Method Of Operating A Dental Polishing Apparatus And Dental Polishing Apparatus

Abstract

A method of operating a dental polishing apparatus is provided, having a polishing unit driven by a dental machine tool. The polishing unit includes a circular polishing core and a circular polishing assembly particularly surrounding the polishing core. The polishing assembly also has a workpiece to be polished and the polishing assembly deforms elastically when in contact with the workpiece. A numerically controlled steering device moves the polishing assembly along a trajectory on and relative to the workpiece. The workpiece is immersed into the polishing assembly with a constant or substantially constant degree of immersion. The controller adjusts the degree of immersion based on process parameters.

Claims

1. A method for operating a dental polishing device comprising a polishing unit which is driven by a dental machine tool, where the polishing unit comprises a circular polishing core and a circular polishing assembly, which circular polishing assembly surrounds the polishing core, the polishing device also comprising a workpiece to be polished, and the polishing assembly being elastically deformed when applied against the workpiece, the method comprising the following steps: a numerically controlled controller (40) moves the polishing assembly (14) along a trajectory (38) on the workpiece (22) relative to the workpiece (22), in which the workpiece (22) is immersed into the polishing assembly (14) with a constant or substantially constant degree of immersion (26) and the controller (40) adjusts the degree of immersion (26) based on process parameters.

2. The method for operating the dental polishing device according to claim 1, wherein the process parameters comprise wear behaviour of the polishing assembly (14) determined empirically or in an individual series of tests, and wherein the process parameters are dependent on an 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 contact pressure between the polishing assembly (14) and the workpiece (22).

3. A method for operating a dental polishing device comprising a polishing unit which is driven by a dental machine tool, where the polishing unit comprises a circular polishing core and a circular polishing arrangement which circular polishing arrangement surrounds the polishing core, the polishing device also comprising a workpiece to be polished, and the polishing arrangement being elastically deformed when it is applied against the workpiece, the method comprising the following steps: a numerically controlled controller (40) moves the polishing assembly (14) along a trajectory (38) on the workpiece (22) relative to the workpiece, in which trajectory the workpiece (22) is immersed into the polishing assembly (14) with a constant or substantially constant degree of immersion (26), and wherein at least one dimension of the polishing assembly (14) and/or the dimensions of the workpiece (22) is measured continuously or repeatedly by a camera sensor, an optical sensor, a mechanical sensor or an acoustic sensor, and wherein the controller (40) adjusts the degree of immersion (26) based on a measurement result.

4. The method for operating the dental polishing device according to claim 3, wherein the measurement is carried out as a real-time measurement, and wherein the controller (40) carries out a regulation of the trajectory (38), via a polishing force determined by the sensor or derived from an output signal of the sensor, and/or wherein the regulation carries out the rotational speed of the dental machine tool (34) and/or adjusts the polishing force.

5. The method for operating the dental polishing device according to claim 1, wherein at least one dimension of the workpiece (22) is measured via a sensor prior to execution of the trajectory (38), and wherein the controller (40) determines the trajectory (38) of the polishing unit (12) prior to the execution.

6. The method of operating a dental polishing device according to claim 1, wherein a predetermined degree of immersion (26) is greater than 0.05 mm and less than 0.5 mm for immersion devices with a diameter of up to 3 mm, and greater than 0.2 mm and less than 2 mm for tools with a diameter of more than 3 mm.

7. The method for operating the dental polishing device according to claim 1, wherein the numerically controlled controller (40) has a memory in which a virtual trajectory (38) is stored which corresponds to a contour of the workpiece (22), but reduced by a predetermined degree of immersion (26), that is, closer to the workpiece (22) than corresponds to the actual diameter of the polishing assembly (14), if necessary taking into account a tool reference point (34).

8. The method for operating the dental polishing device according to claim 1, wherein, with a dental restoration part (20) as the workpiece (22), the controller (40) excludes preparation boundaries of the dental restoration part (20) from the polishing such that a negative degree of immersion (26) is specified at the preparation boundaries, or a virtual protective geometry is inserted over excluded surfaces.

