DE4201013A1 - Arrangement for detecting position of rotating tool - contains reliable sensor circuit rotating with machine element, inductive transfer to static evaluation circuit - Google Patents

Abstract

The arrangement contains at least one sensor (S1,S2) arrangement with position sensor producing a relative position signal and an inductive signal transfer device which passes the signal to a fixed evaluation circuit. The transfer device contains at least one coil (L1,L2) coupled to the sensor arrangement and one coupled to the evaluation circuit. A short circuit stage contains the coil coupled to the sensor arrangement and a switch operated by the sensor arrangement which opens and closes the short circuit stage when the tool reaches a defined relative position. ADVANTAGE - The arrangement contains a reliably operating electrical circuit rotating with the rotating machine element.

Description

The invention relates to a device for position detection of a rotating tool relative to the tool supporting co-rotating machine element and for over transfer of the location information to a stationary machine part, comprising at least one machine element side Sensor arrangement from at least one position sensor for Generation of an indication of the relative position of the tool Position signal and at least one inductive signal transmission device for transmitting the position signal a stationary evaluation circuit with at least one Induction coil pair from one with the sensor arrangement coupled machine element-side coil and one with the evaluation circuit coupled machine part side Kitchen sink.

From EP-04 19 716-A1 is a device of this type known. The position sensor assigned to a jaw requires electrical energy for its operation is supplied via a pair of induction coils. That from Sensor output analog signal is before transmission digitized and serial via the pair of induction coils transferred to the evaluation circuit. The necessary for this other electronic rotating with the tool Circuit is relatively complex, which is due to the requ the high speed stability at the required high functional reliability of particular disadvantage is.

A device is known from DE 29 27 525-C2, at which is a button attached to a machine head for Sensing the position of a workpiece a short circuit Circuit opens as soon as it is on the workpiece to the system is coming. The short circuit is in a probe built in instead of a tool in the machine head is to be clamped. To that when connecting the probe  Avoid creating an electrical connector the, the position signal is from a probe, from the coil removed from the machine head axis (with coil axis perpendicular to the machine head axis) on one of her in the direction the machine head axis opposite fixed Transfer coil. An opening or closing of the short final circuit causes a change in the mutual induction of the coils of the induction coil pair and thus a detectable change in the parameters (Frequency, amplitude, phase position, damping) of a stationary coil having resonant circuit. The total three mechanical switches of the Short circuit are depending on the deflection of the Button opened immediately by this, so that a Power supply, especially battery power supply, the Sensor head-side sensor arrangement is not required. The probe is rigid with the measurement during the measurement rail head connected, in a predetermined Angular position in which the coils of the induction coil pair face each other exactly.

The invention has for its object a device of the type mentioned at the beginning for the position detection of a rotie tool relative to a tool carrying the tool co-rotating machine element and for the transmission of the Position information on a stationary machine part ben, in which the co-rotating electrical circuit has a simplified structure with reliable function.

This problem is solved by at least one short Final circuit, comprising the machine element side Coil and at least one from the respective sensor order operated switch for opening or closing the short circuit when reaching a pre relative position of the tool.  

The short circuit has an extremely simple structure because it only requires the coil and the switch; a Energy supply is not necessary. The two possible states (open or closed) of the short final circuit affect the stationary coil very different, so that the quasi binary location ascertained by the evaluation circuit itself Rotation of the tool is extremely reliable.

The two coils of the pair of coils can be eccentrically Axis of rotation can be arranged, with each full Rotation of the tool the two coils turn once to encounter. The in the two states of the short-circuit Circuit strongly different induction effect of the rotating coil on the fixed coil is for one Differentiation of both states by the evaluation circuit generally sufficient, at least with low rota tion speed. However, is particularly preferred seen that at least one of the two coils, preferred have both coils, the pair of coils the axis of rotation surround concentrically. This measure ensures a continuous Nuclear signal transmission regardless of movement of the tool, i.e. when rotating, even at high speeds and even at a standstill, regardless of the rotational position of the tool.

