Inertia estimation method and inertia estimation device

Abstract

To eliminate an estimation error caused by variation in a torque constant and inertia in a driving system in work-piece inertia estimation of a position control device of a machine tool or the like.SOLUTION: An inertia estimation method comprises estimating inertia in a driving system including a work-piece as total inertia in motor shaft conversion Jn≒Je, based on torque and acceleration of the driving system when accelerating and decelerating the driving system in a state where the work-piece is attached to the driving system; estimating inertia in the driving system excluding the work-piece as actual reference inertia Jb', based on the torque and the acceleration of the driving system when accelerating and decelerating the driving system in a state where the work-piece is removed from the driving system; and estimating inertia Jw' of the work-piece based on at least the total inertia in motor shaft conversion Je and the actual reference inertia Jb'.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses an inertia estimation method and an inertia estimation device for machine tools and the like. [Background technology]

[0002] When the feed axis of a machine tool or the like is driven by a servo motor, a position / speed control system is configured to control the position and speed of the motor and the load attached to the motor according to commands from a numerical control device. In order to accurately control the position and speed of the motor and the load, it is necessary to determine the control parameters based on the inertia of the motor and the load. Since the inertia of the load varies depending on the workpiece, various inertia estimation methods have been proposed.

[0003] As an example of a method for estimating inertia, a technology is disclosed in Patent Document 1 and elsewhere in which, when the drive shaft is accelerated or decelerated, the section in which acceleration or deceleration occurs is set as an integration section, and the load inertia converted into the motor shaft is estimated from the integrated value of the motor acceleration detection value and the integrated value of the motor torque in the integration section.

[0004] FIG. 6 is a block diagram of a conventional inertia estimation device. A subtractor 7 calculates the deviation between a position command value Pc generated by a position command generator 1 and a position detection value Pd of the motor 4 or load 6 detected by a position detector 5. When the deviation calculated by the subtractor 7 is input to a feedback controller 2, the feedback controller 2 outputs a torque command Tc. A current controller 3 drives the motor 4, to which the load 6 is attached, in accordance with the torque command Tc. An inertia calculator 11 calculates an accelerating or decelerating section from the second-order differential value of the position command value Pc. The inertia calculator 11 also calculates inertia from the second-order differential value of the position detection value Pd and the torque command Tc. The output of the inertia calculator 11 is the work inertia Jw, which will be described later.

[0005] Furthermore, as a method for changing control parameters according to inertia, Patent Document 2 discloses a technology in which reference control parameters for each of a plurality of workpiece inertia values ​​are stored in advance, and control parameters suited to the control characteristics of the machine are calculated from the stored reference control parameters according to the inertia value of the workpiece actually being handled, and the calculated control parameters are changed.

[0006] An example of a method for changing servo parameters using the techniques of Patent Document 1 and Patent Document 2 will be described below. Fig. 5 shows an operation chart for inertia estimation and servo parameter setting. First, the inertia of the drive system is estimated using the technique described in Patent Document 1 etc. Next, the work inertia is calculated from the estimated inertia. Then, the servo parameters are set according to the calculated work inertia. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6009397 [Patent Document 2] Patent No. 6290619 Summary of the Invention [Problem to be solved by the invention]

[0008] In Patent Document 1, inertia is estimated by canceling out friction and gravity components. However, Patent Document 1 does not take into consideration estimation errors due to variations in the torque constant of the motor or the inertia of the reducer. Therefore, if the workpiece inertia is estimated using the technology in Patent Document 1 and the servo parameter changing technology described in Patent Document 2 is used, there are cases where an appropriate parameter cannot be selected due to an inertia estimation error.

[0009] This problem will be explained using mathematical formulas. First, the torque τ of a moving object, the inertia J of the object, and the angular acceleration α of the object are expressed by the following formula (1).

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[0010] Inertia estimation uses the above relational expression, and the section in which the object is accelerating or decelerating when it is accelerated or decelerated is set as the integration section. The estimated value Je of the total inertia converted into the motor shaft is calculated from the integrated value of the motor torque and the integrated value of the motor acceleration detection value in the integration section.

