GB2083433A - Improvements in pantograph suspensions - Google Patents

Abstract

A pantograph suspension provided for suspending equipment from overhead, comprises a lazy tongs arrangement 1 whose upper end is fixed to means 2 for mounting the suspension and whose lower end is provided with an equipment coupling 4. Springs 14 are connected between the upper end of the lazy tongs arrangement and a point along the length thereof for balancing the suspension. Braking means 18, e.g. a rotary inertia brake, at the top of the suspension having a cable 20 connected to the bottom thereof, are provided for braking downward movement of the lower end of the lazy tongs arrangement when the downward acceleration exceeds a predetermined value. Thus, in the event of failure of one or more of the springs 14, the sudden downward movement of the lower end of the lazy tongs arrangement causes the brake means 18 to engage. <IMAGE>

Description

SPECIFICATION Improvements in or relating to pantograph suspensions The present invention relates to pantograph suspensions. Such suspensions may, for instance, be used in television or film studios to suspend lighting equipment from an overhead gallery. In such a case, the upper end of the suspension is mounted from the gallery and the lower end has a coupling for mounting apparatus such as a luminaire. The pantograph suspension is in the form of a "lazy tongs" arrangement and allows the height of the luminaire to be adjusted. One or more springs are provided to balance the suspension and its load in any vertical position thereof.

According to the invention, there is provided a pantograph suspension comprising a lazy tongs arrangement whose upper end is fixed to means for mounting the suspension and whose lower end is provided with a coupling for attaching an apparatus to be suspended, spring means connectable between the upper end and a point along the length of the lazy tongs arrangement for balancing the suspension and apparatus when attached thereto, and braking means connected between the upper and lower ends of the lazy tongs arrangement for braking downward movement of the lower end when the downward acceleration exceeds a predetermined value.

Preferably, the braking means comprises a cable connected at one end to the lower end and at the other end wound around a rotatable drum connected to an inertia brake. Preferably, the inertia brake comprises a fixed ratchet member, a movable ratchet member comprising a flywheel rotatably mounted on the drum shaft and biased away from the fixed ratchet member, a drive member fixed to the drum shaft, and a plurality of ball bearings disposed between the movable ratchet member and the drive member, each ball bearing being received in a part spherical recess in the drive member and in a circumferentially extending recess of the movable ratchet member having a depth which reduces in the circumferential direction of movement of the drum corresponding to downward movement of the lower end. The drum may be provided with a return spring tending to rewind the cable on the drum so as to keep the cable taut. The force exerted by the return spring need only be relatively small as the cable normally carries no load, so that the effect on balancing of the suspension with apparatus attached thereto is negligible.

Preferably, the return spring is of the type which exerts a substantially constant force over the whole of its working range.

Preferably the lazy tongs arrangement comprises two spaced apart lazy tongs linkages interconnected by a plurality of horizontal shafts.

Preferably the spring means comprises one or more pairs of springs of the type which exerts a substantially constant force over the whole of its working range, the springs of the pair or one of the pairs being connectable to respective shafts on opposite sides of the lazy tongs arrangement at different points along the length thereof to allow different loads to be balanced.

During normal vertical positioning involving relatively slow downward movement of the coupling with, for instance, a luminaire attached thereto, the bias of the movable ratchet member away from the fixed ratchet member is sufficient to keep the two members out of engagement.

However, in the event of sudden failure of one or more of the springs of the spring means, the coupling and luminaire accelerate rapidly downwardly, thus pulling the cable causing the drum to accelerate. The drive member accelerates at the same rate but, because of the flywheel inertia, the movable ratchet member cannot accelerate so quickly. The ball bearings thus ride along the variable depth recesses of the movable ratchet member and push it into engagement with the fixed ratchet member so as to prevent further rotation of the drum. Further downward movement of the luminaire is thus prevented by the cable. Thus, the chance of injury to personnel or of damage caused by such failure of the pantograph suspension is substantially reduced.

