Machining machine with a power pickup, method for operating such a machining machine and method for calibrating the power pickup of such a machining machine

Description

Technical area

[0001] The invention relates to a metal-cutting machine with a force transducer according to the preamble of the independent claim. The invention also relates to a method for operating such a metal-cutting machine. The invention also relates to a method for calibrating the force transducer of such a metal-cutting machine. State of the art

[0002] Machining machines are well-known. Common examples of machining machines include lathes, milling machines, sawing machines, and so on. Machining machines shape a workpiece by removing material through a cutting tool. The cutting tool exerts a force. The workpiece can be made of any material, such as metal, wood, or plastic. The cutting tool is made of a hard, strong, and tough material, such as metal or ceramic. Common tools used for machining include chisels, turning tools, milling cutters, countersinks, saw blades, and so on.

[0003] During machining, the workpiece and tool move against each other. Both the workpiece and the tool are moved in a straight line or in a circular motion. The machining machine has several drive units, such as electric drive units, pneumatic drive units, etc.

[0004] For cost-effective and consistently high-quality workpiece production, it is desirable to measure the tool force. This is because the tool force and the elevated temperatures encountered during machining lead to wear on the cutting wedge. This wear changes the cutting edge geometry of the cutting wedge. A worn cutting wedge requires greater tool force to machine the workpiece, resulting in higher energy consumption for the machining machine and also reducing the surface quality and dimensional accuracy of the workpiece.

[0005] EP0433535A1 discloses an arrangement with a multi-component force transducer for measuring the tool force during the machining of a workpiece in a machine tool. The multi-component force transducer is clamped in a recess of a machine part by frictional engagement.

[0006] A disadvantage of the EP0433535A1 arrangement is that the tool force is not measured where it acts, i.e., at the cutting wedge, but rather remotely, in a machine component. There, the tool force is measured indirectly as the mechanical stress occurring in the machine component. This mechanical stress, in turn, is influenced by the dimensions and mass of the machine component. Furthermore, the multi-component force transducer is arranged in a force shunt within the machine component. In a force shunt, however, only a small portion of the mechanical stress occurring there is measured. All of this leads to a less accurate measurement of the tool force. Accuracy in measuring tool force indicates the deviation of the measured tool force from the actual tool force; the more accurately the tool force is measured, the smaller the deviation of the measured tool force from the actual tool force.

[0007] The machining of a workpiece usually takes place in a chronological sequence of production steps requiring several tools. The tools are therefore changed frequently. In each new production step, a new tool is aligned with the workpiece, and the tool and workpiece are moved relative to each other. For quick and cost-effective tool changes and alignment, the machining machine is equipped with a tool holder. The tool holder holds the tools required for the production steps. To change to a new tool and to align the new tool with the workpiece, the tool holder is moved. For this purpose, the tool holder is attached to a tool arm.It is therefore the tool arm, which is moved by a drive unit, to align a tool in the tool holder required for a manufacturing step with the workpiece and then to move the tool and workpiece relative to each other. EP0444657A1 shows a grinding robot with a six-component force transducer for measuring the tool force applied when grinding a workpiece. The grinding robot has a multi-dimensionally movable arm. The arm is moved by servo motors. A grinder is located at the end of the arm. The grinder has its own drive for grinding the workpiece. The six-component force transducer is located between the end of the arm and the grinder. JPS60172446A1 also reveals a robot for machining a workpiece. For this, the robot uses a tool attached to one end of a movable arm.To measure the contact pressure of the tool on the workpiece, a strain gauge is arranged between the end of the arm and the tool.

[0008] A first object of the present invention is to accurately measure the tool force acting during the machining of a workpiece in a machine tool using a force transducer. This object is to be achieved, in particular, for a machine tool with a tool holder that is moved by a drive unit via a tool arm. A second object of the invention is to arrange a force transducer in the machine tool in a space-saving manner for measuring the tool force acting during the machining of a workpiece. And a third object of the invention is to enable cost-effective measurement of the tool force acting during the machining of a workpiece using a force transducer. Description of the invention

[0009] At least one of these tasks is solved by the features of an independent claim.

[0010] The invention relates to a machining machine according to claim 1.

[0011] The invention is based on the finding that, for precise alignment of the required tools on the workpiece and precise movement of the required tools relative to the workpiece, the required tools are held inelastically by the tool holder, and the tool holder is inelastically attached to the tool arm. The inventors have now recognized that the inelastic mechanical transitions from the required tools, via the tool holder, to the tool arm also allow for a largely undamped force transmission of the tool force from one of the required tools into the tool arm. This is because any elastic deformation dampens the force transmission of the tool force and distorts the measurement of the tool force. It has been recognized that the arrangement of the force transducer in the main force path, spatially between an upper arm and a lower arm, enables precise measurement of the tool force.The force sensor is located inside a two-part tool arm, which saves space and is also cost-effective, as the predetermined external dimensions of a conventional tool arm are retained, and a conventional machining center does not need to be modified. Only the conventional tool arm is replaced by a tool arm according to the invention.

[0012] Further advantageous solutions to the problem are provided in the features of the dependent claims. Short description of the drawings

[0013] The invention is explained below by way of example with the aid of drawings. This shows Fig. 1 schematically shows parts of a first embodiment of a machining machine with one force transducer; Fig. 2 in exploded view parts of a second embodiment of a machining machine with two force transducers; Fig. 3 a flowchart with method steps for calibrating the at least one force transducer of the machining machine according to Fig. 1 or 2 ; and Fig. 4 schematically shows parts of an embodiment of a calibration device for carrying out the process steps according to Fig. 3 with the second embodiment of the machining machine with two force transducers according to Fig. 2 .

[0014] In principle, identical parts in the drawings are provided with the same reference numerals. Ways to implement the invention

[0015] Fig. 1 and 2show parts of two embodiments of a machining machine 1 for machining a workpiece 9. The machining machine 1 has a drive unit 10, a machine arm 11, at least one force transducer 12.1, 12.2, a tool holder 13, and several required tools 14. The machining machine 1 is arranged in an orthogonal coordinate system with three axes x, y, z; the three axes are also referred to as the transverse axis x, the horizontal axis y, and the vertical axis z.

[0016] The workpiece 9 is made of any material such as metal, wood, plastic, etc. The machining of the workpiece 9 takes place in a sequence of processing steps using several tools 14. In the first embodiment of the machining machine 1 according to Fig. 1Two tools 14.1, 14.2 are required in two processing steps. In a first production step, a first tool 14.1 is required, and in a second production step, a second tool 14.2 is required. Of course, the person skilled in the art can also use the invention for machining a workpiece with more than two tools. Thus, in the second embodiment of the cutting machine 1 according to Fig. 2 eight tools 14.1 - 14.8 are required in eight processing steps.