Simple, possibly also subsequent installation of the device according to the invention in a machine tool thereby ensures that the machine element side Coil a machine tool spindle carrying the tool surrounded.

To avoid signal transmission interference from outside to eliminate falling electromagnetic fields from the outset close, it is suggested that the outer of the two Coils is provided with a magnetic shield.  

In order to be able to determine inclined positions of the tool, the use of two diametrically opposed to each other becomes a rotati on-axis opposite position sensors proposed.

It is particularly preferably provided that the at least one position sensor from a short-circuit Circuit arranged mechanical switch formed is in a given position of the tool preferably actuated directly from the tool. The mechanical switches, preferably microswitches, no energy supply. He is more reliable Function available at low cost. With the preferred immediate actuation of the mechanical scarf Through the tool you get a particularly reliable position measurement.

Simple construction with reliable position measurement further promoted by the fact that the machine element several mechanical switches are attached, which in the Short circuit are connected in series. Only in the correct position and orientation of the tool actuate all mechanical switches through the tool tigt (closed), so that only a short circuit is brought into its closed state.

So that the mechanical switch when the tool is removed reliably assume their respective open positions, it is suggested that the mechanical switches in their the respective opening position is spring-loaded.

In some applications, especially when Dirt and moisture can occur, it is from Advantage if the position sensor without a mechanical switch gets along. For this it is proposed that the at least a position sensor comprises a magnetic field sensor, wherein for Avoiding a battery further suggests that another for the energy supply of the magnetic field sensor  Induction coil pair is provided from one with one primary power supply circuit connected machine part-side coil and one with a secondary Power supply circuit connected machine element sided coil. The circuitry only increases insignificant. For example, if the primary (fixed) Coil operated with AC voltage, so the secondary (= co-rotating) power supply circuit in this Trap be from a simple rectifier circuit stand.

In a preferred embodiment of the invention provided that the position sensor is a magnet, in particular permanent magnets, and that the magnetic field Sensor a when the predetermined relative position of the Tool-induced magnetic field changes detected. The magnet integrated in the position sensor, the one is the best permanent magnet for the sake of simplicity Magnetic field ready, which by the metallic tool is changed when the predetermined relative position is reached - This change is caused by the magnetic field sensor detected. This saves you from having to attach Magnets on the tool itself; any structural Changes to the tool therefore do not have to be made will.

As more affordable and less than that Reliable working magnetic field sensor a Hall effect sensor has turned out.

The sensor signal from magnetic field sensors, in particular Hall effect sensors is generally temperature dependent. This affects the accuracy of measurement To eliminate dependency, it is suggested that the Position sensor a circuit to compensate for a temperature-dependent change in the sensor signal points.  

For a precise assessment of the situation, especially under Berück view of the tool orientation, is, as already mentions the use of two spaced apart Position sensors are an advantage. Especially when using Magnetic field sensors is a further development of the invention advantageous, which is characterized in that the Sensor arrangement comprises two position sensors, the sensorsi signals are fed to a common AND gate, which is the switch for opening and closing the Short circuit operated. As a result, is only a single short circuit with a single Switch required.

In another embodiment of the invention, it is provided hen that at least one magnet, preferably permanentma gnet, with the tool is motion-coupled, and that the magnetic field sensor one when the tool is moved occurring magnetic field changes are detected. This measure This allows the tool to be precisely positioned especially when at least two, preferably four, alternating polarity towards the magnets Axis of rotation are arranged in succession. It leaves then not only a predetermined end position of the work detect stuff, but also one or more twos location.

So that the tool itself can remain unchanged proposed that the at least one magnet on a Tool holding device, preferably a pliers holder, is attached.

A simple, if necessary subsequent attachment of the Magnets is made possible by the fact that the at least one Magnet as a magnetic ring concentric to the axis of rotation is trained.  

