EP0620084A1 - Clamping device for clamping workpieces - Google Patents

Abstract

The invention relates to a clamping device for clamping workpieces on machine tables, apparatus or pallets with a hydraulically or pneumatically actuated clamping force-holding element (14) in which the holding force is produced via holding elements (14). The clamping device and the clamping force-holding element (14) are combined, either in a housing (1) or in the case of separate housings are interconnected. The clamping piston (3) of the clamping device and the adjusting piston (6,7) of the holding element (14) are situated, however, approximately perpendicular to one another. The clamping piston (3) is connected in the lower part fixedly to a push rod (4) which terminates in the shape of a wedge (5). The holding element (14) has two pistons (6,7), between which a piston rod (8) is arranged. The piston rod (8) is likewise formed in the shape of a wedge in the region (15) below the push rod (4), so that both wedge faces (10,11) slide on one another. In addition, a wedge groove (10) is formed in the piston rod. The push rod (4) is provided in the region of its wedge face (15) with a wedge bevel (11) adapted to the wedge groove (10). If the piston rod (8) slides under the push rod (4), the push rod (4) penetrates by way of its wedge bevel (11) into the wedge groove (10) of the piston rod (8), thus resulting in a large friction area between these elements. <IMAGE>

Description

The invention relates to a hydraulically or pneumatically operated clamping force holding element for tendons or clamping devices for clamping workpieces on machine tables, devices or pallets.

It is known to clamp workpieces on machine tables, devices and / or pallets by means of clamping devices. Depending on the machining process, forces have to be applied to ensure that the workpiece remains immovable in its position during the machining process.

As long as the clamping force is maintained, the clamping device is adequately secured. However, if the clamping force fails, e.g. because the hydraulic flow or air pressure fails, the clamping force is usually no longer sufficient to secure the workpiece in such a way that it remains immovable in relation to the machining forces.

One has therefore gone over to taking safety precautions by means of which the tensioning element maintains the clamping pressure regardless of the power flow of the power flux. It is known to drill holes in the piston rod of the tensioning element, into which pins engage when tensioned and thus prevent the piston rod from being moved. It is also known to have a second one parallel to the piston rod of the tensioning element To guide the piston rod and to provide both piston rods over a certain section with the same or opposite wedge-shaped surfaces. Between these wedge-shaped surfaces there acts a tappet, which is also wedge-shaped at its ends and inhibits the movement of the two piston rods. This means that when the force acts backwards, especially with an unfavorable wedge angle, a considerable loss of clamping force can occur.

With reduced tension, self-locking is caused, which is retained even if the power flow is interrupted. When using pins, however, these are subjected to bending and must be large enough, which leads to the fact that the clamping elements are oversized. When using wedge-shaped surfaces, two pistons lying in parallel must be provided, as a result of which the tensioning element must be designed in a complex manner, which leads to relatively large tensioning units.

The clamping units, which are used in particular on pallets and devices, must be kept as small as possible. They are required to hold each workpiece securely and to ensure the clamping pressure on the workpiece in the event of hydraulic or pneumatic failure.

The holding force is dependent on the frictional force of the two wedge surfaces lying on one another. The flatter the angle between the wedge surfaces, the greater the holding force. However, a flat angle requires a relatively large construction with a long stopping distance. A steep angle allows short distances and thus a short design, but has the disadvantage of the lower holding force and the lower self-locking.

The invention is therefore based on the object of connecting a clamping device to a clamping force holding element in such a way that a small structural unit is retained Clamping pressure, on the other hand, is fully effective in every situation, regardless of the clamping device flow, which provides self-locking. Furthermore, the holding element should only be subjected to pressure and not to train.

According to the invention, this is achieved by additionally inserting a wedge into the wedge surfaces of the elements sliding on one another, to which both elements are adapted, so that salvation enters a keyway, which increases the surface pressure and creates a frictional force between the wedge surfaces sliding on one another, which is many times larger.

