This invention relates to a mast of the type which allows an amenity (such as a lighting assembly) to be raised to the mast-head or lowered to ground level by means disposed at or adjacent to the foot of the mast.

Masts carrying lighting or other amenities are commonly used, for example to illuminate roads, airports and industrial areas. These masts are often of considerable height, and it is undesirable and costly to service and maintain the amenities while they are situated at the top of their masts. Consequently, means of lowering an amenity to the bottom of the mast may be provided, for example in the form of a steel rope wound around a reel at the bottom of the mast and connected to the amenity. However, if the weight of the amenity at the top of the mast is permanently carried by the steel rope, failure of the rope, caused for example by wear or rusting, will allow the amenity to drop to the bottom of the mast, exposing bystanders to considerable danger, and causing damage to the amenity itself.

An object of the present invention is to provide a lighting mast comprising a latching mechanism for securing an amenity at the mast-head which obviates or mitigates the above disadvantages.

According to the invention there is provided a mast of the type which allows an amenity to be raised to the mast head or lowered to ground level by means disposed at or adjacent to the foot of the mast, comprising a latching mechanism operative releasably to retain the amenity in a predetermined latched position at the mast-head, the latching mechanism being automatically engaged when the amenity is raised through said predetermined position and lowered back into that position, and being automatically disengaged when the amenity is subsequently raised out of said predetermined position.

Preferably, the latching mechanism comprises at least one latching device including a latching arm and a latch member which are mutually engaged when the amenity is in said predetermined position, one of the latching arm and the latch member being mounted on the mast-head and the other being mounted for movement relevant to the mast with the amenity.

Conveniently, the latch member is mounted on the mast-head and the latching arm is mounted for movement with the amenity.

Desirably, the latching arm is biased into a neutral position but is held in a position displaced from said neutral position when the amenity is in said predetermined latched position, such that raising

of the amenity from said latched position causes the latching arm to move to its neutral position under the action of the bias.

Advantageously, the latch member includes a profiled surface and a detent, the profiled surface being engaged by the latching arm as the amenity is raised towards said predetermined position, such engagement causing the latching arm to be moved out of its neutral position against the action of the bias, subsequent movement of the amenity past said predetermined position causing the latching arm to disengage from the profiled surface and move to a position in which it is generally aligned with the detent, subsequent lowering of the amenity into said predetermined position causing the latching arm to engage with the detent.

Preferably, the or each latching device also includes an abutment member fixed relative to the latch member, the latching arm moving into engagement with the abutment member after it disengages from the profiled surface of the latch member, the latching arm being held by the abutment member in a position displaced from the position it occupies when engaged with the detent.

Conveniently, the latch member includes a second profiled surface which is engaged by the latching arm after the amenity has been raised from its predetermined latched position and is subsequently lowered, such engagement causing the latching arm to be moved into a position displaced from its neutral position, lowering of the amenity below said predetermined position causing the latching arm to disengage from the second profiled surface and move to its neutral position under the action of the bias.

Desirably, engagement of the latching arm with the first-mentioned profiled surface causes the latching arm to be moved in one direction from its neutral position, and engagement of the latching arm with the second profiled surface causes the latching arm to be moved in the opposite direction from its neutral position.

Advantageously, the latching arm is moveable about a pivot.

Preferably, the latching arm is biased into its neutral position by spring means disposed around the pivot.

Conveniently, the latching arm is oriented generally vertically when in its neutral position.

Desirably, the or each latching device includes two such latch members which are disposed in generally parallel spaced apart relation, and the latching arm is received between the latch members

and has a cross-piece at or adjacent its end which engages the two latch members.

Advantageously, three such latching devices are provided in equally-angular spaced relation around the mast.

Preferably, the amenity is carried on a generally annular frame which includes a plurality of inwardly-extending arms, the latching arm of the or each latching device is carried by a respective one of said inwardly-extending arms, and each inwardly extending arm carries at its inner end a roller which engages the mast.

Conveniently, the amenity is raised and lowered by means of at least one cable, and the or each cable is fastened to the generally annular frame at a respective one of said inwardly-extending arms.

