MANUFACTURING DEVICE FOR A DENTAL RESTORATION

Description

[0001] The present invention relates to a manufacturing device for a dental restoration and a manufacturing method for a dental restoration.

[0002] Currently, when producing dental restorations using milling or grinding processes, the linear meters traveled by a grinder along milling paths are added up to determine grinder wear. Once an empirical value is reached, a message is issued to the operator that the grinder should be replaced. However, the actual wear of the grinder cannot be determined in this way. Even if a user uses an old or defective grinder, a machine would not notice. Therefore, these methods are prone to errors. JP 6 712236 B2 discloses a milling machine with a machining tool in which the wear of the machining tool is determined based on a spindle motor current of the milling machine.

[0003] It is therefore the technical object of the present invention to more accurately predict wear of a tool during the processing or production of a dental restoration.

[0004] This technical problem is solved by the subject matter according to the independent claims. Technically advantageous embodiments are the subject matter of the dependent claims, the description, and the drawings.

[0005] According to a first aspect, the technical problem is solved by a manufacturing device for a dental restoration, comprising a tool for machining a blank; a detection device for detecting a spindle current of a rotary spindle; and a calculation device for calculating wear of the tool based on the spindle current. The tool can be a milling tool, a grinding tool, or a polishing tool. The manufacturing device achieves, for example, the technical advantage of being able to detect a worn or defective tool.

[0006] In a technically advantageous embodiment of the manufacturing device, the calculation device is configured to calculate the wear from several measured values ​​of the spindle current. This achieves the technical advantage, for example, of improving the accuracy of the calculation.

[0007] In a further technically advantageous embodiment of the manufacturing device, the calculation device is configured to sum or average the spindle current from several measured values. This achieves, for example, the technical advantage of further improving the calculation of the spindle current.

[0008] In a further technically advantageous embodiment of the manufacturing device, the calculation device is configured to calculate wear from a sliding time window for the spindle current. This achieves the technical advantage, for example, of obtaining precise and current values ​​for the spindle current during machining.

[0009] In one embodiment of the manufacturing device according to the invention, the calculation device is configured to calculate an interval for the middle 50% of the spindle current values. This achieves the technical advantage, for example, that the spindle current value can be determined precisely and outliers in the values ​​are ignored.

[0010] In a further technically advantageous embodiment of the manufacturing device, the calculation device is designed to calculate the wear from the width of the interval. This achieves, for example, the technical advantage of establishing a proportional relationship between the width of the interval and the wear.

[0011] In a further technically advantageous embodiment of the manufacturing device, the calculation device is designed to calculate the wear of the tool proportionally to the width of the interval. This achieves the technical advantage, for example, of allowing wear to be determined quickly and easily.

[0012] In a further technically advantageous embodiment of the manufacturing device, the manufacturing device is designed to compensate for tool wear during processing. This achieves the technical advantage, for example, that the dental restoration can be manufactured with high precision even when the tool is beginning to wear.

[0013] In a further technically advantageous embodiment of the manufacturing device, the manufacturing device comprises a replacement device for replacing a worn tool with an unworn tool. This achieves the technical advantage, for example, that a worn tool can be replaced in a simple manner.

[0014] In a further technically advantageous embodiment of the manufacturing device, the replacement device is designed to automatically change the tool when a predetermined wear level is exceeded. This achieves the technical advantage, for example, that machining can be immediately continued with a new tool when a tool becomes worn. Furthermore, no material is wasted or scrap is produced. The data could also be saved and used for quality control purposes.

[0015] According to a second aspect, the technical problem is solved by a manufacturing method for a dental restoration, comprising the steps of detecting a spindle current of a rotary spindle; and calculating wear of the tool based on the spindle current. The manufacturing method achieves the same technical advantages as the manufacturing device according to the first aspect.

[0016] In a technically advantageous embodiment of the manufacturing method, wear is calculated from several measured values ​​of the spindle current. This also achieves the technical advantage of improving the accuracy of the calculation.

[0017] In another technically advantageous embodiment of the manufacturing method, wear is calculated from a sliding time window for the spindle current. This also achieves the technical advantage of further improving the calculation of the spindle current.

[0018] In one embodiment of the manufacturing method according to the invention, an interval is calculated for the middle 50% of the spindle current values. This also achieves the technical advantage, for example, that the spindle current value can be determined precisely and outliers in the values ​​are ignored.

[0019] In another technically advantageous embodiment of the manufacturing method, wear is calculated from the width of the interval. This also achieves the technical advantage of establishing a proportional relationship between the width of the interval and wear.

[0020] Embodiments of the invention are illustrated in the drawings and are described in more detail below.

[0021] They show: Fig. 1 shows a schematic representation of a manufacturing device for a dental restoration; Fig. 2 shows a deviation between the target and actual dimensions across various test specimens; Fig. 3 shows a view of a milling tool; Fig. 4 shows a schematic distribution of measured values ​​for the spindle current; Fig. 5 shows several interquartile ranges depending on the target-actual differences of consecutively manufactured test specimens; and Fig. 6 shows a block diagram of a manufacturing process for a dental restoration.

