US3525227A

US3525227A - Mine roof supports

Info

Publication number: US3525227A
Application number: US746070A
Authority: US
Inventors: Kenneth George Hancock; Peter Frank Eastwood; Brian Worrall; Ronald Roy Reeves
Original assignee: Gullick Ltd
Current assignee: Gullick Ltd
Priority date: 1967-07-19
Filing date: 1968-07-19
Publication date: 1970-08-25
Anticipated expiration: 1987-08-25
Also published as: JPS4834641B1; DE1758675B1

Description

g- 5, 1970 K. G. HANCOCK ET AL 3,525,227

MINE ROOF SUPPORTS 6 SheetsSheet 1 Filed July 19, 1968 75%?69 .f /Qj/f/ 2;

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MINE ROOF SUPPORTS 6 Sheets-Sheet 2 Filed July 19, 1968 @lJ/i/ ix Aw/Aw v 4' Aug. 25, 1970 K. G. HANCOCK A 3,525,227

MINE ROOF SUPPORTS Filed July 19, 1968 e Sheets-Sheet 5 wwmfxdlwvd WM .sr/V d lflwar/ tm Aug. 25, 1970 K. G. HANCOCK ET AL MINE ROOF SUPPORTS 6 Sheets-Sheet 4 Filed July 19, 1968 AT A, l:

Aug. 25, 1970 HANCOCK ET AL 3,525,227

MINE ROOF SUPPORTS 6 Sheets-Sheet 5 Filed July 19. 1968 MM MW Aug. 25, 1970' K. 3. HANCOCK ET AL I 3,525,227

I I MINE ROOF SUPPORTS I Filed July 19, 1968 6 Sheets-Sheet 6 BY m M &

United States Patent 3,525,227 MINE ROOF SUPPORTS Kenneth George Hancock, Lower Walton, Warrington, Peter Frank Eastwood, Grappenhall, Warrington, Brian Worrall, Clock Face, near Bold, St. Helens, and Ronald Roy Reeves, Great Sankey, Warrington, England, assignors, by mesne assignments, to Gullick Limited, Wigan, Lancashire, England Filed July 19, 1968, Ser. No. 746,070 Claims priority, application Great Britain, July 19, 1967, 33,218/67; Aug. 21, 1967, 38,509/67 Int. Cl. E2111 23/00 US. Cl. 61-45 8 Claims ABSTRACT OF THE DISCLOSURE Mine roof supports of the advancing type comprise one or more roof contacting members, one or more floor contacting members with one or more props arranged therebetween and having two laterally spaced apart support advancing rams pivotally connected to the support and adapted for connection to an anchorage, for example a coalface conveyor. Guide surfaces are provided on the support to co-operate with complementary first surfaces carried by adjacent supports, or co-operating first surfaces carried by independently movable parts of the same support, whereby during advancing movement of the support it is guided relative to an adjacent roof supporting member or members.

This invention, relates to advancing mine roof supports of the type comprising one or more roof contacting members, one or more floor contacting members with one or more props arranged therebetween and having two laterally spaced apart support advancing rams pivotally connected to the support and adapted for connection to an anchorage, for example a coalface conveyer. More particularly the invention concerns the guidance of such a support during its advancing movement.

The advancing rams referred to may be single acting and used to advance the support to the conveyer or they may be double acting. In the latter case they may be used to advance the conveyor when the support is set to the roof and subsequently (the conveyer being retained in its advanced position by adjacent supports), used to advance the support, after its release from supporting the roof, up to the conveyor. Longitudinal movement of the conveyer frequently occurs during its advancement and provision for this must be made in the manner in which the advancing rams are connected between the conveyer and the support; otherwise the rams will be damaged, for example by bending of their piston rods. Provision should also be made to ensure that when the support is advanced it takes up a position normal to the conveyer. A number of proposals have been made for guiding the advancing movement of the support over at least a part of its travel into a position normal to the conveyer, such guidance being provided from a member or members connected to the conveyer. However these proposals rely on there being no obstruction to the advance of the support so that both rams operate generally in synchronism. In practice advance of the support is not infrequently partially obstructed so that one ram closes whilst the other cannot do so and due to this the support is twisted round to such 3,525,227 Patented Aug. 25, 1970 "ice a degree that one or other of the rams fouls the support and is damaged, usually by bending of the piston rod. The purpose of this invention is to provide a mine roof support in which this problem is overcome.

