Workpiece mass estimation device

Abstract

The purpose of the present invention is to accurately estimate the quality of a workpiece. A workpiece mass estimation device includes an excitation unit, a calculation unit, an estimation unit, and an estimation unit. The excitation unit instructs, to the motor control unit, a scanning excitation for performing an excitation that fluctuates the motor output and varying the excitation frequency. The calculation unit calculates, on the basis of motor information detected at a plurality of detection points in time during the execution period of the scanning excitation, a comprehensive inertia that is the inertia of the driven body for each detection point in time. The estimation unit estimates, from within the execution period, a point in time at which it is determined that the change in the integrated inertia accompanying the change in the adjacent excitation frequency is the smallest. The estimation unit calculates the inertia of the workpiece and estimates the mass of the workpiece by calculating a value obtained by subtracting the inertia of a general driven body including the rotor, the transmission mechanism, and the workpiece placement unit from the comprehensive inertia corresponding to the estimated time point.

Description

Technical Field

[0001] The present disclosure relates to a workpiece mass estimating device for estimating the mass of a workpiece placed on various machines such as machine tools. Background Art

[0002] Some machines, such as machine tools, include a workpiece loading unit, a motor, sensors, and a motor control unit. A workpiece is loaded on the workpiece loading unit. The motor drives the workpiece loading unit. The sensor detects the motor's status. This includes, for example, the motor's current value and rotational speed. The motor control unit performs feedback control of the motor based on the detected motor status.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-55923 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The total mass of the driven bodies driven by the motors changes according to the mass of the workpieces placed on the workpiece loading portion. Therefore, the inertia of the driven bodies also changes according to the mass of the workpieces. According to the change in inertia, the acceleration and deceleration of the driven bodies by the motors will change. Excessive acceleration and deceleration will place an excessive load on the machine and cause mechanical failure. On the other hand, too little acceleration and deceleration will worsen the operating efficiency of the machine. Therefore, it is necessary to adjust the acceleration and deceleration of the driven bodies by the motors to the optimal acceleration and deceleration. Therefore, some machines adjust the acceleration and deceleration of the driven bodies by the motors to the optimal acceleration and deceleration according to the mass of the workpiece input by the operator.

[0008] This technology allows for adjustment of the acceleration and deceleration of the driven object, but the operator must manually input the workpiece mass each time. Therefore, a method for automatically estimating the workpiece mass is proposed as follows. First, an excitation command is transmitted to the machine's motor control unit to cause the motor output to fluctuate, thereby exciting the motor output. Based on motor information such as current feedback and speed feedback values detected by sensors, the inertia of the driven object at that time is identified. The inertia of non-workpiece components is subtracted from the identified inertia of the driven object to calculate the inertia of the workpiece and estimate the workpiece mass.

[0009] However, the present inventors have focused on the following problem: This structure can cause the following problem: Specifically, if the excitation frequency is a predetermined frequency, such as the resonant frequency that resonates with the machine, significant errors may occur in the motor information detected by the sensor, leading to significant errors in the calculated inertia. Consequently, it is impossible to accurately estimate the mass of the workpiece.

[0010] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to enable estimation of the mass of a workpiece with high accuracy.

[0011] Solutions for solving problems

[0012] The workpiece mass estimation device disclosed herein is a workpiece mass estimation device for estimating the mass of a workpiece, wherein the machine includes a workpiece loading portion for loading the workpiece, a motor having a rotor and a stator for rotating the rotor, a transmission mechanism for transmitting a motor output as a force for rotating the rotor to the workpiece loading portion, a sensor for detecting motor information indicating a state of the motor, and a motor control portion for controlling the motor based on the detected motor information. The machine drives a driven object including the rotor, the transmission mechanism, the workpiece loading portion, and the workpiece through the motor output. The workpiece mass estimation device includes:

[0013] an excitation unit for instructing the motor control unit to perform scanning excitation, wherein the scanning excitation is for performing excitation to cause the motor output to fluctuate and for varying the excitation frequency;

[0014] a calculation unit for calculating, based on the motor information detected at a plurality of detection time points during the execution period of the scanning excitation, a comprehensive inertia serving as the inertia of the driven body at each of the detection time points;

[0015] an estimating unit that estimates, from within the execution period, a time point at which it is determined that a change in the comprehensive inertia caused by a change to an adjacent excitation frequency is minimum; and

[0016] An estimating unit calculates the inertia of the workpiece by subtracting the inertia of a general driven body including the rotor, the transmission mechanism, and the workpiece placement unit from the comprehensive inertia corresponding to the estimated time point, thereby estimating the mass of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a diagram showing the configuration of a workpiece mass estimating device and a machine tool according to this embodiment.

