GB2113578A

GB2113578A - A device for the locking in position of a workpiece support on a machine tool

Info

Publication number: GB2113578A
Application number: GB08234127A
Authority: GB
Inventors: Bernhard Drassdo; Frank Mehnert; Peter Klengel; Horst-Heinrich Stollberg
Original assignee: Werkzeugmaschinenkombinat Fritz Heckert VEB
Current assignee: Werkzeugmaschinenkombinat Fritz Heckert VEB
Priority date: 1981-12-03
Filing date: 1982-11-30
Publication date: 1983-08-10
Also published as: DD205108A1; DE3240662A1; CH657802A5; GB2113578B; DD205108B1; JPS58109237A; FR2517580A1

Abstract

To ensure a rapid, clearance free and simultaneously multi-dimensional, repeatedly accurate locking without the use of additional devices of a workpiece support (1) on a machine tool (10), locking elements (14) are disposed in pairs in clamping units such that at least one pair of locking elements (14) is parallel to and at least one pair of locking elements is at right angles to the forward direction of a workpiece support (1). The locking elements (14) are formed as one- armed levers with round ends and are pivotally disposed on a base plate (12) under the action of springs which connect levers (9) fixed relative to elements (14) such that the opposite ends of elements (14) project obliquely upwardly. The spacing of the ends is so great in this position that the ends contact contact surfaces (4) of locating members (2) with a boss (5) being located between the ends and clamped thereby when the locking elements are moved downwardly to an "in-line" position. <IMAGE>

Description

SPECIFICATION A device for the locking in position of a workpiece support in a machine tool The invention relates to a device for the accurate locking in position of a movable workpiece support in a machine tool.

Widely varying locking devices are at present in use. The East German Patent Specification 122 336 discloses, for example, a device for the locking in position of a workpiece support in a machine tool, in which two index bolts are disposed on the workpiece support and are each inserted in a locking sleeve on the worktable. The free end of the index bolt is formed to be spherical and engages with its greatest diameter in the tolerances of a clearance fit of the respective locking sleeve. As machining must be carried out in this respect with additional coarse positioning cylinders, comparatively high costs are incurred.

The East German Patent Specification 88874 discloses a locking device for a workpiece support unit on a machine tool, in which the index bolt is formed at one end as a thin-wall hollow body in which a pressure medium is disposed. In the case of pressure actuation in the end position of the index bolt in the back support, this generates contact between the shell of the index bolt and the back support.

The index bolt itself is connected directly with the pressure chamber for the bolt movement via a pressure transmission piston. This apparatus, although avoiding the intermediate stage of coarse positioning, as the clearance fit may be maintained coarser, also leads to relatively high costs.

The East German Patent Specification 122 934 discloses a device for the locking in position of a workpiece support, which operates with roll-shaped, horizontally disposed clearance elements which are offset by 90 .

Although this device is constructed without hydraulics, it requires a high degree of mechanical complexity.

The object of the invention is to equip a machine tool with a device for the positional fixing of a workpiece support which enables a reproducible, accurate planar or spatial locking of a movable workpiece support on a machine tool using comparatively simple mechanical means.

The drawbacks illustrated in the description of the known technical solutions suggest that locking may only take place in this respect using additional means, such as hydraulic elements or the like, or only with an increase in the degree of mechanical complexity.

In order to counter these drawbacks, the object of the invention is to provide a device for the locking in position of a workpiece support on a machine tool, in which clamping units are disposed offset by 90 with respect to one another, and enable, without additional elements, a rapid clearance-free and simultaneously multi-dimensional, i.e. taking place in all required directions, repeated accurate locking, in which the locking forces automatically increase to the required level and are maintained constant until release.

