Servo motor control with self-measuring function and self-monitoring function of mechanical stiffness

Abstract

Servo motor control (101; 102), which controls a servo motor (20) for driving a machine tool, comprising: a speed command generation unit (1) configured to generate a speed command value of the servo motor (20); a speed detection unit (2) configured to detect the speed of the servo motor (20); a torque command generation unit (3) configured to generate a torque command value of the servo motor (20) based on the velocity command value and the detected velocity; a sinusoidal wave generation unit (4) configured to generate a sinusoidal disturbance wave; a frequency response calculation unit (5) configured to add the sinusoidal disturbance value generated by the sine wave generation unit (4) to the velocity command value, thereby generating a frequency response based on an output from a velocity control loop (10). 1 is calculated when the sinusoidal disturbance value has been entered into the speed control loop (10), which includes the torque command generation unit (3) and the speed detection unit (2); a resonant frequency detection unit (6) configured to detect a resonant frequency, which is a frequency at which an amplification of the calculated frequency response 1 maximized; a resonant frequency storage unit (7) configured to store the resonant frequency detected by the resonant frequency acquisition unit (6); at least one filter (8) configured to attenuate a specific frequency band component contained in the torque command value; and a resonance frequency comparison unit (9) which is configured to measure the stiffness of a machine tool on the basis of the resonance frequency stored in the resonance frequency storage unit (7) and to adjust the filter (8) with respect to the resonance frequency.

Description

AREA OF INVENTION

[0001] The present invention relates to a servo motor control system. In particular, the present invention relates to a servo motor control system with a self-measuring and self-monitoring function for mechanical stiffness. BACKGROUND OF THE INVENTION

[0002] A technology that applies a band elimination filter to a torque command value to stabilize a servo control system of a machine tool has been widely used. In a general filter tuning procedure, a sine wave or square wave sweep is performed on a speed control loop comprising a torque command generation unit and a speed sensing unit, allowing the frequency response of the speed control loop to be measured. Next, a graph, visualized as a Bode plot, is examined in detail so that a resonant frequency can be identified. Even if the Bode plot is not visualized, a technology for automatically tuning the band elimination filter has been developed, since the resonant frequency can be specified.

[0003] Since the characteristics of automatic adjustment do not depend on the adjustment strategy or the skills of a technician performing manual adjustment, the result is obtained with relatively low variability. The automatic filter adjustment function measures the stiffness of a machine tool with a variance lower than that achieved with manual measurement.

[0004] One method for adjusting a band-elimination filter involves detecting a frequency with a vibration level exceeding a threshold to suppress mechanical resonance, thereby automatically adjusting multiple band-elimination filters (for example, JP 2012 - 23 834 A). In this prior art, if two band-elimination filters have adjacent center frequencies, the filter bandwidth of the first filter is widened.

[0005] The preceding state of the art discloses an automatic adjustment algorithm for several band elimination filters. However, the subject matter of the state of the art is merely the execution of a simple adjustment to resolve a resonance. In effect, the state of the art replaces the adjustment of a servo control system directly before the delivery of a machine. The state of the art does not disclose how to deal with long-term changes and individual differences in the stiffness of a machine tool as a long-term installation or an industrial mass-produced product.

[0006] US 2007 / 0205740A1 describes a method for automatically adjusting a vibration suppression filter. JP 2004318492A describes a control method for suppressing a resonant frequency of a machine that is to be excited to vibrate, and for determining the machine's properties. BRIEF SUMMARY OF THE INVENTION

[0007] Therefore, it is an object of the present invention to provide a servo motor control system that can offer comprehensive inspection technology, enabling predictive maintenance inspections of a machine without destruction or disassembly, as well as simple stabilization of a servo control system. This object is achieved by a servo motor control system according to claim 1.

