Bearing device, spindle device comprising the same, load estimation method and program

Abstract

To easily and highly accurately estimate working load applied to a bearing device.SOLUTION: A bearing device 1 rotatably supports a spindle 2 that works a workpiece by rotational drive. The bearing device 1 comprises a load sensor 71, a storage 103, and a processor 101. The load sensor 71 outputs a signal indicating a detected value of load applied to the bearing device 1. The storage 103 stores a correspondence map 93 between a rotational speed of the spindle 2 and the detected value of the load sensor 71 during non-working of the workpiece. The processor 101 estimates working load applied to the bearing device 1 during working of the workpiece on the basis of a signal from the load sensor 71. When the rotational speed of the spindle 2 is controlled to a predetermined speed, the processor 101 acquires a first load indicated by the signal from the load sensor 71 and a second load which is the detected value of the load sensor 71 corresponding to the predetermined speed in the correspondence map 93, and estimates the difference between the first load and the second load as the working load.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a bearing device, a spindle device including the same, a load estimation method, and a program.

Background Art

[0002] The main shaft provided in a spindle device such as a machine tool is supported by a bearing device. When the bearing device is damaged, the operation of the spindle device must be stopped and the main shaft must be replaced. During the replacement work, the productivity of the work site where the spindle device is installed can be significantly reduced. Therefore, techniques for early detection of damage (or the possibility of damage) to the bearing device have been proposed.

[0003] For example, Japanese Patent No. 5168352 (Patent Document 1) discloses a collision detection device in a machine tool. 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 of the drive motor from 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 of the drive motor is during machining or non-machining, and sets a motor current limit value based on the result of the determination. Thereby, a load current setting value indicating a reference current value for determining the presence or absence of a collision between the structure provided with the drive motor and the workpiece, and the motor current is limited so that the motor output torque of the drive motor becomes equal to or less than a certain value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a bearing device or a spindle device including the same, there is a demand for a technique that improves the estimation accuracy of the load applied to the bearing device during machining (hereinafter also referred to as "machining load") without adopting a complicated device configuration.

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

Means for Solving the Problems

[0007] A bearing device according to an aspect of the present disclosure rotatably supports a spindle that rotates and drives a workpiece for machining. The bearing device includes a load sensor, a storage, and a processor. The load sensor outputs a signal indicating a detection value of the load applied to the bearing device. In the storage, a correspondence relationship between the rotation speed of the spindle and the detection value of the load sensor when the workpiece is not being machined is stored. The processor estimates the machining load applied to the bearing device during machining of the workpiece based on the signal from the load sensor. When the rotation 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 detection 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.

[0008] A load estimation method according to another aspect of the present disclosure estimates, by a computer, the machining load applied to a bearing device during machining of a workpiece by rotationally driving a spindle. The bearing device includes a load sensor that outputs a signal indicating a detection value of the load applied to the bearing device. A correspondence relationship between the rotation 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 first and second steps. The first step is to acquire a first load indicated by the 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 rotation speed of the spindle is controlled to a predetermined speed. The second step is to estimate the difference between the first load and the second load as the machining load.

Advantages of the Invention

[0009] According to the present disclosure, the processing load applied to the bearing device can be estimated simply and with high accuracy.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

[0012] In the following embodiments, a configuration in which the bearing device according to the present disclosure is applied to the main shaft of a machine tool will be described as an example. However, the application of the bearing device according to the present disclosure is not limited to the main shaft of a machine tool. The bearing device according to the present disclosure can also be applied to a similar structure in the industrial field or the automotive field.

[0013] [Embodiment] [Overall Configuration] FIG. 1 is a diagram showing an example of the overall configuration of a machine tool according to the present embodiment. The machine tool 100 is a spindle device, and includes a bearing device 1, a main shaft 2, a machine body 3, and a motor 4. The bearing device 1 includes a plurality (four in this example) of bearings 5 and at least one (three in this example) of spacers 6. The machine tool 100 further includes a controller 10.

