GB1567770A - Apparatus for clamping - Google Patents

Description

(54) APPARATUS FOR CLAMPING (71) We, LE BRONZE INDUSTRIEL RENE LOISEAU, a French body corporate of 49 rue de Paris, 93001 Bobigny, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to apparatus for bringing about from a common fixed support clamping contact of two opposed elements on a body. It is more particularly applicable to resistance-welding tongs, in which two electrodes are applied with clamping on both sides of parts to be joined together.

In assembly lines use is commonly made of automatic welding machines which assure the automatic movement and operation of the welding tongs, a set-up which enables working at very high rates and improvement in the working conditions.

When use is made of tongs, the two arms of which move simultaneously and symmetrically under the action of common driving means, for example a jack, it is necessary that the relative positions of the welding tongs and the parts to be joined together are extremely accurate. Indeed, if the parts to be joined together are not appropriately centered between the two electrodes, a first electrode will come into contact with the parts and continue its movement until the second electrode is applied to the parts which will thus undergo deformation. In the event that the resistance to the deformation of the parts to be joined together is greater than the force driving the tongs, closure of the electrodes could not take place.

The accurate centering of the parts to be joined together involves appreciable waste of time and necessitates constant supervision of the settings.

An object of the present invention is to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided a clamping apparatus comprising a fixed support, two clamping members each carried by a movable arm on said support and a fluid-operated jack for controlling movement towards one another of said clamping members, a first one of said arms being fixedly connected with a cylinder of said jack, said first arm and said cylinder forming a first unit movable relative to said support, the second arm being operatively connected with a piston of said jack, said second arm and said piston forming a second unit movable relative to said support, and said first and second units having a common degree of freedom relative to said support in the plane of said movement towards one another of the clamping members, The two opposed members are brought from a fixed common support into clamping contact on a body intercepting a line of mutual approach of said member, the two members having a common degree of freedom in said axis of mutual approach, with respect to said fixed support, whilst said two members are brought closer to one another from opposite directions and are pressed on to said body.

In this way, when one of the clamping members comes into contact with the body, it comes to rest, while the other member continues to draw nearer, and, when the clamping takes place, there is balancing of the forces applied respectively to each clamping member.

Preferably, the first and second units are moved by translation; alternatively, the first and second units are moved by pivoting about a common axis.

Preferably, the clamping members are welding electrodes.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a diagram explanatory of the method according to the invention; Fig. 2 depicts an apparatus, with some parts removed, according to a first embodiment of the invention; and Fig. 3 depicts an apparatus, with some parts removed, according to a second embodiment of the invention.

Referring to the drawings, Fig. 1 shows two clamping members symbolized by two points Si and S2. The clamping members are brought from a fixedly common support symbolized by a point 0, into clamping contact on a body symbolized by a point P.

The clamping members Si and S2 move along a circular arc C by pivoting about the point 0 and thus allows the clamping members S1 and S2 a common degree of freedom relative to the fixed support 0, along the line in which they draw nearer together, i.e., along the circular arc C, whilst they are brought closer to one another from opposite directions and are pressed on to the body P.

In Fig. 1, the points Si and S2 represent a mean position of the members at a given instant in the course of their mutual approach, i.e., for a given value of angle W.

The clamping members Si and S2 have a common degree of freedom (pivoting in the plane of the drawing) with respect to the point 0, as indicated by the circular arcs Sll S'1, and S12 Sii2 for the members Si and S2 respectively. This means that the member Si is free to move between S1, and Sili, the element S2 then moving simultaneously in the same direction and through the same distance between S12 and Sill2.

The point Sl 2 represents the mean position of the clamping members Si and S2 when they are in contact with one another.

As they always have a common degree of freedom with respect to the point 0, they are free to move between Sill,2 and Sll,2.

In these circumstances, if the body P is situated between 5111,2 and Sly 2, the first member which comes into contact with the body P, in the present case Si, comes to rest by reason of its degree of freedom, whilst the member S2 continues to draw nearer until contact is made with the body P, on the one hand because the stopping of the member S, corresponds with a movement of the members Si towards Sli, a fact that automatically involves movement of members S2 towards Sol2. and on the other hand because of the reduction of the angle B.

