WO1987002923A1

WO1987002923A1 - Clamping device

Info

Publication number: WO1987002923A1
Application number: PCT/SE1986/000513
Authority: WO
Inventors: Lennart Skoglund; Kenneth Hedin
Original assignee: Lagan Press Ab
Priority date: 1985-11-11
Filing date: 1986-11-11
Publication date: 1987-05-21
Also published as: SE501475C2; EP0245426A1; AU6623386A; SE8505313D0; SE8505313L

Abstract

A device for clamping a tool (1) on, for example, a table (2) in a hydraulic press, has clamping fixtures (3) arranged on said table and distributed around the tool (1), said clamping fixtures being movable into clamping engagement with an abutment (13) on the object (1). Each clamping fixture (3) is reciprocable towards and away from the object (1) and has a clamping arm (5), an attachment (6) and a dog (7). The clamping arm (5) is pivotally mounted on said attachment (6) and has an abutment face (11) and a clamping face (12). The dog (7) is movable relative to the attachment (6) and the clamping arm (5) and has a sloping face (20) abutting against a sloping face (22) on the clamping arm (5). The dog (7) continues its movement when the abutment face (11) of the clamping arm (5) strikes the object (1) so that the movement of the clamping arm (5) and the attachment (6) is restricted, whereby the dog (7), via the sloping faces (20, 22), swings said clamping arm (5) and moves the clamping face (12) thereof into clamping engagement with the abutment (13) on the tool (1), whereupon the dog (7) is stopped.

Description

CLAMPING DEVICE

The invention relates to a device for automatically clamping an object, such as a tool or a workpiece, on a frame, for example on a table in a hydraulic press or like machine, said device having at least one clamping fixture associated with said frame and movable into clamping engagement with an abutment on the object.

In a prior art device of the above-mentioned type, the object to be clamped is pushed by hand into a position abutting one or more positioning pins or the like protruding from the frame, whereupon clamping fixtures movable by hand along adjusting slots in the frame are pushed close up to the object, and the clamping fixtures are caused, either by hand or by pneumatic or hydraulic means, to clampingly engage the abutment of the object.

A major disadvantage of this prior art device is that the accurate positioning of the object, like the accurate adjustment of the clamping fixtures, requires a considerable manual effort by specially trained personnel. Because of the high accuracy re¬ quired, this work also is time-consuming and tiring, especially when the objects to be clamped are changed fairly frequently. In another prior art device of the type referred to above, it has been endeavoured to reduce the above- mentioned disadvantages by providing the side of the object abutting the frame with guide grooves which usually are T-shaped, the object being pushed with its guide grooves over clamping fixtures which are in the form of bolts with T-shaped heads and which project above the frame, to abut on, for example, positioning pins or the like, whereupon the T-shaped bolt heads either are turned through a quarter turn or moved axially into clamping engagement with the "shelves" of the T-shaped guide grooves.

According to another variant on this theme, the side of the object abutting against the frame has one or more threaded holes by which a corresponding number of threaded bolts countersunk in the frame in the initial position are movable into clamping engagement by being screwed up from the frame.

These two last-mentioned embodiments suffer, like the first-mentioned one, from the disadvantage that they require high accuracy and thus specially trained personnel. Furthermore, the two last-mentioned embodiments suffer from the common disadvantage that the objects must be provided with specially made guide grooves and/or threaded holes so that their total manufacturing cost will be considerably higher, espe¬ cially for the tools of hydraulic presses or the like where as many as several hundreds of tools may be associated with each press. The principal aim of the invention is to provide an automatic and efficient clamping device that can be used for objects which, in principle, may have any desired shape and which, for their clamping, merely require a simple and inexpensive abutment, in its simplest form an external shoulder or flange, and which thus entirely lack expensive and complicated guide grooves, threaded holes and the like.

According to the invention, this aim is achieved in that the clamping fixture is reciprocable towards and away from the object by means of a driving mecha¬ nism and comprises a clamping arm, an attachment and a dog, said clamping arm being pivotally mounted on said attachment and provided on the end facing the object with an abutment face and a clamping face, said dog being restrictedly movable relative to said attach¬ ment and said clamping arm and having a sloping face abutting against a sloping face on said clamping arm in the area of its end facing away from the object, whereby said dog, when the abutment face of said clamping arm strikes the object so that the movement of said clamping arm and said attachment toward the object is restricted, continues its movement toward the ob¬ ject under the action of said driving mechanism and thereby, and via said sloping faces, swings said clamp¬ ing arm and moves the clamping face thereof into clamping engagement with the abutment on the object, whereupon the dog is stopped, and vice versa.

