DENTAL MACHINE TOOL

Abstract

The invention relates to a dental machine tool, in particular a dental milling machine (10), having a tool (12) that is changeable in particular via a tool bank (16), and a workpiece holder (14) for receiving a workpiece such as a dental blank made of ceramic, composite or plastics material such as PMMA, and having a housing (24) which is closable during machining by the machine tool, and having a negative-pressure connection to the housing (24). At least one air nozzle (30) that is fitted on or in the housing (24) is directed towards the workpiece and/or the workpiece holder (14) and/or the tool (12) and/or the tool bank (16) and/or a pane of a front flap of the machine tool. Said air nozzle (30) is equipped with at least one electrode for generating an electric field in the region of the nozzle or in front of the latter, and at least one nozzle comprising at least one electrode is directed towards that side of the workpiece or of the workpiece holder (14) on which the tool (12) machines the workpiece. At least two electrodes of an ionizer extend in a spaced-apart manner over a substantial part of the housing (24), and as a result of the application of an in particular pulsating AC voltage provides spatial deionization of the air flowing through the housing (24) and/or deionization of the surfaces of the workpiece, workpiece holder (14), tool (12) and/or window (28) and of the chips produced by the machining operation.

Claims

1. A dental machine tool, in particular a dental milling machine (10) comprising: a tool (12), the tool (12) changeable via a tool bank (16), a workpiece holder (14) for receiving a workpiece, a housing (24) which is closable during machining by the machine tool, a negative-pressure connection to the housing (24), characterized in that at least one air nozzle (30) that is fitted on or in the housing (24) is directed towards the workpiece and/or the workpiece holder (14) and/or the tool (12) and/or the tool bank (16) and/or a pane of a front flap of the machine tool, and comprising at least one electrode for generating an electric field in the region of the nozzle or in front of the nozzle, and that the at least one nozzle comprising at least one electrode is directed towards that side of the workpiece or of the workpiece holder (14) on which the tool (12) machines the workpiece and that at least two electrodes of an ionizer extend in a spaced-apart manner over a substantial part of the housing (24), and as a result, application of pulsating AC voltage provides spatial deionization of the air flowing through the housing (24) and/or deionization of the surfaces of the workpiece, workpiece holder (14), tool (12) and/or window (28) and of the chips produced by the machining operation.

2. The dental machine tool as claimed in claim 1, characterized in that the electrode is connected with a voltage generator which produces an electric voltage of more than 1 kV.

3. The dental machine tool as claimed in claim 1, characterized in that a voltage generator which is connected with the electrode produces an AC voltage.

4. The dental machine tool as claimed in claim 1, characterized in that the machine tool comprises a door (26) through which the workpieces and tools can be inserted and removed, and in that the at least one air nozzle (30) with the at least one electrode is arranged above the door, in particular adjacent to the latter.

5. The dental machine tool as claimed in claim 4, characterized in that the dental machine tool comprises a window (28) in the housing (24) or in a door (26) of the housing, and in that the outflow direction of at least one air nozzle (30) is directed towards the window (28).

6. The dental machine tool as claimed in claim 4, characterized in that a plurality of air nozzles with at least one electrode each are arranged next to one another and extend transversely over a front side of the housing (24) of the dental machine tool, over more than half of the width of the machine tool, said front side being possibly equipped with a door (26).

7. The dental machine tool as claimed in claim 1, characterized in that at least one air nozzle (30) is equipped with at least one electrode or two electrodes and that at least one air nozzle (30) outputs air in an air nozzle (30) which is directed towards the workpiece and/or the tool (12).

8. The dental machine tool as claimed in claim 1, characterized in that the at least one electrode forms part of an ionizer, and that an air flow channel extends between the at least one air nozzle (30) and the negative-pressure connection of the housing (24), and that the ionizer is directed towards the air flow channel, upstream of the tool/workpiece.

9. The dental machine tool as claimed in claim 1, characterized in that at least one air nozzle (30) is directed towards shanks of the tools in a tool bank (16).

10. The dental machine tool as claimed in claim 1, characterized in that each air nozzle (30) which is equipped with at least one electrode comprises two opposite electrodes which extend in the form of a partial ring around an outflow channel which is configured between 0.5 cm and 5 cm in front of the air nozzle (30), and that the electrodes deionize the air flow over a distance of more than 1 cm.

