US3475778A

US3475778A - Dockboard

Info

Publication number: US3475778A
Application number: US642089A
Authority: US
Inventors: John A Merrick; Adrian P Hovestad
Original assignee: Service Steel & Eng Ltd
Current assignee: Service Steel & Eng Ltd
Priority date: 1967-05-29
Filing date: 1967-05-29
Publication date: 1969-11-04
Anticipated expiration: 1986-11-04
Also published as: CA919359A; GB1229613A; GB1229614A

Description

NOV. 4, 1969 J. A MERR|CK IETAL 3,475,778

DOCKBOARD 4 Sheets-Sheet 1 Filed May 29, 1967 IA-VVEXTORS v1 E RRICK FIG-4 PATENT AGENTS Now-M4, 1969 v 4.1. A. MERRICK ETAL 3,475,778

DOCKBOARD 4 sheets-shed 2 Filed May 2Q. 1967 w M T @K ,l. S Xw T E N wml# E ME G MP 4c, A AM .M E mm OD m JAA/V m FIGQ Nov. 4, 1969 y .1,A. MERRICK ETAL 3,475,778

DOCKBOARD Filed May 29, 1967 4 Sheets-Sheet 5 I.\-\7E \TUR. JOHN A. MERRICK ADRIAN P. HO\/ESTAD` PATENT AGENTS Nov. 4, 1969 J. A MERR|CK ETAL 3,475,778

DOCKBOARD 4 Sheets-Sheet Filed May 29. 19e? FIGJO PATENT AGENTS D m m 0K5 M .7C Amm WRHU v E. IMD.. if AN NMM Hm @A5 Y B United States Patent C) DOCKBOARD .lohn A. Merrick, Dundas, Ontario, and Adrian P. Hovestad, Burlington, Ontario, Canada, assignors to Service Steel & Engineering Limited, Hamilton, Ontario, Canada Filed May 29, 1967, Ser. No. 642,089 Int. Cl. B65g 11/14 U.S. Cl. 14-71 32 Claims ABSTRACT OF THE DISCLOSURE A new dockboard has a ramp assembly comprising a main plate pivoted to the dockboard frame, and a lip plate at the front of the main plate; means for automatically extending the lip plate comprise a latchable telescoping assembly disposed beneath the main plate, the telescoping assembly changing length as the main plate moves about its pivot, and the latch being operative during pivoting movement of the main plate in one direction to prevent telescoping of the assembly, so that it operates to extend the lip plate.

Field of the invention The invention is concerned with dockboards of the kind wherein a ramp assembly comprises a main plate pivoted to frame means and a lip plate disposed at the front edge of the main plate, and means are provided for automatically extending the lip plate from a stored inoperative position to an extended operative position in which it forms an extension of the main plate.

Description of the prior art A number of such dockboards have been proposed hitherto, and as specific examples may be mentioned U.S. patent specification Nos. 3,137,017; 3,203,002 and 3,249,- 95 6. In the dockboard constructions described therein the lip plate is pivoted to the main plate, and a flexible connection is provided between the dockboard frame and the pivoted lip plate; the main plate is moved upward and at a predetermined point of its upward movement the flexible connection becomes taut and further movement of the main plate is accompanied by elevating pivoting movement of the lip plate.

Summary of the invention It is the principal object of the invention to provide a dockboard of the kind specified and comprising a new mechanism for automatically extending the lip plate.

It is another object to provide a dockboard of the kind specied and comprising a new mechanism for restoring the ramp assembly automatically to its stored condition when required.

In accordance with the present invention there is provided a new dockboard comprising frame means, a main plate having a front edge, means pivotally connecting the main plate with the said frame means for pivoting movement about a respective rst pivot axis, a lip plate, means mounting the lip plate at the main plate front edge for movement relative to the main plate between a stored position and an operative extended position, and lip-extending means operative to move the lip plate from its stored position to its operative position upon movement of the main plate about said rst pivot axis, said lipextending means comprising, telescoping means connected to the said frame means at a point spaced from said first pivot axis and to the lip plate so that movement of the main plate about the rst pivot axis attempts to change the length of the said telescoping means, and a rst latch means operative over a predetermined range of movement of the main plate to latch the said telescoping means against change of length and thereby cause the telescoping means to move the lip plate to its extended position.

In a particular preferred embodiment the lip plate rear edge is pivoted to the main plate front edge, so that the" lip plate pivots about a respective second pivot axis relative to the main plate between the said stored and extended positions.