In a particularly preferred embodiment of the invention It is provided that at least two sensor arrangements are provided from each a position sensor, which each have a signal transmission device with short circuit is assigned, and that an evaluation circuit to the two signal transmission devices connected from the respective sensor signals the current position of the tool or the tool holder establishment determined. The two sensor signals can Accept two values each (open or closed Short circuit). For the combination of both sen Sensor signals are therefore four different signal patterns possible, so that a total of four different tools were derived from the signal pattern determined in each case are. The two signals are evaluated therefore particularly simple, in particular it is not required The passage of magnets past a sensor add up.

The respective number and arrangement of both position sensors as well as the tool-fixed magnet depends on the stroke of the Tool clamps. In a proven arrangement provided that at least two, preferably four, Magnets successively in the direction of the axis of rotation are arranged, with particular preference being provided that the magnets have alternating polarity.

You get a spatial resolution corresponding to half Center distance of immediately successive magnets, if provided according to a development of the invention is that the two position sensors of the two sensor arrangement a mutual center distance from each other have, which is essentially an odd number Multiples of half the center distance directly on top of each other corresponds to other magnets.  

The induction coil pairs can according to a first Embodiment of the invention in the direction of rotation successive axis or alternatively in one plane perpendicular to the axis of rotation lie risch.

The invention is based on several execution examples explained with reference to the drawing. It shows

Figure 1 is a simplified sectional view of a machine tool in the spindle area, which is provided with a first embodiment of the inventive device for position detection.

FIG. 2 shows a basic circuit diagram of the device for position detection according to FIG. 1;

3 is a sectional view corresponding to Figure 1 with a second embodiment of the device for position detection..;

FIG. 4 shows a basic circuit diagram of the device for position detection according to FIG. 3;

Fig. 5 is a sectional view corresponding to Figures 1 and 3 with another embodiment of the device for position detection.

Fig. 6 is a schematic circuit diagram of the device for detecting the position of FIG. 5 and

Fig. 7 is an illustration of the sensor signals of the means for detecting the position of Fig. 5 and 6.

The inventive device for detecting the position of rotating tool is used in the following example of a machine tool with integrated work tool clamp explained; however, there are other types the machine tool possible, in which the device according to the invention a reliable fix development of the relative position of the tool, in particular the Adherence to a target position, ensures and at the same time disturbances affecting the situation, e.g. B. tool breakage quickly displays. Signal acquisition in the rotating system requires only little effort with a simple structure and reliable function. The transfer of the location signals to the fixed system are non-contact. The signal acquisition and the signal evaluation take place on spatially separated places, namely on the one hand in the rotie system and on the other hand in the fixed system. In the embodiments described below there is a continuous signal transmission from the rotie render on the fixed system, because to the axis of rotation concentric toroidal coils can be used. In the first in the following embodiment to be described is none Power supply to the rotating system required.

A machine tool spindle 10 rotating about an axis of rotation 12 is indicated in FIG. 1. This is rotatably mounted in a stationary machine part 18 via two pivot bearing arrangements 14 , 16 . At the left free spindle end, the spindle 10 is provided with an inner cone 20 , into which a corresponding outer cone 22 of a tool 24 (here, for example, a milling head) can be inserted. To fix the tool 24 in the spindle 10 , the spindle is provided with an integrated clamping device 26 , consisting of a collet 28 displaceable in the spindle 10 in the direction of the rotational axis 12 at the left end in FIG. 1 of a pull rod 29 , one surrounding the pull rod Belleville spring assembly 30 for pretensioning the collet 28 in its right-hand end position in FIG. 1 (tool clamping position) and a fluid-actuated actuating device 32 engaging the right train end, for the collet 28 to counteract the spring force in the one on the left in FIG. 1 End position (tool gripping position) to move. In this end position, an undercut head 34 can be pushed at the cone tip of the tool 24 between the collet arms 36 of the collet 28 . If the actuating device 32 is then deactivated, the collet 28 pulls the tool 34 under the force of the plate spring assembly 30 in FIG. 1 to the right into the other end position, wedge-like contact surfaces on the tong arms 36 and / or on the inner circumference surrounding the arms 36 40 of the spindle 10, move the arms 36 radially inward to grip the head 34 behind.

