Central clamping device for clamping workpieces that are to be machined

Abstract

The invention relates to a central clamping device (1) for clamping workpieces that are to be machined. It comprises a main body (2), two clamping jaws (4, 5) which are arranged movably on the main body (2) along linear guides (3) and serve to clamp the workpiece, and a threaded spindle (6) with two spindle nuts (7), for moving the two clamping jaws (4, 5) relative to each other along the linear guides (3) by rotation of the threaded spindle (6). The spindle nuts (7) are formed separately from the clamping jaws (4, 5), and each of the spindle nuts (7) is assigned precisely to one of the two clamping jaws (4, 5). According to the invention, various relative positions between the clamping jaws (4, 5) and the spindle nuts (7) can be set in the direction of movement of the clamping jaws (4, 5) so that, with the relative positions of the spindle nuts (7) on the threaded spindle (6) unchanged, various clamping widths can be realized. It is thereby possible to divide a desired large clamping width range into several small clamping width sub-ranges and to greatly shorten the threaded spindle (6), so that very compact central clamping devices (1) with large clamping width ranges can be realized and, in this way, the accessibility during the machining of the workpieces is considerably improved.

Description

[0001] Center clamping device for clamping workpieces to be machined

[0002] Technical area

[0003] The invention relates to a center clamping device for clamping workpieces to be machined and to a method using the center clamping device according to the preambles of the independent claims.

[0004] State of the art

[0005] Center clamping devices for clamping workpieces to be machined have become an indispensable part of mechanical production today. They form the center of the machining zone and have a decisive influence on manufacturing precision. The requirements for such center clamping devices are diverse. In addition to the basic requirements of high rigidity and good repeatability, there is also a need to be able to cover the largest possible clamping range with a single clamping device. At the same time, and in some contradiction to the latter need, it is also desirable for the center clamping devices to require as little space in the manufacturing zone and to create as few interference points as possible, e.g. to avoid unnecessarily long spindle overhangs, which increase the potential for collision with the machining tools and may require unnecessarily long machining tools.

[0006] In particular, the latter combination of requirements of the largest possible clamping range with the smallest possible space requirement is not satisfactorily met by the center clamping devices known today. Description of the invention

[0007] The task therefore arises to provide a technical solution with which the previously mentioned deficit of the state of the art can be reduced.

[0008] This problem is solved by the subject-matter of the independent patent claims.

[0009] According to these, a first aspect of the invention relates to a center clamping device for clamping workpieces to be machined.

[0010] The center clamping device comprises a base body for fastening the device to the machine table of a machine tool, two clamping jaws arranged on the base body so as to be displaceable along linear guides for clamping the workpiece and a threaded spindle with two spindle nuts for displacing the two clamping jaws relative to one another along the linear guides by rotating the threaded spindle. The spindle nuts are designed separately from the clamping jaws and each of the spindle nuts is assigned to exactly one of the two clamping jaws. According to the invention, different relative positions between the clamping jaws and the spindle nuts can be set in the direction of displacement of the clamping jaw so that different clamping widths can be achieved with unchanged relative positions of the spindle nuts on the threaded spindle.

[0011] This makes it possible to divide a desired large clamping range of the center clamping device into several small clamping ranges, which are adjacent to one another or, preferably, at least slightly overlap. This, in turn, makes it possible to shorten the threaded spindle significantly, because it then only needs to provide a thread length for each spindle nut, which allows the spindle nut to be moved by half the clamping range. Accordingly, large clamping ranges can be achieved even with very short threaded spindles, and interference points caused by protruding threaded spindles in the production zone can be avoided.

[0012] It is preferred that the relative positions between the clamping jaws and the spindle nuts in the displacement direction of the clamping jaws be adjustable without tools. This eliminates the need for a tool to convert the center clamping device to a different clamping range, and such a tool can therefore neither be lost nor forgotten in the machining area.

[0013] Advantageously, the relative positions between the clamping jaws and the spindle nuts can be adjusted in predefined steps in the direction of displacement of the clamping jaws, preferably positively, e.g., by positioning or locking bolts. In this way, the clamping forces can be transmitted reliably and precisely.