SUMMARY OF THE INVENTION According to the present invention a mine roof support of the type described comprises first guide surfaces carried by the support and adapted to co-operate with complementary first surfaces carried by adjacent supports, or co-operating first surfaces carried by independently movable parts of the same support, whereby the support, or that part thereof to which the aforementioned rams are connected, is guided relative to an adjacent roof supporting member or members over a substantial part of the support advancing stroke of the rams and the restraint imposed by the co-operating guide surfaces is removed over the final advancing movement of the support so as then to permit lateral movement thereof.

Preferably the first guide surfaces carried by the support comprise forward and rear sections providing discontinuous guide surfaces.

Preferably the connection of the rams to the anchorage comprises link members pivotally connected to the rams and adapted for pivotal connection to the anchorage, each link member having a second guide surface arranged to co-operate with a second surface on the support so as to guide the support into a predetermined position relative to the anchorage during closure of the rams, the link members being so formed and the pivotal connections between the anchorage, the link members and the rams being so arranged that, when the support approaches its fully advanced position, the axis of each ram is inclined to a line joining the pivotal connections at the anchorage and the support, whereby a leverage is exerted on the link members tending to exert a lateral force on the support so as to steer it into a predetermined positlon relative to the anchorage or restrain it from moving away from that position.

Preferably the second guide surface on each link member is formed with a projection cam or the like beyond which the leading edge of the co-operating second surface on the support passes, when the support is fully advanced to the anchorage, so that the support is guided or steered into its predetermined position even though it may not be fully advanced to the anchorage.

Preferably the connections of the link members to the anchorage are arranged to permit relative vertical movement.

The link members may be provided with abutment surfaces for engagement with the anchorage so that, when double acting rams are provided, the anchorage may be advanced thereby.

Means may be provided to prevent overlapping of link members of adjacent supports, for example, during lateral movement of the anchorage relative to the supports. I

The invention is described by way of example only With reference to the drawings in which:

FIGS. 1(1) (A), 1(I)(B), 1(II) (C) and 1(II) (D) show diagrammatically in plan successive positions of the parts in the advance of a mine roof support;

FIG. 2 is a diagrammatic scrap view in plan illustrating one method of connecting an advancing ram to an anchorage, e.g. a coalface conveyor;

FIG. 3 is a diagrammatic plan view showing in part only one ram, a preferred link member, the co-operating second surface of a support and an anchorage;

FIG. 4 is an elevation showing the connections between the ram, link member and anchorage of FIG. 3;

FIGS. 5(I) (A), 5(I) (B), 5(II) (C), and 5(II) (D) show diagrammatically in plan successive positions of the parts in the advance of a mine roof support; and,

FIGS. 1(I) (A)-1(II)-(D) are referred to collectively in some instances in the following descriptions as FIG. 1; and, FIGS. 5(1) (A)-5(II) (D) are referred to collectively in some instances as FIG. .5; and,

FIG. 6 is a fragmentary perspective view of two outer support elements and an inner or third support element, showing cooperating guide surfaces on the support elements.

Referring to FIGS. 1 and 5, a composite mine roof support is shown which consists of two

outer support elements

2, 3 in conjunction with an inner or third roof support element 4. The

elements

2, 3 are similar and each has a

base

5A, 5B, two hydraulically operated

telescopic props

6A, 7A, 6B, 7B, resiliently mounted thereon and a roof contacting member in the form of a

roof bar

8A, 8B respectively carried by the props in known articulated manner, Brackets 9, 10 are secured to the rear ends of the

bases

5A, 5B respectively. The

bases

5A, 5B are connected together by a substantial metal plate 11 having side lugs 12 which span the brackets 9, 10 and are connected to them by transversely disposed pins 13, the latter being located by split pins (not shown).

First and second double

acting advancing rams

35, 36 have their piston rods pivotally connected to brackets 17 on the

bases

5A, 5B and their cylinders are pivotally connected to links 38 (FIG. 1), 95 (FIG. 5) which are in turn pivotally connected to a conveyor 30, all the pivot axes being in the vertical plane.

The third roof of support element 4 comprises a base '41, two hydraulically operated props 43., 44 resiliently mounted thereon and a roof bar 42 carried by the props in known articulated manner. The base 41 has sideways clearance (see position D) between the

bases

5A, 5B the amount of clearance provided on either side being not less than the maximum anticipated longitudinal movement of the conveyor 30 during one cycle of advance.

