Engine control device

Abstract

Motor control device (1) for controlling a spindle motor (3) which drives a tool or a workpiece in a machine tool, the motor control device (1) comprising: a first low-pass filter (24) which averages torque command values ​​or drive current values ​​of the spindle motor (3) and calculates averaged first load information of the spindle motor (3); and a time constant calculation unit (22) which calculates, as the time constant of the first low-pass filter (24), a first time constant based on a cutoff frequency according to a rotational speed of the spindle driven by the spindle motor (3) or, if the spindle rotates the tool, a second time constant based on a cutoff frequency corresponding to a value generated by multiplying a number of cutting teeth of the tool by the rotational speed of the spindle.

Description

Background of the inventionField of the invention

[0001] The present invention relates to a motor control device that controls a spindle motor of a machine tool. Related technology

[0002] Machine tools are machines that cut a workpiece, for example, by rotating a tool driven by a spindle motor. In such machine tools, the load on the spindle motor fluctuates during machining. If the spindle motor load fluctuation (machining disturbance) is large, a machining abnormality may occur in the workpiece or an abnormality in the machine tool (e.g., in the tool). Conversely, if the spindle motor load fluctuation (machining disturbance) is small, the machining time increases.

[0003] Therefore, in a numerical control device, for example, it has been considered to automatically control machining conditions (e.g., a feed rate (feed speed) of the feed axis) in response to the load information of the spindle motor (see, for example, Patent Document 1). Alternatively, it has been considered to display the load information of the spindle motor, for example, with the numerical control device. This allows a machine tool operator to manually control the machining conditions in response to the displayed load information. For example, when the load fluctuation (machining disturbance) of the spindle motor is large, it is possible to prevent the occurrence of a machining abnormality in the workpiece or an abnormality in the machine tool (e.g., in the tool) by lowering the feed rate of the feed axis.On the other hand, when the load fluctuation (machining disturbance) of the spindle motor is small, it is possible to shorten the machining time by increasing the feed rate of the feed axis.

[0004] Patent Document 1: PCT International Publication No. WO-2013 / 088 849 A1. Overview of the invention

[0005] For example, if the spindle motor load fluctuation (machining disturbance) is too large, automatic control of the feed rate of the feed axis by the numerical control device becomes difficult. Furthermore, the load information displayed by the numerical control device fluctuates, making manual control of the feed rate of the feed axis by the machine tool operator difficult.

[0006] In this regard, it has been considered to average the load fluctuation (machining disturbance) of the spindle motor using a filter. However, as far as the present inventors know, in order to sufficiently suppress the load fluctuation (machining disturbance) of the spindle motor, it is necessary to increase the time constant using a well-known first-order filter, and the responsiveness of controlling machining conditions (for example, a feed rate of the feed axis) decreases.

[0007] An object of the present invention is to provide a motor control device that suppresses fluctuation of load information of a spindle motor and is capable of suppressing a decrease in responsiveness thereof when performing control of machining conditions.

[0008] The problem is solved by an engine control device having the features of patent claim 1.

[0009] (1) A motor control device (e.g., the motor control device 1 described below) according to the present invention is a motor control device for controlling a spindle motor (e.g., the spindle motor 3 described below) that rotates a tool or a workpiece in a machine tool, the device including: a first low-pass filter (e.g., the first low-pass filter 24 described below) that averages torque command values ​​or drive current values ​​of the spindle motor and calculates averaged first load information of the spindle motor; and a time constant calculation unit (e.g.,the time constant calculation unit 22 described below) which calculates, as the time constant of the first low-pass filter, a first time constant based on a cutoff frequency according to a rotational speed of the spindle driven by the spindle motor or, in the case where the spindle rotates the tool, a second time constant based on a cutoff frequency corresponding to a value generated by multiplying a number of cutting teeth of the tool by the rotational speed of the spindle.

[0010] (2) In the motor control device as described in (1), the time constant calculation unit may calculate the first time constant so that the cutoff frequency of the first low-pass filter does not become higher than the rotational speed of the spindle, or the second time constant so that the cutoff frequency does not become higher than a value generated by multiplying a number of cutting teeth of the tool by the rotational speed of the spindle.

[0011] (3) The motor control device as described in (1) or (2) may further include: a second low-pass filter (e.g., the second low-pass filter 26 described below) that averages the torque command values ​​or drive current values ​​of the spindle motor and calculates averaged second load information of the spindle motor, wherein the time constant of the second low-pass filter may be fixed regardless of the rotational speed of the spindle and is larger than the time constant of the first low-pass filter, and the time constant of the first low-pass filter may be variable according to the rotational speed of the spindle.