The advantage of the invention is that the size of the support area on the tensioning piston is independent of the total stroke length of the tensioning piston. The stroke of the actuating piston is also not influenced by different tensioning piston strokes. The actuating piston is released by different piston diameters, so that the restoring force is many times greater than the actuating force. The connection between the plunger and the piston rod creates an effective self-locking in all situations.

Fig.1

Zeigt die Spannvorrichtung mit integriertem Spannkrafthalteelement im gespannten Zustand

Fig. 2

ist eine Seitenansicht dazu

Fig. 3

zeigt die Kolbenstange des Halteelementes

Fig.4

zeigt die Spannvorrichtung im entspannten Zustand.

Fig. 5

zeigt den Kräfteverlauf.

Fig. 6

zeigt eine verkürzte Ausführungsform im entspannten Zustand

Fig. 7

zeigt eine verkürzte Ausführungsform im Spannzustand

Fig. 8

zeigt den verkürzten Keilkolben und

Fig. 9

zeigt die verzahnten keilflächen.

The invention is described in more detail with reference to drawings:

Fig. 1

Shows the clamping device with integrated clamping element in the clamped state

Fig. 2

is a side view of this

Fig. 3

shows the piston rod of the holding element

Fig. 4

shows the tensioning device in the relaxed state.

Fig. 5

shows the course of forces.

Fig. 6

shows a shortened embodiment in the relaxed state

Fig. 7

shows a shortened embodiment in the tensioned state

Fig. 8

shows the shortened wedge piston and

Fig. 9

shows the toothed wedge surfaces.

The tensioning device consists of a housing 1, which accommodates all elements and parts. A clamping head 2 with its clamping piston 3 is mounted in the housing 1. The clamping head carries the clamping elements of known type necessary for clamping workpieces. A clamping force holding element 14 is connected to the housing 1 transversely to the direction of action of the clamping head 2. The housing 1 and the housing of the clamping force element 14 can also be part. On the side of the tensioning piston 3 opposite the tensioning head 2, a plunger 4 is arranged, which is firmly connected to the tensioning piston 3. The lower end of this plunger 4 is provided with a wedge surface 5. Over the length of the wedge surface 5, the plunger 4 is provided with wedge bevels 11 on both sides towards the center line.

The clamping force holding element 14 consists of two actuating pistons 6 and 7 which are arranged inside the housing to the left and right of the effective range of the clamping head 2. A piston rod 8 is provided between the actuating pistons 6 and 7. In subsection 15, i.e. Below the tappet 4, the piston rod 8 has a wedge surface 9 on its side facing the tappet 4. The inclination of the wedge surface 9 and the wedge surface 5 are adapted to one another. The piston rod 8 also has a bore 12 which is so large that the plunger 4 passes through the bore 12. This bore 12 thus receives the plunger 4 in the relaxed state of the device.

The inclination of the wedge surfaces 5 and 9 is kept relatively steep and is therefore not sufficiently self-locking. Thus, the surface friction would cause one another sliding surfaces 5 and 9 can not be guaranteed that the holding force is fully effective in every state. In order to increase the holding force, a keyway 10 is therefore additionally introduced into the wedge surface 9 of the piston rod 8. This keyway 10 runs the length of the key surface 9 and cuts a piece into the piston rod 8, as shown in FIG. 2. Corresponding to this keyway 10, the plunger 4 is provided with wedge bevels 11 on both sides in its lower part parallel to the key surface 5. These wedge bevels 11 are in turn adapted exactly to the bevels of the keyway 10, so that the surfaces slide on one another. This also creates a friction surface that significantly increases the friction force.