[0008] A servo motor controller according to an embodiment of the present invention is a controller which controls a servo motor for driving a machine tool and comprises: a speed command generation unit for generating a speed command value of the servo motor; a speed sensing unit for sensing a speed of the servo motor; a torque command generation unit for generating a torque command value of the servo motor based on the speed command value and the sensed speed; a sine wave generation unit for generating a sinusoidal disturbance value;a frequency response calculation unit for adding the sinusoidal disturbance generated by the sine wave generation unit to the speed command value, thereby calculating a frequency response based on an output from a speed control loop when the sinusoidal disturbance has been input into the speed control loop, which includes the torque command generation unit and the speed sensing unit; a resonant frequency sensing unit for sensing a resonant frequency, which is a frequency at which the gain of the calculated frequency response is maximized; a resonant frequency storage unit for storing the resonant frequency sensed by the resonant frequency sensing unit; at least one filter for attenuating a specific band component contained in the torque command value;and a resonance frequency comparison unit for measuring the stiffness of a machine tool based on the resonance frequency stored in the resonance frequency storage unit, and adjusting the filter with respect to the resonance frequency. DESCRIPTION OF THE DRAWINGS

[0009] These and other features and advantages of the present invention are better understood by reading the following detailed description in conjunction with the drawings, wherein: Fig. 1 a configuration diagram of a servo motor control according to the first embodiment of the present invention; Fig. 2 a diagram which illustrates a model obtained by simplifying a machine; Fig. 3 a flowchart to explain an operating procedure of a servo motor control according to the first embodiment of the present invention; Fig. 4 is a diagram illustrating an example where stiffness values ​​of several machines are compared with a manufacturing reference value; Fig. 5 is a flowchart for explaining an operating procedure of a servo motor control according to the second embodiment of the present invention; Fig. 6 is a diagram that illustrates an example of a time-dependent change in the stiffness of a machine; Fig. 7 is a flowchart to explain an operating procedure of a servo motor control according to the third embodiment of the present invention; Fig. 8 a flowchart to explain an operating procedure of a servo motor control according to the fourth embodiment of the present invention and Fig. 9 is a configuration diagram of a servo motor control according to the first embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED VERSION

[0010] A servomotor control system according to the present invention is described below with reference to the drawings. It should be noted that the technical scope of the present invention is not limited to the following embodiments and extends to the invention as defined in the appended claims and equivalents thereof. [First embodiment]

[0011] With reference to the drawings, a servo motor control according to the first embodiment of the present invention is described. Fig. Figure 1 is a configuration diagram of a servo motor controller according to the first embodiment of the present invention. A servo motor controller 101 according to the first embodiment of the present invention comprises a velocity command generation unit 1, a velocity detection unit 2, a torque command generation unit 3, a sine wave generation unit 4, a frequency response calculation unit 5, a resonant frequency detection unit 6, a resonant frequency storage unit 7, a filter 8, and a resonant frequency comparison unit 9.

[0012] The speed command generation unit 1 generates a speed command value to drive a servo motor 20. The speed command value generated by the speed command generation unit 1 is output to an adder 13. In the adder 13, the speed command value is added to a sinusoidal disturbance value generated by the sine wave generation unit 4, and the resulting value is output to a subtractor 14.

[0013] The speed detection unit 2 detects the speed of the servo motor 20. The speed of the servo motor 20 can be detected, for example, by an encoder provided in the servo motor 20; however, the present invention is not limited to this. In the subtractor 14, a value of the speed of the servo motor 20, detected by the speed detection unit 2, is subtracted from the speed command value to which the sinusoidal disturbance value has been added, and a resulting value is output to the torque command generation unit 3.

[0014] The torque command generation unit 3 generates a torque command value for the servo motor based on the velocity command value and the detected velocity. As described above, the sinusoidal disturbance value generated by the sine wave generation unit 4 has been added to the velocity command value. The torque command value generated by the torque command generation unit 3 is output to the filter 8 and the frequency response calculation unit 5.

[0015] The frequency response calculation unit 5 adds the sinusoidal disturbance value generated by the sine wave generation unit 4 to the speed command value, thereby calculating a frequency response based on an output from a speed control loop 10 when the sinusoidal disturbance value has been input into the speed control loop 10, which comprises the torque command generation unit 3 and the speed sensing unit 2. The frequency response calculated by the frequency response calculation unit 5 is output to the resonant frequency sensing unit 6.

[0016] The resonance frequency detection unit 6 detects a resonance frequency, which is a frequency at which the amplification of the calculated frequency response is maximized, and outputs the resonance frequency to the resonance frequency storage unit 7.