[0014] The bearing device 1 is a rolling bearing device that rotatably supports the main shaft 2. The main shaft 2 is directly connected to the rotation shaft of the motor 4. The motor 4 rotates according to a drive command from the controller 10. Thereby, the main shaft 2 rotates. 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 shaft 2. The table 32 is a machining table configured to fix a workpiece (object to be machined) W. The bed 33 is a base that supports the entire machine tool.

[0015] The four bearings 5 are arranged at the boundary portion between the housing 31 and the main shaft 2. The four bearings 5 rotatably support the main shaft 2. One spacer 6 is arranged between two adjacent bearings 5. However, the number of installed bearings 5 and spacers 6 is not particularly limited. The bearing device 1 may include three or five or more bearings 5 and a plurality of corresponding spacers 6, or may include two bearings 5 and a single spacer 6.

[0016] [Configuration of Bearing Device] Figure 2 is a diagram showing an example of the configuration of the bearing device 1 in more detail. Figure 3 is an enlarged view of the bearing 5 shown in Figure 2. Referring to Figures 1 to 3, the bearing 5 is a rolling bearing, for example, an angular ball bearing. The bearing 5 includes an inner ring 51, an outer ring 52, rolling elements 53, and a cage 54.

[0017] An annular inner ring raceway surface is formed on the inner ring 51. An annular outer ring raceway surface is formed on the outer ring 52. The inner ring 51 and the outer ring 52 are arranged at intervals 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 that are rotatably arranged between the inner ring raceway surface of the inner ring 51 and the outer ring raceway surface of the outer ring 52, for example, spherical members. The cage 54 is annular and holds a plurality of rolling elements 53 at intervals in the circumferential direction thereof.

[0018] The spacer 6 includes an inner ring spacer 61 and an outer ring spacer 62. In the example shown in Figure 2, one inner ring spacer 61 and one outer ring spacer 62 are arranged between two bearings 5. By inserting the main shaft 2 into the inner diameter portion of the inner ring 51 and the inner diameter portion of the inner ring spacer 61, and inserting the outer diameter portion of the outer ring 52 and the outer diameter portion of the outer ring spacer 62 into the housing 31, the main shaft 2 is rotatably supported.

[0019] 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.

[0020] The load sensor 71 is, for example, a strain gauge whose electrical resistance changes in response to strain. The load sensor 71 may be a pressure sensor that converts the pressure applied to the contact surface into an electrical signal. The load sensor 71 may be a thin-film sensor (a thin-film strain gauge or a thin-film pressure sensor). The load sensor 71 may be a combination of multiple types of sensors (such as a strain gauge, a pressure sensor, a thin-film sensor, etc.). The load sensor 71 may output a value obtained by calculating or converting the output from those combinations.

[0021] The load sensor 71 is installed, for example, on the outer-race spacer 62 which is a non-rotating ring. The load sensor 71 detects the load applied to the outer-race spacer 62. The signal indicating the detection result by the load sensor 71 is transmitted to the controller 10 (see FIG. 1) via the first wiring 81 installed on the outer-race spacer 62. The first wiring 81 is also used for supplying power from a power supply circuit (not shown) to the load sensor 71.

[0022] Although not shown, the bearing device 1 may include a wireless communication device instead of the first wiring 81. The wireless communication device is a device that uses radio waves in the 2.4 GHz frequency band such as Wi-Fi (registered trademark) or Bluetooth (registered trademark), for example. The signal indicating the detection result by the load sensor 71 is transmitted to the controller 10 by wireless communication. Thereby, processing of the housing 31 for routing the first wiring 81 becomes unnecessary. Also, the work of incorporating the outer-race spacer 62 into the housing 31 becomes easier. For power supply to the load sensor 71 and the wireless communication device, a generator that generates electricity as the main shaft 2 rotates can be used, for example.