[0018] Figure 2 This is a graph showing the relationship between the excitation frequency and the estimated total inertia.

[0019] Figure 3 This is a graph showing the waveforms of the detection values in frequency bands other than the first frequency band.

[0020] Figure 4 Graph showing the waveforms of the respective detection values in the first frequency band.

[0021] Figure 5 It is a graph showing the transition value of the detected current value.

[0022] Figure 6 This is a graph showing changes in waveforms due to scanning excitation.

[0023] Figure 7 This is a graph showing the relationship between the excitation frequency and the estimated total inertia.

[0024] Figure 8 It will Figure 7 An enlarged view of a portion of VIII is shown.

[0025] Figure 9 is a flowchart showing a process of estimating the quality of a workpiece. DETAILED DESCRIPTION

[0026] [First embodiment]

[0027] like Figure 1 As shown, the workpiece mass estimation device 100 of this embodiment is installed in a machine tool 200. The machine tool 200 includes a motor control unit 50, a sensor 60, a motor 70, a transmission mechanism 80, and a workpiece placement unit 90.

[0028] The workpiece loading section 90 is provided so as to be movable in a rotational or linear direction. A workpiece W is loaded on the workpiece loading section 90. The motor 70 includes a rotor 78 and a stator 76 that rotates the rotor 78. Hereinafter, the output from the stator 76 to the rotor 78 will be referred to as "motor output Mo." The transmission mechanism 80 transmits the motor output Mo from the rotor 78 to the workpiece loading section 90. The transmission mechanism 80 may also include a speed reducer such as a gear.

[0029] Hereinafter, the group of components driven by the motor output Mo will be referred to as the "driven body Db." The driven body Db includes the rotor 78, the transmission mechanism 80, the workpiece loading unit 90, and the workpiece W. Furthermore, the components of the driven body Db excluding the workpiece W will be referred to as the "general driven body." Hereinafter, the inertia of the driven body Db will be referred to as the "comprehensive inertia J," and the inertia of the general driven body will be referred to as the "general inertia."

[0030] The sensor 60 detects motor information Mi indicating the state of the motor 70. The motor information Mi includes the current value of the motor 70 and the rotation speed of the rotor 78. The motor control unit 50 performs feedback control on the motor 70 based on the motor information Mi detected by the sensor 60.

[0031] Next, the workpiece mass estimation device 100 is described. The workpiece mass estimation device 100 includes an excitation unit 10, a calculation unit 20, an estimation unit 30, and an estimation unit 40. The excitation unit 10, the calculation unit 20, the estimation unit 30, and the estimation unit 40 are, for example, composed of the same computer as the main body. The computer has, for example, a CPU, ROM, RAM, memory, etc. In addition, Figure 1 , although the workpiece quality estimation device 100 and the machine tool 200 are shown as being independent of each other, the workpiece quality estimation device 100 may be incorporated into the machine tool 200 .

[0032] The vibration unit 10 outputs an excitation command Vc to the motor control unit 50. The excitation command Vc is an excitation command for causing the motor output Mo to fluctuate. More specifically, the excitation command Vc is, for example, a command that adds a fixed-frequency sinusoidal wave to the position command, torque command, or rotational speed command of the motor control unit 50.

[0033] The calculation unit 20 calculates the total inertia J based on the current value Iq of the motor 70 and the rotation speed ω of the rotor 78 detected by the sensor 60 during the excitation period. Specifically, the total inertia J is calculated according to the following equation 1, for example.

[0034] [Number 1]

[0035]

[0036] In this equation (1), "Kt" represents the torque constant Kt of motor 70, "Iq" represents the current value Iq of motor 70, "ω" represents the rotational speed ω of rotor 78, and "t" represents the elapsed time t. Furthermore, in equation (1), "-" represents the average value of the values sampled over a certain number of seconds.

[0037] In Equation 1, "F(ω)" represents the friction force F(ω). Friction force F(ω) is the sum of viscous friction and Coulomb friction, and is expressed as a function of the rotational speed ω of rotor 78. In Equation 1, the friction force F(ω), as the posterior term, can be ignored as long as it is small compared to the product of the torque constant Kt and the average current value, as the anterior term. If it is not small, for example, a previously determined friction force F(ω) can be substituted into F(ω) in Equation 1.

