Workpiece mass estimation device

Abstract

The purpose of the present invention is to enable accurate estimation of the mass of a workpiece. This workpiece mass estimation device comprises a vibrating unit, a calculation unit, an identification unit, and an estimation unit. The vibration unit commands a motor control unit to perform vibration to agitate output of a motor and to perform a sweep vibration to vary the vibration frequency. The calculation unit, on the basis of motor information detected at a plurality of detection times within the period of execution of the sweep vibration, calculates the overall inertia as the inertia of a driven body for each detection time. The identification unit identifies the time, within the execution period, that has the vibration frequency for which the change in the overall inertia associated with the change to the adjacent vibration frequency is determined to be the least. The estimation unit, by calculating a value obtained by subtracting the inertia of a general driven body that includes a rotor, a transmission mechanism, and a workpiece loading unit from the overall inertia corresponding to the identified time, calculates the inertia of a workpiece to estimate the mass of the workpiece.

Description

Workpiece mass estimation device

[0001] The present disclosure relates to a workpiece mass estimation device that estimates the mass of a workpiece loaded on various machines such as machine tools.

[0002] Some machines, such as machine tools, are equipped with a workpiece loading section, a motor, a sensor, and a motor control section. A workpiece is loaded onto the workpiece loading section. The motor drives the workpiece loading section. The sensor detects the state of the motor. The state of the motor includes, for example, the current value and rotation speed of the motor. The motor control section performs feedback control of the motor based on the detected state of the motor.

[0003] JP 2015-55923 A

[0004] The total mass of the driven body driven by the motor varies depending on the mass of the workpieces loaded on the workpiece loading section. Therefore, the inertia of the driven body also varies depending on the mass of the workpieces. This change in inertia changes the acceleration / deceleration of the driven body caused by the motor. Excessive acceleration / deceleration places an excessive load on the machine, leading to machine failure, while insufficient acceleration / deceleration reduces the work efficiency of the machine. Therefore, it is necessary to adjust the acceleration / deceleration of the driven body caused by the motor to an optimal acceleration / deceleration. For this reason, some machines adjust the acceleration / deceleration of the driven body caused by the motor to an optimal acceleration / deceleration based on the workpiece mass input by the operator.

[0005] While this technology allows for the adjustment of the acceleration / deceleration of the driven body, it requires the operator to manually input the workpiece mass each time. Therefore, a method has been proposed for automatically estimating the workpiece mass, as follows: First, a vibration command to vibrate the motor output is sent to the machine's motor control unit, causing the motor output to vibrate. The inertia of the driven body at this time is identified based on motor information such as the current feedback value and rotational speed feedback value detected by the sensor. The inertia of the workpiece is calculated by subtracting the inertia caused by factors other than the workpiece from the identified inertia of the driven body, and the workpiece mass is then estimated.

[0006] However, the present inventors have noticed that such a configuration can cause the following problem. That is, when the excitation frequency is a predetermined frequency such as a resonant frequency with the machine, a large error occurs in the motor information detected by the sensor, which in turn causes a large error in the calculated inertia. As a result, the mass of the workpiece cannot be estimated accurately.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to enable the mass of a workpiece to be estimated with high accuracy.

[0008] A workpiece mass estimation device according to the present disclosure includes a workpiece loading section on which a workpiece is loaded, a motor having a rotor and a stator for rotating the rotor, a transmission mechanism for transmitting motor output as a force for rotating the rotor to the workpiece loading section, a sensor for detecting motor information indicating the state of the motor, and a motor control section for controlling the motor based on the detected motor information, and is a workpiece mass estimation device for estimating the mass of the workpiece for a machine that drives a driven body including the rotor, the transmission mechanism, the workpiece loading section, and the workpiece by the motor output, and includes: a vibration excitation section that commands the motor control section to apply sweep vibration that vibrates the motor output and varies the vibration frequency; a calculation section that calculates a total inertia as the inertia of the driven body for each detection time point based on the motor information detected at a plurality of detection time points within an execution period of the sweep vibration excitation; and an indexing section that indexes, within the execution period, a time point of an excitation frequency at which it is determined that a change in the total inertia accompanying a change to an adjacent excitation frequency becomes minimum. and an estimation unit that calculates the inertia of the workpiece by subtracting the inertia of a general driven body including the rotor, the transmission mechanism, and the workpiece loading unit from the total inertia corresponding to the determined time point, thereby estimating the mass of the workpiece.