[0017] During the machining of workpiece 9, the required tools 14 perform a cutting motion in a transverse plane xy defined by the transverse axis x and the vertical axis z. The required tools 14 also perform a feed motion along the horizontal axis y during this machining process. In doing so, the required tools 14 exert a tool force Kw on the workpiece 9. The tool force Kw has three force components: Kwx, Kwy, and Kwz. Due to the cutting motion, the tool force Kw has a transverse thrust component Kwx in the direction of the transverse axis x and a vertical thrust component Kwz in the direction of the vertical axis z. Due to the feed motion, the tool force Kw also has a horizontal force component Kwy in the direction of the horizontal axis y.

[0018] The tool holder 13 holds the tools 14 required for the manufacturing steps. The tool holder 13 is made of mechanically resistant material such as steel, tool steel, etc. In the first embodiment of the machining machine 1 according to Fig. 1 The tool holder 13 holds two required tools 14.1, 14.2. In the second embodiment of the machining machine 1 according to Fig. 2 The tool holder 13 holds eight required tools 14.1 - 14.8.

[0019] As in the first embodiment of the machining machine 1 according to Fig. 1As shown, each required tool 14.1, 14.2 has at least one cutting wedge 14.11, 14.12 and a shank 14.21, 14.22. The cutting wedge 14.11, 14.12 is made of a hard, strong, and tough cutting material such as metal, ceramic, etc. A first required tool 14.1 has a triangular cutting wedge 14.11, a second required tool 14.2 has a rectangular cutting wedge 14.21. In the second embodiment of the machining machine 1 according to Fig. 2 Each required tool 14.1 - 14.8 has two cutting wedges and a shank. The cutting wedges are located at opposite ends of the shank.

[0020] The tool holder 13 is made of a material with a high modulus of elasticity greater than 200 GPa. This is in contrast to a conventional cast iron tool holder with a normal modulus of elasticity of 110 GPa. Due to the high modulus of elasticity, the tool holder 13 transmits the tool force Kw with twice the elasticity of the conventional tool holder.

[0021] The required tools 14 are held in the tool holder 13 by their shanks. The tool holder 13 has several holding elements and several recesses for this purpose.

[0022] In the first embodiment of the machining machine 1 according to Fig. 1A first recess 13.21 accommodates the first shaft 14.21 and a first holding means 13.11. A second recess 13.22 accommodates the second shaft 14.22 and a second holding means 13.12. The first and second holding means 13.11, 13.12 are wedge-shaped and hold the shaft 14.21, 14.22 in the recess 13.21, 13.22 according to the mechanical principle of the inclined plane with a holding force. The first recess 13.21 and the second recess 13.22 are arranged one above the other with respect to the vertical axis z.

[0023] In the second embodiment of the machining machine 1 according to Fig. 2Each of the eight recesses 13.21 - 13.28 accommodates a shank of one of the eight required tools 14.1 - 14.8 and a holding element. The holding elements are set screws and project into the recesses 13.21 - 13.28 at a right angle to the horizontal axis y. Each set screw presses against the shank of a required tool 14.1 - 14.8 and holds the required tool 14.1 - 14.8 in the recess 13.21 - 13.28 with a holding force.

[0024] The holding force of the required tools 14 in the tool holder 13 is at least one order of magnitude greater than the tool force Kw, such that the tool holder 13 holds the required tools 14 inelastically. For the purposes of the invention, the adjective "inelastic" means that any point on a required tool 14 and any point on the tool holder 13 always maintain the same distance from each other, regardless of external forces.

[0025] The tool holder 13 is attached to the tool arm 11. The tool arm 11 is made of a mechanically resistant material such as steel, tool steel, etc. The tool arm 11 has an upper arm 11.1, a lower arm 11.2, and at least one connecting element 15. The tool holder 13 is attached to the lower arm 11.2. The drive unit 10 is attached to the upper arm 11.1. The attachment can be made using any fasteners such as a screw connection, a soldered connection, a welded connection, etc.

[0026] The magnitude of the fastening force of the tool holder 13 to the forearm 11.2 and of the fastening of the drive unit 10 to the upper arm 11.1 is at least one order of magnitude greater than the magnitude of the tool force Kw, such that the tool holder 13 is inelastically fastened to the forearm 11.2 and the drive unit 10 is inelastically fastened to the upper arm 11.1.

[0027] The tool arm 11 is made of a material with a high modulus of elasticity greater than 200 GPa. This is in contrast to a conventional machine arm made of cast iron with a normal modulus of elasticity of 110 GPa. A comparatively two-fold higher modulus of elasticity makes technical sense for two reasons: First, the external dimensions of the tool arm 11 are predetermined. However, due to the arrangement of the force transducers 12.1, 12.2 inside the tool arm 11, the tool arm 11 has cavities inside for the force transducers 12.1, 12.2, and the tool arm 11 itself is therefore made of less material. However, for precise alignment of the required tools 14 on the workpiece 9 and for precise movement of the required tools 14 relative to the workpiece 9, a minimum mechanical stability of the tool arm 11 must be met. This minimum mechanical stability of the tool arm 11 is achieved by the high modulus of elasticity greater than 200 GPa. For the purposes of the invention, the terms "precise alignment" and "precise movement" mean a positional accuracy of 11 pm during alignment and movement along the three axes x, y, z.Secondly, due to its high modulus of elasticity, the tool arm 11 transmits the tool force Kw twice as inelastically as the conventional tool arm.

[0028] The upper arm 11.1 and the forearm 11.2 are separate units. For the purposes of the invention, the term "separate unit" means that the upper arm 11.1 and the forearm 11.2 are separate objects. Preferably, the upper arm 11.1 and the forearm 11.2 are mechanically connected to each other in the transverse plane xz. The upper arm 11.1 and the forearm 11.2 are mechanically connected to each other via the connecting element 15.

[0029] In the first embodiment of the machining machine 1 according to Fig. 1The connecting element 15 comprises a first connecting element 15.1. The first connecting element 15.1 is a screw connection with a draw-in screw 15.11, a bore 15.12 in the lower arm 11.2, and an internal thread 15.13 in the upper arm 11.1. The screw connection is parallel to the horizontal axis y. An external thread of the draw-in screw 15.11 extends through the bore 15.12 to the internal thread 15.13. By screwing together the external thread and internal thread 15.13, a screw head of the draw-in screw 15.11 presses the lower arm 11.2 against the upper arm 11.1.

