Procedure for measuring a measurement variable in a process step of a manufacturing process and a measurement chain for carrying out said procedure

Abstract

To provide a procedure for measuring a measured variable (MG) in a manufacturing process.SOLUTION: A procedure comprises the steps of: (i) positioning a tool on a workpiece or a workpiece on the tool; (ii) automatically coupling a positioned measurement unit with an evaluation unit; (iii) automatically generating measurement signals (MS) under an action of the measured variable (MG); (iV) automatically converting the measurement signals (MS) into measurement data (MD); and automatically transmitting the measurement data (MD) to a primary antenna (23).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The invention relates to a procedure for measuring a measurement variable in a process step of a manufacturing process according to the characterizing portion of the first independent claim. The invention also relates to a measurement chain for carrying out said procedure. [Background technology]

[0002] Typically, in a manufacturing process, a workpiece is machined by a tool. In this process, measurement variables such as forces, torques, bending moments, accelerations, vibrations, etc. act on the tool. It is desirable to know the values ​​of the measurement variables for the control of the manufacturing process. For this purpose, a measurement chain is used which comprises several transmission links such as sensors, signal lines and evaluation units. When a measurement variable acts on a sensor, the sensor generates a measurement signal which is transmitted by the signal line to the evaluation unit. For an accurate measurement of the measurement variable, it is advantageous to mount the sensor as close as possible to the tool where the measurement variable is not distorted.

[0003] Such a measurement chain is known from EP 1 323 495 A1. The rotary tool is associated with a sensor arrangement, which comprises a sensor, an AD converter and a coil winding. The sensor detects the value of a measurement variable acting on the rotary tool and generates a measurement signal corresponding to the measured value. The AD converter digitizes the measurement signal to obtain the measurement data. A stationary coil is associated with each sensor arrangement. The measurement data is transmitted from the coil winding to the stationary coil by near-field telemetry. For this purpose, the coil winding and the stationary coil are arranged at a distance of a few millimeters from each other. Furthermore, the stationary coil supplies the sensor arrangement with electrical energy. For this reason, the sensor arrangement does not need its own energy storage device. The stationary coil is connected to a main amplifier. The main amplifier evaluates the measurement data.

[0004] However, EP 1 323 495 A teaches the use of strain gauges as sensors. In precision machining of workpieces, strain gauges have the disadvantage of a limited measurement range and low dynamic measurement resolution compared to piezoelectric sensors. Therefore, in order to obtain an optimal resolution of the measurement signal when using strain gauges, it is necessary to readjust the measurement range several times while changing the magnitude of the measurement signal, which requires a lot of effort. Moreover, for rapidly rotating workpieces, a high dynamic measurement resolution with a measurement frequency of up to 35 kHz is particularly desirable.

[0005] Thus, a mobile system is known from WO2015176189, in which the measurement unit comprises a piezoelectric sensor, an electronic unit and a mobile antenna. The electronic unit conditions and / or compresses the measurement signal from the piezoelectric sensor into measurement data. The mobile antenna transmits the measurement data to a fixed antenna by far-field telemetry. Since far-field telemetry is used, the two antennas can be positioned at a distance of several meters from each other. For interference-free transmission of the measurement data, one of the two antennas is circularly polarized and the other of the two antennas is linearly polarized. The fixed antenna is connected to a data processing unit, which processes the measurement data. In the case of an electrical energy supply, the measurement unit comprises its own energy storage device and / or its own energy generator.

[0006] Typically, a manufacturing process consists of multiple process steps that are performed in a chronological order. For example, a workpiece is machined by a machine tool using different tools in multiple process steps. The different tools are positioned on the workpiece one after the other in the chronological order, and / or the workpiece is positioned on a new tool from time to time. Each process step therefore involves changing the tools and / or the workpiece.

[0007] According to the teaching of EP 1 323 495 A1, a tool change is performed and the sensor device associated with the tool and its fixed coil are also changed with this tool change. The sensor device and its fixed coil are present multiple times per tool. This makes the purchase of the measurement chain expensive. Furthermore, the measurement chain is interrupted with every tool change. In order to reconnect the measurement chain, the sensor device and its fixed coil have to be registered with the main amplifier.

[0008] It is inevitable to interrupt the measurement chain. Moreover, according to WO2015176189, the transmission connection to the fixed antenna is interrupted during the change of the measurement unit and its mobile antenna. In order to reconnect the measurement chain, the two antennas have to re-establish the interrupted transmission connection.

[0009] For a fast and cost-effective manufacturing process, the waiting time during which the measurement chain is interrupted in a process step should be as short as possible.

[0010] A first object of the present invention is to provide a procedure for enabling the measurement of at least one measurement variable by a measurement chain in each of the process steps of a manufacturing process comprising a plurality of process steps, wherein a measurement chain interrupted in a process step is quickly reconnected. A second object of the present invention is to provide said measurement of a measurement variable with high accuracy, high dynamic measurement resolution and short latency.

[0011] Furthermore, a second object of the present invention is to provide a measuring chain for performing a procedure that is cheap to purchase and can be integrated into the machine tools used to perform the process steps with as little effort as possible. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] European Patent Application Publication No. 1323495 [Patent Document 2] International Publication No. 2015176189 Summary of the Invention

[0013] These two objects are achieved by a procedure for measuring a measurement variable in a process step of a manufacturing process and a measurement chain for carrying out said procedure according to the two independent claims.

[0014] The invention relates to a procedure for measuring measurement variables in process steps of a manufacturing process carried out by a machine tool, the manufacturing process being carried out by a machine tool, the procedure using a measurement chain comprising a number of measurement units and an evaluation unit, each of the measurement units comprising a sensor, a transducer unit and a secondary antenna and the evaluation unit comprising a primary antenna, the machine tool being adapted for chronologically processing workpieces by a number of tools in a number of process steps, for which purpose the tools are positioned on the workpieces in each process step, for which a measurement unit is associated with each tool, or for chronologically machining a number of workpieces by one tool in a process step, for which purpose each workpiece is chronologically positioned on a tool associated with each workpiece, or for which the machine tool is adapted for chronologically machining a number of workpieces by one tool in a process step, for which purpose each workpiece is chronologically positioned on a tool associated with each workpiece, The secondary antenna is adapted to handle workpieces, and for that purpose one of the tools is positioned on a workpiece for which a measuring unit is associated with each tool, and the procedure is carried out in process steps by the steps of positioning the tool on the workpiece or positioning the workpiece on the tool, whereby a measuring unit associated with the positioned tool or the positioned workpiece is positioned in a measuring position for measuring a measurement variable, automatically coupling the positioned measuring unit with the evaluation unit by establishing a transmission connection between the secondary antenna and the primary antenna, automatically generating a measurement signal under the action of the measurement variable by a sensor of the positioned measuring unit, automatically converting the measurement signal into measurement data by a converter unit of the positioned measuring unit, and automatically transmitting the measurement data to the primary antenna by the secondary antenna of the positioned measuring unit.

