HK1119625B - Clamping fixture including chuck and workpiece pallet releasably located thereon - Google Patents

Description

Clamping device comprising a chuck and a workpiece pallet releasably located thereon

Technical Field

The present invention relates to a holding fixture constructed as stated in the preamble of claim 1. These holding devices are preferably used for holding tool-provided workpiece pallets (pallets) or positionally limited workpieces, the chucks (chuck) usually being fixedly located on the table of a machine tool or press (press), while the workpiece pallets are repeatedly releasably located precisely on the chucks.

Background

With the known clamping devices, the pressure forces generated are mostly transmitted via contact surfaces provided for this purpose, and the overall tension force has to be handled by the clamping mechanism provided with the clamping members. Such clamping mechanisms typically feature a plurality of spring-loaded clamping balls that engage a clamping surface of a clamping post secured to the workpiece tray or directly engage the workpiece tray itself when the workpiece tray is clamped in place. While this type of gripper has proven to have had a record of success, for some applications it is often advantageous when the workpiece pallet is capable of handling higher tensions. One example of such a use is a powder press, in which a ram (ram) for compacting a powder is fastened to a work pallet. When the actual moulding action involves not only the face of the ram but also, in particular, the inner and/or outer shell faces of the ram, a correspondingly high retraction force is required to retract the ram from the die (die) to enable axial withdrawal of the ram from the highly compacted powder slug. Therefore, there is a case where a pressing force of 30% or more is necessarily applied in the drawing direction in order to draw out the indenter. In other words, for example, when producing compacted iron powder or ceramic powder, a compacting pressure of 100 tons needs to be applied, and in order to move the ram, a force of 30 tons or more needs to be applied in the drawing direction. These forces must of course also be transferred from the workpiece pallet to the chuck when the ram is fastened to the workpiece pallet. It will be appreciated that these high extraction forces cannot be handled by conventional ball gripping mechanisms because the surface pressure tends to be very high due to the very small contact surface of the balls.

ｃA clamping device for ｃA tool of ｃA machine tool comprising ｃA chuck and ｃA tool holder is known from EP- ｃA-0255042. The chuck comprises two pairs of centering rails protruding from its bottom side, which pairs of centering rails are provided with contact surfaces for alignment in the X and Y directions, and the tool holder is further provided with four posts protruding from the surface of the chuck for aligning the tool holder in the Z direction. The tool holder includes a planar surface defining a face for holding the aforementioned post. Two pairs of grooves are also provided in the tool holder, aligned with the centering rails and featuring flexible lips such that the flexible lips contact the rails. In summary, the tool holder features a central bore for receiving a pull rod by means of which the clamping force required to correctly centre the workpiece pallet is transmitted. In this arrangement, the chuck includes a centrally located ball lock that cooperates with the pull rod. It will be appreciated that only relatively little tension can be transmitted by such a pull rod and ball lock.

EP-A-0827806 describes ｃA clamping cylinder for clamping tight pipe joints (pull-in nipples). Such a clamping cylinder is provided with a central bore for receiving a compression fitting. The clamping cylinder features a first outer piston and a second outer piston located radially inside the first outer piston. Disposed between the two pistons are clamping members, referred to as locking pistons, which are used to clamp the compression fitting in place. These locking pistons engage a tab arranged at the front end of the shrink tube fitting, and several locking pistons are evenly distributed circumferentially. The two pistons are axially movable together with the locking pistons, and the locking pistons are also radially adjustable. The outer piston is provided with an inclined surface and is radially loaded by a compression spring such that the locking piston is urged radially inwardly by the inclined surface. These locking pistons are configured as plunger members. Piston release is performed by hydraulic pressure. A serious drawback of such clamping cylinders is that the tray ctz makes the compression fitting easily bendable in the extension direction and can handle only relatively small forces, because the locking pistons are in contact with only a relatively small contact surface of the compression fitting and the pistons, by means of which the compression fitting is positioned in the Z direction, are loaded only in the extension direction by compression springs.