[0030] In the second embodiment of the machining machine 1 according to Fig. 2The connecting element 15 consists of two connecting elements 15.1 and 15.2. The first connecting element 15.1 is a screw connection with a threaded insert 15.11, a bore 15.12 in the lower arm 11.2, and an internal thread 15.13 in the upper arm 11.1. The second connecting element 15.2 is a screw connection with a threaded insert 15.21, a bore 15.22 in the lower arm 11.2, and an internal thread 15.23 in the upper arm 11.1. The two connecting elements 15.1 and 15.2 are arranged parallel to each other in a horizontal plane xy defined by the transverse axis x and the horizontal axis y. The two screw connections are parallel to the horizontal axis y. An external thread of the insertion screw 15.11, 15.21 extends through the bore 15.12, 15.22 to the internal thread 15.13, 15.23. By screwing the external thread and internal thread 15.13, 15.23 together, a screw head of the insertion screw 15.11, 15.21 presses the forearm 11.2 against the upper arm 11.1.

[0031] The magnitude of the connecting force of the mechanical connection between upper arm 11.1 and lower arm 11.2 via the connecting means 15 is at least one order of magnitude greater than the magnitude of the tool force Kw, so that the upper arm 11.1 is mechanically connected inelastically to the lower arm 11.2. Of course, with knowledge of the invention, a person skilled in the art can also use a soldered connection, a welded connection, etc., instead of a screw connection.

[0032] The drive unit 10 is an electric drive unit, a pneumatic drive unit, etc. The drive unit 10 moves the machine arm 11 along the three axes x, y, and z. Of course, the skilled person can also use the invention with more than one drive unit.

[0033] In the first embodiment according to Fig. 1 The machining machine 1 has a force transducer 12.1. In the second embodiment according to Fig.2The machining machine 1 has two force transducers 12.1, 12.2. The at least one force transducer 12.1, 12.2 is spatially arranged in the connection plane 11.3 between the upper arm 11.1 and the lower arm 11.2. With knowledge of the present invention, a person skilled in the art is free to arrange as many force transducers between the upper arm and the lower arm as they wish. The use of a single force transducer is perfectly sufficient for measuring the tool force. The use of two force transducers allows for redundant measurement of the tool force; the two force transducers measure the tool force independently of each other and generate measurement signals for the measured tool force independently of each other. An arithmetic mean can be calculated from these measurement signals, which, statistically speaking, is a more accurate measurement of the tool force than with a single force transducer.

[0034] In the first embodiment of the machining machine 1 according to Fig. 1a force transducer 12.1 has a housing 12.11 made of mechanically resistant material such as steel, tool steel, etc. In the second embodiment of the cutting machine 1 according to Fig.2 a first force transducer 12.1 has a first housing 12.11 and a second force transducer 12.2 has a second housing 12.21.

[0035] In the following, details of the force transducer 12.1, 12.2 are given based on the first embodiment of the cutting machine 1 according to Fig. 1 This detailed description of the force transducer 12.1 also applies to the two force transducers 12.1, 12.2 of the second embodiment of the cutting machine 1 according to Figure 2 .

[0036] The force transducer 12.1 is hollow cylindrical with two housing end faces 12.11', 12.11‴ and a housing bore 12.11". The first housing end face 12.11' of the force transducer 12.1 is in planar contact with the lower arm 11.2, and the second housing end face 12.11''' of the force transducer 12.1 is in planar contact with the upper arm 11.1. The first housing end face 12.11' lies parallel to the transverse plane xz, and the second housing end face 12.11‴ lies in the transverse plane xz. A longitudinal axis of the housing bore 12.11" lies parallel to the horizontal axis y. The diameter of the housing bore 12.11" is dimensioned such that the insertion screw 15.11 protrudes through it.

[0037] The tool force Kw to be measured acts on the force transducer 12.1 via the housing end faces 12.11', 12.11‴. A surface of the housing end faces 12.11', 12.11‴ is at least one order of magnitude larger than a cross-sectional area of ​​the draw-in screw 15.11. A proportion of the tool force Kw measured by the force transducer 12.1 is at least 90%. The force transducer 12.1 is therefore arranged spatially between the upper arm 11.1 and the lower arm 11.2 in the main force connection. The force transducer 12.1 thus measures the tool force Kw with very high sensitivity. In the sense of the invention, the sensitivity is a ratio of the analog measurement signals Sa generated by the force transducer 12 under the effect of the tool force Kw and the tool force Kw acting on the force transducer 12.1.

[0038] The force transducer 12.1 is a piezoelectric force transducer with piezoelectric material 12.12 made of a single crystal such as quartz (SiO 2 ), calcium gallo-germanate (Ca 3 Ga 2 Ge 4 O 14 or CGG), langasite (La 3 Ga 5 SiO 14 or LGS), tourmaline, gallium orthophosphate, etc. and of piezoceramic such as lead zirconate titanate (Pb[Zr x Ti 1-x ]O 3 , 0 ≤ x ≤ 1), etc.

[0039] The piezoelectric material 12.12 is hollow-cylindrical, with end faces parallel to the housing end faces 12.11', 12.11‴ and thus parallel to the transverse plane xz. The tool force Kw to be measured thus acts on the end faces of the piezoelectric material 12.12. The piezoelectric material 12.12 is oriented such that it has the greatest sensitivity to the tool force Kw to be measured on the end faces on which the tool force Kw acts. At the highest sensitivity, the piezoelectric material 12.12 generates the greatest number of electrical polarization charges. Piezoelectric material 12.12 made from a single crystal is therefore cut into hollow cylinders oriented such that it generates the greatest number of electrical polarization charges for a tool force Kw acting on the end faces. Piezoelectric material 12.12 made of piezoceramic is therefore polarized in an electric field and brought into a hollow cylindrical shape by mechanical pressing, so that it generates a maximum number of electrical polarization charges for a tool force Kw acting on the end faces.

[0040] The force transducer 12.1 measures the three tool force components Kwx, Kwy, Kwz of the tool force Kw. For this purpose, the force transducer 12.1 has three piezoelectric elements 12.12', 12.12", 12.12‴ made of piezoelectric material 12.12. A first piezoelectric element 12.12' is oriented such that it generates electrical polarization charges with the highest sensitivity for the shear force component Kx in the direction of the transverse axis x. In this example, a second piezoelectric element 12.12" is oriented such that it generates electrical polarization charges with the highest sensitivity for the shear force component Kz in the direction of the vertical axis z. And in this example, a third piezoelectric element 12.12‴ is oriented such that it generates electrical polarization charges with the highest sensitivity for the normal force component Ky in the direction of the horizontal axis y.