Also in accordance with the invention there is provided a new dockboard comprising frame means, a main plate having a front edge, means pivotally connecting the main plate with the said frame means for pivoting movement about a respective lirst pivot axis, a lip plate, means mounting the lip plate at the main plate front edge for movement relative to the main plate between a stored position and an operative extended position, lip-extending means operative to move the lip plate from its stored position to its operative position upon movement of the main plate about the said lirst pivot axis, an arm connected with the said lip plate and movable thereby, and a reaction member on the frame means disposed for cooperating engagement with the said arm, whereby movement of the lip plate to return to its stored position causes engagement of the arm and the reaction member and the consequent application to the lip plate and thereby to the main plate of a vertically-upwardly-directed force that moves the main plate above its stored position, so that the main plate can thereafter descend under gravity to its stored position with the lip plate in its respective stored position.

Description of the drawings FIGURE 1 is a general perspective view showing the dockboard ramp assembly in its stored position,

FIGURE 2 is a view similar to FIGURE 1 and showing the ramp assembly in a typical operative position,

FIGURE 3 is a plane section taken on the line 3 3 of FIGURE 1 to show the spring-counterbalance and manual lever-handling arrangements,

FIGURE 4 is a plane section taken on the line 4-4 of FIGURE 1 to show the arrangement of the lip-extending mechanism with the ramp assembly in the said stored position,

FIGURE 5 is a perspective view to an enlarged scale of a detail of the said lip-extending mechanism,

FIGURE 6 is a view similar to FIGURE 4 with the ramp assembly in a rst latch latching position and the mechanism set to raise the lip plate,

FIGURE 7 is a View similar to FIGURES 4 and 6 illustrating the raising of the lip plate by the mechanism as the ramp assembly descends from the position of FIG. 6,

FIGURE 8 illustrates the operation of the ymechanism to restore the lip plate to its dependent position and the ramp assembly to its stored position when the latter descends below a predetermined second latch unlatching position,

FIGURE 9 shows a lower storage position to which the ramp assembly can be put when required,

FIGURE 10 illustrates the operation of a safety latch feature in the event that a transport backs against the lip plate while in the latched extended position,

FIGURE 11 is a perspective view from below and to an enlarged scale of a detail of the latch arrangement of the lip-extending mechanism, and

FIGURE 12 is a cross-sectional view of part of another embodiment wherein the lip plate slides relative to the main plate between the stored and extended positions.

Like parts are given the same reference number in all figures of the drawings, and parts are omitted from some of the figures to increase the clarity of illustration, when such parts are not employed in the function illustrated by that ligure.

Description of the preferred embodiments The particular form of dockboard shown herein is adapted to be mounted as an integral unit into a recess in a loading dock or platform so that, with the ramp assembly in -the position shown in FIGURES 1 and 3 (called herein its stored position), the main plate 16 thereof is approximately level with the top surface of the dock, and the lip plate 17 is folded down to be lapproximately flush with the front face of the dock. It will be understood that the term stored position is used for convenience and under some conditions the dockboard will be operative for loading and unloading while in the so-called stored position. The invention also is applicable to other forms of dockboard, such as a free-standing unit without a surrounding dock, and a unit of the type especially adapted for use with a stepdown dock. The term frame means is used herein for convenience in terminology, and in the embodiment illustrated comprises a box-like frame assembly; in other embodiments the frame means may instead comprise, for example, only the means by which the ramp assembly and its associated mechanism are fastened to a suitable supporting structure, which may be the dock, in which case the said supporting structure operatively connects the fastening means together.

This particular dockboard comprises a frame assembly 18 of welded sheet metal, made sufiiciently rigid for transport, installation and subsequent use in known manner, as by suitable strengthening edges and cross bracing members such as 19; with this embodiment the frame assembly when installed is supported by the surrounding concrete of the dock 15. The main plate 16 has its rear edge hinged to the frame assembly by a pivot 20, the axis of the pivot being horizontal. The lip plate is hinged to the front edge of the main plate by a pivot 21 having its axis parallel to that of the pivot 20. Referring especially to FIGURES 1, 3 and 4, in the stored position illustrated the main plate is horizontal and the lip plate is generally vertical, in what is called herein its dependent position, with its front edge engaged behind a pair of spaced stops 22.

Spring means 'comprising one or more heavy helical compression springs 23 are connected between a member 24 fixed to the frame 18 and a bracket 25 fixed to the underside of the main plate. Two extreme positions of this particular ramp assembly (called herein its first latch latching and second latch unlatching positions) are shown respectively in FIGURES 6 and 8, and it will be seen that as the springs 23 shorten and provide more spring force their upwardly-acting component is reduced; the arrangement of these spring means is made such that, in all positions of the ramp assembly whether the lip plate is in the said extended or in the said dependent position, the effective Weight of the assembly just overcomes the bias of the spring means. With the lip plate in extended position, as shown in FIGURE 7, the effective Weight of the ramp assembly acting against the spring means is increased, whereupon the assembly moves more positively downward.

The ramp assembly of this embodiment is moved by hand and to facilitate its handling a lever handle 26 is provided, the handle vbeing movable longitudinally through a slot 27 in the main plate, from a stored position shown in FIGURE 3 in broken lines to an operative position shown in solid lines. In the stored position the lever is completely concealed beneath the main plate so that it does not obstruct the passage of traffic. A ring 28 permits the operator to grasp the lever and also engages a bracket 29 to retain the lever in its lowermost position.

