Method for operating a dental polishing device and dental polishing device

Abstract

The invention proposes a method for operating a dental polishing device, which has a polishing unit, which is driven by a dental machine tool. The polishing unit comprises a circular polishing core and a polishing assembly, which is circular and in particular surrounds the polishing core. The polishing device also has a workpiece to be polished, and the polishing assembly is elastically deformed when it is applied to the workpiece. A digitally controlled control device moves the polishing device along a movement path relative to the workpiece on the workpiece. The workpiece is sunk into the polishing assembly with a constant or substantially constant sinking-in dimension. The control device readjusts the sinking-in dimension on the basis of a process parameter.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for operating a dental polishing device, to a method as described above, to a dental polishing device, to a dental machine tool and to a CAM software for a dental machine tool. BACKGROUND

[0002] Dental restorations, which can also be referred to as workpieces, are manufactured by means of a dental machine tool. The workpieces are produced by the machine tool by means of a material-removing method. The method comprises in particular milling, but also rotary grinding. Rotary grinding has the particular advantage for polishing that the tool can be in constant motion. Neither deceleration nor acceleration phases are noticeable.

[0003] The manufacture is usually carried out digitally, that is to say by means of a CNC machine tool. The machine tool guides the tool over the workpiece along a predetermined path, that is to say a movement path. This relative movement is based on milling data, which predefine the movement path. However, even when the movement path has a fine resolution of for example 0.05 mm, a certain roughness remains on the surface of the workpiece. This is the case even when a fine milling with a particularly small advance is used as the last step of the actual manufacturing process.

[0004] Therefore, polishing is usually carried out after the actual manufacturing process, that is to say after milling or rotary grinding. For this purpose, a separate polishing device is used, or the lathe is directly equipped with a polishing tool.

[0005] At this point, the polishing tool is moved along a specific movement path relative to the surface of the workpiece. The polishing tool is for example significantly softer than a milling cutter. The polishing tool should be guided along the surface of the workpiece on the surface of the workpiece with a defined pressure, so that a polishing action results, which is combined from the deformation of the surface of the workpiece and the removal of roughness peaks.

[0006] The polishing tool is at this point clamped into the machine tool with its shank and carries a polishing unit, which consists of a polishing core, which is circular and hard, and a polishing assembly, which surrounds the polishing core and is softer than the polishing core.

[0007] The movement path is set in such a way that the workpiece sinks into the polishing assembly, which surrounds the polishing core.

[0008] Usually, the polishing tool is replaced when it is worn, that is to say no longer has a sufficient polishing action.

[0009] Dental restorations, which can also be referred to as workpieces, are manufactured by means of a dental machine tool. The workpieces are produced by the machine tool by means of a material-removing method. The method comprises in particular milling, but also rotary grinding. Rotary grinding has the particular advantage for polishing that the tool can be in constant motion. Neither deceleration nor acceleration phases are noticeable. A dental restoration can also have sharp edges. One example is the edge of a crown, which faces the gums. When the edge is particularly sharp, this edge can cause the polishing assembly to wear very quickly.

[0010] The wear of the polishing assembly is sometimes very high. It is therefore proposed to replace the polishing assembly and the polishing tool prophylactically after at least an assumed service life, even if this leads to early replacement and thus to higher costs in many cases.

[0011] It is also proposed to improve the accuracy of the movement path of the polishing tool in order to improve the use, but without achieving the desired significant improvement. SUMMARY

[0012] It is therefore the object of the present application to realize a method for operating a dental polishing device according to the application and a dental polishing device according to the application and a dental machine tool according to the application and a CAM software for a dental machine tool according to the application, which realize a better use of the polishing assembly without additional costs.

[0013] A special digitally controlled control device or a specially set digital control device is used with the method according to the application. The control device guides the polishing assembly along a specific movement path on the workpiece to be polished. In the embodiment of the application, the movement path corresponds to a constant or substantially constant sinking dimension of the workpiece into the polishing assembly. According to the application, however, the movement path is readjusted on the basis of specific process parameters. The process parameters can be, for example, the feed, the material of the workpiece, the surface of the workpiece, the material of the polishing assembly, the shape of the polishing assembly and / or the pressure between the polishing assembly and the workpiece.

[0014] In the actual implementation, a correlation with time or path length is established. This correlation is derived in a material-specific test in relation to the previous finishing strategy.

[0015] The polishing device according to the application comprises a polishing unit, which is formed by a polishing assembly and a polishing core. The polishing assembly surrounds the hard polishing core or at least partially surrounds the polishing core in a manner known per se.

[0016] In addition, the polishing device comprises a workpiece to be polished. The workpiece is unpolished at the beginning of the polishing process, but is milled to completion. As a rule, the workpiece has been manufactured in a dental machine tool by milling or rotary grinding and is ready for polishing.

[0017] Alternatively, the workpiece can also be manufactured in another way and can require a polishing process.

[0018] The workpiece is supported on a workpiece holder, for example by adhesive connection, by screw connection or by clamping means. The holder is clamped into a machine tool for the polishing process. The polishing method according to the application is carried out until the workpiece is sufficiently polished.