[0041] The electrical polarization charges must be removed from the end faces. The force transducer 12.1 has electrodes 12.13 for this purpose. The electrodes 12.13 are made of electrically conductive material 12.3 such as copper, gold, etc., and are hollow cylindrical. Each electrode 12.13 is arranged directly on one of the end faces of the piezoelectric elements 12.12', 12.12", 12.12‴. The force transducer 12.1 thus has a total of six electrodes 12.13. Three signal electrodes 12.13', 12.13'', 12.13''' detect electrical polarization charges as analog measurement signals Sa from the first end faces, and three ground electrodes 12.13ʺʺ detect electrical polarization charges from the second end faces. The analog measurement signals Sa are proportional to the magnitude of the tool force Kw. The three signal electrodes 12.13', 12.13", 12.13‴ are electrically insulated from the housing 12.11, and the three ground electrodes 12.13ʺʺ are electrically connected to the housing 12.11.The ground electrodes 12.11 are connected and are at the electrical ground potential of the housing 12.11. Because the ground electrodes 12.13ʺʺ are all at the same electrical ground potential, they have the same reference symbol. The three signal electrodes 12.13', 12.13", 12.13‴ are electrically connected by a signal cable 12.14. The signal cable 12.14 carries the analog measurement signals Sa from the signal electrodes 12.13', 12.13", 12.13‴ to an evaluation unit 16.

[0042] For each production step with a required tool 14, the force transducer 12.1 generates analog measurement signals Sa 1 . The analog measurement signals Sa include analog transverse thrust signals Sa 1 ' for a transverse thrust component Kwx in the direction of the transverse axis x, analog vertical thrust signals Sa 1 " for a vertical thrust component Kwz in the direction of the vertical axis z, and analog horizontal force signals Sa 1 ‴ for a horizontal force component Kwy in the direction of the horizontal axis y. Each production step lasts 1 to 100 seconds. The force transducer 12.1 generates the analog measurement signals Sa 1 with a temporal resolution in a frequency range from 1 kHz to 50 kHz.

[0043] In order for the electrodes 12.13 to remove all generated electrical polarization charges from the end faces of the piezo elements 12.12', 12.12", 12.12‴, and to ensure that no electrical polarization charges remain on the end faces of the piezo elements 12.12', 12.12'', 12.12''' and distort the measurement of the tool force Kw, the electrodes 12.13 are mechanically preloaded against the end faces of the piezo elements 12.12', 12.12", 12.12‴. The mechanical preload of the force transducer 12.1 closes micropores between the electrodes 12.13 and the end faces of the piezo elements 12.12', 12.12", 12.12'''. The mechanical preload of the force transducer 12.1 is achieved by the connecting element 15. The connecting element 15.1 is formed by the screw connection of the draw-in screw 15.11 through the bore 15.12 in the lower arm 11.2 and through the housing bore 12.11" in the housing 12.1 with the internal thread 15.13 in the upper arm 11.1.By tightening the external thread and internal thread 15.13, the screw head of the insertion screw 15.11 presses the lower arm 11.2 against the upper arm 11.1 and mechanically pre-tensions the electrodes 12.13 against the end faces of the piezoelectric elements 12.12', 12.12", 12.12'''. With the mechanical connection of the upper arm 11.1 to the lower arm 11.2, the connecting element 15 also mechanically pre-tensions the force transducer 12.1. The mechanical pre-tension corresponds to the connection force of the mechanical connection between the upper arm 11.1 and the lower arm 11.2.

[0044] The evaluation unit 16 includes at least one converter unit 16.1, at least one computer 16.2, at least one input unit 16.3 and at least one output unit 16.4.

[0045] The force sensor 12.1 is electrically connected to the converter unit 16.2 via the signal cable 12.14. The converter unit 16.1 converts analog measurement signals Sa 1 derived from the signal electrodes 12.13', 12.13", 12.13‴ via the signal cable 12.14 into digital measurement signals Sd 1. For each manufacturing step with a required tool 14, the converter unit 16.1 converts analog measurement signals Sa 1 into digital measurement signals Sd 1. The converter unit 16.1 converts analog lateral thrust signals Sa 1 ' into digital lateral thrust signals Sd 1 ', it converts analog vertical thrust signals Sa 1 " into digital vertical thrust signals Sd 1 ʺ, and it converts analog horizontal force signals Sa 1 ‴ into digital horizontal force signals Sd 1 ‴. The digital measurement signals Sd 1 include the digital transverse thrust signals Sd 1 ', the digital vertical thrust signals Sd 1 " and the digital horizontal force signals Sd 1 ‴.

[0046] Computer 16.2 has at least one data processor and at least one data memory. Computer 16.2 can be operated via input unit 16.3. Input unit 16.3 can be a keyboard for entering control commands. Within the meaning of the invention, the verb "operate" means that computer 16.2 is started, controlled, and shut down by a person using control commands via input unit 16.3. Computer 16.2 reads in the digital measurement signals Sd 1. Computer 16.2 displays read-in digital measurement signals Sd 1 on output unit 16.4. Output unit 16.4 can be a screen for graphically displaying the evaluated digital measurement signals. When evaluating the digital measurement signals Sd 1, computer 16.2 reads reference signals R and calibration factors α i . The reference signals R are specific to the material of the workpiece 9 and to the cutting material of the required tool 14.The properties of the material and the cutting tool material, such as strength, toughness, and hardness, are crucial. For each material of the workpiece 9 and each cutting tool material of the required tool 14, reference signals R are stored in the data memory of the computer 16.2 and can be read from the data memory by the computer 16.2. For each required tool 14, a reference signal R comprises a transverse thrust reference signal R', a vertical thrust reference signal R", and a horizontal force reference signal R‴.

[0047] The tool force Kw measured by the force transducer 12.1, 12.2 is also specific to a position i of the required tool 14 relative to the force transducer 12.1, 12.2. In the second embodiment according to Fig. 2the tool arm 11 of the machining machine 1 has eight recesses 13.21 - 13.28 in eight different positions i, i = 1 ... 8 and the machining machine 1 has two force transducers 12.1, 12.2. Each of the eight recesses 13.21 - 13.28 is at different distances from each of the two force transducers 12.1, 12.2. The different distances from each of the recesses 13.21 - 13.28 to each of the two force transducers 12.1, 12.2 result in each required tool 14 being arranged in a specific position i relative to the force transducer 12.1, 12.2, so that the force flow of the tool force Kw is also specific to the position i of the required tool 14 relative to each of the two force transducers 12.1, 12.2.

[0048] Therefore, for each position i, calibration factors α i are stored in the data memory of computer 16.2 and can be read from the data memory by computer 16.2. Each calibration factor α i comprises a transverse thrust calibration factor α i ', a vertical thrust calibration factor α i ", and a horizontal force calibration factor α i ‴.