The actuating device 32 can be actuated electromagnetically. In the illustrated embodiment, hydraulic actuation is provided. An actuating piston 39 can be seen at the right end of the pull rod 29 , the right end face of which in FIG. 1 delimits a fluid space 38 within a cylinder-like housing 42 . A fluid line 43 opening into the space 38 is shown broken off.

The reliable detection of the position of the tool 24 in its clamping position is used in the following to be described, generally designated 44 device. It comprises an area 46 which also rotates with the tool and a stationary area 48 . The area 46 is in turn formed by a short-circuit circuit 50 from a coil designated with L1 and two designated with S1 and S2, switches connected in series. These are biased into their respective open positions by springs 52, which are only indicated in FIG. 2. Both switches S1, S2 are shown in FIG. 1 with respect to the axis 12 diametrically opposite one another on a tool-side end face 53 in such a way that they are actuated in the correct clamping position of the tool 24 by one end face of a tool flange 54 , ie both are each closed GE . The short circuit 50 is then closed. If, however, the tool 24 has not been pulled far enough to the right in FIG. 1 by the collet 28 or / and is not oriented exactly parallel to the axis, at least one of the two switches S1, S2 remains open and thus also the short-circuit circuit 50 .

Although the short-circuit circuit 50 does not have its own voltage source, its switching state (open or closed) can be easily determined inductively, with the aid of a fixed coil L2 as part of the fixed area 48 . The coil L2 is shown in FIG. 2 inductive element of a resonant circuit 56, the capacity Capa is denoted by C. The resonant circuit is kept in vibration by means of an adjustable oscillator 58 . Since the two coils L1 and L2 are directly opposite one another in such a way that, according to FIG. 1, both coils are arranged concentrically to one another and the stationary coil L2 surrounds the rotating coil L1, the coil L1 influences the inductance of the resonant circuit 56 , in different ways, depending on whether the short circuit 50 is closed or open. In the former case, induction circuit current is induced in the short-circuit circuit with corresponding counter-induction in the coil L2. When the short-circuit circuit is open, on the other hand, the induction effect and thus also the mutual induction is significantly reduced. Closing the short-circuit circuit 50 accordingly results in a change in at least one of the parameters of the resonant circuit 56 : frequency, amplitude, phase position and damping of the resonant circuit 56 . This parameter change can be detected by measurement, as is given, for example, in DE 29 27 525-C2 with respect to the change in the oscillation frequency.

Since the short-circuited short-circuit 50 draws energy from the resonant circuit 56 due to the induction effect, the short-circuiting of the circuit 50 can also be detected by monitoring the energy supply required for the resonant circuit 56 to maintain an oscillation with a predetermined amplitude and in the event of a sudden increase or Fall of this energy to a change in the switching state of the short-circuit circuit 50 closes. A corresponding evaluation unit 60 is indicated in FIG. 2, which tracks the current consumption of the oscillator 58 and, when there is a corresponding change, outputs a signal to a downstream amplifier 62 . This, in turn, is connected to the central processing unit of the machine tool, which evaluates the signals and is referred to as CPU. The CPU issues an alarm or switches off the machine tool if the short-circuit circuit 50 maintains its open state after changing a tool or during operation, or if the short-circuit circuit 50 changes into its open state during operation.

Monitoring the current consumption of the oscillator at inductive proximity switches are known per se (see Brochures "Inductive proximity switches General 2 / 0.1" and "Inductive Analog Encoder General 2 / 10.1" from Pepperl and Fuchs, P.O.Box 31 04 40, D-6800 Mannheim 31).

In order to keep electromagnetic interference signals away from the coils L2 and L1, a magnetic shield 64 indicated in FIG. 1 (preferably in the form of a magnetic return ring surrounding the outer coil L2) can be provided. The routing of the electrical lines can be seen in FIG. 2. Connection lines 66 between the switches S1, S2 and the coil L1 are indicated in FIG. 1 with a dash-dot line, as are connection lines 68 between the coil L2 and the other electronic parts (C; 58 , 60 , 62 ) which are on an outside of the hollow cylinder-shaped machine part 18 surrounding the spindle 10 are attached.

