GB2083195A - Lamp mounting for projectors - Google Patents

Abstract

A lamp mounting for mounting a number of lamps 8, 9 in a projector includes a rotatable turntable 2 mounted on a plate 1 in the projector housing. The turntable is normally held in position by a locking mechanism 3. The locking mechanism can be released by a manually operable member to allow the turntable to be rotated. Thus if one of the lamps 8, 9 burns out in operation another lamp can be brought into the operative position simply by rotation of the turntable 2. The turntable can be rotatable automatically by means of a spring 5. <IMAGE>

Description

SPECIFICATION Lamp mounting for projectors This invention relates to a lamp mounting for holding a number of lamps in a projector, the lamps being alternately movable into the optical axis of the projector to form its light source.

Transparency projectors and other projectors for still or moving film require a powerful light source to provide full and uniform illumination of the projected images on a projection screen. On the other hand, the limited space conditions in such projectors, and the high optical standards mean that the light sources must be small and extremely powerful.

One of the consequences of this small size requirement is that the lamps heat up intensively and have only a limited life because of these high thermal stresses. It is particularly disadvantageous if the lamps burn out during the projection of a series of transparencies, talks or films because the result is a relatively long interruption for the lamp to be changed, something that frequently has to be done in a darkened room.

To obviate these disadvantages, lamp mountings for transparency projectors have been designed in which two lamps are mounted on a lampholder so that they are pivotable in a vertical plane into the optical position out of a reverse position laterally outside the optical axis as soon as the lamp previously in operation burns out. The projectionist can thus very easily and rapidly insert a replacement lamp after one of the lamps has burnt out. However, a disadvantage of these designs is the relatively large amount of space required laterally and the expensive and complex construction of the lampholder. Problems also arise in respect of a reliable electrical connection for the new lamps pivoted into the operating position, since operational reliability is inadequate.

It is an object of this invention to provide a lamp mounting without the above disadvantages and one which allows burnt-out lamps to be rapidly replaced with high operational reliability, with simple construction and small dimensions.

According to the present invention there is provided a lamp mounting for mounting a number of lamps in a projector so that the lamps are movable successively into the optical axis of the projector in order to provide its light source, characterised in that a turntable is mounted rotatably on a plate within the lamp housing, the lamps being mounted on said turntable, said turntable carrying separate switch contacts and a locking mechanism is provided between the plate and the turntable, the arrangement being such that when the locking mechanism is released, the turntable is rotatable from the operating position for one of the lamps into the operating position for another lamp.

A particular advantage of the invention is the very simple way in which a lamp change is carried out. If, for example, one of the projector lamps burns out during a transparency or film show or the like, the projectionist operates a press button, adjusting lever or the like, for example, to unlock the rotatable turntable, which then automatically turns through a predetermined angle, in response to a torsion spring, into a second operating position in which the reserve lamp is then on the optical axis of the projector. Depending upon the housing construction, the interlocking mechanism can be released either directly from outside or else after a window provided for the purpose in the housing has been opened.It takes only a few seconds to change a lamp in this way, and this procedure can be carried out in dark rooms so that there is no need to interrupt a showing of a series of still pictures or a talk.

One aspect of the invention which is particularly advantageous in respect of the small dimensions comprises two lamps each provided with a reflector and disposed in an arrangement in which they are offset by 180 on the turntable. In this case, when the locking mechanism is released, the turntable is rotated through half a turn by means of a spiral leaf spring wound for example, around the turntable pivot, so that a replacement lamp is then on the optical axis. The provision of two lamps on the turntable, i.e. just a single replacement lamp, is sufficient, since it is extremely rare for two lamps to burn out in immediate succession. On completion of the projection, the projectionist then has sufficient time to replace the burnt-out lamp in the usual way.

The use of just two lamps also provides a compact arrangement so that the dimensions of the projector are not increased and even existing projectors can be subsequently fitted with a lamp mounting of this kind.

In a very operationally reliable and readily operated embodiment of the invention, the locking mechanism comprises a rocking lever one end of which is pivotally connected to the fixed plate while its other end is movable into an unlocking position against the force of a spring pressing the rocking lever upwards. When the rocking lever is depressed, an abutment or stop provided in the middle part of the lever releases the turntable previously biassed by the torsion spring so that the turntable can no rotate through the preset angle, e.g. 180 . Simultaneously with this rotary movement, a switch contact provided on the middle part of the rocking lever is released from the corresponding contact on the turntable.On completion of the rocking movement the replacement lamp pivoted into position is automatically electrically connected by the fact that a contact associated with this replacement lamp makes contact with the switch contact on the rocking lever. In orderto determine the appropriate rotary movements, the two switch contacts are secured on the turntable at different heights, the lampholders being offset 90 from these switch contacts and being electrically connected thereto.

The invention will be described now by way of example only with particular reference to the accompanying drawings. In the drawings: Figure lisa diagrammatic plan view of a lamp mounting with two diametrically opposite lamps each provided with a reflector; Figure 2 shows the lamp mounting of Figure 1 in a diagrammatic side elevation, and Figure 3 is a view of the end of the rocking lever provided with an actuating rod.

The lamp mounting illustrated in the drawing comprises a plate 1 fixed in the housing and carrying a circularturntable 2 rotatable thereon. The turntable is made from insulating plastics material. A locking mechanism 3 is mounted on the plate 1 next to the turntable 2.

Afixed pivot 4 extending through a central bore in the turntable 2 is provided on the plate 1 and a spiral strip spring 5 is wound around said pivot. The two ends of this spring 5 are secured respectively to the pivot 4 and the turntable 2. A bent section member 6 is also secured to the plate 1 and its freely projecting collar engages over a radially projecting flange 7 of the turntable 2so that the latter is guided securely on the plate during its rotary movement.