[0015] The invention also relates to a machine tool for carrying out a procedure in which each of the measuring units positioned at a measuring position can be coupled with an evaluation unit to establish a transmission connection between the secondary antenna and the primary antenna.

[0016] In the procedure according to the invention, each process step comprises moving and positioning one of a plurality of measuring units at a measurement position. A measurement variable is measured by the positioned measuring unit at this measurement position during the process step. However, moving and positioning the measuring unit at the measurement position leads to an interruption of the measurement chain between the measuring unit and the evaluation unit. However, the measurement chain according to the invention can be reconnected by coupling the positioned measuring unit with the evaluation unit. This coupling establishes a transmission connection between the secondary antenna of the positioned measuring unit and the primary antenna of the evaluation unit. The measurement chain is reconnected by this coupling. This coupling occurs automatically. For the purposes of the invention, the adverb "automatically" means that the transmission connection is automatically established by the positioned measuring unit and the evaluation unit without human intervention. This automatic coupling leads to a rapid reconnection of the measurement chain.

[0017] Advantageous embodiments of the invention are set forth in the dependent claims.

[0018] In the following, the invention will be explained in more detail, by way of example, with reference to the drawings, in which: [Brief description of the drawings]

[0019] [Figure 1] 1 shows a flow chart of procedural steps of a procedure for measuring a measurement variable MG during a process step of a manufacturing process. [Diagram 2] 2 shows a view of a part of a first embodiment of a measuring chain 1 for carrying out the procedure according to FIG. 1, in which the measuring chain 1 is part of a first machine tool 3. [Diagram 3] 3 shows a cross-sectional view of a part of the first machine tool 3 according to FIG. 2. [Figure 4] 2 shows a view of a portion of a second embodiment of a measuring chain 1 for carrying out the procedure according to FIG. 1, in which the measuring chain 1 is a component of a second machine tool 4. [Diagram 5] 5 shows a cross-sectional view of a part of the second machine tool 4 according to FIG. [Figure 6] 1 shows a view of a portion of a third embodiment of a measuring chain 1 for carrying out the procedure according to FIG. 1, in which the measuring chain 1 is a component of a third machine tool 4. [Figure 7] 7 shows a cross-sectional view of a part of a third machine tool 4 according to FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Like reference numbers refer to like objects throughout the drawings.

[0021] Figure 1 shows a flow chart of procedural steps of a procedure for measuring a measurement variable MG in a process step of a manufacturing process. The measurement variable MG can be force, torque, bending moment, acceleration, vibration, etc.

[0022] To perform the procedure, a measurement chain 1 is used which comprises a number of measurement units 10, 10', 10'' and an evaluation unit 20. Figures 2 to 7 show parts of three embodiments of the measurement chain 1 for performing the procedure. Firstly, the measurement chain 1 is described in schematic form. Then, further details of the measurement chain 1 are described in sections dedicated to each of the three embodiments.

[0023] Each of the multiple measurement units 10, 10', 10'' comprises a sensor 11, 11', 11'', a converter unit 12, 12', 12'', and a secondary antenna 13, 13', 13''. For example, the multiple measurement units 10, 10', 10'' include a first measurement unit 10 comprising a first sensor 11, a first converter unit 12, and a first secondary antenna 13, a second measurement unit 10' comprising a second sensor 11', a second converter unit 12', and a second secondary antenna 13, and a third measurement unit 10'' comprising a third sensor 11'', a third converter unit 12'', and a third secondary antenna 13''.

[0024] Each of the plurality of measurement units 10, 10', 10'' comprises a secondary housing 17, 17', 17''. Thus, there are a plurality of secondary housings 17, 17', 17''. For example, the plurality of secondary housings 17, 17', 17'' comprises a first secondary housing 17 with a first secondary interior space 19 for accommodating a first converter unit 12 and a first secondary antenna 13, a second secondary housing 17' with a second secondary interior space 19' for accommodating a second converter unit 12' and a second secondary antenna 13', and a third secondary housing 17'' with a third secondary interior space 19'' for accommodating a third converter unit 12' and a third secondary antenna 13''. The plurality of secondary housings 17, 17', 17'' are made of mechanically resistant materials such as sheet metal, plastic, etc.

[0025] Furthermore, the evaluation unit 20 comprises a primary housing 27 for accommodating the primary antenna 23. The primary housing 27 comprises a primary interior space 29. The primary antenna 23 is arranged within the primary interior space 29. The primary interior space 29 protects the primary antenna 23 from harmful external conditions such as dirt, coolants, electromagnetic interference, etc. The primary housing 27 is also made of a mechanically resistant material such as sheet metal, plastic, etc.

[0026] In a first step of the procedure, a positioning I of one of the multiple measuring units 10, 10', 10'' at a measuring position 15 for measuring a measurement variable MG is performed. The measuring unit 10, 10', 10'' is moved to the measuring position 15 and remains at this measuring position 15 during the process steps.

[0027] The second step of the procedure involves automatically coupling the positioned measuring unit 10, 10', 10'' with the evaluation unit 20 by establishing a transmission connection between the secondary antenna 13, 13', 13'' and the primary antenna 23 II.

[0028] Due to this coupling II of the positioned measuring unit 10, 10', 10'' and the evaluation unit 20, the primary antenna 23 generates and radiates an electromagnetic alternating field EW. In Figures 3 and 5, the electromagnetic alternating field EW is represented by a curved circle segment. Preferably, the electromagnetic alternating field EW has a frequency of 125 kHz. The range of the electromagnetic alternating field EW is limited in such a way that only the secondary antennas 13, 13', 13'' of the measuring unit 10, 10', 10'' that are completely positioned at the measurement position 15 can receive the electromagnetic alternating field EW.

[0029] As soon as and as long as the secondary antenna 13, 13', 13'' receives the electromagnetic alternating field EW, electrical energy is supplied to the measurement unit 10, 10', 10''. Preferably, the secondary antenna 13, 13', 13'' is an induction coil with several turns and a capacitor. The electromagnetic alternating field EW induces a voltage in the induction coil, which charges the capacitor with electrical energy. The electrical energy is used to operate the measurement unit 10, 10', 10''. Once the capacitor is charged, the measurement unit 10, 10', 10'' is supplied with sufficient electrical energy to operate the measurement unit 10, 10', 10''. Preferably, the capacitor is charged within an operation readiness time BT of 100 ms, preferably within an operation readiness time BT of 20 ms.