[0019] In an embodiment of the application, too, a constant or substantially constant sinking dimension of the workpiece is worked with. But additionally at least one dimension of the polishing assembly is measured, in particular the diameter or the radial extension is measured. Alternatively, too, the dimension of the workpiece can be measured. The measurement takes place by means of sensors or for example by means of a camera. Now, on the basis of the result of the measurement, the movement path is readjusted by the specialized control device according to the application.

[0020] Indirect measurements, too, can be carried out: for example, sound wave measurements can be carried out. From the measurement result, the contact strength is inferred and thus indirectly the wear of the polishing assembly.

[0021] In this connection, according to the application, first of all the movement path with constant sinking dimension, which is calculated by the control device and which is determined to be advantageous for the polishing action, is determined. Now, starting from this standard movement path, the deviation is determined.

[0022] The deviation can lead to a smaller sinking depth or to a greater sinking, on the one hand. In this connection, the movement path is readjusted. The readjustment can take place once in advance, for example on the basis of the material parameters of the workpiece and / or of the polishing assembly. Or, for example, on the basis of the shape of the polishing assembly. For example, in this connection, the polishing action of disc-shaped and cone-shaped polishing assemblies can be optimized.

[0023] With this embodiment, too, tool wear can be taken into account. When the tool wear is greater, then the sinking dimension is increased in order to thereby regain the same polishing effect.

[0024] It is desired that the sinking dimension is not increased. The sinking dimension is readjusted, whereby the sinking dimension is equalized to the original value. The readjustment amount is increased. Here, it is based on the definition that the sinking dimension is related to the original tool, that is to say to the nominal diameter.

[0025] The expression "sinking dimension" here means the dimension of the workpiece and its surface sinking into the movement path, which is obtained on the surface of the polishing assembly with its nominal diameter, that is to say in the unused state of the polishing assembly, when moved through the movement path without the workpiece.

[0026] This sinking dimension can be readjusted relatively easily, since the nominal dimension of the new tool, that is to say of the polishing assembly, and the surface of the workpiece and thus also the profile are known.

[0027] At this point, the actual sinking dimension is increased as the tool wears, which compensates for the degradation of the polishing effect due to tool wear.

[0028] According to the application it is also alternatively provided that the readjustment takes place during the polishing process.

[0029] To this end a sensor or camera is provided. The sensor detects the diameter or other radial extension of the polishing assembly, but alternatively the dimensions of the workpiece, and transmits the measurement to the control device. The control device now readjusts the movement path dynamically.

[0030] With this measure it is also possible to keep the actual polishing effect constant, but it is also possible to adapt the actual polishing effect to the polishing state. If a finishing edge, for example a gingival edge of a crown, is polished, the control device can reduce the sinking depth. Thereby it is achieved that the tool wear is significantly reduced, but also that the crown edge is not removed too much.

[0031] Furthermore, it is ensured that a finishing edge, for example a crown edge, is not overheated when being polished.

[0032] When an inner corner of a workpiece is to be polished with a pointed polishing tool, the same measure and the same measure is reasonable according to the application.

[0033] The application is not limited to the new manufacture of such a dental polishing device. Rather, a dental machine tool, for example a milling machine, can also be used according to the application and equipped with a dental polishing device. To this end, the CAM software of the machine tool is changed or reinstalled and the machine tool is equipped with a polishing tool.

[0034] At this point, the upgrade of the software achieves a control device according to the application with which the sinking dimension can be readjusted on the basis of process parameters or on the basis of the measurement of a sensor. The firmware of the machine tool also belongs to the CAM software to be updated.

[0035] Alternatively, a polishing driver program can also be implemented according to the application, by means of which the movement data of the machine tool are influenced so that instead of the movement path corresponding to the movement data a movement path is moved through which is offset by the sinking dimension according to the application.

[0036] In another embodiment of the application, a CAM software for a dental machine tool is proposed, which software retrofits the dental machine tool to a dental polishing device. The CAM element achieves a control device, or the control device is retrofitted by means of an upgrade, with which the sinking dimension is readjusted on the basis of process parameters or on the basis of the measurement of a sensor.

[0037] Ceramics for dental purposes can be very hard. An example for this is a crown made of lithium disilicate. The matching polishing tool rotates for example at 10,000 revolutions per minute and applies a pressing force of 4 N. This leads to a significant wear.

[0038] When the desired pressing force should be for example 4 N and the average spring constant can be for example 10 N / mm, a value of for example 0.4 mm is determined as initial sink-in size by the control device first. Depending on the wear behavior, parameters for readjusting the sink-in size are determined empirically.

[0039] At a rotational speed of approximately 9,000 revolutions per minute, a readjustment of the sink-in size by 4 pm / s or 0.2 pm / mm is practical. At a polishing time of 3 minutes, a relatively constant path speed of 20 mm / s leads to a machining path of a length of 3,600 mm being achieved. Thus, in both cases, the maximum readjustment of the sink-in size is 720 pm, whether the parameter setting of 4 pm / s or 0.2 pm / mm is chosen. These values should only be understood as exemplary for illustrating the described relationship. The range of readjustment can be significantly different according to the application, for example between 0.5 pm / s and 20 pm / s or between 50 nm / mm and 1.5 pm / mm. The initial sink-in size can also be in the range of 50 pm to 1.5 mm.

