Induction coil unit and method for controlling inductive heating process for induction coil unit

Abstract

To provide an induction coil unit, and a method for controlling an inductive heating process for an induction coil unit.SOLUTION: To increase the degree of automation and operational safety in an induction coil unit, a temporal profile or a frequency profile of a coil current and / or of a coil voltage and / or of an input current and / or of an input voltage is determined for a sleeve portion inserted into an induction coil, during an inductive heating process in the sleeve portion inserted into the induction coil. Further, the (coil current) profile and / or the (coil voltage) profile and / or the (input current) profile and / or the (input voltage) profile is then analyzed. Based on an analyzed profile or an evaluated profile, in particular based on a profile behavior and / or a profile change and / or a profile change behavior, a decision is made as to whether an uninterrupted heating process is continued or ended.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an induction coil unit comprising an induction coil into which a sleeve portion of a tool holder can be inserted, and a method for controlling an induction heating process for an induction coil unit in which a sleeve portion of a tool holder is inserted into the induction coil of the induction coil unit. [Background technology]

[0002] Such generic induction coil units are known from the prior art, for example from US Pat. No. 5,399,633.

[0003] These known induction coil units are used to thermally expand the tool holder by means of the alternating magnetic field which can be generated by the induction coil and thereby induced in the tool holder inserted in the induction coil of the induction coil unit, so that the tool can be inserted in its expanded state in the tool holder, which then is held tightly and symmetrically by the tool holder after a cooling process of the latter, this process being also called in shorthand the inductive shrink fit of the tool to the tool holder and known per se.

[0004] For a more detailed description of the technical and operational background, reference should therefore be made to the above mentioned patent applications.

[0005] However, in such known induction coil units, for their efficient operation, i.e. for the inductive shrink-fit of the tool in the tool holder, in particular during the heating of the tool holder, the induction coil unit must be individually adjusted in various operating parameters, for example with regard to the heating time among others, to the respective tool holder currently held therein, which requires considerable manual intervention and therefore results in a potentially significant increase in the cycle time for changing tools in different types of tool holders. Apart from this, manual intervention is always also a potential source of errors.

[0006] On the other hand, if such adjustments are not made or are not made correctly for the currently held tool holder, operation of the induction coil unit may in some cases be inefficient, since the desired eddy currents are not properly induced in the tool holder. In particularly unfavorable cases, for example if the heating time is too long, the tool holder may even overheat and therefore be destroyed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent Application Publication No. 1867211A1 [Patent Document 2] German Patent Application No. 102015016831.2 [Patent Document 3] German Patent Application No. 102019112521.9 [Patent Document 4] European Patent Application No. 19176562.7 [Patent Document 5] German Patent Application Publication No. 19915412A1 Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to provide an induction coil unit and a method for controlling an induction heating process for an induction coil unit which is able to overcome the above-mentioned drawbacks of induction coil units as known from the prior art, in particular an induction coil unit which can be automated to a higher degree and therefore operated with shorter cycle times, while at the same time maintaining high operational safety. [Means for solving the problem]

[0009] This object is achieved by an induction coil unit and a method for controlling an induction heating process for an induction coil unit with the features of the respective independent patent claims. Advantageous developments of the invention are the subject of the dependent claims and the following description and relate both to an induction coil unit and to a method for controlling an induction heating process for an induction coil unit.

[0010] Any terms used, such as top, bottom, front, back, left, or right, unless expressly defined otherwise, are to be understood in the ordinary manner, including with respect to the drawings herein. Terms such as radial and axial, where they are used and unless expressly defined otherwise, are to be understood with respect to the central axis, or axis of symmetry, of the components described herein, including with respect to the drawings herein.

[0011] The expressions "substantially", where they are used, may be understood (in accordance with the High Court's understanding) to mean "to an extent that is still significant in practice". Possible deviations from exactitude thus implied by this concept may arise unintentionally (so to speak, without any functional basis) due to manufacturing or assembly tolerances etc.

[0012] The induction coil unit and method for controlling an induction heating process for the induction coil unit provide an induction coil within the induction coil unit into which a sleeve portion of a tool holder can be inserted (as relates to the arrangement) or is inserted (as relates to the method).

[0013] method 1. A method for controlling an induction heating process for an induction coil unit, e.g. a shrink fitting apparatus, in which a sleeve portion of a tool holder is inserted into an induction coil of the induction coil unit, the method comprising: During the particularly uninterrupted induction heating process of the sleeve portion inserted in the induction coil, the time or frequency profile of the coil current, i.e. in simple terms the amperage of the coil current generated in the coil or in the coil circuit over a certain time or frequency, and / or the time or frequency profile of the coil voltage, i.e. in other terms the voltage of the coil current present in the coil or that can be tapped off in the coil circuit over a certain time or frequency, and / or - the time or frequency profile of the input current and / or voltage, i.e. in simple terms the amperage and / or voltage of the current generated upstream of the coil or upstream of the coil circuit over a period of time or frequency is specified for the sleeve portion inserted into the induction coil.