[0022] Fig. 1 shows a schematic representation of a manufacturing device 100 for a dental restoration 200. The dental restoration 200 is, for example, a crown, a bridge, a veneer, an abutment, an inlay, an onlay, a splint or a partial or full denture.

[0023] The manufacturing device 100 comprises a tool 101 for machining a blank 201, such as a milling tool or a grinding tool. The tool 101 shapes the blank 201 into the desired shape of the dental restoration 200 using a machining process. The blank is, for example, a disk made of zirconium oxide. The tool 101 is driven by an electric motor 113 and rotated by a rotating spindle 117. An electric spindle current flows through the electric motor 113 of the rotating spindle 117.

[0024] The manufacturing device 100 additionally comprises a detection device 103 for detecting the spindle current of the rotary spindle 117 for the tool 101 during machining of the blank 201. The detection device 103 can comprise a current sensor that measures the electrical current flowing through the electric motor 113. The spindle current can be detected using existing sensor or machine data, so that no additional sensors are used. The higher the values, such as the standard deviation or the IQR, of the electrical spindle current during machining, the greater the wear of the tool 101. The higher the IQR, the greater the wear of the tool 101. For example, the current sensor can continuously obtain digital values ​​for the spindle current.

[0025] To calculate the precise wear of tool 101, manufacturing device 100 includes a calculation device 105. This can be formed by a microprocessor 115 with a memory 109. Microprocessor 115 receives the digital values ​​for the spindle current and processes them using an algorithm to obtain a digital value for wear. The digital value for wear can then be stored in memory 109.

[0026] The calculation device is thus capable of continuously and in real time calculating the wear of the tool 101 based on the spindle current. The spindle current is used to analyze the condition of the tool 101. For example, the condition of the tool 101 can be determined using the spindle current when machining dental glass ceramics.

[0027] However, the calculation device 105 can also be configured to assign a predetermined wear of the tool 101 to a detected spindle current. In this case, a digital look-up table can be used to assign a corresponding wear of the tool 101 to each value for the spindle current.

[0028] For example, this allows the actual condition of the tool 101 to be determined during each machining operation. This allows old, worn, or defective tools to be identified in a timely manner. A dimensional deviation during production can be corrected based on the determined wear of the tool 101.

[0029] The manufacturing device 100 can also control the rotational speed of the tool 101 based on the detected spindle current. Starting at a predetermined wear level, the rotational speed, infeed, and / or feed rate of the tool 101 can be adjusted or reduced. This can reduce the load on the tool 101 at the end of its service life. The manufacturing device 100 increases the quality of the dental restoration and produces less scrap.

[0030] The determined wear of tool 101 can then be compensated during machining of the dental restoration 200. If the wear of tool 101 is, for example, 5 µm, this value can be added to the actual position of tool 101 during milling to obtain a desired target position. This allows the dental restoration 200 to be produced in the desired dimensions even if tool 101 is partially worn.

[0031] Furthermore, the manufacturing device 100 can comprise a replacement device 111 for replacing a worn tool 101 with an unworn tool 101. For this purpose, for example, several identical tools 101 are provided in a magazine. As soon as the tool 101 used to machine the dental restoration 200 reaches a predetermined level of wear, it is automatically replaced with a new tool 101 from the magazine, for example, by an electromechanical changing mechanism or gripper. This allows numerous dental restorations 200 to be manufactured in series without requiring user intervention.

[0032] Fig. 2 shows a deviation between the nominal and actual dimensions for different tools 101 over an increasing number of test specimens PK. The older the tool, the further the actual dimension (measured on the component) deviates from the nominal dimension. The deviation increases by 2 µm per test specimen.

[0033] The increasing deviation can lead to rejects during manufacturing. For example, with a crown, the hole becomes smaller by 2 µm for each crown produced. After approximately 40 test specimens (deviation of 80 µm), the crown no longer fits the stump. In this case, a manufactured crown or bridge might not fit a patient because the dimensions are incorrect.

[0034] If a deviation is determined based on the spindle current, a 10-second analysis is sufficient to determine wear at a high sampling rate. The condition of tool 101 can be predicted to within ±7 test specimens, which corresponds to a deviation of approximately ±14 µm. Each milled test specimen results in approximately 2 µm of tool wear.

[0035] The sampling rate describes the frequency at which an analog signal is read within a specific time and converted into a discrete-time signal. For example, the sampling rate for spindle current is 10 kHz. This allows 10,000 spindle current measurements to be obtained per second.

[0036] The spindle current can be recorded in a sliding time window, so that the spindle current measured values ​​for a specified past period are always used. The time window therefore includes a specified set of more recent measured values. This means that older measured values ​​that fall outside the sliding time window are no longer taken into account when calculating the spindle current.

[0037] Fig. 3 shows a view of a tool 101. The tool can be, for example, a grinder or a milling cutter for the dental restoration 200. The tool 101 includes, for example, a diamond-coated milling surface 107. The milling surface 107 is in contact with the blank 201 in order to mill the dental restoration therefrom.

[0038] Fig. 4 shows a schematic distribution of measured values ​​for the spindle current. The probability density for the spindle current is plotted as a function of the standard deviation σ.