[0049] For evaluation, the computer 16.2 calibrates digital measurement signals Sd 1 of a required tool 14 by multiplying them by a calibration factor α i of the position i of the required tool 14 relative to the force transducer 12.1, 12.2. For each process step, the computer 16.2 calculates a difference Δ between the calibrated digital measurement signal Sd 1 and the read-out reference signal R for the material of the workpiece 9 and the cutting material of the required tool 14. α i * Sd 1 − R = Δ ≤ T = 10 % * R

[0050] The computer 16.2's data memory contains at least one predefined tolerance value T, which is read out for each manufacturing step. Each predefined tolerance value T comprises a predefined transverse shear tolerance value T', a predefined vertical shear tolerance value T'', and a predefined horizontal force tolerance value T‴.

[0051] For each manufacturing step, the difference Δ is compared with the predefined tolerance value T. If the difference Δ is less than or equal to the predefined tolerance value T, the required tool 14 is not worn and is reused; if the difference Δ is greater than the predefined tolerance value T, the required tool (14) is worn and is replaced. As a first approximation, the predefined tolerance value T is equal to 10% of the reference signals R.

[0052] The evaluation by the computer 16.2 is also carried out for digital measurement signals Sd 1 ' , Sd 1 " , Sd 1 ‴ of the tool force components Kwx, Kwy, Kwz of the tool force Kw.

[0053] For each process step, the computer 16.2 calculates a cross-thrust difference Δ' between the calibrated digital cross-thrust measurement signal Sd 1 ' and the read-out cross-thrust reference signal R' for the material of the workpiece 9 and the cutting material of the required tool 14. If the cross-thrust difference Δ' is less than or equal to the predefined cross-thrust tolerance value T', the required tool 14 is not closed and is reused, and if the cross-thrust difference Δ' is greater than the predefined cross-thrust tolerance value T', the required tool (14) is closed and is replaced. As a first approximation, the predefined cross-thrust tolerance value T' is equal to 10% of the cross-thrust reference signal R'. α i ′ * Sd 1 ′ − R ′ = Δ ′ ≤ T ′ = 10 % * R ′

[0054] For each process step, the computer 16.2 calculates a vertical shear difference Δ" between the calibrated digital vertical shear measurement signal Sd 1 " ' and the read-out vertical shear reference signal R" for the workpiece material 9 and the cutting material of the required tool 14. If the vertical shear difference Δ" is less than or equal to the predefined vertical shear tolerance T'', the required tool 14 is not worn and continues to be used; if the vertical shear difference Δ" is greater than the predefined vertical shear tolerance T'', the required tool (14) is worn and is replaced. As a first approximation, the predefined vertical shear tolerance T" is equal to 10% of the vertical shear reference signal R". α i ′ ​ ′ * Sd 1 ′ ​ ′ − R ′ ​ ′ = Δ ′ ​ ′ ≤ T ′ ​ ′ = 10 % * R ′ ​ ′

[0055] For each process step, the computer 16.2 calculates a horizontal force difference Δ‴ between the calibrated digital horizontal force measurement signal Sd 1 ‴ and the read horizontal force reference signal R‴ for the workpiece material 9 and the cutting material of the required tool 14. If the horizontal force difference Δ‴ is less than or equal to the predefined horizontal force tolerance T‴, the required tool 14 is not worn and continues to be used; if the horizontal force difference Δ‴ is greater than the predefined horizontal force tolerance T‴, the required tool (14) is worn and is replaced. As a first approximation, the predefined horizontal force tolerance T‴ is equal to 10% of the horizontal force reference signal R‴. α i ′ ​ ′ ​ ′ * Sd 1 ′ ​ ′ ​ ′ − R ′ ​ ′ ​ ′ = Δ ′ ​ ′ ​ ′ ≤ T ′ ​ ′ ​ ′ = 10 % * R ′ ​ ′ ​ ′ Analogously, when using two force transducers, as in the second embodiment of the cutting machine according to Fig. 2The first and second analog measurement signals are generated by the two force transducers, and these signals are converted into first and second digital measurement signals by the converter unit. For each required tool, the computer calculates a sum of the first and second digital measurement signals, multiplies this sum by a calibration factor for a specific position of the required tool, and then subtracts a reference signal representing the pairing of workpiece material and cutting tool material from this calibrated sum.

[0056] Fig. 3 Figure 1 shows a flowchart with process steps 210-260 for calibrating the at least one force transducer 12.1, 12.2 of the machining machine 1 of the two embodiments according to Figure 2. Fig. 1 or 2 . Fig. 4shows parts of an embodiment of a calibration device 2 for carrying out the process steps according to Fig. 3 with the second embodiment of the machining machine 1 according to Fig. 2 .

[0057] The calibration device 2 has a calibration contact 21, a calibration force transducer 21, a calibration drive unit 20 and an evaluation unit 26.

[0058] In a first process step 210, a machine arm 11 is provided with a required tool 14 and with at least one force transducer 12.1, 12.2.

[0059] In a further process step 220, the force transducer 12.1, 12.2 is contacted with the evaluation unit 26. The evaluation unit 26 has at least one transducer unit 26.1, at least one computer 26.2, at least one input unit 26.3 and at least one output unit 26.4.

[0060] In the embodiment of the calibration device 2 according to Fig. 4Two force transducers 12.1, 12.2 are electrically connected to the converter unit 26.2 via signal cables 12.14, 12.24.

[0061] In a further process step 230, a calibration force Kk is applied to a required tool 14 by the calibration device 2.

[0062] The calibration device 2 comprises a calibration drive unit 20, a calibration contact 21 and a calibration force transducer 22.

[0063] The calibration drive unit 20 is an electric drive unit, a pneumatic drive unit, etc. The calibration drive unit 20 moves the calibration contact 21 and the calibration force transducer 22 along the three axes x, y, and z. The calibration drive unit 20 precisely aligns the calibration contact 21 with the required tools 14 in positions i in the tool holder 13 and applies the calibration force Kk to the required tool 14. The calibration force Kk has three calibration force components Kkx, Kky, ​​and Kkz. The calibration force Kk has a transverse thrust calibration component Kkx in the direction of the transverse axis x, a vertical thrust calibration component Kkz in the direction of the vertical axis y, and a horizontal force calibration component Kkz in the direction of the horizontal axis z.