[0040] It is furthermore important for the tooth that the amount of material removed on the restoration is limited to an absolute minimum and that no profile changes are made on the restoration.

[0041] In a conventional lapping process, the tool is always sunk into the blank, from which the workpiece is made and then the finished restoration, into contact with the final geometry of the workpiece. Apart from a small wear on the tool, the material removal takes place mainly on the blank. In the method according to the application, which comprises a polishing based on NC data, the workpiece already has its final geometry. The method according to the application only improves the surface quality. If the tool is guided over the surface as in a conventional machining process, no sufficient contact force between tool and workpiece occurs. In the present application, the contact force necessary for the polishing process is achieved in such a way that the workpiece is sunk into the rotating tool with the polishing assembly by a determined sink-in depth. The sink-in size is determined by the theoretical sink-in depth in the Silhouette of the unloaded rotating tool Figure 2 .

[0042] Since material removal takes place mainly on the tool and not on the workpiece, according to the application the distance between the tool reference point and the workpiece geometry is constantly reduced in order to keep the sinking depth within a constant range. Even for tools that experience high wear, this ensures the sinking dimension and thus a sufficiently high contact force.

[0043] The most important adjustment parameters for the sinking dimension are the pressing force and the stiffness of the rotating tool. These adjustment parameters in turn depend on many other factors of the tool and the workpiece, here only a few are mentioned: grain size, binder, wear, material, surface quality, strength, feed, rotational speed or coolant.

[0044] A stable polishing process is preferably achieved according to the application with a sinking dimension of more than 0.05 mm. The sinking dimension is limited upwards by the stiffness of the tool. Values of up to 1 mm are advantageous according to the application. But especially for soft and large tools, it is also possible to significantly exceed this value.

[0045] A sinking depth can be achieved both in the radial direction and in the axial direction relative to the rotational axis of the tool. It is also possible to combine both directions. But if a radial sinking dimension is used, a tool with a diameter of more than 3 mm is preferred.

[0046] For process stability and adjustability, another important feature is the change in the distance between the tool reference point and the tool geometry over time. It is preferred that this distance does not change in total over a period of 10 seconds compared to the size of the initial sinking dimension.

[0047] For large dental restorations, a predetermined sinking dimension can result in strong material removal at the beginning of the polishing, but at the end of the polishing almost no polishing is achieved due to tool wear. Here, it is particularly advantageous to use an embodiment according to the application that enables dynamic readjustment during the polishing process.

[0048] In an advantageous design of the application, the spring constant of the polishing assembly is taken into account. The spring constant can be associated with the sinking dimension according to the application. For a nominal tool diameter, the sinking dimension determined according to the application is the quotient of the pressing force and the spring constant.

[0049] When the desired pressing force should be, for example, 4 N and the average spring constant can be, for example, 10 N / mm, a value of 0.4 mm can first be determined as the starting sinking dimension by the control device. This value is dynamically increased as the tool wears.

[0050] In an advantageous design of the embodiment of the application, the precalculation of the movement path can be dispensed with and the movement path is calculated and determined adaptively. The sensor or camera adaptively adjusts the sinking dimension by means of the control device, so that the relative movement between workpiece and tool is continuously readjusted in terms of the spacing or force between workpiece and tool.

[0051] In this solution, the control device is integrated in the CNC machine or in the CAM software.

[0052] The control device determines the sinking dimension. In order to achieve a good polishing action, the pressing force is advantageously in an optimum working range. For polishing assemblies which are common in the dental sector, for example, of a size and diameter of between 8 mm and 12 mm, the optimum working range for the pressing force is approximately 4 N, that is to say, for example, between 3 and 6 N. For tools with a smaller diameter, the pressing force is expected to be reduced. In principle, it applies that the smaller the tool diameter, the smaller the pressing force. For a 3 mm tool, it can be 2 N. For a 10 mm tool, it is 4 N. Here, 8 mm to 12 mm is preferred, but from 3 mm to more than 15 mm ensures that the function is achieved.

[0053] Due to the correlation of these parameters, a smaller spring constant is advantageous, as is derived from the quotient mentioned above.

[0054] But when the polishing assembly is pressed too much, that is to say, so much that the polishing core comes into action, the spring constant increases sharply. This working point should be avoided as far as possible according to the application. Therefore, a polishing assembly according to the application with a spring constant of, for example, 10 Newton per millimetre is advantageous.

[0055] It is particularly advantageous according to the application that the control device stores a virtual movement path in advance, for example, in a memory. This virtual movement path corresponds to the contour of the workpiece, but with a reduced sinking dimension. Here, reduced means closer to the workpiece than would be the case with the actual diameter of the polishing assembly. That is to say, if a milling cutter were used instead of a polishing tool with the same data, significantly more material would be removed.

[0056] The virtual movement path makes it possible to achieve simple programming and to determine milling data, for example, in STL format.

[0057] In a further advantageous design, the polishing of the grinding edges and other sharp edges is excluded. This can also be achieved in advance in the virtual movement path, in that a negative sinking dimension is provided at these locations or the workpiece geometry is expanded by a virtual protective geometry at the locations to be excluded. In this way, it is possible to completely avoid large wear of the tool at these locations.

