Control device for an electric motor

Abstract

Provided is a control device capable of automatically determining whether or not to activate an inertia estimation function. A control device (10) for an electric motor includes a first inertia estimation section (11) that estimates whether or not a variation in inertia of a driven body exists based on at least any one of first information related to an operation program or operation setting of a device provided with the electric motor, second information obtained from a detection device for detecting a shape of the driven body driven by the electric motor, and third information indicating an operation state of the electric motor, and a second inertia estimation section (12) that performs estimation of the inertia of the driven body in a case where the first inertia estimation section (11) estimates that a variation in the inertia of the driven body exists.

Description

TECHNICAL FIELD

[0001] The present application relates to a control device of an electric motor. BACKGROUND

[0002] In a system in which an electric motor is used to drive each driving shaft in a machine tool or the like, the inertia of a driven body including a workpiece, a worktable on which the workpiece is mounted, and the like varies depending on the workpiece that is the subject of machining. Thus, in order to accurately control each shaft in such a machine tool, it is necessary to accurately know the inertia of the driven body. There are proposed machine tools provided with a function of estimating the inertia of a driven body (for example, Patent Literature 1, Patent Literature 2, and Patent Literature 3).

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2010-148178

[0006] Patent Literature 2: Japanese Patent Application Publication No. 2014-007816

[0007] Patent Literature 3: Japanese Patent Application Publication No. 2016-181193 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] In order to perform inertia estimation, it is necessary to cause the machine tool to stably perform a specific action, and thus the execution of the inertia estimation function generally takes time. Generally, the start of such an inertia estimation function is often performed in accordance with the judgment of an operator. It is desirable to provide a control device capable of automatically judging whether or not the inertia estimation function needs to be started.

[0010] SOLUTION TO PROBLEM

[0011] One embodiment of the present disclosure is a control device of an electric motor, including: a first inertia estimation section that estimates whether or not there is a variation in inertia of a driven body driven by the electric motor, based on at least any one of first information related to a program or a setting of an operation of a device provided with the electric motor, second information obtained from a detection device that detects a shape of the driven body, and third information that indicates an operation state of the electric motor; and a second inertia estimation section that performs estimation of the inertia of the driven body, in a case where it is estimated by the first inertia estimation section that there is a variation in the inertia of the driven body.

[0012] EFFECT OF THE INVENTION

[0013] According to the above-described structure, it is possible to automatically estimate whether or not there is a variation in inertia and start the inertia estimation function.

[0014] These objects, features, and advantages of the present application will become more apparent from the following detailed description of an exemplary embodiment thereof, from the drawings attached hereto, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a block diagram showing the configuration of a system including a control device of a motor involved in one embodiment.

[0016] Figure 2 is a diagram for explaining a condition in which a jig is changed in a machine tool.

[0017] Figure 3 is a diagram for explaining a condition in which a program is changed in a machine tool.

[0018] Figure 4 is a diagram for explaining a condition in which the end of one program to the start of the next program in a machine tool.

[0019] Figure 5 is a diagram showing a condition in which a workpiece is imaged by a vision sensor in a machine tool.

[0020] Figure 6 is a diagram showing a condition in which a jig is imaged by a vision sensor in a machine tool.

[0021] Figure 7 is a diagram for explaining a difference in the number of kinds of processing due to a difference in workpieces.

[0022] Figure 8 is a diagram for explaining an action of estimating a variation in inertia of a driven body at the time of non-cutting and the like.

[0023] Figure 9 is a diagram for explaining an action of estimating a variation in inertia of a driven body when a feed shaft is acted upon at a constant acceleration.

[0024] Figure 10 is a diagram showing an example of a time progression of acceleration and torque of a feed shaft.

[0025] Figure 11A is a diagram for explaining a condition in which workpieces having different inertias are used in a machine tool.

[0026] Figure 11B is a diagram for explaining a condition in which workpieces having different inertias are used in a machine tool.