A specific embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which :-

Figure 1 is a schematic view from the side of a lighting mast with a lighting assembly in a raised position,

Figure 2 is a view from above of the lighting assembly,

Figure 3 is a view from the side of a section of a mast-head and a latching device,

Figure 4 is a view from the rear of the mast-head and the latching device; and

Figure 5 is a view from the side of the mast-head and the latching device, with a cross-piece of the latching device illustrated in different positions.

Referring first to Figure 1, a lighting mast comprises a mast 2 of circular cross-section on top of which is situated a mast-head 4. A lighting assembly 6 is positioned around the mast-head 4. The lighting assembly 6 comprises an outer ring 8 to which lights 10 are attached, three arms 28 (see Figure 2) which extend radially inwards from the outer ring 8, each arm 28 supporting a latching mechanism 12, and an inner ring assembly 14. Steel ropes 16, attached to each of the inwardly extending arms 28, pass over pulleys 18 situated inside the mast-head 4 and combine into a single steel rope 20, which is wound around a reel 22 at the bottom of the mast 2.

The lighting assembly 6 is shown in more detail in Figure 2. The outer ring 8 of the assembly comprises two arcuate tubes 26 which are secured together by means of connecting plates 24 at their ends 8. The radial arms 28 are disposed at intervals of 120 degrees within the outer ring 8. An outer end 27 of each arm 28 is of box-section construction. An inner end of each arm 28 comprises two laterally spaced elements 30.

Referring now also to Figure 3, a rod 32 extends between the two laterally spaced elements 30 of each arm 28, and a latching arm 42 of a latching device 40 forming part of the latching mechanism 12 is pivotably attached to each rod 32. A pin 34 is similarly disposed adjacent to the inner end of each arm 28, and the three steel ropes 16 are attached to the lighting assembly 6 via these pins 34. A rubber roller 36, flared at either end to accommodate the convex surface of the mast-head 4, is disposed at the inner end of each of the arms 28. Also disposed at the inner end of each arm is an arcuate bump ring 38 positioned below the roller 36 which forms a section of just less than 120 degrees of a circle. Each of these rings 38 is fixed at its midpoint to the respective arm 28, the three rings 38 in combination forming the aforesaid assembly 14.

Figures 3 and 4 show one of the latching devices 40, the other latching devices being identical in construction to the one illustrated. The latching arm 42 of the latching device 40 has at its tip a cross-piece 43 which extends either side of the arm 42. The latching arm 42 is pivotably supported close to its lower end by the aforesaid rod 32, and is urged to a vertical orientation by two springs 44 disposed around the rod 32. The springs 44 are located at their upper sections around mountings 62 which are attached to the pivot rod 32. The springs are not free to pivot about the rod 32, and are fixed in one position. A pin 64 below the pivot rod 32 extends either side of the latching arm 42. Projecting legs 44a of the springs 44 are in contact with the pin 64, and exert force against the pin 64 when the latching arm 42 deviates from a vertical orientation. Screws 49- are provided to allow adjustment of the force exerted by the springs 44 on the arm 42.

A plate 48 whose underside is coloured is fixed to the lower end of the latching arm 42. Two vertical plates 45 extend downwards from below the rod 32. The lower edges of the plates 45 are connected by a horizontal plate 46 which partially obscures the coloured underside of the plate 48 when viewed from below:

Two vertically-arranged latch members 50 are provided at the mast-head 4. The members 50 are disposed parallel to each other and are spaced apart to allow the latching arm 42, but not the cross- piece 43 at the tip of the arm 42, to pass between them. The members 50 are attached by their outer sides to two plates 56 which extend from the mast-head. An abutment or baulk plate 54 is fixed to and interconnects the plates 56 above the latch members 50.

The two latch members 50 are identical, each having a profiled underside 50a which slopes diagonally upwards and away from the mast-head. A short vertical edge 50b extends from an upper end of the profiled underside 50a to the top of the member 50. A detent 50c extending either side of the baulk plate 54 is provided in an upper surface of each latch member 50. A profiled inner edge 50d slopes diagonally downwards from the detent 50c and towards the mast-head, to a corner from which a vertical edge 50e extends to the bottom of each member.