[0030] When the measurement unit 10, 10', 10'' is ready for operation, the secondary antenna 13, 13', 13'' establishes a transmission connection to the primary antenna 23. Preferably, the establishment of the transmission connection to the primary antenna 23 occurs immediately after the measurement unit 10, 10', 10'' has reached an operation-ready state. To establish the transmission connection to the primary antenna 23, the secondary antenna 13, 13', 13'' transmits an identification number ID to the primary antenna 23. The identification number ID is stored in a data memory of the measurement unit 10, 10', 10''. Preferably, the data memory is arranged in the converter unit 12, 12', 12''. The identification number ID identifies the measurement unit 10, 10', 10'' in an unambiguous manner. The primary antenna 23 receives the identification number ID. In Fig. 3 and Fig. 5, the transmission of the identification number ID is shown as a curved circle segment. The primary antenna 23 forwards the identification number ID to the evaluation unit 20. The evaluation unit 20 identifies the measuring unit 10, 10', 10'' based on the transmitted and received identification number ID. Upon receiving the identification number ID and identifying the measuring unit 10, 10', 10'', the coupling II between the positioned measuring unit 10, 10', 10'' and the evaluation unit 20 is completed.

[0031] In a third step of the procedure, automatic generation III of the measurement signal MS by the sensor 11, 11', 11'' of the positioned measuring unit 10, 10', 10'' occurs under the influence of the measurement variable MG.

[0032] The sensors 11, 11', 11'' are adapted to detect a measurement variable MG and generate a measurement signal MS of the detected measurement variable MG. The sensors 11, 11', 11'' detect and generate a measurement signal MS every time unit. The time unit may be 1 millisecond (ms), 100 microseconds (100 μs), etc. The reciprocal of the time unit is the dynamic measurement resolution. Thus, the sensors 11, 11', 11'' generate a series of measurement signals MS in time, where each measurement signal MS has a magnitude and a time.

[0033] The sensors 11, 11', 11'' may be piezoelectric sensors, piezoresistive sensors, strain gauges, etc. Each sensor 11, 11', 11'' comprises a signal cable 14, 14', 14''. The signal cable 14, 14', 14'' is configured to transmit a measurement signal MS to the transducer unit 12, 12', 12''.

[0034] Preferably, the sensors 11, 11', 11'' are piezoelectric sensors. Piezoelectric sensors comprise a piezoelectric material such as quartz, piezoelectric ceramics, etc. A measuring variable MG acts on the piezoelectric material in the form of a tensile and / or compressive load. Under the action of the measuring variable MG, the piezoelectric material generates a measuring signal MS in the form of an electric charge. The amount of charge is proportional to the numerical value of the measuring variable MG. According to Fig. 3, Fig. 5 and Fig. 7, the piezoelectric sensor is mechanically preloaded with a preload force by using preloading means 16, 16', 16'', such as a screw, a sleeve, etc. This mechanical preload allows the piezoelectric material to detect both tensile and compressive loads. The piezoelectric sensor is characterized by a high dynamic measurement resolution of up to 35 kHz.

[0035] In a fourth step of the procedure, an automatic conversion IV of the measurement signals MS into measurement data MD by the converter units 12, 12', 12'' of the positioned measuring units 10, 10', 10'' is performed.

[0036] The converter units 12, 12', 12'' are adapted to digitize the measurement signal MS to obtain measurement data MD. Preferably, the converter units 12, 12', 12'' for piezoelectric sensors comprise a charge amplifier. The charge amplifier amplifies the charge of the piezoelectric sensor and converts it into a voltage. The converter units 12, 12', 12'' digitize the voltage into measurement data MD. The magnitude and timing of the measurement signal MS are converted and digitized into the magnitude and timing of the measurement data MD.

[0037] Preferably, the converter units 12, 12', 12' are adapted such that the converter units 12, 12', 12'' convert the measurement signal MS into measurement data MD and generate unit data ED indicating the unit of the digitized measurement variable MG. For example, a measurement variable MG that is a force has the unit Newton (N), a measurement variable MG that is a torque or bending moment has the unit Newton meter (Nm) and a measurement variable MG that is an acceleration or vibration has the unit acceleration due to gravity (g).

[0038] Preferably, the converter unit 12, 12', 12' is adapted to read out, from the data memory of the measurement unit 10, 10', 10'', calibration data KD of the sensor 11, 11', 11'', which is generating a measurement signal MS under the action of the measurement variable MG. The calibration data KD specify the sensitivity of the sensor 11, 11', 11'', as a function of the temperature at which the sensor 11, 11', 11'', generated the measurement signal MS. In the case of a piezoelectric sensor, the calibration data KD may also specify the sensitivity of the sensor 11, 11', 11'', as a function of the magnitude of the mechanical preload force at which the sensor 11, 11', 11'', generated the measurement signal MS.

[0039] Preferably, the converter unit 12, 12', 12' is adapted to read serial number data SD of the converter unit 12, 12', 12'' from the data memory of the measurement unit 10, 10', 10''. The serial number data SD unambiguously identifies the converter unit 12, 12', 12'' which converts and digitizes the measurement signal MS into measurement data MD.

[0040] Furthermore, in a fifth step of the procedure, an automatic transmission V of the measurement data MD by the secondary antenna 13, 13', 13'' of the positioned measuring unit 10, 10', 10'' to the primary antenna 23 is performed.

[0041] The secondary antenna 13, 13', 13" is adapted to transmit the measurement data MD to the primary antenna 23. Preferably, the secondary antenna 13, 13', 13" transmits the measurement data MD to the primary antenna 23 at a carrier frequency of 13.56 MHz and a high transmission rate SR of up to 1.6 Mbit / s. Thus, the sensor 11, 11', 11" can measure the measurement variable MG with a high dynamic measurement resolution of up to 35 kHz and the secondary antenna 13, 13', 13" can transmit the measurement data MD to the primary antenna 23 with a resolution of up to 24 bits at a transmission rate SR of up to 1.6 Mbit / s.

[0042] Preferably, the secondary antenna 13, 13', 13'' is adapted to transmit the unit data ED, the calibration data KD and the serial number data SD together with the measurement data MD to the primary antenna 23.