The lip-extending mechanism comprises a telescoping arm assembly constituted by an outer, hollow, square 4 cross-section member 30 pivoted at its rear end to th frame assembly by a pivot 31, the axis of the pivot being parallel to and spaced vertically from the axis of pivot 20. An inner, hollow, square cross-section member 32 slides freely inside the outer member 30, and another outer, hollow, square cross-section member 33 slides freely over an extension 32a: (FIGURE 10) at the front end of the inner member 32. Referring especially to FIGURE 10, a relatively stiff helical spring 34 is mounted in the enclosure formed between the extension 32a and the hollow member 33 and constantly urges the member 33 in the forward direction. A bolt 35 passes freely through a 'cross piece 36 at the end of the inner member 32 and carries at its other end a clevis 37, which is connected by a pivot 38 to a depending arm 39 rigid with the lip plate 17. The engagement of the cross piece 36 and the head of the bolt 35 limits the forward movement of the latter, while the compression of the spring 34 is adjusted by means of nuts 40.

A first gravity-operated latch member 41 is pivoted to the frame about the same pivot 31 as the telescopic arm assembly and comprises a nose-piece 42 (see especially FIGURE 5) that will pass through a slot 43 in the outer member 30 to engage behind the rear end of the inner member 32. An extension 44 of the member 41 extends to one side of the outer member 30, and in a predetermined lower range of movement of the ramp assembly engages an upwardly-biased, latch-disengaging plunger 45 mounted in a channel 46 fixed to the frame assembly, the plunger being urged upwardly by a surrounding spring 47.

A second gravity-operated latch member comprises an arm 48 pivoted at 49 to a bracket 50 that is in turn fastened to the inner member 32 and movable therewith. A latch nose at the rear end of the arm 48 can engage a latch plate 52 fixed t0 shaft 53 which is pivotally mounted by brackets 54 (FIGURE 11) to the underside of the main plate. The mounting of the plate 52 on its shaft is such that rearwardly-acting force on the arm 48 acts along a line passing through the pivot axis of the shaft, and there is no tendency for the shaft to rotate under the action of this force and release the latch. A downward extension 55 fixed to the shaft 53 is engageable in certain positions of the ramp assembly via a screw 56 with a disengagement member 57 fixed to one side of the outer member 30, the screw permitting adjustment of the actual point of engagement between itself and the member 57. A mechanism for restoring the ramp assembly automatically to its stored condition comprises an arm 58 which is pivoted at 59 to a depending portion of the bracket 50, and which has an extension 60 and a cam nose 61 that engage in predetermined positions of the ramp assembly with a reaction member 62 fastened to the frame means, in this embodiment fastened to the frame oor. The lowermost position to which the arm 58 can fall under gravity about the pivot 59 is set by a screw 63,

The operation of the lip-extending mechanism can now be described. With the dockboard in the stored position illustrated by FIGURES 1, 3 and 4 both the said first and second latches are disengaged. The transport to be loaded or unloaded, indicated generally herein by the reference 64, is backed up to the dock while the ramp assembly is in this position. The lever 26 is now moved to its operative position by an operator standing on the dock 15, and the ramp assembly is swung upward towards the position shown in FIGURE 6. The distances between the two

pivots

20 and 31 are fixed, but the distance between the two

pivots

21 and 31 increases as the ramp assembly moves upward, and the Vinner member 32 slides within the outer member 30 (arrow 64) until at the elevated first latch latching position, with this embodiment the position illustrated by FIGURE 6, the first latch member 41 falls into place (arrow 65) behind the inner member rear end.

The operator now pushes the ramp assembly downward; the telescoping arm assembly cannot decrease in length because of the irst latch, which is operative between the frame and arm assemblies, and as the ramp assembly moves downward (arrow 66, FIGURE 7) the lip plate is rotated upward (arrow 67). Another consequence of this downward movement is that the arm 48 of the second latch moves longitudinally forward relative to the latch plate 52; at a second latch latching position illustrated by FIGURE 7, at which the ramp assembly is just above 'what is called herein its upper operative po sition, and the lip plate is approximately at its point of greatest elevation relative to the main plate, the latch nose 51 slips down under gravity in front of the plate 52 (arrow 68) and the second latch is now engaged. It is an important function of the spring 34 that if the second latch has not engaged by the time that the lip plate is at its maximum extension, the spring will compress under further downward movement of the main plate and shorten the telescopic arm the small amount required for this latching to take place; the spring thereby ensures the successful operation of the second latch without the need for extreme criticality in manufacturing and setting tolerances.

