GB1588308A - Drrop-back catch assembly for a vertical conveyance - Google Patents

Description

(54) DROP-BACK CATCH ASSEMBLY FOR VERTICAL CONVEYANCE (71) We, QUALTER HALL & CO. LIMI TED, a British Company of Johnson Street, Barnsley, South Yorkshire, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to drop-back catch assembly for vertical conveyors such as lifts, mine cages and mine skips, and to a vertical conveyor and shaft therefor equipped with such an assembly.

Such a conveyor usually includes some form of winding means located above the conveyor to control its ascent and descent. If the conveyor is unintentionally drawn above its normal upper limit of travel it must be restrained from descending again until the winding means has been inspected and, if necessary, repaired. For example, if the conveyor failed to stop or decelerate at its normal upper limit, on reaching the very uppermost limit of travel the winding means may break or become detached from the conveyor. To prevent descent after the conveyor has over-run in this manner, it is known to provide catches on the conveyor and a rack adjacent the conveyor path in which the catches automatically engage. Alternatively the rack may be on the conveyor and the catches located beside its path of movement.

According to the present invention there is provided a drop-back catch assembly to arrest the descent of a vertical conveyor on reaching a position above its normal upper limit of travel the assembly including two parts, a first one of which is to be fixed to the conveyor and the other of which is to be fixedly located adjacent the path of movement of the conveyor so as to co-act with the first part when the conveyor travels beyond its normal upper limit, one of said parts comprising a rack and the other comprising a plurality of pawls each biassed so as to catch in the rack when relatively moving in one direction past it and rotatable about an axis inwardly against the bias when moving relatively past it in the other direction, each pawl being so biassed by a pair of torsion springs arranged respectively on opposite axial sides of the pawl and each torsion spring comprising a non-circular inner member located in a noncircular inner member located in a non-circular space in a housing with a plurality of elastomer bodies located between the inner member and the housing in corners of the housing so that relative rotation about said axis of the inner member and the housing resiliently compresses the bodies, the pawl being fast with one of said inner member and housing.

Preferably the drop-back catch assembly alse includes release means to retract the pawls frorr engagement with the rack teeth to free the conveyor.

It is to be understood that the present inven tion also extends to a vertical conveyor provided with at least one drop-back catch assembly of the invention. Preferably the conveyor is fitted with four sets of pawls, one at each corner, and four corresponding racks are fitted adjacent the conveyor's path of movement.

Alternatively if the space available so demands, two or three sets of pawls may be used.

A particular embodiment of the invention will now be described by way of example with reference to the drawing accompanying the Provisional Specification, wherein: Figure 1 is an exploded view of a pawl mounted in a frame, Figure 2 is a half-section elevation of a pawl and frame Figure 3 is the view along arrow A of Figure 2, Figure 4 is a longitudinal section through Figure 2 to show the pawl and rack arrangement.

With reference to Figures 1 to 3, the pawl 2 has a shaft 4 extending from its opposite flat sides 6. The portions 8 of the shaft 4 adjacent the sides 6 form cylindrical journals and co-act with corresponding bearing surfaces 10 in a frame 12. The portions 14 of the shaft 4 remote from the sides 6 are square in cross section transverse to the axis and each forms part of a torsion spring 16. The shaft portions 14 extend concentrically into respective tubes 1 8 fixedly mounted on the frame 12. Both the tubes 10 have an inner surface of square cross section of such a dimension that faces of the shaft portions 14 can subtend agngle of 45 with respective inner surfaces of the tubes.In each of the spaces formed between the inner surface, of the tubes 18 and the respective face of the shaft portion 14 is inserted a cylindrical elastomer body 20. Each body 20 may be made from suitable resilient material in this case rubber, and, as shown in the cross section view of Figure 3, has three contact points: one with the face of the shaft portion 14 and two with the inner surface of the tube 18. Such a com bination of two concentric polygonal tubes separated by a number of elastomeric bodies is conventionally known as a Neidhart spring after its inventor's name. In the present arrange ment two such torsion springs are employed to bias the pawl outwardly for engagement with the teeth of a rack.

As shown in Figure 2 an outer captive plate 22 is added to cover the end of the tube 18 and the rubber bodies 20 and shaft 4 inside it.

Four frames 12 are mounted longitudinally by means of bolts 24, at respective corners of a vertical conveyor. Toothed racks, corresponding to the pawls, are fixed longitudinally to respective specially located steel columns in the well of the conveyor at a level immediately above the conveyor's normal upper limit of travel. In such an arrangement the pawls are pivotably mounted in their respective frames to be biassed in an outward and downward direction to engage with appropriately fashioned teeth in the rack. As shown in Figure 4, teeth 26 of the rack 28 need not have the same spacing as the pawls 4 on the frame 12 but each tooth should be shaped to engage only one pawl.

