EP0101257B1

EP0101257B1 - Lampholder

Info

Publication number: EP0101257B1
Application number: EP83304504A
Authority: EP
Inventors: Patrick John Doherty
Original assignee: KUDOS LIGHTING Ltd
Current assignee: KUDOS LIGHTING LIMITED
Priority date: 1982-08-09
Filing date: 1983-08-04
Publication date: 1987-05-27
Also published as: EP0101257A1; WO1984000854A1; AU575536B2; JPS59501807A; AU1825483A; DE3371840D1

Description

The present invention relates to safety lampholders.
Conventional lampholders comprise a body supporting fixed terminals to which electrical cables are connected, the body defining a socket into which a lamp bulb is in use inserted. Contacts often in the form of resiliently mounted pins are exposed within the socket to contact an inserted bulb, the contacts being permanently electrically connected to the fixed terminals.
When no bulb is present in the socket the contacts are exposed and can be easily touched. This can happen for example when replacing a faulty bulb in an overhead lampholder, or by accidentally putting ones finger in an empty socket from which a faulty bulb has been removed. Children are particularly at risk in the latter case when bedside or other free standing lampholders are provided.
Conventional three pin socket outlets into which cable terminating plugs are inserted generally have their live and neutral terminals covered by a shutter, the shutter being pulled away when an earth pin of a plug is inserted into the earth terminal socket. Such socket outlets are relatively safe as if one is to electrically contact the live terminal a pin must first be inserted into the earth terminal socket and then a further pin must be inserted into the live terminal socket. In contrast, in conventional lampholders not only are the live and neutral terminals not protected by a shutter but also the common socket in which they are located is large enough to enable a finger to be inserted.
The danger represented by conventional lampholders has been previously recognised and various attempts have been made to isolate the contacts within the socket from the cable terminals except when a bulb is present in the socket.
In prior arrangements, one or both of the contact pins are spring mounted in the lampholder body so that unless they are pushed up from within the socket in an axial direction relative to the socket they do not contact the cable terminals. Unfortunately unless the spring force applied to the contacts is large the contacts can be easily pushed up with a finger. On the other hand, if the spring force is large it becomes difficult to insert a bulb into the socket, and even more difficult to remove a bulb as the contacts tend to become embedded in the soft lead provided in at least one terminal of conventional bulbs. Damage to the bulb can result and the lampholderfeels far to tight. An example of such a lampholder is to be seen in US-A-:-2 306 741.
In another prior arrangement described in U.S. Patent No. 4,222,623 the contacts are supported on a rotatable or linearly movable carrier. When a bulb is inserted the carrier moves transversely relative to the socket against the action of a return spring from a first position in which the contacts are isolated from the cable terminals to a second position in which the contacts are electrically connected to the cable terminals. A spring loaded locking device is provided which releases the carrier for movement only when one of the contacts is depressed. This is not satisfactory however as either the locking device spring and return spring are relatively weak and can therefore be easily overcome by an inserted finger or the springs are relatively strong and an excessively stiff mechanism results.
A further prior arrangement is described in British Patent Specification 2,069,252. This arrangement also relies upon rotation of a carrier, rotation being prevented unless the contacts have been depressed. However the same stiffness problems result as the spring force on the contacts must be considerable if accidental activation is to be prevented. A pressure as high as 7 to 10lbs (3.18 to 4.55 Kg) on both contacts is mentioned.
It is an object of the present invention to provide an improved lampholder.
According to the present invention, there is provided a safety lampholder comprising a housing defining a socket into which in use a lamp bulb is inserted in an axial direction relative to the socket, fixed cable terminals supported by the housing and to which in use power supply cables are connected, contacts accessible within the socket for making electrical connections with an inserted bulb, a carrier mounted in the housing and supporting at least a part of each of the contacts, the carrier being movable as a result of insertion of a bulb between a first position in which the contacts are isolated from the terminals and a second position in which the contacts are electrically connected to the terminals, and means to bias the carrier to the first position in the absence of a bulb, wherein the carrier is engaged by at least one pin which bears against an inserted bulb and moves axially with it relative to the housing as the bulb is inserted into or removed from the housing, said at least one pin being located adjacent a wall of the socket so that an inerted finger cannot exert a substantial axial force upon it, and wherein said at least one pin, said carrier and said housing are shaped such that movement of the carrier between the first and second positions requires rotation of the carrier relative to the housing, and such that insertion of a bulb into the socket results in the said at least one pin being moved by contact with the bulb so as to cause said rotation of the carrier.
As the or each pin is located adjacent the wall of the socket it engages only the outer periphery of an inserted bulb and this makes it extremely difficult to move the pin axially without using a tool to engage the pin.tip. As the axial force required to connect the contacts and terminals must be applied to the pins, and such a force is difficult to apply, the spring force which must be overcome can be relatively small. The lampholder is thus easy to use and does not feel stiff to the user.
The carrier may be freely accessible within the socket. Preferably two spaced apart pins are provided.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 illustrates a first embodiment of the invention for receiving a bayonet bulb; and
Figs. 2to 15 illustrate in detail a second embodiment of the invention for receiving a bayonet bulb, Fig. 2 being a schematic sectional view illustrating the relative orientations of the contact carrier and the lampholder housing, Figs. 3 to 6 being respectively a top end view, a socket end view; an axial section on the line 5-5 of Fig. 3, and an axial section on the line 6-6 of Fig. 3 of the housing, Figs. 7 and 8 being underside and axial section views of the lampholder cap, Figs. 9 and 10 being side and end views of the contact carrier, Fig. 11 being an end view of a latch, Figs. 12 and 13 being side views taken on lines 12-12 and 13-13 of Fig. 11, and Figs. 14 and 15 illustrating terminals suitable for forming the contacts and the fixed terminals respectively.

