Spindle unit of machine tool and system using the same

Abstract

To provide a spindle unit of a machine tool and a system using the same, capable of dynamically measuring machining stress applied to the spindle unit, improving machining accuracy (improving quality and yield), detecting abnormality, and improving the service life of a grinding wheel and a tool blade to reduce cost.SOLUTION: A spindle unit 1 of a machine tool includes a plurality of radial permanent magnets 16 arranged on a circumference with an axial direction of a main spindle 10 as a longitudinal direction, axial permanent magnets 42-1 and 42-2 arranged in a direction perpendicular to an axis of the main spindle 10, a radial stress detection unit configured to detect displacement of the radial permanent magnets 16, an axial stress detection unit configured to detect displacement of the axial permanent magnets 42-1 and 42-2, a wireless unit 22 configured to wirelessly transmit outputs of the radial stress detection unit and the axial stress detection unit, and a power supply 23 for the wireless unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a spindle unit of a machine tool that is capable of measuring stress acting on the spindle unit during machining such as grinding and performing feedback control, and to a system using the same. [Background technology]

[0002] Machining conditions such as grinding are determined by the tool's rotation speed and feed rate. However, machine tools can generate vibrations due to factors such as changes in cutting depth and processing stress during cutting, and grinding wheels and tools can deteriorate, resulting in a decrease in machining accuracy (quality and yield). While technology for detecting cutting loads is known as a solution, it is difficult to detect the load acting on tools and rotating axes in rotating machine tools. Therefore, in the past, to suppress vibrations such as chatter vibrations during machining, the load (current value, etc.) on the spindle unit's main shaft and workpiece rotation motor were monitored, and vibration-damping functions were installed in the tool holding device.

[0003] Patent Document 1 describes a method of detecting the load on a machine tool's spindle by disposing a bearing-type sensor at the tip of the spindle of a spindle unit. This bearing-type sensor disposes a rolling bearing between the housing and the spindle, and uses a strain gauge attached to the outer periphery of the outer ring to detect strain generated each time the rolling elements of the bearing pass the position of the strain gauge, thereby detecting the magnitude of the load on the spindle.

[0004] Furthermore, Patent Document 2 describes that the axial load of the spindle of the spindle unit is taken into consideration as a new parameter to improve machining accuracy. The axial load is measured by providing an encoder, whose detection surface characteristics change alternately in the circumferential direction, on the outer circumferential surfaces of a pair of angular contact ball bearings, and a sensor positioned opposite the detection surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-159260 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-238415 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above-mentioned conventional technology, it is difficult to know the magnitude and direction of the force actually applied to the tool or workpiece from the load (current value, etc.) of the motor of the tool rotation axis or workpiece rotation axis, etc., and it is not possible to perform feedback control of accurate and effective machining conditions. Also, the technology described in Patent Document 1 has difficulty in detecting the load with high accuracy. Furthermore, not only is the shaft length of the spindle unit long, but a dedicated space is required for installing the sensor.

[0007] The method described in Patent Document 2 only measures the axial load, and is unable to dynamically determine the magnitude and direction of the force acting on the tool or workpiece, making it difficult to provide feedback control of accurate and effective machining conditions.

[0008] The object of the present invention is to solve the problems of the prior art described above and to provide a spindle unit for a machine tool, which measures the machining stress acting on the spindle unit flexibly and dynamically depending on the situation, and which sequentially performs feedback control (real-time control) of machining conditions, thereby improving machining accuracy (improving quality and yield), detecting abnormalities, and extending the service life of grinding wheels and tool blades to reduce costs, and a system using the same. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides a spindle unit for a machine tool having a main spindle having a tool holder attached to its tip end, supported radially by radial bearings, supported axially by thrust bearings, and connected at its other end to a rotating shaft of a motor, the spindle unit comprising: a plurality of radial permanent magnets arranged circumferentially with the axial direction of the main spindle as the longitudinal direction; axial permanent magnets arranged perpendicular to the axis of the main spindle; a radial stress detection unit that detects displacement of the radial permanent magnets; an axial stress detection unit that detects displacement of the axial permanent magnets; a wireless unit that wirelessly transmits outputs from the radial stress detection unit and the axial stress detection unit; and a power supply to the wireless unit.