9. The method for operating the dental polishing device according to claim 1, wherein a targeted degree of immersion is determined in advance, based on at least one series of measurements which represents a function of the degree of immersion (26) via a polishing force, measured via a respective current consumption or rotational speed of the rotary drive of the machine tool (34).

10. The method for operating the dental polishing device according to claim 1, wherein the controller (40) determines wear of the polishing assembly (14) from a drop in the polishing force at a predetermined degree of immersion (26) and emits a signal when the polishing force at the predetermined degree of immersion (26) falls below a threshold value at the predetermined degree of immersion (26), and wherein the signal readjusts the compensation movement and/or indicates a tool change.

11. The method for operating the dental polishing device according to claim 1, wherein the controller (40) controls the relative movement between the workpiece (22) and the polishing assembly (14) along the trajectory (38) such that a speed of movement, during contact, is greater than a minimum value of 5 mm/sec or 10 mm/sec, and less than a maximum value of 30 mm/sec or 20 mm/sec.

12. The method for operating the dental polishing device according to claim 1, wherein the polishing assembly (14) is brought into contact with the workpiece (22) exclusively in regions outside the axis and/or a tip of the polishing assembly (14).

13. The method for operating the dental polishing device according to claim 1, wherein the polishing assembly (14) comprises bristles or flaps (20) extending in a circular, plate-shaped, cup-shaped, or cone-shaped manner around the polishing core (16).

14. The method for operating the dental polishing device according to claim 1, wherein the polishing assembly (14) has a diameter (32) which increases with a rotational speed, and the degree of immersion (26) is determined in relation to the increased diameter (32) such that the rotational speed is adapted to the desired degree of immersion (26).

15. A dental polishing device comprising a polishing unit which is in driving connection with a dental machine tool, where the polishing unit comprises a circular polishing core and a circular polishing assembly surrounding the polishing core, a workpiece to be polished, and wherein the polishing assembly is elastically deformed when in contact with the workpiece, wherein a numerically controlled controller (40) is provided, which controls the movement of the polishing assembly (14) along a trajectory (38) on the workpiece (22) relative to the workpiece, and wherein the controller (40) has a degree of immersion control unit, by which the degree of immersion (26) can be adjusted.

16. The dental polishing device according to claim 15, wherein a constant or substantially constant degree of immersion (26) with which the workpiece (22) is immersed in the polishing assembly (14) can be set with the degree of immersion control unit, and wherein the immersion degree (26) can be readjusted with the immersion degree control unit based on process parameters or based on a sensor or a camera for recording at least one dimension of the polishing assembly (14) and/or dimensions of the workpiece (22), and/or wherein the immersion degree (26) can be readjusted with the immersion degree control unit, based on a measurement result.

17. A dental machine tool comprising a retrofitted dental polishing device which comprises a controller implemented by CAM software or retrofitted by an update of the CAM software, with which a degree of immersion can be readjusted based on process parameters or based on a measurement result of a sensor.

18. A computer program product for a dental machine tool comprising program code with is stored on a non-transitory machine-readable medium, the machine readable medium comprising computer instructions executable by a processor, which computer instructions cause a controller of a dental polishing device integral or retrofitted on the dental machine tool to perform the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0098] Further details, advantages and features of the invention will be apparent from the following description of several embodiments of the invention with reference to the drawing, wherein:

[0099] FIG. 1 shows an exemplary view of a polishing tool for carrying out a process according to the invention in one embodiment;

[0100] FIG. 2 shows a schematic view of an embodiment of a dental polishing device according to the invention for carrying out a method according to the invention for operating a dental polishing device;

[0101] FIG. 3 shows a diagram showing the contact pressure plotted against the allowance as the difference between the tool diameter and the CNC diameter; and

[0102] FIG. 4 shows a representation of a model for calculating the virtual trajectory for realising the process according to the invention;

[0103] FIG. 5 shows a schematic representation of an embodiment with a bounding box on dental indications;

[0104] FIG. 6 shows a schematic representation of the pressing force plotted against the machining time or the machining distance;

[0105] FIG. 7 shows a schematic representation of an adaptive control of the trajectory, in an embodiment according to claim 3; and

[0106] FIG. 8 shows a schematic representation of a trajectory, in an embodiment according to claim 1.

