Dental sintering furnace

Abstract

A dental sintering furnace constituted of: a plurality of walls; a chamber defined by the plurality of walls; a DC power source arranged to output DC power; one or more resistive heating elements arranged to receive the output DC power and generate heat within the chamber; and a control unit arranged to control the output DC power.

Description

DENTAL SINTERING FURNACETECHNICAL FIELD

[0001] The present disclosure relates substantially to the field of sintering, and more particularly to a dental sintering furnace.BACKGROUND

[0002] Dental crowns, bridges, frameworks and other restoration devices are typically manufactured through sintering, which is a heat treatment process in which a large quantity of loose aggregate material is subjected to a sufficiently high temperature and pressure to cause the loose material to become a compact solid piece. Typically, such a process takes 12 - 16 hours and is performed in a specialized laboratory. As a result, when a patient needs a dental apparatus, it may take several weeks from the time measurements are taken until it can be used for the patient. There is thus a long felt need for a small sintering furnace which can efficiently, and quickly, prepare dental apparatuses in the dental clinic itself.SUMMARY

[0003] Accordingly, it is a principal object of the present invention to overcome at least some of the disadvantages of prior art sintering furnaces by providing a dental sintering furnace comprising: a plurality of walls; a chamber defined by the plurality of walls; a direct-current (DC) power source arranged to output DC power; one or more resistive heating elements arranged to receive the output DC power and generate heat within the chamber; and a control unit arranged to control the output DC power.

[0004] In some examples, the dental sintering furnace further comprises a current limiter arranged, responsive to a resistance of the one or more resistive heating elements, to limit a current of the output DC power to a predetermined magnitude value.

[0005] In some examples, the dental sintering furnace further comprises a temperature sensor arranged to output an indication of a temperature of the one or more resistive heating elements, wherein, responsive to the resistance of the one or more resistive heating elementsbeing above a predetermined resistance value, the control unit is arranged to control the output DC power responsive to the output indication of the temperature sensor.

[0006] In some examples, the control unit comprises a proportional-integral-derivative (PID) controller, the control of the output DC power responsive to the output indication of the temperature sensor being performed by the PID controller.

[0007] In some examples, the control of the output DC power is such that the temperature of the one or more resistive heating elements maintains a predetermined temperature profile over a predetermined period of time.

[0008] In some examples, the control of the output DC power comprises a control of a magnitude value of a DC current output by the DC power source within a predetermined voltage amplitude range.

[0009] In some examples, the control of the output DC power comprises a control of an amplitude value of a DC voltage output by the DC power source within a predetermined current magnitude range.

[0010] In some examples, the control of the output DC power comprises a control of a value of the output DC power.

[0011] In some examples, the one or more resistive heating elements comprises one or more molybdenum disilicide heating elements.

[0012] In some examples, the one or more resistive heating elements comprises one or more silicon carbide heating elements.

[0013] In some examples, the DC power source comprises an alternating-current (AC) to DC power converter.

[0014] In some examples, a dental sintering method is provided, the method comprising: providing direct-current (DC) power to one or more resistive heating elements, the one or more resistive heating elements arranged to receive the output DC power and generate heat within a chamber of a dental sintering furnace; and controlling the output DC power.

[0015] In some examples, the method further comprises, responsive to a resistance of the one or more resistive heating elements, limiting a current of the output DC power to a predetermined magnitude value.

[0016] In some examples, the method further comprises: detecting an indication of a temperature of the one or more resistive heating elements; and responsive to the resistance of the one or more resistive heating elements being above a predetermined resistance value, controlling the output DC power responsive to the output indication of the temperature.

[0017] In some examples, the controlling the output DC power comprises proportional- integral-derivative (PID) control.

[0018] In some examples, the control of the output DC power is such that the temperature of the one or more resistive heating elements maintains a predetermined temperature profile over a predetermined period of time.

[0019] In some examples, the control of the output DC power comprises a control of a magnitude value of a DC current output by the DC power source within a predetermined voltage range.

[0020] In some examples, the control of the output DC power comprises a control of an amplitude value of a DC voltage output by the DC power source within a predetermined current magnitude range.

[0021] In some examples, the control of the output DC power comprises a control of a value of the output DC power.

[0022] In some examples, the one or more resistive heating elements comprises one or more molybdenum disilicide heating elements.

[0023] In some examples, the one or more resistive heating elements comprises one or more silicon carbide heating elements.

[0024] In some examples, the method further comprises: receiving alternating -current (AC) power; and converting the received AC power to the output DC power.