In FIGS. 3 and 4, a further embodiment of the device 44 is shown for position detection. Components that correspond in function to those in FIGS . 1 and 2 have the same reference number, each increased by the number 100. Reference is hereby expressly made to the associated description. The following primarily deals with the differences between the two embodiments.

In the second exemplary embodiment, the mechanical switches S1 and S2 are replaced by electromagnetically operating position sensors SE1 and SE2, which are positioned at the same point on the spindle 110 . Each position sensor SE1, SE2 consists of a magnetic field sensor B1 or B2 (Hall effect sensor), to which a permanent magnet M1 or M2 is attached. In addition, a circuit labeled T1 or T2 for compensating temperature influences on the analog sensor signals is provided. The signals from the respective magnetic field sensor B1 or B2 and the temperature compensation circuit T1 or T2 are each fed to a differential amplifier 70 and then to a threshold value detector SCHW1 or SCHW2. The outputs of SCHW1 and SCHW2 are connected to an AND gate 72 which, when the input signals are both high, for example, closes a switch S1 as part of the short-circuit circuit 150 , which otherwise keeps the circuit open.

The inductive signal transmission from the rotating system to the stationary system takes place in the same way via the two coils L1 and L2 together with the downstream resonant circuit 156 and evaluation circuit with oscillator 158 , evaluation circuit (threshold value detector) 160 and amplifier 162 as in the embodiment according to FIGS. 1 and 2 .

The magnetic field sensors B1 and B2, however, in contrast to the mechanical switches S1 and S2, require an energy supply which, for. B. can be realized by a battery. In the preferred exemplary embodiment shown, a again inductively operating power supply circuit 74 is provided instead of the battery. The fixed region 76 of this circuit consists of an alternating current generator G, which supplies a stationary coil labeled L4 with alternating current via a amplifier 78 . The coil L4 surrounds a rotating coil L3 corresponding to the coil L2, with both pairs of coils L1 / L2 and L3 / L4 according to FIG. 3 being arranged successively in the direction of the axis of rotation 112 . A corresponding induction alternating current is induced in the coil L3 and is converted into a DC voltage denoted by U at the pole terminals 82 , 83 via a rectifier 80 of the rotating region 77 of the circuit 74 indicated in FIG. 4. This DC voltage is supplied to the magnetic field sensors B1 and B2 in a manner not shown.

In this way, one contains a device 144 that manages without mechanical and dirt and moisture-sensitive parts for detecting the position of the rotating tool 124 . The signal acquisition and signal evaluation takes place spatially separated, namely on the one hand in the rotating system and on the other hand in the fixed system. The coils L1 and L4 are designed as coils concentric to the axis 112 , so that signal transmission is possible independently of the movement of the tool and, when stationary, regardless of the respective rotational position. The reception and evaluation logic consists of conventional proximity switch modules. The position detection of the tool 124 only presupposes that it consists of a metallic tool, since the magnetic field is generated by the permanent magnets M1 and M2. The sensitivity of the magnetic field sensors B1 and B2 is so great that the correct position of the tool 124 can be detected with great accuracy. Depending on the design, position deviations in the range of 0.04 mm can be detected. The arrangement according to the invention works reliably and extremely quickly, so that interference, for. B. broken tool, can be detected quickly. Because of the non-contact transmission, the problems that occur with conventional signal transmission from the rotating component to the fixed component via sliding contacts or the like are eliminated.

In FIGS. 5-7, a further 244 described embodiment of the device according to the invention is shown for position detection. The structure of the spindle area of the machine tool shown corresponds to the structure already explained with reference to FIG. 1, so that reference is made to the associated description. The inventive device for position detection is also explained in the following only insofar as it differs from the two embodiments described above, so that for the rest, reference is expressly made to the corresponding description. Components which correspond in function to those of the exemplary embodiments described above are provided with the same reference numerals, but increased by the number 200 in comparison to the exemplary embodiment according to FIGS . 1 and 2 or by the number 100 in comparison to the exemplary embodiment according to FIG. 3 and 4th