[0058] It is also possible to perform a series of tests in advance for the advantageous sinking dimension for common dental restorations. Now, for example, a test polishing process is performed with different sinking dimension values for three different sizes of tooth crowns. Furthermore, in order to assess the necessary readjustment speed for wear compensation, such a test polishing process can be performed in order to ascertain how quickly the sinking dimension changes over time.

[0059] This can be optimized in such a way that, for the practice, a desired sinking dimension is determined for the same type of tooth crown, but which can be changed by readjustment according to the application.

[0060] In an advantageous design of the application, the polishing force can also be measured. This applies both to the series of tests and to the case in practice. This can be done, for example, in such a way that the power consumption of the machine tool is determined. The power consumption increases with increasing polishing force and decreases with decreasing polishing force, so that the polishing force can be determined by the power consumption of the machine tool. Alternatively, the polishing force can be derived or determined by means of a force sensor or by means of a reduction in the rotational speed of the machine tool.

[0061] With conventional polishing devices, the milling track of the milling machine equipped with the polishing tool is directly followed. This usually results in unsatisfactory polishing results. In an advantageous design of the application, it is provided that the polishing assembly is placed on the surface of the workpiece and that the movement track extends in the direction of the edge of the workpiece.

[0062] It is particularly advantageous in this case if the movement track extends transversely to the direction of rotation of the polishing assembly, that is to say, for example, parallel to the axis of the polishing tool carrying the polishing assembly.

[0063] The polishing unit consisting of the polishing assembly and the polishing core can be designed in any suitable manner. The polishing assembly can have, for example, bristles or a sheet. The bristles or the sheet extend radially outwardly or at least partially radially outwardly from the polishing core. It is also possible to use an inclined extension in order to form a conical polishing unit.

[0064] The bristles or the sheet can also be bent so as to form a bowl-like shape of the polishing unit. The axial tip at which the angular velocity of the polishing unit is equal to zero is preferably not engaged with the workpiece, so that no wear occurs here. Therefore, at the axial tip of the polishing unit, the angle of the axis relative to the surface should clearly differ from 90 degrees, for example, be less than 80 degrees.

[0065] The polishing tool according to the application consists of a polishing unit and a shank. The shank is clamped in or can be clamped in the spindle of the machine tool. The shank can also be made of spring steel, which influences, for example, increases the spring constant of the polishing tool. This can be advantageous in some applications.

[0066] Alternatively, the flexible tool can also be implemented in the following way: it is three-part, with a core = handle made of steel, an inner ring = soft foam and an outer ring = polishing medium.

[0067] In an advantageous design variant, a plurality of machining passes are implemented with offset movement paths. The path spacing can be chosen to be large and for this purpose the plurality of machining passes are implemented offset by half the path spacing. An example of this is:

[0068] 1. Polishing of all faces with a path spacing of 0.3 mm

[0069] 2. Repeated polishing of all faces with a path spacing of 0.3 mm, but offset by 0.1 mm from the first pass and in a different order

[0070] 3. Repeated again with an offset of 0.1 mm.

[0071] This embodiment reduces the point-like effect of tool changes.

[0072] In another advantageous design variant, the movement path is not only composed of a line at a defined height or in the form of a spiral around the contour, but is formed in a circular or "high / low / forward / backward" movement, similar to the case set in a cycloidal milling.

[0073] In another advantageous design variant, a special order is set for the faces to be polished: the deep grooves are polished with a new, fine tool. Alternatively: the faces are first polished, then the old tool is sacrificed in such a way that it is pressed into the groove.

[0074] This alternative is based on the assumption that the tool becomes finer with wear and tear and that the surface quality is improved in the new polishing process due to the changed tool properties. Also, the front part of the tool along the movement direction has different properties than the rear part of the tool, which can be implemented so that the polishing process can be accelerated.

[0075] In another advantageous design variant, the predetermined tool path is determined independently of the geometry data of the restoration piece, in particular in relation to the block size or the geometry.

[0076] The control device has a sink-in size control unit with which the sink-in size can be readjusted. The readjustment takes place on the basis of process parameters or on the basis of the measurement results of sensors, in particular as described here in the remainder.

[0077] It is particularly advantageous according to the application that an existing dental machine tool, for example a milling machine, can be used for the method according to the application. By equipping a polishing tool which is common on the market and by equipping the software which is adapted to form the control device according to the application, the dental machine tool can be used as a dental polishing device according to the application.

[0078] In an advantageous design it is provided that the polishing assembly is part of a polishing tool which can be connected to the drive non-rotatably, in particular can be clamped with its shank into a tool spindle of the drive, and which is connected to the shank of the polishing tool non-rotatably.

[0079] In another advantageous design it is provided that the control device readjusts the movement path when the polishing force, which is measured in particular by the current consumption of the rotary drive of the machine tool, is below a predefined value.

