Bearing device, spindle device provided with same, load estimation method, program, load sensor calibration method, and processing load calculation method

Abstract

A bearing device (1) rotatably supports a main shaft (2) that processes a workpiece through rotational driving. The bearing device (1) is provided with a load sensor (71), storage (103), and a processor (101). The load sensor (71) outputs a signal that indicates a detection value of a load applied to the bearing device (1). The storage (103) has stored therein a correspondence map (93) between rotational velocities of the main shaft (2) and detection values of the load sensor (71) when no workpiece is being processed. The processor (11), on the basis of the signal from the load sensor (71), estimates a processing load to be applied to the bearing device (1) when the workpiece is being processed. If the rotational velocity of the main shaft (2) has been controlled to a prescribed velocity, the processor (101): acquires a first load indicated by the signal from the load sensor (71), and a second load which is a detection value of the load sensor (71) corresponding to the prescribed velocity in the correspondence map (93); and estimates the difference between the first load and the second load as the processing load.

Description

Bearing device, spindle device equipped with same, load estimation method, program, load sensor calibration method, and processing load calculation method

[0001] The present disclosure relates to a bearing device, a spindle device including the bearing device, a load estimation method, a program, a method for calibrating a load sensor, and a method for calculating a processing load.

[0002] The main spindle of a spindle device of a processing machine or the like is supported by a bearing device. If the bearing device is damaged, the operation of the spindle device must be stopped and the main spindle must be replaced. During this replacement work, productivity at the work site where the spindle device is installed can be significantly reduced. Therefore, a technique for early detection of damage (or potential damage) to the bearing device has been proposed.

[0003] For example, Japanese Patent No. 5,168,352 (Patent Document 1) discloses a collision detection device for a processing machine. The collision detection device includes a drive motor, a load current detection means for detecting the load current of the drive motor, an error detection means for detecting an error in the drive motor based on a position command and a feedback signal from the drive motor, and a control means for controlling the drive of the drive motor. The control means determines whether the drive motor is operating during or not during processing, and sets a motor current limit value based on the result of this determination. This limits the load current setting value, which indicates a reference current value for determining whether or not a collision has occurred between the structure on which the drive motor is installed and the workpiece, and the motor output torque of the drive motor so that the motor current is kept below a certain level.

[0004] Japanese Patent No. 5168352 JP 2022-53084 A

[0005] There is a demand for a technology that improves the accuracy of estimating the load applied to a bearing device during machining (hereinafter also referred to as "machining load") in a bearing device or a spindle device equipped with the same, without adopting a complex device configuration.

[0006] The present disclosure has been made to solve the above-mentioned problems, and one of the objects of the present disclosure is to easily and highly accurately estimate the processing load applied to a bearing device.

[0007] A bearing device according to the present disclosure supports a spindle that is rotationally driven to machine a workpiece. The bearing device includes a load sensor, a storage device, and a processor. The load sensor outputs a signal indicating a detected value of a load applied to the bearing device. The storage stores a correspondence between the rotational speed of the spindle and the detected value of the load sensor when the workpiece is not being machined. The processor estimates a processing load applied to the bearing device when the workpiece is being machined based on the signal from the load sensor. When the rotational speed of the spindle is controlled to a predetermined speed, the processor acquires a first load indicated by the signal from the load sensor and a second load that is the detected value of the load sensor that corresponds to the predetermined speed in the correspondence relationship, and estimates the difference between the first load and the second load as the processing load.

[0008] A load estimation method according to the present disclosure estimates, by a computer, a processing load applied to a bearing device when a workpiece is machined by rotationally driving a spindle. The bearing device includes a load sensor that outputs a signal indicating a detected value of the load applied to the bearing device. A correspondence relationship between the rotational speed of the spindle and the detected value of the load sensor when the workpiece is not being machined is stored in the computer. The load estimation method includes first and second steps. The first step is a step of acquiring, when the rotational speed of the spindle is controlled to a predetermined speed, a first load indicated by a signal from the load sensor and a second load that is the detected value of the load sensor corresponding to the predetermined speed in the correspondence relationship. The second step is a step of estimating the difference between the first load and the second load as the processing load.

[0009] A spindle device according to the present disclosure includes a bearing unit. The bearing unit is equipped with a load sensor. The spindle device has a calculation unit and a memory unit. The calculation unit calculates a processing load applied to the bearing unit from output information output from the load sensor. The bearing unit has a rotatable main shaft. The memory unit stores a first relationship between the measured load and first output information. The measured load is applied to the bearing unit when the main shaft is stationary. The first output information is output from the load sensor when the measured load is applied to the bearing unit. The calculation unit calculates the processing load from the output information based on the first relationship.

[0010] A method for calibrating a load sensor according to the present disclosure includes a step of preparing a spindle device having a bearing unit and a load measuring jig, and a storing step. The bearing unit is equipped with a load sensor. The bearing unit has a rotatable main shaft. The storing step includes a step of storing a first relationship used to calculate a processing load applied to the bearing unit. In the step of storing the first relationship, the first relationship between the measured load and first output information is stored. The measured load is measured with the bearing unit pressing the load measuring jig while the main shaft is stationary. The first output information is output from the load sensor when the measured load is measured.

[0011] According to the present disclosure, the processing load applied to a bearing device can be estimated easily and with high accuracy.

[0012] 13 is a diagram showing an example of the overall configuration of a machine tool according to a first embodiment. FIG. 14 is a diagram showing an example of the configuration of a bearing device in more detail. FIG. 15 is an enlarged view of the bearing shown in FIG. 2. FIG. 16 is a diagram showing an example of the hardware configuration of a controller. FIG. 17 is a flowchart showing an example of the processing procedure for load estimation processing when a workpiece is not being machined by a machine tool. FIG. 18 is a conceptual diagram showing an example of a correspondence map 93 generated when a workpiece is not being machined by a machine tool. FIG. 19 is a flowchart showing a first example of the processing procedure for load estimation processing when a workpiece is being machined by a machine tool. FIG. 19 is a diagram showing an example of a situation in which a load sensor output and a vibration sensor output are synchronized. FIG. 20 is a diagram showing an example of a load sensor output when a workpiece is being machined and an example of a load sensor output when a workpiece is not being machined. FIG. 21 is a flowchart showing a second example of the processing procedure for load estimation processing when a workpiece is being machined by a machine tool. FIG. 22 is a diagram for explaining stages in a machining cycle of a machine tool. FIG. 23 is a cross-sectional view showing a schematic configuration of a bearing unit according to a second embodiment. FIG. 24 is a partially enlarged cross-sectional view of the left main part of FIG. 12. FIG. 25 is a cross-sectional view taken along line XIV-XIV in FIG. 13. FIG. 26 is a schematic structural diagram of a load sensor. FIG. 27 is a diagram showing a schematic configuration of a load sensor. FIG. 28 is a functional block diagram of a data processing unit that processes output information from the load sensor. FIG. 1 is a side view of a spindle device in which an axial measured load is measured. FIG. 2 is a graph showing the relationship between first output information output from a plurality of load sensor elements and the axial measured load. FIG. 3 is a side view of a spindle device in which a radial measured load is measured. FIG. 4 is a plan view of a spindle device in which a radial measured load is measured. FIG. 5 is a graph showing the relationship between first output information output from a plurality of load sensor elements and the radial measured load. FIG. 6 is a graph showing a first relationship and a second relationship. FIG. 7 is a cross-sectional view of a bearing unit of embodiment 3. FIG. 8 is a cross-sectional view of a bearing unit of embodiment 4.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0014] In the following embodiments, a configuration in which a bearing device according to the present disclosure is applied to a machine tool spindle will be described as an example. However, the application of the bearing device according to the present disclosure is not limited to machine tool spindles. The bearing device according to the present disclosure can also be applied to similar structures in the industrial or automotive fields.

[0015] [First Embodiment] <Overall Configuration> Figure 1 is a diagram showing an example of the overall configuration of a machine tool according to the first embodiment. The machine tool 100 is a spindle device, and includes a bearing device 1, a main spindle 2, a machine body 3, and a motor 4. The bearing device 1 includes a plurality of (four in this example) bearings 5 ​​and at least one (three in this example) spacer 6. The machine tool 100 further includes a controller 10.

[0016] The bearing device 1 is a rolling bearing device that rotatably supports the main spindle 2. The main spindle 2 is directly connected to the rotating shaft of a motor 4. The motor 4 is driven to rotate in accordance with a drive command from a controller 10. This causes the main spindle 2 to rotate. The machine body 3 includes a housing 31, a table 32, and a bed 33. The housing 31 houses the bearing device 1 and the main spindle 2. The table 32 is a processing table configured to fix a workpiece (object to be machined) W. The bed 33 is a base that supports the entire machine tool.

[0017] The four bearings 5 ​​are disposed at the boundary between the housing 31 and the main shaft 2. The four bearings 5 ​​rotatably support the main shaft 2. One spacer 6 is disposed between two adjacent bearings 5. However, the number of bearings 5 ​​and spacers 6 to be installed is not particularly limited. The bearing device 1 may include three or five or more bearings 5 ​​and a corresponding number of spacers 6, or may include two bearings 5 ​​and a single spacer 6.

[0018] <Configuration of Bearing Device> Fig. 2 is a diagram showing an example of the configuration of bearing device 1 in more detail. Fig. 3 is an enlarged view of bearing 5 shown in Fig. 2. Referring to Figs. 1 to 3, bearing 5 is a rolling bearing, for example an angular contact ball bearing. Bearing 5 includes an inner ring 51, an outer ring 52, rolling elements 53, and a cage 54.