[0043] Preferably, the evaluation unit 20 comprises a data memory in which converter unit-specific data D12 is stored. The converter unit-specific data D12 comprises, for a converter unit 12, 12', 12'' of the measurement chain 1, the time constant of the converter unit 12, 12', 12'', the noise of the converter unit 12, 12', 12'', etc. The evaluation unit 20 is adapted to assign the converter unit-specific data D12 of the converter unit 12, 12', 12'', which is a conversion and digitization of the measurement signal MS into measurement data MD, to the serial number data SD transmitted together with the measurement data MD. The evaluation unit 20 reads out the assigned converter unit-specific data D12 from the data memory.

[0044] The evaluation unit 20 is adapted to evaluate the measurement data MD. For example, the evaluation unit 20 displays a graphical representation of the measurement data MD in a time series, where the vertical axis indicates the magnitude of the measurement data MD and the horizontal axis indicates the time of the measurement data MD. The evaluation unit 20 takes into account the unit data ED, the calibration data KD and the converter unit-specific data D12 when evaluating the measurement data MD. Preferably, the evaluation unit 20 displays the unit data ED in a graphical representation. Preferably, the evaluation unit 20 corrects the measurement data MD by the calibration data KD and the converter unit-specific data D12. For example, the evaluation unit 20 multiplies the magnitude of the respective measurement data MD by the sensitivity of the sensors 11, 11', 11'' as a function of temperature and / or by the sensitivity of the sensors 11, 11', 11'' as a function of the mechanical preload. For example, the evaluation unit 20 filters the measurement data MD with the time constant of the converter unit 12, 12', 12'' and / or represents the noise of the converter unit 12, 12', 12'' in a graphical representation in the form of error bars. All these measurements increase the accuracy of the measurement of the measurement variable MG.

[0045] First embodiment In a first embodiment according to Fig. 2, the measuring chain 1 is a component of a first machine tool 3, such as a lathe, a turret lathe, etc. A detail of the first machine tool 3 is shown in Fig. 3. Preferably, the first machine tool 3 is a turret lathe, which comprises a turret 30 and a number of tool holders 31, 31', 31'' arranged on the turret 30. The tool holders 31, 31', 31'' are replaceably mounted on the turret 30. Preferably, the tool holders 31, 31', 31'' are mounted on the turret 30 by means of mounting means 32, 32', 32'', such as screws, bolts, etc. The turret 30, the tool holders 31, 31', 31'' and the mounting means 32, 32', 32'' are made of a mechanically resistant material, such as steel, tool steel, etc.

[0046] Each tool holder 31, 31', 31'' receives a tool 33, 33', 33''. The tools 33, 33', 33'' are also made of a mechanically resistant material such as steel, tool steel, etc. Preferably, the tools 33, 33', 33'' are clamped to the tool holder 32, 32', 32'' by clamping means 34, 34', 34'', such as screws, pins, etc. The tools 33, 33', 33'' have cutting blades made of a hard, solid and tough cutting material such as metal, ceramic, etc. Figure 2 shows, for example, three tool holders 31, 31', 31'' and three tools 33, 33', 33''. The three tool holders 31, 31', 31'' and three tools 33, 33', 33'' include a first tool holder 31 that receives a first tool 32, a second tool holder 31' that receives a second tool 32', and a third tool holder 31'' that receives a third tool 33''.

[0047] The turret 30 is movably arranged on the first machine tool 3. On the first machine tool 3, the turret 30 is rotatable about a longitudinal axis Z, which is shown in FIG. 2 by a curved double arrow. By rotating the turret 30 about the longitudinal axis Z, the tools 33, 33', 33'' can be positioned on the workpiece 2 one after the other in a chronological sequence. The workpiece 2 consists of any material, such as metal, plastic, glass, etc. The workpiece 2 is machined by the tools 33, 33', 33'' in several process steps in a chronological sequence. For each process step, one of the tools 33, 33', 33'' is positioned on the workpiece 2, and the workpiece 2 is machined by the positioned tool 33, 33', 33''. As shown in FIG. 2, the first tool 33 is for example positioned on the workpiece 2. The measurement variable MG to be measured acts on the positioned tool 33, 33', 33'' during the machining. Preferably, the change of tool 33, 33', 33'' on the workpiece 2 occurs within a set-up time of 500 ms.

[0048] A measuring unit 10, 10', 10'' is assigned to each tool holder 31, 31', 31''. According to FIG. 2, for example, three tool holders 31, 31', 31'' and three measuring units 10, 10', 10'' are shown. The three measuring units 10, 10', 10'' comprise a first measuring unit 10 on a first tool holder 31, a second measuring unit 10' on a second tool holder 31' and a third measuring unit 10'' on a third tool holder 31''. Each measuring unit 10, 10', 10'' comprises a sensor 11, 11', 11'', a transducer unit 12, 12', 12'' and a secondary antenna 13, 13', 13''.

[0049] According to FIG. 3, each tool holder 31, 31', 31'' comprises a recess 35, 35', 35''. The sensor 11, 11', 11'' of the measuring unit 10, 10', 10'' associated with the tool holder 31, 31', 31'' is arranged in the recess 35, 35', 35''. Preferably, the recess 35, 35', 35'' is located inside the tool holder 31, 31', 31'', and the sensor 11, 11', 11'' is completely accommodated in the recess 35, 35', 35''. The recess 35, 35', 35'' protects the sensor 11, 11', 11'' from harmful external conditions such as dirt, coolant, electromagnetic radiation, etc. The tool holder 31, 31', 31'' is provided with a feedthrough which guides the signal cable 14, 14', 14'' from the recess 35, 35', 35'' to the outside of the tool holder 31, 31', 31''. The feedthrough is waterproof.

[0050] Preferably, the secondary housing 17, 17', 17'' is placed on the turret 30. The secondary housing 17, 17', 17'' is held on the turret 30 by holding means 18, 18', 18'', such as screws, bolts, etc. The secondary housing 17, 17', 17'' is placed at a spatial distance from the sensor 11, 11', 11''. Preferably, the secondary housing 17, 17', 17'' is placed at a spatial distance of 10 cm or less from the sensor 11, 11', 11''.

[0051] When a tool holder 31, 31', 31'' is exchanged on the turret 30, the tool holder 31, 31', 31'' is exchanged together with the measuring unit 10, 10', 10'' associated therewith. For this purpose, the tool holder 31, 31', 31'' to be exchanged is removed from the turret 30 by loosening its mounting means 32, 32', 32'', and the secondary housing 17, 17', 17'', connected to the tool holder by the signal cable 14, 14', 14'', is removed by loosening its holding means 18, 18', 18''. The new tool holder 31, 31', 31'' is then attached to the turret 30 by its mounting means 32, 32', 32'', and the secondary housing 17, 17', 17'', connected to the tool holder by the signal cable 14, 14', 14'', is attached to the turret 30 by its holding means 18, 18', 18''. Exchanging a tool holder 31, 31', 31'' with its associated measuring unit 10, 10', 10'' is quickly and easily accomplished.