[0080] In another advantageous design it is provided that the control device controls the movement path in such a way that the polishing assembly is placed onto the workpiece on one face of the workpiece and in such a way that the movement path has a direction from the face, in particular from the center of the face, of the workpiece to an adjacent edge of the workpiece, respectively. BRIEF DESCRIPTION OF DRAWINGS

[0081] Further details, advantages and features of the application result from the following description of embodiments of the application with reference to the drawings.

[0082] wherein:

[0083] Figure 1 An exemplary view of a polishing tool for carrying out the method according to the application is shown in one embodiment;

[0084] Figure 2 A schematic view of one embodiment of a polishing device according to the application for carrying out the method according to the application for operating a dental polishing device is shown;

[0085] Figure 3 A graph for representing the extrusion force is shown, the extrusion force being annotated with respect to a measure which is the difference between the tool diameter and the CNC diameter; and

[0086] Figure 4 A diagram for calculating a model for a virtual movement path for implementing the method according to the application is shown;

[0087] Figure 5 A schematic view of one embodiment of a bounding box with dental features is shown;

[0088] Figure 6 A schematic view of the extrusion force annotated with respect to the machining time or machining distance is shown;

[0089] Figure 7 schematic representation of an adaptive adjustment of a movement path, shown with an embodiment according to the application; and

[0090] Figure 8 schematic representation of a movement path, shown with an embodiment according to the application. DETAILED DESCRIPTION

[0091] In Figure 1 a dental polishing tool 10 is shown schematically. This dental polishing tool comprises a polishing unit 12. The polishing unit 12 consists of a polishing assembly 14 and a polishing core 16. The polishing unit 12 is supported on a shank 18 and forms the polishing tool 10 together with the shank.

[0092] The shank 18 is determined for being guided and clamped by a tool spindle of a machine tool.

[0093] In the shown embodiment, the polishing assembly 14 mainly consists of a plurality of circularly extending sheets 20. The sheets 20 are respectively anchored in the polishing core 16 and extend radially therefrom slightly obliquely in a manner known per se. The sheets are equipped with a granular polishing agent and serve for realizing a polishing action.

[0094] For polishing, the sheets are guided along a dental restoration 22 on the dental restoration, which is at the same time the workpiece 22.

[0095] Here, a polishing force is applied, which causes the sheets 20 to be pressed in the direction of the polishing core 16 or to be partially pushed aside laterally, that is to say, the polishing assembly 14 is pressed in.

[0096] This basic principle is known per se and is described here for the purpose of explanation of the used designations.

[0097] In this exemplary embodiment, the diameter of the polishing assembly 14 is 9 mm, while the diameter of the polishing core is 4 mm.

[0098] The workpiece 22 is shown in Figure 2 Furthermore, a polishing device 24 is shown in Figure 2 and is respectively shown in a left-hand end side view and a right-hand side view. The polishing device 24 comprises the workpiece 22 and the polishing assembly 14.

[0099] According to the application, the polishing unit 12 is guided on the workpiece 22 in such a way that there is a constant or substantially constant sinking-in dimension 26.

[0100] Furthermore, a known tool diameter 28 is taken as a starting point. This tool diameter corresponds to the diameter of the tool in the unused state. The polishing tool 10 is clamped into the CNC machine 30 and is thus guided over the surface of the workpiece 22 such that the sinking depth 26 is formed. For this purpose, the tool 10 is assumed to have a diameter which differs from the tool diameter 28 by the sinking dimension 26 for the CNC data. This diameter is referred to as the CNC diameter 32.

[0101] Control is based on a tool reference point 34. The tool reference point is located on the axis 36 of the polishing tool 10 in the case of this example.

[0102] There is provided here a control device 40 which is shown schematically and which is part of the CNC machine 30. The control device 40 controls the movement of the tool reference point 34 in space and also the movement of the workpiece 22 in space. The relative movement between the tool 10 and the workpiece 22 results from the movement difference and thus also the movement path 38, that is to say also the relative movement between the tool 10 and the workpiece 22. In the case of the example, the movement path 38 is a circular path. Figure 2 In the view shown on the right, the movement proceeds from right to left in the illustration of the drawing, that is to say, substantially parallel to the axis 36.

[0103] The material removal and in particular the material deformation proceeds transversely to the movement path 38, in the case of the example, in the direction of the axis 36. Figure 2 In the case of the illustrations on the right, this proceeds into or out of the plane of the drawing.

[0104] During the polishing process according to the application, the tool 10 is subject to wear. This wear also results in the fact that the actual current tool diameter is smaller than the tool diameter 28.

[0105] In order to compensate for this, the movement path 38 is readjusted and is readjusted in the direction of the tool reference point 34 being brought closer to the workpiece 22.

[0106] This change in the movement path 38 is controlled by the control device 40. This control is based on any suitable selection of parameters, for example the feed, the material of the workpiece, the shape of the workpiece, the material of the polishing assembly, the shape of the polishing assembly 14 and / or the pressing force between the polishing assembly 14 and the workpiece 22.

[0107] In another embodiment, a sensor 42 is used which is connected to the control device 40 and readjusts the movement path 22. The dimensions of the polishing assembly 14 and / or of the workpiece 22 are measured using the sensor and preferably continuously.

[0108] The sensor 42 is preferably an optical sensor or a camera. However, mechanical sensors, contact sensors or acoustic sensors can also be used instead of such sensors, or the signals of the control device can be evaluated instead of sensors.