[0019] The inner ring 51 is formed with an annular inner ring rolling surface. The outer ring 52 is formed with an annular outer ring rolling surface. The inner ring 51 and the outer ring 52 are arranged with a gap between them in the vertical direction in the figure. In this example, the inner ring 51 is a rotating ring, and the outer ring 52 is a non-rotating ring (fixed ring). The rolling elements 53 are members, such as spherical members, that are arranged to roll freely between the inner ring rolling surface of the inner ring 51 and the outer ring rolling surface of the outer ring 52. The cage 54 is annular and holds the multiple rolling elements 53 at intervals from one another in the circumferential direction.

[0020] Spacer 6 includes an inner ring spacer 61 and an outer ring spacer 62. In the example shown in Fig. 2, one inner ring spacer 61 and one outer ring spacer 62 are arranged between two bearings 5. Spindle 2 is inserted into the inner diameter portion of inner ring 51 and the inner diameter portion of inner ring spacer 61, and outer diameter portions of outer ring 52 and outer ring spacer 62 are inserted into housing 31, thereby rotatably supporting spindle 2.

[0021] The bearing device 1 further includes at least one sensor 7 and at least one wiring 8. The at least one sensor 7 includes, for example, a load sensor 71 and a vibration sensor 72. The at least one wiring 8 includes, for example, a first wiring 81 and a second wiring 82.

[0022] The load sensor 71 is, for example, a strain gauge whose electrical resistance changes in response to strain. The load sensor 71 may also be a pressure sensor that converts pressure applied to a contact surface into an electrical signal. The load sensor 71 may also be a thin-film sensor (a thin-film strain gauge or a thin-film pressure sensor). The load sensor 71 may also be a combination of multiple types of sensors (strain gauges, pressure sensors, thin-film sensors, etc.). The load sensor 71 may output a value calculated or converted from the output of the combination.

[0023] The load sensor 71 is installed, for example, on the outer ring spacer 62, which is a non-rotating ring. The load sensor 71 detects the load applied to the outer ring spacer 62. A signal indicating the detection result by the load sensor 71 is transmitted to the controller 10 (see FIG. 1 ) via a first wiring 81 installed on the outer ring spacer 62. The first wiring 81 is also used to supply power to the load sensor 71 from a power supply circuit (not shown).

[0024] Although not shown, the bearing device 1 may include a wireless communication device instead of the first wiring 81. The wireless communication device is, for example, a device that uses radio waves in the 2.4 GHz frequency band, such as Wi-Fi (registered trademark) or Bluetooth (registered trademark). A signal indicating the detection result by the load sensor 71 is transmitted to the controller 10 via wireless communication. This eliminates the need to process the housing 31 to route the first wiring 81. It also simplifies the process of incorporating the outer ring spacer 62 into the housing 31. Note that a generator that generates electricity as the spindle 2 rotates can be used to supply power to the load sensor 71 and the wireless communication device.

[0025] It is also possible to provide a torque sensor (not shown) instead of the load sensor 71. However, since a torque sensor is generally installed on the inner ring spacer, which is a rotating ring, it rotates along with the rotational drive of the main shaft. Therefore, mounting a torque sensor requires a signal transmission mechanism for a rotating body (such as a slip ring or a telemeter). In contrast, this embodiment employs a load sensor 71 that can be installed on the outer ring spacer 62, which is a non-rotating ring. This makes it easier to route the first wiring 81 (i.e., to supply power to the load sensor 71 and obtain a signal from the load sensor 71).

[0026] The vibration sensor 72 is installed, for example, in the housing 31. The vibration sensor 72 may be installed in the outer ring spacer 62, the table 32, or the bed 33. The vibration sensor 72 detects vibrations in the housing 31 (the outer ring spacer 62, the table 32, or the bed 33). A signal indicating the detection result by the vibration sensor 72 is transmitted to the controller 10 via the second wiring 82. The second wiring 82 is also used to supply power to the vibration sensor 72.

[0027] As with the first wiring 81, the bearing device 1 may also include a wireless communication device instead of the second wiring 82. A signal indicating the detection result by the vibration sensor 72 is transmitted to the controller 10 via wireless communication.

[0028] Although not shown, the bearing device 1 may include a strain sensor instead of or in addition to the vibration sensor 72. The strain sensor is installed in the housing 31, outer ring spacer 62, table 32, or bed 33, similar to the vibration sensor 72, and detects strain at the installation location. A signal indicating the detection result by the strain sensor is also transmitted to the controller 10 via wiring (or wireless communication). The vibration sensor 72 and the strain sensor correspond to the "vibration strain sensor" according to the present disclosure.

[0029] 4 is a diagram showing an example of the hardware configuration of the controller 10. The controller 10 includes a processor 101, a memory 102, a storage 103, an input / output interface (I / O interface) 104, and a communication interface 105.

[0030] The processor 101 is an arithmetic processing device such as a central processing unit (CPU) or a microprocessing unit (MPU). The memory 102 is a volatile storage device such as a dynamic random access memory (DRAM) or a static random access memory (SRAM). The storage 103 is a nonvolatile storage device such as a hard disk drive (HDD), a solid state drive (SSD), or a flash memory. The storage 103 stores a system program 91 including an operating system (OS), a control program 92 including computer-readable code, and a correspondence map 93 for controlling the motor 4 (rotational drive of the spindle 2) based on signals from the sensor 7. The processor 101 reads the system program 91, the control program 92, and the correspondence map 93 stored in the storage 103, loads them into the memory 102, and executes them to perform various arithmetic processing, including the load estimation processing described below. The correspondence map 93 corresponds to a "correspondence" according to the present disclosure. The "correspondence" according to the present disclosure may be defined in other data formats (e.g., tables, relational expressions, etc.).

[0031] The input / output interface 104 receives a signal output from the sensor 7 (hereinafter referred to as "sensor output") via the wiring 8. The input / output interface 104 converts the sensor output into a digital signal and outputs the converted sensor output to the processor 101. The input / output interface 104 also includes a drive circuit for the motor 4. When the input / output interface 104 receives a drive command including a target rotation speed of the motor 4 from the processor 101, the input / output interface 104 converts the drive command into a signal format suitable for driving the motor 4 and outputs the converted drive command to the motor 4. The input / output interface 104 corresponds to an "interface" according to the present disclosure.

[0032] The communication interface 105 is configured to communicate with an external device of the machine tool 100 (for example, a management server that controls a plurality of machine tools including the machine tool 100).

[0033] <Estimation of Processing Load> In this embodiment, the controller 10 estimates the load applied to the bearing device 1 when the workpiece W is being processed (hereinafter referred to as the "processing load") based on the sensor output both when the workpiece W is being processed and when the workpiece W is not being processed. This process is referred to as the "load estimation process."

[0034] Hereinafter, the rotation speed of the spindle 2 will be referred to as the "spindle rotation speed N." Because the spindle rotation speed N is equal to the rotation speed of the rotary shaft of the motor 4, the spindle rotation speed N may be read as the rotation speed of the rotary shaft of the motor 4. Furthermore, the output from the load sensor 71 (a signal transmitted from the load sensor 71 to the controller 10) will be referred to as the "load sensor output." Similarly, the output from the vibration sensor 72 will be referred to as the "vibration sensor output." The vibration sensor output can be read as the strain sensor output (output from the strain sensor) as appropriate.

[0035] <<During Non-Machining>> Figure 5 is a flowchart showing an example of the processing procedure for load estimation processing when machine tool 100 is not machining workpiece W. Each step is realized by software processing by controller 10, but may also be realized by hardware (electrical circuitry) arranged within controller 10. Hereinafter, steps will be abbreviated as S. The same applies to the flowcharts of Figures 7 and 10 described below.

[0036] The way in which the spindle rotation speed changes when machining the workpiece W is set in advance by the user (administrator) of the machine tool 100. The setting related to how the spindle rotation speed changes (the rotation drive pattern of the spindle 2) may be stored in the storage 103 of the controller 10, or may be stored outside the controller 10 (such as in a management server). The processing shown in the flowchart of Fig. 5 is executed when a predetermined condition is met (for example, when an operation is received from a user who is preparing to machine the workpiece W).

[0037] In S101, the controller 10 determines the scanning range of the spindle rotation speed N in accordance with a preset manner in which the spindle rotation speed changes during machining of the workpiece W. The controller 10 also determines the scanning step δN of the spindle rotation speed N in accordance with a preset manner in which the spindle rotation speed changes during machining of the workpiece W (S102). A preferred method for setting the scanning range of the spindle rotation speed N and the scanning step δN will be described later with reference to FIG.

[0038] In S103, the controller 10 sets the spindle rotation speed N(i) (i is a natural number) to an initial value N(1) (the lowest value within the scanning range in this example).

[0039] In S104, the controller 10 determines whether the elapsed time since the spindle rotation speed N(i) was set to a new value has reached a predetermined specified time. As the spindle rotation speed N(i) increases, heat generated between the rolling elements 53 of the bearing device 1 and the rolling surfaces (the inner ring rolling surface and the outer ring rolling surface) increases. This generated heat is then transmitted through the housing 31 and the spindle 2, raising the temperature of various parts of the machine tool 100 (particularly the components of the bearing device 1). This temperature increase does not occur immediately, but rather occurs with a time delay depending on the heat capacity of the housing 31, the spindle 2, etc. In addition, the machine tool 100 may be cooled using a coolant (e.g., oil cooling). The specified time is determined by the user of the machine tool 100 so that it is equal to or longer than the time required for the temperature of the machine tool 100 (particularly the components of the bearing device 1) to saturate, taking into account the temperature increase due to heat generation in the bearing device 1 and the temperature decrease due to cooling of the machine tool 100. In other words, the specified time is set to be equal to or longer than the time it takes for machine tool 100 to reach a new thermal equilibrium state after the spindle rotation speed N(i) increases.