[0023] Instead of the load sensor 71, it is also conceivable to provide a torque sensor (not shown). However, generally, since the torque sensor is installed on the inner ring spacer which is a rotating ring, it rotates together with the rotational drive of the main shaft. Therefore, in order to mount the torque sensor, a signal transmission mechanism for a rotating body (slip ring, telemeter, etc.) is required. On the other hand, in the present embodiment, a load sensor 71 that can be installed on the outer ring spacer 62 which is a non-rotating ring is adopted. As a result, the routing of the first wiring 81 (that is, the power supply to the load sensor 71 and the signal acquisition from the load sensor 71) becomes easy.

[0024] The vibration sensor 72 is installed on, for example, the housing 31. The vibration sensor 72 may be installed on the outer ring spacer 62, may be installed on the table 32, or may be installed on the bed 33. The vibration sensor 72 detects the vibration of the housing 31 (outer ring spacer 62, table 32, or 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 for the power supply to the vibration sensor 72.

[0025] Regarding the second wiring 82 as well as the first wiring 81, the bearing device 1 may 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 by wireless communication.

[0026] 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 on the housing 31, the outer ring spacer 62, the table 32, or the bed 33 in the same manner as the vibration sensor 72, and detects the 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 by wireless communication). The vibration sensor 72 and the strain sensor correspond to the "vibration and strain sensor" according to the present disclosure.

[0027] <Configuration of the controller> FIG. 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.

[0028] The processor 101 is an arithmetic processing device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The memory 102 is a volatile storage device such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory). The storage 103 is a non-volatile storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or a flash memory. The storage 103 stores a system program 91 including an OS (Operating System), a control program 92 including computer-readable code, and a correspondence map 93 for controlling the motor 4 (rotation drive of the main shaft 2) based on the signal from the sensor 7. The processor 101 reads out the system program 91, the control program 92, and the correspondence map 93 stored in the storage 103, expands them in the memory 102, and executes them to realize various arithmetic processes including the load estimation process described later. Note that the correspondence map 93 corresponds to the "correspondence relationship" according to the present disclosure. The "correspondence relationship" according to the present disclosure may be defined by other data formats (such as a table or a relational expression).

[0029] 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. Further, the input / output interface 104 includes a drive circuit for the motor 4. When the input / output interface 104 receives a drive command including the target rotation speed of the motor 4 from the processor 101, it converts the drive command into a signal format suitable for driving the motor 4 and outputs the converted drive command to the motor 4. Note that the input / output interface 104 corresponds to the "interface" according to the present disclosure.

[0030] The communication interface 105 is configured to communicate with an external device of the machine tool 100 (for example, a management server that comprehensively manages a plurality of machine tools including the machine tool 100).

[0031] <Estimation of machining load> In the present embodiment, the controller 10 estimates a load applied to the bearing device 1 during machining of the workpiece W (hereinafter referred to as "machining load") based on the sensor output both during machining of the workpiece W and during non-machining of the workpiece W. This process is referred to as "load estimation process".

[0032] Hereinafter, the rotation speed of the main shaft 2 will be referred to as "main shaft rotation speed N". Since the main shaft rotation speed N is equal to the rotation speed of the rotation shaft of the motor 4, the main shaft rotation speed N may be read as the rotation speed of the rotation shaft of the motor 4. Further, the output from the load sensor 71 (the signal transmitted from the load sensor 71 to the controller 10) will be referred to as "load sensor output". Similarly, the output from the vibration sensor 72 will be referred to as "vibration sensor output". The vibration sensor output can be appropriately read as the strain sensor output (the output from the strain sensor).

[0033] ≪During non-machining≫ FIG. 5 is a flowchart showing an example of a processing procedure for load estimation processing during non-machining of the workpiece W by the machine tool 100. Each step is realized by software processing by the controller 10, but may also be realized by hardware (electric circuit) arranged in the controller 10. Hereinafter, the steps are abbreviated as S. The same applies to the flowcharts of FIGS. 7 and 10 described later.