The position of the tool therefore designated 224 is now not detected by direct contact of the tool with the corresponding sensors, but by the fact that the axial position of the collet 228 is determined. Due to the special design of the position detection, it is possible to determine not only the correct assumption of a single position (end position), but also other positions that are essential for the clamping function. In the exemplary embodiment shown, three positions are detected, namely "collet released" (left end position shown in FIG. 5 due to actuation of the actuating device 232 ); "Clamping position with tool" (actuating device 232 deactivated); "Clamping position without tools" (right end position of the collet 228 ). In order to be able to differentiate these positions from one another, a plurality of permanent magnets of alternating polarity are attached to the collet, in the exemplary embodiment shown a total of four permanent magnets 84 , 86 , 88 and 90 . These permanent magnets can be designed as magnetic rings which are pushed onto a reduced-diameter section 91 of the pull rod 229 and fixed there. Opposite these permanent magnets radially outward, two magnetic field sensors B1 and B2 (in particular Hall effect sensors) are mounted in the spindle 210 receiving the collet 228 , namely at a mutual center distance a, which immediately follows the magnets an odd multiple of half the center distance b corresponds. In the illustration according to FIG. 6, the center distance A is about 5 times the half of the center distance b. Due to this different division, the position resolution can be reduced to approximately half the center distance b; with the same division, the resolution would correspond approximately to the center distance b.

This is also apparent from Figure 7, the profile of the two sensor signals of the magnetic sensors B1 (upper half) and B2 (lower half) for passage of the permanent magnets. 84 - represents 90 during an axial displacement of the clamping tool (direction X). Here, however, it is assumed that the alternating row of permanent magnets continues, as represented by the permanent magnets 92 and 94 shown in broken lines in FIG. 6 is Darge. The relative position according to FIG. 6 is indicated by an arrow pointing vertically downward in FIG. 7. As the permanent magnets with polarity S or N pass, the signal level also changes accordingly. The signal level assigned to the polarity S is e.g. B. indicated as a high level and the polarity N assigned level as a low level. Four areas A, B, C and D can be distinguished from one another. In area A, sensor B1 detects polarity S as well as sensor B2. As soon as the row of permanent magnets is moved so far that the dividing line between magnets 88 and 90 has passed sensor B1 so far that sensor B1 now mainly detects the magnetic field of magnet 90 with polarity N, its signal falls to the low level ab, whereas the sensor B2 is still in the influence of the magnet 84 with polarity S (area B in Fig. 7). As soon as the magnet 86 with polarity N is detected by the detector 82 , a low level signal is obtained from both sensors B1, B2 (area C). The area D follows, in which the sensor B1 already detects the next magnet 92 with polarity S. Then areas A, B etc. follow cyclically. In this way, four location areas can be easily distinguished.

The additionally drawn permanent magnets 92, 94 can also be omitted if the magnetic field sensor B1 also emits a defined signal assigned to the polarity S or N if it is not opposed to any magnet. In Fig. 7, the dashed line 96 indicates the waveform that results when sensor B1 emits a high level signal in the absence of a magnet.

The position range D according to FIG. 7 can, for example, be assigned to the already mentioned left end position "collet released" (for tool change) and the "tool clamping position". The area A can then be assigned to the right end position of the collet "clamping position without tools".

The transmission of these two binary signals from the sensors B1 and B2 for determining the respective area A, B, C and D takes place in the manner already described above with the aid of a short-circuit circuit 250 'and 250 ''. The switch S1 'in the circuit 250 ' is actuated by the sensor B1 and the switch S1 '' of the circuit 250 '' by the sensor B2. Each short-circuit circuit 250 ', 250 ''is in turn a fixed resonant circuit 256 ' or 256 '' assigned to the inductive detection of the switching state of the respective short-circuit. The signal detection can according to Fig. 2 and 4, again with the help of an oscillator 258 'and 258' 'done with a downstream evaluation circuit (threshold detector 260' and 260 '') of the respectively required for maintaining a predetermined vibrational energy detected. Via a downstream amplifier 262 'or 262 '', the two resulting signals are transmitted to the CPU, which then derives the position information from FIG. 7 in accordance with the respective signal pattern and, if appropriate, triggers an alarm or switches off the machine tool.

