Dental furnace

Abstract

The invention relates to a dental furnace comprising a firing hood equipped with a heating device that is movably supported for the opening and closing of the dental furnace relative to a base intended for receiving a dental restoration part, and further comprising a heat detection device that is directed towards an area above the base, in particular towards one or more dental restoration parts, and further comprising a control or regulating device for the dental furnace that is coupled to the heat detection device, wherein the heat detection device is configured as a thermal imaging camera (30) which is directed towards the area above the base while the firing hood (12) is partially or completely opened, and which feeds an at least two-dimensional image in the form of a matrix of the one or more inserted dental restoration parts (60) to the control or regulating device and/or to a muffle (26) that is intended for the generation of the dental restoration parts (60).

Claims

1. A dental furnace comprising a firing hood equipped with a heating device that is movably supported for lifting and/or tilting to open and close the dental furnace relative to a base intended for receiving a dental restoration part, and a heat detection device that is directed towards an area above the base, towards one or more dental restoration parts, and a control or regulating device for the dental furnace that is coupled to the heat detection device, wherein the heat detection device is configured as a thermal imaging camera (30) which is directed towards the area above the base laterally from outside the furnace while the firing hood (12) is partially or completely opened, and which feeds an at least two-dimensional image in the form of a matrix of the one or more inserted dental restoration parts (60) to the control or regulating device and/or to a muffle (26) that is intended for the production of the dental restoration parts (60).

2. The dental furnace as claimed in claim 1, wherein the control device evaluates the individual matrix elements of the matrix both with respect to the temperature detected and the configuration by where there are warm regions (44, 26) and where there are not, and identifies the individual matrix elements as relevant or not relevant for a process control.

3. The dental furnace as claimed in claim 1, wherein the control or regulating device detects and evaluates the thermal image (34) of the detected object, with respect to its relative position with regard to the base and/or the firing hood (12) and to the dental furnace (10).

4. The dental furnace as claimed in claim 1, wherein the control or regulation device detects and evaluates the thermal image (34) with respect to its temporal development (1. derivative) and based on the location-based change of temperature identifies the dental restorations and the matrix elements relevant for the process control, and controls the dental furnace (10) depending on said matrix elements.

5. The dental furnace as claimed in claim 4, wherein the control or regulating device controls the closing and/or opening of the firing hood (12) depending on the temporal development of the thermal image (34) and/or the control or regulating device controls or regulates the temperature in the firing hood (12) depending on the temporal development of the thermal image (34).

6. The dental furnace as claimed in claim 1, wherein the thermal imaging camera (30) is calibrated with respect to the temperature and that each matrix element is configured as a temperature sensor.

7. The dental furnace as claimed claim 1, wherein the closing movement of the firing hood (12) of the furnace and/or the temperature of the firing hood (12) is regulated and/or controlled by the control device based on the temperature at matrix elements selected in the image according to a set or target course of the temperature.

8. The dental furnace as claimed in claim 1, wherein a display device (70) is attached to the dental furnace (10) or associated therewith, and that the thermal image (34) of the detected object or objects is represented on the display device (70) in color, wherein warm regions (44, 26) are represented more reddish or brighter and cold regions (44, 26) are represented more bluish or darker, and/or identified objects are marked in different colors and the background is displayed in greyscale, or that identified objects are framed or highlighted in a visible manner.

9. The dental furnace as claimed in claim 1, wherein the thermal imaging camera (30) is supported sideways next to the area above the base, outside the moving area of the firing hood (12), and with respect to its detection direction is directed towards the objects horizontally, or orthogonally, with a dimensional tolerance of less than 5.

10. The dental furnace as claimed in claim 1, wherein the control or regulating device comprises a filter device that hides warm regions (44, 26) outside the area above the base, on which the object may be accommodated.

11. The dental furnace as claimed in claim 1, wherein an additional temperature sensor is provided for the control or regulation of the temperature of the heating device of the dental furnace (10), and that said temperature sensor is coupled to the control or regulating device for the adjustment to the output signal of the thermal imaging camera (30).

12. The dental furnace as claimed in claim 1, wherein the control device comprises an evaluation device, with the aid of which objects, may be identified due to their thermal image (34) and the temporal development thereof during the heating, or during the closing of the firing hood (12), with respect to the positions, shapes, dimensions and numbers.

13. The dental furnace as claimed in claim 1, wherein the control or regulating device comprises a storage device, in which the thermal image (34) of a detected object and positions at which dental objects that have been identified as being relevant for the process control may be stored.