As shown in FIGURE 7, the plunger 45 has engaged the latch extension 44, but the spring 47 is too weak to disengage the first latch while it is still under the load imposed by the ramp assembly. Any further downward movement of the ramp assembly can only take place by compressing the spring 34, and such compression takes place until the weight of the ramp assembly that is not neutralized by the main spring means 23 is fully taken up by the spring 34. The dockboard is now in a tioating condition at which its weight is fully neutralized by springs; if at this point the ramp assembly is given even a slight upward jerk or push to what is called a iirst latch unlatching position, the telescoping arm assembly elongates sufficiently to unload the iirst latch and allow the plunger 45 to push the latch arm 41 out of engagement. In actual practice this oating condition can only be achieved by moving the ramp very slowly, and at the usual speed of operation the additional downward force, due to the kinetic energy of the assembly, always overloads the spring 34, which promptly bounces and lifts the ramp assembly a distance suiiicient to unload the iirst latch, the whole action taking place quickly and smoothly. It should also be noted that the extent of possible downward movement of the plunger 45 is limited and after the plunger has moved its full extent it will stop and positively force the member 41 out of engagement and unlatch the first latch.

The lip plate is now held extended by the second latch means, which are operative between the main and lip plates, so that the lip plate will remain in the same attitude relative to the main plate during movement of the ramp assembly between what is called herein its upper operative position (approximately the position shown in solid lines in FIGURE 7) and its lower operative position (approximately the position shown in solid lines in FIGURE 8). The ramp assembly now moves gently down ward under its own weight to the position shown in broken lines in FIGURE 7, in which the lip plate rests on the transport 64 to permit movement of wares, etc. over the assembly between the truck and the dock. The body of a loaded transport will rise as it is unloaded, and vice versa, and the ramp assembly can rise and fall with the transport body without change of its attitude.

A particularly advantageous feature of our new dockboard is that it will return automatically to its stored position of FIGURE 4 upon the transport driving away from the dock, even when the final operative position of the ramp assembly is below the stored position. Referring especially to FIGURES 7 and 8, as the ramp assembly moves downward (arrow 69) the second latch member 55 moves rearward relative to the outer arm member 30,

and, at a second latch unlatching position shown in FIG- URE 8, which is just below the above-mentioned lower operative position of the ramp assembly, the engagement of the screw 56 and the plate 57 rotates the shaft 53 and disengages the second latch (arrow With the second latch disengaged the main and lip plates can pivot freely relative to one another. At this time the extension 60 of the arm 58 is resting on the block 62 with the nose 61 thereof in engagement with the front edge of the block.

The arm 58 and the members 32 to 39 together constitute what are called herein propping means operative between the lip plate and the block 62, the effect of the propping means being to relieve the spring means 23 of at least a substantial portion of the weight of the lip plate, to the extent that the spring means are able to lift the main plate as long as the lip plate is propped in this manner. The action of the propping means is therefore that, as soon as the second latch is released, a portion of the weight of the lip plate is relieved from the ramp assembly and carried directly by the frame means via the propping means. The spring means 23 thereupon moves the main plate upward, moving the pivot 21 and the corresponding rear edge of the lip plate upward, the prop means remaining meanwhile in engagement with the block 62. The pivot 59 and the associated end of the arm 58 move upward with the upward movement of the main plate, causing the extension 60 to pivot against the top face of the block 62 and lift the nose 61. The arrangement is such that as the main plate reaches a position which is just above the stored position (i.e. the position shown in broken lines in FIGURE 8) the nose is lifted clear of the block, whereupon the propping means are no longer effective. The weight of the ramp assembly now overcomes the spring means and the assembly moves downward, moving the nose 61 over the top of the block so that the prop cannot obstruct the downward movement. As the main plate reached the said broken line position above the stored position the lip plate reached its fully dependent position with its lower edge just clear of the stops 22, and the ramp assembly now settles gently to rest under its own weight, to the position shown in FIG- URE 4 with the lip plate lower edge behind the stops 22.

To show that it is a propping action which is obtained reference may be made to the situation illustrated by FIG- URE 7, wherein the lip plate is resting on the transport 64, the transport constituting the propping means. If at this time the second latch is manually disengaged the main plate immediately lifts, dragging the forward edge of the lip plate rearward over the transport oor until the edge clears the floor, whereupon `the lip plate drops directly to the stored position and the ramp assembly drops directly downward.

Clearly such an operation cannot be obtained as a result of the rotation of the lip plate about its pivot, since there is no mechanism operative for the transfer of force from the lip plate to the main plate.