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[0011] In equation (2), Kt is the torque constant and i is the current command value. Furthermore, of the total inertia of the drive system converted into the motor shaft, if the motor side inertia (including rotor inertia) is Ja, the load side inertia (excluding work inertia) is Js, the total gear ratio of the drive system is R, and the work inertia is Jw, then the total inertia Jn of the drive system converted into the motor shaft when a workpiece is loaded is expressed by equation (3). In this specification, the ratio of the output side speed n to the input side speed m is expressed as the gear ratio R (=n / m).

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[0012] Therefore, the workpiece inertia estimated value Jw' is estimated by removing the motor-side inertia Ja and the load-side inertia Js from the estimated motor-shaft converted total inertia Je (≈Jn).

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[0013] In the following explanation, (Ja+R 2 ·Js) is called the reference inertia Jb.

[0014] In inertia estimation, the torque constant uses the nominal value from the motor specifications, so it is clear from equation (2) that variations in the motor torque constant are superimposed on the estimated inertia value as a multiplicative error. Also, because the motor-side inertia Ja and load-side inertia Js use the machine design values, it is clear from equation (4) that variations in the inertia of the reducer, ball screw, etc. are superimposed as an additive error. [Means for solving the problem]

[0015] The inertia estimation method disclosed in this specification is characterized in that, with a workpiece attached to the drive system, the drive system is accelerated and decelerated, and the inertia of the drive system including the workpiece is estimated as a motor shaft converted total inertia based on the torque and acceleration of the drive system at that time; with the workpiece detached from the drive system, the drive system is accelerated and decelerated, and the inertia of the drive system not including the workpiece is estimated as an actual reference inertia based on the torque and acceleration of the drive system at that time; and the inertia of the workpiece is estimated based on at least the motor shaft converted total inertia and the actual reference inertia.

[0016] The inertia estimation device disclosed in this specification includes an inertia calculation unit that calculates the inertia of the drive system based on the torque and acceleration of the drive system when the drive system is accelerated or decelerated, and an inertia storage unit that temporarily stores the inertia calculated by the inertia calculation unit, wherein the inertia calculation unit is configured to estimate the inertia of the drive system with a workpiece attached and store the estimated inertia in the inertia storage unit as a motor shaft converted total inertia, estimate the inertia of the drive system with the workpiece removed and store the estimated inertia in the inertia storage unit as an actual reference inertia, and estimate the inertia of the workpiece based on at least the motor shaft converted total inertia and the actual reference inertia. [Effects of the Invention]

[0017] According to the technology disclosed in this specification, an accurate inertia can be estimated by removing the estimation error from the estimated total inertia converted into the motor shaft. [Brief explanation of the drawings]

[0018] [Figure 1] 4 is a chart showing a procedure for inertia estimation and servo parameter setting in the first embodiment. [Figure 2] 10 is a chart showing a procedure for inertia estimation and servo parameter setting in the second embodiment. [Figure 3] 10 is a chart showing a procedure for inertia estimation and servo parameter setting in the third embodiment. [Figure 4] FIG. 2 is a block diagram of an inertia estimation device. [Figure 5] 10 is a chart showing a conventional procedure for inertia estimation and servo parameter setting. [Figure 6] FIG. 1 is a block diagram of a conventional inertia estimation device. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment will be described below. In the embodiment shown below, a method is used in which the section of acceleration or deceleration during acceleration / deceleration operation based on equations (1) and (2) is defined as an integration section, and inertia is estimated from the integrated value of motor torque and the integrated value of motor acceleration detection value in the integration section. In the following description, the axial movement accompanying this inertia estimation and the inertia estimation based on this axial movement are referred to as "inertia estimation operation."

[0020] [Example 1] In the first embodiment, an inertia estimation method for removing additive errors will be described. In this embodiment, it is assumed that there is variation in the inertia of the reducer, ball screw, etc. in the drive system. If the error from the true value of the motor-side inertia is ΔJa and the error from the true value of the load-side inertia is ΔJs, the total inertia Jn converted into the motor shaft of the drive system when a workpiece is loaded is expressed by equation (5).

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[0021] Therefore, the estimated workpiece inertia value Jw' is calculated by removing the reference inertia Jb from the estimated motor shaft converted total inertia value Je (≒ Jn). When equation (5) is substituted into equation (4) assuming Je = Jn, it is clear from equation (6) that an error occurs in the estimated workpiece inertia value Jw' with respect to the workpiece inertia Jw.