[0009] 7 is a configuration diagram showing a workpiece mass estimation device and a machine tool of the present embodiment. FIG. 8 is a graph showing the relationship between excitation frequency and estimated overall inertia. FIG. 9 is a graph showing waveforms of each detection value in frequency bands other than a first frequency band. FIG. 10 is a graph showing waveforms of each detection value in the first frequency band. FIG. 11 is a graph showing transition values ​​of detected current. FIG. 12 is a graph showing changes in waveform due to sweep excitation. FIG. 13 is a graph showing the relationship between excitation frequency and estimated overall inertia. FIG. 14 is an enlarged view of portion VIII shown in FIG. 7. FIG. 15 is a flowchart showing the procedure for workpiece mass estimation.

[0010] 1, a workpiece mass estimation device 100 of this embodiment is installed on 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 loading unit 90.

[0011] The workpiece loading section 90 is provided so as to be movable in a rotational direction or a linear direction. A workpiece W is loaded on the workpiece loading section 90. The motor 70 has 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 the "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 include a reducer such as a gear.

[0012] Hereinafter, the group of parts 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 section 90, and the workpiece W. Hereinafter, 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 "total inertia J," and the inertia of the general driven body will be referred to as the "general inertia."

[0013] 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 of the motor 70 based on the motor information Mi detected by the sensor 60.

[0014] Next, the workpiece mass estimation device 100 will be described. The workpiece mass estimation device 100 includes a vibration unit 10, a calculation unit 20, an indexing unit 30, and an estimation unit 40. The vibration unit 10, the calculation unit 20, the indexing unit 30, and the estimation unit 40 are, for example, mainly configured using the same computer. The computer includes, for example, a CPU, ROM, RAM, memory, etc. Note that while the workpiece mass estimation device 100 and the machine tool 200 are shown as separate entities in FIG. 1, the workpiece mass estimation device 100 may also be incorporated within the machine tool 200.

[0015] The vibration unit 10 outputs a vibration command Vc to the motor control unit 50. The vibration command Vc is a command to vibrate the motor output Mo. More specifically, the vibration command Vc is a command to add a sinusoidal command of a constant frequency to, for example, a position command, a torque command, or a rotational speed command by the motor control unit 50.

[0016] The calculation unit 20 calculates the total inertia J based on the current value Iq of the motor 70 detected by the sensor 60 during the vibration application period and the rotational speed ω of the rotor 78. Specifically, the calculation unit 20 calculates the total inertia J based on the following equation 1, for example.

[0017]

[0018] In this equation 1, "Kt" is the torque constant Kt of the motor 70, "Iq" is the current value Iq of the motor 70, "ω" is the rotational speed ω of the rotor 78, and "t" is the elapsed time t. Also, in equation 1, "" indicates the average value of values ​​sampled within a certain number of seconds.

[0019] Furthermore, in this equation 1, "F(ω)" is the friction force F(ω). The 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 the rotor 78. The friction force F(ω), which is the latter term in equation 1, may be ignored if it is minute compared to the product of the torque constant Kt and the average current value, which is the former term. If it is not minute, for example, a friction force F(ω) that is known in advance is substituted for F(ω) in equation 1.

[0020] The estimation unit 40 calculates the inertia of the workpiece W by subtracting a pre-stored general inertia from the total inertia J calculated by the calculation unit 20, and estimates the mass of the workpiece W.