[0040] Controller 10 waits until the elapsed time since the start of the increase in spindle rotation speed N(i) reaches a specified time (NO in S104). When the elapsed time reaches the specified time (YES in S104), controller 10 acquires load sensor output L(1) at spindle rotation speed N(1) (S105). This acquires load sensor output L(1) under conditions where machine tool 100 has reached a new thermal equilibrium state after the increase in spindle rotation speed N(i).

[0041] In S106, the controller 10 determines whether the spindle rotation speed N has exceeded the scanning range (upper limit of the scanning range). If the spindle rotation speed N has not exceeded the scanning range (NO in S106), the controller 10 increments i by 1 (S107), i.e., increases the spindle rotation speed N(i) by the scanning step δN, and returns the process to S103. This repeats the process of acquiring the load sensor output L(i) at the spindle rotation speed N(i).

[0042] If the spindle rotation speed N(i) exceeds the scanning range (YES in S106), the controller 10 completes the scanning of the spindle rotation speed N(i). Then, the controller 10 generates a correspondence map 93 indicating the correspondence between the spindle rotation speed N(i) and the load sensor output L(i) for all i (i=1 to the value of the spindle rotation speed N at the time of completion of scanning), and stores the generated correspondence map 93 in the storage 103 (see FIG. 4) (S108).

[0043] 6 is a conceptual diagram showing an example of correspondence map 93 generated when machine tool 100 is not machining workpiece W. The horizontal axis represents spindle rotation speed N (command value given to motor 4 from controller 10). The vertical axis represents load sensor output L.

[0044] When machine tool 100 is not machining, the spindle rotation speed N and load sensor output L typically have a relationship such that the load sensor output L increases monotonically as the spindle rotation speed N increases, as shown in FIG.

[0045] The scanning range and scanning step δN of the spindle rotation speed N when the workpiece W is not being machined are preferably determined in accordance with the rotational drive pattern of the spindle 2 when machining the workpiece W. More specifically, the scanning range and scanning step δN of the spindle rotation speed N when the workpiece W is not being machined are preferably determined so as to cover the entire scanning range of the spindle rotation speed N when machining the workpiece W and to include each set value of the spindle rotation speed N when machining the workpiece W.

[0046] For example, when the spindle rotation speed N during machining of the workpiece W is N = 1000 [min －１ ], 2000[min －１ ], 1000[min －１ ], 1500[min －１ ], the scanning range of the spindle rotation speed N when the workpiece W is not being processed is 1000 [min －１ ]~2000[min －１ ] range, and the scanning step δN is 500 [min －１ ]. As a result, all spindle rotation speeds N during machining of the workpiece W are set to N = 1000 [min －１ ], 1500[min －１ ], 2000[min －１ ], the correspondence between the spindle rotation speed N and the load sensor output L when the workpiece W is not being machined is obtained.

[0047] The scanning step δN of the spindle rotation speed N may be set smaller. In the above example, δN=100 [min －１ ]. A smaller scanning step δN can suppress the increase in heat generated between the rolling elements 53 of the bearing device 1 and the rolling surface, thereby suppressing a sudden rise in temperature of the components of the bearing device 1. Therefore, the time required for the machine tool 100 to reach a new thermal equilibrium state can be shortened, so the specified time can be set to a short time. In addition, a smaller scanning step δN also reduces the change in centrifugal force of the spindle 2, thereby suppressing a decrease in load estimation accuracy.

[0048] In addition, when the load sensor outputs L for each of a plurality of spindle rotation speeds N when the workpiece W is not being machined are acquired, it is also possible to estimate the load sensor outputs L that have not been acquired from the acquired load sensor outputs L. For example, N=1000 [min －１ ] and the load sensor output L at N=1500 [min －１ ], when the load sensor output L is acquired, the load sensor output L is acquired when N=1100, 1200, 1300, 1400 [min －１ ] may be obtained by interpolation. Extrapolation based on the load sensor output L that has already been obtained is also possible.

[0049] Here, it has been explained that the scanning range of the spindle rotation speed N and the scanning step δN when the workpiece W is not being machined are determined in accordance with the rotational drive pattern of the spindle 2 when the workpiece W is being machined. However, the scanning range of the spindle rotation speed N when the workpiece W is not being machined may be determined within a predetermined range. The scanning step δN may be determined to a predetermined fixed value.

[0050] 7 is a flowchart showing a first example of the processing procedure for load estimation processing when machine tool 100 is machining workpiece W. The first example is preferably performed under a situation where spindle rotation speed N is constant over time (including a situation where the spindle rotation speed N is maintained at the same speed for a sufficiently long time). The processing shown in this flowchart is performed when a predetermined condition is met (for example, at a predetermined cycle during machining of workpiece W).

[0051] In S201, the controller 10 acquires the load sensor output from the load sensor 71 during machining of the workpiece W. The acquired value is referred to as "load La." The load La corresponds to the "first load" according to the present disclosure.

[0052] In S202, the controller 10 acquires the vibration sensor output from the vibration sensor 72 at the same time as the load sensor output is acquired (at the same timing as the processing in S201).

[0053] In S203, the controller 10 compares the load sensor output with the vibration sensor output to determine whether or not they are synchronized.

[0054] 8 is a diagram showing an example of a situation in which the load sensor output and the vibration sensor output are synchronized. The horizontal axis represents elapsed time, and the vertical axis represents the sensor output (load sensor output or vibration sensor output).

[0055] 8, the load sensor output and the vibration sensor output are substantially constant from time t10 to time t11. From time t11, both the load sensor output and the vibration sensor output increase. In this way, when the load sensor output and the vibration sensor output show similar trends of change at the same timing, it can be said that the load sensor output and the vibration sensor output are synchronized.

[0056] More specifically, the controller 10 calculates, for example, the rate of change of the load sensor output (amount of change per unit time) and the rate of change of the vibration sensor output. Based on the rate of change of the load sensor output, the controller 10 can determine whether the load sensor output is increasing, remaining constant, or decreasing. The same applies to the vibration sensor output.

[0057] If the load sensor output and the vibration sensor output increase at the same time (if the time difference between the start of the increase in the load sensor output and the start of the increase in the vibration sensor output is shorter than a predetermined time), the controller 10 determines that the load sensor output and the vibration sensor output are synchronized. By detecting the synchronization between the load sensor output and the vibration sensor output, it is possible to reliably detect that processing of the workpiece W has started (or is currently being processed) (details will be described later). Note that although an increase in the sensor output has been described as an example, a decrease in the sensor output may also be detected.

[0058] On the other hand, unlike the above, if the load sensor output and the vibration sensor output show different change trends, for example, if the load sensor output increases but the vibration sensor output remains constant, or if the vibration sensor output increases but the load sensor output remains constant, the controller 10 determines that the load sensor output and the vibration sensor output are asynchronous. If they are asynchronous, it is possible that machining of the workpiece W has not started, or that some kind of abnormality has occurred in the machine tool 100 (such as abnormal heat generation in the bearings 5 ​​and / or the spindle 2, or abnormal vibration due to damage to the bearings 5, etc.).

[0059] 7, if the load sensor output and the vibration sensor output are asynchronous in S203 (NO in S203), the controller 10 ends the series of processes without executing the subsequent processes. If the load sensor output and the vibration sensor output are synchronized (YES in S203), the controller 10 advances the process to S204 and acquires the spindle rotation speed N in the processes of S201 and S202.

[0060] In S205, the controller 10 acquires the correspondence map 93 to acquire the load sensor output L when the workpiece W is not being machined, which corresponds to the spindle rotation speed N acquired in S204. The acquired value is referred to as "load Lb." Load Lb corresponds to the "second load" according to the present disclosure.

[0061] 9 is a diagram showing an example of the load sensor output (load La) when the workpiece W is being machined and the load sensor output (load Lb) when the workpiece W is not being machined. The horizontal axis represents elapsed time, and the vertical axis represents the load sensor output L. It can be seen that after time t21, the load La and the load Lb diverge.

[0062] 7 and 9, in S206, the controller 10 calculates the difference ΔL=La−Lb between the load sensor output (load La) acquired in S201 and the load sensor output (load Lb) acquired in S205.

[0063] In S207, the controller 10 estimates the difference ΔL calculated in S206 as the processing load applied to the bearing device 1 when the workpiece W is processed.

[0064] As described above, in the first example, the load sensor output (load Lb) is acquired when the workpiece W is not being machined. Load Lb corresponds to the load during air cutting when the cutting edge of the tool attached to the tip of the spindle 2 is not in contact with the workpiece W, and is equivalent to the baseline load (a reference where load = 0). Therefore, by calculating the difference between the load sensor output (load La) and load Lb when the workpiece W is being machined, it is possible to quantify how much the load has increased from the baseline load due to contact between the cutting edge of the tool and the workpiece W. This quantification can be achieved with a simple configuration that requires only the installation of load sensor 71. Therefore, according to this embodiment, the machining load in bearing device 1 can be estimated easily and with high accuracy.