[0064] In the embodiment of the calibration device 2 according to Fig. 4The calibration contact 22 is finger-shaped and has a tip for applying the calibration force Kk. The calibration contact 22 is made of a mechanically resistant material such as steel, tool steel, etc. The calibration contact 22 is made of a material with a high modulus of elasticity greater than 200 GPa. Due to this high modulus of elasticity, the calibration contact 22 transmits the calibration force Kk more inelastically than a calibration contact made of a material with a lower modulus of elasticity.

[0065] The calibration force transducer 22 measures the three calibration force components Kkx, Kky, ​​Kkz of the calibration force Kk. The calibration force transducer 22 can operate according to any measuring principle. The calibration requirement is that the calibration force transducer 22 measures the calibration force components Kkx, Kky, ​​Kkz of the calibration force Kk with an accuracy at least one order of magnitude greater than that of at least one force transducer 12.1 and 12.2. The calibration force transducer 22 is electrically connected to the converter unit 26.2 via a calibration signal cable 22.14.

[0066] In a further process step 240, calibration force components Kkx, Kky, ​​Kkz are measured by the force transducer 12.1, 12.2 and by the calibration force transducer 22 of the calibration device 2.

[0067] The first force transducer 12.1 generates the first analog measurement signals Sa 1. The first analog measurement signals Sa 1 include the first analog transverse thrust signals Sa 1 ' for a transverse thrust calibration component Kkx in the direction of the transverse axis x, the first analog vertical thrust signals Sa 1 " for a vertical thrust calibration component Kkz in the direction of the vertical axis z, and the first analog horizontal force signals Sa 1 ‴ for a horizontal force calibration component Kky in the direction of the horizontal axis y.

[0068] The second force transducer 12.2 generates second analog measurement signals Sa 2 . The second analog measurement signals Sa 2 comprise second analog transverse thrust signals Sa 2 ' for a transverse thrust calibration component Kkx in the direction of the transverse axis x, second analog vertical thrust signals Sa 2 '' for a vertical thrust calibration component Kkz in the direction of the vertical axis z and second analog horizontal force signals Sa 2 ‴ for a horizontal force calibration component Kky in the direction of the horizontal axis y.

[0069] The calibration force transducer 22 generates analog calibration signals Ka. The calibration signals Ka include analog transverse thrust calibration signals Ka' for a transverse thrust calibration component Kkx in the direction of the transverse axis x, analog vertical thrust calibration signals Ka" for a vertical thrust calibration component Kkz in the direction of the vertical axis z, and analog horizontal force calibration signals Ka‴ for a horizontal force calibration component Kky in the direction of the horizontal axis y.

[0070] In a further process step 250, measurement signals Sa of the force transducer 12.1, 12.2 and calibration signals Ka of the calibration force transducer 22 are derived to the evaluation unit 26.

[0071] In the embodiment of the calibration device 2 according to Fig. 4 The converter unit 26.1 converts analog measurement signals Sa 1 , Sa 2 derived from the signal electrodes via the signal cables 12.14, 12.24 of the two force transducers 12.1, 12.2 into digital measurement signals Sd 1 , Sd 2 .

[0072] The converter unit 26.1 converts first analog transverse thrust signals Sa 1 ' into first digital transverse thrust signals Sd 1 ', it converts first analog vertical thrust signals Sa 1 " into first digital vertical thrust signals Sd 1 ", and it converts first analog horizontal force signals Sa 1 ‴ into first digital horizontal force signals Sd 1 ‴. The first digital measurement signals Sd 1 comprise the first digital transverse thrust signals Sd 1 ', the first digital vertical thrust signals Sd 1 ", and the first digital horizontal force signals Sd 1 ‴.

[0073] The converter unit 26.1 converts second analog transverse thrust signals Sa 2 ' into second digital transverse thrust signals Sd 2 ', it converts second analog vertical thrust signals Sa 2 " into second digital vertical thrust signals Sd 2 ", and it converts second analog horizontal force signals Sa 2 ‴ into second digital horizontal force signals Sd 2 ‴. The second digital measurement signals Sd 2 comprise the second digital transverse thrust signals Sd 2 ', the second digital vertical thrust signals Sd 2 " and the second digital horizontal force signals Sd 2 ‴.

[0074] The converter unit 26.1 converts analog calibration signals Ka derived from the calibration force transducer 22 via the signal cable 22.14 into digital calibration signals Kd.

[0075] The converter unit 26.1 converts analog transverse thrust calibration signals Ka' into digital transverse thrust calibration signals Sd', it converts analog vertical thrust calibration signals Ka" into digital vertical thrust calibration signals Kd", and it converts analog horizontal force calibration signals Ka‴ into digital horizontal force calibration signals Kd‴. The digital calibrator signals Kd include the digital transverse thrust calibration signals Kd', the digital vertical thrust calibration signals Kd'', and the digital horizontal force calibration signals Kd‴.

[0076] In a further method step 260, the derived measurement signals Sa 1 and the derived calibration signals Ka are compared in the evaluation unit 26.

[0077] The computer 26.2 comprises at least one data processor and at least one data memory. The computer 26.2 can be operated via the input unit 26.3. The input unit 26.3 can be a keyboard for entering control commands. For the purposes of the invention, the verb "operate" means that the computer 26.2 is started, controlled, and switched off by a person via the input unit 26.3 using control commands. The computer 26.2 reads the digital measurement signals Sd1 and Sd2 along with the digital calibration signals Kd. The computer 26.2 displays the calibrated digital measurement signals Sd1 and Sd2 and the digital calibration signals Kd on the output unit 26.4. The output unit 26.4 can be a screen for the graphical display of the evaluated digital measurement signals.

[0078] The computer 26.2 compares digital measurement signals Sd1 and Sd2 with digital calibration signals Kd. The comparison is specific to a position i of a required tool 14. The calibration contact 22 exerts a calibration force Kk on a third required tool 14.3 in a third recess 13.23. The third recess 13.23 is the third position i = 3, and the required tool 14.3 is located in the third position i = 3.

[0079] When adjusting the embodiment of the calibration device 2 according to Fig. 4 The computer 26.2 calculates a layer-specific sum (Sd 1 + Sd 2 ) i of the first and second digital measurement signals Sd 1 , Sd 2 and compares it layer-specifically with the digital calibration signal Kd i . The result of this comparison is a layer-specific calibration factor α i . α i * Sd 1 + Sd 2 i = Kd i i = 1 If the layer-specific sum (Sd1 + Sd2) i is identical to the digital calibration signal Kd i, the layer-specific calibration factor α i = 1.00. Typically, the layer-specific calibration factor α i varies in a range from 0.85 to 1.15.

