CA1098881A

CA1098881A - Linear arrestors

Info

Publication number: CA1098881A
Application number: CA297,332A
Authority: CA
Inventors: Joseph E. Domagala
Original assignee: SELTRUST ENGINEERING Ltd
Current assignee: SELTRUST ENGINEERING Ltd
Priority date: 1977-02-22
Filing date: 1978-02-20
Publication date: 1981-04-07
Also published as: FR2380928A1; FR2380928B1; DE2807267C2; BE864174A; AU3353078A; DE2807267A1; GB1601809A; SE7801837L; AU519936B2; ZA781049B

Abstract

ABSTRACT

A vehicle arrestor comprises a light carriage positioned in the path of a vehicle to be arrested.
Strips of ductile material are secured by at least one end alongside the path. The carriage carries a set of rollers for each strip. The strip passes through the sat of rollers along a sinuous path such that when the vehicle drives the carriage along the path, the strip travels through the set of rollers and is reversely bent plastically at each roller with consequent absorption of energy.

Description

This invention relates to arrestors for vehicles, such as mine cages, trains, aircraft and ships, such arrestors comprising a length of deformable tensile material and a device defining a non-straight path through the device for the length of ductile materialt When the device moves longitudinally rela-tive to the length of material or vice versa, a substantially constant retardation force opposing such movement is generated partly by friction and partly by the work needed to effect any plastic deformation of the material that takes place as it is moved along the non-straight path.
In most potential applications for such arrestors, it is essential that the value of the retardation should, in addition to remaining substantially constant, lie consistently within narrow limits. If the deceleration or retardation i9 too great, people travelling in the vehicle will be killed or injured and if the deceleration or retardation is too small, the vehicle will not be brought to rest within the available distance, leading to impact of the vehicle at the end of its travel again with consequent death or injury. Generally, the arrestor will lie dormant, often for many years, but must be immediately available and operate consistently at its designed retardation in the event of a sudden emergency.
Proposals for arrestors of the kind with which the invention is concerned have existed for over 70 years. French Patent Specification No. 328841 of 1903 discloses a pair of arrestors to be mounted one on each side of a lift shaft. Each arrestor consists of four cables on which are engaged a plurality of arresting devices comprising transverse vertical plates carrying pegs arranged in three vertical spaced rows, the pegs in the middle row being aligned with the spaces between

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", , the pegs in the upper and lower rows and the diameter and spacing of the pegs is such that each wire ...... ~

~ 2~ -rope is constrained to ~ollow a non-straight path past the pegs of the middle row and just fits in the gaps between the peg of the middle row and the adjacent pegs of the upper and lower rows. Each peg of the middle row has two wire ropes in contact with it. In the event of overspeeding of the lift cage, a claw extends from the latter and engages the plate of the arrestor device, the intention being that the latter is moved downwardly along the wire ropes against the drag exerted by the ropes as they are pulled through the non-straight paths and past the pegsO British Patent Specifications Nos, 19623 of 1901 and 25469 of 1904 both describe arrangements for arresting a mine cage in the event of breakage of the winding rope. The cage is guided by four guide ropes each o~ which passes between a pair of rollers carried by a lever arm pivoted to a corner of the cage. If the winding rope should break or otherwise lose tension, the lever arms are tilted by springs and by the downward movement of the cage relative to the guide ropes into a position in which the rollers "bind" the guide ropes by forcing the latter to adopt a doubly bent configuration.
All such devices relying on deformaticn of wire ropes, operate very largely by friction. While energy is absorbed by doing work in bending and straightening successive portions of the ropes, this work is absorbed in overcoming friction between the individual wires of the ropes. Their performance is -therefore unpredictable since the various coefficients of friction will vary with the state of the various surfaces for example in accordance with the amount of oil or grease and rust on the ropes.

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More recen~ly, arrestors have been proposed in U.S. Patents Nos. 257g753r 2979163, 2980213, 3017163, 3211260 and 3377044 in which a coil of strip is contained in a housing and has i-ts outer end passed around a large number of rollers or pegs. At the start of an arresting operation, at least the leading portion of the strip (and all of the rollers) have to be rapidly accelerated up to the initial speed to the object to be decelerated, resulting in a violent jerk. The large number of rollers or pegs and the complex path to be followed by the strip as it is unwound and drawn over the rollers or pegs results in high friction and thus possibly inconsistent operation if the device has been neglected for many years while at the same time the inevitable bul~ and weight of the housing and strip render such devices unsuitable for a large number of applications such as on railways and in lift shafts where the space between the vehicle and surrounding structure is to be minimal and where the thickness and width of the strip required for a scaled-up version suitable for mine lift cages, ships and trains would re~uire impossibly massive and heavy installations to support and guide the strip.
Figures 1 and 2 of Belgian Patent Specification No.
477757 show an arrestor supporting a lift cage and comprising a pair of strips having their upper ends fixed to transom fixed to the lower end o the lift cable while an adjacent part of each strip passes down through a guide carried by the lift cage.
The upper end of each guide defines an S-shaped path for the strip partly by means of rollers and partly by curved guide surfaces in frictional contact with the strip. Accordingly, the retardation exerted by the arrestor will vary to a great extent in accordance with the state of the guide surfaces and ;~t: .