[0027] Figure 12A is a diagram showing a time waveform of a torque command in a condition of Figure 11A

[0028] Figure 12B is a diagram showing a time waveform of a torque command in a condition of Figure 11B ​a graph showing a frequency characteristic of a time waveform of the torque command of the synchronous motor.

[0029] Figure 13A is a graph showing a frequency characteristic of a time waveform of the torque command of the synchronous motor. Figure 12A

[0030] Figure 13B is a graph showing a frequency characteristic of a time waveform of the torque command of the synchronous motor. Figure 12B DETAILED DESCRIPTION

[0031] Next, an embodiment of the present disclosure will be described with reference to the drawings. In the drawings to be referred to, the same reference numerals are assigned to the same structural or functional parts. The scale of these drawings is appropriately changed for easy understanding. In addition, the mode shown in the drawings is one example for implementing the present invention, and the present invention is not limited to the mode shown in the drawings.

[0032] Figure 1 is a block diagram showing the structure of a system including the control device 10 of the synchronous motor according to one embodiment. The control device 10 of the synchronous motor according to the present embodiment (hereinafter referred to as "control device") controls an amplifier 30 based on a position command from a higher-level control device 20 such as a computer numerical control device (CNC), thereby causing a synchronous motor 41 (hereinafter referred to as motor 41) that drives a driven body 51 to operate at a prescribed command speed. The motor 41 can be, for example, a motor for driving control of a spindle or a feed shaft in a machine tool, or can be a motor that causes a joint shaft of a robot to perform rotational operation. The driven body 51 driven by the motor 41 can include a table, a robot arm, and a workpiece that can be attached to and detached from them, and can also include a moving portion of the motor 41 itself.

[0033] Hereinafter, Figure 1 The system described is explained assuming that the motor 41 constitutes a machine tool 1. The position, speed, and torque of the motor 41 are controlled by the control device 10 that performs servo control. It is also possible that the control device 10 is connected to the higher-level control device 20 for each axis.

[0034] In Figure 1 ​​In the structure, a position command generated by command calculation in the upper-level control device 20 is transmitted to the control device 10, and is received by the position control section 2. The position control section 2 transmits a speed command to the speed control section 3 on the basis of the received position command. The speed control section 3 transmits a current command to the current control section 4 on the basis of the received speed command. The current control section 4 transmits a voltage command to the current amplification circuit 31, which constitutes the amplifier 30 for driving the motor 41. The motor 41 operates at a prescribed command speed using electric power input from the current amplification circuit 31, thereby driving the driven body 51.

[0035] A sensor 42 for detecting the speed and position of the motor 41 is provided in the motor 41. Data relating to the speed and position detected by the sensor 42 is fed back to the position control section 2, the speed control section 3, and the first inertia estimation section 11 and the second inertia estimation section 12 described later, respectively, in the control device 10.

[0036] The first inertia estimation section 11 estimates whether or not the inertia of the driven body is subject to variation on the basis of at least one of first information relating to a program of operation (a machining program) or a setting of operation of the machine tool 1, second information obtainable from a detection device (an external sensor 52) for detecting the shape of the driven body driven by the motor 41, and third information indicating the state of operation of the motor 41. The second inertia estimation section 12 performs estimation of the inertia of the driven body in a case where it is estimated by the first inertia estimation section 11 that the inertia of the driven body is subject to variation.

[0037] The estimation of inertia performed by the second inertia estimation section 12 will be described. The second inertia estimation section 12, when receiving a signal (a start instruction) indicating that the inertia of the driven body is subject to variation from the first inertia estimation section 11, applies a speed-up / down command for performing a specific operation to the motor 41, and estimates the inertia of the driven body 51 on the basis of a speed value fed back from the motor 41 and a current value fed back from the amplifier 30. The inertia J [kgm 2 ] of the driven body 51 can be calculated by the following equation using the current value I [A], the acceleration value a [rad / s 2 ], the speed value ω [rad / s], and the torque constant Kt of the synchronous motor.