[0021] Next, the problem to be solved by this embodiment will be described with reference to Figures 2 to 5. Hereinafter, the frequency at which the motor output Mo is vibrated will be referred to as the "excitation frequency fv." Depending on the excitation frequency fv, a large error will occur in the motor information Mi detected during the execution of vibration, and a large error will also occur in the calculated total inertia J. As a result, it will be impossible to accurately estimate the mass of the workpiece W.

[0022] Specifically, frequency bands in which errors may be large include the following first to third frequency bands B1 to B3.

[0023] First, the first frequency band B1 shown on the left side of Fig. 2 will be described. The first frequency band B1 is a frequency band in which the moving speed of the workpiece loading unit 90 becomes so slow that Coulomb friction becomes dominant. In frequency bands greater than this first frequency band B1, Coulomb friction F(ω) becomes sufficiently small. Therefore, as shown in Fig. 3, no dead zone occurs between the current value Iq and the rotational speed ω. Note that the dead zone here is a section in which the value hardly changes.

[0024] On the other hand, in the first frequency band B1, stick-slip-like behavior occurs in the movement of the workpiece loading unit 90 due to Coulomb friction. As a result, a dead zone Dz occurs in one or both of the current value Iq and the rotational speed ω, as shown in Fig. 4. Due to this dead zone Dz, as shown in Fig. 2, in the first frequency band B1, the error in the calculated total inertia J becomes large, and the mass of the workpiece W cannot be estimated with high accuracy.

[0025] Next, the second frequency band B2 shown in the center of Fig. 2 will be described. The second frequency band B2 is a frequency band in which the commanded excitation frequency fv overlaps with the natural frequency of the entire machine tool 200. In this second frequency band B2, the current value Iq is amplified, as shown in Fig. 5. As a result, in this second frequency band B2, as shown in the center of Fig. 2, the error in the calculated total inertia J becomes large, making it impossible to accurately estimate the mass of the workpiece W.

[0026] Next, the third frequency band B3 shown on the right side of Fig. 2 will be described. The third frequency band B3 is a frequency at which the movement speed of the workpiece loading unit 90 becomes faster as it moves outside the band of the control response in the control of the motor 70. In this third frequency band B3, the current value becomes unstable as shown in Fig. 5. Therefore, in this third frequency band B3, as shown on the right side of Fig. 2, the error in the total inertia J becomes large, and the mass of the workpiece W cannot be estimated with high accuracy.

[0027] Therefore, if the vibration frequency fv is selected randomly as shown in Figure 2, there is a risk that the vibration frequency fv belonging to any of the first to third frequency bands B1, B2, and B3 will be selected, in which case the mass of the workpiece W cannot be estimated with high accuracy.

[0028] In order to solve the above problems, in this embodiment, the vibration unit 10 and the calculation unit 20 shown in FIG. 1 are configured as follows, and the workpiece mass estimation device 100 further includes an indexing unit 30.

[0029] 6, the vibration unit 10 commands the motor control unit 50 to perform sweep vibration, which varies the vibration frequency fv within a predetermined variation range vR. Specifically, the vibration unit 10 inputs a torque command value to the motor control unit 50 to perform vibration, and commands the sweep vibration by varying the vibration frequency fv of the torque command value.

[0030] 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, instead of this, the excitation frequency fv may be varied 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 in which the excitation frequency fv is varied during sweep excitation can be changed by an operator or the like.

[0031] When sweep excitation is performed, the sensor 60 shown in Fig. 1 detects motor information Mi at a plurality of detection times P within the execution period of the sweep excitation. The calculation unit 20 calculates the total inertia J for each detection time point P based on the motor information Mi at the plurality of detection times P, as shown in Fig. 7 .

[0032] Hereinafter, adjacent detection times P ｎ-1 , P ｎ The change in the overall inertia J between these two points is called the "change rate ΔJ." As shown in Fig. 8, the calculation unit 20 calculates the change rate at each detection point P. This calculation is performed, for example, based on the following equation 2.