[0034] How the spindle rotation speed changes during machining of the workpiece W is set in advance by the user (administrator) of the machine tool 100. The setting regarding the way of change of the spindle rotation speed (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 a management server). The processing shown in the flowchart of FIG. 5 is executed when a predetermined condition is satisfied (for example, when an operation by the user who is preparing for machining of the workpiece W is received prior to machining of the workpiece W).

[0035] In S101, the controller 10 determines the scanning range of the spindle rotation speed N according to the preset way of change of the spindle rotation speed during machining of the workpiece W. Further, the controller 10 determines the scanning step δN of the spindle rotation speed N according to the preset way of change of the spindle rotation speed during machining of the workpiece W (S102). A preferable setting method for the scanning range and the scanning step δN of the spindle rotation speed N will be described later with reference to FIG. 6.

[0036] In S103, the controller 10 sets the spindle rotation speed N(i) (i is a natural number) to the initial value N(1) (the lowest value within the scanning range in this example).

[0037] 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. When the spindle rotation speed N(i) increases, the heat generated between the rolling elements 53 of the bearing device 1 and the rolling surfaces (inner ring rolling surface and outer ring rolling surface) increases. Then, the generated heat is transmitted through the housing 31 and the spindle 2, raising the temperature of various parts of the machine tool 100 (especially the components of the bearing device 1). This temperature rise does not occur immediately, but there is a time delay corresponding to the heat capacity of the housing 31, the spindle 2, etc. Also, the machine tool 100 is cooled (for example, oil-cooled) using a coolant as the case may be. The above-mentioned specified time is determined by the user of the machine tool 100 so as to be the time required for the temperature of the machine tool 100 (especially the components of the bearing device 1) to saturate, or longer, taking into account the temperature rise due to the heat generation of the bearing device 1, the temperature drop due to the cooling of the machine tool 100, etc. In other words, the specified time is set to be equal to or longer than the time it takes for the machine tool 100 to reach a new thermal equilibrium state after the increase in the spindle rotation speed N(i).

[0038] The controller 10 waits until the elapsed time since the start of the increase in the spindle rotation speed N(i) reaches the specified time (NO in S104). When the elapsed time reaches the specified time (YES in S104), the controller 10 acquires the load sensor output L(1) at the spindle rotation speed N(1) (S105). Thereby, the load sensor output L(1) under the condition that the machine tool 100 has reached a new thermal equilibrium state after the increase in the spindle rotation speed N(i) is acquired.

[0039] In S106, the controller 10 determines whether the spindle rotation speed N has exceeded the scanning range (the upper limit value of the scanning range). When the spindle rotation speed N has not exceeded the scanning range (NO in S106), the controller 10 increments i by 1 (S107), that is, increases the spindle rotation speed N(i) by the scanning step δN and returns the process to S103. Thereby, the process of acquiring the load sensor output L(i) at the spindle rotation speed N(i) is repeated.

[0040] When 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 showing the correspondence between the spindle rotation speed N(i) and the load sensor output L(i) for all i (from i = 1 to the value at the completion of the scanning of the spindle rotation speed N), and stores the generated correspondence map 93 in the storage 103 (see FIG. 4) (S108).

[0041] FIG. 6 is a conceptual diagram showing an example of the correspondence map 93 generated when the workpiece W is not being machined by the machine tool 100. The horizontal axis represents the spindle rotation speed N (command value given from the controller 10 to the motor 4). The vertical axis represents the load sensor output L.

[0042] Typically, as shown in FIG. 6, the spindle rotation speed N and the load sensor output L when the workpiece W is not being machined have a relationship in which the load sensor output L increases monotonically as the spindle rotation speed N increases.

[0043] The scanning range and the scanning step δN of the spindle rotation speed N when the workpiece W is not being machined are preferably determined according to the rotational drive pattern of the spindle 2 when the workpiece W is being machined. More specifically, the scanning range and the scanning step δN of the spindle rotation speed N when the workpiece W is not being machined preferably cover the entire scanning range of the spindle rotation speed N when the workpiece W is being machined and include each set value of the spindle rotation speed N when the workpiece W is being machined.