[0025] Additional features and advantages of the invention will become apparent from the following drawings and description.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the patent specification, including definitions, governs. As used herein, the articles "a" and "an" mean "at least one" or "one or more" unless the context clearly dictates otherwise. As utilized herein, “and / or” means any one or more of the items in the list joined by “and / or”. As an example, “x and / or y” means any element of the three-element set { (x), (y), (x, y) } . In other words, “x and / or y” means “x, y or both of x and y”. As another example, “x, y, and / or z” means any element of the seven-element set { (x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}.

[0027] Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0028] In addition, use of the “a” or “an” are employed to describe elements and components of examples of the instant inventive concepts. This is done merely for convenience and to give a general sense of the inventive concepts, and “a” and “an” are intended to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

[0029] As used herein, the term "about", when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of + / -10%, more preferably +1-5%, even more preferably + / -1%, and still more preferably + / -0.1% from the specified value, as such variations are appropriate to perform the disclosed devices and / or methods.

[0030] The following examples and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be illustrative, but not limiting in scope. In various examples, one or more of the above-described problems have been reduced or eliminated, while other examples are directed to other advantages or improvements.BRIEF DESCRIPTION OF DRAWINGS

[0031] For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding sections or elements throughout.

[0032] With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred examples of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how several forms of the invention may be embodied in practice. In the accompanying drawings:

[0033] FIGs. 1A - IB illustrate various views of a dental sintering furnace, in accordance with some examples;

[0034] FIG. 1C illustrates a more detailed example of the dental sintering furnace of FIG. 1A; and

[0035] FIG. ID illustrates a high-level flow chart of a method of operation of the dental sintering furnace of FIGs. 1A - 1C.DETAILED DESCRIPTION OF CERTAIN EXAMPLES

[0036] In the following description, various aspects of the disclosure will be described. For the purpose of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the different aspects of the disclosure. However, it will also be apparent to one skilled in the art that the disclosure may be practiced without specific details being presented herein. Furthermore, well-known features may be omitted or simplified in order not to obscure the disclosure. In the figures, like reference numerals refer to like parts throughout. In order to avoid undue clutter from having too many reference numbers and leadlines on a particular drawing, some components will be introduced via one or more drawings and not explicitly identified in every subsequent drawing that contains that component.

[0037] FIG. 1 A illustrates a perspective view of a dental sintering furnace 10 and FIG. IB illustrates a high-level schematic view of dental sintering furnace 10. FIG. 1C illustrates a high- level schematic view of a more detailed example of dental sintering furnace 10. FIG. ID illustrates a high-level flow chart of a method of operation of dental sintering furnace 10, FIGs. 1A - ID being described together. In one example, dental sintering furnace 10 comprises: a plurality of walls 20; a chamber 30 defined by walls 20; a DC power source 40; one or more resistive heating elements 50; and a control unit 60. In one example, dental sintering furnace 10 further comprises a current limiter 70. In another example, dental sintering furnace 10 further comprises one or more temperature sensors 80.

[0038] Walls 20 are not limited to walls exhibiting respective angles therebetween. For example, walls 20 can include a generally circular structure, where each wall 20 is defined as a respective portion of the circular structure. In one example, chamber 30 defines an area completely surrounded by walls 20. In one example, at least one wall 20 comprises a door which allows access to chamber 30.

[0039] In one example, DC power source 40 comprises an alternating-current (AC) to DC power converter 90. In such an example, an input of AC to DC power converter 90 is coupled to an AC power source 95, such as an AC power mains. In one further example, AC to DC power converter 90 comprises a full-wave rectifier. In another further example, AC to DC power converter 90 comprises a switched mode power supply.

[0040] Each resistive heating element 50 generates a predetermined amount of heat responsive to an electric current flowing therethrough. In one example, resistive heating elements 50 comprise molybdenum disilicide ( MoSii) heating elements. In another example, resistive heating elements 50 comprise silicon carbide (SiC) heating elements. In one example, resistive heating elements 50 are each arranged to generate heat in excess of 1,600° C, however this is not meant to be limiting in any way, and lower temperatures can be provided without exceeding the scope of the disclosure.

[0041] In one example, control unit 60 is implemented, without limitation, as one of, or a combination of, a dedicated analog circuitry, an application- specific integrated circuit (ASIC), a field programmable gate array (FPGA) or a microprocessor. In another example, control unit60 comprises a control loop 65. In one further example, control loop 65 is an analog-controlled control loop. In another further example, control loop 65 is a digital-controlled control loop. In one example, control loop 65 comprises a proportional-integral-derivative (PID) controller. In one example (not shown), control unit 60 comprises one or more of: a current amplitude sensor, arranged to measure a magnitude of an electric current; a voltage sensor, arranged to measure an amplitude of a voltage; or an electric power sensor, arranged to measure a value of electric power.

