GB2205058A

GB2205058A - Pallet clamping and locating

Info

Publication number: GB2205058A
Application number: GB08809119A
Authority: GB
Inventors: Arnold Dassler
Original assignee: Schwaebische Huettenwerke Automotive GmbH
Current assignee: Schwaebische Huettenwerke Automotive GmbH
Priority date: 1987-04-16
Filing date: 1988-04-18
Publication date: 1988-11-30
Anticipated expiration: 2008-04-18
Also published as: DD268652A5; GB2205058B; DE3713023C2; IT8820216A0; DE3713023A1; IT1217426B; GB8809119D0; FR2613970B1; FR2613970A1

Description

J._ k, Devices for Clamping Pallets The invention relates to devices for

clamping pallets onto pallet clamping beds.

Pallets are intended for lowering the non-productive periods when machining workpieces, as changing the workpiece will represent an idle period and has to be carried out as quickl y as possible. The function of the pallet clamping bed is therefore to accept the pallet in the machine station in which the workpiece is being machined. Its function is to position and stop the pallet accurately during the cutting process. The pallet clamping bed can then be firmly attached to a rigid machine bed or rotatable on a round bed or a turning machine.

22 f' S n -H U U J However, the precondition for machining workpieces on a pallet will be that accurate positioning will always be maintained. It will be necessary to secure the workpiece with maximum precision in its position at a high repetition accuracy. This means that the exact connection between the pallet and the pallet clamping bed must be subject to stringent specifications. For example, no deformation should occur when the pallet is clamped onto the pallet clamping bed. The pallet must also be held securely.

1 1 R 1 It has previously been proposed to pull the pallet from the top onto the pallet.clamping had via a hydraulic system. Indexing bolts in the pallet clamping bed, which are pushed into holes in the pallet to be clamped, are intended for backlash-free positioning. However, in such cases the problem will arise that expansion in the material resulting from different temperatures has to be considered. For this reason the bolts, generally three of them in a row are shaped as truncated cones but are chamfered at positions at 90 degrees displaced with respect to each other around their circumferences. The resulting free surfaces will in this way provide compensating zones for expansion in the material.

However, this has the disadvantage that it is necessary to use special equipment to carry out the required tests for exact positioning, which should establish whether the pallet has been correctly positioned on the pallet clamping bed. However, such test equipment is elaborate and therefore expensive. Furthermore, the production of the indexing bolts in the known shape is even more expensive.

According to the invention there is provided a device for clamping pallets onto a pallet clamping bed i 1 1 k which has several indexing bolts with a truncated cone shape in at least indexing zones, and in which the bolts can enter holes in the pallet to be clamped or into a component connected to the pallet, so that the pallet is aligned on the pallet clamping bed, the holes being located in a component insert which has dimensions such-that it can be deformed elastically transverse to the direction of insertion in the area of the holes and the shape of the whole circumference of each of the indexing bolts conforming to the shape of the holes.

Because in this case the holes according to the invention are located in a separate inserted component, which on the basis of its elasticity or compliance will allow expansion, e.g. because of temperature increases, it will now be possible to adapt the indexing bolts with their circumferential surfaces exactly to the holes. This means that the indexing bolts may be of simple design and do not have to be machined.in a separate production process.

An enclosed circular shaped contact surface is provided between the indexing bolts and the correspondence holes. This means that it will be possible to carry out tests as to whether the pallets - 4 on the pallet clamping bed are accurately positioned or clamped using considerably simpler methods. This can for example be carried out with suitable equipment, such as e.g. contact maker, a test air supply etc.

The elasticity or compliance of the inserted components transverse to the direction of.insertion or clamping direction can be achieved in different ways.

The component insert may be a disc having recesses, grooves, holes etc. which extend in the direction of insertion, on at least one of its faces.

The recesses, grooves, holes, etc. will produce a weakening in the material so that it will produce the desired compliance, which generally speaking will move only in the lower area. The recesses may be circular slots concentric with respect to the hole. The recesses may extend in from both faces.

The depth of the circular slots is preferably greater than half the thickness of the disc and the circular slots preferably have different diameters, so as to achieve a suitable flexibility.

This arrangement will produce a meandering type or t - concertina type design with a correspondingly high elasticity.

It has been established that it is generally speaking sufficient if two holes with the corresponding indexing bolts are provided for each pallet. Accurate centering will be achieved in this manner.