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[0022] The problem with the conventional method is that the reference inertia Jb is used as a fixed value. Therefore, by providing a means for updating the reference inertia Jb, estimation errors are eliminated.

[0023] FIG. 1 shows an operation chart for inertia estimation and servo parameter setting in the first embodiment. The difference from FIG. 4 is that in addition to the operation chart for normal inertia estimation, there is also an operation chart for reference setting. In the chart for reference setting, first, jigs and workpieces attached to the drive system are removed to create a state in which an inertia equivalent to the reference inertia Jb (hereinafter referred to as "actual reference inertia Jb'") can be estimated. Next, inertia is estimated in the same way as in normal operation. Then, as shown in equation (7), the estimated inertia value Je' is set as the actual reference inertia Jb'.

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[0024] After this reference setting is implemented, the reference inertia is replaced with Jb' in the inertia estimation during normal operation, so that the error can be removed from the estimated work inertia Jw'.

[0025] Explaining this using a formula, the inertia value Je' estimated when the reference is set, that is, the actual reference inertia Jb', is expressed by formula (8).

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[0026] Equation (9) shows that by replacing the reference inertia Jb in equation (4) with the actual reference inertia Jb' in equation (8), the additive error component can be removed from the estimated work inertia Jw'.

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[0027] In the second embodiment, an inertia estimation method that removes multiplicative errors will be described. In this embodiment, it is assumed that there is variation in the torque constant of the motor. When the variation in the torque constant is ΔK, the estimated value Je of the total inertia converted into the motor shaft is expressed by equation (10).

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[0028] When equation (10) is substituted into equation (4) assuming Je=Jn, it is clear from equation (11) that an error occurs in the work inertia estimated value Jw' with respect to the work inertia Jw.

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[0029] The multiplicative error cannot be removed by the method shown in the first embodiment. Therefore, the estimation error is removed by replacing the reference inertia Jb with the actual reference inertia Jb' and expressing the work inertia as a relative value to the actual reference inertia Jb'.

[0030] FIG. 2 shows an operation chart of inertia estimation and servo parameters in the second embodiment. The difference from FIG. 1 is that the work inertia relative value Jw' / Jb' is calculated and the servo parameters are set according to the work inertia relative value Jw' / Jb'. In the chart for setting the reference, first, the jig and work attached to the drive system are removed to create a state in which an inertia equivalent to the reference inertia Jb (i.e., actual reference inertia Jb') can be estimated. Next, inertia is estimated in the same way as in normal operation. Then, as in the first embodiment, the estimated inertia Je' is set as the actual reference inertia Jb'.

[0031] After this reference setting is performed, the reference inertia Jb is replaced with the actual reference inertia Jb', so that the error can be removed from the estimated workpiece inertia Jw'.

[0032] Explaining this using a formula, the inertia value Je' estimated at the time of setting the reference, i.e., the updated reference inertia Jb', is expressed by formula (7) as in Example 1. Therefore, the estimated value Jw' / Jb' of the work inertia relative value is expressed by formula (12) using formulas (7) and (10).

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[0033] On the other hand, when there is no multiplicative error, the estimated value Jw / Jb of the work inertia relative value is expressed by equation (13).

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[0034] It is clear from equations (12) and (13) that the estimated values ​​of the work inertia relative value match. Therefore, it is shown that the multiplicative error component can be removed by setting the servo parameters from the work inertia relative value. [Example 3]

[0035] In the third embodiment, an inertia estimation method that removes additive and multiplicative errors will be described. When the error from the true value of the motor-side inertia is ΔJa, the error from the true value of the load-side inertia is ΔJs, and the variation in the torque constant is ΔK, the estimated value Je of the total inertia converted into the motor shaft is expressed by equation (14) using equations (5) and (10).

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[0036] When additive and multiplicative errors are superimposed, the errors cannot be removed by the methods shown in Examples 1 and 2. Therefore, the estimated errors can be removed by providing a means for updating the reference inertia using a calibration workpiece whose inertia value is known.