The forces exerted by the members Si and S2 on both sides of the body P are therefore equal and are balanced, a situation which removes any risk of deformation of the bodv P. The members Si and S2 are centred of their own accord on the body P, and the circular arc S'1.2 Slll 2 corresponds to the self-centering travel. Any body situated at any point between S1,2 and Sill,2 could be clamped between the members Si and S2 without being deformed.

In Fig. 2 there is shown apparatus for putting the above described method into practice.

The apparatus of Fig. 2 includes a fixed support 1, two clamping members 2 and 3 constitute by welding electrodes, carried respectively by an arm 4 and an arm 5 movable with respect to the support 1, and a control jack 6.

The arm 4 is fixedly connected to the cylinder 7 of the jack 6 with which it forms a unit (P7) movable with respect to the fixed support 1. The arm 5 is fixedly connected to a rod 8 of a piston 9 of the jack 6, through the intermediary of a link 10.

The arm 5, the link 10, the rod 8 and the piston 9 form a unit (5-8-9-10) movable with respect to the fixed support 1. The units (P7) and (5-8-9-10) can be moved by pivoting about a common pivot spindle 11 mounted on the fixed support 1.

The arm 4 and the arm 5 are each connected through a strut 12 and 13, respectively, to a hingle-pin 14 common to the struts 12 and 13. The hinge-pin 14 can move with play in an oblong slot 15 located in the fixed support 1. The slot has a variable width, which increases in the direction away from the base 16 of the fixed support 1. The reference numerals 17-18 denote inlet pipes for a fluid for controlling the jack 6.

The operation of the apparatus is the following: when a fluid under pressure is supplied into the chamber 19 of the jack 6, the piston 9 moves downwards, while the cylinder 7 rises, this involving movement of the electrodes 2 and 3 closer together. The pivotal movement of one of the units (P7) or (5--100--8-9) about the spindle 11 involves a pivotal movement to the same extend of the other unit (5-10-8-9) or (4-7) through the intermediary of the links 12 and 13. At the same time, the pin 14 common to the two links 12 and 13 is moved lengthwise of the slot 15 towards the wider part thereof. The play between the pin 14 and the slot 15 allows the selfcentering of the electrodes 2 and 3. If one of the electrodes 2 or 3 gets into contact with a part to be joined up, it comes to rest, while the other electrode continues to be moved on the one hand under the action of the jack 6, and on the other hand by transverse movement of the pin 14 in the slot 15. The degree of freedom, or selfcentering travel of the electrodes 2 and 3, is a function of the play of the pin 14 in the slot 15. In the embodiment described, the degree of freedom is the more important the nearer the electrodes draw to one another. Of course. by modification of the dimensions and of the shape of the slot 15, the degree of freedom can be changed as desired.

In Fig. 3 there is shown another embodi ment of an apparatus according to the invention. In this embodiment, the clamping members are moved by translation instead of being moved by pivoting, but the principle remains the same.

The apparatus of Fig. 3 comprises a fixed support 20, two clamping members 21 and 22 constituted by welding electrodes, carried respectively by an arm 23 and an arm 24, movable relative to the support 20, and a control jack 25.

The arm 23 is fastened at one end 26 of a slider 27 mounted in a bore 28 of the fixed support 20 while the other end 29 of the slider 27 is connected by a carrier 30 to the cylinder 31 of the jack 25. The arm 23, the slider 27, the carrier 30 and the cylinder 31 form a first unit (23-27, 30--31) movable relative to the fixed support 20. The arm 24 is mounted on and in the extension of a rod 32 of the piston 33 of the pack 25.

The arm 24, the rod 32 and the piston 33 form a second unit (243233) movable relafive to the fixed support 20. The arm 23 and the arm 24 are moved in parallel directions and the arm 23 as well as the electrode 21 are of such a shape that the ends 211 and 221 of the electrodes 21 and 22 are moved along a common axis 34.

A slider 35 is made fast with the rod of the piston 32 by means of a connecting member 36. The slider is moved in a bore 37 of the fixed support 20, and it prevents rotation of the arm 24.

The slider 27 includes means for resting on the support 20, constituted by the lower face 38 of the end 26 and by the carrier 30.

The slider 35 also includes resting means constituted by the end 39 of the member 36 the position of which on the rod 32 is adjustable.