Should the conveyor be overwound and continue beyond its normal upper limit of travel the pawls 4 will strike the rack 28, but will repeatedly retract due to their sprung mounting and run over the teeth 26 of the rack. When the conveyor comes to rest and starts to fall the pawls 4 will lock into the teeth of the rack, and thus prevent any further descent of the conveyor. The steel columns on which the racks are mounted are resiliently suspended from the top of the well to ameliorate, to some extent, the effect of a sudden halt of the conveyor.

For reasons of safety whenever a conveyor is unintentionally overwound the winding means should be inspected for signs of stretching or any other damage that it may have sustained. Similarly the conveyor may be intentionally drawn above its normal upper limit of travel to carry out any necessary maintenance or inspection work. In either case the dropback catch assembly of the present invention ensures that the conveyor will not descend until the pawls are released from their locking position. Although not illustrated in the accompanying drawings, it is a relatively simple matter to provide a lever arrangement, for instance as in known drop-back catch gear, which can retract all the pawls into the frame to allow the conveyor to descend to below the racks. The pawls will then be reset, by means of the lever arrangement, to return them to their former positions.The lever arrangement may be readily attached to one end of the pawl shaft by omitting the captive plate 22. If required, extraneous locking means may be provided to padlock the lever arrangement may be readily attached to one end of the pawl shaft by omitting the captive plate 22. If required, extraneous locking means may be provided to padlock the lever arrangement in any predetermined position.

Although only one embodiment of the present invention has been described above it is to be understood that other forms of drop-back catch assembly come within the scope of the present invention. For example the racks may be fixed to the conveyor and the frames carrying the pawls, fixed inside the conveyor wall.

However since the height of the overwound space at the top of the conveyor well is usually several times the height of the conveyor the embodiment of the invention described above is the preferred form. Fewer pawls, the more expensive and complex part of the assembly, are therefore needed.

In the illustrated embodiment, the pawls are fixed to the inner members of the Neidhart springs; they may alternatively be fixed to the housing which in that case would rotate about the inner member.

Furthermore, in the illustrated embodiment, the fixed rack is relatively inaccessibly mounted in the head gear (i.e. above any normal access point to the well) but requires no maintenance or lubrication. The tilting pawls on the conveyor can be maintained from any convenient landing, say ground level and complex and expensive automatic lubrication systems are not required. A small maximum fallback (e.g. 11 on over-run of the conveyor can be achieved, and the assembly can be inexpensive.

WHAT WE CLAIM IS: 1.A drop-back catch assembly to arrest the descent of a vertical conveyor on reaching a position above its normal upper limit of travel, the assembly including two parts, a first one of which is to be fixed to the conveyor and the other of which is to be fixedly located adjacent the path of movement of the conveyor so as to co-act with the first part when the conveyor travels beyond its normal upper limit, one of said parts comprising a rack and the other comprising a plurality of pawls each biassed so as to catch in the rack when relatively moving in one direction past it and rotatable about an axis inwardly against the bias when moving relatively past it in the other direction, each pawl being so biassed by a pair of torsion springs arranged respectively on opposite axial sides of the pawl and each torsion spring comprising a non-circular inner member located in a noncircular space in a housing with a plurality of elastomer bodies located between the inner member and the housing in corners of the housing so that relative rotation about said axis of the inner member and the housing resiliently compresses the bodies, the pawl being fast with one of said inner member and housing.

2. A drop-back catch assembly according to Claim 1 wherein each said torsion spring has

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   the face of the shaft portion 14 and two with the inner surface of the tube 18. Such a com bination of two concentric polygonal tubes separated by a number of elastomeric bodies is conventionally known as a Neidhart spring after its inventor's name. In the present arrange ment two such torsion springs are employed to bias the pawl outwardly for engagement with the teeth of a rack.

   As shown in Figure 2 an outer captive plate

   22 is added to cover the end of the tube 18 and the rubber bodies 20 and shaft 4 inside it.

   Four frames 12 are mounted longitudinally by means of bolts 24, at respective corners of a vertical conveyor. Toothed racks, corresponding to the pawls, are fixed longitudinally to respective specially located steel columns in the well of the conveyor at a level immediately above the conveyor's normal upper limit of travel. In such an arrangement the pawls are pivotably mounted in their respective frames to be biassed in an outward and downward direction to engage with appropriately fashioned teeth in the rack. As shown in Figure 4, teeth 26 of the rack 28 need not have the same spacing as the pawls 4 on the frame 12 but each tooth should be shaped to engage only one pawl.