DETAILED DESCRIPTION

[0107] A dental polishing tool 10 is shown schematically in FIG. 1. This comprises a polishing unit 12. The polishing unit 12 includes a polishing assembly 14 and a polishing core 16. The polishing unit 12 is mounted on a shaft 18 and together with the shaft 18 forms the polishing tool 10.

[0108] The shank 18 is intended to be guided and held clamped by the tool spindle of a machine tool.

[0109] In the embodiment shown, the polishing assembly 14 comprises, inter alia, a plurality of flaps extending in a circular manner. The flaps 20 are each anchored in the polishing core 16 and extend radially from the latter in a manner known per se at a slight angle. They are equipped with granular abrasives and serve the polishing effect.

[0110] For polishing, they are guided along a dental restoration part 22, which is also a workpiece 22.

[0111] In this case, a polishing force is exerted which causes the flaps 20 to be pressed in the direction of the polishing core 16, or to be partially pushed away laterally, i.e., the polishing assembly 14 is pressed in.

[0112] This basic principle is known in itself, and the description here serves to clarify the terms used.

[0113] In the exemplary embodiment, the diameter of the polishing assembly 14 is 9 mm and that of the polishing core is 4 mm.

[0114] The workpiece 22 is shown in FIG. 2. FIG. 2 also shows the polishing device 24, in front view on the left and a side view on the right. The polishing device 24 consists of the workpiece 22 and the polishing assembly 14.

[0115] According to the invention, the polishing unit 12 is guided over the workpiece 22 in such a way that a constant or substantially constant degree of immersion 26 is provided.

[0116] For this purpose, a known tool diameter 28 is assumed. This corresponds to the diameter of the tool in the unused state. The polishing tool 10 is clamped in a CNC machine tool 30 and the tool is guided over the surface of the workpiece 22 in such a way that the degree of immersion 26 is produced. For the CNC data, it is assumed that the tool 10 has a diameter that differs from the tool diameter 28 by the degree of immersion 26. This diameter is referred to as the CNC diameter 32.

[0117] The control is carried out based on a tool reference point 34. In the example, this is located on the axis 36 of the polishing tool 10.

[0118] A schematically shown control device 40 is provided, which is part of the CNC machine tool 30. The control device 40 controls the spatial movement of the tool reference point 34 and also the spatial movement of the workpiece 22. The relative movement between tool 10 and workpiece 22 and thus the trajectory 38, and so at the same time the relative movement between tool 10 and workpiece 22, results from the difference in movement. In the view shown on the right in FIG. 2, the movements in the drawing are from right to left, i.e., essentially parallel to axis 36.

[0119] The material removal and in particular the material reshaping occurs transversely to this trajectory 38, in the drawings in FIG. 2 to the right into or out of the drawing plane.

[0120] During the polishing process according to the invention, wear of the tool 10 occurs. This wear also results in the actual current tool diameter being smaller than the tool diameter 28.

[0121] To compensate for this, the trajectory 38 is readjusted in the direction of greater convergence between the tool reference point 34 and the workpiece 22.

[0122] This change in trajectory 38 is controlled by the control device 40. The control occurs based on any suitably selected 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 contact pressure between the polishing assembly 14 and the workpiece 22.

[0123] In a further embodiment, a sensor 42 is used which is connected to the control device 40 and readjusts the trajectory 22. The sensor is used to measure the polishing assembly 14 and/or the dimensions of the workpiece 22, preferably continuously.

[0124] The sensor 42 is preferably an optical sensor or camera. However, it is also possible to use a mechanical sensor instead, as well as a tactile sensor or an acoustic sensor, or to evaluate the signals from the control device instead of the sensor.

[0125] As can be seen from FIG. 2 in comparison with FIG. 1, the radial extension of the polishing assembly 14, i.e., the radial length of the flaps 20, is significantly greater than the degree of immersion 26, corresponding to the difference between the tool diameter 28 and the CNC diameter 32.

[0126] This reliably prevents the application of excessive pressure to the polishing assembly 14. The disadvantage of applying excessive pressure would be extremely high wear and, in addition, a drastic drop in elasticity.