According to the invention, in a locking device clamping units are arranged offset by 90 with respect to one another, locking elements are disposed in pairs in clamping units on the machine tool in such a way that at least one pair of locking elements is parallel to and at least one pair of locking elements is at right angles to a forward direction of a workpiece support, the locking elements being forced as one-armed levers whose ends are rounded and being disposed on a base plate of the respective clamping unit under the action of springs in such a way that the opposite ends of the levers project obliquely upwardly and their mutual spacing is greater than the spacing between limit surfaces formed as contact surfaces on a boss secured to the workpiece support, the arrangement being such that when the workpiece support is lowered, the first upwardly extending ends of the locking elements come into contact with the contact surfaces.

Preferably a locating member is embodied with its support arm and the boss which is disposed thereon such that there is a very high spring rate of the locating member in the respective locking direction and only a low spring rate in all the other directions. This enables both a clearance-free and simultaneously multi-dimensional locking of the workpiece in clamping units disposed on the machine tool.

The clamping units preferably comprise respective base plates with contact surfaces disposed internally on two opposite sides.

Two supports acting as pivot supports for the locking elements are respectively externally disposed on the two other opposite sides of the base plates.

Lifting elements, which are respectively connected with the locking elements by means of a bolt and a spacer sleeve to form a unit, are conveniently disposed on both sides of a locking element on a shaft which acts as a pivot shaft for the locking elements. Each such lifting element may include a lever which is rigidly connected at right angles thereto, whose free end is provided with a bore, the respective free ends of two opposite levers of the cams being connected by means of a spring.

An eccentric stop may be disposed in an adjustable and lockable manner on each pivot support in the pivot area of the free end of the respective lifting element.

The rounded ends of the locking elements may also be provided in each case with a roll.

Moreover, the device may include a hydrau lic cylinder-piston unit pivoted to one of the lifting elements in the clamping unit acting in the adjustment direction for the forward and reverse supply of the workpiece support.

The device may advantageously be embodied such that the holding force for locking may be exclusively applied by the lowering movement of the workpiece support, wherein at the final point of the lowering movement, i.e. with the locking elements extended and a pivot angle a = zero, the maximum holding force F is achieved.

As a result of the resilient configuration of the locking contact a small correction movement is also possible in the directions orthogonal to the respective unit within one clamping unit during the locking process.

However, it is also possible to achieve closure of the locking elements in cases in which the total lowering movement of the workpiece support may not be carried out from the required height or may only be carried out with an inadmissible complexity. This may be carried out either by lifting the entire clamping unit or simply by lifting a raisable plate within the clamp fixing unit which is substantially more favourable.

This movement may also be carried out proportionately, i.e. such that the workpiece support travels the smaller path and the clamping unit---or simply the raisable plate within the clamping unit-travels the larger path, which may be carried out by a pistoncylinder unit which is known per se.

The main advantage of the device also lies in that the actuation force is very small in relation to the holding force, this ratio being expressed by the expression: R FB = (2 sina + 4y ~) F.

L In which: F = holding force on locking, FB = actuation force, a = opening or pivot angle of the locking elements, R = radius of the locking elements, L = effective length of the locking elements, = coefficient of friction.

To help understanding of the invention, two specific embodiments thereof will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 shows an outline arrangement of the clamping units on a machine tool, Figure 2 is a section along the line A-A of Fig. 1, and Figure 3 is an outline arrangement of the solution with a raisable plate.

Referring first to Figs. 1 and 2, the lower side of a detachable workpiece support 1 has rigidly fixed thereto three locating members, 2, 2', 2" each of which has a holding arm 8 whose free end is reinforced and is provided on its lower side with a surface 4 from which there projects a boss 5 with contact surfaces 6. The directions, both forwards and backwards, in which the workpiece suport may be moved, are shown by the arrows, 7, 8, 9.

Clamping units 11. 11', 11" corresponding in number to locating locking members 2, 2', 2" are rigidly fixed to the machine tool 10, one of these units being provided for the direction of adjustment 7 and two for the direction of adjustment 8. The clamping units 11, 11', 11" consist in each case of a base plate 12 having a raised edge which is provided on two, internal, opposite sides with contact surfaces 13. Locking elements 14 formed as one-armed levers are pivotably disposed between the contact surfaces 13 on the base plate 12 and have an operating length L and are provided at their ends with a radius R.