In use, the lighting assembly 6 is raised and lowered relative to the mast 2 by means of the reel 22 and the steel ropes 20 and 16 in order to permit the lights 10 to be serviced at ground level. Figure 3 shows the lighting assembly 6 in a position during its raising when it is approaching its final, operational position on the mast head 4. The lighting assembly 6 is guided in this movement by the rollers 36 on the radial arms 28 engaging the mast-head 4. As the lighting assembly 6 is raised further from the illustrated position, the cross-piece 43 of the latching arm 42 of each latching device 40 comes into contact with the profiled undersides 50a of the members 50. Continued raising of the lighting assembly 6 causes the cross-piece 43 to slide along the undersides 50a, thereby causing the arm 42 to pivot away from its vertical position to the right as viewed in Figure 5, against the bias of the springs 44.

Figure 5 shows the assembly in a condition in which the cross-piece has ridden over the upper ends of the undersides 50a and is engaged with the vertical edges 50b of the plates 50. When the latching arm 42 is in this configuration, the right hand legs 44a of the springs 44 as viewed in Figure 5 are not in contact with the rod 64. Further raising of the lighting assembly 6 will then cause the cross-piece 43 to ride over the upper ends of those vertical edges 50b, whereupon the springs 44 cause the latching arm 42 to pivot to the left as viewed in Figure 5, thereby bringing the cross-piece 43 into contact with the baulk plate 54. The cross-piece 43 then occupies the position indicated at 43a. The lighting assembly 6 is now at the top of its ascent and is prevented from being raised any further by the inner ends of the radial arms 28 coming into contact with a lip 66 on the underside of the mast¬ head 4. The points at which the arms 28 come into contact with the lip 66 are protected by pieces 60 of resilient material such as rubber or plastics.

The lighting assembly 6 is then lowered from this uppermost position, thereby disengaging the cross-piece 43 from the baulk plate 54. As the cross-piece 43 disengages from the baulk plate 54, the latching arm 42 is permitted to pivot to the left as viewed in Figure 5, under the action of the springs 44, until it engages the left hand end of each detent 50c. The cross-piece 43 is now disposed in the position indicated at 43b. When the cross-pieces 43 of the latching arms 42 are located in their respective detents 50c, the lighting assembly 6 is firmly secured at the mast-head 4.

In order to lower the lighting assembly 6, it is first raised from its operational position so as to disengage the cross-piece 43 of each latching device 40 from the respective detents 50c. The latching arm 42 is thereby allowed to return to a vertical orientation with its cross-piece 43 in the position indicated at 43c, under the action of the springs 44.

Lowering the lighting assembly 6 from this position will bring the cross-piece 43 into contact with the diagonally sloping edges 50d of the latch plates 50. As the cross-piece 43 slides along these edges 50d, the latching arm 42 is caused to pivot away from its vertical position to the left as viewed in Figure 5. As the cross-piece 43 is further lowered (as indicated at 43d), the edges 50e keep the arm 42 biased away from its vertical position. Lowering the lighting assembly 6 still further will bring the the cross-piece 43 to the lower ends of the edges 50e, whereupon the cross-piece 43 disengages from the plates 50 and the latching arm 42 returns to a vertical orientation under the action of the springs 44, as depicted in Figure 3.

Throughout the engaging and disengaging processes, the orientation of each latching arm 42 can be monitored by an operator at the foot of the mast through observation of the coloured undersides of the plates 48 at the lower ends of the arms 42. In particular, the plate 48 is obscured by the horizontal plate 46 when the cross-piece 43 of the latching arm 42 is engaged with the baulk plate 54. When the lighting assembly 6 is lowered from this position, and the latching arm 42 pivots so as to engage the cross-piece 43 with the left-hand ends of the detents 52, the coloured plate 48 partially extends beyond the right-hand edge of the horizontal plate 46 and is visible from below, indicating to an operator that the cross-piece 43 is correctly positioned and the weight of the lighting assembly 6 is being carried by the latching mechanism 12.