Abstract:
Disclosed is a tool system including a drive for driving a tool holder including an electromagnetic generator for generating electrical energy from inertial energy of the tool holder. The tool holder may be driven in rotation, wherein the electromagnetic generator comprises a rotor part, which is rotatably mounted on the tool holder, and a stator part on the tool holder cooperating with each other for generating a voltage by electromagnetic induction. Alternatively, an axially movable inertial mass can be used for utilization of an oscillating linear movement.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of international patent application PCT/EP2014/057874, filed on Apr. 17, 2014 designating the U.S., which international patent application has been published in German language and claims priority from German patent application 10 2013 105 831.0, filed on Jun. 6, 2013. The entire contents of these applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a tool clamping system having a mechanically drivable tool holder for clamping a tool. 
         [0003]    Tool clamping systems of this type have been known for decades and are used in many ways when machining workpieces. 
         [0004]    For some years, it has been required in some machining centers with rotating tools, in addition to the conventional cutting tools, to also provide for measurement-based applications or monitoring operations of the tool. These are generally applications in which a measurement system, usually based on electromechanical principles, is mounted on a spindle interface. On the one hand the connection and guidance is to be ensured by the machine kinematics, and on the other hand the sensing of the measured values and transfer thereof to the controller are to be made possible. Here, the energy supply of the measurement system must be provided usually by batteries or accumulators. The data transfer to a fixed evaluation station takes place as standard via infrared transmitters and receivers, and increasingly also via radio, such as WIFI or Bluetooth. 
         [0005]    However, the supply by means of battery or accumulator is usually a limiting variable, since the assurance of the energy supply thus leads to additional maintenance and supervision effort. The charging station is normally located outside the machine tool, or the application in question must be removed from the machine tool in order to change the battery. In addition, the energy supply in the case of sensor systems or possibly also actively operating, actuator systems generally constitutes a limitation. As a result, and due to the extremely harsh environment in the working area of machine tools, the equipping of tools known per se with additional intelligence is not successful in principle. 
         [0006]    On this basis, there is a need for tool monitoring systems that can operate with machine tools without external energy supply. 
       SUMMARY OF THE INVENTION 
       [0007]    It is a first object of the invention to disclose a tool clamping system comprising a mechanically drivable tool holder for clamping a tool, which system allows an energy supply for generating electrical energy without an external voltage supply in the form of a battery or an accumulator. 
         [0008]    It is a second object of the invention to disclose a tool clamping system which allows for generating electrical energy for driving a sensor configured for monitoring an operating parameter of the tool clamping system. 
         [0009]    It is a third object of the invention to disclose a tool clamping system which allows for generating electrical energy to facilitate a wireless communication of a sensor signal from the tool or the tool holder to an external monitoring unit. 
         [0010]    These and other objects are achieved according to one aspect of the invention by tool clamping system for clamping a tool, comprising: 
         [0011]    a tool holder for holding a tool; 
         [0012]    a rotary drive for driving said tool holder rotatingly about a longitudinal axis thereof; 
         [0013]    an electromagnetic generator comprising a stator part being mounted on said tool holder and a rotor part being rotatably mounted on said stator part; 
         [0014]    wherein said stator part and said rotor part cooperate as an electromagnetic generator configured for generating electrical energy from inertial energy of said rotor part relative to said stator part. 
         [0015]    Since the tool clamping system is always moved with a certain inertia during operation, this inertial energy is utilized in accordance with the invention in order to generate electrical energy. This electrical energy can be used in the region of the tool or the tool clamping in order to supply a feedback via the tool or the tool clamping system during operation, such that the machining process can be better controlled and/or monitored. 
         [0016]    The tool holder is driven in rotation and the device is configured for the generation of electrical energy from the inertial energy of the rotating tool clamping system. 
         [0017]    Rotating tools do not, in principle, always have to be brought to operating rotational speed. Since manufacturing installations are designed to minimize nonproductive time, a rotational speed ramp is generally implemented at the limit of the electric spindle capability. This rotational speed acceleration can be used in order to recover electrical energy from the inertial energy of the rotating tool clamping system. 