The base plate 12 is fastened to the machine tool 10 at its end faces by connecting strips 15. Two supports 16 are rigidly disposed in each case on the lateral surfaces of the base plate 12 and form the pivot supports for the locking elements 14.

Each locking element 14 has a shaft 17.

Beside each locking element 14, at both ends of its shaft, it has a lifting element 18 and a lever 19 which are rigidly connected together at right angles on the axis of the shaft.

Connection of each locking element 14 and respective lifting elements 18 is produced by a spacer sleeve 20 on a bolt 21 extending between the lifting elements. Each lever 19 has at its free end a bore 22. The levers 19 respectively disposed opposite one another, on one side of the base plate 12, are connecte, with a spring 23, engaged in the bores 22.

At the point of intersection of each lifting element 18 with the lever 19 there is provided a bore which receives the shaft 17. Via the shafts 17, the locking elements 14 and the lifting elements 18 with their levers 19 are pivotably connected to the base plate 12 by means of two supports 16.

An eccentric stop 24 is lockably and adjustably disposed on each support 16 in the pivot area of the end of the lifting element 18 which is still free.

The clamping unit 11 acting in the direction of adjustment 7 has the special feature consisting in that a hydraulic cylinder-piston unit 25 is additionally pivoted on one of the unit's lifting elements 18. The locating members 2, 2', 2" may also be retained by means of respective brackets 26.

The embodiment of Fig. 3 is based on the same principle. Three clamping units 31, 31', 31"~only one of which is shown---are each disposed in a respective counter-bore in the machine tool 10 and correspond to the number of locating elements 2, 2', 2". These clamping units 31, 31', 31" have a body 32 which is rigidly connected to a cylinder jacket 33. The body 32 is provided with a rectangular slot 34 in which a raisable plate 35 may be moved up and down. The lifting plate is therefore connected with a cylinder 36.

A support 37 is disposed as a pivot support on the longitudinal sides of the raisable plate 35 for each locking element 14. The locking elements 14 are pivotably mounted on the body 32 in the supports 37 by means of shafts 38.

A piston 39 with a spring 40 is mounted in the raisable plate 35 in a blind bore under each of the two locking elements 14. A fixed piston 42 is attached to a closure plate 41 of the cylinder jacket 33 within the cylinder.

The operation of the device is as follows: If a workpiece support 1 is to be fixed multi-dimensionally to the machine tool 10, the former is roughly positioned in the direction of adjustment 7 in that it is longitudinally adjusted such that its locating member 2 contacts the locking element 14 opposite the direction of travel. The locking element 14 disposed opposite this moves over when pressed down. The workpiece support 1 is then moved in the direction 9, i.e. it is lowered. At this stage, it is the surfaces 4 of the locating members 2 which first contact the free ends of the locking elements 14 which are in a position pivoted from the base surface of the base plate 12 or the body 32 by the angle a by the springs 23 or 40, this pivoting being limited by the eccentric stop 24.On further lowering of the workpiece support 1, the locking elements 14 begin to close and, when the angle a has become zero, i.e. the lowering movement has been completed, the locking elements 14 are in contact with the contact surfaces 6 of the locating members 2, as a result of which the workpiece support 1 is clamped to the machine tool 10. The other ends of the locking elements 14 are simultaneously supported on the contact surfaces 13 of the base plate 12 or in the slot 34 in the body 32. The holding force F for locking achieves its maximum value in this extended position.

As at least one clamping unit 11 is required for each direction in the case of multi-dimensional locking, it is not possible, as a result of the comparatively long arms 3 of the locating members 2, for the clamping units 11 to act upon one another, as, during the locking process, i.e. during the lowering of the workpiece support 1, a small correction movement is still possible in the clamping unit 11 in the direction orthogonal to the respective unit 11 as a result of the resilient configuration of the locating member 2.

In order to release the workpiece support 1 from the clamping units 11, it is simply necessary to raise the workpiece support 1.