[0017] The resonance frequency storage unit 7 stores the resonance frequency detected by the resonance frequency acquisition unit 6. If the resonance frequency measurement has been performed several times, the resonance frequency storage unit 7 stores the resonance frequency from each measurement and maintains a history of the resonance frequencies. Furthermore, the resonance frequency storage unit 7 can also store a reference resonance frequency, which serves as a reference for comparison with the detected resonance frequency. In addition, if the resonance frequency is measured at a predetermined time, the resonance frequency storage unit 7 can also store temporal data correlated with data relating to the detected resonance frequency.

[0018] Filter 8 attenuates a specific frequency band component contained in the torque command value output by the torque command generation unit 3. Fig. Figure 1 illustrates an example in which a filter 8 is provided; however, the present invention is not limited to this. Two or more filters can also be provided.

[0019] The resonance frequency comparison unit 9 measures the stiffness of a machine tool based on the resonance frequency stored in the resonance frequency storage unit 7 and adjusts the filter 8 with respect to the resonance frequency.

[0020] As described above, the servo motor control according to the first embodiment of the present invention is characterized in that the stiffness of a machine tool is measured based on the resonant frequency. A method for measuring the stiffness of a machine tool based on the resonant frequency is described below.

[0021] The machine tool is simplified and treated as a model which is in Fig. Figure 2 illustrates this. In other words, the machine tool is viewed as an accumulation of several spring elements 30 and a load 40. In this way, the mechanical stiffness can be treated as a spring element k. Then a resonance angular frequency ω can be determined. n express the machine using the following equation 1. ωn=kJ

[0022] In equation 1 above, J denotes the moment of inertia of the load.

[0023] Since the moment of inertia of the load J is determined in the machine design, it is possible to estimate the spring element from the measurement of the frequency response. If the resonant angular frequency deviates from a reference value ω n0 on ω n If the spring element changes from k0 to k', a ratio k' / k0 can be calculated from the following equation 2. k'k0=(ωn1ωn0)2

[0024] The value of the reference value ω n0This can also be a value determined by machine design, or, in the case of a mass-produced model, it can be the resonant angular frequency of a test model. In a specific individual case, a profile can also be stored as a resonant angular frequency at the time of manufacture. Since it is considered that the stiffness of the spring element decreases due to loosening of the assembly and similar issues with mechanical parts, it should be assumed that, although stiffness decreases with age, it will not improve.

[0025] For example, if the resonance angular frequency decreases by 10% (reaching 90% of the reference value), k' / k0 can be calculated using the following equation 3. k'k0=(1−0.1)2=0.92=0.8I

[0026] From equation 3 above, it can be deduced that the mechanical stiffness has been reduced by 19%.

[0027] As described above, according to the servomotor control of the first embodiment of the present invention, it is possible to measure the mechanical stiffness from the detected resonant frequency.

[0028] Next, with reference to the schedule outlined in Fig. Figure 3 illustrates an operating method of servo motor control according to the first embodiment of the present invention. First, in step S101, the sine wave generation unit 4 generates a sinusoidal interference wave. The generated sinusoidal interference wave is fed into the adder 13, which is contained in the speed control loop 10, and is added to a speed command value.

[0029] Next, in step S102, the speed detection unit 2 detects the speed of the servo motor 20. A speed detection value, which is a value of the detected speed, is entered into the subtractor 14.

[0030] Next, in step S103, the torque command generation unit 3 generates a torque command from the velocity command value and the velocity sensing value. The generated torque command is output to the filter 8 and the frequency response calculation unit 5.

[0031] Next, in step S104, the frequency response calculation unit 5 calculates a frequency response from the sinusoidal disturbance value and the output from the speed control loop 10, for example, the torque command value. The calculated frequency response is output to the resonant frequency detection unit 6.

[0032] Next, in step S105, the resonance frequency acquisition unit 6 records a maximum value of the frequency response. The recorded maximum value of the frequency response is output to the resonance frequency storage unit 7.

[0033] Then, in step S106, the resonant frequency storage unit 7 stores a resonant frequency.

[0034] Finally, in step S107, the resonance frequency comparison unit 9 extracts the resonance frequency from the resonance frequency storage unit 7 and measures the stiffness of a machine tool based on the resonance frequency. Furthermore, the resonance frequency comparison unit 9 adjusts the filter 8 with respect to the resonance frequency.