[0033]

[0034] Here, "J ｎ " is the nth detection time point P ｎ The total inertia J is ｎ－１ " is the n-1th detection time point P ｎ-1 The total inertia J is ΔJ ｎ " is the n-1th detection time point P ｎ-1 and the nth detection time P ｎ is the rate of change ΔJ between

[0035] The indexing unit 30 indexes the detection time point P at which the rate of change ΔJ is smallest from among the multiple detection time points P at which the rate of change ΔJ is calculated by the calculation unit 20. As a result, the indexing unit 30 indexes the excitation frequency fv at which it is determined that the change in the overall inertia J accompanying a change to an adjacent excitation frequency fv is smallest from among the excitation frequencies fv within the execution period of the sweep excitation, that is, from within the predetermined fluctuation range vR shown in Fig. 7. This makes it easier for the indexing unit 30 to index the excitation frequency fv that does not overlap with any of the first to third frequency bands B1, B2, and B3 shown in Fig. 7.

[0036] This is because, first, in the first frequency band B1, the estimated total inertia J always slopes downward, so the rate of change ΔJn tends to be large. Also, in the second and third frequency bands B3, the estimated total inertia J slopes upward and then immediately slopes downward, so the rate of change ΔJn tends to be large. For this reason, the rate of change ΔJ tends to be smallest at the detection time P of the excitation frequency fv that does not belong to any of the first to third frequency bands.

[0037] However, in the second and third frequency bands B2, the total inertia J at the n-1th detection time point Pn-1 coincidentally exists on both sides of the peak of the curve showing the transition of the estimated total inertia J. ｎ－１ and the total inertia J at the nth detection time Pn ｎ In this case, the rate of change ΔJ at the detection time point P near the peak in the second or third frequency band B2 may be minimized.

[0038] In order to completely avoid such a problem, the indexing unit 30 may be configured to index the detection time point at which the rate of change ΔJ is minimum based on an additional condition. Specifically, for example, after the detection time point P at which the rate of change ΔJ is minimum is indexed in the above formula 2, the rate of change ΔJ is further indexed by replacing "n-1" with "n-2" in the formula 2. ｎ In that case, the rate of change ΔJ ｎIf the detection time P exceeds the predetermined value, the detection time P at which the rate of change ΔJ is minimum may be determined from the remaining detection times P excluding the detection time P.

[0039] The estimation unit 40 shown in FIG. 1 calculates the inertia of the workpiece W by subtracting the general inertia from the total inertia J at the detection time P determined by the indexing unit 30, thereby estimating the mass of the workpiece W.

[0040] Thereafter, the estimation unit 40 transmits, for example, the estimated mass of the workpiece W to the motor control unit 50. In this case, the motor control unit 50 changes the control mode of the motor 70 and the acceleration / deceleration conditions based on the received mass of the workpiece W.

[0041] Next, the above-described flow of estimating the mass of the workpiece W will be described with reference to Fig. 9. In the following, "S" stands for "step."

[0042] First, in S1, the workpiece mass estimation device 100 determines whether sweep vibration is being performed. If a negative determination N (No) is made, the determination in S1 is repeated, for example, at predetermined time intervals. On the other hand, if a positive determination Y (Yes) is made, the process proceeds to the next step S2.

[0043] In S2, the calculation unit 20 acquires the motor information Mi from the sensor 60. In the following S3, the calculation unit 20 calculates the overall inertia J based on the motor information Mi. In the following S4, the calculation unit 20 calculates the overall inertia J at the current detection time P ｎ The total inertia J ｎ and the previous detection time P ｎ-1 The total inertia J ｎ-1 The rate of change ΔJ is calculated based on the above. In the following S5, the calculation unit 20 determines whether the current vibration frequency fv is within a predetermined fluctuation 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.