Two replaceable lamps 8,9 are secured diametrically opposite one another on the turntable 2, and associated with each lamp is a fixed reflecting screen 10 and 11 respectively. Two insulators 12, 13 are also secured by screws 14 on the turntable 2 and the actual lampholders 16, 17 for securing the lamps 8,9 and the electrical contacts 18, 19 for the lamps are secured on the radial outer wall of the insulators. As will be apparent more particularly from Figure 2 switch contacts 20,21 in the form of U-sections are disposed respectively at the top and bottom of the turntable with respect to the drawing, and offset angularly by 90" relative to the lamps 8,9. Contact 20 is connected to lamp contact 19 via a short lead 22 and contact 19 leads via another lead 23 to a junction point 24 and then to a connecting lead 25.The bottom switch contact 21 with respectto Figure 1 is also connected via a short lead 26 to lamp contact 18 and via a connecting lead 27 to the junction point 24 and then to the mains lead 25.

The locking mechanism 3 mounted on plate 1 consists of a rocking lever 30 the right-hand end of which (in Figure 1) is mounted about horizontal pivots 32 in a stirrup-shaped bearing 31. As will be seen particularly from Figure 2 the right-hand end 33 of the lever 30 extends obliquely upwards and has a tag 34 for connection of the second mains lead 35 (compare Figure 1). A stop shoulder 36 is formed on the middle part of the lever 30 for abutment by the switch contacts 20, 21 in one or other operating position (see Figure 2). In addition, a metal strip is inserted in the middle part of the lever between the tag 34 and the shoulder 36 to provide an electrical connection between the connecting lead 35 and the respective switch contacts 20,21. At its free end the rocking lever has a holder 37 in which a push rod 38 engages (Figure 3).Between holder 37 and a supporting stud 39 on the plate 1 there is clamped a coil spring 40 which continuously hold the rocking lever in the locking position shown in Figures 2 and 3. An oblique and subtantially tangentially extending guide ramp 41 is formed on the rocking lever 30 in continuation of the shoulder 36 and when the turntable 1 is turned back from the "reserve position" into the normal operating position i.e. after the dead lamp has been replaced by a new lamp, the ramp 41 presses the rocking lever 30 down against the force of the spring 40 as the switch contacts run on to said ramp.

The above-decribed lamp mounting and turntable operate as follows: In the normal operating condition, lamp 8 is in operation. If this lamp fails to operate, e.g. if it burns out, the projectionist simply presses the rod 38 shown in Figure 3 and this causes the lever 30 to pivot about pivots 32 against the force of spring 40.

Shoulder 36 thus disengages from the U-shaped switch contact 21. The force of the spiral spring wound around the pivot 4 causes turntable 2 to be rotated through 180 . During this rotary movement the electrical connection between the switch contacts 20,21 and the mains lead 35 is broken. Just before the end of this rotary movement, the top switch contact 20 in Figure 1 comes into contact with the metal strip 29 forming the co-acting contact, strip 29 being mounted between tag 34 and shoulder 36.

As soon as contact 20 again abuts shoulder 36 and lamp 9 is in the operating position previously occupied by lamp 8, lamp 9 is also connected to the mains supply via switch contact 20, connecting lead 22, lead 23 and the junction point 24 with the mains lead 25. As soon as reserve lamp 9 has been brought into its operating position, therefore, it automatically lights up without any need to actuate additional switches or the like.

On completion of the showing of a series of slides, for example, or a talk using projected transparencies, or the showing of a film,the burnt-out lamp can be replaced in the usual way, the turntable then being simultaneously turned back through 1800 so that the new lamp is then in the operating position.

When that lamp burns out, the rod 38 can be actuated for the automatic changeover again. Alternatively, the lamp changeover can be effected manually by a separate actuating element, in which case the spiral spring 5 may be dispensed with.

Claims (8)

1. A lamp mounting for mounting a number of lamps in a projector so that the lamps are movable successively into the optical axis of the projector in order to provide its light source, characterised in that a turntable is mounted rotatably on a plate within the lamp housing, the lamps being mounted on said turntable, said turntable carrying separate switch contacts and a locking mechanism is provided between the plate and the turntable, the arrangement being such that when the locking mechanism is released, the turntable is rotatable from the operating position for one of the lamps into the operating position for another lamp.

2. A lamp mounting according to claim 1 char acterised in that two lamps each provided with a reflector are mounted on the turntable.

3. A lamp mounting according to claim 1 or 2 characterised in thattheturntable is rotatable by means of a spring.

4. A lamp mounting according to claim 3 wherein the spring is a spiral leaf spring wound around the pivot of the turntable.

5. A lamp mounting according to any one of claims 1 to 4 characterised in that the locking mechanism comprises a rocking lever one end of which is pivotally connected to the plate while its free end has an actuating member acting against the force of a compression spring, the middle part of said lever bearing a switch contact and an abutment shoulder, two angularly offset switch contacts on the turntable being associated therewith and acting as co-acting abutments.

6. A lamp mounting according to claim 5 characterised in that the lampholders are secured on the turntable at positions spaced angularly by 90" relative to the switch contacts and are electrically connected thereto.

7. A lamp mounting according to claim 6 characterised in that the two switch contacts are secured on the turntable at different heights and an inclined guide ramp is formed on the free end of the rocking lever and, when the turntable is manually turned back against the force of the spiral spring, said ramp produces an automatic downward movement of the rocking lever by guiding the switch contact on to said ramp.

8. A lamp mounting substantially as hereinbefore described with reference to and as shown in the accompanying drawings.