GB2204263A

GB2204263A - A clamp

Info

Publication number: GB2204263A
Application number: GB08808188A
Authority: GB
Inventors: Laurence John Potter
Original assignee: RHOMBUS TOOLS Ltd
Current assignee: RHOMBUS TOOLS Ltd
Priority date: 1987-04-29
Filing date: 1988-04-08
Publication date: 1988-11-09
Anticipated expiration: 2008-04-08
Also published as: JPS63312076A; GB2204263B; DE3813342A1; DE3813342C2; GB8808188D0; GB8710128D0

Description

2 G 111 d', 9 C 3 2 -g,, ji, A CLAMP This invention relates to a clamp and

is particularly concerned with a clamp of the type which comprises a movable arm provided with a jaw and mounted on a spine. Usually, with clamps of this type, a fixed jaw is provided on the spine.

The applicant has previously proposed a clamp of this type which comprises a first member slidably mounted on the spine, a second member pivotally mounted on the first member and provided with a jaw, and a screw member for rotating the second member relative to the first member in order to grip a workpiece. With this previously proposed clamp, by operating the screw member it is possible to obtain a very high gripping force on a workpiece. However, operation of a screw member is inevitably slow and there are situations where it is required to operate a clamp quickly.

It is an object of this invention to provide an improved clamp in which the second member can be rotated relative to the first member quickly.

According to this invention, there is provided a clamp comprising a spine, a first member slidably mounted on the spine, a second member pivotally connected to the first member and provided with a jaw, and a device for rotating the second member relative to the first member in order to grip a workpiece, in use, the first member, the second member and the rotating device forming a movable arm, wherein the rotating device comprises a link having one end pivotally connected to one of the first and second members, a lever pivotally connected to the other of said first and second members, and'means interconnecting the lever 2 to the other end of the link so that displacement of the lever causes rotation of the second member relative to the first member.

With the clamp of this invention, the movable arm is slid along the spine so that the jaw lightly engages a workpiece. The workpiece can then be gripped firmly and quickly by operating the lever.

Preferably, the means interconnecting the lever and the link is a circular bearing member mounted eccentrically on the pivot connecting the lever to said other of the first and second members and being received in a circular aperture in said other end of the link.

The provision of a circular bearing member mounted eccentrically on a pivot pin provides a strong and compact interconnection between the link and the lever.

Preferably, the pivotal connection between the first and second members is located between the spine and the jaw, and conveniently the rotating device is located on the opposite side of the spine from the jaw.

Advantageously. the first member is provided with a pair of friction pads for gripping the spine.

The spine may be provided with a fixed jaw or a second movable arm may be provided on the spine.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is plan view of a f irst clamp embodying this invention; 3 Figure 2 is a cross-section on the line 2-2 of Figure 1; Figure 3 is a crosssection on the line 3-3 of Figure 2; Figures 4a to 4c are diagrams showing the varying mechanical advantage which can be achieved with the clamp of Figure 1; and Figure 5 is a plan view of another clamp embodying the present invention.

Referring now to Figure 1, the clamp comprises a movable arm 10 slidingly mounted on a spine 11. one end of the spine 10 is bent and terminates with a fixed jaw 12. The movable arm 10 carries a movable jaw 13 which faces the fixed jaw 12. A screw 14 engages the other end of spine 11 in order to prevent the arm 10 from being accidentally disengaged from spine 11. As shown in Figure 2, the spine 11 is provided with a pair of curved recesses which result in the spine 11 have a strong but lightweight construction.

Referring back to Figure 1. the movable arm 10 comprises a first member 16 slidingly mounted on the spine 11. a second member 17 pivotally connected by a rivet 18 to the first member 16, and a device 19. which will be described in more detail below. for rotating the second member 17 relative to the first member 16.

The pivotal connection between the first and second members is located between the spine 11 and the jaw 13.

and the rotating device is located on the opposite side of the spine from the jaw 13.