[0080] By analogy, when using a single force transducer, as in the first embodiment of the machining machine according to Fig. 1 Analog measurement signals are generated by the force transducer and converted into digital signals by the converter unit. The computer then compares these digital signals with digital calibration signals, specifying the position of each signal. When using only one force transducer, only the digital signals from that single transducer are available, and therefore no position-specific sum of digital signals from two force transducers is generated.

[0081] During the calibration process, the computer 26.2 calculates a position-specific sum (Sd 1 ' + Sd 2 ') i of the digital transverse thrust signals Sd 1 ', Sd 2 ' and compares it with the position-specific digital transverse thrust calibration signal Kd i '. One result of the calibration is a transverse thrust calibration factor α i '. α i ′ * Sd 1 ′ + Sd 2 ′ i = Kd i ′ i = 1

[0082] During the alignment process, the computer 26.2 calculates a position-specific sum (Sd i " + Sd 2 ") i of the digital vertical thrust signals Sd 1 ", Sd 2 " and compares it with the position-specific digital vertical thrust calibration signal Kd i ". One result of the alignment is a vertical thrust calibration factor α i ". α i ′ ​ ′ * Sd 1 ′ ​ ′ + Sd 2 ′ ​ ′ i = Kd i ′ ​ ′ i = 1

[0083] During the calibration process, the computer 26.2 calculates a position-specific sum (Sd 1 ‴ ' + Sd 2 ‴) i of the digital horizontal force signals Sd 1 ‴, Sd 2 ‴ and compares it with the position-specific digital horizontal force calibration signal Kd i ‴. One result of the calibration is a horizontal force calibration factor α i ‴. α i ′ ​ ′ ​ ′ * Sd 1 ′ ​ ′ ​ ′ + Sd 2 ′ ​ ′ ​ ′ i = Kd i ′ ​ ′ ​ ′ i = 1

[0084] The calibration factor α i can be stored in the data memory of the computer 16 of the evaluation unit 16. Each transverse thrust calibration factor α i ', each vertical thrust calibration factor α i " ' and each horizontal force calibration factor α i ‴ can also be stored in the data memory of the computer 16 of the evaluation unit 16. List of reference symbols

[0085] 1 Machining machine 2 Calibration device 9 Workpiece 10 Drive unit 11 Machine arm 11.1 Upper arm 11.2 Lower arm 12.1, 12.2 Force transducer 12.11, 12.12 Housing 12.11', 12.11‴ Housing end face 12.11'' Housing bore 12.12 Piezoelectric material 12.12' - 12.12‴ Piezoelectric element 12.13 Electrically conductive material 12.13' - 12.13‴ Signal electrode 12.3ʺʺ Ground electrode 12.14, 12.24 Signal cable 13 Tool holder 13.11, 13.12 Holding device 13.21 - 13.28 Recess 14, 14.1 - 14.8 Required tool 14.11, 14.12 Cutting wedge 14.21, 14.22 Shank 15, 15.1, 15.2 Fastener 15.11, 15.21 Draw-in screw 15.12, 15.22 Bore 15.13, 15.23 Internal thread 16, 26 Evaluation unit 16.1, 26.1 Converter unit 16.2, 26.2 Computer 16.3, 26.3 Input unit 16.4,26.4 Output unit 20 Calibration drive unit 21 Calibration contact 22 Calibration force transducer 22.14 Calibration signal cable 210 - 260 Process steps α Calibration factor α' Transverse thrust calibration factor α" Vertical thrust calibration factor α‴ Horizontal force calibration factor Δ Difference Δ' Transverse thrust difference Δ" Vertical thrust difference Δ‴ Horizontal force difference i Position Kw Tool force Kwx, Kwy, Kwz Tool force component Kk Calibration force Kkx, Kky, ​​Kkz Calibration force component Sa 1 , Sa 2 Analog measurement signal Sa 1 ', Sa 2 ' Analog transverse thrust signal Sa 1 " , Sa 2 " Analog vertical thrust signal Sa 1 ‴, Sa 2 "analog horizontal force signal Sd 1 , Sd 2 digital measurement signal Sd 1 ', Sd 2 'digital transverse thrust signal Sd 1 " , Sd 2 "digital vertical thrust signal Sd 1 ‴,Sd 2 ‴digital horizontal force signal RReference signal R'Transverse thrust reference signal R''Vertical thrust reference signal R‴Horizontal force reference signal KaAnalog calibration signal Ka'analog transverse thrust calibration signal Ka"analog vertical thrust calibration signal Ka‴analog horizontal force calibration signal Kddigital calibration signal Kd'digital transverse thrust calibration signal Kd"digital vertical thrust calibration signal Kd‴digital horizontal force calibration signal TPredefined tolerance size T'Predefined transverse thrust tolerance size T"Predefined vertical thrust tolerance size T‴Predefined horizontal force tolerance size xTransverse axis yHorizontal axis zVertical axis xyTransverse plane,

Claims

1. A cutting machine (1) for chip-removing machining of a workpiece (9), said chip-removing machining being performed in a chronological sequence of manufacturing steps by using a plurality of required tools (14.1 - 14.8); comprising a tool holder (13) for simultaneously holding said required tools (14.1 - 14.8); comprising a tool arm (11) for connecting said tool holder (13) with a drive unit (10); and which drive unit (10) moves the tool arm (11), by which movement of the tool arm (11) one of the required tools (14) can be aligned with a workpiece (9) in each manufacturing step, wherein said tool arm (11) comprises an upper arm (11.1) and a lower arm (11.2), wherein the upper arm (11.1) and the lower arm (11.2) are separate units and are mechanically connected to one another by a connecting means (15); wherein the upper arm (11.1) is secured to the drive unit (10); wherein the lower arm (11.2) is secured to the tool holder (13); wherein at least one force transducer (12. 1, 12.2) is arranged in a position between the upper arm (11.1) and the lower arm (11.2), wherein during chip-removing machining of a workpiece (9) said force transducer (12.1, 12.2) is capable of measuring a tool force (Kw) exerted by any of the required tools (14.1 - 14.8) in the main flow of forces; and wherein said connecting means (15) with the mechanical connection of the upper arm (11.1) to the lower arm (11.2) mechanically preloads the force transducer (12.1, 12.2).

2. The cutting machine (1) according to claim 1, wherein the tool holder (13) is made of a material having a high modulus of elasticity of more than 200GPa.

3. The cutting machine (1) according to any of the claims 1 or 2, wherein the tool arm (11) is made of a material having a high modulus of elasticity of more than 200GPa.