The frictional force depends on the surface pressure and thus on the normal force F₂ and F₃ between the bevels 11 and the corresponding bevels of the keyway 10th

Die Reibkraft, bzw. die Lösekraft zwischen den Schrägen der Keilnut 10 und den Keilschrägen 11 folgt der Formel:

${\text{F}}_{\text{löse}}\text{= ( F₂ + F₃ ) * µ}$

Diese um ein Mehrfaches größere Kraft reicht somit aus, um die in Spannstellung befindliche Spannvorrichtung in jeder Situation sicher und fest zu halten. Es besteht Selbsthemmung.Which forces are now effective can be seen from the force diagram according to FIG. 5.
The diagram takes the following course:

The frictional force or the loosening force between the bevels of the keyway 10 and the wedge bevels 11 follows the formula:

${\text{F}}_{\text{solve}}\text{= (F₂ + F₃) * µ}$

This force, which is several times greater, is therefore sufficient to hold the clamping device in the clamping position securely and firmly in any situation. There is self-locking.

The inclination of the surfaces to one another has an influence on the construction of the device. The smaller the design can be kept, the more universal the area of application of the clamping device. The double wedge system ensures a short stroke of the actuating piston with a large support area on the tensioning piston. E.g. an inclination of 20 ° for the wedge surfaces 5 and 9 and a wedge angle of 30 ° for the wedge bevels 11 in the keyway 10, so with a stroke of 15mm on the actuating piston, a support area of 5.4mm on the tensioning piston is achieved, i.e. almost a third.

The flow of force in the direction of clamping can be further increased in the clamping force holding element 14 in that a spring 13 also acts in the clamping direction. This means that the restoring force must also overcome the spring force. This spring also offers additional security against vibrations if vibrations occur.

From what has been said it is clear that the restoring force must be greater than the force required to tension the actuating piston.

This is achieved according to the invention in that the piston surfaces of the two actuating pistons 6 and 7 are different. Actuating piston 6 is adapted in its effective cross section to the flow of force that is necessary to allow the piston rod 8 to slide safely under the tappet 4. Actuating piston 7, on the other hand, is approximately three times larger in its effective cross section for the introduction of force, which also means that the restoring force is three times larger.

So far it has been assumed that the effective surface for the frictional forces consists of a wedge surface with an inserted keyway and a corresponding counter surface. Instead of this keyway connection, a spline can also be used be provided between the piston rod and the plunger, so that the formation of a plurality of interlocking teeth results in an increase in area, which leads to less wear during the service life,
The linear expansion of the clamping force holding element can be further reduced. For this purpose, the clamping force holding element 14 is designed differently. the piston rod 8 and its actuating piston 6 become part of the housing 1. This goes from Fig. 6 u. 7 out. Fig. 6 shows the shortened embodiment in the relaxed state and Fig. 7 in the tensioned state.

The clamping force holding element 14 consists of a cylindrical sliding mandrel 19 which is fixedly connected to the housing and on which the wedge piston 16 can be slid. For this purpose, a cylinder bore 17 is provided in the wedge piston 16. The length of this cylinder bore is approximately 95% of the total length of the wedge piston.

This cylinder bore can be arranged both centrally and off-center, that is to say eccentrically. The eccentric arrangement has the advantage that a larger wall thickness from the wedge slope to the cylinder bore is retained when the pressure is exerted on the wedge slope 18. In addition, the wedge piston is then additionally protected against rotation.

The clamping force holding element 14 is further shortened further by eliminating the actuating piston 7 and the bore 12 and for this purpose the wedge piston 16 is intended for pressurizing directly on its end face 27. This means that the wedge piston is in direct contact with the pressure medium and that when the pressure is released, all wedge surfaces are under the pressure of the medium. Thus, the wedge piston 16, in order to prevent an additional, one-sided pressing in the cylinder bore 17 by the pressure medium, must be equipped with pressure relief grooves, not shown, on its circumference.

The effective cross-sectional area of the plunger 4 is significantly smaller than the ring cross-sectional area caused by Clamping head 2 and clamping piston 3 are formed, since the pressure from the tappet cross section and from the ring cross section of the clamping head 2 and clamping piston 3 are opposed to one another during relaxation.

The mode of action is as follows:
6 shows the state of the relaxed element. If the pressure line 24 is pressurized, a pressure is built up in the chamber 26, which acts on the end face 28 in the cylinder bore 17 of the wedge piston 16 and drives it to the right from the position shown in FIG. 6, the clamping head 2 simultaneously is moved upwards. As soon as the clamping process is completed, the plunger 4 is fixed by the wedge piston 16, as shown in FIG. 7.