[0039] Multiple measurements can be used to calculate the spindle current. From a set of different spindle current measurements, the 50% that are closest to a mean value can be determined. If a sample of measurements is sorted by size, the interquartile range (IQR) indicates the width of the interval Q1 to Q3 in which the middle 50% of the sample elements lie.

[0040] The interquartile range of the measured values ​​for the spindle current can also be used to determine the wear of the tool 101. For example, the interquartile range of the measured values ​​for the spindle current can be determined during the milling process of the dental restoration 200. However, this can also be done afterward. The interquartile range increases linearly with the wear of the tool 101. The dimensional error also increases linearly due to the wear on the dental restoration. Therefore, it is possible to determine the wear of the tool from the interquartile range.

[0041] Fig. 5 shows interquartile ranges as a function of target-actual differences between consecutively manufactured test specimens with a tool, thus visually depicting the correlation between tool wear and the IQR. The number of manufactured test specimens is plotted on the x-axis. The y-axis shows the difference between a target dimension and an actual dimension and an interquartile range (IQR) in µm. The greater the difference between the target dimension and the actual dimension, the greater the interquartile range (IQR) from the measured spindle current values.

[0042] The interquartile range (IQR) of the spindle current is linearly related to the wear of the tool 101. Therefore, the actual condition of the tool 101 can be determined in real time ("on the fly") from the determined interquartile range (IQR). The interquartile range behaves like the dimensional deviation (MAE - Mean Absolute Error: 0.015 - 0.022 mm).

[0043] First, a set of spindle current measurements is determined. From these measurements, the interquartile range (IQR) is calculated. The larger this interquartile range, the greater the wear on tool 101.

[0044] Fig. 6 shows a block diagram of a manufacturing method for the dental restoration 200. In the first step S101, the spindle current of the rotary spindle 117 is recorded. A variety of measured values ​​for the spindle current can be recorded here.

[0045] In the subsequent step S102, the wear of tool 101 is calculated based on the spindle current. For this purpose, the measured values ​​can be evaluated, for example, to determine an interquartile range. The wear of tool 101 is determined from the interquartile range, for example, by multiplying it by a proportionality factor. These steps can be performed by the calculation device 105.

[0046] The manufacturing process allows the condition of a tool to be determined on the machine without additional sensor data, a microscope or other technical aids.

[0047] All features explained and shown in connection with individual embodiments of the invention can be provided in different combinations in the subject matter according to the invention in order to simultaneously realize their advantageous effects.

[0048] All method steps can be implemented by devices suitable for performing the respective method step. All functions performed by physical features can be a method step of a method.

[0049] The scope of the present invention is given by the claims and is not limited by the features explained in the description or shown in the figures. LIST OF REFERENCE SYMBOLS

[0050] 100Manufacturing device 101Tool 103Detection device 105Calculation device 107Milling surface 109Digital memory 111Replacement device 113Electric motor 115Microprocessor 117Rotating spindle 200Dental restoration 201Blank

Claims

1. A manufacturing device (100) for a dental restoration (200), comprising: - a tool (101) for machining a blank (201); - a detection device (103) for detecting a spindle current of a turning spindle (117); and - a calculating device (105) for calculating wear of the tool (101) based on the spindle current, characterized in that the calculating device (105) is configured to calculate an interval for the average 50% of the values of the spindle current.

2. The manufacturing device (100) according to claim 1, wherein the calculating device (105) is configured to calculate the wear from a plurality of measured values of the spindle current.

3. The manufacturing device (100) according to claim 2, wherein the calculating device (105) is configured to sum or average the spindle current from a plurality of measured values.

4. The manufacturing device (100) according to any one of the preceding claims, wherein the calculating device (105) is configured to calculate the wear from a sliding time window for the spindle current.

5. The manufacturing device (100) according to claim 1, wherein the calculating device (105) is configured to calculate the wear from the width of the interval.

6. The manufacturing device (100) according to claim 5, wherein the calculating device (105) is configured to calculate the wear of the tool (101) in proportion to the width of the interval.

7. The manufacturing device (100) according to any one of the preceding claims, wherein the manufacturing device (100) is configured to compensate for the wear of the tool (101) during the machining process.

8. The manufacturing device (100) according to any one of the preceding claims, wherein the manufacturing device (100) comprises a replacement device (111) for replacing a worn tool (101) with an unworn tool (101).

9. The manufacturing device (100) according to claim 8, wherein the replacement device (111) is configured to automatically change the tool (101) when a predetermined wear level is exceeded.

10. A manufacturing method for a dental restoration (200), comprising the steps of: - detecting (S101) a spindle current of a turning spindle (117); and - calculating (S102) wear of the tool (101) based on the spindle current, wherein an interval is calculated for the average 50% of the values of the spindle current.

11. The manufacturing method according to claim 10, wherein the wear is calculated from a plurality of measured values of the spindle current.

12. The manufacturing method according to claim 10 or 11, wherein the wear is calculated from a sliding time window for the spindle current.

13. The manufacturing method according to claim 10, wherein the wear is calculated from the width of the interval.