[0042] In one example, current limiter 70 is part of DC power source 40. In another example, current limiter 70 is external to DC power source 40. In such an example, an output of DC power source 40 is in electrical communication with current limiter 70. The term "electrical communication", as used herein, means that electrical power can pass therebetween. Resistive element / s 50 are in electrical communication with DC power source 40.

[0043] In operation, dental zirconia is milled into a predetermined shape, such as a dental crown. The milled zirconia is placed within chamber 30. Responsive to a user input, DC power source 40 is operated. In stage 1000, DC power source 40 outputs DC power to resistive heating elements 50. In an example where DC power source 40 comprises an AC to DC power converter 90, AC power is received from AC power source 95 and AC to DC power converter 90 converts the received AC power to DC power.

[0044] Prior art dental sintering furnaces are all powered by AC power. Advantageously, by providing DC power to resistive heating elements 50, up to 100% of the power can be provided to resistive heating elements 50. In contrast, in typical AC powered dental sintering furnaces, part of the power cycle is lost. For example, in diode for alternating current (DIAC) based AC power sources, a portion of every half cycle is lost until the breakdown voltage is reached. Additionally, structural deterioration of resistive heating elements 50 happens at a slower rate when being powered by DC current than with AC current.

[0045] As the DC current flows through the one or more resistive heating elements 50, the resistance to the current generates heat within chamber 30. In one example, resistive heating elements 50 exhibit a near-zero resistance at room temperature, with the resistance increasing when resistive heating elements 50 are heated. Thus, in one example, in stage 1010, responsive to the resistance of resistive heating elements 50, current limiter 70 limits the magnitude of DC current being provided to resistive heating elements 50, until the resistance of resistive heatingelements 50 increase to a predetermined resistance value. In one further example, current limiter 70 operates in accordance with the load voltage at the output thereof. Particularly, current limiter 70 limits the DC current to a maximum magnitude value until the voltage across each resistive heating element 50 does not increase past a predetermined threshold when the magnitude of the DC current increases. In one example, current limiter 70 comprises one or more elements that limit the current flowing therethrough in response to the voltage thereacross, such that when the load voltage is low the current is limited. In another example, current limiter 70 detects the load voltage, or load resistance, and limits the current responsive to a detected low load voltage or resistance. In one example, current limiter 70 is thyristor- based.

[0046] Once the resistance of resistive heating elements 50 increases past the predetermined resistance value, current limiter 70 ceases to limit the magnitude of the DC current. From that point, in stage 1020, control unit 60 controls the output DC power of DC power source 40. As will be described below, the control of the output DC power can be implemented either by: adjusting the current magnitude; adjusting the voltage amplitude; or adjusting the overall power output. In one example, control unit 60 controls the output DC power responsive to the output of temperature sensor / s 80, which provide an indication of the temperature of resistive heating elements 50. In one further example, temperature sensor / s 80 measure the average temperature within chamber 30. In another further example, temperature sensor / s 80 directly measure the temperature of resistive heating elements 50. In one further example, as described above, control unit 60 comprises a PID controller arranged to control the output DC power.

[0047] In one example, control loop 65 of control unit 60 controls the magnitude of the output DC current in order to maintain a predetermined temperature profile over a predetermined period of time, indicated by temperature sensor / s 80, i.e. an increase in current magnitude causes an increase in temperature and a decrease in current magnitude causes a decrease in temperature. In one further example, control unit 60 controls the value of the magnitude of the output DC current, while maintaining the voltage across resistive heating elements 50 within a predetermined amplitude range.

[0048] In another example, control loop 65 of control unit 60 controls the amplitude of the output DC voltage in order to maintain the predetermined temperature profile over the predetermined period of time, i.e. an increase in voltage amplitude causes an increase intemperature and a decrease in voltage amplitude causes a decrease in temperature. In one further example, control unit 60 controls the value of the amplitude of the output DC voltage, while maintaining the current flowing through resistive heating elements 50 within a predetermined magnitude range.

[0049] In another example, control loop 65 of control unit 60 controls the power value of the output DC power in order to maintain the predetermined temperature profile over the predetermined period of time. Particularly, the current magnitude and the voltage amplitude are adjusted accordingly. Thus, an increase in power causes an increase in temperature and a decrease in power causes a decrease in temperature. In one example, the current magnitude and voltage amplitude values of the desired power values are determined responsive to predetermined parameters.