[0035] As described above, according to the servomotor control of the first embodiment of the present invention, based on a structure for automatically adjusting a band damping filter based on the measurement of the resonant frequency, the resonant frequency is considered a physical quantity that indicates the stiffness of a machine. In this way, it is possible to dynamically measure the stiffness of a mechanical system driven by a servomotor without disassembling the machine. [Second embodiment]

[0036] Next, a servo motor controller according to a second embodiment of the present invention is described. The servo motor controller according to the second embodiment has a similar configuration to the servo motor controller according to the first embodiment, which is described in Fig. Figure 1 illustrates this. The servomotor control according to the second embodiment differs from the servomotor control according to the first embodiment in that the resonant frequency comparison unit 9 compares the resonant frequency stored in the resonant frequency storage unit 7 with a reference resonant frequency, thereby detecting a change in the stiffness of a machine. Since other configurations of the servomotor control according to the second embodiment are similar to those of the servomotor control according to the first embodiment, a detailed description of these is omitted.

[0037] When using the servomotor control according to the second embodiment of the present invention, corresponding individual differences in the stiffness of mass production machines are measured and compared with each other, so that it is possible to evaluate a dynamic fluctuation in the stiffness of mechanism units. Fig. Figure 4 illustrates an example of a diagram in which stiffness values ​​of several machines, for example machines with machine numbers 1 to 6, have been compared with a manufacturing reference value. Fig. Figure 4 illustrates that the mechanical stiffnesses of machines numbered 1 to 3 and 5, hatched with solid lines, meet the manufacturing reference, but the mechanical stiffnesses of the unhatched machines numbered 4 and 6 do not meet the manufacturing reference. In the example shown in Fig. As illustrated in Figure 4, it is possible to easily confirm that an inspection is required without disassembling the machines, since machines 4 and 6 do not meet the manufacturing reference value. When the servo motor control according to the second embodiment of the present invention is used, it is possible to improve quality management and manufacturing know-how for a machine tool as a finished product, rather than for individual mechanical parts.

[0038] Next, with reference to the schedule outlined in Fig. Figure 5 illustrates an operating method for servo motor control according to the second embodiment of the present invention. Since steps S201 to S207 are shown in the flowchart, which is illustrated in Fig. 5 is illustrated, resembling steps S101 to S107 in the flowchart for servo motor control according to the first embodiment, which is shown in Fig. Since the illustration in section 3 shows the following, a detailed description is omitted.

[0039] In step S208, the resonance frequency comparison unit 9 determines whether the resonance frequency stored in the resonance frequency storage unit 7 is lower than a reference resonance frequency. If the resonance frequency comparison unit 9 determines that the resonance frequency is greater than or equal to the reference resonance frequency, the procedure returns to step S201 and the resonance frequency measurement is performed again. Furthermore, as a result of measuring the resonance frequency of a specific machine over a predetermined time period, if it can be confirmed that the measured resonance frequency is not lower than the reference resonance frequency, the resonance frequencies of other machines can be measured to determine the presence or absence of a reduction in mechanical stiffness.

[0040] On the other hand, if the resonance frequency comparison unit 9 determines that the resonance frequency is smaller than the reference resonance frequency, the resonance frequency comparison unit 9 detects the reduction in mechanical stiffness in step S209.

[0041] If a stiffness fluctuation notification unit, which will be described later, has been provided, the stiffness fluctuation notification unit will finally indicate the need for a machine inspection in step S210.

[0042] As described above, according to the servomotor control of the second embodiment of the present invention, the reference value of the resonant frequency is compared with an actually measured value, making it possible to measure a deviation from the reference value and to inspect a component assembly. For example, in the case of the production of 10 identical machine tools, a measurement result from machine number 1 is used as a reference value, making it possible to detect and address stiffness deviations relative to the other nine machines in a single production process, thus achieving a quality improvement. [Third embodiment]

[0043] Next, a servo motor controller according to a third embodiment of the present invention is described. The servo motor controller according to the third embodiment has a similar configuration to the servo motor controller according to the first embodiment, which is described in Fig. Figure 1 illustrates this. The servomotor control according to the third embodiment differs from the servomotor control according to the first embodiment in that the resonant frequency storage unit 7 stores a profile of resonant frequencies in each measurement, and the resonant frequency comparison unit 9 compares the resonant frequency stored in the resonant frequency storage unit 7 with the profile of resonant frequencies in order to detect a decreasing tendency in the stiffness of a machine. Since other configurations of the servomotor control according to the third embodiment are similar to those of the servomotor control according to the first embodiment, a detailed description of these is omitted.