Referring to Fig. 1, an embodiment is illustrated in which the carrier is freely accessible to an inserted finger. Movement of the carrier is prevented unless two pins extending along the socket wall are pushed in an axial dirction. The pins cannot be pushed by an inserted finger as a result of it being difficult to engage the pins with ones finger.
The lampholder of Fig. 1 comprises a single piece housing 20 supporting fixed terminals 21, 22 and receiving a carrier 23 which is force fitted by pushing it over an internal flange 24. The carrier supports spring contacts 25 arranged to make electrical connections with the terminals 21, 22 when the carrier is moved towards the terminals.
The carrier is generally circular when viewed from the socket but is provided with two oppositely arranged lugs 26, 27 which in the position shown engage in an annular groove 28 located between the flange 24 and a thickened portion 29 of the housing 20. Two axially extending grooves (not shown) communicate with the groove 28 and when the lugs are aligned with these axial grooves the carrier can move towards the terminals 21, 22.
A latch is provided comprising a central portion 30 extending across and above the carrier between the contacts 25 and two pins 31 (only one of which is shown) extending through peripheral slots 32 in the carrier and along slots (not shown) in the inside wall of the socket. Each slot 32 has an inclined edge surface 33 which engages a similarly inclined edge of the respective pin. A spring 34 bears against the central portion 30 of the latch.
With the pins in the position shown, that is before a bulb is inserted, the carrier cannot rotate relative to the housing because of the presence of the pins and their engagement with the socket wall, and the carrier cannot be moved axially because the lugs 26, 27 bear against the thickened portion 29 of the housing wall. When a bulb is inserted, its end engages the tips of the latch pins 31 pushing them upwards against the spring 34. The inclined portions of the pins slide against the corresponding inclined portions 33 of the carrier, causing it to rotate. This rotation aligns the lugs 26, 27 with the axial grooves so that when the bulb terminals engage the contacts 25 the carrier 23 is pushed towards the terminals 21, 22 to make electrical connections between the terminals and contacts.
Thus, although a finger can be inserted into direct contact with the carrier, the carrier cannot be moved. The tips of the pins 31 do not provide sufficient grip for an inserted finger to move the latch. Accidental electrocution is accordingly avoided.
Referring now to Figs. 2 to 15, a further embodiment of the invention will be described. The principle of operation of this embodiment is similar to that of the embodiment of Fig. 1 but its constructional detail differs in several respects.
Fig. 2 schematically illustrates the lampholder housing 35 which supports fixed spring strip terminals 36 and a carrier 37 which supports spring strip contacts 38. When a bulb is inserted the carrier initially rotates to move the contact 38 shown in Fig. 2 to the right and thereafter the carrier moves towards the terminal 36 to make sliding contact between the terminal 36 and the contact 38. It will be seen that the carrier supports two axially extending arms 39. The latch member which causes the carrier to rotate is not shown in Fig. 2.
Figs. 3 to 6 illustrate the housing 35 of Fig. 2 in detail, Figs. 3 and 4 being respectively top and bottom views taken on lines 3-3 and " of Fig. 2, and Figs. 5 and 6 being axial sections taken on lines 5-5 and 6-6 of Fig. 3. The terminals 36 of Fig. 2 are inserted through apertures 40 (Figs. 3 and 4), wires being fed to the terminals radially from a position on the housing axis, beneath lugs 41, and into through holes 42.
The housing defines conventional bayonet slots 43, axial slots 44 arranged on opposite sides of the housing, and axial keyways 45 also arranged on opposite sides of the housing. The inside of the housing also defines recessed areas 46.
Figs. 7 and 8 illustrate the lampholder cap, the cap being provided with apertures 47 which engage over lugs 48 (Fig. 5) such that the cap is a snap fit on the housing. Keyways 49 cooperate with grooves 50 (Fig. 3) to ensure correct orientation of the cap on the housing.
Figs. 9 and 10 illustrate the carrier 37 previously shown in Fig. 2 and its arms 39. The carrier is provided with two slots 51 with inclined edges 52, 53, two slots 54 immediately adjacent respective arms 39, and two slots 55 to receive the terminals 38 (Fig. 2). The inclined edges 53 are provided on projections 56. For the sake of clarity, only one arm 39 and one projection 56 are shown in Fig. 10. The arms 39 are resilient and support hooks 57 on their ends.
Referring now to Figs. 11 to 13, various views of a latch are shown. The latch comprises a central portion 58 supporting a pin 59 and two end portions or pins 60 defining inclined surfaces 61.
Referring now to Figs. 11 to 13, various views of a latch are shown. The latch comprises a central portion 58 supporting a pin 59 and two end portions or pins 60 defining inclined surfaces 61.
