GB2177448A - Improvements in or relating to clamping devices - Google Patents

Abstract

A clamping device, adapted for use in association with the top of a ladder, to grip a structure against which the ladder is at rest and so hold the ladder steady. The device comprises at least one pair of co-operating clamping jaws 8, 19, 27, 28, the jaws being carried by arms which constitute the opposite sides of a parallelogram linkage. Once one jaw is hooked on contact with the structure, simple pulling of the foot of the ladder away from the structure tends to change the shape of the parallelogram so that the jaws meet and positively grip the structure. The application describes devices suitable for connection to ladders with both solid and hollow rungs. <IMAGE>

Description

SPECIFICATION Improvements in or relating to clamping devices This invention relates to clamping devices. It relates in particular to such devices when adapted for use in association with the top of a ladder, so that when the ladder is erected or extended against a building or other structure the clamp can be addressed to some part of the structure and then closed to grip that part so as to hold the ladder steady. US Specifications Nos. 3910380 and 4018301 show examples of the range of clamping devices that have already been proposed expressly for this purpose. However these examples exhibit disadvantages that have been typical of the range as a whole: complexity of both movement and mechanism, involving many pivot axes, and the need for the clamp to be either an integral part of the ladder or to be secured to it by a means of connection that cannot be quickly or easily undone.

Also, once a ladder top carrying the clamp of either of US 3910380 or 4018301 is addressed to the part of a structure that is to be gripped, the complexity of the mechanism tends to require the operator then to move the foot of the ladder carefully and somewhat precisely if a good grip is to be effected; simple pulling of the ladder foot away from the structure could easily dislodge such complicated clamps from what they were intended to grip.

The present invention seeks to provide a clamp with fewer essential parts than have been customary hitherto, and simpler operation, and in particular one that lends itseif to easier connection to and disconnection from a ladder. According to the invention a clamping device comprises a base member, defining first and second pivot axes, separated from but parallel to each other; first and second arm members mounted to pivot about the first and second axes respectively; a link, pivotally connected to the first and second arm members at third and fourth pivot axes respectively, so that the four pivot axes lie at the vertices of a parallelogram linkage; a first claw member associated with the first arm member, and a second claw member associated with the second arm member, whereby as the parallelogram linkage changes shape to reduce or increase the distance between the parallel first and second arm members, the two claw members either approach whereby they may grip an object lying within, or open whereby such an object may be released.

At least one of the jaw members may be angled whereby movement of the linkage to increase or reduce the distance between the arm member is reflected in a magnified relative movement of the tips of the claw members. One of the claw members may be fixed to the link.

The first arm member may comprise two separate arms, both pivotted on the first axis but at points spaced apart along that axis, and the second arm member may also comprise two separate arms in a similar arrangement relative to the second axis, the two pairs of first and second arms each supporting a pair of jaws which move in synchronism with each other to grip or release an object.

The base member may comprise a framework adapted for attachment to a ladder. The framework may include means to engage with the stiles of a ladder, or clamps to grip the outer surface of a rung of the ladder, or rod-like members to pass down the middle of a hollow rung of a ladder.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a perspective view of one clamping device in the open position: Figure 2 is a similar perspective view of the same device in a more closed position; Figure 3 is a perspective view of a second device in the open position, and Figure 4 is another perspective view of the device of Figure 3 when in a more closed position.

All the figures show a ladder having stiles 1,2 and rungs 3, and reference 4 indicates the top end of the ladder. The clamping device of Figures 1 and 2 comprises a channel-section plate 5, the base 6 of which abuts the rungs 3 while the flanges 7 lie inboard of but parallel to the stiles 1,2. "U"-shaped rung clamps 8, of which one is shown, fit around the rungs; the free ends of these clamps are secured to the base 6 to hold the device 5 in position.

Matching rows of holes 9 are drilled in flanges 7.

These holes receive pivot pins which serve to define first and second pivot axes, as will be described; which matching pair of holes is chosen in each of the flanges 7 depends on the size of the object that the clamping device is to grip.

In Figures 1 and 2 a first arm member comprises two arms 10,11, pivotted one to each of the flanges 7 on a common first pivot axis 12 defined in this example by the topmost holes 9. A second arm member comprises second arms 15,16, pivotted one to each of the flanges 7 along an axis 17 defined in this example by the next-to-topmost holes 9. The free ends of arms 15, 16 are formed into upwardly- pointing claws 18, 19.

Arms 10 and 15,11 and 16 are joined by being pivotted, along axes 20 and 21,to parallel limbs 22, 23 of a link member which also comprises across- beam 24 and upper limbs 25,26 terminating in downwardly-pointing claws 27, 28 respectively.