Other valuable auxiliary features of our new dockboard will now be described. One situation that arises frequently is that the transport is to be fully loaded, but the last wares cannot be placed in position because of the presence of the lip plate; in this case we have provided means to enable the ramp assembly to be returned by the operator to the stored position, so that loading can be completed, witlliout the need to move the transport away from the doc Referring especially to FIGURES 9 and 1l, a key member 74 having two parallel arms 75 and 76 is mounted for both longitudial and rotational movement in a bracket 77 fixed to the underside of the main plate 16. This key member can be used to unlatch the second latch, and for this purpose the operator reaches through a slot 78 in the ramp plate, grasps the key member 74, lifts it vertically, and then rotates it anticlockwise (arrow 79) as seen in FIGURE 11, so that the arm is aligned with a rearward extension 80 on the latch shaft 53; the key member is now pushed downward a distance suicient to rotate the shaft 53 until the second latch is released. The action of the unlatched lip plate and the counterbalance spring means is to cause the main plate to lift and the lip plate to move back toward its stored dependent position, its front edge sliding on the transport floor; when the lip plate leaves the transport floor it immediately falls to its fully dependent position and the whole ramp assembly then moves downward, either under its own weight or with the assistance of the operator if required, until it has reached the stored position of FIGURE 4.

It may be found at this time, or under other circumstances of operation, that the transport is below the iiush stored position, making loading or unloading difficult or impossible, and we have therefore made provision for the ramp assembly to be moved to a lower stored position shown in FIGURE 9. With the lip plate in dependent position the operator lifts the ramp assembly using the lever arm 26, and then pulls upward on the key member 74 to engage a stop 76a on the arm 76 with a corresponding projection 58a of the arm 58. The operator lifts both the assembly and the key member until a latch member 81 on the arm 58 engages in front of a cooperating latch member S2 on the outer arm member 30. The telescoping arm assembly is now latched against change of length, and as the assembly is lowered the lip plate is elevated a suflicient amount for its lower edge to clear the upper stops 22. Thereafter the key 74 is pushed downward until the

latch members

81 and 82 are disengaged by the action of a stop 76]; on the arm 76; the lip plate now pivots toward the dock and can be engaged with the lower stop 22a, as seen in FIGURE 9.

Another possibility for which provision has been made is the case when a transport moves backward heavily against the dockboard While the lip is extended and latched. An impact involving a very small movement of the lip can be accommodated by compression of the spring 34 (FIG. l0), but this spring is stiff and its range of movement is relatively small, and any greater impact could easily seriously damage the lip and perhaps the whole dockboard.

Referring especially to FIGURE l0, a safety mechanism to guard against this possibility employs a third safety latch, comprising an arm 8-3 pivoted at 84 to an assembly 85 carried on the member 33. A latch nose 86 at the rear end of the arm 83 is arranged to engage a latch plate 87 on the rod 53 just before the second latch becomes engaged. Any rearward movement of the transport 64 (arrow 88) causes corresponding movement of the member 33, assembly 8S and arm 83 (arrow 89); the

point of engagement of nose 86 and plate 87 is above the axis of shaft 53, and such movement of the arm 83 will rotate the shaft to release the sec-ond latch and allow the lip plate to pivot, without damage to itself or to the remainder of the dockboard.

Referring especially now to FIGURE 12, in the specific embodiment described above the lip plate 17 is pivoted to the main plate 16 and is dependent therefrom in its Stored position. The invention also is applicable to a dockboard having a ramp assembly of the type illustrated by FIGURE 12, wherein the lip plate is moved by the telescoping arm assembly from an extended position shown in solid lines to a stored position shown in broken lines and in which it is accommodated beneath the main plate, the lip plate being mounted by guides 88 for sliding movement between the two positions.

In the embodiments particularly described and illustrated the ramp assembly is moved manually, and spring means 23 are employed to oppose its weight and make it capable of operation by a single operator of average strength. The invention also is applicable to a dockboard in which the assembly is counterbalanced by a weight and/or the movement of the assembly is by means of a motor, such as a hydraulic or pneumatic piston and cylinder. In a motorised embodiment the motor may be operated to raise the assembly to the position of FIGURE 6 and then shut off, whereupon the assembly will move `downwards under its own weight, elevating the lip plate at the same time; it will usually be desirable to arrange that the motor also controls the downward movement so that the assembly can be lowered gently to the required position.

It will also be apparent to those skilled in the art that various modifications are possible to the apparatus as particularly described, within the scope of the invention. For example, in these embodiments the telescoping means are operative to extend the lip plate as the main plate descends, but it is also possible for them to extend the lip as the main plate is raised, by simple reversal of the direction of action of the connection between the telescoping arm means and the lip plate. In other embodiments the upward movement of the main plate causes the telescoping arm means to decrease in length instead of increase, and the first latch means then are operative to prevent an increase in the length of the telescoping arm means, as they are operative to extend the lip upon upward or downward movement of the main plate about its pivot axis.