The cylinder of a third advancing ram 45 has a horizontal pivot connection to the base 41 and its piston rod has a vertical pivot connection at 67 to a lever 68 intermediate the ends thereof. The ends of the lever 68 have vertical pivot connections at 69, 70 to the rear ends of two members 71, 72 whose forward ends, cranked at a small angle, are horizontally pivotally connected at 73, 74 to the inwardly facing sides of the

bases

5A, 5B of the

elements

2 and 3 respectively.

The roof bar 42 comprises a rigid main portion 58 to which is bolted a narrower front portion 59 in the form of a leaf spring.

Plates 53A, 54A (FIG. 1) bolted to the

bases

5A, 5B have

tapered edges

55, 56 which comprise first guide surfaces which co-operate with complementary first surfaces on the third roof support element 4 whereby the

outer elements

2, 3 of the support are guided over a substantial part of the support advancing stroke of the

rams

35, 36. As shown in FIG. 6, the complementary first surfaces are constituted by an upwardly inclined plate 140 at the front end of the base 41 and a generally vertical plate 141 on each side which is joined to the upwardly inclined plate 140.

Referring now to FIG. 2 each link 38 comprises similar upper and lower link portions (the lower being masked in the drawing by the upper) having a common vertical pivot connection 90 to the conveyor 30 and they are arranged above and below a thrust member 91 which comprises an extension on the ram cylinder towards the conveyor 30. The thrust member 91 is slotted at 92 and a pin 93 passes through the link portions and the slot 92. The length of the slot 92 is such that on extension of the ram the free end 94 of the thrust member 91 engages a thrust plate or the like (not shown) on the conveyor 30 leaving clearance between the end of the slot 92 remote from the conveyor 30 and the pin 93.

Referring to FIG. 5, similar, but shorter, forward plates 53A, 54A are provided on the

bases

5A, 5B of the support of FIG. 5. The plates 53A are respectively formed with

guide surfaces

53B, 55 and 54B, 56.

Rear plates

105, 106 are also provided, bolted to the

bases

5A, 5B towards their rear ends, at such a height that they are clear of the upper surface of the base 41, each being provided with guide surfaces (forming a part of the first guides) 107, 108, 109, 110 similar to the

surfaces

53B, 55 and 54B, 56 provided on the plates 53A, 54A. Two bearing pads 111, 112 are mounted on a cross member 113 above the rear end of the base 41 in the way of the plates 105, 106 (positions A and B) which co-operate with the

surfaces

107, 108, 109, 110.

Referring now to FIG. 3 the cylinder of the ram 36 is pivotally connected at 95A to one end of a link 95 whose other end is pivotally connected at 95B to a bracket 96 which is secured as by bolts and nuts to a coalface conveyor 30. The link 95 has at its forward end two

surfaces

97, 98 inclined at an angle to one another, which define limits of angular movement of the link 95 relative to the conveyer 30 by abutment with the bracket 96. As shown, the surface 97 is abutting the bracket 96 and thereby limiting angular movement of the ram 36 away from the "base 5B. In this position the line of action of the ram 36 is shown at 99 and its lever arm about the pivot 95B is shown at 100. The link 95 is provided with a second guide surface 101 culminating in a projection or cam 102 which guide surface and cam are adapted to co-operate with a second surface on the support which may conveniently be a vertical surface extending rearwardly from a forward location 103 on the base 5B. The link may also include vertical surfaces 104 at its side remote from the support, seen more clearly in FIG. 4, for a purpose to be described. Also depicted in FIG. 3, in chain dotted lines, is the position of the ram 36, link 95 and base 5B when the support has been fully advanced to the conveyor 30 and guided--in a manner to be describedinto a predetermined position relative to the conveyor 30. In this position the surface 98 on the link 95 abuts the bracket 96 and the cam 102 may engage the co-operating second surface on the support or may have a small clearance therefrom. The line of action of the ram 36 has now moved to 99A whilst the length of the lever arm has reduced from that shown at to that shown at 100A, and it will be seen that the line of action of the ram, which lies along its axis, is inclined to a line joining its rear pivotal connection to the support (at bracket 17) (FIG. 5) and the pivotal connection at 953 of the link 95 to the conveyor 30. A leverage is thus exerted on the link 95 which, if its surface 98 has not yet abutted the bracket 96, imparts a lateral force on the support to steer it towards its final predetermined position as the ram 36 approaches its fully closed position. When the surface 98 does abut the bracket 96 the leverage exerted on the link 95 now acts to restrain movement of the support from its predetermined position. There is also shown in chain dotted lines part of the ram and link of an adjacent support, to which further reference will be made later.