[0065] It is also conceivable that only the load sensor output is monitored by the controller 10. However, in that case, there is a risk that the estimation accuracy of the machining load may decrease when noise is superimposed on the load sensor output. In contrast, in this embodiment, the controller 10 monitors the vibration sensor output in addition to the load sensor output, that is, two different characteristics, load and vibration, are monitored. Since it is unlikely that noise is simultaneously superimposed on the two sensor outputs, if the two are synchronized, it is highly likely that the workpiece W is being machined normally and that the load sensor output indicates an accurately detected load. Therefore, according to this embodiment, it is possible to further improve the estimation accuracy of the machining load.

[0066] 10 is a flowchart showing a second example of the processing procedure for load estimation processing when machine tool 100 is machining workpiece W. The second example is preferably performed under a situation in which spindle rotation speed N changes over time (including a situation in which the spindle rotation speed N is maintained at the same speed for a short period of time). The processing shown in this flowchart is performed when a predetermined condition is met (for example, at a predetermined cycle during machining of workpiece W).

[0067] Machining cycles are repeatedly performed in machine tool 100, and in S301, controller 10 determines which stage machine tool 100 is currently in. Controller 10 can determine the current stage, for example, based on the vibration sensor output and the drive current value of motor 4. The current value of a servo motor (not shown) used in a feed device for workpiece W can also be used to determine the stage.

[0068] 11 is a diagram for explaining the stages in the machining cycle of machine tool 100. In general, the machining cycle of a machine tool is divided into four stages. The four stages include (1) a spindle stop stage where the spindle is stopped, (2) a spindle rotation stage where the spindle starts to be rotated and the spindle rotation speed increases, (3) a spindle movement stage where the spindle moves to a machining position for the workpiece W while being rotated, and (4) a machining stage where the workpiece W is actually machined.

[0069] 10, in S302, the controller 10 determines whether the current stage determined in S301 is a machining stage. If the current stage is not a machining stage (NO in S302), that is, if the current stage is a spindle stop stage, a spindle rotation stage, or a spindle movement stage, the controller 10 ends the series of processes without executing any further processes.

[0070] On the other hand, if the current stage is the machining stage (YES in S302), the controller 10 proceeds to S303. The processes of S303 to S309 are similar to the processes of S201 to S207 in the first example (see FIG. 7), and therefore detailed description thereof will not be repeated.

[0071] As described above, in the second example, as in the first example, the load sensor output (load Lb) is acquired when the workpiece W is not being machined. By calculating the difference between the load sensor output (load La) and the load Lb when the workpiece W is being machined, it is possible to quantify how much the load has increased from the baseline load due to contact between the tool cutting edge and the workpiece W. Therefore, according to this embodiment, the machining load in the bearing device 1 can be estimated easily and with high accuracy.

[0072] In the process of machining the workpiece W by the machine tool 100 (see FIGS. 7 and 10), it has been explained that the machining load is estimated when the load sensor output and the vibration sensor output are synchronized. As mentioned above, this is because monitoring the outputs of two different sensors improves the accuracy of estimating the machining load. However, the controller 10 may estimate the machining load without considering whether the load sensor output and the vibration sensor output are synchronized. In other words, the vibration sensor 72 may not be installed. Alternatively, the processes of S202 and S203 in FIG. 7 may be omitted, and the processes of S304 and S305 in FIG. 10 may be omitted.

[0073] [Embodiment 2] <Configuration of bearing unit> Fig. 12 is a cross-sectional view showing the schematic configuration of a bearing unit 501 according to embodiment 2. Fig. 13 is a partially enlarged view of the main part on the left side of Fig. 12. Fig. 13 mainly shows a bearing device 550. Fig. 14 is a cross-sectional view taken along line XIV-XIV in Fig. 13.

[0074] 12 is a bearing unit 501 that constitutes part of a spindle device 500, and is used, for example, as a built-in motor type bearing unit for a machine tool. A motor 540 is built into one end of a main shaft 504. A cutting tool such as an end mill is connected to the other end of the main shaft 504.

[0075] The bearing unit 501 includes a bearing 505 including bearings 505a and 505b, a spacer 506 arranged adjacent to the bearings 505a and 505b, a spacer 509 located on the opposite side of the spacer 506 from the bearing 505b and arranged adjacent to one end of the bearing 505b, a motor 540, and a bearing 516 arranged rearward of the motor 540. The main shaft 504 extends along a central axis A. The main shaft 504 is supported by the plurality of bearings 505a and 505b so as to be rotatable about the central axis A. The plurality of bearings 505a and 505b are provided in a housing 503 embedded in the inner diameter portion of the outer cylinder 502.

[0076] 13 , bearing 505a includes an inner ring 505ia, an outer ring 505ga, rolling elements Ta, and a cage Rta. Bearing 505b includes an inner ring 505ib, an outer ring 505gb, rolling elements Tb, and a cage Rtb. Bearing 505a and bearing 505b are spaced apart from each other in the direction along central axis A (axial direction z). Spacer 506 includes an inner ring spacer 506i and a first outer ring spacer 506g.

[0077] An inner ring 505ia of bearing 505a and an inner ring 505ib of bearing 505b are fitted in an interference fit (press-fit) state on the main shaft 504. An inner ring spacer 506i is disposed between the inner ring 505ia and the inner ring 505ib. A first outer ring spacer 506g is disposed between the outer ring 505ga and the outer ring 505gb.

[0078] The bearing 505a is a rolling bearing in which a plurality of rolling elements Ta are arranged between an inner ring 505ia and an outer ring 505ga. The plurality of rolling elements Ta are arranged along the circumferential direction of the central axis A. The plurality of rolling elements Ta are spaced apart by a cage Rta. The bearing 505b is a rolling bearing in which a plurality of rolling elements Tb are arranged between an inner ring 505ib and an outer ring 505gb. The plurality of rolling elements Tb are arranged along the circumferential direction of the central axis A. The plurality of rolling elements Tb are spaced apart by a cage Rtb.

[0079] The bearings 505a and 505b may be bearings capable of bearing a load in the axial direction z. The bearings 505a and 505b may be any of angular contact ball bearings, deep groove ball bearings, tapered roller bearings, etc. An angular contact ball bearing is used in the bearing device 550 shown in Fig. 13. The two bearings 505a and 505b are installed in a back-to-back (DB) configuration.

[0080] The bearing unit 501 according to the second embodiment is a bearing unit 501 using a structure in which the main shaft 504 is supported by three bearings 505a, 505b, and 516, but it may also be a bearing unit 501 using a structure in which the main shaft 504 is supported by two or four or more bearings.

[0081] Bearing 516 is a single-row rolling bearing, such as a cylindrical roller bearing. Bearings 505a and 505b, which are angular contact ball bearings, receive a load in the radial direction θ and a load in the axial direction z acting on main shaft 504. Single-row bearing 516, which is a cylindrical roller bearing, receives a load in the radial direction θ acting on bearing unit 501.

[0082] The housing 503 fixes an outer ring 505ga of the bearing 505a and an outer ring 505gb of the bearing 505b. A coolant flow path G1 is provided in the housing 503. Specifically, the coolant flow path G1 is provided between the housing 503 and the outer cylinder 502. By flowing a coolant through the coolant flow path G1, the bearings 505a and 505b can be cooled.

[0083] The assembly of bearing unit 501 will be described. First, bearing 505a, spacer 506, bearing 505b, and spacer 509 are inserted into main shaft 504 in this order. Next, nut 510 is tightened to fix bearing 505a, spacer 506, bearing 505b, and spacer 509 in place. In this manner, a preload is applied along a path that follows line of force P1, as shown in FIG. 13 .

[0084] Specifically, by tightening the nut 510, a pressing force acts on the end face of the inner ring 505ib of the bearing 505b via the spacer 509. This pressing force presses the inner ring 505ib toward the inner ring spacer 506i. This pressing force is transmitted to the inner ring 505ib, the rolling elements Tb, and the outer ring 505gb. In other words, this pressing force applies a preload between the raceway surfaces of the inner ring 505ib and the outer ring 505gb and the rolling elements Tb.

[0085] Tightening the nut 510 also applies a pressing force from the outer ring 505gb to the first outer ring spacer 506g. This pressing force is transmitted to the outer ring 505ga, the rolling element Ta, and the inner ring 505ia in the bearing 505a. In other words, this pressing force also applies a preload between the raceway surfaces of the inner ring 505ia and the outer ring 505ga of the left bearing 505a and the rolling element Ta.

[0086] The preload applied to the bearings 505a and 505b is determined, for example, by the amount of movement of the nut 510. However, the amount of movement of the nut 510 is limited by the difference in width between the first outer ring spacer 506g and the inner ring spacer 506i.

[0087] [Correction based on Rule 91 09.06.2025] Next, as shown in FIG. 13 , the main shaft 504 with bearings 505a and 505b attached is inserted into the housing 503. Specifically, one end of the second outer ring spacer 507, which is located to the right of the outer ring 505gb of bearing 505b, abuts against the stepped portion 503a provided on the housing 503. The other end of the second outer ring spacer 507 abuts against the right end surface of the outer ring 505gb of bearing 505b. Finally, the front cover 512 is fixed to the housing 503 using bolts (not shown). In this way, the front cover 512 presses against the outer ring 505ga of bearing 505a, the first outer ring spacer 506g, the outer ring 505gb of bearing 505b, and the second outer ring spacer 507, thereby fixing the main shaft 504 in the housing 503 via the bearings 505a and 505b.