Another important aim of the invention is to facilitate, before the object is clamped, the centering thereof in an exactly predetermined centered position by means of said clamping device, in the event that the object should have been slightly shifted from this position. In this manner, one need not be ex¬ cessively careful in placing the object on the frame. To this end, at least two, but preferably three or more clamping fixtures are uniformly distributed on the frame on both sides of or about the object to be clamped, said clamping fixtures being movable in synchronism toward and away from the object, and if the object should be shifted from the centered po¬ sition, the clamping fixture (or fixtures) which first strikes the object with the abutment face of its clamping arm, will move the object toward the centered position against the action of the associated compression spring, until the compression springs of all clamping fixtures balance one another in the centered position, where- upon the dogs of the clamping fixtures via the sloping faces swing the associated clamping arm to move its clamping face into clamping engagement with the abut¬ ment of the object.

The invention will be described in more detail below, reference being had to an embodiment especially preferred at present and illustrated in the accompanying drawings. Fig. 1 is a top plan view of the preferred embodiment of the clamping device according to the invention, a part having been cut away to show the underlying details. Figs. 2-4 are sectional views of a part of the device according to line II-II in Fig. 1 and illustrate the function of a clamping fix¬ ture.

The clamping device illustrated in the drawings is intended primarily for clamping a tool 1 on a table 2 or a base plate in a hydraulic press not shown in detail. It is pointed out, however, that the clamping device may be used whenever an object 1 in the form of a tool, a workpiece or the like is to be clamped on a frame 2 in optional position in an optional machine. In the embodiment illustrated, the device com- prises four clamping fixtures 3 associated with the frame 2 and uniformly distributed about the object 1. The number of clamping fixtures may, however, vary from one to, in principle, any number, depending int. al . on size and shape of the object 1. By means of a driving mechanism 4 which will be described below, each clamping fixture 3 is re- ciprocable toward and away from the object 1. Each clamping fixture 3 comprises as its main components a clamping arm 5, an attachment 6 and a dog 7. The clamping arm 5 is essentially in the form of an elongate prismatic element and is pivotally mounted, at its end 8 facing the object 1, on the attachment 6 by means of a pin 9 which is held in position by means of a stop screw 10. At its end 8, the clamping arm 5 has a vertical abutment face 11 and a substantially horizontal clamping face 12. The clamping face 12 can be moved, in the manner described below, into clamping engagement with an abutment 13 on the object 1 in the form of a circumferential flange. The attachment 6 has an upstanding part 14 ex¬ tending from below into a recess in the clamping arm 5 and having a hole (not shown) through which the pivot pin 9 extends. Furthermore, the attachment 6 has a horizontal part 15 having a smooth throughbore 16 for accommodating a feed screw 26 described below in connection with the driving mechanism 4. The dog 7 is in the form of an upstanding essen¬ tially parallelepipedal element, and has in its top side 17 a recess 18 for accommodating a slide 19 of hardwearing, preferably hardened material. The slide 19 can rotate in the recess 18 and has a small planar sloping face 20 in sliding engagement with part of a sloping face 20 formed by the underside 21 of the clamping arm 5 in the area of the end 23 of the clamping arm 5 facing away from the object 1.

The dog 7 is restrictedly movable relative to the attachment 6 and the clamping arm 5, such that the dog, when the abutment face 11 of the clamping arm 5 during movement of the clamping fixture 3 in the direction of the arrow I in Fig. 2 reaches and strikes the edge of the object 1 (see Fig. 3), whereby the movement of the clamping arm 5 and the attachment

6 in the direction of arrow I is restricted, will continue its movement a short way in the direction of arrow I and, via the sloping faces 20 and 22, will swing the clamping arm 5 and move the clamping face 12 thereof into clamping engagement with the abutment 13 on the object 1 (see Fig. 4), whereupon the dog

7 is stopped. For detaching the object 1, the course of events is essentially the reverse.

In order to provide a self-locking wedging effect between the dog 7 and the clamping arm 5, the slope of the sloping faces 20, 22 relative to the direction of movement I is chosen fairly small, maximally about 10°.

In the embodiment illustrated, the driving mecha- nism 4 comprises a power-driven feed screw 26 mounted in the frame 2 by means of bearings 24 and 25. For threaded engagement with the feed screw 26, the dog 7 has a threaded throughbore 27, while the feed screw 26 has a running fit in the above-mentioned smooth throughbore 16 in the attachment 6 to guide the attach¬ ment during its movement in the direction of arrow I.