[0052] According to FIG. 2, for example, a first measuring unit 10 is positioned at a measuring position 15 , a first sensor 11 of the first measuring unit 10 detecting a measurement variable MG acting on a first tool 33 .

[0053] The sensors 11, 11', 11'' and the secondary housings 17, 17', 17'' are in fact rotatable about the longitudinal axis Z on the turret 30 and therefore are movably arranged on the first machine tool 3, whereas the primary housing 27 has a fixed arrangement on the first machine tool 3. Preferably, the primary housing 27 is attached to the turret 30 by fastening means such as screws, bolts or the like which are not shown in the figures. The secondary housings 17, 17', 17'' and the primary housing 27 are movable relative to each other.

[0054] For a measuring unit 10, 10', 10'' positioned at the measuring location 15, the first machine tool 3 is adapted to position the secondary housing 17, 17', 17'' of the measuring unit 10, 10', 10'' positioned at the measuring location 15 at a transmission distance 25 from the primary housing 27. Preferably, the transmission distance 25 between the secondary housing 17, 17', 17'' of the measuring unit 10, 10', 10'' positioned at the measuring location 15 and the primary housing 27 is equal to the range of the electromagnetic alternating field EW.

[0055] Second embodiment In a second embodiment according to Fig. 4, the measuring chain 1 is part of a second machine tool 4, such as a clamping system, a zero-point clamping system. A detail of the second machine tool 4 is shown in Fig. 5. Preferably, the second machine tool 4 is a zero-point clamping system, which comprises a carrier unit 40 and a number of clamping units 41, 41', 41''. In each case, one of the clamping units 41, 41', 41'' is changeably mounted on the carrier unit 40. The clamping units 41, 41', 41'' can be exchanged without zero-point loss in the zero-point clamping system.

[0056] Preferably, the clamping units 41, 41', 41'' are fixed in the clamping module 46 of the carrier unit 40 by clamping means 42, 42', 42'', such as pins, bolts or the like. According to FIG. 4, each of the clamping units 41, 41', 41'' comprises, for example, four clamping means 42, 42', 42'', which can be fixed in the four clamping modules 46 of the carrier unit 40. After the clamping means 42, 42', 42'' are inserted in the clamping module 46, the clamping means 42, 42', 42'' are held in position in the clamping module 46 by a positive lock, such as by a spring force. Release of the attachment occurs pneumatically. Preferably, the clamping units 41, 41', 41'' can be exchanged within a set-up time of 500 ms. The carrier unit 40, the clamping units 41, 41', 41'', the clamping means 42, 42', 42'', and the clamping module 46 are made of a mechanically resistant material, such as steel, tool steel, or the like.

[0057] Each of the multiple clamping units 41, 41', 41'' accommodates a workpiece 2, 2', 2''. The workpieces 2, 2', 2'' are made of any material, such as metal, plastic, glass, etc. Preferably, the workpieces 2, 2', 2'' are clamped in the clamping units 41, 41', 41'' by clamping means 44, 44', 44'', such as vices, clamps, etc. Referring to FIG. 4, for example, three clamping units 41, 41', 41'' and three workpieces 2, 2', 2'' are shown. The three clamping units 41, 41', 41'' and three workpieces 2, 2', 2'' include a first clamping unit 41 accommodating a first workpiece 2, a second clamping unit 41' accommodating a second workpiece 2', and a third clamping unit 41'' accommodating a third workpiece 2''.

[0058] Thus, there is a plurality of workpieces 2, 2', 2''. The second machine tool 4 is adapted to machine each of the plurality of workpieces 2, 2', 2'' by means of a tool 43 in a process step. For this purpose, the workpieces 2, 2', 2'' accommodated in the clamping units 41, 41', 41'' are positioned on the tool 43 of the second machine tool 4 in chronological order, and each positioned workpiece 2, 2', 2'' is machined by means of the tool 43. According to FIG. 5, the tool 43 comprises a cutting blade made of a hard, solid and tough cutting material, such as metal, ceramic, etc. During machining, the detected measurement variable MG acts on the positioned workpieces 2, 2', 2''.

[0059] The measuring units 10, 10', 10'' are arranged in each of the multiple clamping units 41, 41', 41''. Referring to FIG. 4, for example, three clamping units 41, 41', 41'' and three measuring units 10, 10', 10'' are shown. The three measuring units 10, 10', 10'' comprise a first measuring unit 10 associated with the first clamping unit 41, a second measuring unit 10' associated with the second clamping unit 41', and a third measuring unit 10'' associated with the third clamping unit 41''.

[0060] According to FIG. 5, the measuring units 10, 10', 10'' are positioned at a measuring position 15, the sensors 11, 11', 11'' of the measuring units 10, 10', 10'' detecting the measuring variables MG acting on the workpieces 2, 2', 2''.

[0061] Preferably, the measuring unit 10, 10', 10'' is clamped together with the workpiece 2, 2', 2'' in clamping means 44, 44', 44''. The sensor 11, 11', 11'' is clamped in a recess 45, 45', 45'' in close spatial proximity to the workpiece 2, 2', 2''. According to FIG. 5 the sensor 11, 11', 11'' is clamped in direct mechanical contact with the workpiece 2, 2', 2''.

[0062] Preferably, the secondary housing 17, 17', 17'' is arranged on the clamping unit 41, 41', 41''. Preferably, the secondary housing 17, 17', 17'' is identical to the housing of the clamping unit 41, 41', 41'' in certain areas. The secondary housing 17, 17', 17'' is arranged at a spatial distance from the sensor 11, 11', 11''. Preferably, the secondary housing 17, 17', 17'' is arranged at a certain spatial distance of less than 10 cm from the sensor 11, 11', 11''.

[0063] In order to change the workpiece 2, 2', 2'' held in the clamping unit 41, 41', 41'', the clamping means 44, 44', 44'' can be detached from the workpiece 2, 2', 2'' to be changed and reconnected with the new workpiece 2, 2', 2''. Preferably, the sensor 11, 11', 11'' is left in the recess 45, 45', 45'' during the change. Only the workpiece 2, 2', 2'' is changed. Releasing and re-establishing the clamping of the workpiece 2, 2', 2'' and the sensor 11, 11', 11'' is simple and fast. Thus, the workpiece 2, 2', 2'' can be changed while the sensor 11, 11', 11'' with the transducer unit 12, 12', 12'' and the secondary antenna 13, 13', 13'' and the secondary housing 17, 17', 17'' remain on the clamping unit 41, 41', 41''.