         [0018]    In accordance with a further embodiment of the invention the tool holder can be driven in an oscillating manner and the device is configured for the generation of electrical energy from the inertial energy of the oscillating tool clamping system. 
         [0019]    Here, the oscillation may be in particular a longitudinal oscillation, i.e. a linear movement back and forth in the axial direction. However, a rotary oscillation is also conceivable in principle, i.e. an oscillating rotary movement back and forth about an axis of rotation. The oscillating movement may additionally also be superimposed by a rotational movement, of which the inertia likewise can be used for energy generation. 
         [0020]    As already indicated above, the oscillation may be a longitudinal oscillation, i.e. the tool holder can be driven back and forth in an oscillating manner in the longitudinal direction. For this purpose, the device for generating electrical energy may have an inertial mass mounted axially movably on a shaft of the tool holder. 
         [0021]    In this way a movement oscillating in the longitudinal direction can be utilized very easily for energy generation. 
         [0022]    In accordance with a further embodiment of the invention the tool holder is designed to receive a honing tool. 
         [0023]    Honing tools are generally driven in rotation on the one hand, and on the other hand the honing tool moves in a longitudinal movement oscillating back and forth, such as when a bore, for example a cylinder bore, is machined in a diesel engine or a petrol engine. 
         [0024]    Since the honing tool during honing is itself changed as a result of workpiece removal, the honing tool must be tracked during the honing process. A force measurement or a path measurement would be advantageous for this purpose in order to allow an optimized tracking of the tool. The honing process can be improved further still when this is monitored continuously by a force or path measurement. In accordance with the invention the generated energy can be used in order to transfer the force or the position of the honing stones preferably wirelessly to a controller, by means of which the honing process can be monitored and controlled. 
         [0025]    In accordance with a development of the invention the inertial mass is mounted axially movably between two preferably resilient stops. 
         [0026]    A defined deflection in the axial direction is defined in this way. 
         [0027]    Further, the tool clamping system, on the shaft and the inertial mass, may have at least one winding, which cooperates with a magnet for generation of an induction voltage from the movement oscillating back and forth in the longitudinal direction and/or the rotary movement. 
         [0028]    In accordance with a further embodiment of the invention the at least one magnet, preferably in the form of a permanent magnet, cooperates on the one hand with at least one winding or a magnet array on the other hand, wherein the at least one magnet is preferably provided on the inertial mass and the at least one winding or the magnet array is preferably provided on the shaft. 
         [0029]    A simple utilization of the generated voltage is thus made possible by tapping at the winding or the magnet array on the shaft. 
         [0030]    In accordance with a further embodiment of the invention a maximum amplitude in the axial direction defined in the axial direction between the two stops is greater than the axial length of the at least one magnet. 
         [0031]    An effective voltage generation is thus ensured. 
         [0032]    In accordance with a further embodiment of the invention the at least one winding has a magnet core, of which the axial length deviates from the axial length of the at least one magnet. 
         [0033]    A large magnetic detent moment is thus avoided and an axial movement of the inertial mass is facilitated. 
         [0034]    As a result of these measures, a very effective energy recovery can be ensured. 
         [0035]    In a further embodiment of the invention the device for generating electrical energy is designed as a voltage generator on the tool holder, comprising a rotor, which is rotatably mounted on the tool holder preferably by means of a rolling bearing, and comprising a stator part on the tool holder for voltage generation by electromagnetic induction. 
         [0036]    A voltage can be generated in this way directly at the tool holder with relatively little additional effort. This voltage can be utilized for example in order to supply voltage to sensors for example and to evaluate signals thereof. 
         [0037]    In accordance with a further feature of the invention the inertial mass is mounted magnetically, preferably by means of permanent magnets, or by means of a sliding or rolling bearing. 
         [0038]    Particularly in the case of a magnetic mounting, a very precise, low-loss mounting is provided, for example on a shaft of the tool holder. 
         [0039]    In an advantageous development of the invention the rotor has a pole system with permanent magnets, said pole system being assigned induction windings on the stator part. 
         [0040]    A low-wear generator for voltage generation is thus provided directly on the stator part. 
         [0041]    The voltage generator can be formed in an advantageous embodiment of the invention as a drum rotor with hollow-cylindrical structure or as a disk rotor. 