[0012] (4) In the motor control device as described in any one of (1) to (3), the rotational speed of the spindle may be a speed command value or a speed feedback value of the spindle.

[0013] (5) In the motor control device as described in any one of (1) to (4), the time constant calculating unit may switch between setting the first time constant as the time constant of the first low-pass filter or setting the second time constant as the time constant of the first low-pass filter so that the magnitude of a fluctuation of the first load information becomes smaller.

[0014] (6) In the motor control device as described in (5), the time constant calculation unit may switch between setting the first time constant as the time constant of the first low-pass filter or setting the second time constant as the time constant of the first low-pass filter based on the magnitude of a fluctuation of the first load information.

[0015] (7) In the motor control device as described in (5), the time constant calculation unit may switch between setting the first time constant as the time constant of the first low-pass filter or setting the second time constant as the time constant of the first low-pass filter based on an external command.

[0016] According to the present invention, it is possible to provide a motor control device that can suppress fluctuation in load information of a spindle motor and suppress a decrease in responsiveness thereof when performing control of machining conditions. Short description of the drawings Fig. 1 is a view illustrating a control system including an engine control device according to the present embodiment; Fig. 2 is a side view of an example of a tool; Fig. 3 is a plan view of an example of a tool; Fig. 4 is a graph illustrating observation results of a torque command value input to a first low-pass filter (dotted line) and first load information output from the first low-pass filter (solid line); Fig. 5 is a graph illustrating observation results of a torque command value input to a first low-pass filter (dotted line) and first load information output from the first low-pass filter (solid line); Fig. 6 is a graph illustrating observation results of a torque command value input to a first low-pass filter (dotted line) and first load information output from the first low-pass filter (solid line); and Fig. 7 is a graph showing observation results of a torque command value input to a first low-pass filter (dotted line) and first load information output from the first low-pass filter (solid line). Detailed description of the invention

[0017] An example of an embodiment of the present invention will now be explained with reference to the accompanying drawings. Note that identical or corresponding portions in the respective drawings are denoted by the same reference numerals.

[0018] Fig. 1 is a view illustrating a control system including an engine control device according to the present embodiment. Fig. The control system shown in Fig. 1 includes a motor control device 1 and a numerical control device 2 and controls a spindle motor 3 and a feed axis motor (not shown) of a machine tool.

[0019] The spindle motor 3 rotates a tool in the machine tool, which, for example, performs a cutting operation on a workpiece. The spindle motor 3 is equipped with an encoder 4 that detects, for example, the rotational speed (RPM) of the spindle driven by the spindle motor 3. The detected speed is used as a speed feedback value (speed RK).

[0020] The numerical control device 2 calculates a speed command value (a rotational speed) of the spindle driven by the spindle motor 3 based on a machining program and supplies the calculated speed command value to the motor control device 1. Furthermore, the numerical control device 2 can acquire first load information of the spindle motor 3 from the motor control device 1 and automatically control the machining conditions (for example, a feed rate of the feed axis) according to the acquired first load information. Furthermore, the numerical control device 2 can acquire second load information of the spindle motor 3 from the motor control device 1 and display the acquired second load information on a display unit. The machine tool operator can thereby manually control the machining conditions according to the displayed second load information.For example, when the load fluctuation (machining disturbance) of the spindle motor 3 is large, it is possible to prevent the occurrence of a machining abnormality in a workpiece or the occurrence of an abnormality in the machine tool (e.g., in the tool) by lowering the feed rate of the feed axis. Conversely, when the load fluctuation (machining disturbance) of the spindle motor 3 is small, it is possible to shorten the machining time by increasing the feed rate of the feed axis.

[0021] The motor control device 1 controls the spindle by controlling the spindle motor 3 based on the speed command value calculated by the numerical control device 2. The motor control device 1 includes a subtractor 11, a speed control unit 12, and a current control unit 14. The subtractor 11 obtains the error between the speed command value and the speed feedback value detected by the encoder 4. The speed control unit 12 calculates a torque command value of the spindle motor 3 based on the error obtained by the subtractor 11. The current control unit 14 calculates a drive current value for driving the spindle motor 3 based on the torque command value calculated by the speed control unit 12 and supplies the calculated drive current value to the spindle motor 3.