[0014] In a preferred embodiment of the center clamping device according to the invention, the spindle nuts are guided in guides in the clamping jaws and can be displaced relative to the clamping jaw in the direction of displacement of the respective clamping jaw after a connection or fixation has been released, in order to set the desired relative positions. This results in a compact and very rigid design of the center clamping device.

[0015] It is preferred that the guides in the clamping jaws are designed in such a way that they create a rotational positive connection in both directions of rotation of the threaded spindle between the spindle nuts and the clamping jaws. This has the advantage that those components or contours which transmit the clamping forces between the spindle nuts and the clamping jaws are kept free from torques which are transmitted between the threaded spindle and the spindle nuts. This is advantageously achieved in such a way that the spindle nuts have the shape of a polygon viewed in the direction of the axis of rotation of the spindle and the guides in the clamping jaws have a shape complementary to this. Guide contours of this type can be manufactured relatively easily and with high precision.

[0016] Furthermore, it is preferred that the spindle nuts be fixable in several defined relative positions with respect to the clamping jaws, in particular by means of positioning or locking pins provided on the clamping jaws. In this way, the clamping forces can be transmitted securely and precisely by positive locking, and no additional components are required that could be lost.

[0017] It is advantageous that the clamping ranges resulting from the respective defined relative positions between the spindle nuts and the clamping jaws overlap. This ensures a continuous, complete clamping range.

[0018] In a further preferred embodiment, the clamping jaws can be removed from the base body and the spindle nuts, advantageously without tools, and can then be rearranged on the guides of the base body in a 180° rotated position and connected to the spindle nuts in several defined relative positions, advantageously by means of positioning or locking pins provided on the clamping jaws. This allows the clamping range of the center clamping device according to the invention to be significantly increased.

[0019] As with non-rotated clamping jaws, it is preferred here too that the clamping ranges resulting from a 180° rotated arrangement of the clamping jaws overlap at the respective defined relative positions between the spindle nuts and the clamping jaws. It is particularly preferred if these overlap with the clamping ranges resulting from a non-rotated arrangement of the clamping jaws at the respective defined relative positions. In this way, a seamless overall clamping range can be provided.

[0020] In embodiments in which the spindle nuts can be fixed in several defined relative positions with respect to the clamping jaws by means of positioning or locking bolts provided on the clamping jaws, it is preferred that it is visible from the outside whether the positioning or locking bolts are engaged or not. This can prevent incorrect clamping and damage to the center clamping device due to tensioning if the positioning or locking bolts are not correctly inserted or engaged.

[0021] In yet another preferred embodiment of the center clamping device according to the invention, the clamping jaws are each formed from a base jaw, which is arranged on the base body so as to be displaceable along linear guides, and a top jaw, which is fastened to the base jaw and is in contact with the clamped workpiece when a workpiece is clamped. In this way, the areas of the clamping jaws that come into contact with the workpiece, namely the top jaws, can be designed either as soft or hard jaws, or as shaped jaws tailored to a specific workpiece.

[0022] It is preferred that the top jaws be snapped onto the base jaws and, in particular, that they can be assembled and disassembled without tools. This eliminates the need for additional components that could get lost.

[0023] When using top jaws, it is also preferred that the top jaws form a defined positive connection with the base jaws in both clamping directions of the center clamping device, particularly in the form of dovetail stops for both clamping directions. In this way, the top jaws can be used for both external and internal clamping, even with a 180° rotated arrangement of the base jaws, as previously described.

[0024] It is further preferred that the top jaws have clamping screws by means of which they can be clamped in the dovetail stops, wherein the clamping screws on the base jaws are each supported in recesses in the stop surface of the dovetail stop that is not active in this clamping direction. This ensures a secure fit of the top jaws on the dovetail stops of the base jaws, regardless of the clamping forces.