[0037] FIG. 3 shows an operation chart of inertia estimation and servo parameters in the third embodiment. The difference from FIG. 1 is that a calibration workpiece is loaded to estimate the load inertia, and the estimated inertia is set as the second actual reference inertia Jb". In the chart for setting the reference, first, the jigs and workpiece attached to the drive system are removed to create a state in which an inertia equivalent to the actual reference inertia Jb' is estimated. Next, inertia is estimated in the same way as in normal operation. Then, as in the first and second embodiments, the estimated inertia value Je' is set as the actual reference inertia Jb'. Furthermore, a calibration workpiece whose inertia value is known is loaded, and inertia is estimated. Finally, the inertia value Je" estimated when the calibration workpiece is loaded is set as the second actual reference inertia Jb", as shown in equation (15).

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[0038] After this reference setting is implemented, the reference inertias Jb' and Jb'' are substituted during normal operation, so that the error can be removed from the estimated work inertia Jw'.

[0039] To explain using equations, the inertia values ​​Je', Je'' estimated at the time of setting the reference, i.e., the updated reference inertias Jb', Jb'' are expressed by equations (16) and (17), respectively, where Jwb is the workpiece inertia for calibration.

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[0040] From equations (16) and (17), the torque constant error ΔK of the motor can be calculated as in equation (18).

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[0041] From equations (14) and (16), the work inertia Jw is expressed as in equation (19).

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[0042] From equations (18) and (19), the estimated work inertia value Jw' is expressed as in equation (20).

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[0043] In equation (20), the multiplicative error component is removed using the coefficients shown in equation (21).

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[0044] In addition, in equation (20), the elimination of the additive error component is performed by the calculation shown in equation (22).

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[0045] Therefore, it is shown that the additive error component and the multiplicative error component can be removed from the work inertia estimated value Jw' shown in equation (20).

[0046] Figure 4 shows a block diagram of the inertia estimation device of Examples 1 to 3. The same elements as those in the conventional example are given the same reference numerals, and their explanations will be omitted. The differences from the conventional example are that inertia estimator 13 has inertia storage unit 12 in addition to inertia calculation unit 11, and that a reference setting flag is input to inertia calculation unit 11.

[0047] When the reference setting flag is ON, the inertia Je estimated by the inertia calculation unit 11 is notified to the inertia storage unit 12. When the reference setting flag is OFF, the inertia calculation unit 11 estimates the work inertia Jw using the actual reference inertia Jb notified from the inertia storage unit 12.

[0048] The inertia storage unit 12 stores the inertia Je notified from the inertia calculation unit 11 as an actual reference inertia Jb, and notifies the inertia calculation unit 11 of the actual reference inertia Jb.

[0049] According to the inertia estimation device of FIG. 4, it is possible to incorporate the inertia estimation methods shown in the first to third embodiments.

[0050] Although preferred embodiments of the present invention have been described above, those skilled in the art can make various modifications, omissions, and additions to the above-described embodiments without departing from the scope of the present invention. For example, the torque command value used in inertia calculation can be replaced with a current command value converted from the torque command value. Furthermore, as an axis operation for inertia estimation, instead of accelerating and decelerating the drive shaft, a method of estimating inertia by applying a sinusoidal torque command can be used.

[0051] The configuration of the control device according to the above-described embodiment can be applied to control devices for robots and various other industrial machines having a drive shaft driven by an electric motor.

[0052] The configuration of the inertia estimation device shown in Fig. 4 may be realized by a processor (e.g., a CPU) included in the inertia estimation device executing various software stored in a storage device, or may be realized by a configuration mainly using hardware such as an FPGA (Field Programmable Gate Array). A program for executing a control method corresponding to the above-described processing executed by the inertia calculation unit 11 and the inertia storage unit 12 can be recorded on various computer-readable recording media (e.g., semiconductor memory such as a ROM or flash memory, magnetic recording media, or optical disks such as a CD-ROM or DVD-ROM). [Explanation of symbols]

[0053] 1 Position command generation unit, 2 FB controller, 3 Current controller, 4 Motor, 5 Position detector, 6 Load, 7 Subtractor, 11 Inertia calculation unit, 12 Inertia storage unit, 13 Inertia estimator.