Referring to Figs. 14 and 15, the carrier contact 38 and fixed terminal 36 are illustrated. The carrier contact comprises a central apertured portion 62 which when the pin is mounted in the carrier is located within the slot 55 (Fig. 9), the slot being shaped such that the contact aperture is positively engaged. The contact is thus a simple push in fit. The fixed contact 36 comprises an aperture having a first portion 63 of circular cross section larger than the diameter of an insulated wire to which it is to make a connection and a second portion 64 in the form of a slot the width of which is less than the diameter of the conductor wire. The head of the terminal supports a flange 65. In use, the terminal is pushed into the slot 40 (Fig. 3) until the circular aperture 63 is aligned with the through holes 42 (Fig. 5). The unstripped wire is then pushed through the terminal so that its end is located in the hole 42. The terminal is then pushed fully in so that the flange 65 engages in a slot 66 shown in outline in Figs. 3, 5 and 6. This final movement of the terminal secures it in position and also simultaneously forces the conductor wire into the terminal slot 64, the edges of the slot cutting through the wire insulation. Pre-stripping of thee wire insulation is thus not necessary.
To assemble the illustrated lampholder, the terminals 36 are pushed partially into the housing and the contacts 38 are pushed fully into the carrier as described above. The latch pins 60 are located in the carrier slots 51 and a compression spring is placed over the latch pin 59. This sub assembly is then pushed into the housing with the latch engaging slots 44 until the carrier hooks 57 snap into the housing recesses 46. A cable is then passed through the cap and secured to the terminals, and the cap is snapped onto the housing. The lampholder is then complete.
If an attempt is made to push the carrier towards the terminals with a finger, the carrier is prevented from moving as it comes into contact with the keyways 45. If a bulb is inserted, the latch pins are engaged and the latch moves axially. The cooperating inclined surfaces 52, 53 and 61 of the latch and carrier cause the carrier to rotate until the keyways 45 are aligned with the slots 54, whereafter the carrier is pushed into the housing until the terminals 36 engage the contacts 38.
Although in the embodiments of Fig. 1 and Figs. 2 to 15 the carrier is first rotated and then moved axially, it could be arranged that no axial movement of the carrier is necessary, merely a rotational movement caused by cooperation with an axially moved latch mechanism.
It will be appreciated that switch devices may be incorporated in the lampholders if so required. Furthermore, it will be appreciated that the described embodiments may be easily adapted to accommodate screw-type bulbs. If the lampholder has the structure of Figs. 2 to 15 but is adapted for a screw type bulb, the pins which extend along the socket wall can be recessed in grooves so that they do not protrude above the lampholder screw thread. Thus only a bulb which engages in the screw thread can engage the tips of the pins.
The embodiment of Figs. 2 to 15 has a snap-on cap. As an alternative however the head of the lampholder housing can be extended to define a tube through which the supply cable runs. A bore communicates with the tube and a screw which extends through and engages a thread in the lampholder cap engages in the bore. The screw thus secures the cap in position and when tightened traps the cable within the tube to prevent it from being pulled out accidentally.
It will also be appreciated that the above lampholder safety mechanisms can be provided in an adaptor which can be fixed to a conventional lampholder. An adaptor of this type could prove useful where the purchaser does not want to remove existing lampholders and wire in new ones. In the case of adaptors for bayonet fittings, the adaptor could have a structure such that it locks onto the spring mounted contacts in the conventional lampholder as a result of these contacts engaging in suitable recesses. The adaptor could not then be removed accidentally. The bayonet pin of the adaptor could be made removable however so that the adaptor could be removed using a pair of pliers if so desired.
It is possible to combine a sharpened spring loaded centre pin with a latch actuated by pins extending along the socket wall. The latch and a rotatable carrier cooperate as in the embodiment of Figs. 2 to 15 but the latch and carrier are locked together until the centre pin is depressed. This can be achieved by for example providing a square section portion on the centre pin which engages in mating square apertures in the latch and carrier unless the centre pin is depressed. This combined centre pin and latch arrangement is very safe indeed as it is necessary to push both the centre pin and the latch pins to move the carrier.
In the latch and carrier mechanisms described, rotation of the carrier is achieved by cooperating faces of the latch and carrier sliding relative to each other. In the case of bayonet bulb fittings, it is possible to cause or assist rotation by providing suitable slotted members secured to the carrier, the bulb bayonet pins engaging the slotted members as the bulb is inserted.