What we claim is:

1, A dockboard comprising frame means, a main plate having a front edge, means pivotally connecting the ramp plate with the said frame means for pivoting movement about a respective first pivot axis, a lip plate, means pivotally mounting the lip plate at the main plate front edge about a second pivot axis for movement relative to the main plate between a stored position and an operative extended position, and lip-extending means operative to move the lip plate from its stored to its operative position upon movement of the main plate about said first pivot axis, said lip-extending means comprising telescoping means connected to the said frame means at a point spaced from said first pivot axis and to the lip plate so that movement of the main plate about the first pivot axis attempts to change the length of the said telescoping means, a first latch means operatively connected between the frame means and said arm means and operative over a predetermined range of movement of the main plate to latch the said telescoping means against change of length and thereby cause the telescoping means to move the lip plate to its extended position, and second latch means operatively connected between the main plate and the lip plate and latched by the action of the said telescoping means when the lip plate has been moved thereby to the said extended position to latch the lip plate in the extended position.

2. A dockboard as claimed in claim 1, wherein the said telescoping means increase in length as the main plate is raised, and are latched by the first latch means against decrease in length as the main plate moves downward from an uppermost position, so that downward movement of the main plate from the said uppermost position to an upper operative position is accompanied by extension of the lip plate.

3. A dockboard as claimed in claim 1, wherein the said telescoping means comprise first and second members disposed in telescoping relation to one another and operatively connected between the frame means and the lip plate, a third member disposed in telescoping relation to one of the first and second members, and spring means operative in the direction of telescoping movement of the telescoping means between the third member and its associated member.

4. A dockboard as claimed in claim 2, wherein the said telescoping means comprise a first member pivoted to the said frame means about a respective third pivot axis spaced from the first pivot axis, a second member in telescoping relation to the first member and latchable by the first latch means to prevent movement thereof toward the said third pivot axis and thereby prevent decrease in length of the telescoping means, the said second latch means comprising a latch arm carried by the second member, and a cooperating latch member carried by the main plate.

5. A dockboard as claimed in claim 4, wherein the said second latch means carried by the main plate comprise a rotatable latch member engaged by the said second latch means arm along a line passing through the axis of rotation of the rotatable member.

6. A dockboard as claimed in claim 5, wherein means for unlatching the second latch means upon movement of the ramp plate below a predetermined position comprises disengagement means movable with the said first telescoping member and operatively engageable with the said latch rotatable member to rotate the latter and thereby unlatch the latch.

7. A dockboard as claimed in claim 1 and comprising a safety latch means connected to and movable with the lip plate, and operative under the action of a force upon the lip plate in the general plane of the ramp assembly and of greater than predetermined magnitude to unlatch the second latch means and thereby permit the lip plate to pivot relative to the main plate.

8. A dockboard as claimed in claim 5, wherein the said rotatable latch member of the second latch is engaged by safety latch means connected to and movable with the lip plate, and operative under the action of a force upon the lip plate in the general plane of the lip assembly and of greater than predetermined magnitude, the safety latch means engaging said rotatable latch member along a line displaced from the said axis of rotation, so that the said movement of the safety latch means with the second telescoping member rotates the rotatable latch member and thereby unlatches the second latch means.

9. A dockboard as claimed in claim l, wherein means for unlatching the first latch means comprise a spring loaded plunger engageable with the first latch over a predetermined lower range of movement of the main plate, and the said telescoping means includes spring means compressible in the direction of telescoping motion of the telescoping means by the load of the ramp assembly, the load of the assembly upon the first latch holding it in engagement against the action of the said plunger, and the said spring means permitting unloading of the first latch whereupon the plunger can unlatch the said first latch.

10. A dockboard as claimed in claim 1, and comprising spring means operably connected between the frame means and the ramp assembly and urging the assembly for upward movement, said spring means normally being unable to move the ramp assembly upward against the weight thereof acting downward under gravity, prop means operably engageable between the lip plate and the frame means upon movement of the main plate below a lower operating position, said prop means in said operative engagement relieving the spring means of at least part of the weight of the ramp assembly such that the spring means moves the ramp assembly upward above its said stored position, and prop disengaging means disengaging the prop means from between the lip plate and the frame means upon movement of the ramp assembly above the stored position, so that the ramp assembly thereafter descends under gravity to its stored position.

11. A dockboard as claimed in claim 10, and comprising fourth latch means carried by the said telescoping means, cooperating fourth latch means on the said prop means, means operable by an operator for manually engaging the said fourth latch means upon upward movement of the ramp assembly and thereby latching the telescoping means against change in length, whereby downward movement of the ramp assembly with the fourth latch means latched so extends the lip as to permit the assembly to be moved to a lower stored position.

12. A dock-board as claimed in claim 1, wherein the telescoping means comprise, a first telescoping member pivoted to the frame means, a first latch member pivoted to the frame means, a second telescoping member pivotally connected with the lip plate and telescoping with respect to the rst member, the second member being engageable with the said first latch member to constitute rst latch means, a second latch member carried by the second telescoping member, another second latch member mounted on the underside of the main plate and engageable with the first mentioned second latch member to constitute said second latch means, the first latch being latched upon upward movement of the ramp assembly above a first latch latching position and the second latch being latched upon downward movement of the ramp assembly to a second latch latching position above an upper operative position of the ramp assembly, means for unlatching the first latch means upon movement of the ramp assembly to a first latch unlatching position below the said second latch latching position, and means for unlatching the second latch means upon movement of the ramp assembly to a second latch unlatching position below a lower operative position of the assembly.