ｃA clamping device is also known from EP- ｃA-1068919, which is capable of handling relatively high tilt and torque loads. Such clamping devices comprise a chuck positioned within the working range of the machine tool and a workpiece carrier for mounting on the chuck for clamping to the chuck. The first positioning means on the chuck and the second positioning means on the workpiece carrier cooperate as an alignment member in pairs to position the workpiece carrier in X, Y and the Z direction. A clamping device is likewise provided for clamping the workpiece carrier in the position defined by the positioning means on the chuck. The clamping device comprises a plurality of clamping balls positioned along a circular ring, the effective line in the clamping force of the clamping balls lying substantially on or inside the area of the imaginary cylindrical housing parallel to the Z-axis cutting the first and second positioning means. The compressive load is transferred from the workpiece carrier to the chuck primarily through the Z contact surfaces where the workpiece carrier rests when the chuck is clamped. While such a clamping device is capable of handling relatively high compression loads and of transmitting high torques and tilting moments on the one hand, on the other hand, the transmission of tensile forces is limited for the reasons mentioned at the outset.

Disclosure of Invention

The object of the invention is to make a holding fixture more elaborate, which comprises a chuck and a workpiece pallet releasably located thereon, so that the workpiece pallet can also handle high-tension loads.

For this purpose, the invention provides a holding fixture comprising a chuck and a workpiece tray releasably located thereon, the chuck being provided with: a clamping mechanism for positioning the workpiece tray, the clamping mechanism comprising a plurality of clamping members configured as plungers and characterized by a front portion provided with a compression surface for surface contact with the clamping surface of the workpiece tray; the workpiece tray comprises a clamping surface extending substantially along its housing surface for contact with the plunger during clamping, and the clamping member makes full surface contact with the clamping surface of the workpiece tray over a large surface area, wherein the chuck is provided with a support surface at the bottom of the opening, and the workpiece tray comprises a flat contact surface at its bottom side, which is in contact with the support surface of the chuck when clamping the workpiece tray to the chuck in the Z-direction.

The gist of the invention is that the chuck is provided with plunger-type gripping members which engage the outer side of the workpiece tray, i.e. gripping surfaces extending substantially along the surface of the housing over a large surface area. This meets the basic requirement of a workpiece pallet that is capable of handling high tensile forces when these forces are transmitted to the chuck, since the clamping surfaces extending along the housing surface of the workpiece pallet provide a substantially larger contact surface for the clamping members than the clamping columns.

In order to ensure an absolutely repeatable accuracy of the positioning of the workpiece tray when clamped to the chuck, first centering members are arranged on the chuck, which first centering members cooperate with further centering members on the workpiece tray to position the workpiece tray in the X and Y directions relative to the chuck when clamped.

Drawings

Preferred exemplary aspects of a holding fixture according to the invention will now be described in detail with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a holding fixture including a chuck and a work piece pallet;

FIG. 2a is a top view of the chuck;

FIG. 2b is a bottom perspective view of the workpiece tray;

FIG. 3 is a horizontal cross-sectional view through the holding fixture;

FIG. 4 is a vertical sectional view through the holding fixture in a locked condition;

FIG. 5 is a vertical sectional view through the holding fixture in a released state;

FIG. 6 is a perspective view showing the bushing of the chuck and the plunger;

fig. 7 is a vertical sectional view through an alternative example aspect of a holding fixture, shown on an enlarged scale.