[0044] In S6, the indexing unit 30 indexes the detection time point P at which the rate of change ΔJ is smallest from among the plurality of detection times P at which the rate of change ΔJ has been calculated.

[0045] In the next step S7, the estimation unit 40 calculates the total inertia J at the calculated detection time point P. In the next step S8, the estimation unit 40 calculates the inertia of the workpiece W and estimates the mass of the workpiece W by subtracting the general inertia from the calculated total inertia J.

[0046] The configuration and effects of this embodiment are summarized below.

[0047] The vibration unit 10 inputs a torque command value to the motor control unit 50 for vibration and varies the vibration frequency fv of the torque command value, thereby causing the motor control unit 50 to execute sweep vibration.

[0048] The calculation unit 20 calculates the total inertia for each detection time point P based on the motor information Mi detected at multiple detection time points P during the execution period of the sweep excitation. The indexing unit 30 indexes, from within the execution period of the sweep excitation, the time point of the excitation frequency fv at which it is determined that the change in total inertia accompanying a change to the adjacent excitation frequency fv is minimum. As a result, as described above, it is possible to efficiently index the time point of the excitation frequency fv that does not overlap with any of the first to third frequency bands B1, B2, and B3.

[0049] The estimation unit 40 calculates the inertia of the workpiece W by subtracting the general inertia from the total inertia J corresponding to the time point determined in this manner, thereby estimating the mass of the workpiece W. This allows the mass of the workpiece W to be estimated with high accuracy. Based on the mass of the workpiece W estimated with high accuracy, the machine tool 200 can, for example, adjust the motor output Mo to an appropriate value, neither too much nor too little, and adjust the acceleration / deceleration of the driven body Db to an appropriate value, neither too much nor too little.

[0050] Moreover, the excitation unit 10 is configured to be able to change the variation range vR within which the excitation frequency fv is varied during sweep excitation, allowing the operator to set the variation range vR as appropriate.

[0051] Other Embodiments The above-described embodiment can be modified, for example, as follows. The workpiece mass estimation device 100 may be installed on a machine other than the machine tool 200. The vibration unit 10 may input a position command or a rotational speed command as vibration input, instead of inputting a torque command value as vibration input.

[0052] According to the above embodiment, it is possible to realize the workpiece mass estimation device described in Supplementary Notes 1 to 4 below.

[0053] [Supplementary Note 1] A work mass estimation device (100) comprising: a work loading section (90) on which a work (W) is loaded; a motor (70) having a rotor (78) and a stator (76) that rotates the rotor (78); a transmission mechanism (80) that transmits a motor output (Mo) as a force that rotates the rotor (78) to the work loading section (90); a sensor (60) that detects motor information (Mi) that indicates a state of the motor (70); and a motor control section (50) that controls the motor (70) based on the detected motor information (Mi), wherein the work mass estimation device (100) estimates a mass of the work (W) for a machine (200) that drives a driven body (Db) including the rotor (78), the transmission mechanism (80), the work loading section (90), and the work (W) using the motor output (Mo), an excitation unit (10) that commands the motor control unit (50) to perform sweep excitation that vibrates the motor output (Mo) and varies the excitation frequency (fv); a calculation unit (20) that calculates a total inertia (J) as the inertia of the driven body (Db) for each detection time point (P) based on the motor information (Mi) detected at a plurality of detection time points (P) within an execution period of the sweep excitation; and an indexing unit (30) that indexes, within the execution period, a time point of the excitation frequency (fv) at which it is determined that a change in the total inertia (J) accompanying a change to an adjacent excitation frequency (fv) is minimum. an estimation unit (40) that calculates the inertia of the work (W) by calculating a value obtained by subtracting the inertia of a general driven body (Db) including the rotor (78), the transmission mechanism (80), and the work loading unit (90) from the total inertia (J) corresponding to the determined time point, thereby estimating the mass of the work (W).

