WO1992017311A1

WO1992017311A1 - Integrated double drive cylinder

Info

Publication number: WO1992017311A1
Application number: PCT/NL1992/000063
Authority: WO
Inventors: Marinus Willem Nugteren; Horst Kaldowski
Original assignee: Machinefabriek Sempress B.V.
Priority date: 1991-04-05
Filing date: 1992-04-03
Publication date: 1992-10-15
Also published as: NL9100595A; DE9215263U1

Abstract

The invention relates to a pneumatic drive cylinder for a sport welding electrode, comprising a working cylinder. In order to increase the controllability of the drive cylinder the working cylinder is arranged to cause the spot welding electrode to move within a work region with a limited length, and a transport cylinder is arranged for causing the working cylinder to move from a rest position to a work region. The first part of the stroke length can thus be covered at a higher speed and the force with which the spot welding electrode presses onto the workpiece can be varied, whereby the cycle time can be shortened. According to a preferred embodiment the transport cylinder encloses the drive cylinder and the drive cylinder forms the piston of the transport cylinder. This results in mass reduction.

Description

INTEGRATED DOUBLE DRIVE CYLINDER

The invention relates to a pneumatic drive cylin¬ der for a spot welding electrode, comprising a working cylinder.

Such pneumatic drive cylinders are generally known.

In these known pneumatic drive cylinders a com¬ plete stroke is performed for each spot welding operation. This means that for each spot weld performed by the spot welding electrode arranged on the piston rod of the pneumatic spot welding cylinder the drive cylinder must move wholly from the retracted starting position to the active position, and after completing the spot welding operation must move back again to the starting position. The stroke of such a pneumatic drive cylinder usually lies in the range between 50 and 100 mm.

This means that at each stroke a considerable amount of compressed air is required, while each stroke also takes a long time duration, which is particularly important in the case of operations which are performed with a short cycle time, for example on a conveyor belt. With respect to the shape of the workpiece to be subjected to a spot welding operation it is often not possible to employ a spot welding cylinder with a smaller stroke. The use of a cylinder with a smaller stroke is on the one hand attractive due to the small amount of com¬ pressed air used and the shorter time duration, while on the other hand due to the shorter stroke length the posi¬ tion and the movement of the piston can also be controlled; the relevant air volume is in any case small. Such a pneumatic drive cylinder is known from

GB-A-1151775 which is provided with a working cylinder which is arranged to cause the spot welding electrode to move within a work region with a limited length, and a transport cylinder for causing the working cylinder to move from a rest position to a work region, wherein the transport cylinder encloses the working cylinder.

As a result of these steps it is possible to make a choice between a stroke with a great length and a stroke with a short length so that a stroke with a great length only has to be performed when the shape of the workpiece so requires.

In this known spot welding cylinder the transport cylinder encloses the working cylinder such that the work¬ ing cylinder forms the piston of the transport cylinder. A very compact construction is thus obtained. In this known cylinder use is made of a single source, wherein air coming directly from the source is always supplied to the transport cylinder at a pressure which corresponds with that of the air source.

The circuit further comprises means to supply air to the spot welding cylinder, wherein this can take place at the same pressure or at a lowered pressure. In the latter case the air is guided for this purpose through a reducing valve.

In this known spot welding cylinder the return movement of both the spot welding cylinder and the trans¬ port cylinder takes place using the pressure of the air source. It is thus not possible in the return movement to comply with the condition that the pressure in the spot welding cylinder is smaller than in the transport cylinder.

Moreover, the spot welding cylinder and the trans- port cylinder cannot be controlled independently of one another during the return movement, so that it is not possible to cause only the spot welding cylinder to return in order to have the spot welding cylinder already in the starting position for a following spot weld, with this known spot welding cylinder a complete return movement must be performed.

The object of the present invention is to provide such a spot welding cylinder wherein the advantages described in the preamble are obtained and wherein it is possible to cause an independent return movement of the spot welding cylinder to take place. This object is achieved through a control device for controlling the supply and discharge of air indepen¬ dently of one another from and to the transport cylinder and the spot welding cylinder.

The integrated spot welding cylinder in low-noise embodiment has a reduced piston speed adapted to this purpose. By now distributing the total stroke length over the stroke length of the transport cylinder and the work stroke of the integrated spot welding cylinder the trans¬ port path can now be covered at optimal and thus high speed, whereby the cycle time is limited.

Since the work stroke of the integrated spot welding cylinder is very short the piston speed can now be geared optimally to the welding process without this essentially affecting the cycle time. During a series of welding cycles the force with which the electrode presses on the workpiece will have to vary. This is achieved by operating pressure variation of the integrated spot welding cylinder. This pressure adjustment can now take place rapidly due to the small stroke volume resulting from the short stroke length which likewise reduces the cycle time.

The integrated embodiment leads to reduction of dimensions and mass which is extremely important for use on rapidly moving welding robots, wherein the mass to be moved, in relation to mass forces, must remain as small as possible, partially with respect to reducing the cycle time.