[0038] J = Kt x I / a = Kt x I / (dω / dt)...(1)

[0039] The method of calculating the acceleration a = dω / dt in formula (1) will be described. Let the speed value ω(t) at a certain time t be fed back from the sensor 42 at a sampling period T. The acceleration a at this time can be calculated as a = (ω(t) - ω(t-T)) / T using the difference between the speed value ω(t) fed back at a certain time t and the speed value ω(t-T) fed back at a time (t-T) one sampling period before the time t.

[0040] In order to accurately estimate the inertia using the feedback signal as described above, it is necessary to perform the estimation after the torque generated by the acceleration / deceleration command has stabilized, and therefore the estimation of the inertia takes a certain amount of time. The inertia estimated by the second inertia estimation section 12 is used in the determination of the time constant of the acceleration / deceleration command and the calculation of the speed control gain that determines the responsiveness of the speed control.

[0041] Next, a specific example of the action of the first inertia estimation section 11 estimating whether the inertia of the driven body has changed will be described. The specific example of the action includes the following.

[0042] (1) When the jig is changed (estimation based on the second information)

[0043] (2) When the program is changed (estimation based on the first information)

[0044] (3) Time interval of the program (estimation based on the first information)

[0045] (4) Two-dimensional image obtained by the vision sensor (estimation based on the second information)

[0046] (5) Three-dimensional coordinates obtained by the vision sensor (estimation based on the second information)

[0047] (6) Number of processing types (estimation based on the first information)

[0048] (7) Measurement at the time of non-cutting or the like (estimation based on the third information)

[0049] (8) Measurement at the time of constant acceleration (estimation based on the third information)

[0050] (9) Estimation from the torque waveform (estimation based on the third information)

[0051] In addition, in the above examples of action, the examples of action (1) to (6) are mainly processing performed before the program or process is started, and the examples of action (7) to (9) are processing that can be performed during the running of the processing program. In addition, in the case of the examples of action (4), (5) using the vision sensor, it is also possible to perform during the running of the processing program.

[0052] (1) When the jig is changed

[0053] In a case where the jig for fixing the workpiece is changed, it can be considered that the shape of the workpiece also becomes a different shape. Accordingly, the first inertia estimation section 11 detects whether the jig for fixing the workpiece is changed. Also, in a case where the jig is changed, the first inertia estimation section 11 estimates that the inertia of the driven body is varied in accordance with the case where the shape of the workpiece is changed. Figure 2 The jig on the machine tool 1, the workpiece fixed to the jig, and the spindle support section 101 are illustrated. In the case of the present action example, the jig is provided in advance with an identification information holding body (bar code, IC tag, ID chip, etc.) for holding identification information inherent to the jig. In the case of the present action example, the identification information holding body 91 is provided in advance in the jig 71. The identification information holding body 91 is provided in advance in the jig 71. Figure 2 The left side of FIG. 7 shows a state where the jig 71 is used as the jig for fixing the workpiece Wl in the machine tool 1 and machining is performed by the tool installed in the spindle support section 101. In the case of the present action example, the workpiece Wl is a workpiece having a certain shape. Figure 2 The right side of FIG. 7 shows a state where the jig 72 different from the jig 71 is used in order to fix a workpiece W2 different in shape from the workpiece Wl on the machine tool 1.

[0054] The jig 71 is provided with an identification information holding body 91 for holding identification information of the jig 71. The jig 72 is provided with an identification information holding body 92 for holding identification information of the jig 72. In this case, the external sensor 52 is a reading device for reading the identification information held by the identification information holding bodies 91, 92. As an example, in a case where the identification information holding bodies 91, 92 are bar codes, the external sensor 52 is a bar code reader. The bar code reader is installed, for example, in a position of the spindle support section 101 of the machine tool 1 where the identification information holding bodies 91, 92 can be read.

[0055] The first inertia estimation section 11 causes the external sensor 52 to read the identification information held by the identification information holding body 91 (or 92) at a prescribed timing before starting execution of the machining program, for example. Then, in a case where the identification information of the jig 72 read this time is different from the identification information of the jig 71 read last time, the first inertia estimation section 11 estimates that the inertia is varied in accordance with the case where the shape of the workpiece is varied and causes the second inertia estimation section 12 to perform estimation of the inertia.