[0064] The sensors 11, 11', 11'' and the secondary housings 17, 17', 17'' are in fact variably attached to the carrier unit 40 by clamping units 41, 41', 41'', and are therefore movably arranged on the second machine tool 4, whereas the primary housing 27 is fixedly arranged on the second machine tool 4. Preferably, the primary housing 27 is identical to the housing of the carrier unit 40 in certain areas. The secondary housings 17, 17', 17'' and the primary housing 27 are movable relative to each other.

[0065] For the measuring unit 10, 10', 10'' positioned at the measuring location 15, the second machine tool 4 is adapted to position the secondary housing 17, 17', 17'' of the measuring unit 10, 10', 10'' positioned at the measuring location 15 at a transmission distance 25 from the primary housing 27. Preferably, the transmission distance 25 is less than or equal to 10 mm. Preferably, the transmission distance 25 between the secondary housing 17, 17', 17'' of the measuring unit 10, 10', 10'' positioned at the measuring location 15 and the primary housing 27 is equal to the range of the electromagnetic alternating field EW.

[0066] Third embodiment In a third embodiment according to Fig. 6, the measuring chain 1 is a component of a third machine tool 5, such as an industrial robot, an industrial robot with exchangeable heads. A detail of the third machine tool 5 is shown in Fig. 7. Preferably, the third machine tool 5 is an industrial robot, comprising a manipulator 50 and a plurality of exchangeable heads 51, 51', 51''. Each of the plurality of exchangeable heads 51, 51', 51'' is exchangeably attached to the manipulator 50. Preferably, the exchangeable heads 51, 51', 51'' are attached to the manipulator 50 by coupling means 52, 52', 52'', such as connectors, medium couplings, etc. Preferably, the exchangeable heads 51, 51', 51'' on the manipulator 50 can be exchanged within a set-up time of 500 ms. The manipulator 50, the exchangeable heads 51, 51', 51'' and the coupling means 52, 52', 52'' are made of mechanically resistant materials, such as steel, tool steel, etc.

[0067] Each of the multiple interchangeable heads 51, 51', 51'' accommodates a tool 53, 53', 53''. Referring to FIG. 6, for example, three interchangeable heads 51, 51', 51'' are shown having three tools 53, 53', 53''. The three interchangeable heads 51, 51', 51'' and the three tools 53, 53', 53'' include a first interchangeable head 51 accommodating a first tool 53, a second interchangeable head 51' accommodating a second tool 53', and a third interchangeable head 51'' accommodating a third tool 53''.

[0068] The first tool 53 is embodied as a parallel gripper with two gripping arms 53.1, 53.2 between which a gripping force can be exerted. The gripping force is the measurement variable MG.

[0069] The second tool 53' is embodied as a magnetic gripper comprising two magnets 53.1', 53.2' between which a magnetic attraction force can be exerted, the magnetic attraction force being the measurement variable MG.

[0070] The third tool 53''' is embodied as a suction gripper comprising a vacuum pump 53.1''' capable of generating a vacuum and a suction device 53.2''' capable of exerting a suction force as a result of the vacuum. The suction force is the measurement variable MG.

[0071] The third machine tool 5 is adapted to handle the workpiece 2 in a process step. The handling may be any type of handling, holding, transporting, processing etc. In the example according to figures 6 and 7, the first tool 53 grips the egg-shaped workpiece 2 by means of gripping arms 53.1, 53.2. For this purpose, the first tool 53 exerts a gripping force on the workpiece 2 acting between the gripping arms 53.1, 53.2. Due to this gripping force the workpiece 2 is held by the first tool 53 and can be handled.

[0072] The measurement units 10, 10', 10'' are arranged on each of a number of exchangeable heads 51, 51', 51''. Referring to FIG. 6, for example, three exchangeable heads 51, 51', 51'' and three measurement units 10, 10', 10'' are shown. The three measurement units 10, 10', 10'' comprise a first measurement unit 10 associated with a first exchangeable head 51, a second measurement unit 10' associated with a second exchangeable head 51'', and a third measurement unit 10'' associated with a third exchangeable head 51''.

[0073] Thus, according to Figures 6 and 7, the first measuring unit 10 is positioned at the measuring position 15 and the first sensor 11 of the first measuring unit 10 detects the gripping force acting on the first tool 53 as measurement variable MG.

[0074] According to FIG. 7, the first exchangeable head 51 comprises a recess 35. The first sensor 11 of the first measuring unit 10 associated with the first exchangeable head 51 is arranged in the recess 35. Preferably, the recess 35 is located inside the first exchangeable head 51 and the first sensor 11 is completely accommodated in the recess 35. The recess 35 protects the first sensor 11 from harmful external conditions such as dirt, coolant, electromagnetic radiation, etc. The first exchangeable head 51 comprises a feed-through which guides the signal cable 14 from the recess 35 to the outside of the exchangeable head 51. The feed-through is waterproof.

[0075] Preferably, the first secondary housing 17 is disposed on the first replaceable head 51. The first secondary housing 17 is fastened to the first replaceable head 51 by fastening means such as screws, bolts, etc. (not shown). The first secondary housing 17 is disposed at a spatial distance from the first sensor 11. Preferably, the first secondary housing 17 is disposed at a certain spatial distance of 10 cm or less from the first sensor 11.

[0076] The sensors 11, 11', 11'' and secondary housings 17, 17', 17'' are in fact interchangeably fixed to the manipulator 50 by tool heads 51, 51', 51'', and are therefore movably arranged on the third machine tool 5, whereas the primary housing 27 is fixedly arranged on the third machine tool 5. Preferably, the primary housing 27 is held on the manipulator 50 by retaining means such as screws, bolts or the like, not shown. The secondary housings 17, 17', 17'' and primary housing 27 are movable relative to each other.