When the lower end of the lazy tongs arrangement is raised, the return spring rewinds the cable on the drum so as to keep it taut. The two ratchet members remain out of engagement or slip over each other freely for movement in this direction.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a side view of a pantograph suspension constituting a preferred embodiment of the present invention; Figure 2 shows a front view of the pantograph suspension of Fig. 1; Figure 3 is a side view of an inertia braking mechanism of the pantograph suspension of Fig. 1; Figure 4 is a cross-sectional view of the inertia braking mechanism of Fig. 3; Figure 5 is a front view of a movable ratchet member forming part of the mechanism of Fig. 3; Figure 6 is a cross-sectional view of the movable ratchet member of Fig. 5; Figure 7 is a rear view of the movable ratchet member of Fig. 5; Figure 8 is a cross-sectional view on the line A-A of Fig. 7; Figure 9 is a front view of a fixed ratchet member; and Figure 10 is a cross-sectional view of the fixed ratchet member of Fig. 9.

The pantograph suspension shown in the accompanying drawings comprises a lazy tongs arrangement 1 connected at its upper end to a mounting member 2 and at its lower end via two brackets 3 to a coupling 4 for mounting an apparatus to be suspended, such as a luminaire.

The lazy tongs arrangement 1 comprises two similar lazy tongs linkages 5 and 6 which are spaced apart and interconnected by a plurality of shafts 7. The uppermost shaft 7 is fixed to the mounting 2.

The mounting is arranged to be suspended from an overhead gallery in a film or television studio. For instance, the mounting 2 may be fixed to an overhead trolley having wheels for running along overhead tracks of the gallery, the trolley being connected to the mounting 2 by a bracket which passes through a slot in the overhead track.

Thus, the horizontal position of the pantograph suspension may be adjusted as desired by pushing the pantograph suspension and trolley along the overhead track.

The coupling 4 is of the standard type and has a bore extending from its lower end in the longitudinal direction of the pantograph suspension. The coupling is arranged to receive a corresponding coupling on the luminaire of the type comprising a cylindrical protrusion having an upper lateral through bore and a lower annular groove. A handle 8 of the coupling 4 is connected to a threaded shaft 9 which is received in a threaded bore of the coupling 4 and can be screwed in by hand so as to project into the annular groove of the coupling on the luminaire to connect the luminaire to the pantograph suspension. A split pin 10 is connected to the coupling 4 by a cable 11 and can pass through an opening 12 in the coupling 4 so as to pass through the upper lateral bore of the luminaire coupling.

Alternatively, if the coupling 4 is to be used with a luminaire coupling of the type having two longitudinally spaced annular grooves, then a further hand wheel and threaded shaft may be screwed into another bore of the coupling 4 which can be provided at 13 as shown in Figure 2.

The pantograph suspension is provided at its upper end with four coiled leaf springs 14 of the type which exerts a substantially constant force over the whole of its working range. The springs 14 are arranged in two pairs, with the springs of each pair being mounted on a respective shaft 1 5 fixed to the mounting 2. One of the springs 14 of each pair is connected at its lower end 1 6 to the lowermost shaft 7 of the lazy tongs arrangement on the corresponding side of the arrangement. The end 1 7 of the other springs 14 of the two pairs can be connected to any of the shafts 7 on the corresponding sides of the arrangement along the length thereof so as to allow any desired load within a given range to be balanced. The end 1 7 of the two other springs 14 are connected to shaft 7 at the same position along the length of the lazy tongs arrangement. Such a pantograph suspension may be capable, for instance, of balancing any load from 30 pounds to 88 pounds.

In an alternative embodiment, the springs 14 whose ends 1 6 are permanently connected to the lowermost shaft 7 are omitted so that only two springs 14 are provided on respective sides of the lazy tongs arrangement. This embodiment is capable of balancing any load from 12 pounds to 33 pounds.