[0056] The present action example is a method of indirectly detecting the case where the shape of the workpiece is changed by detecting the shape of the jig. Therefore, an advantage can be obtained in a state where the workpiece cannot be directly observed from the position of the external sensor 52.

[0057] (2) When the program is changed

[0058] When the machining program is changed to a different program, a case where the shape of the workpiece that becomes the machining target is changed can be considered. Accordingly, when the machining program is changed, the first inertia estimation unit 11 estimates that there is a change in the inertia of the driven body in accordance with the case where the shape of the workpiece is changed. In Figure 3 The left side shows a case where the workpiece Wl 1 is the target of machining in the machine tool 1 based on the program A. In Figure 3 The right side shows a case where the workpiece Wl 2 that is different in shape from the workpiece Wl 1 is the target of machining in the machine tool 1 based on the program B. Further, in Figure 3 In the program A-based machining and the program B-based machining, the same jig is used and the tool is also the same.

[0059] In this case, the first inertia estimation unit 11 acquires information (program name, etc.) for identifying the machining program from the upper-level control device 20. Further, the first inertia estimation unit 11 estimates that there is a change in the inertia in accordance with the case where the shape of the workpiece is changed in a case where the identification information of the acquired program is different from the identification information of the program implemented last time. Then, the first inertia estimation unit 11 causes the second inertia estimation unit 12 to perform estimation of the inertia.

[0060] The program can be judged to be changed using the following method in addition to the example where the judgment is made based on the program name.

[0061] (a1) It is assumed that the origin position of the workpiece that has been determined in the program is measured at the start of the program. In a case where the difference between the origin position measured at the start of the present program and the origin position measured in the previous program exceeds a threshold value, it is judged that the program is changed.

[0062] (a2) In a case where a coordinate system (G54 to G59) of G code that is a workpiece coordinate system is used that was not used in the previous program, it is judged that the program is different. For example, it is assumed that the workpiece coordinate system used in the previous program is only G54 of G code (i.e., the definition content of machining of only one face). It is assumed that the workpiece coordinate system defined in the present program is G54, G55, and G56 of G code (i.e., the definition content of machining of three faces). In this case, the first inertia estimation unit 11 can judge that the program is different in accordance with the difference in the workpiece coordinate system used. Further, these (a1) and (a2) can also be called information related to the action setting of the machine tool 1.

[0063] (3) Time interval of the program

[0064] Generally, the same machining program is often continuously executed without a time interval. Therefore, in a case where a certain time interval is left from the end of execution of a machining program until the start of the next machining program, it is considered that a different machining condition (for example, a condition where the machining program is different) is performed, and a condition where the shape of the workpiece is changed. It is assumed Figure 4 that condition. In Figure 4 the machine tool 1, the machining of the workpiece W41 based on the program A ends at time T1, and the machining of the workpiece W42 based on the next program B starts at time T2. In a case where the interval from the end time T1 of the previous program A until the start time T2 of the present machining program B exceeds a preset set value, the first inertia estimation unit 11 judges that the shape of the workpiece is changed. The set value can be input into the control device 10 by the user via the user interface of the upper control device 20, for example. The set value depends on the kind of the machine tool, the kind of the machining, the kind of the object workpiece, and the like, and thus the user performs the set input on the basis of consideration of these.

[0065] The first inertia estimation unit 11 acquires time information from an internal clock inside the control device 10, stores the end time of the previous program A, and acquires the start time of the present program B. The first inertia estimation unit 11 compares the time interval from the end time T1 of the previous program A until the start time T2 of the present program B with the preset set value. Then, in a case where the time interval is larger than the set value, the first inertia estimation unit 11 estimates that the inertia of the driven body 51 is changed in accordance with the change in the shape of the workpiece, and causes the second inertia estimation unit 12 to perform the estimation of the inertia.