         [0042]    Voltage generators designed as disk rotors are available as standard and can be integrated relatively easily in the tool holder below the shaft receptacle for the tool. 
         [0043]    The induction windings may be connected for example as mono-phase or tri-phase voltage source. The mono-phase connection is preferred in respect of the conditioning effort for the generated voltage. 
         [0044]    The output voltage of the stator part is preferably fed to a rectifier, more preferably a bridge rectifier. 
         [0045]    The output voltage of the stator part is more preferably fed to a device for voltage stabilization, which has at least one capacitor and preferably a Zener diode. 
         [0046]    With a capacitor, in particular what is known as a gold-cap capacitor, a good storage possibility for the generated energy is provided and is also sufficient over a longer period of time for supplying energy to consumers. 
         [0047]    When the tool clamping system is run at nominal rotational speed, a resistance moment is produced, which leads to a slower equalization of the rotational speed of the rotor to the spindle rotational speed. Conversely, when the tool clamping system is braked, a delayed braking of the rotor is produced. 
         [0048]    Depending on the power drain from the induction windings and the respective inertia of the rotor, there is a delayed adaptation of the rotational speed of the rotor to the spindle rotational speed. In an advantageous application-based design of the inertial moment of the rotor, of the windings and of the consumer or of the storage unit, in particular the capacitor, energy can be removed from the system according to the invention over a relatively long time in order to supply energy to a consumer, such as a sensor. 
         [0049]    The output voltage of the voltage generator, which is preferably rectified and voltage-stabilized, can be fed for example to a sensor and/or a transmitter for the wireless transfer of a useful signal to a stationary evaluation circuit. 
         [0050]    The sensor can be provided in order to monitor an operating parameter of the tool clamping system and to feed this to an evaluation circuit. 
         [0051]    The operating parameter may be, for example, the temperature, the acceleration of the tool clamping system, the force exerted onto the tool, the position of the tool, or another operating parameter. 
         [0052]    In a further advantageous embodiment of the invention the sensor is provided on the tool and is coupled to the tool holder via an electric interface for transferring a supply voltage and an output signal. 
         [0053]    A transmitting device is more preferably provided for the wireless transfer of a signal to a stationary evaluation circuit, which is preferably arranged on the tool holder. 
         [0054]    For the wireless transfer, any known methods can be used, such as radio transfer, RFID, Bluetooth, WIFI, etc. 
         [0055]    The tool may be any tool, such as a drilling tool, milling tool, sawing tool or also a different tool or an extension. 
         [0056]    A method for monitoring a machine tool is also disclosed in accordance with the invention, comprising a tool clamping system having a mechanically drivable tool holder for clamping a tool, with which electrical energy is generated from the inertial energy of the tool clamping system and is used to monitor the tool, in particular to monitor operating parameters selected from the group consisting of the temperature of the tool, the temperature of the coolant, the cutting integrity of the tool, the acceleration of the tool, the force transferred to the tool, and the position of the tool. 
         [0057]    In a development of the method according to the invention the electrical energy is generated from a rotary movement of the tool or from a linear movement of the tool relative to a tool holder. 