[0022] Furthermore, the motor control device 1 includes a storage unit 20, a time constant calculation unit 22, a first low-pass filter 24, and a second low-pass filter 26. The storage unit 20 stores the number of cutting teeth of the tool as tool information. The storage unit 20 is a rewritable memory such as an EEPROM.

[0023] The time constant calculation unit 22 acquires the speed command value supplied from the numerical control device 2 and acquires the number of cutting teeth of the tool stored in the storage unit 20. The time constant calculation unit 22 calculates a time constant of the first low-pass filter 24. Specifically, the time constant calculation unit 22 calculates, as the time constant T, the first time constant based on the cutoff frequency corresponding to the rotational speed of the spindle driven by the spindle motor 3. More specifically, the time constant calculation unit 22 calculates the time constant (first time constant) T using a formula (1-1) and a formula (1-2) below so that the cutoff frequency Fc ( / s) of the first low-pass filter 24 becomes not higher than the rotational speed Vcmd (rev / s) of the spindle indicated by the speed command value (that is, a frequency of a machining disturbance described below). T=1 / (2π×Fc) Fc≦Vcmd

[0024] Alternatively, the time constant calculation unit 22 calculates, as the time constant T, a second time constant based on the cutoff frequency corresponding to a value generated by multiplying the number of cutting teeth of the tool by the rotational speed of the spindle driven by the spindle motor 3. More specifically, the time constant calculation unit 22 calculates the time constant (second time constant) T according to the formula (2-1) and the formula (2-2) below, so that the cutoff frequency Fc ( / s) of the first low-pass filter 24 becomes not higher than a value generated by multiplying the number of cutting teeth N of the tool by the rotational speed Vcmd (rev / s) of the spindle (ie, a frequency of machining disturbance described below). T=1 / (2π×Fc) Fc≦Vcmd×N

[0025] The time constant calculation unit 22 switches between setting the first time constant calculated according to the above formula (1-1) and formula (1-2) as the time constant T of the first low-pass filter 24 or setting the second time constant calculated according to the above formula (2-1) and formula (2-2) as the time constant T of the first low-pass filter 24 so that the magnitude of fluctuation (machining noise) of the first load information averaged by the first low-pass filter 24 becomes smaller. For example, the time constant calculation unit 22 may automatically perform switching of the above-mentioned time constant T based on the magnitude of fluctuation of the first load information averaged by the first low-pass filter 24.The time constant calculation unit 22 may, for example, be based on the amplitude magnitude of the first load information or may be based on the magnitude of the fluctuation frequency component through an FFT that analyzes the first load information. Alternatively, the time constant calculation unit 22 may perform switching of the above-mentioned time constant T based on an external command. The external command may be supplied from the numerical control device 2. The numerical control device 2 may automatically determine the fluctuation magnitude of the first load information in the above-mentioned manner, for example, based on the amplitude magnitude of the first load information or the magnitude of the fluctuation frequency component after an FFT has analyzed the first load information. Alternatively, the external command may be manually input by the operator.At this time, the operator can visually determine the magnitude of the fluctuation of the load information based on the magnitude of the amplitude of the load information displayed on the numerical control device 2.

[0026] Note that the tool information is stored in the storage unit of the numerical control device 2, and the time constant calculation unit 22 may acquire the tool information from the numerical control device 2. In this case, the storage unit 20 may not be provided. Furthermore, the time constant calculation unit 22 may use a speed feedback value detected by the encoder 4 instead of the speed command value.

[0027] The first low-pass filter 24 averages the torque command values ​​of the spindle motor 3 by a time constant calculated by the time constant calculation unit 22 and calculates averaged first load information of the spindle motor 3. A second low-pass filter 26 averages the torque command values ​​of the spindle motor 3 by a predetermined calculated time constant and calculates averaged second load information of the spindle motor 3. The time constant of the first low-pass filter 24 is variable according to the spindle speed, as mentioned above. In contrast, the time constant of the second low-pass filter 26 is fixed regardless of the spindle speed. The predetermined time constant of the second low-pass filter 26 is set larger than the time constant of the first low-pass filter 24. In other words, the cutoff frequency of the second low-pass filter 26 is set lower than the cutoff frequency of the first low-pass filter 24.Note that the first low-pass filter 24 and the second low-pass filter 26 may use the drive current value of the spindle motor 3 calculated by the current control unit 14 instead of the torque command value.

[0028] The motor control device 1 and the numerical control device 2 are configured, for example, by a computing processor such as a DSP (digital signal processor) and an FPGA (field-programmable gate array). The various functions of the motor control device 1 and the numerical control device 2 are implemented, for example, by executing predetermined software (program) stored in a memory unit. Various functions of the motor control device 1 and the numerical control device 2 can be implemented through the cooperation of hardware and software, or can be implemented only by hardware (electronic circuits).