[0038] The estimation unit 40 calculates the inertia of the workpiece W by calculating a value obtained by subtracting a pre-stored general inertia from the comprehensive inertia J calculated by the calculation unit 20 , thereby estimating the mass of the workpiece W.

[0039] Next, refer to Figures 2 to 5The issues addressed in this embodiment will now be described. The frequency at which the motor output Mo is excited will be referred to as the "excitation frequency fv." Depending on the excitation frequency fv, significant errors may occur in the motor information Mi detected during the excitation, leading to significant errors in the calculated integrated inertia J. Consequently, the mass of the workpiece W cannot be accurately estimated.

[0040] Specifically, as frequency bands where a large error may occur, there are the following first to third frequency bands B1 to B3 .

[0041] First, yes Figure 2 The first frequency band B1 shown on the left side of the figure is used for explanation. The first frequency band B1 is a frequency band where the moving speed of the workpiece loading unit 90 decreases as the Coulomb friction becomes dominant. In a frequency band larger than the first frequency band B1, the Coulomb friction F(ω) becomes sufficiently small. Therefore, as Figure 3 As shown, there is no dead zone in the current value Iq and the rotation speed ω. Note that the dead zone here refers to a range where the value hardly changes.

[0042] On the other hand, in the first frequency band B1, the movement of the workpiece placement unit 90 produces a stick-slip behavior due to Coulomb friction. Figure 4 As shown, a dead zone Dz is generated in one or both of the current value Iq and the rotation speed ω. Figure 2 As shown, in the first frequency band B1 , the error in the calculated comprehensive inertia J increases due to the dead zone Dz, and the mass of the workpiece W cannot be estimated with high accuracy.

[0043] Then, Figure 2 The second frequency band B2 shown in the left and right center parts is explained. The second frequency band B2 is a frequency band where the indicated excitation frequency fv overlaps with the natural vibration frequency of the entire machine tool 200. In this second frequency band B2, as shown in FIG. Figure 5 As shown in FIG. 1 , the current value Iq is amplified. Therefore, in the second frequency band B2, as shown in FIG. Figure 2 As shown in the left and right center parts of , the error of the calculated comprehensive inertia J becomes large, and the mass of the workpiece W cannot be estimated with good accuracy.

[0044] Then, Figure 2 The third frequency band B3 shown to the right of the 3rd frequency band B3 is explained. The third frequency band B3 is a frequency at which the moving speed of the workpiece loading unit 90 increases as the frequency band becomes outside the frequency band of the control response under the control of the motor 70. In this third frequency band B3, as shown in FIG. Figure 5 As shown in FIG, the current value becomes unstable. Therefore, in the third frequency band B3, as shown in FIG. Figure 2 As shown to the right of , the error of the comprehensive inertia J becomes large, and the mass of the workpiece W cannot be estimated with good accuracy.

[0045] Therefore, assuming that Figure 2 When the excitation frequency fv is randomly selected as shown, an excitation frequency fv belonging to any of the first to third frequency bands B1, B2, and B3 may be selected. In this case, the mass of the workpiece W cannot be estimated accurately.

[0046] In order to solve the above problems, in this embodiment, Figure 1 The above-described excitation unit 10 and calculation unit 20 are configured as follows, and the workpiece mass estimation device 100 further includes an estimation unit 30 .

[0047] like Figure 6 As shown, the excitation unit 10 instructs the motor control unit 50 to perform sweep excitation, causing the excitation frequency fv to vary within a predetermined variation range vR. Specifically, the excitation unit 10 instructs the motor control unit 50 to perform sweep excitation by inputting a torque command value to the excitation unit 50 and varying the excitation frequency fv of the torque command value.

[0048] At this time, the excitation unit 10 varies the excitation frequency fv from the low-frequency end of the variation range vR toward the high-frequency end. However, the excitation frequency fv may alternatively vary from the high-frequency end of the variation range vR toward the low-frequency end. The excitation unit 10 is configured so that the variation range vR within which the excitation frequency fv varies during sweep excitation can be changed by an operator or the like.

[0049] When performing sweep excitation, Figure 1 The sensor 60 shown in FIG. 1 detects the motor information Mi at a plurality of detection time points P during the execution period of the scanning excitation. The calculation unit 20 calculates the motor information Mi at the plurality of detection time points P, as shown in FIG. Figure 7 The comprehensive inertia J is calculated at each detection time point P as shown.