11. The dental machine tool as claimed in claim 1, characterized in that the at least one air nozzle (30) or the plurality of air nozzles is connected to an air control unit which changes the air flow considered over time and gives off air impulses.

12. The dental machine tool as claimed in claim 1, characterized in that via the air nozzle (30) or the air nozzles which are equipped with ionizing electrodes a defined air flow is generated which is directed towards the workpiece, the workpiece holder (14), the tool (12) and/or the tool bank (16), said air flow carrying off the chips produced by the machining process of the machine tool from the generation zone and supplying the chips to the negative-pressure connection.

13. The dental machine tool as claimed in claim 1, characterized in that at least two electrodes of an ionizer extend in a spaced-apart manner from one another over more than a third of the housing (24), in particular more than half of the housing (24) and as a result of the application of pulsating AC voltage provide spatial deionization of the air flowing through the housing (24) and/or deionization of the surfaces of the workpiece, workpiece holder (14), tool (12) and/or window (28) and of the chips produced by the machining operation.

14. The dental machine tool as claimed in claim 1, characterized in that several air nozzles are arranged transversely relative to the front flap of the dental machine tool in at least one row, offset from one another and/or offset angularly.

15. The dental machine tool as claimed in claim 1, characterized in that the sucked off amount of air produced by the negative-pressure connection is larger than the amount of air supplied by the air nozzle or air nozzles and that the inner space of the housing (24) is under negative pressure compared to the ambient air.

16. The dental machine tool as claimed in claim 1, characterized in that the negative pressure at the negative-pressure connection is 50 mbar to 500 mbar compared to the ambient air and that the positive pressure of the positive-pressure source to which the at least one nozzle is connected is more than 0.1 bar.

17. The dental machine tool as claimed in claim 1, characterized in that the amount of air supplied by the positive-pressure source is between 10 and 150 l/min.

18. The dental machine tool as claimed in claim 16, characterized in that the positive pressure of the positive-pressure source to which the air nozzle (30) is connected is controllable.

19. The dental machine tool as claimed in claim 1, characterized in that the at least one air nozzle (30) in the housing (24) is substantially diametrically opposed to the negative-pressure connection such that the air flow channel of the air flow produced by the air nozzle (30) and the negative pressure extends diagonally transversely through the housing (24).

20. The dental machine tool as claimed in claim 1, characterized in that the dental machine tool is a dental milling machine.

21. The dental machine tool as claimed in claim 1, characterized in that the workpiece comprises a dental blank made of ceramic, composite or plastics material such as PMMA,

22. The dental machine tool as claimed in claim 21, characterized in that the plastics material comprises PMMA.

23. The dental machine tool as claimed in claim 2, characterized in that the electrode voltage is between 4 and 8 kV.

24. The dental machine tool as claimed in claim 3, characterized in that a voltage generator produces a square-wave voltage.

25. The dental machine tool as claimed in claim 4, characterized in that the at least one electrode is arranged adjacent to the door.

26. The dental machine tool as claimed in claim 10, characterized in that the distance comprises at least 5 cm.

27. The dental machine tool as claimed in claim 16, characterized in that the positive pressure of the positive-pressure source to which the at least one nozzle is connected is about 0.4 bar.

28. The dental machine tool as claimed in claim 17, characterized in that the amount of air supplied by the positive-pressure source is between 40 and 90 l/min.

29. The dental machine tool as claimed in claim 17, characterized in that the amount of air supplied by the positive-pressure source is between 60 and 70 l/min.

Description

[0034] Further advantages, details and features may be taken from the following description of two exemplary embodiments of the invention in conjunction with the drawings, in which:

[0035] FIG. 1 shows a schematic side view of an inventive dental machine tool in one embodiment which is configured as a dental milling machine;

[0036] FIG. 2 shows an embodiment modified compared with the embodiment of FIG. 1, but in another side view;

[0037] FIG. 3 shows a perspective view of a section of the dental milling machine according to the FIGS. 1 and 2; and

[0038] FIG. 4 shows a partially broken up perspective view of a dental milling machine according to the FIGS. 1 to 3.