Means for returning the cylinder 31 are constituted by a spring 40 mounted between a stud 41 on the cylinder 31 and a stud 42 on the fixed support 20. The reference numerals 43 and 44 denote inlet pipes for a fluid for controlling the jack 25.

The operation of the apparatus is the following: When a control fluid is introduced into the chamber 45 of the jack 25, the piston moves downwards taking along with it the stop 39 which comes into contact with the support 20 and comes to rest. The cylinder 31 is driven upwards until the carrier 30 comes into contact with the support 20, the result of this being to stretch the spring 40.

The electrodes 21 and 22 are then separated from one another to the maximum extent.

When the control fluid is introduced into the chamber 46 of the jack 25, the arm 24 is raised while the spring 40 pulls the cylinder 31 and hence the arm 23 downwards.

If one of the electrodes 21 or 22 gets into contact with a part (not shown), it comes to rest, and the movement of the other electrode is double until it comes in its turn into contact with the part.

When the stop 39 is in contact with the support 20, the stop 38 is no longer there, the maximum distance between the stop 38 and the support 20 depending on the length of the slider 27 by reason of the carrier 30 coming to rest on the support 20, this distance corresponding to the degree of freedom or self-centering travel which may thus be modified by selecting a slider 27 of different length.

The structure of the arms 4, 5 (Fig. 2) and of the arms 23, 24 (Fig. 3) has not been described in detail, as it is well known to those skilled in the art. Therefore, the arms include cooling circuits and means for connection with electric current supply cables which have not been shown for reasons of simplification. Likewise, it may be advantageous to provide damping means (not shown) for the members which come to rest on the support 20 of the apparatus of Fig.

3, such as the stops 38, 39 or the carrier 30 (Fig. 3). These damping means may be constituted by a rubber washer or the like.

For the apparatus of Fig. 2, there may also be provided damping means (not shown) between the pin 14 and the edges of the slot 15.

In a modification, instead of using singlestroke jackets such as the jacks 6 and 25, use may be made of jacks of double-stroke, namely, an approach stroke and a working stroke.

The apparatus for clamping as hereinbefore described is advantageous over known clamping apparatuses in that it allows self-centering of tongs on parts to be welded. Therefore, the slight variations in the relative positioning of the tongs and the parts to be welded have no influence on the quality of the welding and does not risk giving rise to deformation of the parts.

WHAT WE CLAIM IS: 1. Clamping apparatus comprising a fixed support, two clamping members each carried by a movable arm on said support, and a fluid-operated jack for controlling movement towards one another of said clamping members, a first one of said arms being fixedly connected with a cylinder of said jack, said first arm and said cylinder forming a first unit movable relative to said support, the second arm being operatively connected with a piston of said jack, said second arm and said piston forming a second unit movable relative to said support, and said first and second units having a common degree of freedom relative to said support in the plane of said movement towards one another of the clamping members.