The pallet clamping bed may have test air supply pass,ages connected to the air passages in the indexing bolts, the openings of which terminate at the face projecting in the hole. It will be possible to establish in a simple way whether the pallet is clamped on the pallet clamping bed with a snug fit and backlash-free by feeding compressed air, to ensure that a seal is produced by the exact fit of the circumference of the indexing bolts in the holes. It will therefore be possible to establish in this manner whether any foreign bodies have penetrated into the holes, which could therefore produce faulty.clamping, since test air would in such a case escape, which can then be determined in a simple manner using the appropriate test equipment.

The pallet or the pallet clamping bed may be provided with clearance behind the component insert to - 6 provide an elastic spring loading effect in the centre section.

Inaccuracies in the tolerances can be compensated in a simple manner by the facility of an elastic spring-loading, as they can be balanced out by the clearance according to the invention. Such inaccuracies in the tolerances can occur for example on the basis of natural wear and tear. By the design according to the invention, it will in such cases also be possible to maintain positional accuracy.

The required clearnace can then be achieved by the appropriate design or seating of the component insert or of the indexing bolts. The edges of the components insert may be supported on a washer, there being a gap between the pallet and the component insert over the remainder of the surface of the insert.

The indexing bolt or bolts may each have a flange of which only the edges are supported on the pallet clamping bed. In this case it will only be necessary to dimension or design the flange such that it too can yield to a limited extent.

To this end, it will for example be possible for the flange and/or the indexing bolts to be provided with recesses in the centre section to provide a degree of elasticity in the clamping direction.

One embodiment of the present invention is described below by way of example only and with reference to thedrawings in which:

Fig. 1 is a longitudinal section through a pallet and a pallet clamping bed with a clamping mechanism according to the invention; and Fig. 2 is a section like Fig. 1, showing a different design of indexing bolt.

A pallet 1 of conventional design is located above a pallet clampingbed 2. The pallet 1 and the pallet clamping bed 2 are basically of the known type, so that they will not be discussed in greater detail below. The same applies to the equipment for pulling the pallet 1 down onto the pallet clamping bed so as to clamp it. To this end the pallet 1 will generally be provided with two longtiudinal T-shaped slots. similar to the T-slot 3 in the top side of the pallet, which is intended for clamping workpieces. A T-shaped strip is slid into the T-slot not shown, which is pulled down by 1 k.

8 - n hydr2ulic cylinder fitted to the pallet c^lamping bed.

the pallet is pulled onto th.e pallet clamping bed 2 in this manner. The accurate positioning is then achieved by tapered holes 4 in the pallet 1, which accept the suitably adapted indexing bolts 5, which have the same cone-shaped tapering. The two cone surfaces are then exactly matched, so that a suitable seal is produced. Generally speaking, two holes 4 spaced apart with the corresponding indexing bolts 5 will be sufficient for each pallet. The depth of each hole 4 is then chosen such that the corresponding indexing bolt 5 does project completely down to the base of the hole 4.

As is evident, the hole 4 is then not placed directly in the pallet 1, but in a separate component insert 6, which again is rigidly fixed into the pallet, e.g. by screws 7. The component insert 6 may be designed as a disc. Ring-shaped slots 8 and 9 on both faces of the disc shaped component insert 6 each project to the inside of the disc. The diameter of the two ring-shaped slots 8 and 9 are different in this case. The depths of the ring slots can in this way be chosen such that each one is more than half of the thickness of the disc. As is evident, this will produce a meandering shaped or concertina type design, in which case it will only be necessary to ensure a 1 suitable distance between ring slots 8 and 9, so that the material is sufficiently weakened. This can for example be achieved by the distance between the two ring slots 8 and 9 not being greater than or not being considerably greater than the thickness of the slots.

Naturally,.it will be possible to introduce even more ring slots if such is necessary. This will depend on the specifications concerned and on the size of the temperature expansions to be expected.

The component insert 6 and/or a flange 10, from which the indexing bolt 5 protrudes, can be provided with a washer 11 or 12 to match or if necessary compensate for any inaccuracies. The appropriate adaptations can be achieved by suitably replacing the washers 11 or 12.

The pallet clamping bed is provided with a test air supply tube 13, which in each case leads to the centering and positioning system which consists of the hole 4 and the indexing bolts via a cross-connection tube 14. The flange 10 and the indexing bolt 5 have an internal air tube 15 of which the front end terminates in the hole 4 in a suitable free chamber 16. The test air is conveyed into the free chamber via the test air Lu6e 13, ii8e9-ponnontion tuOP IQ End tnc 51r tugc 17 to test whether the pallet has been positioned in the correct position and height onto the pallet clamping bed 2. A corresponding pressure head will be used, which can be used as a measure for the exact positioning, if there are no foreign bodies in the hole which prevent the circumferential surface of the indexing bolt 5 forming a snug fit in the hole 4. The indexing bolt 5 is connected to the clamping bed 2 or a separate intermediate member 8 via the connected flange, which generally speaking forms an integral part of the indexing bolt 5, using screws 17, where the intermediate member 18 is rigidly attached to the pallet clamping bed 2.