The locking elements 14 are released from the contact surfaces 6 of the boss 5 and release the workpiece support 1, as, under the action of the springs 23 and 40, the locking elements are re-pivoted until the lifting elements 18 again contact the stop 24. After lifting of the workpiece support 1, the locking element 14 locking the direction of removal is lowered into the clamping unit 11 for the direction of adjustment 7 by means of the cylinder-piston unit 25 until the angle of pivot a is zero. The workpiece support 1 may then be exchanged.

In the case of the embodiment of Fig. 3, the raisable plate 35 is raised in the direction of adjustment 9 within the clamping unit 31 instead of the workpiece support 1. In this case as well, contact firstly takes place between the free ends of the locking elements 14, which are pivoted by the angle a by means of the springs 40, and the surface 4 of the locating member 2.

On further raising of the raisable plate 35 the locking elements 14 close until they are in firm contact in their extended position with the contact surfaces 6 of the boss 5 and therefore clamp the workpiece support 1 to the clamping unit 11 and therefore the machine tool 10.

In order to release the workpiece support 1, it is simply necessary to re-lower the raisable plate 35. Under the action of the springs 40 the locking elements 14 are re-pivoted and release the locking contact 2 and therefore the workpiece support 1 which may be exchanged.

Claims

1. A device for the locking in position of a workpiece support on a machine tool, in which clamping units are arranged offset by 90 with respect to one another, wherein locking elements are disposed in pairs in clamping units on the machine tool in such a way that at least one pair of locking elements is parallel to and at least one pair of locking elements is at right angles to a forward direction of a workpiece support, the locking elements being formed as one-armed levers whose ends are rounded and being disposed on a base plate of the respective clamping unit under the action of springs in such a way that the opposite ends of the levers project obliquely upwardly and their mutual spacing is greater than the spacing between limit surfaces formed as contact surfaces on a boss secured to the workpiece support, the arrangement being such that when the workpiece support is lowered, the first upwardly extending ends of the locking elements come into contact with the contact surfaces.

2. A device as claimed in claim 1, wherein a locating member carrying the boss is formed in such a way that the locating member has a very large spring stiffness in the respective locking direction and a small stiffness in the other directions, so that a clearance-free and simultaneous multi-dimensional locking of the workpiece support in clamping units disposed on the machine tool is provided.

3. A device as claimed in claim 1 or claim 2, wherein the clamping units respectively comprise a base plate with contact surfaces disposed internally on two opposite sides and having two respective supports formed as pivot supports for the locking elements arranged externally on the other two opposite sides, wherein a lifting element is disposed on a shaft on both sides of a locking element, which lifting element is respectively connected with the locking element by means of a bolt and a spacer sleeve, and wherein each lifting element has a lever which is rigidly attached at right angles thereto, the respective free ends of two opposite levers being connected by a spring, and wherein in the pivot area of the free ends of the lifting element there is disposed, in an adjustable and lockable manner on each said support, an eccentric stop.

4. A device as claimed in claim 1, claim 2 or claim 3, wherein a hydraulic cylinder-piston unit is additionally hinged to one of the lifting elements in the clamping unit for one direction of adjustment.

5. A device as claimed in any preceding claim, wherein the holding force for locking is exclusively applied by the lowering movement of the workpiece support, the arrangement being such that at the end point of the lowering movement, i.e. in the aligned position of the locking elements and with a pivot angle a of zero, a maximum holding force F is also applied.

6. A device as claimed in any preceding claim, wherein the actuation force is very small in relation to the holding force, the ratio depending on the dimensions of the locking elements and is expressed by the expression: R FB = (2 sina + + ~) F.

L

7. A device as claimed in any preceding claim, wherein the approach path from the workpiece support to the clamping unit is divided into a smaller path of the workpiece support and a larger path of a raisable plate of the clamping unit.

8. A device for the locking in position of a workpiece support in a machine tool substantially as hereinbefore described with reference to Figs. 1 and 2 or Figs. 3 of the accompanying drawings.