[0025] It is also preferred that the base jaws have support projections which project in the direction of displacement of the respective clamping jaw towards the other clamping jaw and which support or can support the top jaws when a workpiece is clamped internally using the center clamping device. These support projections are arranged in a crenellated manner on the base jaws at intervals and offset from one another such that the support projections of a first of the base jaws can move into the spaces between the support projections of the other base jaw when the base jaws move together and vice versa. This makes it possible to achieve effective support of the top jaws during internal clamping and at the same time prevent the support projections from significantly restricting the minimum clamping width of the center clamping device.

[0026] In yet another preferred embodiment, the center clamping device comprises a central axial bearing for the threaded spindle, which is fixed between the clamping jaws on the base body, wherein the axial bearing can be fixed in various relative positions on the base body in the displacement direction of the clamping jaws. This makes it possible to adjust the precise center position of the axial bearing according to the method described below, which forms a second aspect of the invention.

[0027] According to this method, which serves to determine the relative position of the axial bearing of the threaded spindle with respect to the base body in the aforementioned preferred embodiment of the center clamping device, the center clamping device is brought into a state in which the fixation between the axial bearing of the threaded spindle and the base body is temporarily released, so that the axial bearing can be moved on the base body in the direction of displacement of the clamping jaws. Stops are also temporarily attached to the two clamping jaws of the center clamping device, which limit their displacement in one of the two displacement directions.

[0028] The two clamping jaws of the center clamping device are then clamped against the stops by rotating the threaded spindle, positioning the axial bearing of the threaded spindle relative to the base body. In this position, the axial bearing of the threaded spindle is then fixed to the base body, and the stops for the two clamping jaws are subsequently removed.

[0029] Brief presentation of the drawings

[0030] Further preferred embodiments of the invention emerge from the dependent claims and from the following description with reference to the figures. In these figures:

[0031] Fig. 1 is a perspective top view of a center clamping device according to the invention;

[0032] Fig. 2 is a side view of the center clamping device from Fig. 1; Fig. 3 is a view like Fig. 2 with one half of the center clamping device shown in section; Figures 4a to 4c are side views of the center clamping device from Fig. 1 with different settings regarding the clamping width range; Figures 5a to 5c are views like Figures 4a to 4c with the clamping jaws rotated by 180°; and Fig. 6 is a section through one of the clamping jaws in the upper area.

[0033] Ways to implement the invention

[0034] Figure 1 shows a perspective top view of a center clamping device 1 according to the invention for a machine tool, and Fig. 2 shows a side view of the center clamping device from Fig. 1, but with a setting for a different clamping range than shown in Fig. 1. Fig. 3 shows a representation like Fig. 2 with one half of the center clamping device shown in section.

[0035] As can be seen from these three figures, the center clamping device 1 comprises a base body 2 on which two clamping jaws 4, 5 are arranged displaceably along linear guides 3. The clamping jaws 4, 5 each consist of a base jaw 4, which is arranged on the base body 2, and a top jaw 5, which is attached to the base jaw 4 and is in contact with the clamped workpiece when clamping it. The top jaws 5 are snapped onto the base jaws 4.

[0036] Furthermore, the center clamping device 1 comprises a threaded spindle 6 with two spindle nuts 7, for moving the two clamping jaws 4, 5 relative to each other along the linear guides 3 in the direction of displacement S by rotating the threaded spindle 6. The threaded spindle 6 has a central axial bearing 13 which is fixed between the clamping jaws 4, 5 on the base body 2, wherein the axial bearing 13 can be fixed in different relative positions on the base body 2 in the direction of displacement S of the clamping jaws 4, 5.

[0037] The spindle nuts 7 are formed separately from the clamping jaws 4, 5 and each of the spindle nuts 7 is received in a guide 8 within one of the two base jaws 4, within which it is fixed in its relative position with respect to the respective clamping jaw 4, 5 by means of two positioning bolts (not visible) provided by the respective base jaw 4, the effect of which can be temporarily canceled by pressing associated actuating buttons 9. For this purpose, the positioning bolts engage from opposite sides radially to the axis of rotation of the threaded spindle 6 under spring pressure in each case in one of three positioning openings 15 provided at specific distances from one another in the spindle nut 6.