[0066] (4) Two-dimensional image obtained by the vision sensor

[0067] Next, an example of the estimation action by the first inertia estimation unit 11 in a case where the vision sensor 110 (camera) is used as the external sensor 52 will be described. As Figures 5-6 shown in FIG. 10, the vision sensor 110 is installed to the upper portion of the spindle support portion 101 in a manner that can photograph a machining region including at least a part of the driven body (for example, the workpiece or the jig).

[0068] In Figure 5 the left side, a condition where the machine tool 1 is machining the workpiece W51 is shown. In Figure 5 the right side, a condition where the machine tool 1 is machining the workpiece W52 having a different shape from the workpiece W51 is shown. In Figure 5In this case, the vision sensor 110 is mounted at a position capable of photographing the workpiece W51 (W52). The first inertial estimation unit 11 acquires an image of the area including the workpiece, for example, captured by the vision sensor 110 at the start of processing. Then, the first inertial estimation unit 11 determines whether the shape of the workpiece has changed by comparing the image of the workpiece W51 acquired during the previous processing with the image of the workpiece W52 acquired during the current processing. Alternatively, the shape of the workpiece in the image can be determined and compared by extracting, for example, a region with a hue specific to the workpiece from the acquired image. Alternatively, other image recognition techniques for extracting features from the image and determining the workpiece in the image can be used.

[0069] When it is determined that the shape of the workpiece has changed by comparing it with a two-dimensional image of the workpiece, the first inertia estimation unit 11 causes the second inertia estimation unit 12 to perform inertia estimation.

[0070] Figure 6 This diagram illustrates an example of how the shape of a fixture is detected by the vision sensor 110. Figure 6 The left side shows the machining process performed by machine tool 1 on workpiece W61 fixed to fixture 171. Figure 6 The right side shows the machining process performed by machine tool 1 on workpiece W62, which is fixed to fixture 172. Figure 6 In this case, the vision sensor 110 is positioned to capture images of at least a portion of the fixture 171 (fixture 172). The first inertial estimation unit 11 acquires an image of the fixture, including the fixture, acquired by the vision sensor 110. Then, the first inertial estimation unit 11 determines whether the shape of the fixture has changed by comparing an image of the fixture 171 acquired during the previous processing with an image of the fixture 172 acquired during the current processing. Alternatively, the shape of the fixture within the image can be determined and compared by extracting, for example, regions with a hue specific to the fixture from the acquired image. Alternatively, other image recognition techniques for extracting features from an image and determining the fixture within the image can be used.

[0071] If the shape of the fixture is determined to have changed by comparing it with a two-dimensional image of the fixture, the first inertia estimation unit 11 considers the shape of the workpiece to have changed and estimates that the inertia of the driven body has changed. Then, the first inertia estimation unit 11 causes the second inertia estimation unit 12 to perform inertia estimation. This example of operation is a method of indirectly detecting a change in the shape of the workpiece by detecting the shape of the fixture. Therefore, it has advantages in situations where the workpiece cannot be directly observed from the position of the vision sensor 110.

[0072] (5) Three-dimensional coordinates obtained by the vision sensor

[0073] Next, an example of an operation when a three-dimensional sensor (stereo camera or the like) capable of acquiring three-dimensional coordinate information of an object is used as the vision sensor 110 will be described. It is assumed that a three-dimensional sensor is used as the vision sensor 110 and three-dimensional coordinate information (three-dimensional image) of a region including the workpiece W51, the workpiece W52 is acquired in the state of Figure 5 In this case, the first inertia estimation unit 11 determines the workpieces as one object present on the table within the three-dimensional image, for example. The first inertia estimation unit 11 compares the three-dimensional shape information of the workpiece W51, the workpiece W52 each determined as such. Thereby, the first inertia estimation unit 11 can more accurately detect whether the shape (for example, volume) of the workpiece has changed. In addition, other image processing techniques for determining the workpiece based on a feature amount within the three-dimensional image can also be used.

