GB2067504A

GB2067504A - Bridging device

Info

Publication number: GB2067504A
Application number: GB8037156A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-11-20
Filing date: 1980-11-19
Publication date: 1981-07-30
Also published as: FR2470076B1; FR2470076A1; DE2946744A1; GB2067504B; DE2946744C2

Abstract

A bridge plate (1) pivotally mounted about a horizontal axis (2) has an extension portion (5) pivotally mounted thereon. A connecting rod arrangement (6, 7) being provided for pivoting the extension portion (5) the rear end of the connecting rod (7) being mounted on a disc (10) which is pivotable about a horizontal axis (8) and there being a flexible tension member (15) for actuating the disc (10) one end of the tension member (15) being anchored and the other end thereof being operationally connected to the disc (10) in such a manner that as the tension member (15) is tightened during the upward pivotal movement of the bridge plate (1) to cause the lever arrangement to effect pivotal movement of the extension portion (5) into its operative position the tension member (15) in its end region adjacent the lever (13) being located on an arcuate guide (14) such that the effective lever arm (b) with which the tension member acts on the disc remains substantially constant over the pivotal path of the disc. <IMAGE>

Description

SPECIFICATION Bridging device The present invention relates to a bridging device.

A bridging device is known which comprises a bridge plate which is pivotally mounted, at its rear end, about a horizontal axis formed on a surface which defines a recess to be bridged. At its free end, the bridge plate has an extension portion pivotally mounted thereon. The extension portion is pivotal from a rest position in which it extends substantially vertically into a working position in which it extends substantially horizontally. In its operative position, the extension portion is placed on a platform to be loaded or unloaded, such as the floor of a vehicle and supports the bridging device. The extension portion is pivoted by means of a pushrod extending in substantially the longitudinal direction of the bridge.

At or near its rear end facing the pivotal axis of the bridge plate, the pushrod is mounted on the free end of a lever which is pivotal about a horizontal axis and which is adapted to be actuated by a flexible tension member. One end of the tension member is anchored within the recess and the other end thereof is operationally engaged with the lever in such a manner that the tension member, when the bridge plate is pivoted upwardly, tightens and thereby causes pivotal movement of the lever.

In such known devices for pivoting the extension portion upwardly, the tension member engages the said lever. Since, however, during upward pivotal movement of the bridge plate, the lever position changes relative to the anchoring point of the tension member, unfavourable forces act on the hinged linkage. In the case of manually actuated bridging devices of the above-described type, this is disadvantageous since it necessitates undue effort on the part of the operator to cause the pivotal movement to take place.

The present invention seeks to provide a mechanism which facilitates the pivoting operation in such a manner a favourable lever ratio is achieved even the extension portion needs to be rapidly pivoted, thus necessitating considerable energy.

In accordance with the present invention, there is provided a bridging device comprising a bridge plate pivotally mounted about a horizontal axis on a surface defining a recess to be bridged, the bridge plate at its free front end having an extension portion pivotally mounted thereon, the extension portion being pivoted from a substantially vertical rest position into a horizontal working or operational position, the extension portion, in its operative position, being locatable on a platform to be loaded or unloaded thereby supporting the device on the platform, a connecting rod arrangement including a connecting rod extending substantially in the longitudinal direction of the bridge being provided for pivoting the extension pOrtion, the rear end of the connecting rod being mounted on the free end of a lever which is pivotable about a horizontal axis and a flexible tension member for actuating the lever one end of the tension member being anchored in the recess and the other end thereof being operationally connected to the lever in such a mannerthatthe tension member is tightened during the upward pivotal movement of the bridge plate so as to cause the lever arrangement to effect pivotal movement of the extension portion into its operative position wherein the tension member, in its end region adjacent the lever is located on an arcuate guide such that the effective lever arm with which the tension member acts on the lever remains substantially constant over the pivotal path of the lever.

By providing such an arrangement it is ensured that a substantially uniform actuating force is produced to cause upward pivotal movement of the bridge plate and for pivoting the extension portion connected thereto into its operative position. The operating force does not, therefore, suddenly and unfavourably increase due to combined operation.

The invention will be further described, by way of example, with reference to the accompanying drawing, the single figure of which shows a side elevational view, partially in section, of a bridging device in accordance with the present invention in its inoperative condition.

The device shown in the drawing comprises a bridge plate 1 pivotally mounted at one of its ends about a horizontal axis 2 on a surface 3 defining a recess to be bridged by the device. From the position shown, the plate 1 may be pivoted upwardly or downwardly about the axis 2. To facilitate this pivotal movement, the bridge plate 1 may be balanced by means of springs, counterweights or the like which are well known and are therefore not shown.