[0077] For the measuring unit 10, 10', 10'' positioned at the measuring location 15, the third machine tool 5 is adapted to position the secondary housing 17, 17', 17'' of the measuring unit 10, 10', 10'' positioned at the measuring location 15 at a transmission distance 25 from the primary housing 27. Preferably, the transmission distance 25 is less than or equal to 10 mm. Preferably, the transmission distance 25 between the secondary housing 17, 17', 17'' of the measuring unit 10, 10', 10'' positioned at the measuring location 15 and the primary housing 27 is equal to the range of the electromagnetic alternating field EW. [Explanation of symbols]

[0078] 1 Measuring chain 2, 2', 2'' workpiece 3. The first machine tool 4. The second machine tool 5. The third machine tool 10, 10', 10'' measurement units 11, 11', 11'' Sensor 12, 12', 12'' Converter Unit 13, 13', 13'' Secondary Antenna 14, 14', 14'' measurement signal cable 15 Measurement position 16, 16', 16'' Preloading means 17, 17', 17'' Secondary Housing 18, 18', 18'' retention means 19, 19', 19'' Primary internal space 20 Evaluation Units 23 Primary Antenna 24 Measurement data line 25 Transmission distance 27 Primary Housing 29 Primary internal space 30 Turret 31, 31', 31'' Tool holder 32, 32', 32'' Mounting means 33, 33', 33'' tools 34, 34', 34'' Clamping means 35, 35', 35'' recess 40 Carrier Unit 41, 41', 41'' Clamp Unit 42, 42', 42'' Clamping means 43 Tools 44, 44', 44'' Clamping means 45, 45', 45'' recess 46 Clamp Module 50 Manipulator 51, 51', 51'' interchangeable heads 52, 52', 52'' coupling means 53, 53', 53'' Tools 53.1, 53.2 Grasping arm 53.1', 53.2' Magnet 53.1'' Vacuum Pump 53.2'' Suction device I Positioning II Automatic join III Automatic generation IV Automatic conversion V Automatic transmission BT operation preparation time D12 Converter unit specific data ED unit data EW electromagnetic exchange field ID Identification Number KD Calibration Data MG Measurement Variables MD measurement data MS measurement signal SD serial number data SR transmission speed Z Longitudinal Axis

Claims

1. A machine tool (3, 4, 5) comprising a plurality of measuring units (10, 10', 10'') and an evaluation unit (20), A procedure for measuring a measurement variable (MG) in a process step of a manufacturing process, wherein each of said measurement units (10, 10', 10'') comprises a sensor (11, 11', 11''), a transducer unit (12, 12', 12'') and a secondary antenna (13, 13', 13''), and said evaluation unit (20) comprises a primary antenna (23), the machine tool (3) is adapted to machine a workpiece (2) by means of a plurality of tools (33, 33', 33'') in a plurality of process steps in chronological order, for which the tools (33, 33', 33'') are positioned on said workpiece (2) in each process step, a measuring unit (10, 10', 10'') being associated with each tool (33, 33', 33'', or or the machine tool (4) is adapted to machine a plurality of workpieces (2, 2', 2'') by means of a tool (43) in chronological order in a process step, whereby each workpiece (2, 2', 2'') is positioned in chronological order on said tool (43) a measuring unit (10, 10', 10'') is associated with each workpiece (2, 2', 2''); or the machine tool (5) is adapted to handle a workpiece (2) in a process step by one of a plurality of tools (53, 53', 53''), for which purpose one of said tools (53, 53', 53'') is positioned on the workpiece (2) and a measuring unit (10, 10', 10'') is associated with each tool (53, 53', 53'', The method further comprising the steps of: (I) positioning a tool (33, 33', 33'', 53, 53', 53'') on said workpiece (2) or a workpiece (2, 2', 2'') on said tool (43), wherein said measuring unit (10, 10', 10'') associated with said positioned tool (33, 33', 33'', 53, 53', 53'') or said positioned workpiece (2, 2', 2'') is positioned at a measuring position (15) for measuring said measurement variable (MG); (II) automatically coupling the positioned measurement unit (10, 10', 10'') with the evaluation unit (20) by establishing a transmission connection between the secondary antenna (13, 13', 13'') and the primary antenna (23); (III) automatically generating a measurement signal (MS) under the effect of said measurement variable (MG) by said sensor (11, 11', 11'') of said positioned measuring unit (10, 10', 10''); (IV) automatically converting said measurement signals (MS) into measurement data (MD) by said converter unit (12, 12', 12'') of said positioned measurement unit (10, 10', 10''); (V) automatically transmitting said measurement data (MD) by said secondary antenna (13, 13', 13'') of said positioned measuring unit (10, 10', 10'') to said primary antenna (23); characterized in that the process step is carried out by In a machine tool (3, 4, 5) for carrying out a procedure for measuring a measurement variable (MG), Each of the measurement units (10, 10', 10'') positioned at the measurement location (15) can be coupled to the evaluation unit (20) for establishing a transmission connection between the secondary antenna (13, 13', 13'') and the primary antenna (23, 23', 23''); said primary antenna (23) generates an electromagnetic alternating current field (EW) and transmits said electromagnetic alternating current field (EW), the range of said electromagnetic alternating current field (EW) being limited such that only those measurement units (10, 10', 10'') that are completely positioned at said measurement location (15) can receive said electromagnetic alternating current field (EW); The machine tool (3, 4, 5), characterized in that as soon as and as long as the secondary antenna (13, 13', 13'') receives the electromagnetic alternating field (EW), electrical energy is supplied to the measuring unit (10, 10', 10''), and the measuring unit (10, 10', 10'') is supplied with sufficient electrical energy to operate the measuring unit (10, 10', 10'') within a readiness time (BT) of 100 ms.

2. 2. The machine tool (3, 4, 5) according to claim 1, characterized in that the secondary antenna (13, 13', 13'') establishes the transmission connection to the primary antenna (23) when the measuring unit (10, 10', 10'') is ready for operation, the secondary antenna (13, 13', 13'') transmits an identification number (ID) which unambiguously identifies the measuring unit (10, 10', 10'' to the primary antenna (23), the primary antenna (23) receives the identification number (ID) and forwards it to the evaluation unit (20), and the evaluation unit (20) identifies the measuring unit (10, 10', 10'') based on the transmitted and received identification number (ID).

3. The machine tool (3) comprises a plurality of tool holders (31, 31', 31''), each tool holder (31, 31', 31'') housing a tool (33, 33', 33''), a measuring unit (10, 10', 10'') is associated with each tool holder (31, 31', 31''), a sensor (11, 11', 11'') of the measuring unit (10, 10', 10'') associated with the tool holder (31, 31', 31'') is arranged in each tool holder (31, 31', 31'', and a measuring unit (10, 10', 10'') positioned at the measuring position (15) is arranged in a measuring position (15) of the measuring unit (10, 10', 10'').

