GB2094751A - Bridging device for ramps - Google Patents

Abstract

A bridging device comprises a bridge plate (1) pivotally mounted on a ramp to be bridged and an extension portion (4) retractably or pivotally mounted on the free end of the bridge plate, by means of which the device is supported on a platform (13). The driving means for pivoting the bridge plate are subject to a dead man control including a switch which does not permit the bridge plate (1) to be lowered if released. In order that the bridging device (1, 4), when in its operative position, can follow any descending movements of the platform (13), the dead man control is released by means of a switch (15) when the extension portion (4) is mounted upon the platform (13). In addition, the device is usually hydraulically operated and a reduction of the pressure in the hydraulic system, such as occurs when the extension portion (4) is located upon the platform (13), may be employed. <IMAGE>

Description

SPECIFICATION Bridging device for ramps The present invention relates to a bridging device for ramps, the device being of the type which comprises a bridge plate pivotally mounted at its rear end about a horizontal axis on the ramp, and a retractable and extensible or inwardly and outwardly pivotable extension portion which is mounted on the free end of the bridge plate remote from the mounting thereof on the ramp. The extension portion is, in its operative position, supported on a platform to be loaded or unloaded. The bridge plate has drive means for causing pivotal movement thereof. The drive means have operating switches associated therewith which are of the type which prevent the bridge plate from lowering if they are not actuated.

Such a known construction of a bridging device meets the requirements of a so-called "dead mann control", the purpose of which is to prevent the bridge plate from lowering itself or being lowered further than desired if the operator is no longer actuating the operating switch. However, this particular safety measure makes it impossible for the bridging device to be operated if the height of the platform changes during loading or unloading.

The present invention seeks to improve a bridging device of the above type so that the advantages of the "dead man control" are retained, but in which, during operation, the bridge plate can vary in height, that is to say, it may even execute downward movements, without an operator needing to be present.

In accordance with the present invention, there is provided a bridging device for ramps, comprising a bridge plate pivotally mounted at one of its ends about a horizontal axis on the ramp to be bridged and an extension portion retractably or pivotally mounted on the free end of the bridge plate remote from the pivotal mounting of the bridge plate, the extension portion, in use, being supported on a platform to be loaded or unloaded, drive means being provided for causing pivotal movement of the bridge plate, the drive means including a locking arrangement comprising an operating switch arrangement which, when not actuated, prevents the bridge plate from pivoting downardly wherein the support of the extension portion on the platform causes the locking device preventing the bridge plate from lowering to be released.

The release of the locking mechanism may be achieved by the extension portion. As the extension portion comes to rest upon the platfkorm to be loaded or unloaded, it executes a small pivotal movement which can be used to actuate a switch for releasing the locking mechanism. In addition, however, resilient deformations of the bridging device itself may be used to actuate a switch. Such deformations may occur when the bridge plate is supported on the paltform solely by means of the extension portion. The small switching movements are also possible during the proces of locating the extension portion on the platform when the bearing play is overcome. It is apparent that appropriate, sensitive switching or feeler elements must be used, but the choice of the particular type of such elements depends upon the circumstances in which the device is being used.

If the drive means includes a hydraulic lifting piston and cylinder arangement for piv oting outing the bridge plate, a switch capable of being actuated by the pressure in the hydraulic system may be employed for releasing the locking arrangement.

Such pressure-responsive switch which, if employed, is located in the pressure system for the lifting cylinder, is inoperative when the extension portion is located upon the platform to be loaded or unloaded. If the extension portion is not so located, an excess pressure prevails within the hydraulic system due to the weight of the extension portion and the bridge plate. This excess pressure is reduced when the extension portion is located upon the platform. Such pressure change actuates or influences the hydraulic switch to release the locking arrangement, so that the bridge plate can be freely pivoted, as desired. Once, however, the extension portion is no longer supported on the platform, the pressure in the hydraulic system rises and the locking arrangement becomes operative again.

Two embodiments of the present invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial longitudinal section through a bridging device for ramps in accordance with the present invention; Figure 2 is a schematic illustration of an electrical circuit diagram for the bridging device shown in Fig. 1; Figure 3 is a longitudinal cross-sectional view through a modified embodiment of a bridging device for ramps in accordance with the present invention, the device being shown in its operative position, and Figure 4 shows part of an electrical circuit diagram for the bridging device shown in Fig.

3.

As shown in Figs. 1 and 3, a bridging device in accordance with the present invention comprises a bridge plate 1 which is pivotally mounted at its rear end about a transverse axis 2. The front end of the bridge plate 1 is provided with an extension portion 4, which extension portion is pivotable about a horizontal axis 3. In its operative position, the extension portion 4 forms an extension of the bridge plate 1. However, in its rest position, the extension portion 4 may be pivoted downwardly with respect to the plate 1. A hydraulic piston and cylinder arrangement 5 is used to pivot the bridge plate 1 about the axis 2 and has a motor-driven pump 6 directly connected thereto. The pump 6 has a reservoir for hydraulic fluid associated therewith.

The hydraulic pressure medium is supplied from the reservoir to the operative cylinder chamber 5 through a line 7 when the bridge plate 1 is to be raised. When the bridge plate 1 is lowered, the pressure medium returns to the reservoir through the line 7, such return being caused by the dead weight of the bridge plate 1 and its accessories.