[0050] Next, the adjacent detection time points P n-1 、P n The change in the combined inertia J between them is called the "rate of change ΔJ". Figure 8 As shown in FIG, the calculation unit 20 calculates the rate of change at each detection time point P. This calculation is performed, for example, according to the following formula 2.

[0051] [Number 2]

[0052]

[0053] Here, "J n " is at the nth detection time point P n The comprehensive inertia J, "J n-1 " is at the n-1th detection time point P n-1 The combined inertia J. "ΔJn ” is the n-1th detection time point P n-1 and the nth detection time point P n The rate of change ΔJ between them.

[0054] The estimation unit 30 estimates the detection time point P at which the change rate ΔJ is the smallest from among the plurality of detection time points P at which the change rate ΔJ has been calculated by the calculation unit 20. Figure 7 In the predetermined variation range vR shown in FIG. 1 , the excitation frequency fv is estimated, which is determined to minimize the change in the comprehensive inertia J caused by the change to the adjacent excitation frequency fv. Figure 7 The excitation frequency fv at which any one of the first to third frequency bands B1, B2, and B3 is superimposed is shown.

[0055] The reason for this is that, first, in the first frequency band B1, the estimated combined inertia J is constantly decreasing, so the rate of change ΔJn tends to be large. Furthermore, in the second and third frequency bands B3, the estimated combined inertia J immediately turns from increasing to decreasing, so the rate of change ΔJn tends to be large. Consequently, the rate of change ΔJ tends to be minimum at the detection time point P of the excitation frequency fv that does not fall within any of the first to third frequency bands.

[0056] However, in the second and third frequency bands B2, there may be accidental occurrences of the estimated total inertia J at the n-1th detection time point Pn-1 on both sides of the top of the curve indicating the transition of the estimated total inertia J. n-1 and the comprehensive inertia J at the nth detection time point Pn n In this case, the change rate ΔJ at the detection time point P near the top in the second or third frequency band B2 may be the smallest.

[0057] In order to completely avoid such problems, the estimation unit 30 may also be configured to estimate the detection time point at which the change rate ΔJ is minimized based on additional conditions. Specifically, for example, in the above formula 2, after the detection time point P at which the change rate ΔJ is minimized is estimated, the change rate ΔJ may be recalculated by replacing "n-1" with "n-2" in the formula 2. n In this case, it is also possible to configure the change rate ΔJ n If the predetermined value is exceeded, the detection time point P at which the change rate ΔJ is the smallest is estimated from the remaining plurality of detection time points P excluding the detection time point P.

[0058] Figure 1The illustrated estimation unit 40 calculates the inertia of the workpiece W and estimates the mass of the workpiece W by calculating a value obtained by subtracting the general inertia from the comprehensive inertia J at the detection time point P estimated by the estimation unit 30 .

[0059] Then, the estimation unit 40 transmits the estimated mass of the workpiece W to the motor control unit 50 , for example. In this case, the motor control unit 50 changes the control method of the motor 70 and the acceleration / deceleration conditions according to the received mass of the workpiece W.

[0060] Next, refer to Figure 9 The following describes the flow of the mass estimation of the workpiece W. In the following, "S" is an abbreviation for "step".

[0061] First, in S1, the workpiece mass estimation apparatus 100 determines whether scanning excitation is being performed. If a negative determination N (No) is made, the determination in S1 is repeated, for example, at predetermined intervals. On the other hand, if a positive determination Y (Yes) is made, the process proceeds to the next S2.

[0062] In S2, the calculation unit 20 obtains the motor information Mi from the sensor 60. In the following S3, the calculation unit 20 calculates the comprehensive inertia J based on the motor information Mi. In the following S4, the calculation unit 20 calculates the comprehensive inertia J based on the detection time point P at this time. n The combined inertia J n , and at the previous detection time point P n-1 The combined inertia J n-1 , to calculate the rate of change ΔJ. In the next S5, the calculation unit 20 determines whether the current excitation frequency fv is within the predetermined variation range vR. If a positive determination Y is made, the process returns to S2. On the other hand, if a negative determination N is made in S5, the process proceeds to S6.

[0063] In S6 , the estimation unit 30 estimates the detection time point P at which the change rate ΔJ is minimum from the plurality of detection time points P for which the change rates ΔJ have been calculated.

[0064] In the next S7 , the estimation unit 40 estimates the comprehensive inertia J at the estimated detection time point P. In the next S8 , the estimation unit 40 calculates the inertia of the workpiece W by subtracting the general inertia from the estimated comprehensive inertia J, thereby estimating the mass of the workpiece W.