[0109] As with Figure 1 As can be seen in comparison with FIG. 2 , the radial extension of the polishing assembly 14 , ie, the radial length of the sheet 20 , is significantly greater than the plunge dimension 26 , which corresponds to the difference between the tool diameter 28 and the CNC diameter 32 .

[0110] This reliably prevents over-compression of the polishing element 14. Over-compression has the disadvantage of extremely high wear and, in addition, a sharp reduction in elasticity.

[0111] In contrast, the spring constant remains substantially constant within the desired range of the immersion dimension 26. The polishing element 14 is elastic and deforms with a substantially constant spring constant upon contact with the surface of the workpiece 22.

[0112] As already mentioned, the spring constant is the quotient of the contact force and the sinking dimension 26. Conversely, the sinking dimension 26 can be calculated from the quotient of the contact force divided by the spring constant.

[0113] For example, at a contact pressure of 4 N and a spring constant of 5 N / mm, a sinking dimension of 0.8 mm is obtained.

[0114] Small spring constants enable a large working range. See below for details. Figure 3 Here the compression force is plotted against a plunge dimension of 26.

[0115] In the exemplary embodiment shown, the optimum contact pressure is 3 N, and the optimum working range is between 2.5 N and 3.5 N. The contact pressure, ie the contact force per unit area, is decisive for the polishing effect.

[0116] Advantageously, the flexibility of the polishing assembly 14 allows for a substantially constant pressing force that is relatively independent of the immersion dimension.

[0117] In this embodiment, the pressing force is higher than in the embodiment described above. Correspondingly, the optimal working range is offset towards the larger direction of the sinking size, which corresponds to the excessive squeezing of the polishing assembly 14.

[0118] In this case, the higher spring constant of the rigid center, ie, the polishing core 16 , comes into play, which entails corresponding disadvantages.

[0119] One solution is to achieve elastic prestressing of the shaft 18 , for example by manufacturing it from spring steel or in the aforementioned three-part embodiment.

[0120] With the elastic pre-tension a flat characteristic curve is obtained at this time.

[0121] Figure 4 The calculation of the tool reference point 34 is shown, which is referred to here as TCP = Tool center point. A virtual tool is provided for the CAM software, which has a diameter of 9 mm and other given dimensions.

[0122] The polishing assembly 14 is referred to here as a flexible spiral tool. This polishing assembly consists of a rigid polishing core 18 and a sheet 20. The sheet 20 extends outwardly pointedly converging, so that its thickness is smaller on the outside than on the inside.

[0123] In Figure 4 the superimposition of the virtual tool with the actual tool is shown below. With the dimensions shown here a deviation of approximately 0.5 mm results.

[0124] The given dimensions are merely exemplary and can be adapted to the requirements over a wider range.

[0125] In Figure 5 an alternative embodiment with a so-called bounding box 44 is shown. The bounding box refers to a virtual geometric shape or "box", in which the object to be machined is located.

[0126] The bounding box 44 can be generated by a sensor system with a distance measurement from the tool to the dental object or by the CAM software. By means of the bounding box 44 an indication of the object to be polished is set, for example, an arc-shaped or square-shaped encompassing structure in a top view, as shown in Figure 5 . Thereby, it is not necessary that the 3D contour data of the dental representation have to be traversed.

[0127] The movement path 22 can also be virtually positioned, for example, in the bounding box 44.

[0128] It is conceivable that the bounding box is calculated automatically in the CAM or that the polishing tool is moved with a predetermined distance to the representation to be polished in the milling machine by means of a sensor system.

[0129] The protective geometry can consist of a virtual space body, which fills the cavities and thereby smoothes the edges of the grinding edge. The cavities are filled with space bodies on the grinding edge until the size of the sinking-in dimension is reached.

[0130] The boundary box can be defined completely independently of the 3D data. For example, a block-specific "boundary box" or a representation-specific program can be implemented: "inlay", crown, bridge, partial denture, denture base, etc. Alternatively, as a pre-treatment for finishing, a cylindrical boundary box is arranged around the 3D data (STL data), for example. At this point, polishing is performed with a constant radius. But here there is no profile to be followed (abfahren). The boundary box is arranged around the profile with a minimum spacing and at this point is elongated outwardly at the highest point to the maximum sinking size.

[0131] The boundary box is arranged around the profile with a minimum spacing and at this point is elongated outwardly at the highest point to the maximum sinking size.

[0132] Figure 6 A graph is shown for displaying the pressing force with respect to the time or the machining distance.

[0133] The dashed curve 46 shows the ideal course: there is a constant force over the entire polishing time.

[0134] The solid curve 48 shows the actual course: the force decreases after the sinking.

[0135] According to the curve 50, an approximation to the ideal course can be achieved by regularly repeating or continuously readjusting the sinking size.

[0136] An adaptive method for operating a dental polishing device of this kind is proposed, the dental polishing device having a polishing unit which is driven by a dental machine tool, the polishing unit having a circular polishing core and a circular and in particular surrounding polishing assembly, the polishing device can also have a workpiece to be polished, and the polishing assembly is elastically deformed when it is applied to the workpiece.