[0088] When front cover 512 is fixed to housing 503, a load is applied in the direction of force line P2 shown in Figure 13 according to the torque applied to tighten the bolts. The load applied when fixing front cover 512 displaces outer ring 505ga, first outer ring spacer 506g, outer ring 505gb, and second outer ring spacer 507 in the direction along central axis A of main shaft 504. The preload applied to the path along force line P1 changes depending on the amount of displacement.

[0089] [Correction based on Rule 91 09.06.2025] As shown in Figure 12, the position of the inner ring 516a of the single-row bearing 516 in the axial direction z is determined by a cylindrical member 515 and an inner ring retainer 519. The cylindrical member 515 is fitted onto the outer periphery of the main shaft 504. The inner ring retainer 519 is fixed by a nut 520 threaded onto the main shaft 504. The outer ring 516b of the bearing 516 is sandwiched between a positioning member 521 fixed to an end member 517 and a positioning member 518. The inner ring 516a slides integrally with the main shaft 504 relative to the end member 517 as the main shaft 504 expands and contracts.

[0090] 12 , a motor 540 that drives the main shaft 504 is disposed between bearings 505 a, 505 b and a single-row bearing 516 in a space 522 provided between the main shaft 504 and the outer casing 502. A rotor 514 of the motor 540 is fixed to a cylindrical member 515 that fits onto the outer periphery of the main shaft 504. A stator 513 of the motor 540 is fixed to a housing 508 that is fixed to the inner periphery of the outer casing 502. A coolant flow path G2 is provided in the housing 508. Specifically, the coolant flow path G2 is provided between the housing 508 and the outer casing 502. The rotor 514 and the stator 513 can be cooled by flowing a coolant through the coolant flow path G2.

[0091] When bearing unit 501 is in operation (while main shaft 504 is rotating), the preload changes as the rotational speed of main shaft 504 increases. Specifically, the centrifugal force acting on rolling elements Ta, Tb increases as the rotational speed of main shaft 504 increases. As a result, first outer ring spacer 506g is compressed in the axial direction z, and second outer ring spacer 507 expands in accordance with the amount of deformation of first outer ring spacer 506g, changing the preload applied to bearings 505a, 505b.

[0092] Furthermore, as the rotational speed of spindle 504 increases, the temperature inside bearing unit 501 increases. As a result, a pressing force is generated along line of force P1 due to thermal expansion of the components that make up bearing unit 501. The pressing force due to thermal expansion generated in conjunction with this temperature change changes the preload applied to bearings 505a and 505b.

[0093] During machining, when a load is applied to a cutting tool attached to the tip of the spindle 504, a load associated with machining (machining load F) is applied to the spindle 504 of the bearing unit 501. The machining load F and preload are detected by a load sensor 511 mounted on the bearing unit 501, as shown in Figures 12 and 13 .

[0094] The load sensor 511 may include a plurality of load sensor elements 511a. Specifically, as shown in FIG. 14, each of the load sensor elements 511a is fixed to a flat portion 506ga of the first outer ring spacer 506g. The first outer ring spacer 506g has, for example, a cylindrical shape. The plurality of flat portions 506ga are provided on the outer diameter surface of the first outer ring spacer 506g.

[0095] The multiple load sensor elements 511a are arranged on the same circumference with respect to the central axis A along which the main shaft 504 extends. As shown in FIG. 14 , in the bearing unit 501 of embodiment 2, flat portions 506ga are provided at four locations equally spaced at 90 degrees on the outer diameter surface of the first outer ring spacer 506g. The load sensor 511 may include four load sensor elements 511a. Each of the four load sensor elements 511a is fixed to a corresponding flat portion 506ga.

[0096] The load sensor 511 may be fixed to a non-rotating ring member, and may be fixed to any of the outer diameter surfaces of the outer rings 505ga, 505gb, the inner diameter surface of the front cover 512, or the inner diameter surface of the housing 503, in addition to the outer diameter surface of the first outer ring spacer 506g.

[0097] Next, a description will be given of the load sensor 511. Fig. 15 is a schematic structural diagram of the load sensor 511. Fig. 16 is a diagram showing the general configuration of the load sensor 511.

[0098] The load sensor 511 may be, for example, a strain sensor. The strain sensor detects, for example, the amount of strain in the first outer ring spacer 506g. When the load sensor 511 is a strain sensor, for example, the strain sensor detects the amount of strain and outputs output information S corresponding to the amount of strain.

[0099] 15 and 16, the load sensor 511 includes a detection unit 524 and a processing unit 525. When the load sensor 511 is a strain sensor, the detection unit 524 may be, for example, a strain gauge.

[0100] As shown in FIG. 16 , the processing unit 525 includes an amplifier 525a and an output unit 525b. The amplifier 525a electrically amplifies the signal from the strain gauge. The output unit 525b outputs the amplified signal from the strain gauge to an external device (e.g., the calculation unit 531) as output information S. The amplified signal from the strain gauge may be, for example, a voltage value. The processing unit 525 may also include a bridge circuit as pre-processing for the amplifier 525a. The bridge circuit converts the amount of change in the resistance value of the strain gauge into a voltage value and outputs the voltage value.

[0101] As shown in FIG. 15 , the load sensor 511 includes a substrate 523. A detection unit 524 and a processing unit 525 are disposed on the substrate 523. The substrate 523 may be, for example, a metal plate having a linear expansion coefficient similar to that of the first outer ring spacer 506g. The detection unit 524 is fixed to the substrate 523 by adhesive or mechanical bonding. The processing unit 525 is an electric circuit board that is miniaturized and fixed to the substrate 523. The detection unit 524 and processing unit 525 are electrically connected by wiring or the like.

[0102] The load sensor 511 may be configured only with a strain gauge that serves as the detection unit 524. The processing unit 525 may be provided outside the bearing unit 501. When the processing unit 525 is provided outside the bearing unit 501, the processing unit 525 may be disposed close to the detection unit 524. In this way, the wiring connecting the detection unit 524 and the processing unit 525 is shorter than when the detection unit 524 and the processing unit 525 are located far apart, and the influence of electrical noise is reduced.

[0103] The detection unit 524 is fixed to the outer diameter surface of the first outer ring spacer 506g via the substrate 523. This allows the load sensor 511 to be constructed within the substrate 523, improving the ease of assembly of the load sensor 511. The substrate 523 is fixed to a flat portion 506ga on the outer diameter surface of the first outer ring spacer 506g. This makes it easy to fix the substrate 523, improving the stability of the output of the load sensor 511. Furthermore, because the flat portion 506ga is provided on the outer diameter surface of the first outer ring spacer 506g, less additional processing of the first outer ring spacer 506g is required. In other words, a simple configuration can be achieved that does not require major changes to the structure of the first outer ring spacer 506g, and a decrease in the rigidity of the first outer ring spacer 506g can be suppressed.

[0104] Although the load sensor 511 has been described as a strain sensor, the load sensor 511 may be any sensor capable of detecting information corresponding to a load, and may be a thin film sensor or a pressure sensor in addition to a strain sensor. The load sensor 511 may be configured to output the output information S by combining these sensors.

[0105] The output information S output from the load sensor 511 does not have to be a voltage value, and may be, for example, a current value in addition to a voltage value. The output information S may be, for example, either a strain amount or a load converted from a voltage value.

[0106] 17 is a functional block diagram of a data processing unit 530 that processes the output information S of the load sensor 511. The output information S of the load sensor 511 is output to the data processing unit 530. The data processing unit 530 may be provided inside the bearing unit 501, and the output information S may be output to the data processing unit 530 via a wired connection. The data processing unit 530 may be provided outside the bearing unit 501, and the output information S may be output to the data processing unit 530 wirelessly. The data processing unit 530 may be, for example, a data processing device such as a personal computer that is installed outside the bearing unit 501.

[0107] The data processing unit 530 includes a calculation unit 531 and a storage unit 532. The calculation unit 531 calculates the processing load F from the output information S of the load sensor 511. The storage unit 532 stores a first relationship R1 and a second relationship R2 obtained in a calibration method for the load sensor 511, which will be described later. The calculation unit 531 calculates the processing load F from the output information S based on the first relationship R1 and the second relationship R2.

[0108] The data processing unit 530 may further include a preload calculation unit 533 and a life estimation unit 534. The preload calculation unit 533 may calculate the preload of the bearing 505 from the output information S of the load sensor 511. The preload of the bearing 505 is a load applied to the bearings 505a and 505b. The preload of the bearing 505 includes, for example, not only the pressing force after the bearing unit 501 is assembled, but also centrifugal force generated with the rotation of the main shaft 504 and pressing force due to thermal expansion generated with a temperature rise of the bearing unit 501.

[0109] As a countermeasure against electrical noise, the output information S may be subjected to low-pass filtering before calculating the processing load F and the preload of the bearing 505. The obtained processing load F and preload of the bearing 505 may also be subjected to low-pass filtering to suppress fluctuations in the measurement values ​​of the processing load F and the preload of the bearing 505.

[0110] The life estimation unit 534 is configured to notify the remaining bearing life and the timing for bearing replacement based on at least one of the processing load F, the preload of the bearing 505, and bearing information (such as the internal specifications of the bearing, the rotation speed N, the number of operations, and the temperature). In particular, if the processing load F and the preload of the bearing 505 can be accurately calculated, damage to the components constituting the bearing unit 501 (such as the bearings 505a and 505b, the spindle 504, and the cutting tool) can be suppressed by monitoring the processing load F and the preload of the bearing 505 during processing. Furthermore, if damage to the components occurs, the processing load F and the preload of the bearing 505 can be utilized to determine the cause. Furthermore, the processing quality and productivity of the object processed by the bearing unit 501 can be improved.