[0010] Furthermore, in the spindle unit of the above-described machine tool, the radial stress detection unit preferably includes a radial electromagnet installed on the outer periphery of the radial permanent magnet at a predetermined radial gap and facing the radial permanent magnet, and a radial strain sensor installed facing the radial electromagnet, and the radial strain sensor preferably detects a repulsive force between the radial permanent magnet and the radial electromagnet which have the same polarity.

[0011] Furthermore, in the spindle unit of the above-mentioned machine tool, it is preferable that the magnetic poles of the radial permanent magnets are magnetized in the radial direction, the radial electromagnets face the radial permanent magnets and are energized in the radial direction, and the radial permanent magnets and the radial electromagnets face each other with the same poles.

[0012] Furthermore, in the spindle unit of the above-mentioned machine tool, it is preferable that the magnetic poles of the radial permanent magnets are magnetized in the circumferential direction, and that the radial electromagnets are opposed to the radial permanent magnets and energized in the radial direction.

[0013] Furthermore, in the spindle unit of the above-mentioned machine tool, it is preferable that the axial stress detection unit comprises an axial electromagnet installed face-to-face with the axial permanent magnet at a predetermined gap in the axial direction, and an axial strain sensor installed opposite the axial electromagnet, and that the axial strain sensor detects the repulsive force between the axial permanent magnet and the axial electromagnet, which have the same polarity.

[0014] Furthermore, in the spindle unit of the above-mentioned machine tool, it is preferable that the axial stress detection unit includes an axial electromagnet installed face-to-face with the axial permanent magnet at a predetermined gap in the axial direction, and a piezoelectric sensor that detects the repulsive force between the axial permanent magnet and the axial electromagnet, which have the same polarity.

[0015] Furthermore, it is preferable that the spindle unit of the above-mentioned machine tool further comprises a torsional stress detection unit having a tip permanent magnet inserted into and fixed to the tip end of the spindle, an other end permanent magnet inserted into and fixed to the other end of the spindle, a tip coil attached circumferentially at a position opposite the tip permanent magnet and spaced a predetermined gap in the radial direction, and an other end coil attached circumferentially at a position opposite the other end permanent magnet and spaced a predetermined gap in the radial direction, and which detects torsional stress acting on the spindle from the phase difference between voltages due to induced electromotive forces generated in the tip coil and the other end coil.

[0016] Furthermore, in the spindle unit of the above-mentioned machine tool, it is preferable that the radial stress detection unit includes a radial coil installed on the outer periphery of the radial permanent magnet at a predetermined radial gap and facing the radial permanent magnet, and detects the displacement of the radial permanent magnet by a voltage due to an induced electromotive force generated in the radial coil.

[0017] Furthermore, in the spindle unit of the above-mentioned machine tool, it is preferable that the axial stress detection unit includes an axial coil installed facing the axial permanent magnet across a predetermined gap in the axial direction, and detects the displacement of the axial permanent magnet by a voltage due to an induced electromotive force generated in the axial coil.

[0018] Furthermore, the present invention provides a system using a spindle unit of a machine tool having a main spindle having a tool holder attached to its tip end, supported radially by radial bearings, supported axially by thrust bearings, and connected at its other end to a rotating shaft of a motor, the spindle unit comprising: a plurality of radial permanent magnets arranged circumferentially with the axial direction of the main spindle as the longitudinal direction; axial permanent magnets arranged perpendicular to the axis of the main spindle; a radial stress detector that detects displacement of the radial permanent magnets; an axial stress detector that detects displacement of the axial permanent magnets; a wireless unit that wirelessly transmits outputs of the radial stress detector and the axial stress detector; and a power supply to the wireless unit, and the system feedback controls machining conditions to the machining control of the machine tool in real time based on the output. [Effects of the Invention]