Referring now to FIG. 4 which includes an elevation of the bracket 96 it will be seen that in the way of the pivot 95B the bracket is formed as a yoke the upper and lower arms of which are spaced apart to permit relative vertical movement between the link 95 and the conveyor 30.

Referring again to FIG. 1 and 5, in position A the roof support is shown ready to advance the conveyor 30 into a position adjacent a new coalface 62 exposed by the passage of a coal cutting machine (not shown). This advance of the conveyor is shown as having taken place in position B. The advance is effected by extension of the

rams

35, 36. Initial movement of the rams causes thrust members 91 (FIGS. 1 and 2) to engage the conveyor 30 whereby the force exerted by the rams is transmitted direct to the conveyor 30 and not through the pins 90, 93. In the case of the support of FIGS. 3 to 5 initial extension of the

rams

35, 36 causes rotation of the links 95 so that their surfaces 97 abut the brackets 96 and the cams 102 move away from the

bases

5A, 5B. The force exerted by the

rams

35, 36 is transmitted to the conveyor 30 via the links 95 and brackets 96. Longidinal or endwise movement of the conveyor 30 can be accommodated by pivotal movement of the

links

38, 95 and the

rams

35, 36. During this operation the roof bars 8A, 8B and 42 will be set in roof supporting position.

Following the advance of the conveyor 30 and its retention in the advanced position by adjacent supports, the

elements

2, 3 of the composite support are released from supporting the roof and the

rams

35, 36 are closed so as to advance the

elements

2, 3 to a position adjacent to the conveyor again. Due to the tension force in the

rams

35, 36 and the

links

38, 95 the

support elements

2, 3 will tend to be advanced into a position normal to the conveyor 30. It will be noted (FIG. 5B) that before advancement of the

elements

2, 3 the links 95 are well forward and clear of the second surfaces on the

bases

5A, 5B so the tension force in the rams will rotate the links 95 so that their surfaces 98 abut the brackets 96, as shown in FIG. 5B. It will of course be clear that the rams, the links and their connections to the support and the conveyor are so arranged that the rams have clearance from the bases of the support in this position even though the maximum anticipated movement of the conveyor transversely of the support has taken place. Such movement will bring the cylinder end of one of the rams towards its associated base and the other will be moved so that it has additional clearance from its associated base.

The

support elements

2, 3 will now be drawn forward and FIGS. 1C and 5C show them partially advanced. Their path of advancement will be defined by the orientation of the third roof support element 4, which is maintained in roof supporting position, due to the first surfaces on the base 41 co-operating with the first guide surfaces. That is to say, the first surfaces on the base 41 co-operate with the plates 53A, 54A (FIGS. 1 and 5) and the pads 111, 112 co-operate with the plates 105, 106 (FIG. 5). When the

surfaces

108, 110 on

plates

105, 106 have moved forward and clear of the pads 111, 112 guidance at the rear end is maintained for a further distance by cooperation of the

surfaces

108, 110 with the upstanding sides of the mounting for the prop 43 as is shown in FIG. 5C. 7

If closure of one or other of the

rams

35, 36 is prevented, for example due to an obstruction between the base 5A and the conveyor 30, the

elements

2, 3 are prevented from twisting round due to closure of the ram 36 by interaction of the guide surfaces which have been described provided between the

bases

5A, 5B and the element 4. The amount to which

elements

2, 3 can be twisted is limited by the clearance between the co-operating guide surfaces and the degree of twist permitted is arranged to be less than that which is required to cause either of the

rams

35, 36 to foul their

respective support elements

2, 3 for example, when the maximum movement of the conveyor transverse to the support has taken place. Thus in this condition if the obstruction is not cleared by the pull of the

rams

35, 36 the advancing movement of the

elements

2, 3 is stalled and action must then be taken to clear the obstruction to enable advance of the

elements

2, 3 to be completed.

Referring now to the position (D) it will be seen that as the

elements

2, 3 approach their fully advanced position, the first guide surfaces 53B, 54B and 108, 110 (FIG. 5) move clear of the co-operating first surfaces on the element 4 so as to permit lateral movement of the

elements

2, 3 and permit any necessary re-alignment of the

elements

2, 3 with the conveyor 30. Guide plates (not shown) may be provided if desired on the conveyor 30 to engage bases 5A, SE to guide the

elements

2, 3 into contact alignment with the conveyor 30 during the final stages of their advancing movement and after release of the restraint to lateral movement of the

elements

2, 3. Alternatively this guidance may be provided by suitable shaping of the links 38, for example as shown at in FIGS. 3 to 5.