[0137] A numerically controlled control device moves the polishing assembly along a movement path relative to the workpiece on the workpiece.

[0138] The workpiece is sunk into the polishing assembly with a constant or substantially constant sinking size, and the control device readjusts the sinking size on the basis of a process parameter.

[0139] The adjustment of the movement path 38 is shown in Figure 7 The reference point 34 actually moves along a movement path which is not horizontally distributed, but has a vertical deflection corresponding to the arrow 52. No path calculation is carried out, but the stored movement path is followed. The movement path can exist in two dimensions as a grid. Three-dimensional movement paths can also be implemented, for example as a cylinder.

[0140] As soon as contact 54 occurs in the horizontal movement, a sound is emitted. This sound is detected by the acoustic sensor 55. The polishing is started and the movement path and thus also the sink-in dimension are continuously readjusted.

[0141] If the surface of the workpiece recedes, as shown at position 56 of the polishing assembly 14 or shortly before, the contact is lost or weakened. This change in sound is detected by the sensor 55 and the movement path 38 is readjusted by the control device.

[0142] By Figure 8 An embodiment without adaptive path adjustment can be seen. The sheet 20 of the polishing assembly 14 is flexible and follows the contour of the workpiece 22. This requires that the tool has sufficient flexibility and walks through a predefined polishing process pattern.

[0143] Any process parameter associated with tool wear is selected. For this purpose a wear characteristic is used which is obtained empirically or determined with separate series of tests. As soon as the wear of the tool is determined on the basis of the wear characteristic, the movement path is readjusted towards the workpiece 22 in accordance with Figure 8 In the illustration of Fig. 5 this is a lowering of the polishing assembly 14.

Claims

1. A method for operating a dental polishing device, the dental polishing device comprising a polishing unit driven by a dental machine tool, the polishing unit comprising a circular polishing core and a circular polishing assembly, the polishing device further comprising a workpiece to be polished, and the polishing assembly undergoing elastic deformation when in contact with the workpiece, characterized in that: A numerically controlled control device (40) moves the polishing assembly (14) relative to the workpiece (22) along a motion path (38), wherein the workpiece (22) is sunk into the polishing assembly (14) with a constant or substantially constant sinking dimension (26), and the control device (40) readjusts the sinking dimension (26) based on process parameters. When a dental restoration is used as the workpiece (22), the control device (40) excludes the grinding edge of the dental restoration from polishing, that is, a negative sinking dimension (26) is predefined on the grinding edge, or a virtual protective geometry is added to the excluded surface.

2. The method for operating a dental polishing device according to claim 1, characterized in that The polishing assembly surrounds the polishing core.

3. The method for operating a dental polishing device according to claim 1, characterized in that The process parameters include wear characteristics of the polishing component (14) that have been determined empirically or in separate test series.

4. The method for operating a dental polishing device according to claim 3, characterized in that The process parameters are related to the advance, the material of the workpiece (22), the shape of the workpiece (22), the material of the polishing assembly (14), the shape of the polishing assembly (14), and / or the pressing force between the polishing assembly (14) and the workpiece (22).

5. The method for operating a dental polishing device according to claim 1, characterized in that Before executing the motion trajectory (38), at least one dimension of the workpiece (22) is measured by a sensor, and the control device (40) determines the motion trajectory (38) of the polishing unit (12) before executing the motion trajectory.

6. A method for operating a dental polishing device, the dental polishing device comprising a polishing unit driven by a dental machine tool, the polishing unit comprising a circular polishing core and a circular polishing assembly, the polishing device further comprising a workpiece to be polished, and the polishing assembly undergoing elastic deformation when in contact with the workpiece, characterized in that: A numerically controlled control device (40) moves the polishing assembly (14) relative to the workpiece (22) along a motion path (38), wherein the workpiece (22) is sunk into the polishing assembly (14) with a constant or substantially constant sinking dimension (26), and at least one dimension of the polishing assembly (14) and / or a dimension of the workpiece (22) is measured continuously or repeatedly, and the control device (40) readjusts the sinking dimension (26) based on the measurement results. When a dental restoration is used as the workpiece (22), the control device (40) excludes the grinding edge of the dental restoration from polishing, that is, predetermines a negative sinking dimension (26) on the grinding edge, or adds a virtual protective geometry to the excluded surface.

7. The method for operating a dental polishing device according to claim 6, characterized in that The polishing assembly surrounds the polishing core.

8. The method for operating a dental polishing device according to claim 6, characterized in that The at least one dimension is a diameter or a radial extension.

9. The method for operating a dental polishing device according to claim 6, characterized in that The measurements are performed by means of cameras, optical or mechanical or acoustic sensors.

10. The method for operating a dental polishing device according to claim 6, characterized in that The measurement is also performed indirectly.

11. The method for operating a dental polishing device according to claim 6, characterized in that The measurements are performed as real-time measurements.

12. Method for operating a dental polishing device according to claim 11, characterized in that The control device (40) regulates the motion path (38) and / or regulates the rotational speed of the dental machine tool and / or adjusts the polishing force obtained by the sensor or derived from the output signal of the sensor.