[0019] According to the present invention, the spindle unit includes a plurality of radial permanent magnets arranged circumferentially with the axial direction of the spindle's main shaft as the longitudinal direction, an axial permanent magnet arranged perpendicular to the axis of the main shaft, a radial stress detector that detects the displacement of the radial permanent magnets, and an axial stress detector that detects the displacement of the axial permanent magnets. This allows for dynamic detection of machining stress. Based on this output, machining conditions can be fed back to the machining control of the machine tool in real time. This allows for improved machining accuracy (improved quality and yield), improved anomaly detection, and cost reductions due to improved service life of grinding wheels and tool blades. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram showing a system configuration according to an embodiment of the present invention; [Figure 2]FIG. 1 is a cross-sectional view showing a configuration of a spindle unit of a machine tool according to an embodiment; [Figure 3] Cross-sectional view of part A in Figure 2 [Figure 4] Cross-sectional view of part B in Figure 2 [Figure 5] FIG. 1 is an explanatory diagram of a radial stress detector according to an embodiment; [Figure 6] FIG. 10 is an explanatory diagram of a radial stress detection unit according to another embodiment; [Figure 7] FIG. 1 is a perspective view illustrating an axial stress sensing portion according to one embodiment. [Figure 8] A diagram in which a torsion stress detector is added to the embodiment shown in FIG. [Figure 9] The induced electromotive force detection circuit of the embodiment shown in FIG. 8 [Figure 10] FIG. 3 is a cross-sectional view showing the configuration of a spindle unit according to another embodiment of the present invention, in which the embodiment shown in FIG. 2 is modified to be a coil detection type; [Figure 11] Cross-sectional view of part A in Figure 10 [Figure 12] The induced electromotive force detection circuit in the X direction in the radial stress detection part in Figure 11 [Figure 13] 11 is a perspective view of the axial stress detection unit at part B in FIG. [Figure 14] Induced electromotive force detection circuit in the axial stress detection unit of another embodiment shown in FIG. 10 [Figure 15] Induced electromotive force detection circuit combining the axial permanent magnet side and the axial permanent magnet side shown in Figure 13 [Figure 16] An induced electromotive force detection circuit in which the wiring, axial coil, and winding direction of the axial coil are reversed compared to the embodiment shown in FIG. 15. [Figure 17] An induced electromotive force detection circuit in which the axial permanent magnets 42-1 and 42-2 are overlapped with each other in the embodiment shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] Fig. 1 is a schematic diagram showing the system configuration according to one embodiment of the present invention, and Fig. 2 is a cross-sectional view showing the configuration of a spindle unit 1 of a machine tool according to this embodiment. The system configuration is mainly composed of a spindle unit 1 and a control unit 2. In the spindle unit 1, the tip end (left end in Fig. 2) of a main spindle 10 protrudes a predetermined length from a housing 11, and a tool holder 12 is attached to the tip. The main spindle 10 is supported by radial bearings 13 and 14 with an appropriate preload, supporting a load applied in the radial direction perpendicular to the center line.

[0022] The load applied in the axial direction of the main shaft 10 is supported by a thrust bearing 15. The other end of the main shaft 10 (the right end in FIG. 2) is on the motor side and is connected to a rotating shaft (not shown) of the motor that rotates at high speed. Note that the radial bearings 13, 14 and thrust bearing 15 may also be fluid bearings, air bearings, etc.

[0023] Part A in Fig. 2 is a radial stress detection part in the x and y directions, and part B is an axial stress detection part in the Z direction; Fig. 3 is a cross-sectional view of part A, and Fig. 4 is a cross-sectional view of part B. In part A, a plurality of radial permanent magnets 16 (four in Fig. 3) are arranged at equal intervals around the outer periphery of main shaft 10, with the axial direction as the longitudinal direction. Circular ring 11-1 attached to housing 11 has a plurality of radial electromagnets 17 (four in Fig. 3) arranged around the outer periphery of radial permanent magnet 16, with a predetermined gap in the radial direction, facing radial permanent magnet 16.

[0024] The radial strain sensor 18 is attached to a portion of the annular ring 11-1 facing the outer periphery of the radial electromagnet 17. The annular ring 11-1 may be integrated as part of the housing 11. The radial strain sensor 18 may be a radial strain sensor in which a lattice-shaped resistance wire or a photo-etched resistance foil is formed on a thin electrically insulating base, or a piezoelectric sensor using a piezoelectric element that utilizes the piezoelectric effect.

[0025] Figure 3 shows the arrangement of the radial permanent magnet 16 and radial electromagnet 17 of the radial stress detection unit. In Figure 3, the magnetic poles of the radial permanent magnet 16 are magnetized as S and N in the radial direction from the center. The radial electromagnet 17 is attached to the annular ring 11-1 and is energized so that it faces the radial permanent magnet 16 and is magnetized as N and N in the radial direction from the center. The radial strain sensor 18 is attached to the outer circumferential annular ring 11-1 at the position where the radial electromagnet 17 is attached, and is installed there.