14. The dental furnace as claimed in claim 13, wherein the storage device stores the thermal image (34) of the object during the drying or closing process and during the firing process and stores the previously detected positions at which dental objects are relevant for the process control, and further uses those already detected positions for further temperature measurements beyond the drying or closing process, during the cooling phase (opening process).

15. The dental furnace as claimed in claim 1, wherein the control device comprises an evaluation device, with the aid of which the closing of the firing furnace may be blocked if the evaluation of the thermal image (34) reveals that the firing hood (12) would collide with the object upon closing.

16. A dental furnace comprising a heating device for the heating of a firing chamber having heating elements disposed at the outer periphery of the firing chamber, said heating device extends above a base intended for accommodating a dental restoration part (60), and a heat detection device that is directed towards an area above the base, towards one or more dental restoration parts (60), a furnace door and a control or regulating device for the dental furnace (10) to which the heat detection device is coupled, wherein the heat detection device is configured as a thermal imaging camera (30), is directed towards the area above the base and feeds an at least two-dimensional image of the one or more dental restoration parts (60) accommodated therein to the control or regulating device, said image being present in the form of a matrix.

17. A process for controlling a dental furnace that heats a dental restoration part via a closable firing hood, said hood is opened and closed by lifting and/or tilting, wherein a heat detection device is directed towards an area above a base that is coupled to the dental furnace, wherein the heat detection device is embodied as a thermal imaging camera (30) and is directed towards the area above the base in case of the firing hood (12) being open or through a suitable viewing window, and wherein a control device is provided that is fed with an at least two-dimensional image in the form of a matrix by the thermal imaging camera (30), said control device evaluating the detected areas (44, 26) of the matrix at least with respect to the temperature thereof.

18. The process as claimed in claim 17, carried out at a dental furnace that is characterized by comprising a firing hood equipped with a heating device that is movably supported for the opening and closing of the dental furnace relative to a base intended for receiving a dental restoration part, and a heat detection device that is directed towards an area above the base, towards one or more dental restoration parts, and a control or regulating device for the dental furnace that is coupled to the heat detection device, wherein the heat detection device is configured as a thermal imaging camera (30) which is directed towards the area above the base laterally from outside the furnace while the firing hood (12) is partially or completely opened, and which feeds an at least two-dimensional image in the form of a matrix of the one or more inserted dental restoration parts (60) to the control or regulating device and/or to a muffle (26) that is intended for the production of the dental restoration parts (60).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, details and features may be taken from the following description of two exemplary embodiments of the invention with reference to the drawings.

(2) FIG. 1 shows a schematic view of an inventive dental furnace comprising a thermal imaging camera and an inserted muffle;

(3) FIG. 2 shows a thermal image of the dental furnace in the embodiment according to FIG. 1;

(4) FIG. 3 shows a modified embodiment of an inventive dental furnace comprising two thermal imaging cameras; and

(5) FIG. 4 shows thermal images which illustrate the heating of dental restoration parts, which have been inserted into a firing furnace, at different points in time t0, t1, t2.

DETAILED DESCRIPTION

(6) In FIG. 1 a dental furnace 10 is illustrated which is formed as a press furnace in the exemplary case.

(7) The furnace comprises a firing hood 12 and a furnace bottom 14 with a firing chamber floor 16. The firing hood 12 is mounted to the furnace bottom 14 via a joint 18 which is not defined in detail and illustrated only schematically to carry out lifting and tilting movements. It is formed in the shape of a hood and therefore surrounds the firing chamber 20. At its periphery it is provided with a firing chamber heating 22 in a way known per se.

(8) The firing chamber 20 as well as the firing hood 12 are formed in a circular manner, wherein the firing chamber has substantially the shape of a hollow cylinder. Thus, it is suitable for receiving cylindrical muffles which are used for the pressing of dental restoration parts. A muffle 26 of this type is illustrated in FIG. 1 on the firing chamber floor 16. For producing the dental restoration part the muffle is loaded with a known molding or blank 28 the diameter of which is illustrated in FIG. 1 increased in size for the sake of clarity and which is inserted into a guide channel in the muffle 26.

(9) The blank is pressed with the help of a pressing drive (not illustrated) in the upper part of the firing hood 12.

(10) It is to be understood that both the pressing pressure and the temperature used to carry out pressing are subject to special requirements and that the respective parameters have to be complied with accurately. Alternatively, the muffle 26 is heated from the outside by the firing chamber heating 22, such that the desired temperature in its interior, i.e. in the area of the inserted blank 28, is only reached in a delayed fashion.