[0065] Next, the structure and effects of this embodiment are summarized.

[0066] The excitation unit 10 can excite the motor control unit 50 by inputting a torque command value, and can cause the motor control unit 50 to perform sweep excitation by varying the excitation frequency fv of the torque command value.

[0067] The calculation unit 20 calculates the comprehensive inertia at each detection time point P based on the motor information Mi detected at multiple detection time points P during the sweeping excitation period. The estimation unit 30 estimates the time point during the sweeping excitation period at which the change in comprehensive inertia associated with a change to an adjacent excitation frequency fv is determined to be minimal. This effectively estimates the time point at which the excitation frequency fv does not overlap with any of the first to third frequency bands B1, B2, and B3.

[0068] The estimation unit 40 calculates the inertia of the workpiece W by subtracting the general inertia from the comprehensive inertia J corresponding to the thus estimated time point, thereby estimating the mass of the workpiece W. This allows for a highly accurate estimation of the mass of the workpiece W. Based on the accurately estimated mass of the workpiece W, the machine tool 200 can, for example, adjust the motor output Mo to an appropriate value without excess or deficiency, and adjust the acceleration and deceleration of the driven body Db to appropriate values without excess or deficiency.

[0069] Furthermore, the excitation unit 10 is configured to be able to change the variation range vR in which the excitation frequency fv is varied during scanning excitation. Therefore, the operator can appropriately set the variation range vR.

[0070] [Other embodiments]

[0071] The above-described embodiment can be modified as follows, for example: The workpiece mass estimation device 100 may be provided for a machine other than the machine tool 200. The vibration unit 10 may vibrate to input a position command or a rotation speed command instead of a torque command value.

[0072] According to the above embodiment, the workpiece mass estimation device of Supplementary Notes 1 to 4 shown below can be realized.

[0073] [Note 1]

[0074] A workpiece mass estimation device (100) is a workpiece mass estimation device (100) for estimating the mass of a workpiece (W) for a machine (200), wherein the machine (200) includes a workpiece loading portion (90) for loading the workpiece (W), a motor (70) having a rotor (78) and a stator (76) for rotating the rotor (78), a transmission mechanism (80) for transmitting a motor output (Mo) as a force for rotating the rotor (78) to the workpiece loading portion (90), a sensor (60) for detecting motor information (Mi) indicating a state of the motor (70), and a motor control portion (50) for controlling the motor (70) based on the detected motor information (Mi). The machine (200) drives a driven body (Db) including the rotor (78), the transmission mechanism (80), the workpiece loading portion (90), and the workpiece (W) by the motor output (Mo). The workpiece mass estimation device (100) includes:

[0075] an excitation unit (10) for instructing the motor control unit (50) to perform scanning excitation, wherein the scanning excitation is for performing excitation to cause the motor output (Mo) to fluctuate and to change the excitation frequency (fv);

[0076] a calculation unit (20) for calculating, based on the motor information (Mi) detected at a plurality of detection time points (P) during the execution period of the scanning excitation, a comprehensive inertia (J) as the inertia of the driven body (Db) at each of the detection time points (P);

[0077] an estimating unit (30) that estimates, from within the execution period, a time point at which the excitation frequency (fv) is determined to have the smallest change in the comprehensive inertia (J) caused by a change to an adjacent excitation frequency (fv); and

[0078] An estimating unit (40) calculates the inertia of the workpiece (W) and estimates the mass of the workpiece (W) by subtracting the inertia of a general driven body (Db) including the rotor (78), the transmission mechanism (80) and the workpiece loading unit (90) from the comprehensive inertia (J) corresponding to the estimated time point.

[0079] [Note 2]

[0080] The workpiece quality estimation device (100) according to Supplementary Note 1, wherein:

[0081] The excitation unit (10) excites the motor control unit (50) by inputting a torque instruction value and changes an excitation frequency (fv) of the torque instruction value, thereby instructing the motor control unit (50) to perform the scanning excitation.

[0082] [Note 3]

[0083] The workpiece quality estimation device (100) according to Supplementary Note 1 or 2, wherein:

[0084] The excitation unit (10) is configured to be able to change a variation range (vR) of the excitation frequency (fv) during the scanning excitation.

[0085] [Note 4]

[0086] The workpiece mass estimation device (100) according to any one of Supplementary Notes 1 to 3, wherein:

[0087] The estimating unit (30) estimates the time point of the excitation frequency (fv) that does not overlap with any of the first frequency band (B1), the second frequency band (B2), and the third frequency band (B3), by estimating the time point of the excitation frequency (fv) determined to be the minimum.