Referring to Figures 2 and 3. the first member 16 comprises a pair of plates 20 and 21 and a pair of friction pads 22 and 23. each of which has a hexagonal cross section. The plates 20 and 21 are held together 4 by a pair of rivets passing respectively through pads 22 and 23. The pads 22 and 23 engage opposite edges of spine 11 and are spaced from each other along the length of spine 11. A leaf spring 24 is attached to pad 22 by a screw 25. The free end of the spring 24 engages an edge of the spine 11 and functions to keep pads 22 and 23 in f irm engagement with the spine 11, with the movable jaw 13 being biased towards fixed jaw 12.

The second member 17 comprises a pair of plates 26 and 27 which are held together at one end by a rivet 28 which passes through the movable jaw 13. The rivet 28 is provided with internal shoulders, not shown.

which keep the sides of jaw 13 spaced f rom the inner surfaces of plates 26 and 27. The rivet 18 passes through aligned apertures in plates 20, 21, 26, and 27. As may be observed in Figures 2 and 3 the rivet 18 is located between spine 11 and movable jaw 13.

The rotating device 19 comprises a link 30 and a lever 31. The link.30 is pivotally connected to the second member 17 by a pivot pin 32 which is secured to the two plates 26 and 27. The lever 31 is pivotally connected to the first member 16 by a pivot pin 33 which is secured to the two plates 20 and 21. The lever 31 is formed from a single piece of metal bent so as to have a generally wU0 shaped cross section providing two lateral webs 34 and 35. In the vicinity of pivot pin 33, the lateral webs 34 and 35 are located inside plates 20 and 21. The link 30 and lever 31 are connected together by a circular bearing member 36 which is mounted eccentrically on pivot pin 33 and secured to the lever 31 so as to move therewith. The bearing member 36 is received in a circular aperture formed in the end of link 30 remote from pivot pin 32.

The bearing member 36 has approximately the same width as link 30. Thus, rotation of lever 31 causes rotation of the second member 17 relative to the first member 16 as the bearing member 36 moves eccentrically around pivot pin 33.

In order to restrain rotation of lever 31, there, is provided a ratchet mechanism comprising a trigger member 40 pivotally mounted on the lever 31 and having a pawl 41 which engages ratchet teeth 42 formed on the link 30. The pawl 41 is biased into engagement with the teeth 42 by a spring 43.

In operation, the movable arm 10 is slid along the spine 11 until the jaws 12 and 13 lightly engage a workpiece. The lever 31 is then rotated anticlockwise.

as viewed in the drawings, so as to cause the first member 17 to rotate relative to the second member 16 around rivet 18. This causes the workpiece to be gripped between the jaws 12 and 13 and the pads 22 and 23 to lock onto spine 11. The gripping force is controlled by the final position of the lever 31.

In order to release the workpiece the trigger 40 is operated so as to release the pawl 41 from the teeth 42. The lever 41 may then be rotated clockwise thereby relieving the gripping force on the workpiece and the movable arm 11 may then be slid away from the workpiece.

The leaf spring 24 ensures that there is no backlash to be taken up during initial rotation of the lever 31 and also prevents the movable arm 10 from sliding along the spine ll.under its own weight.

As previously mentioned, the rotating device 19 is located on the opposite side of the spine 11 f rom the jaw 13. This provides the advantage that the clamp 6 can be used conveniently even where there is limited space in the vicinity of the workpiece and without danger to an operator in the case of a hot workpiece.

However, it is within the scope of the present invention to locate the rotating device 19 on the same side of the spine 11 as the movable jaw 13.

Although a ratchet mechanism provides a particularly attractive way of restraining rotation of the lever 31, it would be possible to use a simpler mechanism. For example, the lever 31 could be restrained by providing friction between it and the second member 16 or link 30.

The arrangement of link 30, lever 31, pivot pin 33, and bearing member 36 for rotating the second member 17 provides a high and variable mechanical advantage as will be explained with reference to Figures 4(a) to 4(c), which show different relative positions of the link 30 and the lever 31 as the lever moves angularly.

When displacing the lever 31, the line of force exerted by the operator will be approximately along arrow F which is midway along the lever. Consequently, the mechanical advantage will be a/b. where a is the distance between the arrow F and the centre of pivot pin 33, and b is the length of the line extending from the centre of pivot pin 33 at right angles to a line passing through the pivot pin 32 and the centre of bearing member 36.