[0014] A time profile or a frequency profile (sometimes also called frequency characteristic) can be understood in the present application in exemplary and simple terms to mean a mapping or a relationship in which the mapping variable of the mapping rule that in particular maps the mapping variable to a second mapped variable is time or frequency, which in this case can then be the aforementioned coil current and / or coil voltage and / or input current and / or input voltage, or a variable that can be derived or obtained / calculated therefrom, such as a phase position or a phase shift.

[0015] Mathematically, this is in simplified form: (coil current / coil voltage / input current / input voltage (or derived variable)) = f (time or frequency) where f = mapping rule / relationship It may be possible to express it by:

[0016] Furthermore, thereafter the (coil current) profile and / or the (coil voltage) profile and / or the (input current) profile and / or the (input voltage) profile or derived variables are analyzed.

[0017] Based on the analyzed or evaluated profile, in particular on the profile behavior and / or the profile changes and / or the profile change behavior, a decision is taken in particular whether the uninterrupted heating process is to be continued or terminated.

[0018] Analyzed may therefore in the present application mean that the profile behavior and / or profile changes and / or profile change behavior of a time or frequency profile are identified or investigated, particularly based on identifiable parameters.

[0019] Here, profile behavior is understood to mean in particular changes in the profile, e.g. rising, falling and / or unchanged profiles, as well as the curvature behavior of the profile, and profile change / behavior is understood to mean changes in the profile itself or as a whole, e.g. changes in the profile over time and / or in the heating temperature of the sleeve portion inserted in the induction coil, i.e. generally over the third dimension.

[0020] The present invention is based on the discovery that, based on the heating or heating temperature of the sleeve portion inserted in the induction coil, there is a change in the magnetic properties, e.g., permeability, of the sleeve portion inserted in the induction coil and, therefore, in the inductance and / or electrical properties, e.g., electrical resistance of the entire system, including the induction coil and the sleeve portion inserted therein.

[0021] The change in permeability or inductance is in this case, as previously specified, more pronounced the closer the heating temperature of the sleeve part inserted in the induction coil is to its Curie temperature Tc, while the change in electrical properties, such as resistance, dominates at greater distances from the Curie temperature Tc, for example at the start of heating below the Curie temperature Tc.

[0022] This in turn means that the "dynamics" of the temperature-dependent change profile of the permeability, inductance and / or electrical properties or resistance, i.e. the profile change / profile change behavior, can be recognized or said changes are reflected therein, showing different effects or advantages in particular in different temperature ranges.

[0023] It has also been specified here that this is reflected in particular in the coil current, the coil voltage, as well as in the input current and input voltage, and therefore also in variable values ​​that can be introduced or obtained / calculated therefrom, such as the phase position or phase shift.

[0024] Expressed in simplified and briefly descriptive terms, in the lower temperature range, changes in particular resistance are reflected in the coil current, coil voltage, and in the input current and input voltage, or in variables that can be derived or obtained / calculated therefrom, such as phase position or phase shift, and as the Curie temperature Tc is approached or approached, changes in permeability / inductance are reflected therein.

[0025] In other words, the profile that most reliably describes / maps / tracks the (heating) condition of the inserted sleeve portion, or most reliably describes / maps the recognized temperature dependent effects, is that of the coil current, coil voltage, and input current and input voltage or variables derived therefrom.

[0026] A parameter (or parameters) recognizing / mapping these dynamics or their changes allows this change to be taken into account / made understandable (in analytical terms) and therefore can be used to define criteria for heating of the inserted sleeve portion.

[0027] Such parameters describing the profile dynamics, i.e. profile behavior or profile changes / profile change behavior, may for example map or represent, particularly in the case of temperature profiles, changes in amplitude (value), particularly amplitude extremes, particularly amplitude maximums, e.g. amperage or voltage dropping / decreasing or remaining constant or increasing / rising.

[0028] Such parameters describing the profile dynamics, i.e. the profile behavior or the profile change / profile change behavior, may for example be the amplitude maximum, in particular the resonant frequency, the amplitude maximum change, the dispersion or curve width / bandwidth, or the dispersion / curve width / bandwidth change and / or the resonant frequency change, in particular also in the case of a frequency profile.

[0029] In other words, in simple illustrative terms, such parameters describing profile dynamics, i.e. profile behavior or profile changes / profile change behavior, are not simply simple characteristic variables that statistically describe particular conditions during power transfer or consumption (e.g., specific amperage / voltage values ​​at a particular time or in a time profile, etc.), but go beyond that to more extensive characteristic variables that map the "dynamics" in the time or frequency profile / in the frequency profile changes.