[0054] [Supplementary Note 2] The workpiece mass estimation device (100) according to Supplementary Note 1, wherein the vibration unit (10) commands the sweep vibration by inputting a torque command value to the motor control unit (50) as an excitation input and varying an excitation frequency (fv) of the torque command value.

[0055] [Supplementary Note 3] The workpiece mass estimation device (100) according to Supplementary Note 1 or 2, wherein the vibration unit (10) is configured to be able to change a fluctuation range (vR) within which the vibration frequency (fv) is varied in the sweep vibration.

[0056] [Supplementary Note 4] The workpiece mass estimation device (100) according to any one of Supplementary Notes 1 to 3, wherein the indexing unit (30) indexes the time point of the excitation frequency (fv) determined to be the minimum, thereby indexing the time point of the excitation frequency (fv) that does not overlap with any of: a first frequency band (B1) in which the movement speed of the workpiece loading unit (90) becomes slower as Coulomb friction becomes more dominant, creating a dead zone in the current value of the motor (70) and the rotation speed of the rotor (78); a second frequency band (B2) in which resonance with the machine occurs; and a third frequency band (B3) in which the movement speed of the workpiece loading unit (90) becomes so fast that it falls outside a band of control response in control of the motor (70).

[0057] According to the workpiece mass estimation device (100) described above in Supplementary Notes 1 to 4, the mass of the workpiece (W) can be estimated with high accuracy.

[0058] Although the present disclosure has been described in detail above, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0059] REFERENCE SIGNS LIST 10 Excitation unit 20 Calculation unit 30 Indexing 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 First frequency band B2 Second frequency band B3 Third frequency band Db Driven body fv Excitation frequency J Total inertia Mi Motor information Mo Motor output vR Fluctuation range W Workpiece

Claims

1. a motor having a workpiece loading section on which a workpiece is loaded, a rotor and a stator that rotates the rotor, a transmission mechanism that transmits motor output as a force that rotates the rotor to the workpiece loading section, a sensor that detects motor information that indicates the state of the motor, and a motor control section that controls the motor based on the detected motor information, and a machine that drives a driven body including the rotor, the transmission mechanism, the workpiece loading section, and the workpiece by the motor output; A workpiece mass estimation device that estimates the mass of the workpiece, a vibration unit that instructs the motor control unit to perform sweep vibration that fluctuates the motor output and varies the vibration frequency; a calculation unit that calculates a total inertia as the inertia of the driven body for each detection time point based on the motor information detected at a plurality of detection time points during an execution period of the sweep vibration; an indexing unit that indexes, from within the execution period, a time point of an excitation frequency at which it is determined that a change in the overall inertia accompanying a change to an adjacent excitation frequency becomes minimum; an estimation unit that calculates an inertia of the workpiece by subtracting an inertia of a general driven body including the rotor, the transmission mechanism, and the workpiece loading unit from the total inertia corresponding to the determined time point, thereby estimating a mass of the workpiece; A workpiece mass estimation device comprising:

2. The workpiece mass estimation device according to claim 1 , wherein the vibration unit inputs a torque command value to the motor control unit for vibration and commands the sweep vibration by varying a vibration frequency of the torque command value.

3. The workpiece mass estimation device according to claim 1 or 2, wherein the vibration unit is configured to be able to change a variation range within which the vibration frequency is varied in the sweep vibration.

4. The indexing unit indexes the time point at which the excitation frequency is determined to be the minimum, a first frequency band in which the moving speed of the workpiece loading unit becomes slower as Coulomb friction becomes more dominant, and a dead zone occurs in the current value of the motor and the rotation speed of the rotor; a second frequency band in which resonance with the machine occurs; a third frequency band in which the moving speed of the workpiece loading unit becomes faster as the moving speed becomes outside the band of the control response in the control of the motor; Identify the time point of the excitation frequency that does not overlap with any of the above. The workpiece mass estimation device according to claim 1 or 2.