[0026] The radial strain sensor 18 only needs to detect the stress acting on the annular ring 11-1 due to the repulsive force between the radial permanent magnet 16 and the radial electromagnet 17, which have the same polarity, or on a part of the housing 11 in place of the annular ring 11-1 if the annular ring 11-1 is integrated with the housing 11. The magnetic poles should be opposite, that is, the same poles should face each other with NS facing SN in Figure 3. Unlike permanent magnets, the magnetic force of the radial electromagnet 17 is adjustable, so it can be adjusted so that the magnetic force is not too strong and interferes with the rotation of the spindle 10.

[0027] FIG. 4 shows the arrangement of the axial permanent magnet 21-2 and axial electromagnet 19-2 that detect stress in the z direction. At part B, a circular axial permanent magnet 21-2 for the Z direction is arranged on the main shaft 10 in a direction perpendicular to the axis. Multiple axial electromagnets 19-2 (four in FIG. 4) are installed facing each other. Axial strain sensors 20-2, which serve as axial stress detection units, are attached to the outer periphery of the flange-shaped portion of the circular ring 11-2 attached to the housing 11 of each axial electromagnet 19-2, facing the axial electromagnet 19-2. The above also applies to the relationship between the axial permanent magnet 21-1 and the axial electromagnet 19-1.

[0028] The portion where the axial electromagnet 19-2 is attached is integrated with the annular ring 11-2 in Fig. 2. In other words, if the annular ring 11-2 is made part of the housing 11, it is sufficient to provide the housing 11 with a flange-shaped portion.

[0029] The wireless unit 22 transmits, by wireless or the like, the outputs of the radial strain sensor 18 of the radial stress detection unit in the x and y directions and the axial strain sensors 20-1 and 20-2 of the axial stress detection unit. The wireless unit 22 and a power supply 23 for the wireless unit 22 are provided at the other end (the right end in FIG. 2) of the spindle 10. The control unit 2 has a stress calculation unit 2-2, a data output unit (display unit) 2-3, and a control power supply 2-1.

[0030] Figure 5 is an explanatory diagram of the radial stress detection unit. Figure 5(a) shows that a force as indicated by the arrow is applied to a tool 24 attached to the tool holder 12, and Figure 5(b) shows the state in which the spindle 10 is displaced at that time. When stress is applied to the spindle 10, it displaces, and the radial permanent magnet 16 attached to it also displaces as shown in Figure 5(b). Then, the repulsive force between the radial permanent magnets 16 and 17, which was balanced when there was no displacement, changes, and stress is generated in the annular ring 11-1, which is detected by the radial strain sensor 18.

[0031] Detection by the radial strain sensor 18 uses the two-gauge method, in which strain gauges are connected to two sides of a bridge circuit and fixed resistors are connected to the other two sides, to obtain output voltages corresponding to stress in the xy directions and the axial direction shown in the figure. Measurement of the stress acting on the spindle 10 during machining can be achieved by calibrating the relationship between output voltage and stress in advance. It is preferable to select duralumin as the material for the annular ring 11-1, which serves as the base material to which the radial strain sensor 18 is attached, taking into account the effects of heat and stress-strain characteristics.

[0032] It is also possible to use a self-temperature-compensating radial strain sensor 18 in which the difference between the linear expansion coefficient of the metallic resistor of the radial strain sensor 18 and the linear expansion coefficient of the housing 11 is offset by the temperature resistance coefficient of the metallic resistor. Furthermore, if active heat dissipation is required as a countermeasure against thermal drift, measures such as cooling with a Peltier element or installation of a water-cooling unit (copper pipe) are also good, and the self-temperature-compensating radial strain sensor 18 can be canceled out by configuring a bridge circuit.

[0033] 6 is an explanatory diagram of a radial stress detection unit according to another embodiment, showing the arrangement of a radial permanent magnet 16 and a radial electromagnet 17 in part A that detects stress. The magnetic poles of the radial permanent magnet 16 are magnetized as S and N in the circumferential direction, counterclockwise, in FIG. 6. The radial electromagnet 17 is energized so as to generate magnetic flux B that faces the radial permanent magnet 16 and is S and N in the radial direction from the center.

