GB2177673A - A mechanical handling clamp - Google Patents

Abstract

A mechanical handling clamp has a pivoted jaw 32 and a co-operating jaw 26. A helical tension spring 50 is connected between the jaw 32 and a lever arrangement 38, such that the lever arrangement 38 and spring 50 provide an over-centre device whereby at one side of the centre location the spring applies a force urging the pivoted jaw 32 in the gripping direction and on the other side of the centre location, the convolutions of the spring close completely so that the spring provides a substantially rigid rod acting between the lever arrangement 38 and the pivotal jaw 32 in the release direction. The over-centre device is actuated manually by a lever attached to a stub axle 44, and in the gripping condition of the device movement of the lever arrangement is limited by a stop 58. <IMAGE>

Description

SPECIFICATION A mechanical handling clamp The present invention relates to clamps used for mechanical handling purposes and especially to lifting clamps, such as those generally referred to as vertical plate lifting clamps. Although the invention will be particularly described with reference to plate lifting, it is to be understood that a clamp in accordance with the invention could be used for any mechanical handling operation where it is required to grip an article.

Mechanical handling clamps are known which comprise a stationary jaw and a co-operating pivoted jaw, having a gripping surface which is eccentric with the pivotal axis, so that the pivoted jaw acts as a cam when the clamp is used to grip an article. Moreover, the arrangement is sometimes such that the caming action produces a wedging effect, whereby any tendency for the article to move out of the jaws results in the application of increased gripping force between the two jaws.

In some clamps of this type, there is a linkage between a shackle which forms part of the clamp and the pivoted jaw so that when the clamp is raised, the pivoted jaw is urged to turn in the clamping direction. It is also known to provide a spring to complement the clamping force.

The pivoted- jaw has to be turned in the opposite direction to the clamping direction (i.e. in the release direction) to release the jaws from the article which has been gripped. This may require the exertion of an appreciable force because of the wedging action of the pivoted jaw against the article. A known mechanical handling clamp utilises a spring acting between the pivoted jaw and a lever and so arranged that within the permitted turning of the lever, the spring passes over-centre so that in one end position it assists the gripping action of the clamp and in the other end position, it releases the pivoted jaw. It will be appreciated however that the releasing force is limited to the force available from the spring.

According to this invention a mechanical handling clamp which has a pivoted jaw and a co-op erating jaw, includes a helical tension spring connected between the pivoted jaw and a lever, the arrangement being such that the lever and spring provide an over-centre arrangement, whereby at one side of the centre location, the spring applies a force urging the pivoted jaw in the gripping direction and on the other side of the centre location, the convolutions of the spring close completely so that it provides a substantially rigid rod acting between the lever and the pivoted jaw in the release direction.

The co-operating jaw is preferably stationary on the clamp, though in some instances, the co-oper ating jaw may itself be a pivoted or sliding jaw.

Preferably the clamp comprises a pair of side plates with the pivoted and co-operating jaws mounted between them, the lever comprising a part mounted between the side plates and having an axle projecting through one of the side plates with an operating lever secured to the axle on the outside of that side plate through which the axle projects, the spring being anchored at one end to the pivoted jaw and at its other end to a point on the part of the lever between the two side plates, but displaced radially from the axle. It is preferred to provide stop means to limit movement of the lever when the spring is on that side of the centre location where it applies force to the pivoted jaw in the gripping direction.

It is further preferred that the pivoted jaw has teeth or serrations on its gripping surface to assist in the gripping action. The co-operating jaw may also have teeth or serrations on its gripping surface.

The spring has as large a mean diameter and wire diameter as can be conveniently provided, giving the size of the clamp itself. This provides a relatively large spring force acting on the pivoted jaw in the gripping direction and ensures the provision of a rod of adequate rigidity, when the spring closes on itself in the release direction of movement.

One construction of a vertical plate lifting clamp in accordance with the invention, will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an elevational view of the clamp with one side plate removed to show the internal construction, the parts being illustrated in an operative or clamping condition, Figure 2 is an end view looking in the direction of arrow II in Figure 1, and Figure 3 is a view similar to Figure 1, but showing the clamp in the open condition.