[0030] Simply put, mathematically speaking, a (mathematical) characteristic variable or higher order derivative in the time profile or frequency profile / frequency profile change.

[0031] It is therefore particularly advantageous, for example, if the profile dynamics are described using the derivative or tangent of the profile or of the profile change and / or of a connecting curve connecting the amplitude values, in particular the amplitude maxima, of the profile, in particular the time profile, i.e. in this case the parameter is the tangent.

[0032] In other words, the parameter may conveniently be mathematically speaking the derivative or tangent of the profile, in particular the time profile, and thus map the change, in particular the time change, of the coil current or coil voltage or input current or input voltage.

[0033] A decision as to whether to continue or terminate the heating process may then be made, in particular using such derivatives or one or more tangents, in particular using the change in one or more slopes of the one or more tangents.

[0034] In particular, transitions in the slope of the tangents, here e.g. from a descending tangent to a horizontal tangent or vice versa, or from a horizontal tangent to an ascending tangent or vice versa, may be of great importance / decision making importance.

[0035] For example, when the parameters of the coil current, of the coil voltage, and / or of the time profile of the input current and / or input voltage thus show a horizontal profile or an ascending profile or a transition from a descending tangent to a horizontal tangent or a transition from a horizontal tangent to an ascending tangent, the heating process may be aborted in the event of such behavior ("abort behavior").

[0036] The same applies equally to the curvature and / or curvature behavior of the profile.

[0037] In particular, aborting may occur, for example, as soon as only one of the (profile) parameters, or the first one (in time) exhibits a predefined, described abort behavior, or alternatively, only when multiple or all (profile) parameters (here: coil current, coil voltage, input current and input voltage) exhibit a predefined abort behavior (a (predefinable) "abort criterion").

[0038] Further stopping criteria can also be defined in this case for each sleeve part, respectively for one specific sleeve part or separately for several specific sleeve parts, e.g. for a larger sleeve part diameter some or all parameters must show stopping behavior and for a smaller sleeve part diameter only one parameter must show stopping behavior.

[0039] Here, it may be particularly advantageous to identify an effective current or voltage profile for a specified time / frequency profile, which when used as another basis for identifying parameters, will more closely reproduce the actual current or voltage profile.

[0040] The same is true if the identified time / frequency profile is scaled, smoothed, averaged, filtered, and / or normalized.

[0041] In particular, it may be advantageous to normalize the profile to a reference voltage, for example to the German reference mains voltage, such that the method can be made independent of specific national differences with their respective mains voltages.

[0042] In addition, it may be advantageous for the decision to be based on the geometry or other physical properties, such as the material or mass, of the sleeve portion inserted into the induction coil of the induction coil unit. Such a geometry may for example be the outer diameter of the inserted sleeve portion.

[0043] This is based on the fact that the variable to be measured (besides temperature) depends crucially on the extent to which the sleeve part fills the centre of the induction coil, i.e. the so-called core, i.e. whether the (outer) diameter of the sleeve part in question is smaller or larger or whether its mass is heavier or lighter.

[0044] In particular, in the case of induction shrink-fit or shrink-fitting machines, the sleeve part of the tool holder inserted in the space circumferentially surrounded by the induction coil forms an essential component of the magnetic circuit. In particular, the sleeve part forms the metal core of the induction coil. The range of inductance to be measured therefore crucially depends on the extent to which the sleeve part fills the centre, i.e. the so-called core, of the induction coil, i.e. whether the (outer) diameter of the sleeve part in question is smaller or larger or whether its mass is heavier or lighter.

[0045] In this regard, it is then advantageous here if the geometry or the outside diameter of the sleeve part to be inserted into the induction coil is determined, in particular automatically, before the start and the inserted sleeve part is therefore "known". This is described, for example, in US Pat. No. 5,399,411, US Pat. No. 5,499,421 and US Pat. No. 5,499,433, the contents of which are incorporated herein by reference.

[0046] Once the inserted sleeve portion is subsequently recognized, it is possible to identify or predefine heating parameters for the inserted sleeve portion or its heating process.

[0047] Such heating parameters may in particular be the shrink fitting / heating frequency and / or the shrink fitting / heating temperature and / or the time of the heating process and / or the maximum time and / or the energy (current integral) of the heating process.

[0048] It is therefore particularly advantageous to define the frequency for the (heating) current (i.e. the shrink-fit / heating frequency) close to, e.g. "slightly" above or below, in particular "slightly" above, the resonance frequency, since the efficiency / effectiveness of heating increases as the shrink-fit / heating frequency approaches the resonance frequency. Defining the shrink-fit / heating frequency equal to the resonance frequency should be avoided, as otherwise resonance effects may lead to overloading of the components of the induction coil unit.