To relax, the pressure line 23 is pressurized and a pressure is built up in the pressure chamber 25, which acts on the end face 27 of the wedge piston 16 and moves it back, a pressure reduction in the pressure chamber 26 simultaneously taking place via valves. The tappet 4 slides down again and the unit is in the relaxed state.

Fig. 8 shows the wedge piston in its shortened version. The difference to Fig. 3 is significant.

FIG. 9 shows another example in which the surfaces sliding on one another are splined between the wedge piston 16 and the plunger 4.

The surfaces of the wedge piston 16 and the plunger 4 lie in a pressure chamber, which means that oil can be used as the pressure medium.

Claims (15)

Clamping device for clamping workpieces on machine tables or pallets with hydraulically or pneumatically operated clamping force holding element, in which the holding force is generated via holding elements which are provided with wedge surfaces which slide on one another, characterized in that the clamping piston (3) of the clamping device and the actuating piston (6; 7) of the clamping force holding element (14) are arranged approximately perpendicular to one another, that the clamping piston merges in its lower part into a plunger (4), the end (5) of which forms a wedge and that between the actuating piston (6; 7 ) a piston rod (8) is arranged, which is wedge-shaped over a section (15) and is provided with a bore (12) in the region of the smallest cross section. Clamping device according to claim 1, characterized in that a wedge groove (10) is machined into the wedge-shaped section (15) of the piston rod (8) and that the plunger (4) in the region of its wedge surface (5) on both sides over the length of the wedge surface (5 ) is provided with bevels (11) which are adapted to the side surfaces of the keyway (10) accordingly. Clamping device according to claim 1, characterized in that the piston rod (8) over the section (15) is designed as a spline and that the plunger (8) is also provided with a spline, and that the splines of the piston rod and the plunger slide into one another . Clamping device according to claim 1 and following, characterized in that the pistons (6; 7) of the clamping force holding element (14) different Have cross-sectional areas for the application of force. Clamping device according to claim 1 and following, characterized in that in the clamping force holding element (14) a spring (13) is attached which supports the flow of force in the clamping direction. Clamping device according to claim 1 and following, characterized in that a bore (12) is made in the piston rod (8) of the clamping force holding element (14) in the adjoining area behind the keyway or toothing, the diameter of which is equal to or greater than the diameter of the tappet (4) is. Clamping device according to claim 1 and following, characterized in that the self-locking of the piston rod (8) and the plunger (4) can be determined by the inclination of the wedge surfaces (5 and 9) together with the wedge bevel (11). Clamping device according to claim 1, characterized in that the clamping force holding element (14) is integrated in the housing (1) of the clamping device Clamping device according to claim 1, characterized in that the clamping force holding element (14) has its own housing which is connected to the housing of the clamping device. Clamping device according to claim 1, characterized in that a cylindrical sliding mandrel (19) is fixedly connected to the housing (1), on which a wedge piston (16) provided with a cylinder bore (17) slides and that in the inside of the sliding mandrel (19) Pressure line (24) is guided, which opens into a pressure chamber (26) at the end of the cylinder bore (17). Clamping device according to claims 1 and 10, characterized in that the end face (27) of the wedge piston (16) can be pressurized via the pressure line (23). Clamping device according to claim 1, 10 and 11, characterized in that pressure relief grooves are arranged on the pressure side in the pressure chamber region (26). Clamping device according to claim 1, 10, 11 and 12, characterized in that the wedge piston (16) is provided with a circumferential piston seal (21) in the region of the full cylinder cross section. Clamping device according to claims 1 and 10, characterized in that the cylinder bore (17) is made eccentrically in the wedge piston (16). Clamping device according to claims 1 and 10 to 14, characterized in that the effective cross-sectional area of the plunger (4) is kept substantially smaller than the ring cross-sectional area formed by the clamping head (2) and clamping piston (3).

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