2. The machine tool (3) according to claim 1, characterized in that for a tool (33, 33', 33"), the sensor (10, 10', 10") of the measuring unit (10, 10', 10") positioned at the measuring position (15) measures the measurement variable (MG) acting on the tool (33, 33', 33") during a process step, and the transducer unit (12, 12', 12") and the secondary antenna (13, 13', 13") of the measuring unit (10, 10', 10") are arranged away from the sensor (11, 11', 11").

4. 4. The machine tool (3) according to claim 3, characterized in that the machine tool (3) is a turret lathe comprising a turret (30) rotatable about a longitudinal axis (Z), the tool holders (31, 31', 31'') are arranged on the turret (30) and can rotate together with the turret (30) about the longitudinal axis (Z), and by rotating the turret (30) about the longitudinal axis (Z), the tools (33, 33', 33'') can be positioned on the workpiece (2) one after the other in time.

5. The machine tool (4) comprises a plurality of clamping units (41, 41', 41''), each clamping unit (41, 41', 41'') housing a workpiece (2, 2', 2''), a measuring unit (10, 10', 10'') is associated with each clamping unit (41, 41', 41''), a sensor (11, 11', 11'') of the measuring unit (10, 10', 10'') associated with the clamping unit (41, 41', 41'') is arranged in each clamping unit (41, 41', 41'') and a measuring position (15) is positioned at the measuring position (15).

2. The machine tool (4) according to claim 1, characterized in that for a constant unit (10, 10', 10''), the sensor (10, 10', 10'') of the measuring unit (10, 10', 10'') positioned at the measurement position (15) measures the measurement variable (MG) acting on the workpiece (2, 2', 2'') during a process step, and the transducer unit (12, 12', 12'') and the secondary antenna (13, 13', 13'') of the measuring unit (10, 10', 10'') are arranged at a distance from the sensor (11, 11', 11'').

6. The machine tool (4) according to claim 5, wherein the machine tool (4) is a zero-point clamping system comprising a carrier unit (40), and each of the plurality of clamping units (41, 41', 41'') is replaceably mounted on the carrier unit (40).

7. The machine tool (5) comprises a plurality of exchangeable heads (51, 51', 51''), each exchangeable head (51, 51', 51'') housing a tool (53, 53', 53''), a measuring unit (10, 10', 10'') is associated with each exchangeable head (51, 51', 51''), a sensor (11, 11', 11'') of the measuring unit (10, 10', 10'') associated with the exchangeable head (51, 51', 51'') is arranged on each exchangeable head (51, 51', 51'') and a measuring position (15) positioned at the measuring position (15) is provided.

2. The machine tool (5) according to claim 1, characterized in that for a constant unit (10, 10', 10''), the sensor (10, 10', 10'') of the measuring unit (10, 10', 10'') positioned at the measuring position (15) measures the measurement variable (MG) acting on the tool (53, 53', 53'') during a process step, and the transducer unit (12, 12', 12'') and the secondary antenna (13, 13', 13'') of the measuring unit (10, 10', 10'') are arranged at a distance from the sensor (11, 11', 11'').

8. The machine tool (5) according to claim 7, characterized in that the machine tool (5) is an industrial robot equipped with a manipulator (50), and each of the plurality of interchangeable heads (51, 51', 51'') is interchangeably attached to the manipulator (50).

9. 8. The machine tool (3, 4, 5) according to claim 3, 5 or 7, characterized in that the converter unit (12, 12', 12'') and the secondary antenna (13, 13', 13'') are arranged in a secondary antenna housing (17, 17', 17'') of the machine tool (3, 4, 5), the primary antenna (23) is arranged in a primary antenna housing (27) of the machine tool (3, 4, 5), and the secondary antenna housing (17, 17', 17'') and the primary antenna housing (27) are movable relative to each other.

10. 10. The machine tool (3, 4, 5) according to claim 9, characterized in that for a measuring unit (10, 10', 10'') positioned at the measuring position (15), the secondary antenna housing (17, 17', 17'') of the measuring unit (10, 10', 10'') positioned at the measuring position (15) is positioned at a transmission distance (25) from the primary antenna housing (27).

11. 11. The machine tool (3, 4, 5) according to claim 10, characterized in that the primary antenna (23) generates an electromagnetic alternating field (EW) and the transmission distance (25) between the secondary antenna housing (17, 17', 17'') of the measuring unit (10, 10', 10'') positioned at the measuring position (15) and the primary antenna housing (27) is equal to the range of the electromagnetic alternating field (EW).

12. 8. The machine tool (3, 4, 5) according to claim 3, 5 or 7, characterized in that the sensor (11, 11', 11'') is a piezoelectric sensor comprising a piezoelectric material, the measurement variable (MG) acting on the piezoelectric material in the form of a tensile and / or compressive load, the piezoelectric material generating a measurement signal (MS) in the form of an electric charge under the action of the measurement variable (MG), the converter unit (12, 12', 12'') comprises a charge amplifier which amplifies the electric charge of the piezoelectric sensor and converts it into a voltage, the converter unit (12, 12', 12'') digitizes the voltage into measurement data (MD), the piezoelectric sensor measures the measurement variable (MG) with a high dynamic measurement resolution of up to 35 kHz, and the secondary antenna (13, 13', 13'') transmits the measurement data (MD) to the primary antenna (23) with a transmission rate (SR) of up to 424 kbit / s.

13. The sensor (11, 11', 11'') is a piezoelectric sensor comprising a piezoelectric material, the measurement variable (MG) acting on the piezoelectric material in the form of a tensile and / or compressive load, the piezoelectric material generating a measurement signal (MS) in the form of an electric charge under the action of the measurement variable (MG), the converter unit (12, 12', 12'') comprises a charge amplifier for amplifying the electric charge of the piezoelectric sensor and converting it into a voltage, the converter unit (12, 12', 12'') digitizing the voltage into measurement data (MD), the converter unit (12, 12', 12'') converting the measurement signal (MS) into measurement data (MD) and producing unit data (ED) indicative of a unit of the digitized measurement variable (MG), 8. The machine tool (3, 4, 5) according to claim 3, wherein the converter unit (12, 12', 12'') generates calibration data of the sensor (11, 11', 11'') from a memory unit of the measuring unit (10, 10', 10''), the converter unit (12, 12', 12'') reads out serial number data (SD) of the converter unit (12, 12', 12'') from the memory unit of the measuring unit (10, 10', 10''), and the secondary antenna (13, 13', 13'') transmits the unit data (ED), the calibration data (KD) and the serial number data (SD) together with the measurement data (MD) to the primary antenna (23).

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