         [0058]    It goes without saying that the features mentioned above and the features yet to be explained hereinafter can be used not only in the specified combinations, but also independently, without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0059]    Further features and advantages of the invention will emerge from the following description of preferred exemplary embodiments with reference to the drawing, in which: 
           [0060]      FIG. 1  shows a perspective view, exposed in part, of a tool clamping system according to the invention; 
           [0061]      FIG. 2  shows a simplified detail of a voltage generator according to the invention in an embodiment as disk rotor; 
           [0062]      FIG. 3  schematically shows a profile of the rotational speed of the tool clamping system depending on time, with delayed profile of the rotor indicated in a dashed manner; 
           [0063]      FIG. 4  shows a schematic illustration of the AC voltage generated by the voltage generator following rectification by a bridge rectifier; 
           [0064]      FIG. 5  shows a possible circuit for rectification and voltage stabilization of the AC voltage generated by the voltage generator; 
           [0065]      FIG. 6  shows a schematic illustration of a sensor that is supplied by the generated, rectified and voltage-stabilized supply voltage U g  in order to operate, with the output signal thereof, an operational amplifier, which in turn operates a transmitter for the wireless transfer of the useful signal to a stationary evaluation circuit; 
           [0066]      FIG. 7  shows a simplified schematic illustration of an electric interface at the end of the tool shaft; 
           [0067]      FIG. 8  shows a perspective illustration of a conventional honing tool with drive shaft; 
           [0068]      FIG. 9  shows a perspective illustration of a tool clamping system according to the invention with a honing tool; 
           [0069]      FIG. 10  shows a partially sectional longitudinal view of the tool clamping system according to  FIG. 9 , from which the structure of the inertial mass with magnet array becomes clearer; 
           [0070]      FIG. 11  shows a schematic illustration of the magnet array according to  FIG. 10 , and 
           [0071]      FIG. 12  shows an enlarged partial view of the magnet array according to  FIG. 10  with permanent magnet for mounting. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0072]    A simplified embodiment of a tool clamping system according to the invention is illustrated prospectively in  FIG. 1  and is designated on the whole by numeral  10 . 
         [0073]    The tool clamping system  10  has a tool holder  12  in the form of an HSK, which can be driven in rotation by a tool spindle, for example of a lathe or miller. The tool holder  12  can be formed for example as a shrink chuck or also as a mechanically clampable chuck. 
         [0074]    A voltage generator designated on the whole by  17  is received above a changeover receptacle  13  on the side facing toward the tool  14 . In the illustrated case the voltage generator  17  has an inner part or stator part  22  received on the tool holder  12 , on which inner part or stator part induction windings  24  are provided. The stator part  22  cooperates with an outer part in the form of a rotor  18  mounted on said stator part by means of a rolling bearing  16 , there being permanent magnets  20  provided on the rotor. 
         [0075]    The rotor  18  with the permanent magnets  20  is thus rotatably mounted on the stator part  22 . 
         [0076]    If the tool clamping system  10  is accelerated by a tool spindle, a relative movement between the rotor  18  and the stator part  22  is thus produced as a result of the inertia of the rotor  18 . By means of the movement of the permanent magnets  20  along the induction windings  24 , a voltage is induced in the induction windings  24  on account of the electromagnetic induction. 
         [0077]    The induced AC voltage can be rectified and stored by means of a capacitor and stabilized by means of a stabilization element, such as a Zener diode. 
         [0078]    For example, this voltage can be supplied to a sensor, which is received in the tool  14 , for which purpose a suitable electric interface  26  is arranged at the outer end of the tool holder  12  in order to ensure the electrical contact with the sensor for voltage supply thereof and for the transfer of an output signal. 
         [0079]    In  FIG. 2  a detail of a voltage generator designated on the whole by  17   a  is illustrated and is designed as a disk rotor. Here, the permanent magnets  20  in question are arranged in a planar manner in a plane of the disc-shaped rotor  18  and cooperate with the induction windings  24 , which are arranged in a planar manner in the direct vicinity of the permanent magnets  20 , likewise in a plane of the stator part  22 . 
         [0080]    The permanent magnets  20  are arranged alternately with reversed polarity. In the event of a rotation of the rotor  18  relative to the stator part  22 , and approximately sinusoidal induction voltage is produced in the induction windings  24  of the stator part  22 . The induction windings  24  may be connected for example in a mono-polar or multi-polar (in particular tri-polar) manner. A mono-polar connection is preferably used, which results in a reduced conditioning effort with the subsequent stabilization of the voltage. 
         [0081]    In  FIG. 3  a rotational speed ramp is plotted over time by way of example and shows the start-up of the tool clamping system  10  to a determined operating rotational speed, followed by a temporary maintenance of the rotational speed and a subsequent braking of the rotational speed to 0. Offset in relation thereto, there is shown in a dashed manner the rotational speed set at the rotor  18  by the delay. 
         [0082]    Of course, the rotor  18  is delayed compared with the tool holder  12 , which results on the one hand by the inertia of the rotor  18 , but on the other hand also by the induced voltage, which under load leads to an electromotive force, which is directed opposite the cause, as is known. 