[0074] Consider a case where a three-dimensional sensor is used as the vision sensor 110 and three-dimensional coordinate information of a region including the jig 171, the jig 172 is acquired as in Figure 6 In this case, the first inertia estimation unit 11 can also determine an object located at a prescribed distance from the vision sensor 110 as a jig, for example, by using the three-dimensional coordinate information. The first inertia estimation unit 11 compares the three-dimensional shape information of the jig 171, the jig 172 each determined as such. Thereby, the first inertia estimation unit 11 can more accurately detect whether the shape of the jig has changed. In addition, other image processing techniques for determining the jig based on a feature amount within the three-dimensional image can also be used. This example of operation is a method of indirectly detecting that the shape of the workpiece has changed by detecting the shape of the jig. Therefore, an advantage can be obtained in a situation where the workpiece cannot be directly observed from the position of the vision sensor 110.

[0075] (6) Number of processing types

[0076] Generally, a processing program of a numerical control device (CNC) has a structure in which subroutines describing specific processing are set by processing type under a main flow controlling the entire flow of processing. Thereby, the number of processing types can be grasped by extracting the number of subroutines in the processing program. The first inertia estimation unit 11 acquires the number of processing types from the processing program held by the upper-level control device 20. The first inertia estimation unit 11 compares the number of processing types extracted from the program executed last time with the number of processing types extracted from the program executed this time. In Figure 7 The left side shows a situation where the machine tool 1 executes processing on the workpiece W71 based on a certain program. In Figure 7The right side shows the machine tool 1 performing machining on a workpiece W72, which has a different shape than workpiece W71, based on a different program than the one used for W71. In this case, due to the different shapes of the workpieces, the specific machining operations will differ, and thus the number of machining types will also be different.

[0077] If the number of processing types in the previous program differs from the number of processing types in the current program, the first inertia estimation unit 11 estimates that the inertia of the driven body 51 has changed based on the change in the shape of the workpiece. In this case, the first inertia estimation unit 11 causes the second inertia estimation unit 12 to perform inertia estimation.

[0078] (7) Measurement of non-cutting time, etc.

[0079] The first inertia estimation unit 11 can also be configured to estimate whether inertia has changed in a manner that does not cause interruption of the machining program during execution. A first example of such an operation is that, during the execution of the machining program in a non-cutting state, when the axis to which inertia estimation is to be estimated has stopped or is moving at a constant speed (so-called non-cutting motion), the axis is excited and its inertia is calculated. Figure 8 The structure of machine tool 1 is shown in the figure. For example... Figure 8 As shown, the machine tool 1 has a spindle motor M11 for driving the spindle at the front end of the spindle support 101. In addition, the machine tool 1 has feed axis motors M12 and M13 for moving the worktable holding the workpiece W81 along the X-axis and Y-axis directions perpendicular to the spindle (Z-axis), respectively.

[0080] For example, let's assume the axis being estimated as the X-axis. In this case, the first inertial estimation unit 11 detects, for example, a state where the feed axis motor M12 is stopped or operating at a constant speed during non-cutting operations by utilizing feedback information from the sensor 42. Upon detecting such a state, the first inertial estimation unit 11 applies vibration to the feed axis and estimates the acceleration a [rad / s²] at that time. 2 The inertia J [kgm] can be obtained from the following equation of motion (2) using the torque T [Nm] and the torque T [Nm]. 2 Furthermore, the torque T [Nm] can be obtained by multiplying the current value fed back from the current control unit 4 by a coefficient.

[0081] Ja=T…(2)

[0082] Furthermore, since the purpose here is to determine whether inertia has changed, the inertia value can be calculated in a shorter time than when the second inertia estimation unit 12 estimates the inertia. Alternatively, if the inertia detected by the above-described excitation vibration is different from the inertia detected by such excitation vibration in the previous operation (for example, if the difference in inertia exceeds a predetermined threshold), the first inertia estimation unit 11 notifies the upper control device 20 to interrupt the machining process, so that the second inertia estimation unit 12 can perform an accurate inertia estimate.