The rotating sensors B1, B2 are supplied with energy in the same way as in FIG. 4 by inductive transmission from the stationary energy-supplying area 176 to the rotating area 177 of the energy supply circuit 174 .

The rotating coils L1, L2, L3 of the two short-circuit circles 250 ', 250 ''and the circuit 174 have the same diameter and are concentric to the axis of rotation 212 in the axial direction one behind the other. The associated stationary coils L6, L5 and L4 are not formed in the illustrated embodiment, for example, as concentric to the coils L1, L2, L3, these outside surrounding coils, but as relatively small coils at the radially inner end of three cylindrical components 95 a, 95 b and 95 c, whose axes 97 are parallel to one another and perpendicular to axis 212 . The components 95 a and 95 b house the circuit parts 256 ', 258 ', 260 ', 262 ' and 256 '', 258 '', 260 '' and 262 '' and can be referred to as binary signal transmitters. The component 95 c serving for inductive energy supply in turn houses the fixed area 176 of the circuit 174 in addition to the coil L4. Due to the sensitivity of the binary signal transmitters consisting of conventional proximity switch components, it is sufficient if the coils L5 and L6 are concentrated in a relatively small area. Since the coils L1 and L2 continue to be formed as concentric ring coils to the axis 212, a position detection results regardless of the respective rotational position of the spindle. Under certain circumstances it is sufficient if the coils L1 and L2 or L3 are limited to the small circumferential area of the spindle in accordance with the coils L5, L6 and L4, but measurement at standstill is only possible if the coils L1, L2 and L3 or L6, L5 and L4 face each other.

An alternative position of the coils including components 95 a ', 95 b' and 95 c 'is indicated in Fig. 6. Here, these components are only offset parallel to the axis 212 . Another, more strongly different from this under the positioning of the coils and the components 95 a '', 95 b '', 95 c '' is indicated in Fig. 5 on the right. Here, the rotating coils L1, L2 and L3 are arranged concentrically to one another in a common plane perpendicular to the axis of rotation 212 and are scanned by the components 95 a '', 95 b '' and 95 c '' arranged parallel to the axis 212 .

The three separate components 95 a, 95 b, 95 c can also be integrated in a common component 98 , as indicated at the top right in FIG. 5. This component 98 then replaces the components 95 a '', 95 b '' and 95 c '' according to FIG. 5, right. With a corresponding design of the spindle housing, the component 98 can also replace the components 95 , 96 and 97 according to FIG. 5, top center.

Claims (23)