[0127] In contrast, the spring constant essentially stays the same in the desired range of the degree of immersion 26. The polishing assembly 14 is elastic and deforms with a substantially constant spring constant when it strikes the surface of the workpiece 22.

[0128] As already mentioned, the spring constant is the quotient of the contact pressure and the degree of immersion 26. Conversely, the degree of immersion 26 can be calculated from the quotient of contact pressure by spring constant.

[0129] For example, a contact pressure of 4 N and a spring constant of 5 N/mm result in a degree of immersion of 0.8 mm.

[0130] A low spring constant allows a large working range. Please refer to the graph in FIG. 3 below. The contact pressure is plotted against the degree of immersion 26.

[0131] In the example 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, i.e., the contact pressure per unit area, is decisive for the polishing effect.

[0132] It is advantageous to achieve an essentially constant contact pressure through the flexibility of the polishing assembly 14, with a relative independence from the degree of immersion.

[0133] In this embodiment example, the contact pressure is higher than in the embodiment example cited above. Accordingly, the optimum working range is shifted towards a greater degree of immersion, corresponding to an overpressure of the polishing assembly 14.

[0134] In this case, the higher spring constant of the stiff centre, i.e., of the polishing core 16, is effective, with the corresponding disadvantages.

[0135] One solution is to implement a spring preload of the shaft 18, for example by manufacturing it from spring steel or in the three-part design described above.

[0136] The spring pre-tensioning then results in a flat characteristic curve again.

[0137] FIG. 4 shows a calculation of the reference point 34 of the tool, which is referred to here as TCP=Tool centre point. A virtual tool is provided for the CAM software, with a diameter of 9 mm and the other specified dimensions.

[0138] The polishing assembly 14 is described there as a flexible spiral tool. It consists of the fixed polishing core 16 and the flaps 20. The flaps 20 taper outwards so that their thickness is less on the outside than on the inside.

[0139] Below in FIG. 4 an overlay of the virtual tool with the actual tool is shown. The dimensions given there result in an offset of approx. 0.5 mm.

[0140] The dimensions given are only exemplary and can be adapted to the requirements in a wide range.

[0141] FIG. 5 shows an alternative embodiment with a so-called bounding box 44. A bounding box is a virtual geometry or “box” within which the object to be machined lies.

[0142] The bounding box 44 can be generated either by means of the sensor system with distance measurement of tool and dental object or by means of the CAM software.

[0143] A bounding box 44 is used, for example, to create a box-shaped or cuboid enclosure of the indication to be polished, as shown in FIG. 5. This eliminates the need to traverse the 3D contour data of the dental indication.

[0144] The trajectory 22 can also be created virtually, e.g., in the bounding box 44.

[0145] It is conceivable that the bounding box is automatically calculated in the CAM, or that the polishing tool is moved at a predetermined distance from the indications to be polished by means of a sensor system in the milling machine.

[0146] A protective geometry can consist of a virtual volume body that fills the cavity and thus smooths the edges of the preparation borders. The cavity is filled with a solid to the level of the degree of immersion above the preparation margin.

[0147] The bounding box can be defined completely independently of 3D data. For example, block-specific trajectories “bounding boxes” or indication-specific programmes: “inlay”, crown, bridge, partial dentures, denture base, etc. can be realised. Or, for example, a cylinder bounding box is placed around 3D data (STL data) in preparation for finishing. Polishing is then carried out with a constant radius, but the contours are not traced.

[0148] The bounding box is placed at a minimum distance around the contours and then stretched outwards to a maximum degree of immersion at the highest point. FIG. 6 shows a diagram representing the pressing force plotted against time or machining distance.

[0149] The dashed curve 46 shows the ideal curve: there is a constant force over the entire polishing time.

[0150] The solid curve 48 shows the real course: After dipping, the force drops.

[0151] An approximation to the ideal course is possible by regularly or continuously adjusting the degree of immersion, according to curve 50.

[0152] An adaptive method for operating a dental polishing device comprising a polishing unit driven by a dental machine tool is provided, said polishing unit consisting of a circular polishing core and a circular polishing assembly surrounding in particular the polishing core, wherein the polishing device also comprises a workpiece to be polished, and wherein the polishing assembly deforms elastically when in contact with the workpiece.