[0034] The radial strain sensor 18 is attached to the housing 11 at the same position as the radial electromagnet 17. The repulsive force between the radial permanent magnet 16 and the radial electromagnet 17 occurs in the same manner as in Fig. 3, so the radial strain sensor 18 only needs to detect the stress applied to the housing 11 due to the repulsive force.

[0035] FIG. 7(a) is a perspective view showing the axial permanent magnet 21-1 side of the axial stress detection unit in the z direction. Multiple axial electromagnets 19-1 (four in the figure) are installed facing the axial permanent magnet 21-1 and equally spaced in the circumferential direction. The axial strain sensor 20-1 is attached to the outer periphery of the annular ring 11-2 so that its resistance value changes in the z direction, which is the axial direction. The axial permanent magnet 21-2 side is similar. When the magnetic flux B of the axial electromagnet 19-1 is oriented in the z direction as shown by the arrow, a repulsive force is generated between the axial electromagnet 19-1 and the axial permanent magnet 21-1.

[0036] When stress is applied in the z direction, the spindle 10 is displaced, the repulsive force changes, and the stress on the annular ring 11-2 is detected by the axial strain sensor 20-1. Detection by the axial strain sensor 20-1 is performed using a one-gauge three-wire method in which a strain gauge is connected to one side of a bridge circuit and fixed resistors are connected to the other three sides, and an output voltage corresponding to the stress in the z direction is obtained.

[0037] Figure 7(b) shows an embodiment in which the axial strain sensor 20-1 of the axial stress detection unit is replaced with a piezoelectric sensor 20'-1. The piezoelectric sensor 20'-1 is sandwiched between the annular ring 11-2, which is the upper structure in the figure, and the axial permanent magnet 21-1. The rest is the same as in Figure 7(a), and the repulsive force between the axial permanent magnet 21-1 and the axial electromagnet 19-1, which have the same polarity, is detected by the piezoelectric effect of the piezoelectric sensor 20'-1, i.e., the voltage generated in response to pressure.

[0038] FIG. 8 is a diagram in which a torsional stress detection unit for the spindle 10 has been added to the embodiment shown in FIG. 2. FIG. 8(a) is a cross-sectional view showing the configuration of the spindle unit 1, and the reference numerals and descriptions of parts similar to those in FIG. 2 are omitted. The tip permanent magnet 30 is cylindrical and is inserted into and fixed to the tip of the spindle 10 on the tool holder 12 side. Two tip coils 31 for detecting induced electromotive force are attached to the housing 11 at positions facing the tip permanent magnet 30, separated by a predetermined gap in the radial direction, and in the circumferential direction. FIG. 8(b) shows a perspective view of the tool holder 12.

[0039] The other-end permanent magnet 32 ​​is cylindrical and is inserted into and fixed to the motor side of the other end (the right end in FIG. 8) of the main shaft 10. The other-end coil 33 that detects the induced electromotive force is attached to the housing 11 at two locations in the circumferential direction, facing the other-end permanent magnet 32 ​​with a predetermined gap in the radial direction. FIG. 8(c) shows a perspective view of the attachment portion.

[0040] Fig. 9 shows the induced electromotive force detection circuit of the embodiment shown in Fig. 8. When current flows through the tip coil 31 and similarly the other-end coil 33 as shown by the arrows, an induced electromotive force is generated according to Lenz's law by the rotation of the tip permanent magnet 30 and similarly the other-end permanent magnet 32. Therefore, the torsional stress acting on the main shaft 10 is detected by detecting the phase difference of the voltage due to the induced electromotive force generated in the tip coil 31 and the other-end coil 33.

[0041] FIG. 10 is a cross-sectional view showing the configuration of a spindle unit 1 showing another embodiment in which the strain detection type is adopted, whereas the embodiment shown in FIG. 2 is a strain detection type. FIG. 10(a) differs from FIG. 8 in that the radial stress detection section in the xy directions at part A and the axial stress detection section in the Z direction at part B are different, and therefore the reference numerals and descriptions of the same parts are omitted. FIG. 10(b) shows a perspective view of the radial stress detection section. However, FIG. 10(b) is a simplified illustration in which the radial permanent magnet 40 is omitted, and it may be the same as the radial permanent magnet 16 in FIG. 2.