[0038] If the positioning bolts are extended by pressing the actuating buttons 9 against the spring load from the positioning openings 15 effective in the respective relative position, the relative position between the spindle nut 7 and the base jaw 4 in the displacement direction S of the clamping jaw 4, 5 can be changed by moving the clamping nut 7 within the guide 8, and a total of three different relative positions between the spindle nut 7 and the clamping jaw 4, 5 in the displacement direction S of the clamping jaw 4, 5 can be set and fixed by moving the positioning bolts into other positioning openings 15 on the spindle nut 7. Thus, three different relative positions between the clamping jaws 4, 5 and the spindle nuts 7 in the displacement direction S of the clamping jaws can be set in defined steps, without the need for tools.

[0039] The actuating buttons 9 are designed in such a way that, when the positioning bolts are inserted as intended, they are flush with the outer surface of the respective base jaw 4 and, in order to extend the positioning pins from the positioning openings 15, they must be pressed inwards against a spring force. If a spindle nut 7 is in an intermediate position in the guide 8 in the base jaw 4, in which the positioning pins cannot engage in any of the positioning openings 15, the actuating buttons 9 remain in their pressed-in positions. This makes it clear from the outside whether the positioning bolts are inserted as intended or have engaged or not.

[0040] Figures 4a, 4b and 4c show side views of the center clamping device 1 in the three different adjustable relative positions between the spindle nuts 7 and the clamping jaws 4, 5, whereby Fig. 4a shows the setting with the smallest clamping width range, Fig. 4b (which is identical to Fig. 2) shows the setting with a medium clamping width range and Fig. 4c shows the setting with the largest clamping width range. For the sake of clarity, the reference numbers have not been entered again here. These can undoubtedly be derived from Figures 1 to 3.

[0041] The positioning openings 15 on the spindle nuts 7 are spaced apart from one another in such a way that the clamping width ranges resulting from the three defined relative positions between the spindle nuts 7 and the clamping jaws 4, 5 overlap.

[0042] As can also be seen from Fig. 1, the spindle nuts 7 have the shape of a polygon when viewed in the direction of the axis of rotation of the threaded spindle 6 or in the direction of displacement S of the clamping jaws 4, 5, and the guides 8 in the clamping jaws 4, 5 have a complementary shape so that there is a rotational positive connection in both directions of rotation of the threaded spindle 6 between the spindle nuts 7 and the clamping jaws 4, 5 and the positioning bolts 9 do not have to absorb any forces in this regard. As can be seen from Figures 5a to 5c, which show representations such as Figures 4a to 4c with reversely oriented clamping jaws 4, 5, the center clamping device 1 is designed in such a way that the clamping jaws 4, 5 can be removed from the base body 2 and from the spindle nuts 7 without tools and can then be arranged again on the guides 3 of the base body 2 in a position rotated by 180°.In these Figures 5a-5c, too, the reference numbers have not been entered again for the sake of clarity. These can also be clearly derived from Figures 1 to 3. Even in this reversed orientation of the clamping jaws 4, 5, the relative positions between the spindle nuts 7 and the base jaws 4 in the displacement direction S of the clamping jaws 4, 5 can be changed by moving the spindle nuts 7 within the guides 8, and by moving the positioning bolts into the positioning openings 15 on the spindle nuts 7, a total of three different relative positions between the spindle nuts 7 and the clamping jaws 4, 5 in the displacement direction S of the clamping jaws 4, 5 can be set and fixed.Thus, even when the clamping jaws 4, 5 are rotated by 180°, three different relative positions between the clamping jaws 4, 5 and the spindle nuts 7 can be set in fixed steps in the displacement direction S of the clamping jaws, without the need for tools.

[0043] The positioning openings 15 on the spindle nuts 7 are spaced apart from one another in such a way that the clamping width ranges resulting from the three defined relative positions between the spindle nuts 7 and the clamping jaws 4, 5 also overlap and, in addition, there is also an overlap with the clamping width ranges which result in the respective defined relative positions when the clamping jaws 4, 5 are arranged in a non-twisted manner as shown in Figures 4a to 4c.