The clamp illustrated in the drawings is intended for use in the lifting of plates such as sheet steel plates, and is itself of substantial construction, being manufactured principally in metal. The clamp has two side plates 10 and 12, the side plates providing various pivotal mountings as will hereinafter appear, and being spaced apart by spacers such as that shown at 14 in Figure 2. Corresponding slots 16 are formed in the side plates 10 and 12, to provide an opening in which the article to be clamped can be received. In Figure 1, part of a steel plate 18, by fitting the clamp has been attached to the plate 18, by fitting the clamp over one edge of the plate, so that a marginal portion of the plate is received within the slots 16.At the end of the clamp remote from the slots 16, there is an axle 20 provided by a bolt, which passes through the side plates 10 and 12, the bolt being secured in position by a nut 22, and a conventional shackle 24 is pivoted on the axle 20. It will be appreciated, that the clamp can be lifted, in order to lift the article such as the plate 18 which is gripped, by attaching a hook in the shackle 24.

A stationary clamping jaw 26 is secured between the side plates 10 and 12, on a pair of pins 28, and the stationary jaw 26 has a toothed operative gripping edge 30, which projects into the space bounded by the slots 16 in the side plates. Thus, when the edge of an article such as the plate 18 is received in the slots 16, it can be pressed against the toothed edge 30 of the stationary jaw 26.

Co-operating with the stationary jaw 26 is a pivoted or cam jaw 32 which is also located between the side plates 10 and 12, and pivoted on an axle 34 which bridges the side plates. The pivoted jaw 32 has a toothed operative edge 36 for engagement with the opposite surface of the article 18 to that which engages with the toothed surface 30 of the stationary jaw 26. This operative surface 36 of the pivoted jaw 32 is curved, but is eccentric with the pivotal axis 34, so that when the pivoted jaw is turned in an anti-clockwise direction (as seen in the drawings) from the open position illustrated in Figure 3 to the closed position illustrated in Figure 1, its operative surface closes towards the gripping surface of the stationary jaw 26. Eventually, the article 18 is gripped between the two jaws as illustrated in Figure 1.Figure 1 also illustrates the fact that for a range of positions of the pivoted jaw 32, corresponding to a range of thicknesses of the plate-like article which is to be gripped, any tendency of the article 18 to move out of the clamp after it has been gripped - i.e. to move downwardly as seen in Figure 1 relatively to the clamp - will tend to turn the pivoted jaw 32 in the gripping di rection, that is to say the anti-clockwise direction as seen in Figure 1. Consequently, any tendency for the plate 18 to escape from the clamp will only tend to tighten the clamping or wedging action of the cam type pivoted jaw 32.

A lever arrangement 38 is also provided, and this comprises a pair of discs 40 and 42 each having a stub axle 44 journalled in one of the side plates 10 and 12, the two stub axles being coaxial with each other, and there being an anchor pin 46 which bridges the discs 40 and 42 and connects them together. The two discs are located between the side plates 10 and 12 as indicated in Figure 2, and one of the stub axles projects through the side plate 10, and on the outside of that plate carries an actuating lever 48 which is keyed to the stub axle, and includes a hand grip portion, whereby the lever 48 can be turned about the axis provided by the stub axles 44. It will be appreciated, that operating the actuating lever 48 turns the entire assembly of the discs 40 and 42 with their anchor pin 46.

A strong helical tension spring 50 is attached at one end to the anchor pin 46 on the lever arrangement 38, and at its other end is anchored to a tail pin 52 extending across a bifurcated tail portion 54 of the pivoted jaw 32. The arrangement is completed by a stop peg 56 which projects from the disc 42, and a fixed stop 58 projecting from the side plate 10 and aligned with the stop peg 56.

The fully open condition of the clamp is illustrated in Figure 3, where it will be noted, that the lever system 38 has been turned to a position in which the anchor pin 46 is near to the bottom of the clamp, and the jaw 32 is fully open, and in fact entirely outside the space provided by the slots 16.