The dog 7 and the attachment 6 mounted in the manner described above on the feed screw 26 also are interconnected via a helical compression spring 28 which has a play on the feed screw 26 and is mounted between the dog 7 and the attachment 6. Furthermore, the dog 7 and the attachment 6 are interconnected via a connecting rod 29 which has a running fit in a throughhole 30 in the dog 7 and, for adjustment of the tension of the compression spring 28, is adjust- ably screwed into a threaded hole 31 in the attachment 6. The connecting rod 29 has a head 32 movable into abutment against the dog 7 on its side 33 facing away from the attachment 6. The arrangement of the compres¬ sion spring 28 and the connecting rod 29 causes the dog 7 during its movement toward the object 1 in the direction of arrow I to push the attachment 6 and the clamping arm 5 before it against the action of the compression spring, and when the movement of the clamping arm 5 and the attachment 6 in the same di- rection is restricted, the dog 7 continues its move¬ ment a short way while compressing the compression spring 28. In its movement away from the object 1, i.e. in the direction opposite the arrow I, for de¬ taching the object, the dog 7 allows the compression spring 28 to expand until the head 32 of the connecting rod 29 engages the side 33 of the dog 7 (see Figs. 4 and 3), whereupon the attachment 6 and the clamping arm 5 are carried along by the dog 7 via the connect¬ ing rod 29 into the initial position shown in Fig. 2. As will be evident from the drawings, the feed screw 26, the compression spring 28, the connecting rod 29 and the major part of the dog 7 and the attach- ment 6 are mounted in a groove 34 in the surface 35 of the frame 2 to which the object 1 is to be clamped. The groove 34 preferably is under a cover 36 to pro¬ tect as far as possible the driving mechanism 4 and the components connected therewith and described below from dirt in the form of chips or the like.

In the embodiment illustrated, the object 1 has been accurately centered in a predetermined position C. If, prior to clamping, the object 1 for some reason should be slightly offset from the centered position C, it may be moved, by means of the clamping device, to the centered position in the following manner. The clamping fixtures 3 are movable in synchronism toward and away from the object 1, and the clamping fixture (or fixtures) 3 which first strikes the object with the abutment face 11 of its clamping arm 5, will move the object toward the centered position C against the action of the associated compression spring 28 until the compression springs 28 of all clamping fix- tures 3 balance one another in the centered position C. After that, the dogs 7 of the clamping fixtures

3 pivot the associated clamping arm 5 via the sloping faces 20, 22 into the position shown in Fig. 4 to move the clamping face 12 into clamping engagement with the abutment 13 of the object 1.

In order to provide the said synchronous movement of the clamping fixtures 3, the driving mechanisms

4 of the fixtures may be connected, in one embodiment, each to one driving motor operating synchronously with one another in some suitable manner.

However, in the preferred embodiment illustrated in the drawings, the driving mechanisms 4 of the clamp¬ ing fixtures 3 are connected to a common driving motor 37 via a transmission 38 comprising on the one hand a conical gear 39 for each driving mechanism 4 between the respective feed screw 26 and a drive shaft 42 rotatably mounted in bearings 40, 41 and, on the other hand, a chain drive 43 with a friction hub 45 mounted on the end 44 of the respective drive shaft 42 facing away from the associated conical gear 39. Nonrotatably mounted on said friction hub is a sprocket 46 carrying an endless chain 47 operated by the driving motor 37.

The embodiment of the invention as described above is at present especially preferred, but it will be appreciated that the invention can be modified in many different ways within the scope of the appended claims. For example, the driving mechanism 4 which is in the form of a feed screw 26 may be replaced by a pneumatic or hydraulic cylinder to move the asso¬ ciated clamping fixture 3 toward and away from the object 1. Also the design of the clamping fixture

3 may be modified in various ways, as long as it has the above-mentioned function of centering and clamping the object 1 to the frame 2.

Claims

1. A device for clamping an object (1), such as a tool or a workpiece, on a frame (2), for example on a table in a hydraulic press or like machine, said device having at least one clamping fixture ( 3 ) asso- ciated with said frame (2) and movable into clamping engagement with an abutment (13) on the object (1), c h a r a c t e r i s e d in that said clamping fixture (3) is reciprocable towards and away from the object (1) by means of a driving mechanism (4) and comprises a clamping arm (5), an attachment (6) and a dog (7), said clamping arm (5) being pivotally mounted on said attachment (6) and provided on the end (8) facing the object (1) with an abutment face (11) and a clamping face (12), said dog (7) being restrictedly movable relative to said attachment (6) and said clamping arm (5) and having a sloping face (20) abutting against a sloping face (22) on said clamping arm (5) in the area of its end facing away from the object (1), whereby said dog (7), when the abutment face (11) of said clamping arm (5) strikes the object (1) so that the movement of said clamping arm (5) and said attachment (6) toward the object (1) is restricted, continues its movement toward the object (1) under the action of said driving mechanism (4) and thereby, and via said sloping faces (20, 22), swings said clamping arm (5) and moves the clamping face (12) thereof into clamping engagement with the abutment (13) on the object, whereupon the dog (7) is stopped, and vice versa.