[0111] The storage unit 532 is configured by a memory circuit mounted on the microcontroller. The calculation unit 531, preload calculation unit 533, and life estimation unit 534 are configured by, for example, a CPU mounted on the microcontroller. Note that a temperature sensor (not shown) may be installed to add temperature correction as needed.

[0112] <Load Sensor Calibration Method> A description will now be given of a method for calibrating the load sensor 511. Fig. 18 is a flowchart showing the method for calibrating the load sensor 511.

[0113] First, a step (S501) of preparing a spindle device 500 is performed. The spindle device 500 has a bearing unit 501, a load measurement jig 561, and a tool 570. The load measurement jig 561 is fixed to a table 562. The tool 570 is attached to the tip of the spindle 504.

[0114] Next, a storing step (S502) is performed. The storing step (S502) includes a step (S502a) of storing the first relationship R1 and a step (S502b) of storing the second relationship R2.

[0115] In the step (S502a) of storing the first relationship R1, the first relationship R1 between the measured load F1 and the first output information S1 is stored in the storage unit 532. The measured load F1 is measured in a state where the bearing unit 501 presses the load measuring jig 561 with the spindle 504 in a stationary state.

[0116] The measured load F1 is a load displayed as a true value, which is a load calculated from information output from a load sensor mounted on the load measuring jig 561, for example. For example, the measured load F1 is applied to the spindle 504 of the bearing unit 501 by pressing the tool 570 attached to the tip of the spindle 504 against the load measuring jig 561. When the measured load F1 is applied to the bearing unit 501, the load sensor 511 outputs first output information S1. In other words, the first output information S1 is output from the load sensor 511 as information corresponding to the measured load F1.

[0117] By measuring a plurality of measured loads F1 each having a different absolute value, first output information S1 corresponding to each of the measured loads F1 is output. In this way, a first relationship R1 between the plurality of measured loads F1 and the first output information S1 corresponding to each of the measured loads F1 is stored in the storage unit 532.

[0118] In the step (S502a) of storing the first relationship R1, multiple measured loads F1 having different vectors may be measured. Specifically, a measured load F1 in the axial direction z and a measured load F1 in the radial direction θ may be measured. The axial direction z is the direction in which the main axis 504 extends. The radial direction θ is a direction perpendicular to the direction in which the main axis 504 extends. In other words, the radial direction θ is a direction perpendicular to the axial direction z.

[0119] [Correction based on Rule 91 09.06.2025] Figure 19 is a side view of the spindle device 500 in which the measured load F1 in the axial direction z is measured. As shown in Figure 19, the tool 570 may be pressed against the load measurement jig 561 in direction D1. Direction D1 is along the axial direction z. In this manner, the measured load F1 is measured while the bearing unit 501 is pressed in the axial direction z. First output information S1 corresponding to the measured load F1 in the axial direction z is output from the load sensor 511.

[0120] 20 is a graph showing the relationship between the first output information S1 output from the multiple load sensor elements 511a and the measured load F1 in the axial direction z. In FIG. 20, the horizontal axis represents the measured load F1 (unit: N) in the axial direction z, and the vertical axis represents the first output information S1. The first output information S1 is, for example, a voltage value (unit: V). Each of the four load sensor elements 511a outputs first output information Sz1, Sz2, Sz3, and Sz4 in response to the measured load F1 in the axial direction z. One of the first output information Sz1, Sz2, Sz3, and Sz4 output from each of the multiple load sensor elements 511a may be used as the output information S corresponding to the measured load F1 in the axial direction z.

[0121] 20, the first output information Sz1, Sz2, Sz3, and Sz4 output from each of the plurality of load sensor elements 511a is not uniform in the circumferential direction of the first outer ring spacer 506g, but varies due to the influence of the dimensional accuracy of the first outer ring spacer 506g, the housing 503, the front cover 512, the bearing 505, etc., assembly variations, radial load, and misalignment of the center of the load application point. Therefore, as shown in FIG. 20, the value Sz1, Sz2, Sz3, and Sz4 obtained by averaging the plurality of first output information Sz1, Sz2, Sz3, and Sz4 is ａｖｅ may be used as the output information S corresponding to the measured load F1 in the axial direction z. The output information S corresponding to the measured load F1 in the axial direction z may be any of the following: a total value of the plurality of first output information Sz1, Sz2, Sz3, Sz4, a maximum value of the plurality of first output information Sz1, Sz2, Sz3, Sz4, a minimum value of the plurality of first output information Sz1, Sz2, Sz3, Sz4, a difference between the maximum and minimum values ​​of the plurality of first output information Sz1, Sz2, Sz3, Sz4, or a value obtained by correcting the plurality of first output information Sz1, Sz2, Sz3, Sz4 depending on the arrangement relationship in the load sensor element 511a.

[0122] FIG. 21 is a side view of the spindle device 500 in which the measurement load F1 in the radial direction θ is measured. FIG. 22 is a plan view of the spindle device 500 in which the measurement load F1 in the radial direction θ is measured. As shown in FIG. 21 , the tool 570 may be pressed against the load measurement jig 561 along direction D2. Direction D2 is a direction perpendicular to the direction in which the spindle 504 extends (axial direction z). From a different perspective, direction D2 is a direction along the radial direction θ. In this way, the measurement load F1 is measured with the bearing unit 501 pressed in the radial direction θ.

[0123] A first relationship R1 between the measured load F1 in at least four directions in the radial direction θ and the first output information S1 corresponding to each of the measured loads F1 may be stored in the storage unit 532. Specifically, as shown in FIG. 22 , the radial direction θ includes a first radial direction θ1 and a second radial direction θ2. The second radial direction θ2 is a direction perpendicular to the first radial direction θ1. The tool 570 may be pressed against the load measuring jig 561 along each of directions D2a, D2b, D2c, and D2d. Note that the direction D2a is the negative direction of the first radial direction θ1 in FIG. 22 . The direction D2b is the negative direction of the second radial direction θ2 in FIG. 22 . The direction D2c is the positive direction of the first radial direction θ1 in FIG. 22 . The direction D2d is the positive direction of the second radial direction θ2 in FIG. 22 .

[0124] 23 is a graph showing the relationship between the first output information S1 output from the multiple load sensor elements 511a and the measured load F1 in the radial direction θ. In FIG. 23, the horizontal axis represents the measured load F1 (unit: N) in the radial direction θ, and the vertical axis represents the first output information S1. For the measured load F1 in the radial direction θ, each of the multiple load sensor elements 511a outputs first output information Sθ1, Sθ2, Sθ3, and Sθ4. For the measured load F1 in the radial direction θ, the values ​​of the first output information Sθ1, Sθ2, Sθ3, and Sθ4 output from each of the multiple load sensor elements 511a differ depending on the direction in which the tool 570 is pressed against the load measurement jig 561. Therefore, the direction and absolute value of the measured load F1 may be uniquely determined from the relationship between the values ​​of the first output information Sθ1, Sθ2, Sθ3, and Sθ4 output from each of the multiple load sensor elements 511a.

[0125] The load measuring jig 561 used when measuring the measurement load F1 in the axial direction z may be different from the load measuring jig 561 used when measuring the measurement load F1 in the radial direction θ. The shape of the load measuring jig 561 may be, for example, a regular hexahedron. When measuring the measurement load F1 in the radial direction θ, the shape of the load measuring jig 561 used may be, for example, a hemispherical shape. In this way, the measurement load F1 in the radial direction θ can be measured with higher accuracy.

[0126] In this way, the first relationship R1 between the measured load F1 measured when the bearing unit 501 is pressing the load measuring jig 561 while the spindle 504 is stationary and the first output information S1 output from the load sensor 511 when the measured load F1 is measured is stored in the memory unit 532.

[0127] In the step (S502a) of storing the first relationship R1, a tool 570 attached to the tip of the spindle 504 presses the load measuring jig 561. The tool 570 may be a cutting tool such as an end mill, a reamer, or a cutting tool that is actually used in machining.

[0128] In the step (S502a) of storing the first relationship R1, a dedicated tool for load measurement may be used so that contact between the tool 570 and the load measurement jig 561 is stable when the tool 570 is pressed against the load measurement jig 561. The dedicated tool for load measurement may have the same weight as the cutting tool. In this way, in the storing step (S502), the first relationship R1 corresponding to the cutting tool used during machining can be obtained with high accuracy. In other words, the machining load F can be accurately calculated according to the cutting tool used during machining.

[0129] Next, a step (S502b) of storing the second relationship R2 is performed. In this step (S502b), the second relationship R2 between the rotation speed N of the main shaft 504 in the rotation state of the main shaft 504 and the second output information S2 is stored in the storage unit 532.

[0130] As described above, when bearing unit 501 is in operation (while main shaft 504 is rotating), centrifugal force is generated as main shaft 504 rotates, and pressing force is generated due to thermal expansion as the temperature of bearing unit 501 rises. That is, while main shaft 504 is rotating, the preload changes due to the influence of the centrifugal force and pressing force due to thermal expansion. As a result, the value of output information S output from load sensor 511 changes as the preload changes. In this state of rotation of main shaft 504, second output information S2 is output from load sensor 511 as output information S in accordance with the amount of change in preload. That is, second output information S2 is output from load sensor 511 as information corresponding to the rotation speed N of main shaft 504.

[0131] In the rotation state of the main shaft 504, the second output information S2 corresponding to each of the plurality of rotation speeds N is output at each of the plurality of rotation speeds N. In this manner, the second relationship R2 between the plurality of rotation speeds N and the second output information S2 corresponding to each of the plurality of rotation speeds N is stored in the storage unit 532.