[0044] According to the servomotor control according to the third embodiment, the stiffness at the time of manufacture is set as a reference value and a long-term change in the stiffness of a machine is monitored, so that it is possible to predict an inspection time of the machine. Fig. Figure 6 shows an example diagram illustrating a long-term change in the stiffness of a machine. Fig. Six black circles indicate that the machine stiffness is higher than the level below which inspection is required, i.e., the machine stiffness is sufficient. A white circle, on the other hand, indicates that the machine stiffness is not higher than the level below which inspection is required, i.e., the machine stiffness is insufficient. In the example shown in Fig. As illustrated in Figure 6, no decrease in stiffness occurs within two years of manufacture, but the machine stiffness shows a downward trend after three years. After five years, the stiffness decrease reaches approximately the level at which an inspection is required. Typically, the inspection of a machine tool, as a production plant, is not performed only at a fixed time. According to the servo motor control of the present invention, a decrease trend curve (or a straight line) is applied, making it possible to predict that an inspection will be required six years after manufacture. In particular, it is possible to predict an inspection time at the point after four years without having to wait for the stiffness measurement after five years. Preferably, the mechanical stiffness can be guaranteed at the time of measurement.As described above, according to the servomotor control of the third embodiment of the present invention, it is possible to measure a machine in perfect condition and predict an inspection time without disassembling individual mechanical parts.

[0045] Next, a procedure for estimating an inspection time point is described in detail. For example, if the mechanical stiffness has decreased by 8% below a reference value (0.92 times the reference value) due to long-term changes, an "inspection time report" is considered. In this case, a resonance angular frequency ω can be used. n ', which is used as a reference value for reporting an inspection time, can be calculated using the following equation 4. ωn'ωn0−k'k0=0.92=0.96

[0046] Accordingly, it is understood that it is sufficient for the inspection time notification to be made when the resonance angular frequency has been reduced by 4%.

[0047] Next, with reference to the schedule outlined in Fig. Figure 7 illustrates an operating method for servo motor control according to the third embodiment of the present invention. Since steps S301 to S307 are shown in the flowchart, which is illustrated in Fig. Figure 7 illustrates steps S101 to S107 in the flowchart for servo motor control according to the first embodiment, which is shown in Fig. Since the illustration in section 3 shows the following, a detailed description is omitted.

[0048] In step S308, the resonance frequency comparison unit 9 determines whether there is a decreasing trend in the resonance frequency stored in the resonance frequency storage unit 7. If the resonance frequency comparison unit 9 determines that there is no decreasing trend in the resonance frequency, the procedure returns to step S301 and the resonance frequency is acquired again after a predetermined time period has elapsed. A history of resonance frequencies is then stored for each measurement.

[0049] On the other hand, if the resonance frequency comparison unit 9 determines that there is a tendency for the resonance frequency to decrease, the resonance frequency comparison unit 9 detects a tendency for the mechanical stiffness to decrease in step S309.

[0050] Next, if a stiffness fluctuation notification unit (to be described later) has been provided, the stiffness fluctuation notification unit in step S310 indicates the need for a machine inspection or a prediction of an inspection time.

[0051] As described above, according to the servomotor control of the third embodiment of the present invention, a profile of resonance frequencies is stored in each measurement, and the tendency of the resonance frequencies to fluctuate is monitored based on this profile. For example, if it is assumed that an automatic filter adjustment is performed periodically for a machine tool, it is possible to track the time and extent (Hz) for which a mechanical resonance has varied, based on the profile of the resonance frequencies. In other words, it is possible to investigate a tendency toward stiffness reduction (to examine the rate at which the mechanical stiffness decreases due to aging). [Fourth embodiment]

[0052] Next, a servo motor controller according to a fourth embodiment of the present invention is described. The servo motor controller according to the fourth embodiment has a similar configuration to the servo motor controller according to the first embodiment, which is described in Fig. Figure 1 illustrates this. The servo motor control according to the fourth embodiment differs from the servo motor control according to the first embodiment in that the resonant frequency comparison unit 9 compares the resonant frequency stored in the resonant frequency storage unit 7 with a reference resonant frequency in order to detect a change in the stiffness of a machine, the resonant frequency storage unit 7 stores a profile of resonant frequencies in each measurement, and the resonant frequency comparison unit 9 compares the resonant frequency stored in the resonant frequency storage unit 7 with the profile of resonant frequencies in order to detect a decreasing tendency in the stiffness of a machine. Since other configurations of the servo motor control according to the fourth embodiment are similar to those of the servo motor control according to the first embodiment, a detailed description of these is omitted.