Claims

1. A safety lampholder comprising a housing (20; 35) defining a socket into which in use a lamp bulb is inserted in an axial direction relative to the socket, fixed cable terminals (21, 22; 36) supported by the housing and to which in use power supply cables are connected, contacts (25; 38) accessible within the socket for making electrical connections with an inserted bulb, a carrier (23; 37) mounted in the housing and supporting at least a part of each of the contacts, the carrier being movable as a result of insertion of a bulb between a first position in which the contacts are isolated from the terminals and a second position in which the contacts are electrically connected to the terminals, and means (34) to bias the carrier to the first position in the absence of a bulb, characterised in that the carrier is engaged by at least one pin (31; 60) which bears against an inserted bulb and moves axially with it relative to the housing as the bulb is inserted into or removed from the housing, said at least one pin being located adjacent a wall of the socket so that an inserted finger cannot exert a substantial axial force upon it, and wherein said at least one pin, said carrier and said housing are shaped such that movement of the carrier between the first and second positions requires rotation of the carrier relative to the housing, and such that insertion of a bulb into the socket results in the said at least one pin being moved by contact with the bulb so as to cause said rotation of the carrier.

2. A safety lampholder according to claim 1, wherein the carrier is directly accessible within the socket and each contact is wholly supported by the carrier.

3. A safety lampholder according to claim 1, wherein said at least one pin (31; 60) is movable axially relative to the carrier, the carrier and said at least one pin having cooperating surfaces (33; 52, 53, 61) such that axial movement of the pin causes the carrier to rotate relative to the housing whereas the carrier cannot be rotated without relative axial movement of the pin.

4. A safety lampholder according to claim 3, wherein movement of the carrier from the first to the second positions requires firstly rotation of the carrier relative to the housing and secondly axial movement of the carrier relative to the housing, axial movement of the carrier prior to said rotation being prevented by cooperating surfaces (26, 27, 29; 45) of the carrier and housing.

5. A safety lampholder according to claim 1, comprising two spaced apart pins (31; 60).

6. A safety lampholder according to claim 5, wherein the pins are supported by a latch member (30; 58), the latch member being engaged in axial grooves within the housing to prevent rotation relative thereto.

7. A safety lampholder according to claim 2, wherein the carrier (37) supports two limbs (39) the ends of which define hook members (57), the hook members being received in recesses defined by the housing to retain the carrier therein.

8. A safety lampholder according to claim 1, wherein each fixed terminal (36) comprises a spring strip inserted through an aperture in the housing.

9. A safety lampholder according to claim 8, wherein each terminal spring strip (36) comprises a circular aperture (63) communicating with a slot (64), and the housing defines a through hole positioned such that an insulated wire may be inserted through the aperture into the hole and the terminal may then be pressed down to force the wire into the slot, thereby cutting through the insulation to make electrical contact with the wire.

10. A safety lampholder according to claim 1, wherein each contact (38) comprises a spring strip inserted through an aperture in the carrier.

11. A safety lampholder according to claim 1, wherein the biassing means comprises a compression spring arranged along the lampholder axis and bearing at one end against the lampholder housing and at the other end directly or indirectly on the carrier.