[0132] In this way, in the above-mentioned method for calibrating the load sensor 511, a spindle device 500 is obtained in which the load sensor 511 mounted on the bearing unit 501 is calibrated based on the first relationship R1 and the second relationship R2 obtained from the storage step (S502).

[0133] <Method of Calculating Processing Load> A method of calculating the processing load F will be described below. As shown in Fig. 18 , a processing step (S503) is performed using bearing unit 501. Memory unit 532 of bearing unit 501 stores first relationship R1 and second relationship R2.

[0134] Fig. 24 is a graph showing the first relationship R1 and the second relationship R2. Based on the first relationship R1 and the second relationship R2 obtained in the storing step (S502), for example, a map shown in Fig. 24 is obtained. In Fig. 24, the horizontal axis indicates the load (unit: N), and the vertical axis indicates, for example, a voltage value (unit: V) as the output information S. The load F10 is, for example, the preload when the main shaft 504 is in a stationary state (when the rotation speed N of the main shaft 504 is 0 rpm) after the bearing unit 501 is assembled. The voltage value V ０ is the voltage value output from the load sensor 511 when the main shaft 504 is in a stationary state and no load is applied to the main shaft 504 of the bearing unit 501. ０ corresponds to the load F10.

[0135] Each of the loads F11 to F1n is the measured load F1 measured when the spindle 504 is in a stationary state in the step (S502a) of storing the first relationship R1. ０１ ~V ０ｎare the first output information S1 output from the load sensor 511 when the loads F11 to F1n are applied to the bearing unit 501 while the spindle 504 is stationary in the step (S502a) of storing the first relationship R1. ０１ ~V ０ｎ The first relationship R1 is a relationship between the loads F10 to F1n and the voltage value V ０ ~V ０ｎ The relation may be:

[0136] Voltage value V １ ~V Ｎ are the second output information S2 output from the load sensor 511 in the rotation state at each rotation speed N of the spindle 504 in the step (S502b) of storing the second relationship R2. ０ ~V Ｎ Each of these corresponds to the rotation state when the rotation speed N of the spindle 504 is 0 to N rpm. For example, the rotation state of the spindle 504 at 1000 rpm is １ The second relationship R2 may correspond to the rotation speed 0 to N of the main shaft 504 and the voltage value V ０ ~V Ｎ The relation may be:

[0137] 24, for example, when the bearing unit 501 performs machining at a rotation speed N of the spindle 504 of 1000 rpm, a voltage value V is output as output information S from the load sensor 511. At this time, the machining load F is calculated from the voltage value V based on the first relationship R1 and the second relationship R2. Specifically, the voltage value V is calculated from the voltage value V based on the second relationship R2. １ and voltage value V ０ The value to be subtracted from the voltage value V based on the second relationship R2 is calculated based on the rotation speed 0 to N and the voltage value V ０ ~V Ｎ The value to be subtracted from the voltage value V may be calculated from a relational expression using any interpolation method based on the rotation speed 0 to N and the voltage value V ０ ~V Ｎ The interpolation method may be, for example, linear interpolation, polynomial interpolation, or spline interpolation.

[0138] Next, the voltage value V is converted to the voltage value V １ and voltage value V ０ The processing load F corresponding to the value obtained by subtracting the difference between the loads F10 to F1n and the voltage value V is calculated based on the first relationship R1. ０ ~V ０ｎ The processing load F may be calculated from a relational expression using any interpolation method based on the loads F10 to F1n and the voltage value V ０ ~V ０ｎ Alternatively, the machining load F may be calculated by interpolating or extrapolating based on the above formula. As the interpolation method, for example, linear interpolation, polynomial interpolation, or spline interpolation may be used. In this way, the machining load F applied to the main spindle 504 of the bearing unit 501 during machining can be accurately calculated.

[0139] By monitoring the accurately calculated processing load F and preload during processing, it is possible to reduce the occurrence of damage to the components (bearings 505a, 505b, spindle 504, cutting tool, etc.) that make up the bearing unit 501, and if damage does occur, the processing load F and preload can be used to identify the cause. Furthermore, it is possible to improve the processing quality and productivity of the object processed by the bearing unit 501.

[0140] <Operation and Effect> The spindle device 500 according to the present disclosure includes a bearing unit 501. The bearing unit 501 is equipped with a load sensor 511. The spindle device 500 includes a calculation unit 531 and a storage unit 532. The calculation unit 531 calculates a processing load F applied to the bearing unit 501 from output information S output from the load sensor 511. The bearing unit 501 has a rotatable main shaft 504. The storage unit 532 stores a first relationship R1 between a measured load F1 and first output information S1. The measured load F1 is applied to the bearing unit 501 when the main shaft 504 is stationary. The first output information S1 is output from the load sensor 511 when the measured load F1 is applied to the bearing unit 501. The calculation unit 531 calculates the processing load F from the output information S based on the first relationship R1.

[0141] [Correction based on Rule 91 09.06.2025] In this way, it is possible to accurately calculate the processing load F applied to the spindle 504 of the bearing unit 501 during processing. As a result, by monitoring the processing load F and preload during processing, it is possible to reduce the occurrence of damage to the components that make up the bearing unit 501 (bearings 505a, 505b, spindle 504, cutting tool, etc.), and if damage does occur, the processing load F and preload can be used to investigate the cause. Furthermore, it is possible to improve the processing quality and productivity of objects processed with the bearing unit 501.

[0142] In the spindle device 500, the memory unit 532 stores a second relationship R2 between the rotation speed N of the spindle 504 and second output information S2 in the rotation state of the spindle 504. The second output information S2 is output from the load sensor 511 in the rotation state of the spindle 504. The calculation unit 531 calculates the processing load F from the output information S based on the first relationship R1 and the second relationship R2.

[0143] In this way, the processing load F applied to the main shaft 504 of the bearing unit 501 during processing can be accurately calculated.

[0144] In the spindle device 500, the load sensor 511 includes a plurality of load sensor elements 511a. The plurality of load sensor elements 511a are arranged on the same circumference with respect to the central axis A along which the main shaft 504 extends.

[0145] In this way, the vector and absolute value of the machining load F can be calculated from the output information S output from the plurality of load sensor elements 511a. As a result, the machining load F applied to the spindle 504 of the bearing unit 501 during machining can be accurately calculated.

[0146] The spindle device 500 further includes a load measuring jig 561. The measurement load F1 is measured in a state where the bearing unit 501 presses the load measuring jig 561.

[0147] In this way, the load measuring jig 561 can be used to obtain the first relationship R1 between the measured load F1 and the first output information S1.

[0148] In the spindle device 500, the direction in which the main shaft 504 extends is defined as the axial direction z. The measurement load F1 is measured in a state in which the bearing unit 501 presses the load measurement jig 561 in the axial direction z.

[0149] In this way, the load measuring jig 561 can be used to obtain the first relationship R1 between the measured load F1 in the axial direction z of the spindle 504 and the first output information S1.

[0150] In the spindle device 500, the direction perpendicular to the direction in which the main shaft 504 extends is defined as the radial direction θ. The measurement load F1 is measured in a state in which the bearing unit 501 presses the load measurement jig 561 in the radial direction θ.

[0151] In this way, the load measuring jig 561 can be used to obtain the first relationship R1 between the measured load F1 in the radial direction θ of the spindle 504 and the first output information S1.

[0152] A method for calibrating a load sensor 511 according to the present disclosure includes a step (S501) of preparing a spindle device 500 having a bearing unit 501 and a load measuring jig 561, and a storing step (S502). The bearing unit 501 is equipped with a load sensor 511. The bearing unit 501 has a rotatable main shaft 504. The storing step (S502) includes a step (S502a) of storing a first relationship R1 used to calculate a processing load F applied to the bearing unit 501. In the storing step (S502a) of the first relationship R1, the first relationship R1 between a measured load F1 and first output information S1 is stored. The measured load F1 is measured in a state in which the bearing unit 501 presses the load measuring jig 561 with the main shaft 504 stationary. The first output information S1 is output from the load sensor 511 when the measured load F1 is measured.

[0153] In this way, it is possible to obtain the first relationship R1 that can accurately calculate the processing load F applied to the spindle 504 of the bearing unit 501 during processing. As a result, by monitoring the processing load F and the preload during processing, it is possible to reduce the occurrence of damage to the components that make up the bearing unit 501 (bearings 505a, 505b, spindle 504, cutting tool, etc.), and if damage occurs, the processing load F and the bearing preload can be used to identify the cause. Furthermore, it is possible to improve the processing quality and productivity of objects processed by the bearing unit 501.

[0154] In the method for calibrating the load sensor 511, the storing step (S502) includes a step (S502b) of storing a second relationship R2 used to calculate the processing load F. In the storing step (S502b) of the second relationship R2, the second relationship R2 between the rotation speed N of the spindle 504 and second output information S2 in the rotation state of the spindle 504 is stored. The second output information S2 is output from the load sensor 511 in the rotation state of the spindle 504.

[0155] In this way, the second relationship R2 can be obtained, which allows accurate calculation of the processing load F applied to the spindle 504 of the bearing unit 501 during processing.

[0156] The method for measuring the processing load F according to the present disclosure includes a step (S501) of preparing a spindle device 500 having a bearing unit 501, and a step (S503) of processing using the bearing unit 501. In the processing step (S503), the processing load F applied to the bearing unit 501 is calculated from output information S output from the load sensor based on a first relationship R1 obtained using a calibration method for the load sensor 511.