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the strip surfaces. ......................................

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Accordingly, for the various reasons set out above, none oE these known arrestors has been widely used for arresting vehicles.
According to the present invention, there is providea an arrestor for stopping or slowing a vehicle in a portion of a substantially predetermined path for the vehicle, the arrestor comprising a flat strip of ductile material extending in the direction of the path in which the arrestor i.5 to operate, the strip being of width greater than thickness and of uniform thickness across its width, the strip being threaded through a set of not more than five rollers carried on a frame for plastic deformation of successive elements of the strip around the rollers when the strip is moved through the set of rollers during an arresting operation, each roller being rotatably mounted on the frame, each roller being rotatable about its axis by the strip when the strip is drawn through the set of rollers with alternate rollers in contact with alternate sides of the strip, the spacing between adjacent roller surfaces being greater than the strip thickness, the axes of all rollers in the set being fixedly located on said frame and with respect to each other, the rollers contin-uously deforming the interposed strip portion by a constant amount irrespective of relative strip-roller movement, the strip extending substantially in the same direction along the .
path as it leaves the set of rollers, the arrestor being mounted on the vehicle or a stationary structure and having one of its frame and the leading end of the strip secured thereto, the other of the frame and strip leadîng end being engayeable by the stationary structure or ~ehicle respectively as the vehicle '~

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reaches the said portion oE the path.
With this arrangement, a major part of the retardation ~orce is generated by work done in plastic deformation of the strip as it passes through the set of rollers. Since each bending operation occurs around a roller there is substantially no frictional slipping contact with the strip so that the state of the strip surface (oily, rusty or painted) does not matter. The bearings of the rollers will have a smaller radius than the roller surfaces so that the drag exerted on the strip by friction in the rollers will be appreciably less than that which would be exerted on the strip by fixed pegs in place of rollers. The frictional drag can be further reduced by appropriate choice of bearing materials.
Improved consistency can be achieved by using self-..............................................................

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lubricating materials ior the bearings, for example bearings incorporating polytetrafluoroethylene. Alternatively, bearings of hard aluminium alloy with perhaps a smear of lubricant may be used.
By keeping the number of rollers in each set small, ~4~m~
not more than five and preferably three, the contribution of friction to the retardation, for example in the bearinys of the rollers is also reduced. By having an odd number of rollers, the emerging strip can be coplanar with the strip entering the set of rollers, thereby helping to ensure that the angle of wrap of the sitrip with each roller can be maintained constant.
In one îorm of embodiment the strip is mounted on stationary st,r~cture adjacent the part of the vehicle path over which the retardation is to ta~e place, for example ahove the normal upper position of the lift cage in a mine shaftO The frame or frames carrying the sets of rollers is then preferably mounted on a light carriage which can be engaged by the cage or other vehicle on overwincl or overshooting. Advantageously, where the vehicle to be arrested has guides for example ropes or rails, the carriage is itselE guided on these guidesO
rn another form of embodlment, the strip in its straight form ~s carried by the vahicle with the rollers engaged with the leading end of the strip and a suitable device i9 provided for engaging the roller frame when the arresting operation is re~uired. ~'his device may be in the fo~ of a iixed projection ~n an overrun part of the vehicle path or a velocit~-or-lac~ of-tension-sensitive device arranged to extend latches ~5 or t,o fire explosive bolt~ into structure alongside the path of the vehicle~