13. A dockboard as claimed in claim 12, and comprising means for manually unlatching the said second latch means while the ramp assembly is between the said second latch latching and unlatching positions.

14. A dockboard as claimed in claim 12, and comprising a third telescoping member in telescoping relation with the said second member and pivotally connecting the telescoping means to the lip plate, and a spring interposed between the second and third telescoping members and operative in the direction of telescoping motion of the telescoping means.

15. A dockboard comprising frame means, a main plate having a front edge, means pivotally connecting the ramp plate with the said frame means for pivoting movement about a respective first pivot axis, a lip plate, means mounting the lip plate at the main plate front edge for movement relative to the main plate between a stored position and an operative extended position, and lip-extending means operative to move the lip plate from its stored to its operative position upon movement of the main plate about the said first pivot axis, said lip-extending means comprising arm means operatively engageable with the frame means and the lip plate, first latch means operable over a predetermined range of movement of the main plate to latch the arm means to the frame means for the arm means to move the lip plate to the operative position upon the said movement of the main plate over the predetermined range, first latch unlatching means operably engageable with the first latch means over another predetermined range of movement of the main plate to urge said latch means to unlatched condition, said unlatching means being inoperative while the first latch means is loaded by the ramp assembly and being operative upon unloading of the first latch means.

16. A dockboard as claimed in claim 15, wherein said unlatching means are operative upon movement of the main plate beyond the said another predetermined range of movement to engage the first latch means positively and unlatch the first latch means while loaded by the ramp assembly.

17. A dockboard as claimed in claim 15, wherein the said lip-extending arm means comprises spring means interposed between the lip plate and the first latch means for unloading the ramp assembly from the first latch means by spring action of the spring means during movenent of the ramp assembly and subsequent reaction thereo 18. A dockboard as claimed in claim 15, wherein the lip plate has front and rear edges, the lip plate rear edge is pivoted to the main plate front edge so that the lip plate pivots about a respective second pivot axis relative to the main plate between the said stored and extended positions, and the said lip-extending arm means are latched by the first latch means to the frame means as the main plate moves downward from an uppermost position, so that downward movement of the main plate is accompanied by extension of the lip plate.

19. A dockboard as claimed in claim 15, wherein said iirst latch means comprise a latch member mounted bythe frame means, and wherein said unlatching means comprises a spring urged plunger mounted by the frame means for operative engagement with the said latch means, and urging the latch member to unlatch the latch means.

20. A dockboard as claimed in claim 17, comprising second latch means having relatively movable latch members and operatively connected by the lip-extending arm means between the main plate and the lip plate to latch the lip plate in the said extended position when it has been moved to that position, and wherein the said spring means is also interposed between the lip plate and the second latch means and permits relative movement of the second latch means latch members for latching thereof after the lip plate has moved to the said extended position.

21. A dockboard comprising frame means, a main plate having a front edge, means pivotally connecting the ramp plate with the said frame means for pivoting movement about a respective rst pivot axis, a lip plate, means mounting the lip plate at the main plate front edge for movement relative to the main plate between a stored position and an operative extended position, and lip-extending means operative to move the lip plate from its stored to its operative position upon movement of the main plate about the said lirst pivot axis, said lip-extending means comprising arm means operatively engageable with the frame means and the lip plate, rst latch means operable over a predetermined range of movement of the main plate to latch the arm means to the frame means and cause the arm means to move the lip plate to the operative position upon the movement of the main plate over the said predetermined range thereof, second latch means having relatively movable latch members and operatively connected by the arm means between the main plate and the lip plate to latch the lip plate in the said extended position when it has been moved to that position, and said arm means comprising spring means interposed between the lip plate and the second latch means and permitting relative movement of the second latch means latch members for latching thereof after the lip plate has moved to the said extended position.

22. A dockboard as claimed in claim 21, wherein the lip plate has front and rear edges, the lip plate rear edge is pivoted to the main plate front edge so that the lip plate pivots about a respective second pivot axis relative to the main plate between the said stored and extended positions, and the said lip-extending arm means are latched by the rst latch means to the frame means as the main plate moves downward from an uppermost position, so that downward movement of the main plate is accompanied by extension of the lip plate.