[0049] Furthermore, it may be advantageous to determine the profile or the time profile and / or the frequency profile through measurements. A suitable measuring means (or a functionally equivalent circuit) or several suitable measuring means (or several circuits) may be provided in the induction coil unit.

[0050] When amperage is measured in this way, it is expedient to use a series-connected current (amperage) measuring means, such as an ammeter or multimeter, or even a measuring coil, and when voltage is measured, it is expedient to use a parallel-connected voltmeter.

[0051] Such a measurement of the profile can in this case be carried out in an input circuit of the circuit of the induction coil unit and / or in an intermediate circuit of the induction coil unit and / or in an output circuit of the induction coil.

[0052] Measurements can also be performed in parallel (in time) at several of the above mentioned points in the circuit.

[0053] unit In order to carry out the method in the induction coil unit, further circuitry is provided such that the induction circuit can be powered.

[0054] It may be advantageous for the circuit to comprise at least one power semiconductor component, in particular at least one insulated gate bipolar transistor (IGBT) and / or metal oxide semiconductor field effect transistor (MOSFET), which have good forward behavior, high reverse voltage and robustness and can be driven with almost no power.

[0055] Furthermore, in the induction coil unit, a control unit is also provided, by means of which the induction coil and the circuit can be controlled, the control unit being furthermore arranged, briefly, to be able to carry out the method (in terms of its basic characteristics, in particular as in all the previously mentioned embodiments and developments).

[0056] This also applies in particular to the control unit controlling the induction coil and the circuit. It also means that during a particularly uninterrupted induction heating process of the sleeve part inserted in the induction coil, the time or frequency profile of the coil current and / or the coil voltage and / or the input current and / or the input voltage as well as the (coil current) profile and / or the (coil voltage) profile and / or the (input current) profile and / or the (input voltage) profile, possibly including their derived variables, can be analysed and based on the analysed or evaluated profiles, in particular on the profile behaviour and / or the profile changes and / or the profile change behaviour, a decision can be made in particular to continue or terminate the uninterrupted heating process.

[0057] Advantageously, one or more measurement devices are also provided, such that one or more time profiles or one or more frequency profiles can be measured.

[0058] Preferably, the measuring device in this case is a current measuring device or a voltage measuring device.

[0059] Also preferably, the measuring device may be installed in the input circuit and / or in the intermediate circuit and / or in the output circuit of the circuit.

[0060] Advantageously, the method (and the induction coil unit) can also be used to recognize an already hot sleeve part of a tool holder inserted in the induction coil of the induction coil unit, the pre-heated state of the sleeve part being identified here by means of the determined parameters.

[0061] For example, if the parameters of the temperature profile already indicate a horizontal or rising profile at the start of the heating process for the inserted sleeve part, this indicates an already pre-heated sleeve part.

[0062] By this method, and also in the case of induction coil units, it is possible to carry out an almost automatic or automated operation, i.e. the inductive shrink-fitting of the tool onto the tool holder, in particular the heating of the tool holder, for each tool holder that has just been inserted into the induction coil unit, so that manual intervention for setting the operating parameters becomes superfluous in this case, on the one hand saving the time previously required for this and on the other hand making it possible to meet high standards with regard to operational safety and errors by means of the automatic / automated operation, thereby ensuring that the unit operates in accordance with the rules. An efficient protection against overheating of the heated / expanded tool holder can also be realized by this method, and in the case of induction coil units.

[0063] The description given so far of advantageous configurations of the invention includes a number of features which are reproduced in the individual dependent claims, possibly together, but which may, however, be considered advantageously either individually or in combination in suitable alternative combinations.

[0064] In particular, each of these features may be combined individually and in any suitable combination with the method according to the invention.

[0065] Although certain terms may be used in the specification and / or claims in the singular or in combination with a number in each instance, the scope of the present invention is not intended to be limited to the singular form or the respective numbers of such terms. Furthermore, the words "a" or "an" should be understood as indefinite articles and not as numbers.

[0066] The above-mentioned characteristics, features and advantages of the present invention and the manner in which they are achieved will become more apparent and more clearly understood upon reading the following description of exemplary embodiments of the invention, which are explained in more detail in conjunction with the drawings, in which like components / parts and functions are designated by like reference numerals.

[0067] The exemplary embodiments are used to illustrate the invention and are not intended to limit the invention to the combination of features set forth therein, including those relating to functional features, and for this purpose, any suitable feature of each exemplary embodiment may be explicitly considered separately, removed from the exemplary embodiment, incorporated into another exemplary embodiment, supplemented therewith, and further combined with any one of the claims. [Brief description of the drawings]

[0068] [Figure 1] 1 shows an induction coil unit according to one embodiment in a central longitudinal cross-sectional view. [Diagram 2] 1 shows a circuit diagram of a circuit supplying an induction coil that can be used in an induction coil unit. [Diagram 3] 4 shows the time profile of the coil current for a sleeve part inserted into the induction coil of an induction coil unit during shrink fitting. [Figure 4] FIG. 3 shows an idealized time profile of the RMS coil current. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Automatic heating control for shrink process using shrink fitting equipment FIG. 1 shows the basic structure of an induction coil unit, which (hereinafter) is also called a shrink fitting device because of its intended function here.