         [0083]    With a mono-phase connection of the induction windings  24 , an approximately sinusoidal induction voltage is produced, which naturally becomes increasingly smaller over time with equalization of the rotational speeds between the rotor  18  and the tool holder  12 . 
         [0084]      FIG. 4  shows the induced voltage following rectification by a bridge rectifier, again in the starting phase (i.e. without considerable reduction of the voltage). 
         [0085]      FIG. 5  shows an exemplary circuit  30 , which can be used for storage and voltage stabilization. The output voltage  32  of the voltage generator  17  or  17   a  is fed to the input of a bridge rectifier  34 . A capacitor C and parallel thereto a Zener diode Z are disposed between the two outputs  36 ,  38  of the bridge rectifier  34 , wherein the Zener diode may additionally also be disposed in series with a resistor (not illustrated). 
         [0086]    The capacitor C is preferably embodied as a gold-cap capacitor, which ensures a particularly high capacitance with particularly low losses and thus enables a long-term storage. Depending on the output voltage peaks of the windings, it may be necessary to adapt this voltage under the breakdown voltage of the storage capacitor. The Zener diode limits the output voltage U g  to a value defined by the Zener diode. The output voltage U g  is available as useful voltage, with the aid of which any electronic components can be supplied, wherein these may preferably be constituted by a sensor, a circuit for signal processing, or for example a transmitter. 
         [0087]    It goes without saying that the components illustrated here are merely purely exemplary in nature and that, instead of the analogue circuit components presented here, digital circuit components are of course also conceivable, as long as the provided energy is sufficient for voltage supply. 
         [0088]    In  FIG. 6  a sensor  40  is illustrated by way of example, which sensor is fed by the generated supply voltage U g  and provides at its output  42  an output signal. 
         [0089]    The sensor may be, for example, a temperature sensor, an acceleration sensor or a force sensor (for example DMS measuring bridge). The sensor  40  may be used to monitor any operating parameters of the tool clamping system, i.e. for example for temperature monitoring, for force monitoring, for monitoring the acceleration. 
         [0090]    According to  FIG. 6  the output signal of the sensor  40  is fed to the input  46  of a downstream operational amplifier  44 , which is likewise supplied by the supply voltage U g . The amplified signal is available at the output  48  of the operational amplifier  44  and can then be fed, where necessary after further processing, to a transmitter  50 , which transfers the signal via an antenna  52  wirelessly to a stationary evaluation circuit  54 , which in turn has a suitable antenna  56 . 
         [0091]    It goes without saying that any known methods can be used for signal processing. Such methods are known and can of course be used within the scope of the present invention. 
         [0092]      FIG. 7  shows by way of example the arrangement of an electric interface  60  in the region between the shaft end of the tool  14  and a receiving bore of the tool holder, which is formed here for example as a shrink holder. 
         [0093]    At the end of the tool shaft of the tool  14 , a contact face  61  is provided on the end face and is electrically insulated from the rest of the tool  14 , for example by means of suitable ceramic layers, and is coupled via a line  58  for example to an associated sensor  40  in the tool  14 . The contact face  61  is assigned a resiliently mounted contact pin  62  on the tool holder  12 , which contact pin is pre-loaded toward the tool  14  via a spring  64 . This contact pin  62  is also electrically insulated in a suitable manner with respect to the rest of the material of the tool holder  12  and is connected for example via a line  66  to an associated evaluation and transmitting unit within the tool holder  12 . 
         [0094]    Here, merely one arrangement for transfer is shown by way of example for merely one pole. It goes without saying that of course further contacts can be provided for the other poles (for example for the voltage supply of the sensor  40 ), possibly in a concentric arrangement. A concentric arrangement has the advantage that a voltage transfer is enabled independently of the position of installation of the tool  14  on the tool receptacle  12 . 
         [0095]    Depending on the application in question for which the present voltage generator is to be used, the inertial moment of the rotor, the windings and the consumer in question and also the associated circuit for storage and voltage stabilization are advantageously coordinated with one another in a suitable manner in order to attain an optimal voltage yield for the application in question, the voltage yield being sufficient over a long period of time for sufficiently supplying energy to the desired monitoring circuit(s) in a suitable manner. 