[0044] As can be seen from Fig. 6, which shows a section through one of the clamping jaws 4, 5 in the upper area, the base jaws 4 and the top jaws 5 are designed in such a way that the top jaws 5 form a defined positive connection with the base jaws 4 in both clamping directions S of the center clamping device 1, specifically in the form of dovetail stops 10 for both clamping directions S. The top jaws 5 have clamping screws 11, by means of which they are clamped in the dovetail stops 10, the clamping screws 11 on the base jaws 4 each being supported in recesses in the stop surface of the dovetail stop 10 which is not active in this clamping direction.

[0045] As can best be seen from Fig. 1, the base jaws 4 of the center clamping device 1 have support projections 12 which project in the direction of displacement S of the respective clamping jaw 4, 5 towards the other clamping jaw 4, 5 and which support or can support the top jaws 5 when a workpiece is clamped internally with the center clamping device 1. As can be seen, these support projections 12 are arranged on the base jaws 4 at intervals and offset from one another in such a way that the support projections 12 of a first of the base jaws 4 can enter the spaces between the support projections 12 of the other base jaw 4 when the base jaws 4 move together and vice versa.

[0046] In order to determine the relative position of the axial bearing 13 of the threaded spindle 6 with respect to the base body 2, the center clamping device 1 is brought into a state in which the fixation between the axial bearing 13 of the threaded spindle 6 and the base body 2 is temporarily released, so that the axial bearing 13 can be moved in the direction of displacement S of the clamping jaws 4, 5 on the base body 2. In addition, stops 14 (see sectioned left half of Fig. 3) for the two clamping jaws 4, 5 of the center clamping device 1 are temporarily attached to the base body 2, which stops limit their displacement towards one another. The two clamping jaws 4, 5 of the center clamping device 1 are then clamped against the stops 14 by rotating the threaded spindle 6, wherein the axial bearing 13 of the threaded spindle 6 is positioned relative to the base body 2.In this position, the axial bearing 13 of the threaded spindle 6 is then fixed to the base body 2 and subsequently the stops 14 for the two clamping jaws 4, 5 are removed again.

[0047] While preferred embodiments of the invention are described in the present application, it is to be clearly understood that the invention is not limited thereto and may be embodied in other ways within the scope of the following claims.

Claims

Patent claims 1. Center clamping device (1) for clamping workpieces to be machined, comprising: a) a base body (2); b) two clamping jaws (4, 5) arranged slidably on the base body (2) along linear guides (3); c) a threaded spindle (6) with two spindle nuts (7) for moving the two clamping jaws (4, 5). 5) relative to each other along the linear guides (3) by rotating the threaded spindle (6) ; wherein each of the spindle nuts (7) is assigned to exactly one clamping jaw (4, 5) and the spindle nuts (7) are designed separately from the clamping jaws (4, 5), and wherein different relative positions between the clamping jaws (4, 5) and the spindle nuts (7) are adjustable in the displacement direction (S) of the clamping jaws (4, 5 .

2. Center clamping device (1) according to claim 1, wherein the relative positions between the clamping jaws (4, 5) and the spindle nuts (7) in the displacement direction (S) of the clamping jaws (4, 5) are adjustable without tools.

3. Center clamping device (1) according to one of the preceding claims, wherein the relative positions between the clamping jaws (4, 5) and the spindle nuts (7) in the displacement direction (S) of the clamping jaws (4, 5) are adjustable in defined steps.

4. Center clamping device (1) according to one of the preceding claims, wherein the spindle nuts (7) are displaceable in guides (8) in the clamping jaws (4, 5) in the displacement direction of the respective clamping jaw (4, 5) relative to the clamping jaw (4, 5).

5. Center clamping device (1) according to claim 4, wherein the guides (8) in the clamping jaws (4, 5) are designed such that they generate a rotary positive locking in both directions of rotation of the threaded spindle (6) between the spindle nuts (7) and the clamping jaws (4, 5).

6. Center clamping device (1) according to claim 5, wherein the spindle nuts (7) have the shape of a polygon when viewed in the direction of the axis of rotation of the threaded spindle (6) and the guides (8) in the clamping jaws (4, 5) have a complementary shape.