23. A dockboard comprising frame means, a main plate having a front edge, means pivotally connecting the ramp plate with the said frame means for pivoting movement about a respective lirst pivot axis, a lip plate, means mounting the lip plate at the main plate front edge for movement relative to the main plate between a stored position and an operative extended position, and lip-extending means operative to move the lip plate from its stored to its operative position upon movement of the main plate about the said first pivot axis, spring means operatively connected between the frame means and the ramp assembly and urging the assembly for upward movement, said spring means normally being unable to move the ramp assembly upwards against the weight thereof acting downward under gravity, and prop means operably engageable between the lip plate and the frame means upon movement of the main plate below a lower operating position, said prop means in said operative engagement relieving the spring means of at least part of the weight of the ramp assembly such that the spring means moves the ramp assembly upward above its said stored position.

24. A dockboard as claimed in claim 23, and comprising prop disengaging means disengaging the prop means from between the lip plate and the frame means upon movement of the ramp assembly above the stored position, so that the ramp assembly thereafter descends under gravity to its stored position.

25. A dockboard as claimed in claim 24, and comprising second latch means operatively connected between the main plate and the latch plate and latched by the action of the lip extending arm means when the lip plate has been moved thereby to the said extended position to latch the lip plate in the extended position, and means for disengaging the said second latch means upon movement of the ramp plate below the said lower operating position.

26. A dockboard as claimed in claim 25, wherein the lip plate has front and rear edges, the lip plate rear edge is pivoted to the main plate front edge so that the lip plate pivots about a respective second pivot axis relative to the main plate between the said stored and extended positions, and the said lip-extending arm means are latched by the iirst latch means to the frame means as the main plate moves downward from an uppermost position, so that downward movement of the main plate is :accompanied by extension of the lip plate.

27. A dockboard as claimed in claim 26, wherein the upward movement of the main plate is accompanied by movement of the lip plate toward its stored position, the lip plate reaching the said stored position as the main plate reaches a position above the stored position, so that the ramp assembly descends under gravity with the lip plate in the stored position.

28. A dockboard as claimed in claim 26, wherein said prop means comprise a prop arm disposed beneath the ramp plate and operatively connected to the lip plate, and said prop disengaging means comprise a prop latch on said prop arm operably engageable with the frame means, and latch disengaging means on said prop arm operable to disengage the prop latch as the ramp assembly reaches the said position above the stored position.

29. A dockboard as claimed in claim 26 wherein said prop means comprise the said lip-extending arm means, a prop arm connected to the lip-extending arm means for operative connection to the lip plate, and said prop disengaging means comprise a prop latch on said prop arm operably engageable with the frame means, and latch disengaging means on said prop arm operable to disengage the prop latch as the ramp assembly 'reaches the said position above the stored position.

30. A dockboard as claimed in claim Z9 wherein said prop arm is pivotally connected to the lip-extending arm means and said prop disengaging means comprise a stationary prop latch member on the frame means, another latch member on the frame means, another latch member on the prop arm, and a latch-disengaging extension on the prop arm spaced from the pivotal connection of the arm with the lip-extending arm means, the pivoting of the prop arm as the ramp assembly moves about the tirst plvot axis operatively engaging the extension and the frame means to disengage the prop arm latch member from the stationary latch member when the ramp assembly moves above the stored position.

3 1. A dockboard comprising frame means, a main plate having a front edge, means pivotally connecting the ramp plate with the said frame means for pivoting movement about a respective iirst pivot axis, a lip plate, means mounting the lip plate at the main plate front edge for movement relative to the main plate between a stored position and an operative extended position, lip-extending means operative to move the lip plate from its stored to its operative position upon movement of the main plate about the said irst pivot axis, said lip-extending means comprising arm means operatively engageable with the frame means and the lip plate, first latch means operable over a predetermined range of movement of the main plate to latch the arm means to the frame means and cause the arm means to move the lip plate to the operative position upon the movement of the main plate over the said predetermined range thereof, second latch means operatively connected by the lip-extending arm means between the main plate and the lip plate to latch the lip plate in the said extended position when it has been moved to that position, and safety latch means connected to and movable with the lip plate, and operative under the action of a force upon the lip plate in the general plane of the ramp assembly and of greater than predetermined magnitude to unlatch the second latch means and thereby permit the lip plate to pivot relative to the main plate.

32. A dockboard as claimed in claim 31, wherein the said second latch means comprise a latch arm carried by said lipextending arm means, a rotatable latch member carried by the main plate and engaged by the said second latch means arm along a line passing through the axis of rotation of the rotatable member, and wherein the said safety latch means engages the said rotatable latch member along a line displaced from the said axis of rotation, so that the said movement of the safety latch means with the lip plate rotates the rotatable latch member and there- 5 by unlatches the second latch means.

References Cited UNITED STATES PATENTS 10 3,327,335 6/1967 Beckwith 14-71 3,137,017 6/1964 Pfleger 14-71 3,203,002 8/1965 McGuire 14-71 3,249,956 5/1966 Zajac 14-71 3,323,158 6/1967 Loomis 14-71 NILE C. BYERS, J R., Primary Examiner