[0044] For example, when the spindle rotation speed N when the workpiece W is being machined changes with time as 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 machined includes the range of 1000 [min -1 to 2000 [min -1 , and the scanning step δN is 500 [min -1It is preferably as follows. Thereby, for all spindle rotation speeds N = 1000 [min -1 , 1500 [min -1 , 2000 [min -1 during the machining of the workpiece W, the correspondence relationship between the spindle rotation speed N and the load sensor output L during non-machining of the workpiece W is obtained.

[0045] The scanning step δN of the spindle rotation speed N may be set smaller. In the above example, δN = 100 [min -1 can be set. The smaller the scanning step δN, the more the increase in the amount of heat generated between the rolling elements 53 of the bearing device 1 and the rolling surface can be suppressed, and thus the rapid temperature rise of the components of the bearing device 1 can be suppressed. Therefore, the time required for the machine tool 100 to reach a new thermal equilibrium state can be shortened, so that the specified time can be set shorter. In addition, since the change in the centrifugal force of the spindle 2 is smaller when the scanning step δN is smaller, a decrease in the load estimation accuracy can be suppressed.

[0046] In addition, when the load sensor output L for each of the plurality of spindle rotation speeds N during non-machining of the workpiece W is obtained, it is also possible to estimate the unobtained load sensor output L from the obtained load sensor output L. For example, when the load sensor output L at N = 1000 [min -1 and the load sensor output L at N = 1500 [min -1 are obtained, the load sensor output L at N = 1100, 1200, 1300, 1400 [min -1 that has not been obtained may be obtained by interpolation. Extrapolation based on the obtained load sensor output L is similarly possible.

[0047] Here, it has been described that the scanning range and the scanning step δN of the spindle rotation speed N during non-machining of the workpiece W are determined according to the rotational drive pattern of the spindle 2 during machining of the workpiece W. However, the scanning range of the spindle rotation speed N during non-machining of the workpiece W may be determined within a predetermined range. The scanning step δN may be determined as a predetermined fixed value.

[0048] <<First Example During Processing>> FIG. 7 is a flowchart showing a first example of a processing procedure for load estimation during machining of a workpiece W by a machine tool 100. The first example is preferably implemented under the condition that the spindle rotation speed N is constant over time (including the situation where the time during which the spindle rotation speed N is maintained at the same speed is sufficiently long). The processing shown in this flowchart is executed when a predetermined condition is satisfied (for example, every predetermined cycle during machining of the workpiece W).

[0049] 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 denoted as "load La". The load La corresponds to the "first load" according to the present disclosure.

[0050] In S202, the controller 10 acquires the vibration sensor output from the vibration sensor 72 at the timing when the load sensor output is acquired (the same timing as the process of S201).

[0051] In S203, the controller 10 determines whether the load sensor output and the vibration sensor output are synchronized by comparing the load sensor output and the vibration sensor output.

[0052] FIG. 8 is a diagram showing an example of a situation where the load sensor output and the vibration sensor output are synchronized. The horizontal axis represents the elapsed time. The vertical axis represents the sensor output (load sensor output or vibration sensor output).

[0053] In the example shown in FIG. 8, during the period from time t10 to time t11, the load sensor output and the vibration sensor output are substantially constant. From time t11, both the load sensor output and the vibration sensor output increase. Thus, when the load sensor output and the vibration sensor output show a similar change tendency at the same timing, it can be said that the load sensor output and the vibration sensor output are synchronized.

[0054] More specifically, the controller 10 calculates, for example, the rate of change of the load sensor output (the amount of change per unit time) and also calculates the rate of change of the vibration sensor output. The controller 10 can determine whether the load sensor output is increasing, constant, or decreasing based on the rate of change of the load sensor output. The same applies to the vibration sensor output.