It will thus be seen that the possibility of damage to the advancing rams is obviated by guiding the advancing movement of a support by reference to the orientation of an adjacent roof support member until the advancing support is close to the conveyor at which stage lateral movement of the support is permitted so that it can then move laterally relative to the conveyor and, if necessary, be guided relative thereto.

One manner in which the support, namely the

elements

2, 3 in this embodiment, can be guided into a predetermined position relative to the conveyor will now be described. Referring to FIG. 5 (d) in which the support is shown fully advanced, no re-alignment with the conveyor having been required (the element 4 is shown midway between the elements 2, 3) the links 95 have their surfaces 98 abutting their respective brackets 96 and the cams 102 are just clear of the co-operating second surfaces on the

bases

5A, 5B. If, however, prior to advance of the

elements

2, 3, the conveyor 30 had moved in the direction of the arrow X'then as the

elements

2, 3 become freed from lateral restraintor as they approach the position of freedom from lateral restraint-the surface at 103 (FIG. 3) on the base 5B engages and then runs along the surface 101 of the link 95 to the cam 102 and as this occurs, the latter is rotated so that its surface 98 moves away from the bracket 96, for example, to the position shown in full lines in FIG. 3. As this occurs the link 95 exerts a leverage on the base SE to move it in the direction of the arrow X and the greater the disparity between the position of the support during its final advancing movement and the position in which it should be relative to the conveyor the greater is the lever arm 100 and consequently so is the correcting force to move the support into the desired predetermined position. It will be appreciated that due to the movement of the conveyor 30 the ram 35 of the support and of adjacent supports will also receive a corresponding movement so that the links 95, of adjacent supports (see FIG. 3) are liable to approach and may overlap and/or foul one another. The vertical surfaces 104 are provided to prevent this occurring.

Movement of the conveyor 30 may occur, for example, in the direction of the arrow X, due to passage of a coal cutting machine when the

elements

2, 3 are in the advanced position adjacent to the conveyor 30. In this position the

rams

35, 36 may be vented and as the conveyor moves the link 95 pivots about the cam 102 which abuts the co-operating surface on the base 5B and in consequence the ram 36 is extended a small amount thus permitting the movement of the conveyor to take place without damage to the support.

It will be observed that the link 95 is so formed that during the final advancing movement of the support, the cam 102 is positioned so that it is enabled to engage the co-operating second surface at 103 a short distance, for example, 4 to 6 inches, before the support reaches its fully advanced position enabling the support to be guided or steered into its predetermined position relative to the conveyor even though the support may not be fully advanced.

Although this invention has been described with refer ence to a particular construction of two part support which includes an adjacent roof support member which is contained by the other part of the support i.e. a sup port having two interconnected roof support elements with a third independent roof support element therevbetween, it will be appreciated that the restraint may equally well be applied by adjacent supports on either side of a support which is being advanced to the conveyor. This differentiates from previous proposals which guide an advancing support relative to the anchorage only or relative to an adjacent support or supports only, neither of which arrangements has been found to be entirely satisfactory in practice.

We claim:

1. A mine roof support comprising at least two roof support elements; means connecting said roof support elements for simultaneous advancing movement, each of said elements comprising a base, a roof bar and at least one extensible prop arranged therebetween; two advancing rams; means connecting said rams one to each of said elements, said rams being adapted for pivotal connection to an anchorage; first guide surfaces carried by said two elements; at least one adjacent support element; complementary guide surfaces on said one adjacent support element, said first guide surfaces being arranged to cooperate with said complementary guide surfaces whereby on closure of said rams to advance said roof support, said first guide surfaces and said complementary guide surfaces guide said roof support relatively to said at least one adjacent support element over a substantial part of the support advancing stroke of said rams, engagement of said cooperating guide surfaces restraining said at least two support elements from lateral movement, and the restraint imposed by said cooperating guide surfaces being removed over the final advancing movement of the support so as then to permit lateral movement thereof.