Claims

1. 1. An inertia estimation method, comprising: With a workpiece attached to a drive system, the drive system is accelerated and decelerated, and the inertia of the drive system including the workpiece is estimated as a motor shaft converted total inertia based on the torque and acceleration of the drive system at that time; accelerating and decelerating the drive system with the workpiece removed from the drive system, and estimating the inertia of the drive system excluding the workpiece as an actual reference inertia based on the torque and acceleration of the drive system at that time; estimating the inertia of the workpiece based on at least the motor shaft converted total inertia and the actual reference inertia; 1. An inertia estimation method comprising:

2. 2. The inertia estimation method according to claim 1, When the actual reference inertia is Jb', the total inertia converted into the motor shaft is Je, and the total gear ratio of the drive system is R, the estimated inertia value Jw' of the workpiece is expressed as Jw'=(Je-Jb') / R ２ The inertia estimation method is characterized by calculating the inertia as follows.

3. 3. The inertia estimation method according to claim 1 or 2, further comprising: Calculating a ratio of the inertia of the workpiece to the actual reference inertia as a workpiece inertia relative value; determining a servo parameter for controlling the drive system based on the work inertia relative value; 1. An inertia estimation method comprising:

4. 4. The inertia estimation method according to claim 3, The workpiece inertia relative value is expressed as (Je-Jb') / (R ２ ・Jb′)

5. 2. The inertia estimation method according to claim 1, further comprising: a calibration workpiece having a known inertia attached to the drive system, accelerating and decelerating the drive system, and estimating the inertia of the drive system including the calibration workpiece as a second actual reference inertia based on the torque and acceleration of the drive system at that time; an inertia of the workpiece is estimated based on the motor shaft converted total inertia, the actual reference inertia, and the second actual reference inertia; 1. An inertia estimation method comprising:

6. 6. The inertia estimation method according to claim 5, an inertia estimation method, characterized in that, when the actual reference inertia is Jb', the motor shaft converted total inertia is Je, the total gear ratio of the drive system is R, the second actual reference inertia is Jb", and the inertia of the calibration workpiece is Jwb, an estimated inertia value Jw' of the workpiece is calculated as Jw' = ​​Jwb (Je - Jb') / (Jb" - Jb').

7. An inertia estimation device for estimating inertia, an inertia calculation unit that calculates the inertia of the drive system based on the torque and acceleration of the drive system when the drive system is accelerated or decelerated; an inertia storage unit that temporarily stores the inertia calculated by the inertia calculation unit; The inertia calculation unit comprises: an inertia of the drive system with a workpiece attached is estimated, and the estimated inertia is stored in the inertia storage unit as a motor shaft converted total inertia; an inertia of the drive system in a state where the workpiece is removed is estimated, and the estimated inertia is stored in the inertia storage unit as an actual reference inertia; estimating the inertia of the workpiece based on at least the motor shaft converted total inertia and the actual reference inertia; The inertia estimation device is configured as follows.

8. 8. The inertia estimation device according to claim 7, When the actual reference inertia is Jb', the motor shaft converted total inertia is Je, and the total gear ratio of the drive system is R, the inertia calculation unit calculates the estimated inertia value Jw' of the workpiece as follows: Jw'=(Je-Jb') / R ２ The inertia estimation device is characterized in that it calculates the inertia as follows.

9. 9. The inertia estimation device according to claim 7 or 8, The inertia calculation unit further An inertia estimation device, characterized in that a ratio of the inertia of the workpiece to the actual reference inertia is calculated as a workpiece inertia relative value.

10. 10. The inertia estimation device according to claim 9, The inertia calculation unit calculates the workpiece inertia relative value as (Je-Jb') / (R ２ ・Jb′)

11. 8. The inertia estimation device according to claim 7, the inertia calculation unit further estimates the inertia of the drive system in a state where a calibration workpiece having a known inertia is attached, and stores the estimated inertia in the inertia storage unit as a second actual reference inertia; the inertia calculation unit estimates the inertia of the workpiece based on the motor shaft converted total inertia, the actual reference inertia, and the second actual reference inertia. An inertia estimation device characterized by:

12. The inertia estimation device according to claim 11, an inertia estimation device characterized in that, when the actual reference inertia is Jb', the motor shaft converted total inertia is Je, the total gear ratio of the drive system is R, the second actual reference inertia is Jb", and the inertia of the calibration workpiece is Jwb, the inertia calculation unit calculates the inertia estimated value Jw' of the workpiece as Jw' = ​​Jwb (Je - Jb') / (Jb" - Jb').

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