[0088] The first frequency band (B1) is a frequency band in which a dead zone is generated between the current value of the motor (70) and the rotation speed of the rotor (78) as Coulomb friction becomes dominant and the moving speed of the workpiece loading portion (90) decreases.

[0089] The second frequency band (B2) is a frequency band in which resonance with the machine occurs.

[0090] The third frequency band (B3) is a frequency band in which the moving speed of the workpiece placing portion (90) increases as the frequency band becomes outside the frequency band of the control response under the control of the motor (70).

[0091] According to the workpiece mass estimation device (100) of the above-mentioned supplementary notes 1 to 4, the mass of the workpiece (W) can be estimated with high accuracy.

[0092] The present disclosure has been described in detail above, but the present disclosure is not limited to the above-mentioned embodiments. These embodiments can be subject to various additions, replacements, changes, partial deletions, etc. without departing from the scope of the present disclosure, or without departing from the scope of the present disclosure derived from the contents recorded in the claims and their equivalents. In addition, these embodiments can also be implemented in combination. For example, in the above-mentioned embodiments, the order of each action and the order of each processing are shown as an example and are not limited to these orders. In addition, the same applies to the use of numerical values or formulas in the description of the above-mentioned embodiments.

[0093] Description of Reference Numerals

[0094] 10: Excitation unit; 20: Calculation unit; 30: Inference unit; 40: Estimation unit; 50: Motor control unit; 60: Sensor; 70: Motor; 76: Stator; 78: Rotor; 80: Transmission mechanism; 90: Workpiece loading unit; 100: Workpiece mass estimation device; 200: Machine tool; B1: 1st frequency band; B2: 2nd frequency band; B3: 3rd frequency band; Db: Driven body; fv: Excitation frequency; J: Comprehensive inertia; Mi: Motor information; Mo: Motor output; vR: Variation range; W: Workpiece.

Claims

1. A workpiece mass estimation device is a workpiece mass estimation device for a machine for estimating the mass of a workpiece, wherein: The machine includes a workpiece loading portion for loading the workpiece, a motor having a rotor and a stator for rotating the rotor, a transmission mechanism for transmitting a motor output as a force for rotating the rotor to the workpiece loading portion, a sensor for detecting motor information indicating a state of the motor, and a motor control portion for controlling the motor based on the detected motor information. The machine drives a driven object including the rotor, the transmission mechanism, the workpiece loading portion, and the workpiece through the motor output. The workpiece mass estimation device includes: an excitation unit for instructing the motor control unit to perform scanning excitation, wherein the scanning excitation is for performing excitation to cause the motor output to fluctuate and for varying the excitation frequency; a calculation unit for calculating, based on the motor information detected at a plurality of detection time points during the execution period of the scanning excitation, a comprehensive inertia serving as the inertia of the driven body at each of the detection time points; an estimating unit that estimates, from within the execution period, a time point at which it is determined that a change in the comprehensive inertia caused by a change to an adjacent excitation frequency is minimum; as well as An estimating unit calculates the inertia of the workpiece by subtracting the inertia of a general driven body including the rotor, the transmission mechanism, and the workpiece placement unit from the comprehensive inertia corresponding to the estimated time point, thereby estimating the mass of the workpiece.

2. The workpiece quality estimation device according to claim 1, wherein: The excitation unit excites an input torque command value to the motor control unit and changes an excitation frequency of the torque command value, thereby instructing the motor control unit to perform the scanning excitation.

3. The workpiece quality estimation device according to claim 1 or 2, wherein: The excitation unit is configured to be able to change a range of variation of the excitation frequency during the scanning excitation.

4. The workpiece mass estimation device according to any one of claims 1 to 3, wherein: The estimating unit estimates the time point of the excitation frequency that does not overlap with any of the first frequency band, the second frequency band, and the third frequency band by estimating the time point of the excitation frequency determined to be the minimum. The first frequency band is a frequency band in which a dead zone is generated between the current value of the motor and the rotation speed of the rotor as Coulomb friction becomes dominant and the moving speed of the workpiece placement portion decreases. The second frequency band is a frequency band in which resonance with the machine occurs. The third frequency band is a frequency band in which the moving speed of the workpiece placing unit increases as the frequency band becomes outside the frequency band of the control response under the control of the motor.

Images