[0039] FIG. 1 shows a dental milling machine 10 having a tool 12, which is configured as a milling spindle in the exemplary embodiment illustrated, a workpiece holder 14, into which a workpiece (not illustrated) may be clamped, and a tool bank 16 which is attached to the workpiece holder in the case of the exemplary embodiment described herein.

[0040] In a way known per se both the tool with the tool drive 20 and the workpiece holder 14 can be moved multi-axially. In the exemplary embodiment illustrated the tool can be moved biaxially and the workpiece holder can be moved triaxially such that a five-axis dental milling machine is provided.

[0041] It is to be understood that instead any other machine tools may be realized, for instance four-axis or six-axis dental milling machines, drilling machines, grinding machines or any other machine tool which is used to effect machining.

[0042] The dental milling machine 10 comprises a milling chamber 22 which is substantially smaller than the remaining housing 24 of the dental milling machine 10, and for instance comprises one tenth to one third of the volume. The housing 24 of the dental milling machine 10 further comprises a door 26 which is equipped with a window 28 which is arranged in a slightly oblique fashion and tilted to the inside at the top and which makes possible to have a look at the workpiece during the machining process by the dental milling machine 10.

[0043] According to the invention, the dental milling machine 10 comprises an air nozzle 30 which is directed towards the workpiece clamped in the workpiece holder 14 in the illustrated exemplary embodiment obliquely from the top/from the side, more specifically, towards the machining region in which the tool 12 machines the workpiece. The orientation refers to the outflow axis of the nozzle, wherein at least the outflow cone of the nozzle always covers the machining region also in case of the five-axis movements of workpiece and tool 12 against one another.

[0044] In the exemplary embodiment illustrated, the air nozzle 30 is fixedly mounted to the housing, wherein it is to be understood that a movable installation is also possible alternatively, which carries along the air nozzle 30 with the tool 12—or the workpiece holder 14.

[0045] According to the invention, the air nozzle 30 comprises electrodes, one electrode 32 of which is schematically apparent in FIG. 1. The electrode 32 extends through the interior of the air nozzle 30 along the air line, that is to say parallel relative to the outflow direction, preferably along the entire length of the nozzle, in the exemplary case over about 4 cm. Opposite to it, that is to say offset by 180°, a further electrode is provided and the electrodes are connected to a voltage generator (not illustrated) which generates an electric voltage which can be controlled between 4 and 8 kV. Preferably, the electric voltage is an alternating voltage, namely a square-wave voltage, and preferably, one of the electrodes—namely the electrode which is not illustrated—is connected to ground.

[0046] The electrode 32 is arranged in the air nozzle 30 in a recessed manner such that protection against contact is provided in this connection. Moreover, the electrode 32 is connected with the voltage generator via a series resistor of at least one megohm.

[0047] Although in FIG. 1 only one air nozzle 30 is illustrated, it is to be understood that in fact a plurality of electrodes is provided. These electrodes are mounted next to one another or one after the other, that is to say above the drawing plane or below the drawing plane, and oriented towards one another obliquely, respectively. The preferred inclined position of the air nozzles strongly depends on the expanding cone of the air flow leaving the air nozzles 30 and amounts to particularly between 5° and 30°.

[0048] Preferably, at least one of the air nozzles is also directed towards the pane or the window 28 obliquely from the side, such that an air flow is produced which flows along the window 28.

[0049] The air nozzles extend substantially parallel to the tool spindle 12 from the top to the workpiece which is not illustrated and which is held clamped in the workpiece holder 14. This allows for direct and targeted air supply of ionized air to the position at which the chips are produced.

[0050] Chips are produced during the machining process of the machine tool 10. If, for instance, a plastic disc, such as a disc made of PMMA, is machined, charged chips are produced by means of the frictional electricity. They adhere to the disc clamped in the workpiece holder, said disc forming the workpiece, but also to the milling cutter as the tool 12 and in particular to the shanks of the tools received within the tool bank 16.

[0051] By means of the targeted supply of deionized air from the air nozzles 30 the chips adhering thereat are deionized in this way and can be removed easily by the air flow in one go.

[0052] This also applies to chips which adhere to the window 28; here, too, the chips are both deionized and carried along by the flow.