1. Device ( 40 , 44 ; 144 ; 244 ) for detecting the position of a rotating tool relative to a co-rotating machine element carrying the tool and for transmitting the position information to a stationary machine part ( 18 ), comprising at least one machine element-side sensor arrangement from at least one position sensor for generating a the relative position of the tool (S1, S2; SE1, SE2; B1, B2) indicating position signal and at least one inductive signal transmission device for transmitting the position signal to a stationary evaluation circuit with at least one induction coil pair (L1, L2; L1, L6; L2, L5) comprising a machine element-side coil (L1; L1; L2) coupled to the sensor arrangement and a machine part-side coil (L2; L6; L5) coupled to the evaluation circuit, characterized by at least one short-circuit circuit ( 50 ; 150 ; 250 ′; 250 ''), comprising the machine element-side coil (L1; L1; L2) and at least one n switches (S1, S2; S1; S1 ', S1'') for opening or closing the short circuit when reaching a predetermined relative position of the tool. 2. Device according to claim 1, characterized in that at least one of the two coils, preferably both coils of the pair of coils (L1, L2; L1, L6; L2, L5) surround the axis of rotation ( 12 ; 112 ; 212 ) concentrically. 3. Device according to claim 2, characterized in that the machine element-side coil (L1; L1; L2) surrounds the tool-carrying machine tool spindle ( 10 ; 110 ; 210 ). 4. Device according to claim 2 or 3, characterized in that the outer of the two coils (L1, L2) is provided with a magnetic shield ( 64 ). 5. Device according to one of the preceding claims, characterized by two diametrically opposed to the axis of rotation ( 12 ; 112 ) opposite position sensors (S1; S2; SE1, SE2). 6. Device according to one of the preceding claims, characterized in that the at least one position sensor is formed by a mechanical switch ( 51 , 52 ) arranged in the short-circuit circuit ( 50 ), which is in a predetermined position of the tool, preferably directly from the tool ( 24 ; 124 ), can be actuated. 7. Device according to claim 6, characterized in that a plurality of mechanical switches ( 51 , 52 ) are attached to the machine element , which are connected in series in the short-circuit circuit ( 50 ). 8. Device according to claim 6 or 7, characterized characterized in that the mechanical switches (S1, S2) in their respective open positions are spring-loaded. 9. Device according to one of the preceding claims, characterized in that the at least one position sensor comprises a magnetic field sensor (B1, B2). 10. The device according to claim 9, characterized in that for the energy supply of the magnetic field sensor, a further induction coil pair (L3, L4) is provided from a machine part-side coil (L4) connected to a primary energy supply circuit ( 176 ) and one with a secondary energy supply Circuit ( 177 ) connected to the machine element-side coil (L3). 11. The device according to claim 9 or 10, characterized in that the position sensor comprises a magnet, in particular permanent magnet (M1, M2), and that the magnetic field sensor (B1, B2) one when reaching the predetermined relative position of the tool ( 124 ) caused magnetic field changes detected. 12. The device according to claim 11, characterized in that that the magnetic field sensor (B1, B2) is a Hall effect sensor is. 13. Device according to one of claims 9-12, characterized characterized in that the position sensor is a circuit (T1, T2) to compensate for a temperature-dependent change of the sensor signal. 14. Device according to one of claims 9-13, characterized in that the sensor arrangement comprises two position sensors (SE1, SE2), the sensor signals of which are each fed to a threshold value detector and then to a common AND element ( 72 ) which switches (S1) actuated to open or close the short circuit. 15. The device according to claim 9, characterized in that at least one magnet, preferably permanent magnet ( 84 , 86 , 88 , 90 ), is motionally coupled to the tool, and that the magnetic field sensor (B1, B2) one upon displacement of the tool ( 224 ) occurring magnetic field changes are detected. 16. The device according to claim 15, characterized in that the at least one magnet on a tool holder device, preferably a collet ( 228 ) is attached. 17. The device according to claim 15 or 16, characterized in that the at least one magnet ( 84 , 86 , 88 , 90 ) is designed as a magnetic ring concentric to the axis of rotation ( 212 ). 18. Device according to one of claims 15-17, characterized in that at least two sensor arrangements each of a position sensor (B1 or B2) are provided, each of which a signal transmission device with short-circuit circuit ( 250 'or 250 '') is assigned , and that an evaluation circuit is connected to the signal transmission devices, which determines the current position of the tool or the tool holding device from the respective sensor signals. 19. Device according to one of claims 15-18, characterized in that at least two, preferably four, magnets ( 84 , 86 , 88 , 90 ) are arranged in succession in the direction of the axis of rotation ( 212 ). 20. Device according to claim 19, characterized in that the magnets ( 84 , 86 , 88 , 90 ) have alternating polarity. 21. Device according to one of claims 18 to 20, characterized in that the two position sensors (B1, B2) a mutual of the two sensor arrangements Center distance (a) from each other, which in essentially an odd multiple of half Center distance (b / 2) immediately consecutive Corresponds to magnets. 22. Device according to one of claims 2-21, characterized in that in the case of a plurality of pairs of induction coils (L1, L2; L1, L6; L2, L5) they follow one another in the direction of the axis of rotation ( 12 ; 112 ; 212 ). 23. Device according to one of claims 2-21, characterized in that in the case of a plurality of pairs of induction coils, these are mutually concentric on a plane perpendicular to the axis of rotation ( 212 ).