[0070] As FIG. 1 shows, the shrink fitting apparatus provides an induction coil 1 with individual turns 2, into whose center a tool holder 4 is inserted, by means of which a tool W, for example here a holding shaft H of a milling cutter, is shrink fitted into or released from a sleeve part HP.

[0071] The operating principles behind shrink fitting and release are described in more detail in US Pat. No. 5,399,633, the contents of which are incorporated herein by reference.

[0072] At its outer periphery, the induction coil 1 is provided with a first sheath 3 made of a non-electrically conductive magnetically conductive material.

[0073] Typically, the first sheath 3 consists of a non-conductive ferrite or metal powder or metal sintered material whose individual particles are insulatingly separated from one another, thereby being substantially magnetically conductive as a whole.

[0074] The first sheath 3 is also designed so that it is completely self-closing in the circumferential direction, i.e. so that it completely covers the circumference of the induction coil 1, thereby, in theory, leaving no "magnetic gaps" other than extraneous local penetrations, such as individual and / or small localized holes, etc.

[0075] As FIG. 1 further shows, in the shrink fitting apparatus, the shield made of a magnetically conductive, non-conductive material does not terminate with the first sheath 3 .

[0076] Instead, magnetic covers 3 a , 3 b made from said material are adjacent to at least one, and better both, end faces of the first sheath 3 and generally in contact with the first sheath 3 .

[0077] At the end face of the induction coil 1 facing away from the tool holder 4, the magnetic cover 3a is preferably designed as a completely or preferably partially replaceable magnetic pole piece, i.e. as a ring-shaped structure having a central hole forming a passage 7 for the tool W to be fastened or released.

[0078] At the end face of the induction coil 1 facing the tool holder 4, the magnetic cover 3b is preferably designed as an essentially flat annular disk, which ideally fully engages with the windings of the induction coil 1 and has a central passage for the sleeve part HP.

[0079] To further enhance the shielding, as also shown in FIG. 1, the induction coil 1 and its first sheath 3 are surrounded at their outer periphery, ideally over most or all of their mutually facing circumferential surfaces, by a second sheath 9, in particular so that the first sheath 3 and the second sheath 9 are in contact with each other.

[0080] This second sheath 9 is made of a non-magnetically conductive electrically conductive material, for example aluminium.

[0081] "Electrically conductive" is understood here to mean a material that allows for the formation of a reasonable degree of eddy currents, rather than a material that is merely locally, so to speak, conductive "grain by grain."

[0082] A special feature of the second sheath 9 is that it is preferably designed to have a sufficient thickness in the radial direction such that eddy currents are generated in it under the influence of the stray magnetic field of the induction coil 1 passing through it, and these eddy currents weaken the unwanted stray magnetic field.

[0083] The second sheath 9 is also surrounded at its periphery by a power semiconductor component 10, which will be explained in more detail later, and which is located directly above the outer periphery of the second sheath 9 within a number of recesses 11 (only one is shown) therein.

[0084] These power semiconductor components 10 have two major main surfaces and four minor side surfaces, the major main surface being preferably more than four times larger than each of the individual side surfaces.

[0085] The power semiconductor components 10 are arranged such that one of their large main surfaces is in thermally conductive contact with the second sheath 9, generally at its outer periphery, and the relevant large main surface of the power semiconductor component 10 is adhesively bonded to the circumferential surface of the second sheath 9 by a thermally conductive adhesive.

[0086] Each of the power semiconductors 10 has a different power supply terminal.

[0087] Furthermore, as also shown in FIG. 1, the capacitors 14a, 14b are arranged together around the induction coil 1 at its outer periphery.

[0088] Capacitor 14a is preferably a smoothing capacitor that is directly part of the power circuit, and capacitor 14b is preferably a resonant circuit capacitor that is also directly part of the power circuit.

[0089] In order to electrically connect the capacitors 14a, 14b, here a number of circuit boards 15a, 15b are provided, each of which engages with the outer periphery of the induction coil 1.

[0090] Each of these circuit boards 15a, 15b preferably forms an annular disk. Each of the circuit boards 15a, 15b is preferably made of FR4 or a similar material commonly used for circuit boards.

[0091] As can also be seen from FIG. 1, the axis of rotational symmetry of each of the two circuit boards 15a, 15b, here designed as annular disks of circuit boards, is here coaxial with the longitudinal axis L of the induction coil (and also of the tool holder 4 / tool ​​W).