[0042] FIG. 11 is a cross-sectional view of part A, showing the arrangement of radial coil 41-1 relative to radial permanent magnet 40. Radial permanent magnet 40 is cylindrical and is inserted radially into and fixed to main shaft 10. At part A, multiple radial permanent magnets 40 (four in FIG. 11) are arranged on the outer periphery of main shaft 10 at equal intervals in the circumferential direction, with the axial direction as the longitudinal direction. The magnetic poles of radial permanent magnet 40 are magnetized as SN or NS from the center in the radial direction. Circular ring 11-1 attached to housing 11 has multiple radial coils 41-1, 41-2, 41-3, and 41-4 (four in FIG. 11) arranged around the outer periphery of radial permanent magnet 40 with a predetermined gap in the radial direction and facing radial permanent magnet 40.

[0043] Radial coils 41-1, 41-2, 41-3, and 41-4 for detecting induced electromotive forces are attached at four locations circumferentially, with a predetermined gap in the radial direction, facing the radial permanent magnets 40 of the annular ring 11-1 attached to the housing 11. The radial coils 41-1, 41-2, 41-3, and 41-4 are arranged in pairs facing each other at 180° angles, as indicated by the symbols y1, y2, x1, and x2. The radial coils 41-1 and 41-2 detect stress in the Y direction, and the radial coils 41-3 and 41-4 detect stress in the X direction.

[0044] FIG. 12 shows the X-direction induced electromotive force detection circuit in the radial stress detection unit in FIG. 11. When a current flows in the X1 circuit on the radial coil 41-1 side as indicated by arrow Q, a voltage X1 is generated due to the induced electromotive force caused by the rotation of the radial permanent magnet 40. The winding directions of the radial coils 41-1 and 41-2 are the same for both the X1 circuit and the X2 circuit. The X2 circuit on the radial coil 41-2 side similarly generates an X2 voltage, and detecting the difference between the two can detect stress in the x-direction. Although the winding direction of the radial coils 41-1 and 41-2 is shown counterclockwise in FIG. 12, it can also be clockwise, which is similar. Stress in the y-direction is detected in the same way, and stress in the y-direction can be detected from the difference between voltages Y1 and Y2.

[0045] Fig. 13(a) shows a perspective view of the axial stress detection unit in the Z direction at part B in Fig. 10. Fig. 13(b) shows an example of magnetization of axial permanent magnets 42-1 and 42-2. At part B, two annular axial permanent magnets 42-1 and 42-2 for the Z direction are arranged on main shaft 10 in a direction perpendicular to the axis. Axial coils 43-1, 43-2, 43-3, and 43-4 are installed on the flange-shaped portions of multiple annular rings 11-2 (four in Fig. 13) attached to housing 11, each facing the axial permanent magnet 42-1.

[0046] Similarly, a plurality of axial coils 43-5, 43-6, 43-7, and 43-8 (four in FIG. 13) are installed on the annular ring 11-2, each facing the axial permanent magnet 42-2. As shown in FIG. 13(b), the axial permanent magnets 42-1 and 42-2 are equally divided in the circumferential direction, for example, divided into two and magnetized alternately in N-S or N-S directions, or divided into four and magnetized alternately in N-S directions.

[0047] FIG. 14 shows the induced electromotive force detection circuit (axial permanent magnet 42-1 side) in the axial stress detection unit. FIG. 14(a) shows the circuit during idling without machining, and FIG. 14(b) shows the circuit during stress loading while machining is in progress. FIG. 14(a) shows the circuit during induced electromotive force detection in the X direction, and the axial coil 43-1 and the axial coil 43-2 are connected to the Z - X1 circuit, Z -An AC induced electromotive force is generated in the X2 circuit, and a voltage is detected. As the axial permanent magnet 42-1 rotates, it periodically passes through the axial coils 43-1 and 43-2 from S to N to S. The AC cycle changes when machining stress is applied to the spindle 10 during machining.

[0048] When machining stress is applied to the main spindle 10 during machining, the main spindle 10 is displaced and the axial permanent magnet 42-1 tilts. This changes the magnetic flux density penetrating the axial coils 43-1 and 43-2, and an induced electromotive force is generated in a direction that cancels this change. - In the X2 circuit, as the south pole approaches, an induced electromotive force is generated in the opposite direction, increasing the magnetic flux.