[0153] A numerically controlled steering device moves the polishing assembly along a trajectory on and relative to the workpiece.

[0154] The workpiece immerses into the polishing assembly by a constant or substantially constant degree of immersion and the control device adjusts the degree of immersion based on process parameters.

[0155] The control of the trajectory 38 is shown in FIG. 7. The actual trajectory of the reference point 34 does not run horizontally, but with vertical deflection, according to the arrows 52. A trajectory calculation is dispensed with, but a stored trajectory is followed. The trajectory can be in a two-dimensional grid. A three-dimensional trajectory, e.g., in cylinder form, is also possible.

[0156] As soon as a contact 54 occurs during the horizontal movement, a noise is generated. This noise is detected by an acoustic sensor 55. Polishing begins and the trajectory, and thus the degree of immersion, is continuously adjusted.

[0157] As soon as the surface of the workpiece jumps back, as shown at or just before position 56 of the polishing assembly 14, the contact is lost or weakens. This change in noise is detected by the sensor 55, and the trajectory 38 is readjusted via the control device.

[0158] FIG. 8 shows an embodiment without adaptive path control. The flaps 20 of the polishing assembly 14 are flexible and follow the contour of the workpiece 22. This requires a sufficiently flexible tool, and a predefined polishing pattern is run.

[0159] Any process parameter correlated with tool wear is selected. For this purpose, the empirically determined wear behaviour or the wear behaviour determined in individual test series is accessed. As soon as tool wear is detected on the basis of this, the trajectory towards the workpiece 22 is readjusted, i.e., the polishing assembly 14 is lowered downwards in the illustration according to FIG. 8.

[0160] In some embodiments, the innovations may be implemented in diverse general-purpose or special-purpose computing systems. For example, the computing environment can be any of a variety of computing devices (e.g., desktop computer, laptop computer, server computer, tablet computer, gaming system, mobile device, programmable automation controller, etc.) that can be incorporated into a computing system comprising one or more computing devices.

[0161] In some embodiments, the computing environment includes one or more processing units and memory. The processing unit(s) execute computer-executable instructions. A processing unit can be a central processing unit (CPU), a processor in an application-specific integrated circuit (ASIC), or any other type of processor. In a multi-processing system, multiple processing units execute computer-executable instructions to increase processing power. A tangible memory may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two, accessible by the processing unit(s). The memory stores software implementing one or more innovations described herein, in the form of computer-executable instructions suitable for execution by the processing unit(s).

[0162] A computing system may have additional features. For example, in some embodiments, the computing environment includes storage, one or more input devices, one or more output devices, and one or more communication connections. An interconnection mechanism such as a bus, controller, or network, interconnects the components of the computing environment. Typically, operating system software provides an operating environment for other software executing in the computing environment, and coordinates activities of the components of the computing environment.

[0163] The tangible storage may be removable or non-removable, and includes magnetic or optical media such as magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other medium that can be used to store information in a non-transitory way and can be accessed within the computing environment. The storage stores instructions for the software implementing one or more innovations described herein.

[0164] Where used herein, the term “non-transitory” is a limitation on the computer-readable storage medium itself—that is, it is tangible and not a signal—as opposed to a limitation on the persistence of data storage. A non-transitory computer-readable storage medium does not necessarily store information permanently. Random access memory (which may be volatile, non-volatile, dynamic, static, etc.), read-only memory, flash memory, memory caches, or any other tangible, computer-readable storage medium, whether synchronous or asynchronous, embodies it.

[0165] The input device(s) may be, for example: a touch input device, such as a keyboard, mouse, pen, or trackball; a voice input device; a scanning device; any of various sensors; another device that provides input to the computing environment; or combinations thereof. The output device may be a display, printer, speaker, CD-writer, or another device that provides output from the computing environment.

[0166] The terms “about” and “substantially” are intended to include the degree of error or uncertainty associated with measurement of the particular quantity or shape as one of ordinary skill in the art would understand.

[0167] The scope of protection of the present invention is given by the claims and is not limited by the features explained in the description or shown to the figures.