In this fully open position, the clamp can be fitted over the marginal portion of a plate element 18, and the toothed gripping surface 30 of the stationary jaw 26 brought into engagement with one face of the plate 18. In order to clamp the plate, the lever system 38 is turned by using the actuating lever 48. The lever system is rotated in an anticlockwise direction, and this has the effect of carrying the anchor pin 46 in an upward arc, this motion being transmitted to the jaw 32, which is turned about the pivot 34, to bring the toothed gripping surface 36 of the jaw 32 into engagement with the plate 18.

The arrangement of the lever system and the spring 50 provides an effective over-centre device, so that after the pivoted jaw 32 has engaged with the plate 18, the turning motion of the lever system in the anti-clockwise direction can be continued, at first extending the tension spring 50, and then when the over-centre location has been passed, alLowing some slight contraction of the tension spring. Once the over-centre location has been passed, the tension spring will itself continue the turning motion of the lever system, to bring the peg 56 into engagement with the stop 58, this representing the end position of the lever system in the gripping direction.However, as clearly illustrated in Figure 1, even when a relatively thin plate is being gripped, the convolutions of the tension spring 50, will still be in an open condition, so that the full force of the tension spring acts between the anchor pin 56 (which is then occupying a fixed location) and the tail pin 52 of the pivoted jaw 32.

Consequently, the tension spring 50 applies a force on the pivoted jaw 32, which provides a gripping force acting between the two jaws on the plate 18.

In this condition, the clamp is fully locked on to the plate 18, and the clamp can then be used for lifting the plate.

When it is required to release the clamp from the plate 18, the lever system 38 is turned in the clockwise direction, by using the manipulating lever 48.

Initially, this will simply extend the spring 50, until the over-centre condition is passed. The spring 50 will then tend to close upon itself, and further rotation of the system 38 in the clockwise direction causes the convolutions of the spring 50 to fully close on to each other. When this condition is arrived at, the spring 50 no long acts as a spring, but instead acts as a substantially rigid rod connected between the anchor pin 46 and the tail pin 52. It is the conversion of the spring from a spring into a rod, which forms a very significant feature of the present invention. Once the rod-like condition has been assumed by the spring 50, any further downward motion of the anchor pin 46 is transmitted to the pivoted jaw 32, which is thereby caused to rotate in the clockwise or release direction. Therefore, even if the pivoted jaw 32 has become wedged on to the plate 18, it is possible to apply an appreciable unlocking force to the jaw 32, through the substantially rigid link provided by the spring 50 with its convolutions in the fully closed condition, this condition is illustrated in Figure 3 of the drawings.

Claims (7)

1. A mechanical handling clamp which has a pi voted jaw and a co-operating jaw, comprising a helical tension spring connected between the pivoted jaw and a lever, the arrangement being such that the lever and spring provide an over-centre arrangement, whereby at one side of the centre location, the spring applies a force urging the pivoted jaw in the gripping direction and on the other side of the centre location, the convolutions of the spring close completely so that it provides a substantially rigid rod acting between the lever and the pivoted jaw in the release direction.

2. A clamp as claimed in Claim 1, in which the co-operating jaw is stationary on the clamp.

3. A clamp as claimed in Claim 1 or Claim 2, comprising a pair of side plates with the pivoted and co-operating jaws mounted between them, the lever comprising a part mounted between the side plates and having an axle projecting through one of the side plates with an operating lever secured to the axle on the outside of that side plate through which the axle projects, the spring being anchored at one end to the pivoted jaw and at its other end to a point on the part of the lever between the two side plates, but displaced radially from the axle.

4. A clamp as claimed in Claim 3, in which stop means is provided to limit movement of the lever when the spring is on that side of the centre location where it applies force to the pivotal jaw in the gripping direction.

5. A clamp as claimed in any one of the preceding claims in which at least one of the jaws has teeth or serrations on its gripping surface to assist in the gripping action.

6. A clamp as claimed in any one of the preceding claims in which the spring has as large a mean diameter and wire diameter as can be conveniently provided, given the size of the clamp itself.

7. A mechanical handling clamp constructed and arranged substantially as herein described, with reference to the accompanying drawings.