2. A mine roof support comprising two roof support elements; means connecting said roof support elements for simultaneous advancing movement, each element comprising a base, a roof bar and at least one extensible prop arranged therebetween; two advancing rams; means connecting said rams one to each of said elements, said rams being adapted for pivotal connection to an anchorage; first guide surfaces carried by said two elements; an independently moveable roof support member arranged between and laterally spaced from said roof support elements; complementary guide surfaces on said independently moveable roof supporting member, said first guide surfaces being arranged to cooperate with said complementary guide surfaces whereby, on closure of said rams to advance said roof support, said first guide surfaces and complementary guide surfaces guide said roof support relatively to said independently moveable roof supporting member over a substantial part of the support advancing stroke of said rams, engagement of said cooperating guide surfaces restraining said two support elements from lateral movement, and the restraint imposed by said cooperating guide surfaces being removed over the final advancing movement of the support so as then to permit lateral movement thereof.

3. A mine roof support as claimed in claim 2, including second surfaces on the support; link members, one pivotally connected to each advancing ram and adapted for pivotal connection to the anchorage; and a second guide surface on each link member arranged to cooperate with said second surfaces on the support so as, on closure of the rams, to guide the support into a predetermined position relative to the anchorage, the link members being so formed and the pivotal connections being so arranged that, when the support approaches its fully advanced position, the axis of each ram is inclined to a line joining the pivotal connection at the anchorage and the support, whereby a leverage is exerted on the link members tending to exert a lateral force on the support so as to steer it into a predetermined position relative to the anchorage or restrain it from moving away from that position.

4. A mine roof support as claimed in claim 3, in which the first guide surfaces comprise forward and rear sections providing discontinuous guide surfaces.

5. A mine roof support as claimed in claim 3, in which the link members include cam portions adapted to engage the support and transmit a lateral force thereto and further comprise generally vertical plate portions adapted to prevent overlapping of the link members with the link members of adjacent supports.

6. A mine roof support as claimed in claim 1, said one adjacent support element comprising a third roof supporting element, said complementary first surfaces being provided on said third roof supporting element, the third element comprising a base, a roof bar and two eX- tensible props arranged therebetween, the third element having lateral clearance from and being located between said first two elements; a third advancing ram pivotally connected between said third element and the first two elements; and means to permit relative vertical and lateral movement between the third element and the first and second elements.

7. A mine roof support as claimed in claim 6, in which the first guide surfaces comprise forward and rear sections providing discontinuous guide surfaces, the first and second advancing rams being double acting; a link member pivotally connected to each of the first and second advancing rams and being adapted for pivotal connection to the achorage; abutment surfaces on the link members adapted to engage the anchorage whereby, on extension of said rams, force is transmitted to said anchorage to move it away from said support; cam portions on the link members adapted to engage the support and transmit a lateral force thereto during closure of the rams; and generally vertical plate portions on the link members adapted to prevent overlapping of the link members with the link members of adjacent supports.

8. A mine roof support comprising a pair of support elements; means connecting said pair of support elements for simultaneous advancing movement, each element comprising a base, a roof bar and at least one extensible prop arranged therebetween; two advancing rams; means connecting said rams, one to each of said elements of said pair, said rams being adapted for pivotal connection to an anchorage; first guide surfaces carried by the pair of elements; an adjacent support element on each side of said pair of support elements; complementary guide surfaces on said adjacent support elements, said first guide surfaces being arranged to cooperate with said complementary guide surfaces whereby, on closure of said rams to advance said roof support, said first guide surfaces and complementary guide surfaces guide said roof support relatively to adjacent roof supporting members over a substantial part of the support advancing stroke of the rams, engagement of said cooperating guide surfaces restraining said two support elements from lateral movement, and in which the restraint imposed by said cooperating guide surfaces is removed over the final advancing movement of the support so as then to permit lateral movement thereof; second surfaces on said support; link members, one pivotally connected to each advancing ram and adapted for pivotal connection to the anchorage; and a second guide surface on each link member arranged to cooperate with said second surfaces on the support so as, on closure of the rams, to guide the support into a predetermined position relative to the anchorage, the link members being so formed and the pivotal connections being so arranged that, when the support approaches is fully advanced position, the axis of each ram is inclined to a line joining the pivotal connection at the anchorage and the support, whereby a leverage is exerted on the link members tending to exert a lateral force on the support so as to steer it into a predetermined 9 10 position relative to the anchorage or restrain it from mov- FOREIGN PATENTS mg away fmm that 1,026,965 4/1966 Great Britain.

References Cited 1,044,907 10/1966 Great Brltaln.

UNITED STATES PATENTS 5 DENNIS L. TAYLOR, Primary Examiner 2,644,311 7/1953 Malloy 61--45 3,333,426 8/1967 Jackson 61-45 248 357 3,355,898 12/1967 Barrett et a1. 6145 3,425,229 2/1969 Groetschel 61-45