List of labels

1 chuck

2 base body

3 liner

4 center hole

5 base plate

6 centering member

7 support surface

8 holes

9 slotted notch

10 plunger piston

11 compression spring

12 front part

13 compression surface

14 notches

15 circumferential shoulder

16 ring piston

17 bottom side

18 top side

19

20 pressure chamber

21

22 workpiece pallet

23 flat underside

24 centering member

25 contact surface

26 shell surface

27 circumferential annular groove

28 shoulder/28 a gripping surface

29 through hole

30 bolt

31 base plate

32

33 lantern ring (Collar)

34 sealing element

35 sealing element

Detailed Description

Referring to fig. 1, there is shown a perspective view of a holding fixture comprising a chuck 1 and a work piece pallet 22. The chuck 1 is fastened to the base plate 31, but as far as possible the chuck 1 is fastened directly to the machine table. The workpiece pallet 22 is used to mount a workpiece repeatedly accurately positioned on the chuck 1. In the context of the present invention, however, the term workpiece pallet is in no way to be understood as being used only for mounting workpieces, since tools and similar devices can also be fastened.

The chuck 1 comprises a cylindrical base body 2 arranged along a bush 3. The bush 3 defines the extent of a central opening 4, the central opening 4 being for mounting a workpiece tray 22 and being configured to be substantially cylindrical. The flat bottom side 23 of the workpiece tray 22 features a centering groove 24 for engaging a centering cam arranged on the chuck 1 when the workpiece tray 22 is positioned on the chuck 1. The perfect cooperation of the centering cams in engagement with the centering grooves 24 positions the workpiece tray 22 precisely in the X and Y directions and, when defined on the chuck 1, in an angular position relative thereto about the Z axis. The workpiece tray 22 is configured to be substantially cylindrical and provided with an annular groove 27, and such annular groove 27 is machined in the housing surface 26 and defines an outer circumferential surface of the workpiece tray 22. One side wall of such annular groove 27 forms a shoulder 28 when used as a clamping surface 28a, such clamping surface 28a being engaged by a clamping member arranged on the chuck 1 during clamping, as will be described below. The clamping surface 28a is inclined, preferably inclined or curved, inwardly from the outside. The workpiece tray 22 features through-holes 29, such through-holes 29 being used, for example, to mount or position a workpiece or tool. The base body 2 is fixedly attached to a base plate 31 by a plurality of bolts 30. The fasteners of the workpiece pallet 22 required to position the workpiece or tool are not shown in the figures.

Referring to fig. 2a, which shows a top view of the chuck 1, the base plate 5 is shown arranged at the bottom of the chuck 1, the chuck 1 being provided with four centering cams 6, which centering cams 6 serve to position the workpiece tray 22. A circular sector shaped support surface 7 extends between each two adjacent centering cams 6. These circular sector-shaped support surfaces 7 together form a Z-stop for the workpiece tray 22. For cleaning purposes, each of these support surfaces 7 is provided with several holes 8, through which holes 8 air can be sprayed to clean the underside of the workpiece tray 22 when the workpiece tray 22 is located in the chuck.

Referring to fig. 2b, there is shown a top perspective view of the workpiece tray 22, particularly illustrating four recesses 24, which recesses 24 are formed to intersect at the flat bottom side 23, which recesses 24 divide the flat bottom side 23 into four flat contact surfaces 25. These grooves 24 correspond in shape and size to the four centering cams 6 of the chuck 1 to align the workpiece tray 22 in the X and Y directions when clamping the workpiece tray 22 to the chuck 1, and in its angular position about the Z axis.

Referring to fig. 3, there is shown a horizontal cross-sectional view of the chuck 1 together with a workpiece pallet 22 located within the chuck 1, particularly four plungers 10, which plungers 10 are used to clamp the workpiece pallet 22 to the chuck 1. The four plungers 10 are mounted radially movably in the bush 3 and are offset by 90 ° from each other. Each of the four plungers 10 is loaded with two compression springs 11 to urge this plunger radially inwardly in the direction of a workpiece tray 22 mounted in the chuck 1. The longitudinal centre lines of the compression springs 11 extend parallel to the insertion direction of the plungers 10. The solid liner (liner)3 is configured such that the solid liner 3 handles the tension forces acting on the plungers 10.