[0053] Next, with reference to the schedule outlined in Fig. Figure 8 illustrates an operating method for servo motor control according to the fourth embodiment of the present invention. Since steps S401 to S407 are shown in the flowchart, which is illustrated in Fig. Figure 8 illustrates steps S101 to S107 in the flowchart for servo motor control according to the first embodiment, which is shown in Fig. Since the illustration in section 3 shows the following, a detailed description is omitted.

[0054] In step S408, the resonant frequency comparison unit 9 determines whether the resonant frequency stored in the resonant frequency storage unit 7 is lower than a reference resonant frequency.

[0055] If the resonance frequency comparison unit 9 determines that the resonance frequency is lower than the reference resonance frequency, the resonance frequency comparison unit 9 detects the reduction in mechanical stiffness in step S409.

[0056] Next, if a stiffness fluctuation notification unit (to be described later) has been provided, the stiffness fluctuation notification unit in step S412 indicates the need for a machine inspection.

[0057] If, on the other hand, the resonance frequency comparison unit 9 determines that the resonance frequency is not lower than the reference resonance frequency, the resonance frequency comparison unit 9 determines in step S410 whether there is a decreasing tendency of the resonance frequency stored in the resonance frequency storage unit 7. If the resonance frequency comparison unit 9 determines that there is no decreasing tendency of the resonance frequency, the procedure returns to step S401 and the acquisition of the resonance frequency is performed again.

[0058] If, on the other hand, the resonance frequency comparison unit 9 determines that there is a tendency for the resonance frequency to decrease, the resonance frequency comparison unit 9 detects a tendency for the mechanical stiffness to decrease.

[0059] Next, if the stiffness fluctuation notification unit to be described later has been provided, the stiffness fluctuation notification unit in step S412 indicates the need for machine inspection or a prediction of an inspection time.

[0060] As described above, according to the servomotor control of the fourth embodiment of the present invention, the reference value of the resonant frequency is compared with an actual measured value, making it possible to measure deviations from the reference value and to inspect a component assembly. For example, in the case of manufacturing 10 identical machine tools, a measurement result from the first machine is used as a reference value, making it possible to detect and manage stiffness deviations relative to the other nine machines in a manufacturing process, thus achieving quality improvement. Furthermore, a profile of resonant frequencies is stored for each measurement, and this profile is used to monitor fluctuations in the resonant frequencies.For example, if it is assumed that an automatic filter adjustment is performed periodically on a machine tool, it is possible to track the time and extent (Hz) of changes in mechanical resonance by monitoring the course of the resonance frequencies. In other words, it is possible to investigate a tendency toward stiffness reduction (to examine the rate at which mechanical stiffness decreases due to aging).

[0061] In other words, it is possible to determine whether or not a reduction in mechanical stiffness has occurred based on whether the resonance frequency is lower than the reference resonance frequency, and to determine whether or not a trend toward a decrease in mechanical stiffness has occurred if it is found that the mechanical stiffness has not decreased. Therefore, it is possible to anticipate a future reduction in mechanical stiffness even if no reduction in mechanical stiffness has actually occurred.

[0062] For the servo motor control according to the preceding fourth embodiment, an example has been described in which it is determined whether the resonant frequency is lower than the reference resonant frequency, and then it is determined whether the resonant frequency exhibits a decreasing tendency; however, the present invention is not limited to this. In other words, it is possible to determine whether the resonant frequency exhibits a decreasing tendency, and then it is possible to determine whether the resonant frequency is lower than the reference resonant frequency. In this case, it is possible to omit the step of comparing the resonant frequency with the reference resonant frequency, since it is possible to confirm that there is no decreasing tendency in mechanical stiffness. [Version 5]