To increase the controllability of the force exerted by the working cylinder, the control device for controlling the air supply to the pneumatic cylinder is such that the force exerted by the transport cylinder is always greater than the force exerted by the working cylinder. As a result of this step the position of the piston of the transport cylinder is fixed so that the forces created by the working cylinder can be apportioned well; in any case a fixed starting point is assumed. The present invention will subsequently be eluci¬ dated with reference to the annexed drawing, in which: fig. 1 shows a schematic sectional view of a cylinder according to the present invention in the rest position; fig. 2 shows a schematic sectional view of the cylinder depicted in fig. 1 in the position wherein the working cylinder is situated in the rest position and the transport cylinder is situated in its position moved com¬ pletely outward; fig. 3 shows a schematic sectional view of the cylinder depicted in fig. 1 wherein both pistons are si¬ tuated in a position moved wholly outward; and fig.4 shows a schematic perspective view of a second embodiment of the invention. The cylinder shown in fig. 1 is formed by a jacket

1 which is fixed at its rear to a rear flange 2 and on its front to a front flange 3. A fixing eye 5 is fixed to the rear flange 2 by means of screws 4. Sealing between respectively the rear flange 2, the front flange 3 and the jacket 1 takes place by means of 0-rings 6 situated in a groove.

Arranged in the thus formed housing of the trans¬ port cylinder is a piston designated in its entirety by 7. This piston 7 forms the piston of the transport cylinder. Arranged in the rear flange 2 for causing the piston 7 of the transport cylinder to move is a chamber 8 which is connected to a pneumatic line 10 by means of a channel 9. The pneumatic line 10 is fixed to the rear flange 2 by means of a coupling 11. Arranged in similar manner in the front flange 3 is a channel 12 which is in communication with a pneumatic line 13 which is fixed against the front flange 3 by means of a coupling 14. By means of supplying air through the line 10 it is thus possible to change the position of the piston 7 to the right to the position indicated in fig. 2.

The piston 7 is connected to a piston rod 15 which extends through an opening arranged in the front flange 3. A seal is also arranged here so that the chamber to the right of the piston 7 remains sealed relative to the envi¬ ronment.

The construction of the piston 7 will now be further elucidated. The piston 7 is formed by a jacket part 16 that is closed at its front side by a cover 17 and closed at its rear by a plate-like element 18.

Arranged on the inner wall of the jacket 1 to guide the piston 7 are two slide rings 19 which have a small friction coefficient on an outer side. The jacket part 16 itself is not otherwise in contact with the inside of the jacket 1. Arranged in the jacket part 16 for the purpose of sealing is a groove 20 in which a sealing body 21 is arranged. In the piston 7 two cylinder cavities 22, 23 are formed which are respectively closed on their front side by a cover 17 and the middle portion of the jacket part 16, and by the middle portion of the jacket part 16 and the plate-like body 18. Respective cylinder linings 24 and 25 are arranged in both cylinder cavities 22, 23.

Arranged in the head end surface of the cover 17 and the plate-like body 18 is an annular groove 26 and 27 respectively, in which a rubber ring 28, 29 respectively is arranged. Both rings 28, 29 serve as buffer to prevent the cover 17 or the plate-like body touching the front flange 3 or the rear flange 2. This would lead to contact of metal on metal and result in noise nuisance as well as unacceptable shock load.

Pistons 30 and 31 are arranged inside the respec- tive cylinder cavities 22, 23. Both pistons are connected to the piston rod 15. Sealing rings 32 and 33 are respec¬ tively arranged for sealing between the piston 30 and the cylinder lining 24, and between the piston 31 and the cylinder lining 25. An O-ring 34 is arranged for sealing of the piston rod 15 against the cover 17. Finally, two ta¬ rings 35 are arranged for sealing the thin portion of the piston rod 15 relative to the jacket part 16.

To make the pistons 30 and 31 move outward air is supplied via a pneumatic line 36 which debouches onto the rear flange 2 and which is fixed thereto, and which line 36 is connected to a channel 37. The channel 37 is connected to an eccentrically arranged pipe 38 extending parallel to the piston rod 15. This pipe 38 extends to a cavity 39 arranged in the jacket part 16, this along a length which varies with the movement of the piston 7. The pipe 38 extends through the plate-like body 18 and is sealed against it. It is thus possible to supply air to the cavity 39 irrespective of the position of the piston 7.

The cavity 39 is connected by means of a channel 40 to the left-hand side of the cylinder cavity 23. In similar manner the cavity 23 is connected with a channel not shown in the drawing to the cavity 24 on the left-hand side of the piston 30. By thus supplying air via the chan¬ nel 36 the pistons 30, 31 will move to the right relative to the piston 7. The spaces on the other side of the pis- tons 30, 31 in the cylinder cavities 22, 23 are connected via a channel 36 via a cavity (not shown in the drawing) and a tube arranged therein to a pneumatic line likewise not shown in the drawing. It is thus possible to indepen¬ dently move the position of the respective pistons 30 and 31 in the piston 7.