   Should the conveyor be overwound and continue beyond its normal upper limit of travel the pawls 4 will strike the rack 28, but will repeatedly retract due to their sprung mounting and run over the teeth 26 of the rack. When the conveyor comes to rest and starts to fall the pawls 4 will lock into the teeth of the rack, and thus prevent any further descent of the conveyor. The steel columns on which the racks are mounted are resiliently suspended from the top of the well to ameliorate, to some extent, the effect of a sudden halt of the conveyor.

   For reasons of safety whenever a conveyor is unintentionally overwound the winding means should be inspected for signs of stretching or any other damage that it may have sustained. Similarly the conveyor may be intentionally drawn above its normal upper limit of travel to carry out any necessary maintenance or inspection work. In either case the dropback catch assembly of the present invention ensures that the conveyor will not descend until the pawls are released from their locking position. Although not illustrated in the accompanying drawings, it is a relatively simple matter to provide a lever arrangement, for instance as in known drop-back catch gear, which can retract all the pawls into the frame to allow the conveyor to descend to below the racks. The pawls will then be reset, by means of the lever arrangement, to return them to their former positions.The lever arrangement may be readily attached to one end of the pawl shaft by omitting the captive plate 22. If required, extraneous locking means may be provided to padlock the lever arrangement may be readily attached to one end of the pawl shaft by omitting the captive plate 22. If required, extraneous locking means may be provided to padlock the lever arrangement in any predetermined position.

   Although only one embodiment of the present invention has been described above it is to be understood that other forms of drop-back catch assembly come within the scope of the present invention. For example the racks may be fixed to the conveyor and the frames carrying the pawls, fixed inside the conveyor wall.

   However since the height of the overwound space at the top of the conveyor well is usually several times the height of the conveyor the embodiment of the invention described above is the preferred form. Fewer pawls, the more expensive and complex part of the assembly, are therefore needed.

   In the illustrated embodiment, the pawls are fixed to the inner members of the Neidhart springs; they may alternatively be fixed to the housing which in that case would rotate about the inner member.

   Furthermore, in the illustrated embodiment, the fixed rack is relatively inaccessibly mounted in the head gear (i.e. above any normal access point to the well) but requires no maintenance or lubrication. The tilting pawls on the conveyor can be maintained from any convenient landing, say ground level and complex and expensive automatic lubrication systems are not required. A small maximum fallback (e.g. 11 on over-run of the conveyor can be achieved, and the assembly can be inexpensive.

   WHAT WE CLAIM IS: 1.A drop-back catch assembly to arrest the descent of a vertical conveyor on reaching a position above its normal upper limit of travel, the assembly including two parts, a first one of which is to be fixed to the conveyor and the other of which is to be fixedly located adjacent the path of movement of the conveyor so as to co-act with the first part when the conveyor travels beyond its normal upper limit, one of said parts comprising a rack and the other comprising a plurality of pawls each biassed so as to catch in the rack when relatively moving in one direction past it and rotatable about an axis inwardly against the bias when moving relatively past it in the other direction, each pawl being so biassed by a pair of torsion springs arranged respectively on opposite axial sides of the pawl and each torsion spring comprising a non-circular inner member located in a noncircular space in a housing with a plurality of elastomer bodies located between the inner member and the housing in corners of the housing so that relative rotation about said axis of the inner member and the housing resiliently compresses the bodies, the pawl being fast with one of said inner member and housing.
2. 2. A drop-back catch assembly according to Claim 1 wherein each said torsion spring has

   four of said elastomer bodies, the said inner member and housing having square external and internal cross-sectional shapes respectively.
3. 3. A drop-back catch assembly according to Claim 1 or Claim 2 including release means to retract the pawls from engagement with the rack teeth to free the conveyor.
4. 4. A drop-back catch assembly according to any one of Claims 1 to 3 wherein the pawls and the rack elements are each regularly spaced apart vertically, the spacing of the pawls being different from that of the rack elements whereby the maximum distance of fall-back is less than either of said spacings.
5. 5. A drop-back catch assembly substantially as herein described with reference to and as shown in the drawings accompanying the Provisional Specification.
6. 6. A vertical conveyor and shaft therefor, equipped with at least one drop-back catch assembly according to any one of the preceding claims.