An inertia braking arrangement 18 is fixed to the mounting 2 by means of two transverse shafts 1 9. The inertia braking arrangement includes a cable 20 fixed to the coupling 4 by means of a loop at its lower end which is looped around a cross-member 21 of the coupling 4. The inertia braking arrangement comprises a housing comprising two angled members 22 and 23 rigidly connected together. A shaft 24 is rotatably mounted in the housing and is fixed to a cable drum 25 formed in two parts connected together and to the shaft 24 by bolts 26. The groove of the cable drum 25 is of a width just sufficient to receive a single turn of the cable 20 so that the cable 20 is wound on the drum in the form of a plurality of single turn layers. A coiled leaf spring 27 is connected to the shaft 24 at one end and is fixed to the housing at a bolt 28 at its other end.

The spring 27 is of the type which exerts a substantially constant force throughout its working range.

The shaft 24 is fixed to a ratchet drive member formed in two parts 29 and 30 by means of a bolt 31. The two parts 29 and 30 of the ratchet drive member are rotationally rigid with each other. The part 30 has formed therein a plurality of recesses, each of which receives a ball bearing 32. Three such ball bearings 32 are provided in the embodiment shown in the drawings. The ball bearings 32 are also received in recesses 33 (Figs 7 and 8) of a movable ratchet member 34 in the form of a flywheel which is rotatable with respect to the ratchet drive member part 29. The recesses 33 extend circumferentially of the movable ratchet member 34 and have a depth which decreases in the anticlockwise direction as illustrated in Figs 7 and 8. The recesses in the part 30 also extend circumferentially of the part 30, but have a depth which decreases in the clockwise direction. The movable ratchet member 34 has a central opening into which a portion 35 extends and fits into a groove in the shaft 24 which is circumferentially iarger than the projection, thus allowing a relative rotational movement between the member 34 and the shaft 24 to permit "inertial lag" of the member 34 to lock the ratchet.

The other side of the movable ratchet member 34 is provided with teeth 36 which have a saw tooth shape in the circumferential direction of the member 34. The teeth 36 face a fixed ratchet member 37 which also has saw tooth-shaped teeth 38 on its side facing the teeth 36 of the movable ratchet member 34. The fixed ratchet member 37 is fixed to the housing by means of bolts 39. A spring 40 is disposed between the fixed and movable rathet members 37 and 34 and urges the two members apart.

In use, the pantograph suspension is suspended from an overhead gallery in a studio and an apparatus such as a luminaire is attached to the coupling 4 as described hereinbefore. The positions of the ends 1 7 of two of the springs 14 are adjusted so that the suspension and luminaire are balanced for vertical movement i.e. the lazy tongs arrangement may be expanded or contracted and the luminaire will remain in a desired vertical position. The spring 27 provides a constant rotational bias ori the cable drum 25 which tends to wind the cable 20 onto the drum, so that the cable 20 whose lower end is connected to the member 21 of the coupling remains taught. The force exerted by the spring 27 need only be relatively small, as the cable 20 does not normally support any Ipad; so that this force does not have any substanti81 effect on the balancing achieved by the springs 14.

When the luminaire attached to the coupling 4 is moved upwardly so that the lazy tongs arrangement 1 is contracted, the drum 25 rewinds the cable 20 under the action of the spring 27.

The shaft 24 thus rotates and causes the ratchet drive member to rotate at the same speed. The drive member transmits this motion via the ball bearings 32 to the movable ratchet member 34.

The movable ratchet member 34 rotates in a direction such that its teeth 36 slip over the teeth 38 of the fixed ratchet member 37, thus providing no impediment to rotary movement of the shaft 24 and cable drum 25. In any event, the spring 40 maintains the fixed and movable ratchet members 37 and 34 out of engagement with each other for normal upward movement of the luminaire and coupling 4.

When the luminaire attached to the coupling 4 is moved downwardly so as to expand the lazy tongs arrangement 1 , the lower end of the cable 20 is also pulled downwardly and is thus unwound from the cable drum 25 against the action of the spring 27. The shaft 24 thus rotates in the opposite direction, as do the parts 29 and 30 of the ratchet drive member. This movement is transmitted to the movable ratchet member 34 by the ball bearings 32 and, for the relatively slow accelerations involved in normal downward movement of the coupling 4 to adjust the height of the luminaire attached thereto, the ball bearings 32 do not substantially ride along the recesses 33 of the movable ratchet member 34. In particular, the inertia-of the movable ratchet member 34 is made such that it can follow the relatively slow acceleration of the ratchet drive member during normal adjustment of the height of the luminaire, and the spring 40 keeps the fixed and movable ratchet members apart so that their teeth do not engage.