[0055] When the load sensor output and the vibration sensor output increase at the same timing (when the time difference between the start timing of the increase in the load sensor output and the start timing 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 the machining of the workpiece W has started (or is in progress) (details will be described later). Here, an increase in the sensor output has been described as an example, but a decrease in the sensor output may also be used.

[0056] On the other hand, different from the above, when the load sensor output and the vibration sensor output show different change tendencies, for example, when the load sensor output increases but the vibration sensor output is constant, or when the vibration sensor output increases but the load sensor output is constant, etc., the controller 10 determines that the load sensor output and the vibration sensor output are asynchronous. In the case of asynchrony, it is possible that the machining of the workpiece W has not started or that some abnormality (such as abnormal heat generation of the bearing 5 and / or the main shaft 2, abnormal vibration due to damage of the bearing 5, etc.) has occurred in the machine tool 100.

[0057] Returning to FIG. 7, when 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. When 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 main shaft rotation speed N in the processes of S201 and S202.

[0058] In S205, the controller 10 obtains the load sensor output L of the workpiece W during non - machining corresponding to the spindle rotation speed N obtained in S204 by acquiring the correspondence map 93. The obtained value is described as "load Lb". The load Lb corresponds to the "second load" according to the present disclosure.

[0059] FIG. 9 is a diagram showing an example of the load sensor output (load La) during machining of the workpiece W and the load sensor output (load Lb) during non - machining of the workpiece W. The horizontal axis represents the elapsed time. The vertical axis represents the load sensor output L. It can be seen that after time t21, the load La and the load Lb deviate from each other.

[0060] Referring to FIGS. 7 and 9, in S206, the controller 10 calculates the difference ΔL = La - Lb between the load sensor output (load La) obtained in S201 and the load sensor output (load Lb) obtained in S205.

[0061] In S207, the controller 10 estimates the difference ΔL calculated in S206 as the machining load applied to the bearing device 1 during machining of the workpiece W.

[0062] As described above, in the first example, the load sensor output (load Lb) during non - machining of the workpiece W is obtained. The load Lb corresponds to the load during air - cut when the tool tip attached to the tip of the spindle 2 is not in contact with the workpiece W, and corresponds to a so - called baseline load (a reference for which the load should be 0). Therefore, by calculating the difference between the load sensor output (load La) during machining of the workpiece W and the load Lb, it is possible to quantify how much the load has increased from the baseline load due to the contact between the tool tip and the workpiece W. This quantification can be realized with a simple configuration that only involves the installation of the load sensor 71. Thus, according to the present embodiment, the machining load in the bearing device 1 can be estimated simply and with high accuracy.

[0063] It may be considered that the controller 10 monitors only the load sensor output. However, in that case, there is a possibility that the estimation accuracy of the machining load may decrease when noise is superimposed on the load sensor output. On the other hand, in the present embodiment, in addition to the load sensor output, the vibration sensor output is monitored by the controller 10, that is, two different characteristics, namely, load and vibration, are monitored. Since the possibility that noise is simultaneously superimposed on the two sensor outputs is low, when both are synchronized, it is highly likely that the work W is being machined normally and the accurately detected load is indicated by the load sensor output. Therefore, according to the present embodiment, the estimation accuracy of the machining load can be further improved.

[0064] ≪Second Example during Machining≫ FIG. 10 is a flowchart showing a second example of the processing procedure of the load estimation process during the machining of the work W by the machine tool 100. The second example is preferably implemented in a situation where the spindle rotation speed N changes over time (including a situation where the time during which the spindle rotation speed N is maintained at the same speed is short). The processing shown in this flowchart is executed when a predetermined condition is satisfied (for example, every predetermined cycle during the machining of the work W).

[0065] In the machine tool 100, the machining cycle is repeatedly executed. In S301, the controller 10 determines which stage the current stage of the machine tool 100 corresponds to. The controller 10 can determine the current stage based on, for example, the vibration sensor output and the drive current value of the motor 4. The current value of a servo motor (not shown) used for the feed device of the work W can also be used for the determination of the stage.