[0157] In this way, the processing load F applied to the spindle 504 of the bearing unit 501 during processing can be accurately calculated based on the first relationship R1 and the second relationship R2. As a result, by monitoring the processing load F and preload during processing, it is possible to reduce the occurrence of damage to the components that make up the bearing unit 501 (bearings 505a, 505b, spindle 504, cutting tool, etc.), and if damage occurs, the processing load F and preload can be used to identify the cause. Furthermore, it is possible to improve the processing quality and productivity of objects processed by the bearing unit 501.

[0158] [Embodiment 3] <Configuration of Bearing Unit> Figure 25 is a cross-sectional view of a bearing unit 501 according to embodiment 3. Figure 25 corresponds to Figure 14. The bearing unit 501 shown in Figure 25 basically has the same configuration as the bearing unit 501 shown in Figures 12 to 14 and can achieve the same effects, but differs in that the load sensor 511 includes three load sensor elements 511a. Specifically, flat portions 506ga are provided at three locations equally spaced 120 degrees apart on the outer diameter surface of the first outer ring spacer 506g. Each of the three load sensor elements 511a is fixed to a respective flat portion 506ga.

[0159] In this way, the processing load F can be calculated accurately if there are at least three or more load sensor elements 511a.

[0160] [Fourth Embodiment] <Configuration of Bearing Unit> Figure 26 is a cross-sectional view of a bearing unit 501 according to a fourth embodiment. Figure 26 corresponds to Figure 25. The bearing unit 501 shown in Figure 26 basically has the same configuration as the bearing unit 501 shown in Figure 25 and can achieve the same effects, but differs in that flat portions 506gb are provided at three locations equally spaced at 120 degrees on the inner diameter surface of the first outer ring spacer 506g. Each of the three load sensor elements 511a is fixed to one of the flat portions 506gb.

[0161] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0162] 1 Bearing device, 2 Main shaft, 3 Machine body, 31 Housing, 32 Table, 33 Bed, 4 Motor, 5 Bearing, 51 Inner ring, 52 Outer ring, 53 Rolling element, 54 Cage, 6 Spacer, 61 Inner ring spacer, 62 Outer ring spacer, 7 Sensor, 71 Load sensor, 72 Vibration sensor, 8 Wiring, 81 First wiring, 82 Second wiring, 10 Controller, 101 Processor, 102 Memory, 103 Storage, 104 Input / output interface, 105 Communication interface, 91 System program, 92 Control program, 93 Correspondence map, 100 Machine tool, 501 Bearing unit, 502 Outer cylinder, 503, 508 Housing, 503a Step portion, 504 Main shaft, 505, 505a, 505b, 516 Bearing, 505ga, 505gb, 516b Outer ring, 505ia, 505ib, 516a Inner ring, 506, 509 Spacer, 506g First outer ring spacer, 506ga, 506gb Flat portion, 506i Inner ring spacer, 507 Second outer ring spacer, 510 Nut, 511 Load sensor, 511a Load sensor element, 512 Front cover, 513 Stator, 514 Rotor, 515 Cylindrical member, 517 End member, 518 Member, 519 Inner ring holder, 520 Nut, 521 Member, 522 Space portion, 523 Board, 524 Detection unit, 525 Processing unit, 525a Amplification unit, 525b Output unit, 530 Data processing unit, 531 Calculation unit, 532 Memory unit, 533 preload load calculation unit, 534 life estimation unit, 540 motor, 550 bearing device, 561 load measurement jig, 562 table, 570 tool, 500 spindle device, A central axis, D1, D2, D2a, D2b, D2c, D2d direction, F processing load, F1 measured load, G1, G2 coolant flow path, N rotation speed, P1, P2 force line, R1 first relationship, R2 second relationship, Rta, Rtb cage, S output information, S1 first output information, S2 second output information, Ta, Tb rolling element, z axial direction, θ radial direction, θ1 first radial direction, θ2 second radial direction.

Claims

1. A bearing device that rotatably supports a spindle for machining a workpiece by rotational drive, the bearing device comprising: a load sensor that outputs a signal indicating a detected value of a load applied to the bearing device; a storage that stores a correspondence relationship between the rotational speed of the spindle and the detected value of the load sensor when the workpiece is not being machined; and a processor that estimates a machining load applied to the bearing device during machining of the workpiece based on a signal from the load sensor. When the rotational speed of the spindle is controlled to a predetermined speed, the processor acquires a first load indicated by the signal from the load sensor and a second load that is the detected value of the load sensor corresponding to the predetermined speed in the correspondence relationship, and estimates the difference between the first load and the second load as the machining load. Bearing device.

2. The bearing device according to claim 1, further comprising an interface that receives a signal from a vibration and strain sensor that detects vibration or strain during machining or non-machining of the workpiece, wherein the processor estimates the machining load using the difference when the signals from the load sensor and the vibration and strain sensor are synchronized.

3. The bearing device according to claim 1 or 2, wherein the bearing device includes an inner ring spacer that is a rotating ring and an outer ring spacer that is a non-rotating ring, and the load sensor is installed on the outer ring spacer.

4. The bearing device according to claim 2, wherein the bearing device includes an inner ring spacer that is a rotating ring and an outer ring spacer that is a non-rotating ring, and the vibration and strain sensor is installed on the outer ring spacer.

5. The bearing device according to claim 4, wherein the load sensor is installed on the outer ring spacer.

6. A spindle device comprising the bearing device according to any one of claims 1 to 5, the spindle, and a housing that houses the bearing device and the spindle.

7. The spindle device according to claim 6, further comprising a vibration and strain sensor that outputs a signal indicating a detected value of vibration or strain, wherein the processor estimates the machining load using the difference when the signals from the load sensor and the vibration and strain sensor are synchronized.

8. The spindle device according to claim 7, wherein the vibration and strain sensor is installed on the housing.

9. The spindle device according to claim 7, further comprising a table configured to fix the workpiece, and a bed that supports the entire spindle device, wherein the vibration strain sensor is installed on one of the table and the bed.

10. The spindle device according to any one of claims 6 to 9, wherein the correspondence relationship is defined to indicate the correspondence relationship between the rotational speed of the spindle and the detection value of the load sensor in the thermal equilibrium state of the spindle device.

11. A load estimation method for estimating, by a computer, a machining load applied to a bearing device during machining of a workpiece by rotational driving of a spindle, wherein the bearing device includes a load sensor that outputs a signal indicating a detection value of the load applied to the bearing device, and the correspondence relationship between the rotational speed of the spindle and the detection value of the load sensor when the workpiece is not being machined is stored in the computer. The load estimation method includes: obtaining a first load indicated by a signal from the load sensor and a second load that is the detection value of the load sensor corresponding to the predetermined speed in the correspondence relationship when the rotational speed of the spindle is controlled to a predetermined speed; and estimating the difference between the first load and the second load as the machining load.

12. A program for causing the computer to execute the load estimation method according to claim 11.

13. A spindle device including a bearing unit, wherein the bearing unit is equipped with a load sensor, and the spindle device has an arithmetic unit that calculates a machining load applied to the bearing unit from output information output from the load sensor, and a storage unit. The bearing unit has a rotatable spindle, and the storage unit stores a first relationship between a measured load applied to the bearing unit in a stationary state of the spindle and first output information output from the load sensor when the measured load is applied to the bearing unit. The arithmetic unit calculates the machining load from the output information based on the first relationship.

14. The memory unit stores a second relationship between the rotational speed of the main shaft in the rotational state of the main shaft and second output information output from the load sensor in the rotational state of the main shaft. The calculation unit calculates the machining load from the output information based on the first relationship and the second relationship. The spindle device according to claim 13.

15. The load sensor includes a plurality of load sensor elements, and the plurality of load sensor elements are arranged on the same circumference with respect to the central axis along which the main shaft extends. The spindle device according to claim 13 or claim 14.

16. The spindle device further includes a jig for load measurement, and the measured load is measured in a state where the bearing unit presses the load measurement jig. The spindle device according to any one of claims 13 to 15.

17. When the direction in which the main shaft extends is defined as the axial direction, the measured load is measured in a state where the bearing unit presses the load measurement jig in the axial direction. The spindle device according to claim 16.

18. When the direction perpendicular to the direction in which the main shaft extends is defined as the radial direction, the measured load is measured in a state where the bearing unit presses the load measurement jig in the radial direction. The spindle device according to claim 16 or claim 17.

19. A method for calibrating a load sensor, comprising a step of preparing a spindle device having a bearing unit and a jig for load measurement, and a step of storing. The bearing unit is equipped with a load sensor, the bearing unit has a rotatable main shaft, and the storing step includes a step of storing a first relationship used for calculating the machining load applied to the bearing unit. In the step of storing the first relationship, the first relationship between the measured load measured in a state where the bearing unit presses the load measurement jig in a stationary state of the main shaft and the first output information output from the load sensor when the measured load is measured is stored.

20. The storing step includes a step of storing a second relationship used for calculating the machining load. In the step of storing the second relationship, the second relationship between the rotational speed of the main shaft in the rotational state of the main shaft and the second output information output from the load sensor in the rotational state of the main shaft is stored. The method for calibrating a load sensor according to claim 19. Step of preparing a spindle device having a bearing unit, and a step of machining using the bearing unit, wherein in the step of machining, the machining load applied to the bearing unit is calculated from output information output from the load sensor based on the first relationship obtained by using the calibration method of the load sensor according to claim 19 or claim 20. A method for calculating a machining load.

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