(11) Obviously, press furnaces of this type can be used to fire muffles of different diameters, such as a muffle of almost twice the diameter of the muffle 26 illustrated in FIG. 1. The height of the muffle used can also vary such that the muffle material to be heated can for instance vary by the factor of 4 from one pressing cycle to the next.

(12) According to the invention, a thermal detection device, which is formed as a thermal imaging camera 30, is attached to the dental furnace 10, namely on the outside of the dental furnace, preferably to the furnace bottom 14.

(13) The field of vision of the thermal imaging camera is directed to an area slightly above the firing chamber floor 16, i.e. where the muffle 26or the dental restoration part in the case of a firing furnaceis placed. The thermal imaging camera 30 is adjusted such that it detects a slightly larger area in the horizontal and vertical direction than the size of the largest muffle 26 used. This can also be seen schematically from FIG. 2.

(14) If necessary, the thermal imaging camera can also be provided with a lens system at its front in order to adjust the size and thus the resolution of the detection range, as required.

(15) For protection reasons the thermal imaging camera 30 is received within a frame 32 which remains intact even if the muffle 26 is bumped inadvertently. Furthermore, it is preferably attached laterally at the rear of the furnace bottom 14, instead of laterally at the front. As a consequence, it does not get in the way on the one hand, and it is directed towards clear space on the other hand, in which typically no other heat sources are disposed.

(16) Preferably, the orientation is selected such that the optical axis of the thermal imaging camera 30 coincides with the vertical axis of the firing chamber 20.

(17) It is to be understood that it is also possible to select a slightly offset orientation if certain areas on the side of the muffle are to be examined specifically. It is also possible to tilt the optical axis horizontally, in the exemplary embodiment illustrated slightly to the top in an appropriate manner, in order to facilitate a better detection of the vertical center of the muffle 26.

(18) It can be seen from FIG. 2 how a thermal image 34 is presented in the thermal imaging camera 30, if a muffle 26which has e.g. been preheated in a preheating furnaceis supported on the firing chamber floor 16 with the firing hood 12 being opened and the firing chamber heating 22 being turned on.

(19) In a preheating furnace the muffle is typically heated to a substantially even temperature.

(20) In FIG. 2 only a very rough heat distribution of the thermal image 34 can be seen. It is to be understood that thermal imaging cameras typically show a color-based resolution of temperature, wherein warm areas are illustrated in yellow, hot areas in red, cooler areas in green and cold areas in blue. The color range has a substantially higher resolution than what is illustrated here such that a temperature difference of, for instance, 2 is apparent due to the corresponding color variance.

(21) A thermal imaging camera with a resolution which is greater than what is illustrated in FIG. 2 by several orders of magnitude, for instance resolutions of 1000 pixels times 1500 pixels, can be implemented without further ado.

(22) However, from FIG. 2 it can also be seen that the surrounding areas 44 which are illustrated without shadings in these Figures correspond to cold areas of the thermal image 34. These are illustrated in blue on the real thermal image and show the cold surrounding.

(23) The contrast between the areas 44 and the area of the muffle 26 makes possible to detect the two-dimensional size of the muffle without further ado and to control and regulate the dental furnace 10 according to requirements.

(24) However, according to the invention the time-dependent change of the thermal image 34 is also important which is caused by the comparison before and after the setting of the muffle.

(25) When evaluating the thermal image 34 a plausibility test is carried out, too. Muffles, but also dental restoration parts in firing furnaces, have a predefined shape each. If hot spots appear in the area 44 of the thermal image, they cannot stem from the muffle or the dental restoration part and can thus be hidden without further ado.

(26) With growing temperatures the contrast between the area 44 and the area 26 increases such that the muffle detection becomes sharper.

(27) Here, the monitoring of the muffle in the heating phase, i.e. when closing the firing hood 12, is described; however, it is to be understood that it is favorable according to the invention that the thermal imaging camera 30 remains at its predefined location and that a thermal image detection is also carried out when opening the firing hood 12. Provided that the operation is failure-free, the muffle must remain at the same location as when the firing hood was closed, and here, too, the desired temperature profile can be adapted to the requirements and the lifting of the firing hood 12 and, if necessary, the turning off of the firing chamber heating 22 can be regulated and controlled.

(28) If the resolution of the thermal imaging camera is accordingly fine, any possible cracks in the muffle can be detected which would run across the thermal image 34 as a slightly hotter line. This would equally apply to chipped gypsum pieces of the muffle, and in this case the flaw could be examined more accurately.