2. A device as claimed in claim 1, c h a r a c ¬ t e r i s e d in that said dog (7) and said attach¬ ment (6) are interconnected via a compression spring (28) fixed between said dog and said attachment, and a connecting rod (29) which has a running fit in a throughhole (30) in the dog (7) and is adjustably screwed into a threaded hole (31) in the attachment (6), and which has a head (32) movable into abutment against said dog on its side (33) facing away from the attachment, said dog (7), when moving toward the object (1), pushing the attachment (6) and the clamping arm (5) before it against the action of the compression spring (28) and, when the movement of said clamping arm and said attachment in the same direction is li¬ mited, continuing its movement while compressing the compression spring (28), said dog (7), when moving away from the object (1) for detachment thereof, per¬ mitting the compression spring (28) to expand until the head (32) of the connecting rod (29) abuts against the og, whereupon the attachment (6) and the clamping arm (5) are carried along by the dog (7) via the con¬ necting rod.

3. A device as claimed in claim 1 or 2, c h a - r a ct e r i s e d in that the slope of the sloping faces (20, 22) relative to the direction of movement of the clamping fixture (3) is sufficiently small to provide a self-locking effect.

4. A device as claimed in any one of the pre¬ ceding claims, c h a r a c t e r i s e d in that the sloping face on the dog (7) is formed by a small planar surface (20) on a slide (19) mounted in a re¬ cess (18) in the top side (17) of the dog (7), said slide being formed of hardwearing, preferably hardened material, and that the sloping face of the clamping arm (5) is formed of a part (22) of the underside (21) of the said arm, or vice versa.

5. A device as claimed in any one of the pre¬ ceding claims, c h a r a c t e r i s e d in that the driving mechanism (4) comprises a power-driven feed screw (26) mounted in the frame (2), that the dog (7) has a threaded throughbore (27) threadedly engaging said feed screw (26), that the attachment (6) has a smooth throughbore (16) in which said feed screw has a running fit to guide the attachment during movement thereof, and that the compression spring (28) has a play on the feed screw (26) between the dog (7) and the attachment (6).

6. A device as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the feed screw (26), the compression spring (28), the connecting rod (29) and the major part of the dog (7) in the attachment (6) are provided in a preferably at least partly covered groove (34) in the surface (35) of the frame (2) on which the object (1) is to be clamped.

7. A device as claimed in any one of the pre¬ ceding claims, in which at least two, but preferably three or more clamping fixtures (3) are uniformly distributed on the frame (2) on both sides of or about the object (1) to be clamped, said object being centered in an exact predetermined position (C), c h a r a c ¬ t e r i s e d in that said clamping fixtures (3) are movable in synchronism toward and away from the . object (1), and that the clamping fixture or fixtures (3) which, if the object has been shifted from the centered position (C), first strikes the object with the abutment face (11) of its clamping arm (5), moves the object toward the centered position against the action of the associated compression spring (28), until the compression springs (28) of all clamping fixtures (3) balance one another in the centered po¬ sition, whereupon the dogs (7) of said clamping fix¬ tures pivot the associated clamping arm (5) via the sloping faces (20, 22) to move the clamping face (12) of said clamping arm into clamping engagement with the abutment (13) of the object (1).

8. A device as claimed in claim 7, c h a r a c - t e r i s e d in that the driving mechanisms (4) of said clamping fixtures (3) are connected each to one drive motor operating in synchronism with one another.

9. A device as claimed in claim 7, c h a r a c ¬ t e r i s e d in that the driving mechanisms (4) of said clamping fixtures (3) are connected to a common drive motor (37) via a transmission (38).

10. A device as claimed in claim 9, c h a r a c ¬ t e r i s e d in that the transmission (38) comprises on the one hand a conical gear (39) for each driving mechanism (4) between the respective feed screw (26) and a drive shaft (42) rotatably mounted in the frame (2) and, on the other hand, a chain drive (43) having a sprocket (46) mounted on the end (44) of the respect¬ ive drive shaft (42) facing away from the associated conical gear (39), said sprocket (46) carrying an endless chain (47) driven by said drive motor (37).