Figure 4(a) shows the position of the lever 31 prior to anticlockwise rotation and Figure 4(b) shows the relative position of the link 30 and lever 31 which 7 gives the lowest mechanical advantage. AS may be observed by comparing Figures 4(b) and (c), the mechanical advantage increases progressively as the lever 31 is rotated anticlockwise from the position shown in Figure 4(b). The mechanical advantage approaches infinity when the centre of pins 32, 33 and bearing member 36 are aligned, namely as b approaches zero. Thus. by appropriate positioning of the movable arm 10 prior to the operating lever 31, a very high gripping force may be achieved.

AS stated above, when gripping a workpiece. the pads 22 and 23 lock onto the spine 11. The ability of the movable arm 10 to grip the spine 11 with sufficient force depends upon the correct spacing of the pads 22 and 23. The force exerted on the jaw 13 by a workpiece both rotates the movable arm about pad 23 and produces a tendency for the movable -arm 10 to slide away from the fixed jaw 12. It can be shown that the movable arm will lock onto the spine 11 with sufficient force to overcome the tendency to slide, providing the following condition is fulfilled:

y/x 2f where x is the distance between the movable jaw and the spine, y is the separation between the friction pads in the direction of the spine axis, and f is the coefficient of friction between the pads and the spine. For satisfactory operation of the clamp, this condition should be fulfilled.

The clamp shown- in Figure 1 may also be used for performing a jacking operation on two workpieces. In order to achieve this, the screw 14 is removed, the movable arm 10 is removed from the spine 11 and rotated 8 through 1800 about an axis perpendicular to the spine 11, and then replaced in position. The outer surface Or 12a of the jaw 12 is then made to engage one workpiece and the jaw 13 engages another workpiece. The lever 31 is then operated to achieve a desired jacking force between the two workpieces.

Another embodiment of the present invention is shown in Figure 5. In this embodiment, a pair of movable arms 109, 110, each of which is identical to the movable arm 10. are slidingly mounted on a straight spine 111. In use, the two arms 109 and 110 are positioned so that their respective jaws lightly engage a workpiece disposed between the arms, and then the lever of one of the arms is operated so that the workpiece is gripped with a desired clamping force.

9

Claims

1 A clamp comprising a spine, a first member slidably mounted on the spine, a second member pivotally connected to the first member and provided with a jaw, and a device for rotating the second member relative to the first member in order to grip a workpiece, in use, the first member. the second member and the rotating device forming a movable arm, wherein the rotating device comprises a link having one end pivotally connected to one of the first and second members, a lever pivotally connected to the other of said first and second members, and means interconnecting the lever to the other end of the link so that displacement of the lever causes rotation of the second member relative to the first member.

2. A clamp as claimed in claim 1. wherein the means interconnecting the lever and the link is a circular bearing member mounted eccentrically on the pivot connecting the lever to said other of the first and second members and being received in a circular aperture in said other end of the link.

3. A clamp as claimed in claim 1 or claim 2, wherein the lever can be restrained against displacement by means of a ratchet and pawl arrangement.

4. A clamp as claimed in claim 3,, wherein a pawl provided on the lever is biased into engagement with ratchet teeth on the link.

5. A clamp as claimed in claim 4, wherein a trigger member is pivotally mounted on the lever, the trigger member defining said pawl which is spring biased into said engagement with the ratchet teeth.

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6. A clamp as claimed in any one of the preceding claims, wherein the pivotal connection between the first and second members is located between the spine and the jaw.

7. A clamp as claimed in any one of the preceding claims, wherein the rotating device is located on the opposite side of the spine from the jaw.

8. A clamp as claimed in any one of the preceding claims, wherein the first member is provided with a pair of friction pads for gripping the spine.

9. A clamp as claimed in any one of the preceding claims, wherein the spine is provided with a fixed jaw facing the jaw on said second member.

10. A clamp as claimed in any one of claims 1 to 8, wherein a second movable arm is provided on the spine.

11. A clamp as claimed in any one of the preceding claims, wherein said link is pivotally connected at its said one end to the second member and said lever is pivotally connected to the first member.

12. A clamp substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Published 1988 at The Patent Office, State House, 66/71 High Holbori-4 London WClR 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.