[0092] The upper one of the two circuit boards, 15a, carries a smoothing capacitor 14a with its connection tabs either passing through the upper circuit board 15a or connected to the upper circuit board 15a using SMD technology, such that the smoothing capacitor 14a is suspended from the upper circuit board 15a.

[0093] The lower one of the two circuit boards, 15b, is designed accordingly, with the resonant circuit capacitor 14b protruding upwards therefrom.

[0094] In summary, the power semiconductor 10 forms a first imaginary cylinder surrounding the induction coil 1, the capacitors 14a, 14 form a second imaginary cylinder surrounding the first imaginary cylinder, the capacitors 14a, 14b which are less sensitive to stray magnetic fields form the imaginary outer cylinder, and the power semiconductor component 10 which relies on the installation space for as little stray magnetic fields as possible forms the imaginary inner cylinder.

[0095] 1 also shows, the induction coil 1 is not "fully wound" over its entire length in the direction of the longitudinal axis L. Instead, it consists here of two winding packages, which are generally cylindrical, each of which forms an end face of the induction coil 1. They are here, for example, spaced apart from one another by at least 1.5 times the length of each of the winding packages in the direction of the longitudinal axis L of the induction coil 1.

[0096] Such an induction coil 1 contributes to reducing the reactive power, since it has no windings in the "central region" which are not necessarily necessary from the point of view of achieving the most efficient possible heating of the sleeve part HP of the tool holder, but which, if present, would tend to generate additional reactive power and would not make a really significant contribution to the heating.

[0097] In order to power the induction coil 1 with as few losses as possible, a circuit is provided which is shown in more detail in FIG.

[0098] As FIG. 2 shows, the circuit therefore has a resonant circuit SKS (see FIG. 2).

[0099] In the resonant circuit SKS, most of the required energy oscillates back and forth (at high frequency) between the induction coil 1 and the capacitor units 14a, 14b. This means that each period, or periodically, it is necessary to feed back the energy extracted from the resonant circuit SKS from its heating power and its other power losses. Therefore, very high losses as before do not occur.

[0100] The power electronics supplying the induction coil 1 are supplied on the input side with the commonly available mains current NST, as shown in FIG. 2, which in Europe (three-phase current, 3f) is 400V / 50Hz (corresponding values ​​in other countries).

[0101] The current obtained from the power grid is converted to a direct current by a rectifier G21, as shown in FIG. 2, which is in turn smoothed by one or more smoothing capacitors 14a (not shown).

[0102] As FIG. 2 also further shows, this DC current is fed into the actual resonant circuit SKS.

[0103] The backbone of the resonant circuit SKS is formed by the power semiconductor component 10, the resonant circuit capacitor 14b and the induction coil 1, which serves for shrink fitting and release.

[0104] The resonant circuit SKS is controlled or regulated by the control electronics SEK, which is supplied with direct current by the rectifier G.

[0105] The power semiconductor component 10 is preferably implemented by an insulated gate bipolar transistor, IGBT for short.

[0106] The control electronics SEK switches the power semiconductor component 10 / IGBT at a frequency that specifies the operating frequency set by the resonant circuit SKS.

[0107] It is important that the resonant circuit SKS does not operate at exactly resonance.

[0108] As a result, voltage peaks would now rapidly destroy the power semiconductor components 10. Instead, the control electronics SEK are designed such that they operate the power electronics or their resonant circuits SKS in a predefinable working range only close to the resonant or natural frequency of the system.

[0109] Preferably, the resonant circuit is controlled or tuned (by the controller 20) such that 0.9≦cosφ≦0.99. Values ​​in the range 0.95≦cosφ≦0.98 are particularly advantageous. This also avoids voltage peaks, thus further supporting miniaturization.

[0110] In order to operate the shrink fitting device 1 in as automated a manner as possible with particular operational safety, the shrink fitting device is provided with an automatic heating controller / regulator which enables an automated shrink fitting operation.

[0111] This heating controller / regulator is implemented by a corresponding controller or regulator 20 of the shrink fitting machine and is essentially based on an analysis of the measured coil current M-SpA, coil voltage M-SpV and / or input current M-EA and / or input voltage M-EV or their time profiles.

[0112] In order to measure the coil current (M-SpA), the coil voltage (M-SpV) and the input current (M-EA) and input voltage (M-EV), the circuit, as also shown in FIG. 2, therefore provides current / voltage measuring means M-SpA (coil current), M-SpV (coil voltage) or M-EA (input current) or M-EV (input voltage), which are accordingly installed in the correspondingly shown positions in the circuit.

[0113] In this case, if the measured variables or their profile also depend on the temperature of the inserted sleeve part of the tool holder in the case of the induction coil used for shrink fitting, this can advantageously also be used for automated heating control, thereby increasing the safety of the shrink fitting apparatus whilst therefore avoiding "manual" sources of error.