[0029] Next, a tool that is rotationally driven by the spindle motor 3 (ie, a spindle) will be explained. Fig. 2 is a side view of an example of a tool, and Fig. 3 is a top view of an example of a tool. The Fig. 2 and Fig. The tool 8 shown in Figure 3 includes five cutting teeth 9 relative to the rotation axis in the direction of the arrow and is driven in rotation in the direction of the arrow by the spindle driven by the spindle motor 3. With such a tool 8 (i) a load fluctuation (machining disturbance) of the spindle motor 3 occurs at the time interval of 1 / 5 times for 1 revolution of the spindle (frequency of 5 times), which is caused by each cutting tooth 9 coming into contact with the workpiece; (ii) a load fluctuation (machining disturbance) of the spindle motor 3 occurs in the time interval of 1 revolution of the spindle, which is caused by the five cutting teeth 9 arranged eccentrically relative to the rotation axis; or (iii) a load fluctuation (machining disturbance) of the spindle motor 3 occurs in the time interval of 1 / 5 times in 1 revolution of the spindle (frequency of 5 times), which is caused by any one of the five cutting teeth 9 arranged eccentrically relative to the rotation axis.

[0030] When the load of the spindle motor 3 fluctuates in this way, for example, automatic control of the feed rate of the feed axis by the numerical control device 2 becomes difficult, as mentioned above. Furthermore, for example, the load information displayed by the numerical control device 2 fluctuates, and manual control of the feed rate of the feed axis by the machine tool operator becomes difficult.

[0031] Therefore, it has been considered to average the load fluctuation (machining disturbance) of the spindle motor 3 using a filter. However, as far as the inventors of the present invention know, in order to sufficiently suppress the load fluctuation (machining disturbance) of the spindle motor 3, it is necessary to increase the time constant using a well-known first-order filter (fixed time constant), and the responsiveness of control of machining conditions (for example, a feed rate of the feed axis) decreases. On the other hand, if the time constant of the first-order filter is made too small, control depending on the machining conditions becomes unstable due to the influence of the load fluctuation (machining disturbance), and the fluctuation (change) of the load indication increases.

[0032] In view of this, according to the motor control device 1 of the present embodiment, the first time constant (the above-mentioned formula (1-1) and formula (1-2)) such that the cutoff frequency of the first low-pass filter 24 becomes not higher than the rotational speed of the spindle, or the second time constant (the above-mentioned formula (2-1) or formula (2-2)) such that the cutoff frequency becomes not higher than a value generated by multiplying the number of cutting teeth of the tool 8 by the rotational speed of the spindle is set as the time constant of the first low-pass filter 24. In other words, the time constant of the first low-pass filter 24 is set so that the cutoff frequency of the first low-pass filter 24 is not higher than the frequency of the load fluctuation (machining disturbance) of the spindle motor 3 generated by the above-mentioned (i) to (iii). This makes it possible to suppress fluctuation of the first load information of the spindle motor 3.In addition, it is possible to shorten the delay time of the first load information, and the decrease of its responsiveness when performing control of the machining conditions can be prevented.

[0033] Furthermore, according to the motor control device 1 of the present embodiment, the time constant calculation unit 22 may switch between setting the first time constant calculated by the above-mentioned formula (1-1) and formula (1-2) as the time constant T of the first low-pass filter 24 or setting the second time constant calculated by the above-mentioned formula (2-1) and formula (2-2) as the time constant T of the first low-pass filter 24 so that the magnitude of a fluctuation of the first load information (machining disturbance) averaged by the first low-pass filter 24 becomes smaller.For example, the above-mentioned (i) load fluctuation (machining disturbance) of the spindle motor 3 caused by each cutting tooth 9 coming into contact with the workpiece and (iii) load fluctuation (machining disturbance) of the spindle motor 3 caused by any one of the five cutting teeth 9 arranged eccentrically relative to the rotation axis are suppressible by both the first low-pass filter 24 of the time constant (the first time constant) T calculated by the above-mentioned formula (1-1) and formula (1-2) and the first low-pass filter 24 of the time constant (the second time constant) calculated by the above-mentioned formula (2-1) and formula (2-2).On the other hand, the above-mentioned (ii) load fluctuation (machining disturbance) of the spindle motor 3 caused by five cutting teeth 9 arranged eccentrically relative to the rotation axis cannot be suppressed by the first low-pass filter 24 of the time constant (the second time constant) T calculated by the above-mentioned formula (2-1) and formula (2-2); however, it can be suppressed by the first low-pass filter 24 of the time constant (the first time constant) calculated by the above-mentioned formula (1-1) and formula (1-2). At this time, the time constant calculation unit 22 can switch to calculate the time constant (first time constant) calculated by the above-mentioned formula (1-1) and formula (1-2) as the time constant of the first low-pass filter 24. The effects of this will be demonstrated below.