[0049] Conversely, Z - In the X1 circuit, the N pole moves away, so an induced electromotive force is generated to increase the magnetic flux in this direction. Therefore, for example, Z - Voltage and Z in the X1 circuit - The inclination in the X direction can be determined by detecting the voltage difference between the idle rotation in FIG. 14(a) and the stress load in FIG. 14(b). The inclination in the Y direction can be determined by detecting the voltage difference between the axial coils 43-3 and 43-4. - Y1 circuit, Z - The same applies if we use a Y2 circuit.

[0050] Fig. 15 shows an induced electromotive force detection circuit combining the axial permanent magnet 42-1 side and the axial permanent magnet 42-2 side shown in Fig. 13. Fig. 15(a) shows the state during idling without machining, and Fig. 15(b) shows the state during stress loading during machining. Figs. 15(a) and 15(b) show the induced electromotive force detection circuit in the X direction, with the axial coil 43-1 and the axial coil 43-2 respectively detecting Zup - X1 circuit and Zup - X2 circuit, the axial coil 43-5 and the axial coil 43-6 are Zdn - X1 circuit and Zdn - An AC induced electromotive force is generated in the X2 circuit, and the voltage is detected.

[0051] The voltage due to the AC induced electromotive force in Figure 15 is the same as that explained in Figure 14, but Zup- X1 circuit and Zdn - The output of the X1 circuit is doubled. Therefore, the noise is reduced equivalently. In the Y direction, the axial coils 43-3 and 43-4 are connected to the Zup - Y1 circuit, Zup - Y2 circuit, axial coils 43-6 and 43-7 are respectively Zdn - Y1 circuit, Zdn - The same applies if we use a Y2 circuit.

[0052] Fig. 16 shows an induced electromotive force detection circuit in which the wiring and the winding directions of the axial coil 43-5 and the axial coil 43-6 are reversed compared to the embodiment shown in Fig. 15. Fig. 16(a) shows the circuit during idling without machining, and Fig. 16(b) shows the circuit during stress loading while machining is in progress. Figs. 16(a) and 16(b) show the circuit for detecting an induced electromotive force in the X direction, and the axial coil 43-1 and the axial coil 43-5 are connected to each other to detect the Z - Connect the X1 circuit, axial coil 43-2, and axial coil 43-6 to form Z - It is an X2 circuit.

[0053] The winding direction of the axial coil 43-1 and the axial coil 43-5 is clockwise and counterclockwise, respectively. The same applies to the axial coil 43-2 and the axial coil 43-6. The voltage due to the induced electromotive force of the AC in FIG. 16 is the same as that explained in FIG. 15, but Z - X1 circuit and Z - The output is doubled by connecting the X2 circuit and the axial coils 43-3 and 43-7 to the Y direction. - Connect the Y1 circuit and the axial coils 43-4 and 43-8 to form Z - The same applies if we use a Y2 circuit.

[0054] Figure 17 shows an induced electromotive force detection circuit in which axial permanent magnets 42-1 and 42-2 are overlapped with the embodiment shown in Figure 16. Figure 17(a) shows the circuit during idling without machining, and Figure 17(b) shows the circuit during machining with stress applied. The axial permanent magnet 42-1 is equally divided in the circumferential direction as shown in Figure 13(b), for example, divided into two and magnetized as N-S or four and magnetized alternately as N-S. The axial permanent magnet 42-2 is magnetized so that it is N-S relative to the N-S of the axial permanent magnet 42-1. The N-S orientation may be reversed.

[0055] 17(a) and 17(b) show an induced electromotive force detection circuit in the X direction, in which the axial coil 43-1 and the axial coil 43-5 are connected to each other to detect the Z - Connect the X1 circuit, axial coil 43-2, and axial coil 43-6 to form Z - It is an X2 circuit.

[0056] The winding direction of the axial coil 43-1 and the axial coil 43-5 is clockwise and counterclockwise, respectively. The same applies to the axial coil 43-2 and the axial coil 43-6. The voltage due to the induced electromotive force of the AC in FIG. 17 is the same as that explained in FIG. 16, but Z - X1 circuit and Z - The X2 circuit provides double the output.

[0057] In the embodiment described above, whether the radial and axial stress detection units are strain detection types or coil detection types, the sensors (strain sensors, piezoelectric sensors, coils) are arranged in the circumferential direction of the spindle 10, so the direction of stress (direction of force) can also be detected in three dimensions. Furthermore, because the output from each sensor is captured periodically, it becomes possible to analyze the force in the rotational direction of the spindle 10 and rotation irregularities, etc., and this can be applied to effective machining control of machine tools.