[0114] (A) (Automatic) recognition of the tool holder / sleeve part currently inserted in the shrink fitting device or its induction coil Before starting heating of a sleeve part (HP, see FIG. 1) inserted in an induction coil (1, see FIGS. 1 and 2), the geometry or outer diameter of the sleeve part inserted in the induction coil is first automatically determined and thus the inserted sleeve part is "known".

[0115] This is described, for example, in US Pat. No. 5,399,623, US Pat. No. 5,499,633, and US Pat. No. 5,499,647, the contents of which are incorporated herein by reference.

[0116] Once the inserted sleeve part is recognised, (previously) defined heating parameters can be defined for the inserted sleeve part or its heating process, e.g. the (respective) shrink fitting / heating frequency, among others.

[0117] The heating process of the inserted sleeve part is then started at its respective shrink-fitting / heating frequency, and simultaneously with the start of the power supply to the induction coil, the measurement of the coil current, coil voltage, input current and input voltage also begins (see in this respect the circuit according to Figure 2).

[0118] (B) The (automated / automatically controlled) shrink fitting process (Figures 3 and 4) Figure 3 (and in idealized form Figure 4) shows how the heating process of the inserted sleeve portion can be controlled 20 based on the time profile 22 of the coil current M-SpA. Figure 4 corresponds to Figure 3 and is an idealized diagram of the coil current M-SpA (with the RMS amperage filtered and smoothed).

[0119] The control (20) based on the coil current profile 22 shown here can also be performed according to the coil voltage M-SpV and / or the input current M-EA and / or the input voltage M-EV or variables derived therefrom, such as phase position and phase shift (since these profiles qualitatively correspond to those of the coil current).

[0120] As shown in Figs. 3 and 4, the coil current M-SpA is continuously measured with a time profile (T (time)) during the heating process using the aforementioned current measuring means M-SaP (coil current).

[0121] Figures 3 and 4 each show a typical (curved) profile 22 of the (measured) coil current M-SpA during heating of the inserted sleeve part (starting from the cold sleeve part until it is tempered, i.e. phases 1 to 4).

[0122] In relation to control, the following can be derived from the coil current profile 22:

[0123] 3 and 4 show that the coil current M-SpA first decreases at the start (in this case the cold sleeve portion) and then over time and during the initial heating of the sleeve portion (phase 1). In other words, the slope of the coil current profile is negative or the tangent applied to the coil current profile has a descending profile.

[0124] After the initial drop, the coil current M-SpA then remains approximately constant in the subsequent time / heating profile (i.e., the slope of the coil current profile is zero or the tangent applied to the coil current profile has a horizontal profile) (phase 2), and the coil current M-SpA then increases or rises again (i.e., the slope of the coil current profile is positive and the tangent applied to the coil current profile has an ascending profile) in the subsequent time profile and during subsequent heating (phase 3) (until the sleeve portion is tempered, i.e., phase 4). This rise now occurs with an increasing slope / slope (phases 3 and 4).

[0125] The curvature behavior of the coil current profile 22 is also obtained according to a slope or tangent decline, rise and level profile.

[0126] The coil controller 20 takes advantage of this expected coil current profile 22 by configuring its control accordingly.

[0127] In this case, the measured coil current M-SpA is continuously transmitted to the controller 20, which continuously determines the slope of the coil current profile 22 or the tangent of the coil current profile 22 together with its curvature behavior.

[0128] When the coil current profile M-SpA subsequently transitions from its horizontal constant phase to an ascending profile (phase 2 to phase 3), i.e. when the tangent starts to rise again (from horizontal) or the slope (and curvature) of the coil current profile 22 becomes positive ("stop criterion" 23), the controller 20 (automatically) stops the heating process, where the heating state of the inserted sleeve portion has now reached a critical phase / temperature.

[0129] Alternatively, if it is desired that a higher heating temperature be allowed, a slope limit value can also be predefined as an "abort criterion" (slope / tangent of phase 4) (alternative abort / alternative abort criterion 24). When the coil current profile then reaches this predefined limit slope, the controller 20 (automatically) stops the heating process.

[0130] Thus, an almost automatic or automated shrink fitting is possible by means of a controller, whereby manual intervention for setting the operating parameters becomes superfluous, which on the one hand saves the time previously required for this, and on the other hand the automatic / automated operation also makes it possible to meet high standards regarding operational safety and errors, thereby ensuring that the unit operates in accordance with regulations. An efficient protection against overheating of the sleeve part is also realized.