[0066] FIG. 11 is a diagram for explaining the stages in the machining cycle of the machine tool 100. Generally, the machining cycle of a machine tool is classified into four stages. The four stages are: (1) a spindle stop stage in which the spindle is stopped, (2) a spindle rotation stage in which the rotational drive of the spindle is started and the spindle rotation speed increases, (3) a spindle movement stage in which the spindle moves to the machining position of the workpiece W while rotating, and (4) a machining stage in which the workpiece W is actually machined.

[0067] Returning to FIG. 10, in S302, the controller 10 determines whether the current stage determined in S301 is the machining stage. If the current stage is not the machining stage (NO in S302), that is, if the current stage is the spindle stop stage, the spindle rotation stage, or the spindle movement stage, the controller 10 ends the series of processes without executing the subsequent processes.

[0068] On the other hand, if the current stage is the machining stage (YES in S302), the controller 10 advances the process to S303. The processes of S303 to S309 are the same as the processes of S201 to S207 in the first example (see FIG. 7), and thus detailed descriptions will not be repeated.

[0069] As described above, also in the second example, similar to the first example, the load sensor output (load Lb) when the workpiece W is not being machined is acquired. By calculating the difference between the load sensor output (load La) when the workpiece W is being machined and the load Lb, it is possible to quantify whether the load has increased from the baseline load due to the contact between the tool edge and the workpiece W. Therefore, according to the present embodiment, the machining load in the bearing device 1 can be estimated simply and with high accuracy.

[0070] In the process during machining of the workpiece W by the machine tool 100 (see FIGS. 7 and 10), it was explained that the machining load is estimated when the load sensor output and the vibration sensor output are synchronized. As described above, this is to improve the estimation accuracy of the machining load by monitoring two sensor outputs that are different from each other. However, the controller 10 may estimate the machining load without considering whether the load sensor output and the vibration sensor output are synchronized. That is, the vibration sensor 72 may not be installed. Alternatively, the processes of S202 and S203 in FIG. 7 may be omitted, or the processes of S304 and S305 in FIG. 10 may be omitted.

[0071] [Appendix] Finally, various aspects of the present disclosure will be summarized and described as appendices.

[0072] (Appendix 1) A bearing device that rotatably supports a spindle for machining a workpiece by rotational drive, the bearing device including 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 a 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.

[0073] In the configuration of Appendix 1, the second load corresponds to the baseline load during air cutting when the spindle (such as the cutting edge of a tool attached to the tip of the spindle) is not in contact with the workpiece. Therefore, by calculating the difference between the first load during machining of the workpiece and the second load sensor output when the workpiece is not being machined, it is possible to quantify whether the load has increased from the baseline load only due to contact with the workpiece. This quantification can be achieved only by installing the load sensor. Therefore, the machining load in the bearing device can be estimated simply and with high accuracy.

[0074] (Appendix 2) The bearing device according to Appendix 1, further comprising an interface for receiving a signal from a vibration and strain sensor that detects vibration or strain during or outside the processing of the workpiece, wherein the processor uses the difference to estimate the processing load when the signals from the load sensor and the vibration and strain sensor are synchronized.

[0075] In the configuration of Appendix 2, it is unlikely that noise is simultaneously superimposed on both the signal from the load sensor and the signal from the vibration and strain sensor. Therefore, when both are synchronized, it is highly likely that the workpiece is processed normally and the correctly detected load is indicated by the signal from the load sensor. Thus, the estimation accuracy of the processing load can be further improved.

[0076] (Appendix 3) The bearing device according to Appendix 1 or 2, comprising an inner race seat that is a rotating ring and an outer race seat that is a non-rotating ring, wherein the load sensor is installed on the outer race seat.

[0077] According to the configuration of Appendix 3, since the load sensor is installed on the outer race seat which is a non-rotating ring, the routing of the wiring for the load sensor becomes easy.

[0078] (Appendix 4) The bearing device according to Appendix 1 or 2, comprising an inner race seat that is a rotating ring and an outer race seat that is a non-rotating ring, wherein the vibration and strain sensor is installed on the outer race seat.