7. Center clamping device (1) according to one of claims 4 to 6, wherein the spindle nuts (7) can be fixed in several defined relative positions with respect to the clamping jaws (4, 5), in particular by means of positioning or locking bolts (9) provided on the clamping jaws (4, 5).

8. Center clamping device (1) according to claim 7, wherein the clamping ranges resulting at the respective defined relative positions between the spindle nuts (7) and the clamping jaws (4, 5) overlap.

9. Center clamping device (1) according to one of claims 4 to 8, wherein the clamping jaws (4, 5) can be removed from the base body (2) and from the spindle nuts (7) in particular without tools and then arranged again on the guides (3) of the base body (2) in a 180° rotated position and can be connected to the spindle nuts (7) in several defined relative positions, in particular by means of positioning or locking bolts (9) provided on the clamping jaws (4, 5).

10. Center clamping device (1) according to claim 9, wherein the clamping jaws (4, 5) resulting from a 180° rotated arrangement at the respective defined relative positions between the spindle nuts (7) and the clamping jaws (4, 5) overlap, and in particular, wherein these overlap with the clamping jaws resulting from a non-rotated arrangement at the respective defined relative positions.

11. Center clamping device (1) according to one of claims 7 to 10, wherein it is visible from the outside whether the positioning or locking bolts (9) are inserted or engaged as intended or not.

12. Center clamping device (1) according to one of the preceding claims, wherein the clamping jaws (4, 5) each consist of a base jaw (4) which is slidably arranged on the base body (2) along the linear guides (3), and an attachment jaw (5) which is attached to the base jaw (4) and is in contact with the clamped workpiece when clamping a workpiece.

13. Center clamping device (1) according to claim 12, wherein the top jaws (5) are snapped onto the base jaws (4), and in particular can be mounted and dismounted without tools.

14. Center clamping device (1) according to one of claims 12 to 13, wherein the top jaws (5) in both clamping directions (S) of the center clamping device (1) form a defined positive fit with the base jaws (4), in particular in the form of dovetail stops (10) for both clamping directions (S) .

15. Center clamping device (1) according to claim 14, wherein the top jaws (5) have clamping screws (11) by means of which they can be clamped in the dovetail stops (10), wherein the clamping screws (11) are supported on the base jaws (4) in recesses in the stop surface of the dovetail stop (10) which is not active in this clamping direction.

16. Center clamping device (1) according to one of claims 14 to 15, wherein the base jaws (4) have support projections (12) which project towards the other clamping jaw (4, 5) in the displacement direction (S) of the respective clamping jaw (4, 5) and which support or can support the top jaws (5) when clamping a workpiece internally with the center clamping device (1), and wherein these support projections (12) are arranged on the base jaws (4) at intervals and offset from each other such that the support projections (12) of a first of the base jaws (4) can enter the intervals between the support projections (12) of the other base jaw (4) when the base jaws (4) are brought together and vice versa.

17. Center clamping device (1) according to one of the preceding claims, further comprising a central axial bearing (13) for the threaded spindle (6) which is fixed between the clamping jaws (4, 5) on the base body (2), wherein the axial bearing (13) can be fixed in different relative positions on the base body (2) in the displacement direction (S) of the clamping jaws (4, 5).

18. Method for determining the relative position of the axial bearing (13) of the threaded spindle (6) with respect to the base body (2) in a center clamping device (1) according to claim 17, comprising the steps: a) providing the center clamping device (1) in a state in which the fixation between a) temporarily suspending the axial bearing (13) of the threaded spindle (6) and the base body (2), so that the axial bearing (13) is displaceable on the base body (2) in the displacement direction (S) of the clamping jaws (4, 5); b) temporarily attaching stops (14) for the two clamping jaws (4, 5) of the center clamping device (1); c) displacing the two clamping jaws (4, 5) of the center clamping device (1) by rotating the threaded spindle (6) against the stops (14), whereby the axial bearing (13) of the threaded spindle (6) is positioned relative to the base body (2); and in this position d) fixing the axial bearing (13) of the threaded spindle (6) on the base body (2); and subsequently e) removing the stops (14).

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