[0058] According to each of the embodiments described above, it is possible to construct a system using the spindle unit 1 that can feedback control the machining conditions to the machining control of the machine tool in real time based on the outputs of the radial stress detector and the axial stress detector. Therefore, with this system, the machining conditions of the machine tool, such as the rotation speed of the tool 24, the feed rate, and the cutting depth in cutting, can be optimally controlled.

[0059] As a result, machining using the system enables improved machining precision (improved quality and yield), abnormality detection, improved service life of grinding wheels and tool blades, and cost reduction. Note that the coil detection type that detects induced electromotive force is superior in terms of resistance to the effects of radial direction due to heat, drift of the piezoelectric sensor 20'-1, and displacement of the spindle 10, radial bearings 13 and 14, and thrust bearing 15. [Explanation of symbols]

[0060] 1...Spindle unit 2...Control unit 2-1...Control power supply 2-2...Stress calculation section 2-3...Data output section 10...Spindle 11. Housing 11-1, 11-2...Circular ring 12...Tool holder 13, 14...Radial bearings 15...Thrust bearing 16, 40...Radial permanent magnet 17...Radial electromagnet 18...Radial strain sensor 19-1, 19-2...Axial electromagnet 20-1...Axial strain sensor 20'-1...Piezoelectric sensor 21-1, 21-2, 42-1, 42-2...Axial permanent magnet 22...Wireless unit 23...Power supply 24...Tools 30...Tip permanent magnet 31...Tip coil 32...Permanent magnet at the other end 33...other end coil 41-1, 41-2, 41-3, 41-4...Radial coils 43-1, 43-2, 43-3, 43-4, 43-5, 43-6, 43-7, 43-8...Axial coil

Claims

1. A spindle unit for a machine tool having a main shaft rotatably supported in a housing, an axial permanent magnet arranged in a flange shape at a midpoint in the longitudinal direction of the main shaft; an axial electromagnet disposed in the housing and spaced apart from the axial permanent magnet in a direction opposite to the longitudinal direction; an axial strain sensor disposed opposite the axial electromagnet, The axial strain sensor is configured to detect the repulsive force between the axial permanent magnet and the axial electromagnet, in a spindle unit of a machine tool.

2. A spindle unit for a machine tool having a main shaft rotatably supported in a housing, a radial permanent magnet arranged along the longitudinal direction of the main shaft; a radial electromagnet disposed in the housing and spaced apart from the radial permanent magnet in a direction radially opposite to the main shaft; a radial strain sensor disposed opposite the radial electromagnet; The radial strain sensor is configured to detect the repulsive force between the radial permanent magnet and the radial electromagnet, and is a spindle unit of a machine tool.

3. 3. The spindle unit of a machine tool according to claim 1, further comprising: a wireless unit that wirelessly transmits the detection result; and a power supply to the wireless unit.

4. A system using a spindle unit of a machine tool having a main spindle rotatably supported in a housing, The spindle unit includes: an axial permanent magnet arranged in a flange shape at a midpoint in the longitudinal direction of the main shaft; an axial electromagnet disposed in the housing and spaced apart from the axial permanent magnet in a direction opposite to the longitudinal direction; an axial strain sensor disposed opposite the axial electromagnet, the axial strain sensor is a spindle unit of a machine tool configured to be able to detect a repulsive force between the axial permanent magnet and the axial electromagnet, A system using a spindle unit of a machine tool, configured to feedback control machining conditions to the machining control of the machine tool in real time based on the results of the detection.

5. A system using a spindle unit of a machine tool having a main spindle rotatably supported in a housing, The spindle unit includes: a radial permanent magnet arranged along the longitudinal direction of the main shaft; a radial electromagnet disposed in the housing and spaced apart from the radial permanent magnet in a direction radially opposite to the main shaft; a radial strain sensor disposed opposite the radial electromagnet; the radial strain sensor is a spindle unit of a machine tool configured to be able to detect a repulsive force between the radial permanent magnet and the radial electromagnet, A system using a spindle unit of a machine tool, configured to feedback control machining conditions to the machining control of the machine tool in real time based on the results of the detection.

6. 6. A system using a spindle unit of a machine tool according to claim 4, wherein the spindle unit further comprises a wireless unit that wirelessly transmits the result of the detection, and a power supply to the wireless unit.

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