         [0096]    An alternative embodiment of the invention will now be explained with reference to the following  FIGS. 8 to 12 , in which the oscillation energy in the case of a honing tool is used for energy generation. 
         [0097]      FIG. 8  shows a conventional tool clamping system  10 ′ for a honing tool  14 ′. The honing tool  14 ′ is received on a shaft  72 , which is driven by a tool spindle  74 . The honing tool  14 ′ has a plurality of honing stones  70 , which are received on the outer surface of the tool holder  12 ′. The shaft  72  is driven in rotation, as is indicated by the arrow  76 . In addition, the shaft  72  is driven with longitudinal oscillation in the axial direction, as is indicated by the arrow  75 . 
         [0098]    By means of a wedge-shaped mounting of the honing stones  70  on the tool holder  12 ′, only a slightly grinding movement without substantial workpiece removal is produced in a first direction of the honing tool  14 ′, whereas, in the reverse direction, on account of the wedge effect, the honing stones  70  bear under pressure against the inner surface of the workpiece to be honed (for example a cylinder bore of an internal combustion engine) and cause a workpiece removal. The honing stones during the course of the honing process receive, in part, removed material of the workpiece, such that an axial adjustment of the tool holder  12 ′ on the shaft is necessary in order to ensure a uniform machining (not illustrated). In the case of conventional honing machines this readjustment is made empirically on the basis of the number of performed strokes of the honing tool  14 ′. 
         [0099]      FIG. 9  now shows a tool clamping system  10   a  for a honing machine that is constructed in accordance with the invention and has a device  78 ,  88 ,  90  for voltage generation from the inertial energy of an oscillating honing tool  14   a . A sensor can be operated with this energy, which sensor either detects the position of the honing tool  14   a  or the force exerted onto the honing tool and transfers this wirelessly, for example via WIFI, to a controller of the honing machine. 
         [0100]    An inertial mass  78  having a magnet array  90  is mounted movably in the axial direction, as indicated by the arrow  84 , on the shaft  72  of the tool clamping system  10   a , which is driven by the spindle  10   a  (or a suitable interface). The inertial mass is movable back and forth between two stops  80 ,  82 , wherein the movement energy is stored by springs  81 ,  83  located therebetween. If the honing tool  14   a  is moved back and forth in an oscillating manner in the direction of the arrow  75 , the inertial mass  78  thus moves back and forth in the direction of the arrow  84  with a certain phase shift relative to the movement of the honing tool  14   a.    
         [0101]    By means of a winding  88  on a magnet core  86  in the form of a laminated core according to  FIG. 10 , a voltage is induced hereby in cooperation with associated permanent magnets  89  on the inertial mass  78  in accordance with the principle of a linear generator. This voltage can be used to operate a sensor and for the wireless transfer of a signal in order to capture and to transfer the absolute position of the honing tool  14   a  or the force exerted onto the honing stones  70 . 
         [0102]    The axial length L M  of the permanent magnets  89  is much shorter than the axial length of the magnet core L K    86  of the winding  88 . An effective voltage generation is thus ensured. 
         [0103]    In order to prevent the production of a large magnetic detent moment as a result of matching axial lengths (L M ) of the permanent magnets  89  and of the magnet core (L K ) of the winding  88 , the axial length (L M ) of the permanent magnets deviates slightly from the axial length of the magnet core  86  (L M ≠L K ). 
         [0104]    It goes without saying that, instead of one winding  88  with a magnet core  86 , a plurality of windings  88  may also be provided on the shaft  72  distanced axially from one another. 
         [0105]      FIG. 11  shows, by way of example, a magnet array  90 , which can be received on the shaft  72  alternatively to the winding  88  in order to ensure a particularly effective energy generation. The magnet array  90  is illustrated in a planar arrangement of the different windings extending in the radial direction. With a magnet array  90  of this type, an effective energy generation can be ensured both from the alternating linear movement of the honing tool  14   a  and from the rotation energy of the inertial mass  78 . 
         [0106]      FIG. 12  shows, by way of example, how permanent magnets  92  provided in the outer periphery of the shaft  72  can be used for the low-loss magnetic mounting of the inertial mass  78  on the shaft  72 .