[0079] (Appendix 5) The bearing device according to Appendix 4, wherein the load sensor is installed on the outer race seat.

[0080] According to the configurations of Appendices 4 and 5, since the vibration and strain sensor is installed on the outer race seat which is a non-rotating ring, the routing of the wiring for the vibration and strain sensor becomes easy.

[0081] (Appendix 6) A spindle device comprising the bearing device according to any one of Appendices 1 to 5, the main shaft, and a housing that houses the bearing device and the main shaft.

[0082] According to the configuration of Appendix 6, similar to the configuration of Appendix 1, the machining load in the bearing device within the spindle device can be estimated simply and with high accuracy.

[0083] (Appendix 7) The spindle device according to Appendix 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.

[0084] (Appendix 8) The spindle device according to Appendix 6 or 7, wherein the vibration and strain sensor is installed in the housing.

[0085] (Appendix 9) The spindle device according to Appendix 6 or 7, further comprising a table configured to fix the workpiece and a bed that supports the entire spindle device, wherein the vibration and strain sensor is installed on one of the table and the bed.

[0086] According to the configurations of Appendices 7 to 9, similar to the configuration of Appendix 2, the estimation accuracy of the machining load can be further improved.

[0087] (Appendix 10) The spindle device according to any one of Appendices 6 to 9, wherein the correspondence relationship is determined to indicate the correspondence relationship between the rotational speed of the main shaft and the detected value of the load sensor in the thermal equilibrium state of the spindle device.

[0088] According to the configuration of Appendix 10, since the correspondence relationship in the thermal equilibrium state of the spindle device is obtained, a decrease in the estimation accuracy of the machining load due to temperature changes in the spindle device (generation of heat accompanying rotational driving of the main shaft) can be suppressed. Therefore, the estimation accuracy of the machining load can be further improved.

[0089] (Appendix 11) A load estimation method for estimating, by a computer, the machining load applied to a bearing device during machining of a workpiece by rotational driving of a main shaft, wherein the bearing device includes a load sensor that outputs a signal indicating a detected value of the load applied to the bearing device, and a correspondence relationship between the rotational speed of the main shaft and the detected value of the load sensor during non-machining of the workpiece is stored in the computer, and the load estimation method includes: when the rotational speed of the main shaft is controlled to a predetermined speed, obtaining 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 estimating a difference between the first load and the second load as the machining load.

[0090] (Appendix 12) A program for causing the computer to execute the load measurement method according to Appendix 11.

[0091] According to the method of Appendix 11 or the program of Appendix 12, similar to the configuration of Appendix 1, 6, the machining load in the bearing device can be estimated simply and with high accuracy.

[0092] The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is indicated by the claims rather than the description of the above embodiments, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Description of Reference Numerals

[0093] 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.

Claims

1. A bearing device that rotatably supports a spindle for machining a workpiece by rotational drive, 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; 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, wherein when the rotational speed of the spindle is controlled to a predetermined speed, the processor acquires 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, and estimates the difference between the first load and the second load as the machining load. A bearing device.

2. 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. The bearing device according to claim 1.

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

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

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

6. A spindle device comprising the bearing device according to claim 1, the spindle, and a housing that houses the bearing device and the spindle.

7. 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. The spindle device according to claim 6.

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

9. further comprising a table configured to fix the workpiece, and a bed that supports the entire spindle device. The spindle device according to claim 7, wherein the vibration distortion 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 main shaft and the detected 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 main shaft, wherein the bearing device includes a load sensor that outputs a signal indicating a detected value of a load applied to the bearing device, wherein a correspondence relationship between the rotational speed of the main shaft and the detected value of the load sensor during non-machining of the workpiece is stored in the computer, wherein the load estimation method includes: obtaining 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 when the rotational speed of the main shaft is controlled to a predetermined speed; estimating a difference between the first load and the second load as the machining load.

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

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