(29) Even if the thermal imaging camera 30 is illustrated as being fixed to a predefined location, it is to be understood that a pivotable mounting is also possible in an alternative embodiment. The thermal imaging camera can then be pivoted from the 45 lateral rear position to the 45 lateral front position, i.e. it can be pivoted by 90 altogether. Especially in firing furnaces for dental restoration parts, this facilitates the three-dimensional detection of the dental restoration parts and insofar quasi a stereoscopic recording of a thermal image.

(30) Thus, the inventive thermal imaging camera 30 can be used to detect flaws but also to identify the dental objects to be fired without further ado.

(31) A further embodiment of an inventive thermal imaging camera is illustrated in FIG. 3. In this solution a firing furnace 10 is used which receives dental restoration parts 60 which are placed on a firing plate 56 which is in turn supported by the furnace bottom 14. The firing chamber heating 22 is typically disposed at the outer periphery of the firing chamber 20 and partially radiates heat downwards when the firing hood 12 is open. In this way, the dental restoration parts 60 are heated even if the firing hood 12 is open. This can be detected by both thermal imaging cameras 30a and 30b which are mounted movably in the exemplary embodiment illustrated. A horizontal visual axis 62 of the thermal imaging camera 30a is directed towards the dental restoration parts 60 and detects them laterally.

(32) In contrast, the thermal imaging camera 30b is directed towards the firing plate 56 in the exemplary embodiment illustrated, and the visual axis 64 coincides with it slightly below the dental restoration parts 60.

(33) However, the thermal image of the thermal imaging camera 30b also detects the dental restoration parts 60, namely due to the inclined orientation of its top side. This facilitates a common and again three-dimensional detection of the thermal image or temperature image of the dental restoration parts 60.

(34) In a way known per se, the furnace bottom 14 comprises a display device 70. Controlled by the control keys 72, it can immediately show the thermal image of the thermal imaging cameras 30a and 30b. It is additionally evaluated by an image detection device and the control of both the closing movement and the supply of the heating energy is carried out in line with the requirements.

(35) FIG. 4 shows 3 thermal images which were taken at points in time t0, t1 and t2 of the working area, i.e. the areas above the base. Threshold values were used for illustrating the temperatures in the image, for the sake of a simple representation. Matrix elements which have a lower temperature than the first predefined threshold value, are illustrated almost black, and elements which have a temperature above this threshold value are illustrated brighter. At point in time t0, directly after placing the firing tray with 3 dental restorations into the firing furnace, almost no temperature differences are noticeable. The objects do not stand out against the background as their temperatures are similar. However, in the image shown a spot with a high temperature is visible in the top right corner. As this spot is not plausible the decision can be made that this is a hot object in the background and therefore these pixels do not have to be considered anymore for further analysis.

(36) However, the inserted dental objects themselves will be heated inevitably and continuously as they have been placed below the hot furnace hood. The heating itself and the speed of the heating and whether the heating is carried out continuously can be determined and calculated by periodically storing the images in a predefined and considered time period. As can be seen, at point in time t1 the firing tray and the objects have already partially heated. At point in time t2 all objects stand out against the background clearly and sharply. Through an appropriate selection of the threshold value mentioned, a selection of objects can be carried out fast and accurately such that it might be possible in t1 already. The background interference illustrated in point in time t0 was either removed in practice or is hidden by the software and not considered in the illustration of the image anymore.

(37) In a modified embodimentwhich is not graphically illustrated herethe firing hood is stationary and the base is movable. Insofar, the firing hood is also mounted movably relative to the base. The base can e.g. be moved vertically such that the firing chamber is closed in the uppermost position of the base and in a lower position of the base the dental restoration parts can be removed. Due to the movement of the base, however, they are automatically shaken such that this embodiment is not preferred.

(38) In a further modified embodiment instead of the firing hood a closed firing chamber is provided which can be accessed via a furnace door from the side. Here, too, a base in the form of a furnace bottom is implemented in the furnace thereat which is designed for receiving one or more dental restoration parts. The thermal imaging camera can be attached to the furnace door in this solution, or to a fixed position outside the furnace door such that the interior of the furnace is detected. Thermal analysis facilitates the detection of the heating of the dental restoration parts located thereat.

(39) In a further modified embodiment a viewing window permeable to infrared radiation is provided in the rear area of the furnace wall. The thermal imaging camera is directed towards this window such that the interior of the firing chamber is detected, and the surrounding space when the furnace door is open. This solution creates stronger contrasts between the hot dental restoration parts and the ambient air.