As is evident from Fig. 1, the washer 11, which is ring-shaped, is only intended to support the outer section of the disc shaped component insert 6. There is a small gap or a clearance on the inside between the back wall of the component insert 6 and the pallet or a spacer washer 19. This means that the facility for flexing to compensate for the tolerance is. available when clamping the pallet 1 onto the pallet clamping bed 2.

The clamping mechanism shown in Fig. 2 is 0 - 11 basically of the same design, so that the same reference symbols have been used for this purpose as in Fig. 1. The main difference exists only in that the spring loading in a kinematic reversal for compensating the tolerance in the clamping direction is achieved by a suitable elasticity or compliance of the indexing bolt 5 with the flange 10. As is evident, the component insert in this case lies essentially flat on its reverse side, to which end a second ring shaped disc has been provided in the inner section of the disc shaped component insert 6. Naturally it will be possible to provide only a single disc instead of two washers 11 and 20 if necessary, and likewise it will also be possible for the component insert 6 to lie with its reverse side directly onto an intermediate section 21 that is rigidly connection to the pallet 1.

The inside of the indexing bolt 5 is partly hollow, in order to achieve the necessary elasticity, which for example is achieved by a suitable sized central hole 22. A ring slot 23 of the appropriate width is also provided in the flange 10. The width and depth of the ring slot 23 is such that there is only a ring-shaped web 24 of relatively low thickness between the indexing bolt 5 and the ring-shaped outer support surface of the flange 10. As is evident, there is a - 12 clearance between a ring-shaped spacer washer 25 under the indexing bolt 5 and the disc referred to above, so th,at the appropriate spring loading is provided. The spacer washer 25 in Fig. 2 and the spacer washer 19 in Fig. 1 also function as stops to limit the play in the spring loading. It will therefore be possible to absorb any expansions in the material without any problem as a result of the deformability of the disc 6 because of the ring slots 8 and 9.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

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Claims

A device for clamping pallets onto a pallet clamping bed which has several indexing bolts with a truncated cone shape in at least indexing zones, and in which the bolts can enter holes in the pallet to be clamped or into a component connected to the pallet, so that the pallet is aligned on the pallet clamping bed, the holes being located in a component insert which has dimensions such that it can be deformed elastically transverse to the direction of insertion in the area of the holes and the shape of the whole circumference of each of the indexing bolts conforming to the shape of the holes.
2. A device according to claim.1, wherein the component insert is designed as a disc, which has recesses, grooves or holes at least on one of its faces, which extend in the direction of insertion.
3. A device according to claim 2, wherein the recesses, grooves or holes are circular slots concentric with respect to the hole.

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4. A device according to claim 2 or 3, wherein the recesses, grooves or holes extend in from both faces of t.he disc.
5. A device according to claim 3 or 4, wherein the depth of each of the slots is greater than half the thickness of the disc and the slots have different diameters.
6. A device according to any of claims 1 to 5, wherein each pallet is provided with two holes for receiving indexing bolts and which are spaced apart.
7. A device according to any of claims 1 to 6, wherein the pallet clamping bed is provided with air supply pasages, which are linked to air passages in the indexing bolts, the openings of which terminate on the face of the bolts which project into the holes.
8. A device according to any of claims 1 to 7, wherein the pallet or the pallet clamping bed is provided with clearance behind the component insert to provide an elastic spring loading in the centre section of the component insert.
9. A device according to claim 8, wherein the edges of 1 the component insert are supported on a washer there being a gap between the pallet and the component insert over the remainder of the surface of the insert.
10. A device accoring to claim 8, wherein the indexing bolts each have a flange of which only the edge section is supported on.the pallet clamping bed.
11. A device according to claim 10, wherein the flange and/or the indexing bolts is provided with recesses in the centre section to provide a degree of elasticity in the clamping direction.
12. A device according to claim 11, wherein the indexing bolt is connected to the edge section of flange via a ring shaped web section of the flange.
13. A device according to claim 8, wherein a spacer washer is provided spaced behind the component insert or the indexing bolt to function as a stop or travel limit.
14._ A device substantially as described above_with reference to the accompanying drawings.
15. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not 4 within the scope of or relating to the same invention as any of the preceding claims.

Published 1988 at The Patent Office, Ltate House, 6671 I-Tigh Holborn. London WC1F. 4TP. Further copies may be obtained from The latent office, SaJes Branch, St Mary Cray, Orpington. Kent BIR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray, Kent. Con. 1/87.