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Where the strip cross-section is cons-tant along the whole length of the strip, the retardation will be constant.
However, by varying the cross-section of the strip along any portion of its length or if required along the whole length of the strip, the retardation may be varied. Thus, for example, the retardation may be arranged to increase during movement along the strip path so as to accommodate vehicles where the load carried by the vehicle may appreciably vary. Conveniently, the variation in strip cross-section may be achieved by using a strip of constant thickness, but varying width.
The invention will now be further described by way of example with reference to the accompanying drawings, in which:-Figure 1 is a perspective view of a lift cage and an arrestor in accordance with the invention positioned to slow-up the lift cage if it should descend beyond its lowermost intended position, : Figure 2 is an elevational view showing components of the arrestor, Figure 3 shows a portion of Figure 2 with part of the frame cut away to show the rollers and strip, Figure 4 is a view similar to Figure 1 of a larger, two storey mine lift cage having two arrestors arranged on each side of its path of travel, Figure 5 shows one method of applying the invention to buffers for railway tracks and Figure 6 shows a modification of Figure 3.
In the embodiment shown in Figures 1 to 3, a mine lift cage 1 (Figure 1) is connected to a winding rope (not shown) by a conventional linkage 2 and is guided on vertical ..
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guide ra.ils 3 ~ the cage :Eor this pwXpose CAxx~n~ sets ~
guide wheels 4 at its upper and lower ends~ . ~,,, .,,, ~, ......

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On each side of the path of the cage 1 a cross beam 5 has its two ends firmly embed~ed in and supported in the lining (not shown) of the mine shaft. The ~uides 3 are anchored to the cross beams 5 by brackets 6, in addition to other conventional supports for the guides.
A mild steel strip 7 of rectangular cross-section, for example 120 mm. x 9 mm. is anchored firmly by its upper end to each of the beams 5. The strips 7 support the carriage 8 of an arrestor, the carriage 8 having suitable means such as the blocks 9 shown in Figure 1 for engaging an appropriately strong part of the frame of the cage 1 when the latter over-shoots its lowermost position.
The construc-tion of the arrestor is shown i.n more detail in Figures 2 and 3, The carriage 8 i5 guided on the same guides 3 as the cage by means of shoes 10 in conventional manner. Alternatively, the carriage may carry light guide rolls for engaging the guides 3 in a similar manner to the rollers 4 provided on the cage 1. At each end, out board of the shoes 10, the carriage 8 carries a set of three rollers 11, 12 and 13 each o~ which is mounted by means of a plain bearing B on a respective shaft 14, 15, 16. Each end of each of the shafts 14, 15, 16 is secured in the appropriate one of the two plates or beams 8A, 8B making up the carriage 8. Preferably, the bearings B are of the self-lubrica-tlng material type, for example, incorporating polytetrafluoroethylene.
As can be seen particularly in Figure 3, the middle roller 12 is offset in the horizontal direction from the upper and lower rollers 11 and 13. The strip 4 is thereby forced to bend around part of the upper roller 11 and then in the opposite direction around a larger portion of the middle roller 12 and . .

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and then finally back around a portion of the lower roller 13 to return to the same plane as part of the strip above the rollers. Accordingly, as the carriage 8 is forced downwards, the rollers 13 at 12 and ll perform successive bending operations in opposite directions on the strip through ~ 8a ''~' '``'' . : . . . ::

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a sufficient angle to cause plastic deformation of the material of the strip during each bending operation thereby absorbing substantial amounts of energy. Since each of the three curved bending surfaces is formed by a roller, the only significant frictional drag will be due to friction in the bearings bet~een the rollers and their shafts and this can be held to a reduced, reasonably consistent value by appropriate design and choice of materials for the bearings and shafts which may for example be of stainless steel ~f it is preferred to leave the bearings dry.
In order to prevent any lateral oscillation of the strip 7 from varying the angles of wrap around the upper and lower rollers 11 and 13, it is preferred to provide the carriage with guide pins (or rollers) 17 and 18 which do not of themsel~es provide any material resistance to movement of the strip ~ past them.
As indicated in Figure 2, it may be found desirable to anchor the lower ends of the strip 7 to further cross beams 50 If desired, the strips 7 may be pre-tensio-r.ed although this will tend to increase the proportion of the retardation forces which are due to friction in the bearingsO `
The blocks 9 on the carriacge 8 (Figure ~ may be arranged to interfit with appropriate sockets in the under frame of the cage 1, so that the cage can then guide the carriage thereby dispensing with the need for the guide shoes or rollers 10.
In the arrangement illustrated in Figure 4, the cage 21 has two storeys and on each side of the path of the cage 21 two arrestor carriages ~ 8 are mounted each on a pair of ~ 7 having their upper ends attached to stub beams 22 supported on cross beams 23. ~iigid cross members 24 are secured to the top of the cage frame and project at each end outwards beyond the sides of the cage sufficiently to en~ble them to stri~e the arrestor ~ g _ . . .