[0063] Next, a servo motor control according to embodiment 5 of the present invention will be described. Fig. Figure 9 illustrates a configuration diagram of a servo motor controller according to embodiment 5. A servo motor controller 102 according to embodiment 5 differs from the servo motor controller 101 according to the first embodiment in that the servo motor controller 102 further comprises a stiffness fluctuation signaling unit 11, which signals the inspection of parts of a machine tool or the entire machine tool or predicts an inspection time when the resonance frequency comparison unit 9 has detected a decrease from a reference value of the mechanical stiffness or a decrease trend in a stiffness measurement curve to be stored. Since other configurations of the servo motor controller 102 according to embodiment 5 differ from those of the servo motor controller 101 (see Figure 9), the servo motor controller 102 is further characterized by the fact that the servo motor controller 102 comprises a stiffness fluctuation signaling unit 11, which signals the inspection of parts of a machine tool or the entire machine tool or predicts an inspection time when the resonance frequency comparison unit 9 has detected a decrease from a reference value of the mechanical stiffness or a decrease trend in a stiffness measurement curve to be stored. Fig. 1) Since the embodiment resembles the first embodiment, a detailed description of it is omitted.

[0064] According to the servo motor control of embodiment 5, the operator can predict the need for an inspection to examine the assembly strength of mechanical parts, or the inspection time itself, based on an individual difference or a long-term change in stiffness in an assembled state. If a significant deviation in stiffness exists at the time of manufacture, the need for an inspection can be quickly determined by comparing a measured value of a resonant frequency with the reference value, and this can be used in quality management. If a long-term change is significant, it is possible to predict the inspection time for parts in advance, leading to an improved ratio of operating costs to machine output.

[0065] As described above, according to the servomotor controls of the embodiments of the present invention, it is possible to measure stiffness fluctuations in a manufacturing process by comparing a resonant frequency with a reference value at the time of machine assembly, and furthermore to monitor long-term changes in mechanical stiffness by regularly measuring them after delivery of the machine. Furthermore, stiffness measurement can be performed without disassembling the machine, and a self-prediction of the maintenance time is possible.

[0066] According to the present invention, it is possible to provide a servo motor control system which can provide a comprehensive inspection technology that enables maintenance inspection prediction of a machine without destruction and disassembly, as well as simple stabilization of a servo control system.

Claims

[1] Servo motor control (101; 102) which controls a servo motor (20) for driving a machine tool, comprising: a speed command generation unit (1) configured to generate a speed command value of the servo motor (20); a speed detection unit (2) configured to detect the speed of the servo motor (20); a torque command generation unit (3) configured to generate a torque command value of the servo motor (20) based on the velocity command value and the detected velocity; a sinusoidal wave generation unit (4) configured to generate a sinusoidal disturbance wave; a frequency response calculation unit (5) configured to add the sinusoidal disturbance value generated by the sine wave generation unit (4) to the velocity command value, thereby generating a frequency response based on an output from a velocity control loop (10). 1 is calculated when the sinusoidal disturbance value has been entered into the speed control loop (10), which includes the torque command generation unit (3) and the speed detection unit (2); a resonant frequency detection unit (6) configured to detect a resonant frequency, which is a frequency at which an amplification of the calculated frequency response 1 maximized; a resonant frequency storage unit (7) configured to store the resonant frequency detected by the resonant frequency acquisition unit (6); at least one filter (8) configured to attenuate a specific frequency band component contained in the torque command value; and a resonance frequency comparison unit (9) which is configured to measure the stiffness of a machine tool on the basis of the resonance frequency stored in the resonance frequency storage unit (7) and to adjust the filter (8) with respect to the resonance frequency. [2] Servomotor control (101; 102) according to claim 1, wherein the resonant frequency comparison unit (9) detects a change in the stiffness of the machine by comparing the resonant frequency stored in the resonant frequency storage unit (7) with a reference resonant frequency. [3] Servo motor control (101; 102) according to claim 1 or 2, wherein the resonance frequency storage unit (7) stores a history of resonance frequencies in each measurement and wherein the resonance frequency comparison unit (9) detects a decreasing tendency in the stiffness of the machine by comparing the resonance frequency stored in the resonance frequency storage unit (7) with the course of the resonance frequencies. [4] Servo motor control (101; 102) according to one of claims 1 to 3, further comprising: a stiffness fluctuation reporting unit (11) configured to report an inspection of parts of the machine tool or the entire machine tool or to predict an inspection time when the resonance frequency comparison unit (9) has detected a decrease in mechanical stiffness from a reference value or a tendency to decrease during a stiffness measurement.

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