4. Use of a tool arm (11) in a cutting machine (1) for chip-removing machining of a workpiece (9), said chip-removing machining being performed in a chronological sequence of manufacturing steps by using a plurality of required tools (14.1 - 14.8); comprising a tool holder (13) for simultaneously holding the required tools (14.1 - 14.8); wherein said tool arm (11) connects the tool holder (13) with a drive unit (10); and which drive unit (10) moves the tool arm (11), by which movement of the tool arm (11) one of the required tools (14) can be aligned with a workpiece (9) in each manufacturing step, wherein said tool arm (11) comprises an upper arm (11.1) and a lower arm (11.2) wherein the upper arm (11.1) and the lower arm (11.2) are separate units; wherein the upper arm (11.1) and the lower arm (11.2) are mechanically connected to one another by a connecting means (15); wherein the upper arm (11.1) is connected with the drive unit (10); wherein the lower arm (11.2) is connected with the tool holder (13); wherein at least one force transducer (12. 1, 12.2) is arranged in a position between the upper arm (11.1) and the lower arm (11.2), wherein during chip-removing machining of a workpiece (9) said force transducer (12.1, 12.2) is capable of measuring a tool force (Kw) exerted by any of the required tools (14.1 - 14.8) in the main flow of forces; and wherein said connecting means (15) with the mechanical connection of the upper arm (11.1) to the lower arm (11.2) mechanically preloads the force transducer (12.1, 12.2).

5. A process for operating a cutting machine (1) according to any of the claims 1 to 3, wherein for chip-removing machining of the workpiece (9) one of the required tools (14.1 - 14.8) is aligned with the workpiece (9) in each manufacturing step; and wherein a tool force (Kw) exerted by the required tool (14.1 - 14.8) during chip-removing machining of the workpiece (9) is measured by the force transducer (12.1, 12.2).

6. The process according to claim 5, wherein during chip-removing machining of the workpiece (9) the required tool (14.1 - 14.8) performs a cutting movement in the transverse plane (xz) defined by a transverse axis (x) and a vertical axis (z) so that the tool force (Kw) comprises a transverse shear component (Kwx) in the direction of the transverse axis (x) and a vertical shear component (Kwz) in the direction of the vertical axis (z); wherein during chip-removing machining of the workpiece (9) the required tool (14.1 - 14.8) performs an advancing movement in the direction of a horizontal axis (y) so that the tool force (Kw) comprises a horizontal force component (Kwy) in the direction of the horizontal axis (y); and wherein for each tool force (Kw) measured in a manufacturing step the force transducer (12.1, 12.2) generates analog measurement signals (Sa1, Sa2).

7. The process according to claim 6, wherein said analog measurement signals (Sa1, Sa2) measured by the force transducer (12.1, 12.2) include analog transverse shear signals (Sa1' , Sa2') for the transverse shear component (Kwx) in the direction of the transverse axis (x), analog vertical shear signals (Sa1", Sa2") for a vertical shear component (Kwz) in the direction of the vertical axis (z) and analog horizontal force signals (Sa1", Sa2") for a horizontal force component (Kwy) in the direction of the horizontal axis (y).

8. The process according to claim 6, wherein the cutting machine (1) comprises at least one converter unit (16.1) wherein for each manufacturing step performed with a required tool (14.1 - 14.8) said converter unit (16.1) converts analog measurement signals (Sa1) in digital measurement signals (Sd1).

9. The process according to claim 8, wherein the cutting machine (1) comprises at least one computer (16.2) wherein for each manufacturing step said computer (16.2) loads the digital measurement signals (Sd1, Sd2) ; wherein in said computer (16.2) is stored at least one reference signal (R) for a material of the workpiece (9) and for a cutting material of a required tool (14.1 - 14.8), which reference signal (R) is loaded for each manufacturing step; wherein in said computer (16.2) is stored at least one specific calibration factor (αi) for a position (i) of a required tool (14.1 - 14.8) relative to the force transducer (12.1, 12.2), which calibration factor (αi) is loaded for each manufacturing step; wherein digital measurement signals (Sd1) loaded for each manufacturing step are calibrated by multiplying them with the loaded calibration factor (αi); and wherein for each manufacturing step a difference (Δ) between the calibrated digital measurement signals (Sd1) and the loaded reference signal (R) is calculated.

10. The process according to claim 9, wherein in said computer (16.2) is stored at least one predefined tolerance value (T), which predefined tolerance value (T) is loaded for each manufacturing step; wherein for each manufacturing step the difference (Δ) is compared to the predefined tolerance value (T); and when the difference (Δ) is smaller than / equal to the predefined tolerance value (T) the required tool (14.1 - 14.8) is not subject to abrasion and will be continued to use; and with a difference (Δ) that is greater than the predefined tolerance value (T) the required tool (14.1 - 14.8) is subject to abrasion and will be replaced.

11. The process according to any of the claims 6 to 10, wherein the force transducer (12.1) comprises a first piezoelectric element (12.12'), which first piezoelectric element (12.12') is oriented to generate electrical polarization charges with maximum sensitivity to the transverse shear component (Kwx); wherein the force transducer (12.1) comprises a second piezoelectric element (12.12''), which second piezoelectric element (12. 12'') is oriented to generate electrical polarization charges with maximum sensitivity to the vertical shear component (Kwz); and wherein the force transducer (12.1) comprises a third piezoelectric element (12.12'''), which third piezoelectric element (12.12‴) is oriented to generate electrical polarization charges with maximum sensitivity to the horizontal force component (Kwy).

12. A process for calibrating a force transducer (12.1, 12.2) of a cutting machine (1) according to any of the claims 1 to 3 by using a calibration force transducer (22), wherein in a first process step (210) a machine tool arm (11) of the cutting machine (1) is provided, which machine tool arm (11) comprises a required tool (14.1 - 14.8) and at least one force transducer (12.1, 12.2), wherein said required tool (14.1 - 14.8) is arranged in a position (i) relative to the force transducer (12.1, 12.2); wherein in a further process step (230) a calibration force (Kk) is applied to the required tool (14.1 - 14.8); wherein in a further process step (240) the calibration force (Kk) is measured by the force transducer (12.1, 12.2) and by the calibration force transducer (22); wherein the force transducer (12.1, 12. 2) generates analog measurement signals (Sa1, Sa2) for the calibration force (Kk) measured; wherein the calibration force transducer (22) generates analog calibration signals (Ka) for the calibration force (Kk) measured; wherein analog measurement signals (Sa1, Sa2) are converted in digital measurement signals (Sd1, Sd2); analog calibration signals (Ka) are converted in digital calibration signals (Kd); and wherein in a further process step (260) a comparison of digital measurement signals (Sd1, Sd2) and digital calibration signals (Kd) is carried out, wherein a result of said comparison is a calibration factor (αi) that is specific for the position (i) of the required tool (14.1 - 14.8) relative to the force transducer (12.1, 12.2).