[0050] The DC power is provided to resistive heating element / s 50 for the predetermined period of time. At the end of the predetermined period of time, the dental zirconia has been sintered and can thus be removed from chamber 30.

[0051] Thus, dental sintering furnace 10 is efficiently heated by resistive heating elements 50, such as MoSi2 or SiC, while providing current limiting during start up.

[0052] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate examples, may also be provided in combination in a single example. Conversely, various features of the invention which are, for brevity, described in the context of a single example, may also be provided separately or in any suitable subcombination.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as are commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods are described herein.

[0054] All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the patent specification, including definitions, will prevail. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

[0055] It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the appended claims and includes both combinations and subcombinations of the various features described hereinabove as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description.

Claims

CLAIMS1. A dental sintering furnace comprising: a plurality of walls; a chamber defined by the plurality of walls; a direct-current (DC) power source arranged to output DC power; one or more resistive heating elements arranged to receive the output DC power and generate heat within the chamber; and a control unit arranged to control the output DC power.

2. The dental sintering furnace of claim 1, further comprising a current limiter arranged, responsive to a resistance of the one or more resistive heating elements, to limit a current of the output DC power to a predetermined magnitude value.

3. The dental sintering furnace of claim 2, further comprising a temperature sensor arranged to output an indication of a temperature of the one or more resistive heating elements, wherein, responsive to the resistance of the one or more resistive heating elements being above a predetermined resistance value, the control unit is arranged to control the output DC power responsive to the output indication of the temperature sensor.

4. The dental sintering furnace of claim 3, wherein the control unit comprises a proportional- integral-derivative (PID) controller, the control of the output DC power responsive to the output indication of the temperature sensor being performed by the PID controller.

5. The dental sintering furnace of claim 3 or 4, wherein the control of the output DC power is such that the temperature of the one or more resistive heating elements maintains a predetermined temperature profile over a predetermined period of time.

6. The dental sintering furnace of any one of claims 3 - 5, wherein the control of the output DC power comprises a control of a magnitude value of a DC current output by the DC power source within a predetermined voltage amplitude range.

7. The dental sintering furnace of any one of claims 3 - 5, wherein the control of the output DC power comprises a control of an amplitude value of a DC voltage output by the DC power source within a predetermined current magnitude range.

8. The dental sintering furnace of any one of claims 3 - 5, wherein the control of the output DC power comprises a control of a value of the output DC power.

9. The dental sintering furnace of any one of claims 1 - 8, wherein the one or more resistive heating elements comprises one or more molybdenum disilicide heating elements.

10. The dental sintering furnace of any one of claims 1 - 8, wherein the one or more resistive heating elements comprises one or more silicon carbide heating elements.

11. The dental sintering furnace of any one of claims 1 - 10, wherein the DC power source comprises an alternating-current (AC) to DC power converter.

12. A dental sintering method, the method comprising: providing direct-current (DC) power to one or more resistive heating elements, the one or more resistive heating elements arranged to receive the output DC power and generate heat within a chamber of a dental sintering furnace; and controlling the output DC power.

13. The method of claim 12, further comprising, responsive to a resistance of the one or more resistive heating elements, limiting a current of the output DC power to a predetermined magnitude value.

14. The method of claim 13, further comprising: detecting an indication of a temperature of the one or more resistive heating elements; and responsive to the resistance of the one or more resistive heating elements being above a predetermined resistance value, controlling the output DC power responsive to the output indication of the temperature.

15. The method of claim 14, wherein the controlling the output DC power comprises proportional-integral-derivative (PID) control.

16. The method of claim 14 or 15, the control of the output DC power is such that the temperature of the one or more resistive heating elements maintains a predetermined temperature profile over a predetermined period of time.

17. The method of any one of claims 14 - 16, wherein the control of the output DC power comprises a control of a magnitude value of a DC current output by the DC power source within a predetermined voltage range.

18. The method of any one of claims 14 - 16, wherein the control of the output DC power comprises a control of an amplitude value of a DC voltage output by the DC power source within a predetermined current magnitude range.

19. The method of any one of claims 14 - 16, wherein the control of the output DC power comprises a control of a value of the output DC power.

20. The method of any one of claims 13 - 19, wherein the one or more resistive heating elements comprises one or more molybdenum disilicide heating elements.

21. The method of any one of claims 13 - 19, wherein the one or more resistive heating elements comprises one or more silicon carbide heating elements.

22. The method of any one of claims 13 - 21, further comprising: receiving alternating-current (AC) power; and converting the received AC power to the output DC power.

Images