13. The method for operating a dental polishing device according to claim 12, characterized in that The control device (40) adjusts the motion track (38) via the polishing force.

14. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that The predetermined sinking dimension (26) is greater than 0.05 mm and less than 0.5 mm for polishing components having a diameter of up to 3 mm, and greater than 0.2 mm and less than 2 mm for polishing components having a diameter of greater than 3 mm.

15. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that The numerically controlled control device (40) has a memory in which a virtual movement trajectory (38) is stored, which corresponds to the contour of the workpiece (22) but is reduced by a predetermined immersion dimension (26), that is, is closer to the workpiece (22) than would be the case if it corresponded to the actual diameter of the polishing component (14).

16. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that The numerically controlled control device (40) has a memory in which a virtual motion trajectory (38) is stored, which corresponds to the contour of the workpiece (22) but is reduced in a predetermined immersion dimension (26), that is, when taking into account the tool reference point (34), it is closer to the workpiece (22) than when it corresponds to the actual diameter of the polishing component (14).

17. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that A desired immersion dimension is predetermined based on at least one measurement series, which specifies the immersion dimension (26) as a function of the polishing force.

18. Method for operating a dental polishing device according to claim 17, characterized in that The polishing force is measured via the respectively existing power consumption or the rotational speed of the rotary drive of the machine tool.

19. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that The control device (40) determines the wear of the polishing assembly (14) from a reduction in the polishing force at a predetermined immersion dimension (26), and outputs a signal when the polishing force falls below a threshold value at the predetermined immersion dimension (26).

20. The method for operating a dental polishing device according to claim 19, wherein The signal readjusts the compensating movement and / or instructs a tool change.

21. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that The control device (40) controls the relative movement between the workpiece (22) and the polishing assembly (14) along the motion track (38) so that the movement speed during the bonding period is greater than a minimum value and less than a maximum value.

22. Method for operating a dental polishing device according to claim 21, characterized in that The minimum value is 5 mm / second.

23. The method for operating a dental polishing device according to claim 21, wherein: The minimum value is 10 mm / second.

24. The method for operating a dental polishing device according to claim 21, wherein: The maximum value is 30 mm / second.

25. The method for operating a dental polishing device according to claim 21, wherein: The maximum value is 20 mm / second.

26. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that The polishing assembly (14) is brought into contact with the workpiece (22) only in a region outside the axis and / or a possible tip of the polishing assembly (14).

27. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that The polishing assembly (14) has bristles or sheets (20) that extend in a circular, dish-shaped, bowl-shaped, or conical shape around the polishing core (16).

28. Method for operating a dental polishing device according to any one of claims 1 to 12, characterized in that The polishing element (14) has a diameter (32) that increases with the rotational speed, and the immersion dimension (26) is determined in dependence on this increasing diameter (32).

29. The method for operating a dental polishing device according to claim 28, wherein: The rotation speed is adapted to the desired sinking dimension (26).

30. A dental polishing device comprising a polishing unit in driving connection with a dental machine tool, the polishing unit comprising a circular polishing core and a circular polishing assembly, the polishing device further comprising a workpiece to be polished, and the polishing assembly elastically deforming when in contact with the workpiece, characterized in that: A numerically controlled control device (40) is provided, by means of which a polishing assembly (14) can be moved relative to a workpiece (22) along a motion path (38), and the control device (40) has a plunge dimension control unit, by means of which a plunge dimension (26) can be readjusted. When a dental restoration is used as the workpiece (22), the control device (40) excludes the grinding edge of the dental restoration from polishing, i.e., predetermines a negative plunge dimension (26) on the grinding edge or adds a virtual protective geometry to the excluded surface.

31. The dental polishing device according to claim 30, wherein The polishing assembly surrounds the polishing core.

32. The dental polishing device according to claim 30 or 31, characterized in that The sinking size control unit can be used to set a constant or substantially constant sinking size (26), with which the workpiece (22) is sunk into the polishing assembly (14), and the sinking size control unit can be used to readjust the sinking size (26), the readjustment being based on process parameters or on a sensor or camera for detecting at least one dimension of the polishing assembly (14) and / or a size of the workpiece (22), and / or the sinking size control unit can be used to readjust the sinking size (26) based on measurement results.

33. Dental machine tool, characterized in that The dental machine tool is equipped with a dental polishing device, which has a control device implemented by CAM software or installed by upgrading the CAM software. The control device can be used to readjust the sinking size based on process parameters or based on sensor measurement results. When a dental restoration is used as a workpiece (22), the control device (40) excludes the grinding edge of the dental restoration from polishing, that is, a negative sinking size (26) is pre-specified on the grinding edge, or a virtual protective geometric structure is added to the excluded surface.

34. CAM software for dental machine tools, characterized in that The software adds a dental polishing device to the dental machine tool, and the CAM software implements a control device, or the CAM software is upgraded and equipped with a control device, and uses the control device to readjust the sinking size based on process parameters or based on sensor measurement results. When a dental restoration is used as a workpiece (22), the control device (40) excludes the grinding edge of the dental restoration from polishing, that is, pre-determines a negative sinking size (26) on the grinding edge, or adds a virtual protective geometric structure to the excluded surface.

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