[0034] Fig. 4 to 7 are graphs showing observation results of the torque command value input to the first low-pass filter 24 (dotted line) and first load information output from the first low-pass filter 24 (solid line). The observation conditions of Fig. 4 to 7 are as follows. - Spindle speed Vcmd = 300 min -1 ie frequency caused by 1 rotation of the spindle = 5 Hz - Number of cutting teeth of the tool 8 N = 5 ie frequency caused by the number of cutting teeth N of the tool 8 = 25 Hz - Average load of spindle motor 3 = 80%

[0035] In Fig. 4 and Fig. 5 applies - no fluctuation caused by 1 revolution of the spindle, and - the variation caused by the number N of tool 8 is 5%.

[0036] In Fig. 4, the time constant of the first low-pass filter 24 was set to the time constant calculated in the above-mentioned formula (2-1) and formula (2-2) as Fc=Vcmd×N / 2 (second time constant), and in Fig. 5, the time constant of the first low-pass filter 24 was set to the time constant calculated as Fc=Vcmd / 2 in the above-mentioned formula (1-1) and formula (1-2). According to Fig. 4 and Fig. 5, the fluctuation caused by the number of cutting teeth N of the tool 8 is not as strong as the first low-pass filter 24 of the time constant calculated by the above-mentioned formula (1-1) and formula (1-2) (first time constant); however, it turns out that there is a certain degree of suppression effect by the first low-pass filter 24 of the time constant calculated by the above-mentioned formula (2-1) and formula (2-2) (second time constant).In other words, the above-mentioned (i) load fluctuation (machining disturbance) of the spindle motor 3 caused by each cutting tooth 9 coming into contact with the work is suppressed by both the first low-pass filter 24 of the time constant (the first time constant) calculated by the above-mentioned formula (1-1) and formula (1-2) and the first low-pass filter 24 of the time constant (the second time constant) calculated by the above-mentioned formula (2-1) and formula (2-2).

[0037] Next, Fig. 4 and Fig. 5 out into Fig. 6 and Fig. 7 - the fluctuation caused by 1 revolution of the spindle is 2%. In Fig. 6, the time constant of the first low-pass filter 24 was set to the time constant (second time constant) calculated as Fc=Vcmd×N / 2 in the above-mentioned formula (2-1) and formula (2-2), and in Fig. 7, the time constant of the first low-pass filter 24 was set to the time constant (first time constant) calculated as Fc=Vcmd / 2 in the above-mentioned formula (1-1) and formula (1-2). According to Fig. 6 and Fig.7, it is found that the fluctuation caused by 1 revolution of the spindle is not suppressed by the first low-pass filter 24 of the time constant (the second time constant) calculated by the above-mentioned formula (2-1) and formula (2-2); however, it is suppressed by the first low-pass filter 24 of the time constant (the first time constant) calculated by the above-mentioned formula (1-1) and formula (1-2).In other words, it turns out that the above-mentioned (ii) load fluctuation (machining disturbance) of the spindle motor 3 caused by five cutting teeth 9 arranged eccentrically relative to the rotation axis is not suppressed by the first low-pass filter 24 of the time constant (the second time constant) calculated by the above-mentioned formula (2-1) and formula (2-2); however, it is suppressed by the first low-pass filter 24 of the time constant (the first time constant) calculated by the above-mentioned formula (1-1) and formula (1-2).

[0038] Furthermore, according to the motor control device of the present invention, first load information is calculated by the first low-pass filter 24, and second load information is calculated by the second low-pass filter 26. The time constant of the second low-pass filter 26 is fixed regardless of the spindle speed and is larger than the time constant of the first low-pass filter 24. The fluctuation of the second load information is therefore smaller than the fluctuation of the first load information. Accordingly, by using the first load information when controlling machining conditions, it is possible to suppress a decrease in the responsiveness thereof. On the other hand, by using the second load information that has passed through the second low-pass filter 26 with a larger time constant, it is possible to suppress a decrease in perceptibility when displaying instead of controlling machining conditions.As a result, it is possible to prevent a decrease in its responsiveness when performing control of machining conditions and to prevent a decrease in perceptibility when performing display of load information of a spindle motor.