[0083] (8) Measurement under constant acceleration

[0084] A second example of an operation will be described that estimates whether inertia has changed in a manner that does not cause interruption of the machining program during execution. In this example, when the machining program is executed in a non-cutting state, and the axis to which the inertia is to be estimated is moving with constant acceleration, the first inertia estimation unit 11 calculates the inertia related to that axis. Figure 9 The structure of machine tool 1 is shown in the figure. For example... Figure 9 As shown, in machine tool 1, the worktable 75 on which the workpiece W91 is placed is moved by a feed mechanism, which is driven by a feed axis motor M12. Figure 10 The diagram shows the time shift of acceleration (curve 131) and the time shift of torque (curve 132) as an example of drive control for the feed axis motor M12. The first inertial estimation unit 11, for example, uses information from sensor 42 to detect a constant acceleration a (e.g., in...). Figure 10 (between time t3 and t4). Then, when the acceleration a is constant, the first inertia estimation unit 11 calculates the inertia of the axis as the object using the above-mentioned equation of motion (2).

[0085] Alternatively, if the inertia calculated by the first inertia estimation unit 11 through the above-mentioned operation is different from the inertia calculated by the same operation in the previous operation (for example, if the difference in inertia exceeds a predetermined threshold), the first inertia estimation unit 11 notifies the upper control device 20 to interrupt the machining process, so that the second inertia estimation unit 12 can make an accurate inertia estimation.

[0086] (9) Estimation based on torque waveform

[0087] A third example of an action that can estimate whether inertia has changed in a form that does not incur an interruption of the machining program and the like in the process of execution of the machining program will be described. The first inertia estimation section 11 can also be configured to estimate whether the inertia of the shaft that is the object of inertia estimation has changed (whether the shape of the workpiece has changed) based on the position of the frequency peak obtained by frequency analyzing the time waveform of the torque command for the shaft. The position of the frequency peak obtained by frequency analyzing the time waveform of the torque command varies depending on the resonance frequency of the mechanical system. As shown in FIG. 17, assume a condition in which the workpieces W93 (inertia Ja), W94 (inertia Jb) having different inertias are machined by the machine tool 1. The inertia of the driven body of the feed shaft (feed shaft motor M12) in the state after the workpiece is removed is Jm, and is common. Figure 11A and Figure 11B As shown in FIG. 17, assume a condition in which the workpieces W93 (inertia Ja), W94 (inertia Jb) having different inertias are machined by the machine tool 1. The inertia of the driven body of the feed shaft (feed shaft motor M12) in the state after the workpiece is removed is Jm, and is common.

[0088] Figure 12A The time waveform 141 of the torque command of the feed shaft in the condition of Figure 11A The time waveform 142 of the torque command of the feed shaft in the condition of Figure 12B The time waveform 142 of the torque command of the feed shaft in the condition of Figure 11B The frequency characteristic 151 obtained by frequency analyzing the time waveform 141 of Figure 13A The frequency characteristic 152 obtained by frequency analyzing the time waveform 142 of Figure 12A The frequency characteristic 152 obtained by frequency analyzing the time waveform 142 of Figure 13B As shown in FIG. 17, assume a condition in which the workpieces W93 (inertia Ja), W94 (inertia Jb) having different inertias are machined by the machine tool 1. The inertia of the driven body of the feed shaft (feed shaft motor M12) in the state after the workpiece is removed is Jm, and is common. Figure 12B Figure 13A and Figure 13B As shown in FIG. 17, assume a condition in which the workpieces W93 (inertia Ja), W94 (inertia Jb) having different inertias are machined by the machine tool 1. The inertia of the driven body of the feed shaft (feed shaft motor M12) in the state after the workpiece is removed is Jm, and is common.

[0089] As described above, according to the present embodiment, it is possible to automatically estimate whether inertia has changed and start the inertia estimation function.

[0090] The above-described embodiments have been described using typical embodiments, but it will be understood by those skilled in the art that the above-described embodiments can be changed and various other changes, omissions, and additions can be made without departing from the scope of the present application.