An electrically actuable valve 8 is located in the line 7. The drive means may be switched on and off by the double switch 9, the upper button 10 of which is used to raise the bridge plate 1 and the lower button 11 is used to lower the bridge plate 1.

By pressing the button 11, the valve 8 is opened by being supplied with an electrical voltage from the current source 1 2. Consequently, the bridge plate 1 can be lowered whilst the button 11 is being pressed. If the button is disengaged, i.e. it is no longer being pressed, the valve 8 is closed and the bridge plate 1 is thereby prevented from lowering.

In the extended position of the extension portion 4, there is a small gap S between the rear end of the extension portion 4 and the front end of the bridge plate 1. If, however, the bridge plate 1 has been raised but is then lowered by operating the button 11, the tip of the extension portion 4 can be brought into contact with a platform 1 3 to be loaded or unloaded. So that the bridge plate 1 and the extension portion 4 can follow any possible changes in height of the platform 1 3 when the button 11 is not pressed, which changes may be caused by loading so as to cause lowering of the platform 1 3, a small rearwardly extending lever 14 is mounted on the extension portion 4 and which pivots with the extension portion 4.

If the gap S is closed by the raising of the extension portion 4, the lever 14 actuates an electrical switch 1 5 which, in turndepend- ing on whether or not the button 11 is pressed or not-applies a voltage to the valve 8 so as to release the bridge plate 1 from its locked position.

If, after the operation has been terminated, the bridge plate 1 is raised, a gap S is once again formed. Accordingly, the locking arrangement for preventing the bridge plate 1 from lowering becomes operative again.

The following movement of the bridge plate 1 may be induced by the bridging device being top-heavy, or by other means.

It is apparent that the bridge plate 1 and/or the extension portion 4, and possibly other components of the bridging device, may become resiliently deformed when the extension portion 4 is mounted upon the platform 1 3 to be loaded or unloaded. This is particularly true if the bridge plate 1 is supported exclusively by means of the extension portion 4.

These deformations may also be used to control or actuate the valve 8. In addition, it is also possible to use other locking devices for preventing downward movement of the bridge and to provide other means for releasing the locking device.

In every case, therefore, it is important that the locking device is detached or released when the bridging device is in its operative position, that is to say, when the extension portion is extended and is pivoted outwardly.

A pressure switch 1 6 may also be located in the line 7, which pressure switch 1 6 is actuated by the pressure existing in the line 7.

The switch 1 6 is also an electrical switch and is connected, as shown in Fig. 4, in a manner which is effectively in parallel with the switch 11. In other words, the switches 11 and 1 6 can exert the same influence upon the valve 8.

If, when the extension portion 4 is extended, the bridge plate 1 is to be lowered from its highest position into the operative position shown in Fig. 1, the button 11 is pressed, thereby causing the bridge plate to descend whilst the valve 8 is open. Since the pressure switch 1 6 is also subject to pressure, it does not have any effect on the action of the switch 11. Once the extension portion 4 touches the platform 13, the switch 11 has to be set to operate. However, the hydraulic system is now unloaded. The pressure drops within the line 7, whereby the pressure switch 1 6 is unloaded and automatically replaces the switch 11 or causes the voltage source 1 2 to be applied to the valve 8 to open this latter.

When the extension portion 4 is raised, the bridge plate 1 can therefore pivot and follow the changes in height of the platform 1 3.

If the bridge plate 1 is raised by actuating the switch 10, the pressure within the line 7 rises and, accordingly, return-flow through the valve 8 is, in turn, induced thereby.

Claims (9)

1. A bridging device for ramps, comprising a bridge plate pivotally mounted at one of its ends about a horizontal axis on the ramp to be bridged and an extension portion retractably or pivotally mounted on the free end of the bridge plate remote from the pivotal mounting of the bridge plate, the extension portion, in use, being supported on a platform to be loaded or unloaded, drive means being provided for causing pivotal movement of the bridge plate, the drive means including a locking arrangement comprising an operating switch arrangement which, when not actuated, prevents the bridge plate from pivoting downardly wherein the support of the extension portion on the platform causes the locking device preventing the bridge plate from lowering to be released.

2. A bridging device as claimed in claim 1, wherein the switch arrangement for releasing the locking arrangement is actuated by a change in position or resilient deformation of the bridging device or portions thereof whilst the extension portion is mounted upon the platform.

3. A bridging device as claimed in claim 1 or 2, wherein the switching device is a lever connected to the extension portion.

4. A bridging device as claimed in claim 1 or 2, wherein the extension portion is pivotally mounted on the bridge plate and, prior to being located upon the platform, subtends a small angle with the free end face of the bridge plate, the reduction of the angle causing actuation of the switch plate.

5. A bridging device as claimed in claim 1, wherein the locking device is unlocked as the bridging device is raised.

6. A bridging device as claimed in claim 1, wherein a further switch is provided to release the locking device, the drive means being hydraulically operated, actuation of the switch being influenced by the pressure prevailing in the hydraulic system.

7. A bridging device as claimed in claim 6, wherein the further switch is electrically connected, in parallel, to the operating switch.

8. A bridging device as claimed in claim 6, wherein the switch is associated with a feedline for a hydraulic lifting cylinder, the feedline and the lifting cylinder forming part of the hydraulic system.

9. A bridging device constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 2 or Figs. 3 and 4 of the accompanying drawings.