In the event of failure of one or more of the springs 1 4 balancing the pantograph suspension and load, the luminaire and coupling 4 suddenly accelerate downwardly at a relatively high rate.

The cable 20 is thus pulled downwardly and causes the drum 25 to accelerate at a relatively high rate and, with it, the shaft 24 and the ratchet drive member. The ball bearings 32 attempt to transmit this relatively high acceleration to the movable ratchet member 34 but, because of its flywheel inertia, the member tends to lag behind the ratchet drive member. There is thus a relative rotational displacement between these members and the ball bearings 32 ride along the recesses 33 in the movable ratchet member 34. The movement of the ball bearings is towards the ends of the recesses 33 of lower depth so that the movable ratchet member 34 is urged axially against the action of the spring 40. The teeth 36 of the movable ratchet member 34 thus engage with the teeth 38 of the fixed ratchet member 37, which causes the movable ratchet member to be halted abruptly, and with it the ratchet drive member. The shaft 24 with the cable drum 25 thereon are thus. halted and the engagement between the ratchet teeth prevents further rotation thereof. The cable 20 thus takes up the weight of the luminaire and coupling 4 and prevents further downward movement thereof. By appropriate choice of the bias provided by the spring 40, of the inertia of the movable ratchet member 34, and of the profile 33 in relation to the size of the ball bearings 32, the sensitivity of the inertia braking mechanism can be made such that, although normal downward movement to adjust the height of the luminaire is not impeded, the luminaire falls through a very short distance before it is held by the cable 20 in the event of failure of one or more of the springs 14. Thus, the safety of the pantograph suspension is substantially improved and the risk of injury to personnel or damage below the pantograph suspension is greatly reduced.

Claims (8)

1. A pantograph suspension comprising a lazy tongs arrangement whose upper end is fixed to means for mounting the suspension and whose lower end is provided with a coupling for attaching an apparatus to be suspended, spring means connectable between the upper end and a point along the length of the lazy tongs arrangement for balancing the suspension and apparatus when attached thereto, and braking means connected between the upper and lower ends of the lazy tongs arrangement for braking downward movement of the lower end when the downward acceleration exceeds a predetermined value.

2. A pantograph suspension as claimed in claim 1, in which the braking means includes a cable connected at one end to the lower end and at the other end wound around a rotatable drum connected to an inertia brake.

3. A pantograph suspension as claimed in claim 2, in which the inertia brake comprises a fixed ratchet member, a movable ratchet member comprising a fiywheel rotatably mounted on the drum shaft and biassed away from the fixed ratchet member, a drive member fixed to the drum shaft, and a plurality of ball bearings disposed between the movable ratchet member and the drive member, each ball bearing being received in a part spherical recess in the drive member and in a circumferentially extending recess of the movable ratchet member having a depth which reduces in the circumferential direction of movement of the drum corresponding to downward movement of the lower end.

4. A pantograph suspension as claimed in claim 3, in which the drum is provided with a return spring tending to rewind the cable on the drum so as to keep the cable taut.

5. A pantograph suspension as claimed in claim 4, in which the return spring is arranged to exert a substantially constant force over the whole of its working range.

6. A pantograph assembly as claimed in any one of the preceding claims, in which the lazy tongs arrangement comprises two spaced apart lazy tongs linkages interconnected by a plurality of horizontal shafts.

7. A pantograph suspension as claimed in claim 6, in which the spring means comprises one or more pairs of springs of the type which exerts a substantially constant force over the whole of its working range, the springs of the pair or one of the pairs being connectable to respective shafts on opposite sides of the lazy tongs arrangements at different points along the length thereof to allow different loads to be balanced.

8. A pantograph suspension substantially as herein before described with reference to and as illustrated in the accompanying drawings.