The front portions 12 of these plungers 10 are adapted to the contour of the clamping surface 28a of the workpiece pallet 22 such that each plunger 10 is in contact with a shoulder 28 (fig. 1) of the workpiece pallet 22 forming the clamping surface 28 a. Preferably, each plunger 10 is in full surface contact with the gripping surface 28 a. The four plungers 10 are to be arranged so as to cover a total of approximately 320 ° of the circumference of the workpiece tray 22 towards the front side 12 of the workpiece tray 22, in order to achieve a relatively large contact surface between the clamping members, the plungers 10 and the workpiece tray 22, in contrast to conventional ball clamping mechanisms, in which the balls are only in point contact. The large contact surface between the chuck 1 and the workpiece tray 22 forms a basic requirement for being able to handle a high-tension workpiece tray 22. In any case, however, the surface pressurization is relatively small, even in the case of high extraction forces being effective, due to the large surface contact of the plungers 10 with the gripping surface 28 a.

Referring to fig. 4, there is shown a vertical section through the holding fixture in the locked state and how each plunger 10 is pushed by these compression springs 11 in the direction of a workpiece tray 22 mounted in the chuck 1. Due to the biasing force of the springs 11, the plunger 10 is in surface contact with its bottom side, which acts as the compression surface 13, with the shoulder 28 of the annular groove 27, forming a gripping surface when the workpiece tray 22 is pulled down against the base plate 5 of the chuck 1, until the plunger 10 is in contact with the support surfaces of the chuck 1 with its flat bottom side when the plunger 10 is positioned in the Z-direction in this way. But in any case the profile or inclination of the gripping surface 28a is adapted to the front side of the plungers 10 to pull the workpiece tray 22 downwards against the base plate 5 of the chuck 1 when the plungers 10 are advanced in the Z direction.

In addition to positioning such workpiece trays in the Z direction, such workpiece trays are also positioned in the X and Y directions and, when clamped to the chuck 1, are positioned in an angular position about the Z axis. As already explained above, this positioning is effected by the centering cams 6 of the chuck 1 entering the centering grooves 24 of the workpiece pallet 22.

In order to release the workpiece pallet 22 clamped in the chuck 1, the plungers 10 must be pushed radially outwards when the force of the compression springs 11 is overcome. For this purpose, an actuator in the form of an annular piston 16 is provided, such annular piston 16 comprising a projection 17, such projection 17 being machined with a sloping pressure surface to engage a corresponding notch 14 in a corresponding plunger 10. The substantially flat top side 18 of the annular piston 16 is formed simultaneously with the lower end of the annular pressure chamber 20. As the annular piston 16 moves downwardly, the plunger 10 is pushed radially outwardly by the ledge 17 of the annular piston 16 entering the slot 14 of the plunger 10. Preferably, the annular piston 16 is pneumatically actuated by a pressure chamber 20, the pressure chamber 20 extending above the annular piston 16 receiving a supply of compressed air. Instead of pneumatically actuating the annular piston 16, it is also possible to provide, for example, a hydraulic or electromechanical actuator. But in any case, the plungers 10 are inserted transversely to the longitudinal centre line L of the chuck 1 and the central opening 4, respectively, as the annular piston 16 moves downwards.

When viewed in cross section, it is also apparent how the basic body 2 is formed mainly in an L-shape from its top side, the basic body 2 comprising a substantially radially extending base portion 2 a. The bush 3 is provided with a circumferential shoulder 15, by means of which the bush 3 is supported with its entire surface on the underside of the base 2a of the basic body 2 when the bush 3 is put under tension. This construction, together with the solid structure of the basic body 2 and the solid structure of the liner 3, enables high tensile forces to be handled by the liner 3 and transmitted to the basic body 2.

Referring to fig. 5, a vertical cross-section through the holding fixture in the released state is shown, but without the compression spring. To release the workpiece pallet 22 from locking, the plungers 10 need to be inserted radially outward. For this purpose, the pressure chamber 20 receives a supply of compressed air and is pressurized until the annular piston 16 is pushed downwards. This downward movement of the annular piston 16 causes its projections 17 to enter the slots 14 of the plunger 10, thereby pushing the plunger 10 radially outwardly until its rear side contacts the inner side of the base 2 and enables the workpiece pallet 22 to be removed from the chuck. It is also apparent from the figure how the shoulder of the annular groove 27 forming the clamping surface is radially inclined from the outside inwards.