Limbs 22, 23 are formed with holes 30 at spacings matching those of the holes 9 in flanges 7, and axes 20 and 21 correspond to the topmost and next-totopmost holes 30.

Pivot axes 12, 17,21 and 20 are all parallel to each other and so disposed that the ladder, the arms 10, 11 and 15, 16, and the limbs 22,23 constitute parallogram linkages so that arms 10,15 and 11,16 are always parallel to each other, and limbs 22, 23 are always parallel to the stiles 1, 2 of the ladder.

Because the arms 25, 26 belong to the link member which is mounted to move up and down in a direction parallel to the ladder, while arms 15, 16 are mounted to rotate about axis 17 which lies parallel to the ladder rungs, it will readily be seen that the gap between jaws 18,27 and 19,28 is greatest when the arms 10, 11 and 15, 16 slope downwardly relative to the ladder (as in Figure 1), and least when those arms slope upwardly relative to the ladder (as shown in Figure 2). Gravity tends to bias the clamping device to the position of Figure 1, and the top 4 of the ladder may be anchored to a high horizontal beam or other structural member 31 by addressing the clamping device to the beam and hooking the jaws 27, 28 over it.When the operator then simply pulls the foot of the ladder (not shown awayfromthe beam sothatthe reaction between the latter and the arms 25,26 causes the shape of the parallogram linkages to change, the arms 15 and 16 rise until, as shown in Figure 2, their claw ends 18, 19 engage around the underside of the beam 31 so that the grip of the clamping device upon the beam is complete. When the ladder is now used, any tendency of its foot to slip further away from the beam only tightens the grip of the clamping device.

To disconnect the device from the beam, the foot of the ladder must be brought horizontally closer until arms 15, 16 return to the position of Figure 1 in the reverse of the sequence just described, after which the foot of the ladder may be moved a little closer still so as to unhook claws 27, 28 from the beam, after which the operator may pivot the ladder backwards about its point of contact with the ground, to lift it clear of the beam 31 and so of the structure of which that beam is a part.

The principal difference of the clamping device of Figures 3 and 4 from that of Figures 1 and 2 is that it is intended for a ladder with hollow rungs 3. In place of the channel-section framework 5, two parallel cheek plates 40 perform the same function as the flanges 7 but are held in place relative to themselves and to the ladder by two long bolts 41,42 which pass through the hollow interiors of adjacent rungs of the ladder. Also, in place of the cross member 24 which formed part of the link in Figure 1, now the equivaient member 43 joins the arms 15, 16.

Figures 1 and 2 show engagement between the base 6 of the device and the exterior of the rungs 3, and Figures 3 and 4 show engagement by means of bolts 41,42 passing down the middle of hollow rungs. Another alternative means of engagement, less dependent on the rungs, would be to attach the side members (e.g. 7,40) of the device directly -- by clamps, for instance-to the stiles of the ladder.

It will be apparent that the illustrated geometry will in practice enable the clamping device to grip beams not just of one size but of a useful range of sizes, change of setting of the axes 12, 17,21 and 20 in the range of holes 9,30 only being necessary to accommodate a substantial change in beam size.

Claims (8)

1. A clamping device comprising: a base member, defining first and second pivot axes, separated from but parallel to each other; first and second arm members mounted to pivot about the first and second axes respectively; a link, pivotally connected to the first and second arm members at third and fourth pivot axes respectively, so that the four pivot axes lie at the vertices of a parallelogram linkage; a first claw member associated with the first arm member, and a second claw member associated with the second arm member, whereby as the parallelogram linkage changes shape to reduce or increase the distance between the parallel first and second arm members, the two claw members either approach whereby they may grip an object lying within, or open whereby such an object may be released.

2. A clamping device according to Claim 1 in which at least one of the jaw members is angled whereby movement of the linkage to increase or reduce the distance between the arm members is reflected in a magnified relative movement of the tips of the claws.

3. A clamping device according to Claim 1 in which one of the claw members is fixed to the link.

4. A clamping device according to Claim 1 in which the first arm member comprises two separate arms, both pivotted on the first axis but at points spaced apart along that axis, and in which the second arm member also comprises two separate arms in a similar arrangement relative to the second axis, and in which the two pairs of first and second arms each support a pair ofjaws which move in synchronism with each other to grip or release an object.

5. A gripping device according to Claim 1 in which the base member comprises a framework adapted for attachment to a ladder.

6. A clamping device according to Claim 5 in which the framework includes means to grip the stiles of a ladder.

7. A clamping device according to Claim 5 in which the framework includes clamps to grip the outer surface of a rung of the ladder.

8. A clamping device according to Claim 5 in which the framework includes rod-like members to pass down the middle of a hollow rung of a ladder.