[0053] In one corner of the milling chamber 22 a negative-pressure connection 40 is provided which serves to suck off the chips. The deionized chips are sucked off together with the air supplied by the air nozzles 30 by means of the negative-pressure connection 40 and are thus completely removed from the milling chamber 22.

[0054] In FIG. 2, a modified embodiment compared to the embodiment of FIG. 1 is apparent. Here, the negative-pressure connection 40 is arranged at a slightly different location, and two air nozzles 30 and 31 extend slightly obliquely to one another, as illustrated.

[0055] In the illustrated tool position, the flow axis of the air nozzle 30 is directed to an area just next to the machining position of the tool spindle 12 at the workpiece which is not illustrated, namely towards the door 26 or the window 28. In the exemplary embodiment illustrated, the workpiece holder 14—and thus the workpiece clamped therein—extends perpendicularly to the outflow direction of the air nozzle 30. The workpiece holder 14 is moved regularly during the machining process such that only an instantaneous position is indicated in this connection. A slightly oblique air supply to the workpiece through the air nozzle 30 is preferred in order to provide for a better air flow to remove the chips. Here, an inclination angle of 10° or 40° relative to the position illustrated in FIG. 2 is enough.

[0056] It is also possible to provide a plurality of negative-pressure connections 40, for instance in the rear corners to the right- and to the left-hand side, at the bottom of the milling chamber 22, respectively.

[0057] From FIG. 3 a further embodiment of an inventive machine tool 10 is apparent. This embodiment shows three air nozzles 30, 31 and 33 which are mounted to an air nozzle holder 42 one next to the other and which are arranged relative to one another in an oblique fashion. The distance of the air nozzles 30, 31 and 33 is selected such that, in any case, the area of movement of the workpiece clamped in the workpiece holder 14 is covered by the added up outflow cone of the air nozzles 30, 31 and 33 during the machining process.

[0058] The air nozzles 30, 31 and 33 each comprise air connections 44 which are each connected to a positive-pressure source via hoses. Preferably, the pressure of the positive-pressure source is controllable and may amount to, for instance, between 0.1 bar and 1.0 bar, for instance to about 0.4 bar.

[0059] In an alternative embodiment it is provided to work with a comparatively high pressure of 5 bar to 7 bar. At this pressure, the length of throw of the emitted air is substantially higher, and distant areas of the milling machine, that is to say areas which are spaced apart from the respective nozzle, for instance, by 30 cm, may also be reached easily. In case of high-pressure nozzles of this type it is recommended to lengthen the ionization channel in order to ensure secure ionization of the air in spite of the higher outflow speed.

[0060] In one embodiment of the inventive dental machine tool it is provided to apply an operating voltage of 7 kV to the electrodes, namely at an impulse/pause ratio of between 0.5 to 1 and 2 to 1 using a square wave. The current between the electrodes or between the ionization electrode and the ground is limited to 0.5 mA such that no inadmissibly high current occurs even in case of comparatively humid air.

[0061] The area of the ideal air supply to the workpiece or tool is at a distance of between 50 mm and 250 mm in front of the nozzle.

[0062] A further advantage of the inventive solution is that the cleaning air flow is of comparatively low volume; at an air pressure of 1 bar it amounts to only 68 db measured at a distance of 60 cm next to the air nozzle.

[0063] In a modified embodiment it is provided to work with slightly lower pressure and to limit the current to 20 mA, and, in a third embodiment, to work with a lower voltage, for instance 4 kV and to limit the current to 2.5 mA.

[0064] The negative pressure of the negative-pressure connection may also be controllable, but preferably amounts to about 500 mbar.

[0065] From FIG. 4 a dental milling machine 10 is apparent in an embodiment according to FIG. 3, wherein, here, both the window 28 and the door 26 but also the housing 24 are illustrated partially broken up and allow to have a look at the nozzles 30, 31 and 33.

[0066] In this embodiment, the air nozzle 31 is directed such that its expanded air flow hits the window 28 obliquely from the side and deionizes any chips adhering thereto and carries them along such that they can be removed by means of the pressure connection 40.

[0067] The materials to be machined comprise all of the materials to be machined particularly in the dental field, and primarily the plastic materials PMMA, polyurethane, polyamide, PEEK and composites.

[0068] However, resins and plastic-modified resins may also be machined accordingly.