Referring to fig. 6, there is shown a perspective view of the hub 3 of the chuck 1 together with the plunger 10, which particularly makes apparent the four slot-like notches 9 formed in the hub 3, each of these notches 9 being used for mounting and guiding the plunger 10. The height of each slot 9 is preferably made very precise to match the height of the plunger 10 so that the plunger 10 is practically completely accurately located in the slot 9 in the Z-direction when repeated precise positioning of the workpiece tray 22 in the Z-direction is achieved. Preferably, each notch 9 is 1 to 5 microns higher than the front portion 12 of each plunger 10 to be mounted therein. But in any case these plungers 10 are supported by the bush 3 in the Z direction by surface contact.

Furthermore, the exact matching of the slot-shaped notches 9 with the plungers 10 avoids the entry of dust to a large extent. As is evident from the figures, the cup-shaped front portion 12, the lower compression surface 13 and the circular notches 14 are inside these plungers 14.

The advantages of the clamping device shown and described relate in particular to the solid structure of the chuck and the contact surfaces of these plungers, and the workpiece pallet enables very high tensile forces to be handled by the workpiece pallet and the clamping device, respectively, as a whole.

A holding fixture constructed in accordance with the present invention is particularly suitable for, but not limited to, powder compaction applications in which a ram used to compact powder is secured to a work pallet. But in any case the workpiece pallet is able to handle the high tension and extraction forces required to extract the ram from the die.

However, these holding devices are also suitable for use in multi-level systems comprising, on the one hand, several chucks coaxially stacked and, on the other hand, several tools, such as tubular rams, arranged coaxially with respect to each other.

Fig. 7 shows a vertical sectional view through an alternative exemplary aspect of the holding fixture on an enlarged scale, but only the details of the holding fixture can be clearly seen. In this example, a ring-shaped piston 16a provided for releasing the plungers 10a is arranged below these plungers 10a, and a projection 17a for inserting the plungers 10a is arranged on the top side, but is then assigned to the corresponding plungers 10 a. The workpiece tray 22a features a circumferential collar 33 on the top side, the circumferential collar 33 protruding radially beyond the cylindrical housing surface of the workpiece tray 22 a. A seal 34 is arranged on the top side of the chuck 1a and contacts the bottom side of the circumferential collar 33 when clamping the workpiece tray 22a in place. A further seal 35 is arranged in the region of the bottom of the workpiece tray 22a and is in contact with the underside of the workpiece tray 22 a. These two seals 34, 35 serve to seal the cartridge 1a relatively safely against soiling, these seals 34, 35 protecting in particular the sensitive components of the cartridge 1a, such as the plunger 10a, the piston 16a, etc., against soiling.

Claims (17)

1. A holding fixture comprising a chuck (1) and a workpiece tray (22) releasably located thereon, said chuck (1) being provided with a holding mechanism for positioning said workpiece tray (22), said holding mechanism comprising a plurality of holding members configured as plungers (10) and being characterized by a front portion (12), said front portion (12) being provided with a compression surface (13) for surface contact with a holding surface (28a) of said workpiece tray (22), characterized in that: the workpiece tray (22) comprises a clamping surface (28a) extending substantially along its housing surface (26) for contact with the plunger (10) during clamping and the clamping member makes full surface contact with the clamping surface of the workpiece tray over a large surface area, wherein the chuck (1) is provided with a support surface (7) at the bottom of the bore (4) and the workpiece tray (22) comprises a flat contact surface (25) at its bottom side, the flat contact surface (25) being in contact with the support surface (7) of the chuck (1) when clamping the workpiece tray (22) to the chuck (1) in the Z-direction.

