of Fig.

1 with the bayonet pins of the lamp at AA respectively.

Figure 1B is a side view of a lamp for the holder of Fig. 1.

Figure 5 is an opened out diagram of guideways in the housing of the holder of Fig. 1 showing the bayonet pin, positions AA to DD.

In Figures 1 to 4 there is shown a safety lamp holder having a housing 10 having an upper and outer cylindrical wall 12 in which are a pair of axially extending guideway slot portions 14 for receiving bayonet pins 16 of lamp 20 (Fig. 1B) having a pair of lamp contacts 22. Slots 14 form a lead in part of guideways 18.

Extending at right angles in a clockwise direction from slot portions 14 the guideways 18 each have a further slot portion 24 extending about 50 from position A to position B (see Fig. 5), then for each guideway at right angles to portion 24 an axially extending portion 26 to position C then again at right angles a further clockwise portion 28 extending about 230 and finally at right angles a final axial portion 30 in a reverse direction to portion 14 to a final position D.

Rotatably and axially slidably mounted within housing 10 is a cylindrical shutter means 32 having an upper and outer cylindrical wall 34 fitting immediately inside housing wall 12, an inner and lower cylindrical wall 36 fitting inside a lower part 11 of the housing 10 and a circular shutter 38 between walls 34 and 36. Upper wall 34 has a pair of diametrically opposed axially extending slots 40 which receive bayonet pins 16 in position A and which cooperate with the bayonet pins to rotate and axially move the shutter means 32 from position A to D.

The shutter 38 has a pair of diametrically opposed apertures 42 therein which are misaligned with a pair of electrical contacts 44 in the lower part 11 of housing 10 when the shutter is in position A but which are aligned with the electrical contacts AA in positions B, C and D.

The apertures 42 extend over an elongate arcuate angle of about 230, that is from positions B/C to position d.

Below shutter 38 mounted contacts 44 having suitable springs 46 and terminals 48 for connecting to an electrical supply. The contacts 44 may have an insulating sleeve 50 which is preferably cylindrical around the contact stem so as only to allow a bared contact area or head 52. This assists in preventing a child poke an object such as a pin through a shutter aperture 42, when the shutter is in sliding position A, to contact electrically uninsulated parts of the holder.

Also below shutter 38 is a combined compression and torsion spring 54 anchored between housing 10 at 56 and shutter 38 at 58.

In position A (Fig.s 1 and 1A) the contacts 44 are shielded from outside by shutters 38. No electrically conductive part are evident. A lamp 20 is then inserted into the holder with its bayonet pins 16 in slots 14 and 40. The heads 52 of contacts 44 remain clear of the shutter 38.

The lamp is rotated through SOC to position B and then carrying with it shutter 38 is depressed further into the holder to position C where the heads 52 of contacts 44 protrude through apertures 42. Further rotation carrying with it shutter 38 brings the lamp pins 16 axially in line with position D. Releasing the lamp, the pins 16 are urged upward by spring 54 pressing on shutter 38 until the lamp pins 16 are trapped at position D with contact heads 52 in contact with lamp contacts 22.

Claims (12)

1. A safety bayonet lampholder comprising a housing including a pair of electrical contacts with means to connect them to an electrical supply, the contacts being arranged to make contact with a lamp inserted in the holder a rotatable shutter having a pair of apertures therein, the shutter in a first position before lamp insertion shielding the contacts, the shutter being rotated by lamp insertion to a final position in which the contacts protrude through the shutter apertures to contact the lamp, characterised in that in the first position means are provided so that the shutter is located so as to be clear of the contacts.

2. A lampholder as claimed in Claim 1 wherein the means for locating the shutter clear of the contacts is a spring.

3. A shutter as claimed in Claim 1 or 3 wherein the shutter is subject to pressure urging it to return from the final to the first position.

4. A lampholder as claimed in Claim 3 when dependent on Claim 2 wherein the spring for locating clear of the contacts is also used to urge the shutter back to the first position.

5. A lampholder as claimed in any one of Claims 1 to 4 wherein the shutter has associated therewith a sleeve slidable within the housing, the housing being provided with at least one bayonet pin guideway, the sleeve being arranged to engage with a lamp bayonet pin to move the shutter relatively toward the contacts as guided by the guideway.

6. A lampholder as claimed in Claim 5 wherein the guideway is so constructed as to guide at least one lamp bayonet pin from the first position through a first angle to a position where the contacts align with the shutter apertures and thence through a second angle to a final position where the contacts are still in alignment with the shutter apertures and where the contacts protrude through the shutter to contact a lamp inserted in the holder.

7. A lampholder as claimed in claim 6 wherein the first angle is substantially 50 and wherein the second angle is substantially 230.

8. A lampholder as claimed in any one of claims 1 to 7 wherein the apertures in the shutter are diametrically opposed and are arcuately elongated over an angle of substantially 230.

9. A lampholder as claimed in any one of Claims 5 to 7 wherein the guideway is constructed to retain the lamp in the final position by means of pressure exerted on the shutter in a direction towards the lamp.

10. A lampholder as claimed in Claim 9 wherein the retaining pressure is produced by the spring of any of claims 2 to 4.

11. A lampholder as claimed in any one of claims 1 to 10 wherein the contacts have an insulating sleeve around a stem of each contact.

12. A safety bayonet lampholder substantially as herein described with reference to the accompanying drawings.