To make the pistons 30, 31 move back the described corresponding provision, not shown in the drawing, is arranged which makes it possible to supply compressed air to the spaces of the right-hand side of the pistons 30, 31.

The thus embodied drive cylinder is applied for a spot welding electrode, for example in the automobile industry. For welding bodywork when the conveyor belt has placed the bodywork for welding in the desired position, the transport cylinder is energized so that the piston 7 moves to its outermost position. As soon as this position is reached the control of the air supply is controlled such that the piston 7 is fixed at the position reached. By energizing the working cylinder, the piston rod 15 and the spot welding electrode fixed thereon are subsequently moved to the desired position against the workpiece for welding.

The welding current is then supplied and the welding process takes place. Once the welding process is completed the spot welding electrode is moved away from the workpiece by means of the working cylinder. A second embodiment of the invention is shown in fig. 4. In this embodiment, the cylinder construction of which corresponds with that of the preceding embodiments, a control device 41 is arranged on the cylinder, which device controls the supply and discharge of air from and to the transport cylinder and the spot welding cylinder which are integrated in the cylinder jacket 1. A position detecting device 42 is also arranged.

Arranged on the rear flange 2 for fixing the control device 41 is a mounting plate 43 on which are arranged two controllable valves 44, 45. Both valves 44, 45 are connected to air supply and discharge openings in the rear flange 2 by means of channels (not shown in the drawing) arranged in the mounting plate 43. The line 13 likewise leads to the mounting plate 43. The first valve 44 is controlled by two electro¬ magnetic coils 46, 47 and the second valve is controlled by coils 48, 49. A wire 51 extends from each of the coils via a coupling nut 50. These wires are connected to the electrical control device with which the position of the valves 44, 45 can be controlled.

Further arranged for the supply of air is an air supply line 52 is which is connected to the mounting plate 43 by means of a coupling nut 53. An air discharge hose is arranged in corresponding manner on the other side. On the mounting plate a number of sound dampers and filters 54 are further arranged in the central venting ports. The position detecting device 42 comprises a lever

55 which is fixed to the piston rod 15 and which is clamped onto the piston rod 15 by means of a bolt 56. Fixed on the lever 55 is a shaft 57 onto which a metal ring 58 is fixed. Further arranged on one of the screws 4 are two approach switches 59, 60 which generate a signal when the ring 58 is in their vicinity. These approach switches are generally known in the art and operate for instance by means of magnetism.

The approach switches 59, 60 are connected for example by means of wires 61, 62 to the control device for electrically controlling the magnets 46-49 and therefore the valves 44, 45 connected thereto. They are used to detect the position of the transport cylinder. It is for example possible that, when the ring 58 comes into the vicinity of the approach switch 60 during an outgoing movement of the piston rod 15, the air supply to the transport cylinder is cut off so that the movement of this transport cylinder is stopped. Use is made for this purpose of per se known electrical or electrotechnical circuits.

In many cases, for example when the spot welding cylinder is fixed in a robot arm or other automated piece of tooling, the cylinder will be moved to a new position in order to perform a new spot weld. It will not be necessary for this purpose to energize the transport cylinder. A saving of time and compressed air is thus obtained.

Claims

1. Pneumatic drive cylinder for a spot welding electrode, comprising:

- a working cylinder which is arranged to cause the spot welding electrode to move within a work region with a limited length,

- a transport cylinder for causing the working cylinder to move from a rest position to a work region, wherein the transport cylinder encloses the working cylin¬ der and the working cylinder forms the piston of the transport cylinder, characterized by:

- a control device for controlling independently of one another the air supply and discharge from and to the transport cylinder and the spot welding cylinder.

2. Pneumatic drive cylinder as claimed in claim 1, characterized by position detectors for recording the position of the piston of the transport cylinder.

3. Pneumatic drive cylinder as claimed in claim 1 or 2, characterized in that the control device for the air supply and discharge from and to the transport cylinder and the spot welding cylinder is controlled such that the force exerted by the transport cylinder is always greater than the force exerted by the working cylinder.

4. Pneumatic drive cylinder as claimed in claim 2 , characterized in that the position detectors are formed by approach switches which are arranged in accordance with both outermost positions of the stroke of the transport cylinder.

5. Pneumatic drive cylinder as claimed in claim 4, characterized in that the position of the position detec¬ tors is adjustable.

6. Pneumatic drive cylinder as claimed in claim l 2, 3, 4 or 5, characterized in that the working cylinder is provided with a double piston.

7. Pneumatic drive cylinder as claimed in claim 1, 2, 3, 4, 5 or 6, characterized in that the stroke of the transport cylinder is greater than the stroke of the work- ing cylinder.

8. Pneumatic drive cylinder as claimed in any of the foregoing claims, characterized in that the transport cylinder is provided with at least one buffer for impact- free braking of the movement of the piston of the transport cylinder.

9. Pneumatic drive cylinder as claimed in claim 8, characterized in that the piston of the transport cylinder is provided on both sides with buffers embodied in the form of rubber rings.