[0091] The structure of the control device related to the above-described embodiments can be applied to control devices of robots and other various industrial machines having driven shafts driven by motors.​

[0092] Figure 1 The configuration of the control device 10 shown can be realized by a CPU possessed by the control device 10 executing various software saved in a storage device, or can also be realized by a configuration mainly of hardware such as an ASIC (Application Specific Integrated Circuit). A program that executes a control method equivalent to the above-described processing contents executed by the first inertia estimation section 11 and the second inertia estimation section 12 can be recorded in various recording media (for example, ROM, EEPROM, flash memory and the like semiconductor memory, CD-ROM, DVD-ROM and the like optical disc, magnetic recording medium) that can be read by a computer.

[0093] Explanation of Reference Numerals

[0094] 1: machine tool; 2: position control section; 3: speed control section; 4: current control section; 10: control device; 11: first inertia estimation section; 12: second inertia estimation section; 20: upper control device; 30: amplifier; 31: current amplification circuit; 41: motor; 42: sensor; 51: driven body; 52: external sensor; 101: main shaft support section; 110: vision sensor.

Claims

1. A control device of an electric motor, comprising: a first inertia estimation section that estimates whether or not inertia of a driven body driven by the electric motor is varied, based on at least any one of first information related to an operation program or an operation setting of a device including the electric motor, second information obtained from a detection device that detects a shape of the driven body, and third information that indicates an operation state of the electric motor; and a second inertia estimation section that estimates the inertia of the driven body, in a case where it is estimated by the first inertia estimation section that the inertia of the driven body is varied.

2. The control device of the electric motor according to claim 1, wherein the second information is a two-dimensional image or three-dimensional coordinate information of at least a part of the driven body obtained by a vision sensor as the detection device, the first inertia estimation section judges whether or not a shape of the driven body is varied, based on the two-dimensional image or the three-dimensional coordinate information, and estimates that the inertia of the driven body is varied, in a case where it is judged that the shape of the driven body is varied.

3. The control device of the electric motor according to claim 1, wherein the second information is identification information inherent to the driven body read by a reading device as the detection device from an identification information holding body attached to the driven body, the first inertia estimation section estimates whether or not the inertia of the driven body is varied, based on the identification information of the driven body read by the reading device.

4. The control device of the electric motor according to claim 1, wherein the first inertia estimation section estimates that the inertia of the driven body is varied, in a case where it is judged based on the first information that an operation program executed last time is different from an operation program executed this time.

5. The control device of the electric motor according to claim 1, wherein the first information is information related to a start time or an end time of the operation program, the first inertia estimation section estimates that the inertia of the driven body is varied, in a case where a time interval from the end time of the operation program executed last time to the start time of the operation program executed this time exceeds a set time set in advance.

6. The control device of the electric motor according to claim 1, wherein the first information is information that indicates a number of kinds of processes defined within the operation program, the first inertia estimation section estimates that the inertia of the driven body is varied, in a case where the number of kinds of processes defined within the operation program executed last time is different from the number of kinds of processes defined within the operation program executed this time.

7. The control device of the electric motor according to claim 1, wherein the device is a machine tool that includes a main shaft and a feed shaft as drive shafts, the third information is information that indicates an operation state of the electric motor provided to each of the drive shafts, and the second information is information that indicates a state of the driven body. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The first inertia estimation section estimates whether or not the inertia of the driven body of the subject shaft varies by, when the machine tool is in a non-cutting state and the subject shaft of the drive shaft is stopped or is operating at a constant speed, exciting the subject shaft and measuring the inertia of the subject shaft.

8. The control device of the motor according to claim 1, wherein the third information is information indicating an acceleration of the motor, the first inertia estimation section estimates whether or not the inertia of the driven body of the motor varies by, when the acceleration of the motor is constant, measuring the inertia of the driven body of the motor.

9. The control device of the motor according to claim 1, wherein the third information is information related to a waveform of a torque command for the motor over time, the first inertia estimation section estimates that the inertia of the driven body varies when there is a variation in the position of a frequency peak obtained by frequency analyzing the waveform.

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