[0039] Although one embodiment of the present invention has been explained above, the present invention is not limited to the above-mentioned embodiment, and various changes and modifications are possible. For example, the above-mentioned embodiment explains the motor control device 1 that calculates load information of the spindle motor 3, wherein the spindle motor 3 (spindle) rotates a tool. However, the features of the present invention are not limited thereto and are also applicable to a motor control device 1 that calculates load information of the spindle motor 3, wherein the spindle motor 3 (spindle) rotates the workpiece. Here, the first time constant (the above-mentioned formula (1-1) and formula (1-2)) is set as the time constant of the first low-pass filter 24 based on the cutoff frequency corresponding to the rotational speed of the spindle driven by the spindle motor 3.Thereby, it is possible to suppress a load fluctuation (machining disturbance) of the spindle motor 3 occurring in the time interval of 1 revolution of the spindle driven by the spindle motor 3, which is caused by the workpiece being arranged eccentrically relative to the rotation axis (corresponding to the above-mentioned (ii)).

[0040] Furthermore, the above-mentioned embodiment explains the motor control device 1 that calculates load information of the spindle motor 3 that rotates a tool including five cutting teeth. However, the features of the present invention are not limited thereto and are applicable to a motor control device that calculates cutting tooth load information of the spindle motor 3 that rotates a workpiece including two or more cutting teeth.

[0041] Furthermore, the above-mentioned embodiment explains the motor control device 1 that performs speed control based on a speed command value from the numerical control device 2. However, the features of the present invention are not limited thereto and are also applicable to a motor control device that performs position control based on a position command value from a numerical control device. Explanation of reference symbols 1 engine control device 2 numerical control device 3 spindle motor 4 Coding device 8 Tools 9 cutting tooth 11 Subtraction device 12 Speed ​​control unit 14 Power control unit 20 storage units 22 Time constant calculation unit 24 first low-pass filter 26 second low-pass filter

Claims

[1] Motor control device (1) for controlling a spindle motor (3) which drives a tool or a workpiece in a machine tool, the motor control device (1) comprising: a first low-pass filter (24) which averages torque command values ​​or drive current values ​​of the spindle motor (3) and calculates averaged first load information of the spindle motor (3); and a time constant calculation unit (22) which calculates, as the time constant of the first low-pass filter (24), a first time constant based on a cutoff frequency according to a rotational speed of the spindle driven by the spindle motor (3) or, if the spindle rotates the tool, a second time constant based on a cutoff frequency corresponding to a value generated by multiplying a number of cutting teeth of the tool by the rotational speed of the spindle. [2] The motor control device (1) according to claim 1, wherein the time constant calculation unit (22) calculates the first time constant such that the cutoff frequency of the first low-pass filter (24) does not become higher than the rotational speed of the spindle, or the second time constant such that the cutoff frequency does not become higher than a value generated by multiplying a number of cutting teeth of the tool by the rotational speed of the spindle. [3] Motor control device (1) according to claim 1 or 2, further comprising a second low-pass filter (26) which averages the torque command values ​​or drive current values ​​of the spindle motor (3) and calculates averaged second load information of the spindle motor (3), wherein the time constant of the second low-pass filter (26) is fixed independently of the speed of the spindle and is greater than the time constant of the first low-pass filter (24), and wherein the time constant of the first low-pass filter (24) is variable according to the speed of the spindle. [4] The motor control device (1) according to any one of claims 1 to 3, wherein the rotational speed of the spindle is a speed command value or a speed feedback value of the spindle. [5] The motor control device (1) according to any one of claims 1 to 4, wherein the time constant calculation unit (22) switches between setting the first time constant as the time constant of the first low-pass filter (24) or setting the second time constant as the time constant of the first low-pass filter (24) so ​​that the magnitude of a fluctuation of the first load information becomes smaller. [6] The motor control device (1) according to claim 5, wherein the time constant calculation unit (22) switches between setting the first time constant as the time constant of the first low-pass filter (24) or setting the second time constant as the time constant of the first low-pass filter (24) based on the magnitude of a fluctuation of the first load information. [7] The motor control device (1) according to claim 5, wherein the time constant calculation unit (22) switches between setting the first time constant as the time constant of the first low-pass filter (24) or setting the second time constant as the time constant of the first low-pass filter (24) based on an external command.

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