2. The holding fixture of claim 1, wherein: the chuck (1) includes a central opening (4) configured to mount the workpiece tray (22), and the plunger (10) is insertable transverse to a longitudinal centerline (L) of the opening (4).

3. The holding fixture of any one of claims 1-2, wherein: the workpiece tray (22) includes a cylindrical housing surface (26).

4. The holding fixture of any one of claims 1-2, wherein: the work pallet (22) includes an annular groove (27) formed in a housing surface (26), one side wall of the annular groove (27) forming a shoulder (28) serving as a clamping surface (28 a).

5. The holding fixture of any one of claims 1-2, wherein: the plunger (10) is supported in the Z-direction by a contact surface of a solid bushing (3) of the chuck (1).

6. The holding fixture of claim 5, wherein: the plunger (10) is mounted in a slot-shaped slot (9) of the bush (3).

7. The holding fixture of claim 6, wherein: each notch (9) is 1 to 5 microns higher than the portion of the plunger (10) to be mounted therein.

8. The holding fixture of claim 5, wherein: the chuck (1) comprises a cylindrical base body (2) arranged along the liner (3), the base body (2) comprising a base portion (2a) extending substantially radially, and the liner (3) being provided with a circumferential shoulder (15), the circumferential shoulder (15) being supported in the direction of tensile load by surface contact with the bottom side of the base portion (2a) of the base body (2).

9. The holding fixture of any one of claims 1-2, wherein: the plunger (10) is loaded with a compression spring (11), the longitudinal centre line of the compression spring (11) extending parallel to the insertion direction of the plunger (10).

10. The holding fixture of any one of claims 1-2, wherein: centering members (6) are arranged on the chuck (1) and cooperate with other centering members (24) arranged on the workpiece tray (22) to position the workpiece tray (22) in the X and Y directions relative to the chuck (1) during clamping.

11. The holding fixture of any one of claims 1-2, wherein: the chuck (1) comprises at least two plungers (10), the front portion of the plungers (10) comprising at least one compression surface (13), each compression surface (13) being for surface contact with a gripping surface (28a) of the workpiece tray (22), the compression surfaces (13) of the plungers (10) generally covering at least half of the circumference of the workpiece tray (22).

12. The holding fixture of any one of claims 1-2, wherein: the work pallet (22) is configured in a circular or rectangular shape when viewed in cross section, and a circumferential groove (27) is machined in a housing surface (26) of the work pallet (22), one side wall of the circumferential groove (27) forming a shoulder (28), the shoulder (28) being configured as a gripping surface (28a) for the plunger (10).

13. The holding fixture of any one of claims 1-2, wherein: the chuck (1) comprises at least four plungers (10), the plungers (10) being loaded with compression springs (11) such that a work piece pallet (22) can be mounted within the chuck (1).

14. The holding fixture of any one of claims 1-2, wherein: the chuck (1) is provided with at least one remotely actuated actuator by means of which the plunger (10) can be inserted against the force of the compression spring (11).

15. The holding fixture of claim 14, wherein: the actuator is configured in the form of an annular piston (16), the annular piston (16) comprising a protruding portion (17), the protruding portion (17) featuring an inclined compression surface for insertion of the plunger (10).

16. The holding fixture of any one of claims 1-2, wherein: the clamping surface (28a) of the work piece pallet (22) is inclined inwardly from the outside, and the front portion (12) of the plunger (10) is adapted to the contour of the clamping surface (28a) of the work piece pallet (22) to bring the plunger (10) into large-surface contact with the clamping surface (28a) of the work piece pallet (22).

17. The holding fixture of any one of claims 1-2, wherein: the work piece pallet (22a) is provided with a circumferential collar (33) on its top side, the circumferential collar (33) protruding radially beyond the housing surface of the work piece pallet (22a), and a seal (34) is arranged on the top side of the chuck (1a) and is in contact with the bottom side of the circumferential collar (33) during clamping.