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carriages 8 on overshooting o~ the cage~ the ends of the members 2~ passing between the projecting ends of the stub beams 22.
The ar~estor shown in Figu~e 5 is mounted in a horizontal plane in the position normally used for hydraulic .
buffers at the end cf a length of track 31. The arrestor carriage 8 is supported (by means of wheels or shoes (not shown)) on the rails of the txack 31~ The strips 7 have their ends suitably secured in blocks or frames 32 and 33. The carriage 8 carries buffers 34 for engagement by the buffers 35 of a train 36.
In a variation of the arrangemen~ shown in Figure 5, the strips may have their planes horizontal and be sufficiently slack to curve downwards from the carriage when the latter is in the position shown in Figure 5 and rest in an appropriate channel. The axes of the rollers 11, 12 and 13 will then be horizontal.
Finally, Figure 6 is a view corresponding to Figure 3, but showing an arrangement having five rollers 11, 12, 13, 25 and 26 which provide two further working operations on the strip, but with increased bearing friction in view of the larger number of rollers. It is in general desirable that the number of rollers should not exceed five (to avoid excessive friction), three rollers being considered sufficient for most applications. The arrangement shown in Figures 1 and ~ are for use at the lower end of the travel of the mine cageO
At the upper end similar arrangements may be used, but suitably modified in that the arrestor carriages 8 would be mounted adjacent the anchored lower ends of the strips 7 in a position to be engaged by upward movement of the cage beyond . . .

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its intended uppermost position~ Furthermore, it may in some cases be practical to mount R complete arrestor on the cage so that the strips and carriage normally travel with the cage, but the arrestor carriage can be engaged with a fixed part of the shaft structure in the event of an excessive speed .................... ,.. ,.... v ~ ~ lOa -. , :

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An arrestor for stopping or slowing a vehicle in a portion of a substantially predetermined path for the vehicle, the arrestor comprising a flat strip of ductile material extending in the direction of the path in which the arrestor is to operate, the strip being of width greater than thickness and of uniform thickness across its width, the strip being threaded through a set of not move than five rollers carried on a frame for plastic deformation of successive elements of the strip around the rollers when the strip is moved through the set of rollers during an arresting operation, each roller being rotatably mounted on the frame, each roller being rotatate about its axis by the strip when the strip is drawn through the set of rollers with alternate rollers in contact with. alternate sides of the strip, the spacing between adjacent roller surfaces being greater than the strip thickness, the axes of all rollers in the set being fixedly located on said frame and with respect to each other, the rollers continuously deforming the interposed strip portion by a constant amount irrespective of relative strip-roller movement, the strip extending substantially in the same direction along the path as it leaves the set of rollers, the arrestor being mounted on the vehicle or a stationary structure and having one of its frame and the leading end of the strip secured thereto, the other of the frame and strip leading end being engageable by the stationary structure or vehicle respectively as the vehicle reaches the said portion of the path.

2. An arrestor according to claim 1, including bearings supporting said rollers on the frame, the bearings of the rollers having a smaller radius than the strip engaging surfaces of the rollers.

3. An arrestor according to claim 1, including bearings supporting said rollers on the frame, wherein the bearings of the rollers comprise self-lubricating materials.

4. An arrestor according to claim 3, wherein the bea-rings have bearing surfaces of polytetrafluoroethylene.

5. An arrestor according to claim 1, wherein the or each set of rollers has three said strip engaging rollers.

6. An arrestor according to claim 1, wherein the strip is mounted on stationary structure adjacent the part of the vehicle path over which the retardation is to take place and the frame or frames carrying the sets of rollers is then mounted on a carriage which can be engaged by the vehicle to be stopped or slowed.

7. An arrestor according to claim 6, wherein the car-riage is guided on the same guide as the vehicle.

8. An arrestor according to claim 1, wherein the strip in its straight form is carried by the vehicle with the rollers engaged with the leading end of the strip and a suitable device is provided for engaging the roller frame when the arresting operation is required.

9. An arrestor according to claim 8, wherein the said device is in the form of a fixed projection in an overrun part of the vehicle path.

10. An arrestor according to claim 1, including guide means fixed on said frame for preventing varying of the angle of wrap of said strip around the roller at each end of said set of rollers and therewith for limiting any lateral oscillation of said strip as it enters and leaves the set of rollers, said guide means comprising a guide member engaging the strip closely adjacent the point at which the strip leaves the corresponding endmost roller of the set and on the opposite side of the strip from said corresponding endmost roller, said guide member being positioned to engage but not significantly deflect said strip, so as not to provide any material resistance to movement of the strip past said guide members.

11. An arrestor according to claim 1, in which the strips are supported free of pre-tension and along a straight line extending in opposite directions from said set of rollers such that in use the portion of the strip about to enter the set of rollers is substantially unstressed.