2. Apparatus according to claim 1 in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. ment of an apparatus according to the invention. In this embodiment, the clamping members are moved by translation instead of being moved by pivoting, but the principle remains the same. The apparatus of Fig. 3 comprises a fixed support 20, two clamping members 21 and 22 constituted by welding electrodes, carried respectively by an arm 23 and an arm 24, movable relative to the support 20, and a control jack 25. The arm 23 is fastened at one end 26 of a slider 27 mounted in a bore 28 of the fixed support 20 while the other end 29 of the slider 27 is connected by a carrier 30 to the cylinder 31 of the jack 25. The arm 23, the slider 27, the carrier 30 and the cylinder 31 form a first unit (23-27, 30--31) movable relative to the fixed support 20. The arm 24 is mounted on and in the extension of a rod 32 of the piston 33 of the pack 25. The arm 24, the rod 32 and the piston 33 form a second unit (243233) movable relafive to the fixed support 20. The arm 23 and the arm 24 are moved in parallel directions and the arm 23 as well as the electrode 21 are of such a shape that the ends 211 and 221 of the electrodes 21 and 22 are moved along a common axis 34. A slider 35 is made fast with the rod of the piston 32 by means of a connecting member 36. The slider is moved in a bore 37 of the fixed support 20, and it prevents rotation of the arm 24. The slider 27 includes means for resting on the support 20, constituted by the lower face 38 of the end 26 and by the carrier 30. The slider 35 also includes resting means constituted by the end 39 of the member 36 the position of which on the rod 32 is adjustable. Means for returning the cylinder 31 are constituted by a spring 40 mounted between a stud 41 on the cylinder 31 and a stud 42 on the fixed support 20. The reference numerals 43 and 44 denote inlet pipes for a fluid for controlling the jack 25. The operation of the apparatus is the following: When a control fluid is introduced into the chamber 45 of the jack 25, the piston moves downwards taking along with it the stop 39 which comes into contact with the support 20 and comes to rest. The cylinder 31 is driven upwards until the carrier 30 comes into contact with the support 20, the result of this being to stretch the spring 40. The electrodes 21 and 22 are then separated from one another to the maximum extent. When the control fluid is introduced into the chamber 46 of the jack 25, the arm 24 is raised while the spring 40 pulls the cylinder 31 and hence the arm 23 downwards. If one of the electrodes 21 or 22 gets into contact with a part (not shown), it comes to rest, and the movement of the other electrode is double until it comes in its turn into contact with the part. When the stop 39 is in contact with the support 20, the stop 38 is no longer there, the maximum distance between the stop 38 and the support 20 depending on the length of the slider 27 by reason of the carrier 30 coming to rest on the support 20, this distance corresponding to the degree of freedom or self-centering travel which may thus be modified by selecting a slider 27 of different length. The structure of the arms 4, 5 (Fig. 2) and of the arms 23, 24 (Fig. 3) has not been described in detail, as it is well known to those skilled in the art. Therefore, the arms include cooling circuits and means for connection with electric current supply cables which have not been shown for reasons of simplification. Likewise, it may be advantageous to provide damping means (not shown) for the members which come to rest on the support 20 of the apparatus of Fig. 3, such as the stops 38, 39 or the carrier 30 (Fig. 3). These damping means may be constituted by a rubber washer or the like. For the apparatus of Fig. 2, there may also be provided damping means (not shown) between the pin 14 and the edges of the slot 15. In a modification, instead of using singlestroke jackets such as the jacks 6 and 25, use may be made of jacks of double-stroke, namely, an approach stroke and a working stroke. The apparatus for clamping as hereinbefore described is advantageous over known clamping apparatuses in that it allows self-centering of tongs on parts to be welded. Therefore, the slight variations in the relative positioning of the tongs and the parts to be welded have no influence on the quality of the welding and does not risk giving rise to deformation of the parts. WHAT WE CLAIM IS:

1. Clamping apparatus comprising a fixed support, two clamping members each carried by a movable arm on said support, and a fluid-operated jack for controlling movement towards one another of said clamping members, a first one of said arms being fixedly connected with a cylinder of said jack, said first arm and said cylinder forming a first unit movable relative to said support, the second arm being operatively connected with a piston of said jack, said second arm and said piston forming a second unit movable relative to said support, and said first and second units having a common degree of freedom relative to said support in the plane of said movement towards one another of the clamping members.

2. Apparatus according to claim 1 in

which said first and second units are moved by translation, the first arm being secured to one end of a first slider mounted in a first bore of the fixed support, the other end of said first slider being connected by a carrier to the jack cylinder, the second arm being moounted on and in the extension of the piston rod, said first slider and said piston moving in parallel directions, on one of said arms, or one of the damping members being shaped such that the ends of said clamping members are moved along a common axis, and a second slider fixedly connected to the second unit and moved in a second bore of the fixed support.

3. Apparatus according to claim 2, said first and second slider include means for resting on the fixed support.

4. Apparatus according to claim 3, in which means is provided for returning the jack cylinder towards the fixed support.

5. Apparatus according to claim 1, in which said first and second units are moved by pivoting about a common pivot spindle mounted on the fixed support.

6. Apparatus according to claim 5, in which each arm is connected by at least one strut to a hinge-pin common to said struts, said hinge-pin moving with play in an oblong slot located in said support, the second arm being connected to the piston rod through the intermediary of a link.

7. Apparatus according to claim 6, in which the oblong slot has a variable width, the pin hinging the struts moving towards a wider zone when the clamping members move closer to one another.

8. Apparatus according to any one of claims 1 to 7, in which the clamping members are welding electrodes.

9. Clamping apparatus, substantially as hereinbefore described with reference to Figs. 1 and 2, or Figs. 1 and 3 of the accompanying drawings.