[0131] Although the present invention has been illustrated and described in more detail by means of preferred exemplary embodiments, the invention is not limited to the disclosed examples, other variants can be derived therefrom without departing from the scope of protection of the invention. [Explanation of symbols]

[0132] 1 Induction coil 2 rolls 3 First Sheath 3a,3b Magnetic cover 4 Tool holder 9 Second Sheath 10 Power Semiconductor Components 11 Recess 14a, 14b Capacitor 15a, 15b Circuit board 20 Controller 21 Rectifier G 22 Coil current profile 24 Stopping Criteria H Retaining shaft HP sleeve part M-SpA coil current M-SpV Coil voltage M-EA input current M-EV input voltage SEK Control electronic components SKS resonant circuit W Tool

Claims

1. 1. A method of controlling an induction heating process for an induction coil unit, wherein a sleeve portion of a tool holder is inserted into an induction coil of the induction coil unit, comprising: - during an in particular uninterrupted induction heating process of the sleeve portion inserted in the induction coil, at least one time profile or frequency profile of the coil current and / or of the coil voltage and / or of the input current and / or of the input voltage is determined for the sleeve portion inserted in the induction coil, - A method in which the (coil current) profile and / or the (coil voltage) profile and / or the (input current) profile and / or the (input voltage) profile, possibly variable values ​​derived therefrom, are analysed and a decision as to whether an uninterrupted heating process is to be continued or terminated is taken based on the analysed or evaluated profiles, in particular on profile behaviour and / or profile changes and / or profile change behaviour.

2. The time profiles of the coil current, the input current, the input current and the input voltage are identified, all of the identified time profiles are analyzed, and a decision on whether the heating process is continued or terminated is made based on all of the analyzed profiles, and / or the derived variable is a phase position or a phase shift.

2. The method of controlling an induction heating process of claim 1.

3. A method of controlling an induction heating process as claimed in claim 1 or 2, wherein the time profile or the frequency profile is mapped using RMS current or voltage values.

4. in the analysis of the time profile, profile behaviors and / or profile changes and / or profile change behaviors are identified, and / or in the analysis of the frequency profile, local maxima, in particular resonant frequencies and / or (band)widths or variations are identified, A method for controlling an induction heating process according to any one of claims 1 to 3.

5. In the analysis of the time profile, in particular the RMS, current or voltage values ​​at different times of the induction heating process are analyzed, in particular compared, in particular using the tangent or gradient of the time profile, and / or in the analysis of the frequency profile, this analyzed frequency profile is compared with a reference profile, in particular using the local maxima and / or (band)width or variation. A method for controlling an induction heating process according to any one of claims 1 to 4.

6. In said analyzing said time profile, a plurality of tangents are applied to said time profile and said determination is made taking into account changes in slope of said tangents. A method for controlling an induction heating process according to any one of claims 1 to 5.

7. When making the determination, the geometric shape and / or other physical characteristics of the sleeve portion inserted into the induction coil of the induction coil unit are also taken into account. A method for controlling an induction heating process according to any one of the preceding claims.

8. the time profile or the frequency profile to be analyzed is smoothed, averaged, filtered and / or in particular normalized to a reference mains voltage, in particular a German or European reference mains voltage, before and / or during the analysis, A method for controlling an induction heating process according to any one of the preceding claims.

9. The time profile or the frequency profile is determined using current or voltage measurements, in particular RMS current or RMS voltage being measured. A method for controlling an induction heating process according to any one of the preceding claims.

10. the input current and / or the input voltage are measured in particular in an intermediate circuit downstream of a rectifier or in the input circuit upstream of a rectifier and / or at a connection, A method for controlling an induction heating process according to any one of the preceding claims.

11. is used to recognize an already hot sleeve part of a tool holder inserted in the induction coil of the induction coil unit, wherein a pre-heating state of said sleeve part is identified on the basis of said analyzed time profile or said evaluated temperature-time profile or said analyzed frequency profile or said evaluated frequency profile, in particular on the basis of the profile behavior and / or the profile change and / or the profile change behavior of said time profile or the local maxima and / or the (band)width or variation of said frequency profile. A method for controlling an induction heating process according to any one of the preceding claims.

12. An induction coil unit for carrying out the method according to at least one of claims 1 to 11, comprising an induction coil into which a sleeve part of a tool holder can be inserted, a circuit by means of which said induction coil can be supplied with power; a control unit by means of which said induction coil and said circuit can be controlled and which is adapted to carry out the method according to at least one of claims 1 to 11. An induction coil unit comprising:

13. one or more measuring devices by which one or more time profiles or one or more frequency profiles of the coil current and / or of the coil voltage and / or of the input current and / or of the input voltage can be measured; An induction coil unit according to at least claim 12, characterized in that

14. the measuring device is a current measuring device or a voltage measuring device, and / or the measuring device is installed in the input circuit of the circuit, and / or in the intermediate circuit, and / or in the coil circuit, An induction coil unit according to at least claim 13.

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