Pivotally mounted on the free end of the bridge plate 1 is an extension portion 5, the pivotal axis of which is horizontal. As shown in the drawing, in its rest position, the extension portion 5 extends sub stantiallyvertically. The portion 5 is pivoted into its operational position by rotation through substantially 90 into a position in which the upper surface thereof lies in the same plane as the upper surface of the plate 1.

A mechanism is provided which causes the extension portion 5 to move from its inoperative position into its operative position when the plate 1 is pivoted upwardly about the axis 2. Such a mechanism will now be described.

Connected to the pivotal axis of the extension portion 5 is a lever 6 which, when the extension portion 5 is in its inoperative or vertical position, extends diagonally downwardly in a rearward direction. The lever 6 is hingedly connected to a connecting rod 7 extending in substantially the longitudinal direction of the device but also slightly downwardly. The rear end of the connecting rod 7 is connected to a pin or journal 8 which is located on a disc 10. The disc 10 is pivotable about a horizontal axis 9. It will be appreciated that by pivoting the disc 10 in the direction of the arrow 11, the extension portion 5 will be pivoted in the direction of the arrow 12. This is because a lever arm 13 having a length a is effectively present between the axes 8 and 9.The outer surface of the disc 10 includes an arcuate portion 14 on which a tension member, such as atension-resistantcable 15 is supported. For the whole effective pivotal region of the disc 10 and the axis 9, there is effectively formed a lever arm having a constant length b. The cable 15 is securely anchored at its lower end to, for example, the base of the recess defined bythe sur face 3. If the bridge plate 1 is pivoted upwardly from its rest position, the cable 15 is tensioned until it eventually causes the disc 10 to pivot in the direction of the arrow 11. Such movement, however, also moves the pin 8 and the connecting rod 7 connected thereto, so as to cause upward pivotal movement of the extension portion 5.

The lever arm 13, in its rest position, extends rearwardly and upwardly. This, in combination with the diagonal position of the lever 6, means that no excessive forces can be transmitted. This is, however, in view of the position of the extension portion 5 and the initially slight change in the position of the centre of gravity of the extension portion 5 sufficient for upwardly pivotal movement. With further rotation of the disc 10, the lever ratios become more favourable. Consequently the change in the position of the centre of gravity of the extension portion 5 has been taken into account. The engagement of the cable 15 on the mechanism is thus very favourable, because the effective length b of the lever arm does not vary. This means that the pivoting of the extension portion 5 into its operative position can be effected more easily than has hitherto been the case.

On reaching its operational position, the extension portion 5 is retained by suitable means. The disc 10 has a projection portion 17 at one end of its arcuate surface portion which, in its end position, comes into abutment with a stop member 16 provided on the underside of the plate 1. All of these operations are co-ordinated with one another. Thus, for example, the upward pivotal movement of the extension portion is terminated when the plate 1 reaches its upper end position.

Claims

1. A bridging device comprising a bridge plate pivotally mounted about a horizontal axis on a surface defining a recess to be bridged, the bridge plate at its free front end, having an extension portion pivotally mounted thereon, the extension portion being pivoted from a substantially vertical rest position into a horizontal working or operational position, the extension portion, in its operative portion, being locatable on a platform to be loaded or unloaded, thereby supporting the device on the platform, a connecting rod arrangement including a connecting rod extending substantially in the longitudinal direction of the bridge being provided for pivoting the extension portion, the rear end of the connecting rod being mounted on the free end of a lever which is pivotable about a horizontal axis and a flexible tension member for actuating the lever, one end of the tension member being anchored in the recess and the other end thereby being operationally connected to the lever in such a mannerthatthe tension memberistightened during the upward pivotal movement of the bridge plate so as to cause the lever arrangement to effect pivotal movement of the extension portion into its operative position wherein the tension member, in its end region adja cent the lever is located on an arcuate guide such that the effective lever arm with which the tension member acts on the lever remains substantially con stantoverthe pivotal path of the lever.

2. A bridging device as claimed in claim 1, wherein the front end of the connecting rod cooperates with an additional lever, the additional lever causing the pivotal movement of the extension portion, the additional lever in the rest position, extending diagonally downwardly and rearwardly while the lever connected to the rear end of the connecting rod extends diagonally rearwardly and upwardly when the extension portion is in the rest position.

3. A bridging device as claimed in claim 1 or 2 wherein the guide is located on the outercircumfer- ence of a disc, the disc having a projection portion which, in the end position of the disc, abuts against a fixed abutment member formed in the bridge plate.

4. A bridging device as claimed in any one of claims 1 to 3, wherein the effective lever arm for the tension member is substantially larger than the effective lever arm length.

5. A bridging device as claimed in claim 4, wherein the effective lever arm forthetension member is substantially twice the effective lever arm length.

6. A bridging device constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.