JP2018017689A - Abnormality determination method of feed shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormality determination method of a feed shaft which can determine an abnormality of the feed shaft of a machine tool without adding a sensor.SOLUTION: A frequency characteristic Gin a prescribed position is calculated from a speed command value and speed deviation which are sent from a control part 3 by using frequency characteristic calculation means 5. The frequency characteristic Gin a state 26 that a preload is reduced due to the wear of a rolling face of a support bearing compared with a frequency characteristic Gin a state 25 that a proper preload is applied is increased in a gain characteristic in 10 to 20 Hz. Therefore, a gain characteristic change amount G is calculated by a gain characteristic change amount calculation part 21 which calculates a difference between measurement data Gsent from an initial state storage part 22 which stores a frequency characteristic of a part in an initial state in advance, and acquired measurement data G. By comparing and collating the gain characteristic change amount with a threshold Gwhich is set in advance in an abnormality determination part 23, a state that the bearing is worn is determined to be abnormal.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for determining an abnormality of a feed shaft in a screw feed apparatus that positions a specific position by screw feeding a moving body by rotating a feed shaft such as a ball screw.

In order to realize a stable production system in the operation of machine tools, it is necessary to detect abnormalities in the machine and notify the manager of the machine status to prevent accidents and defects. A method for determining an abnormality in a machine has been proposed.
In a ball screw and a support bearing configured in a feed shaft, in Patent Document 1, an envelope analysis and a frequency analysis are performed on a detection result using a means for detecting a physical quantity signal that inhibits rotation and sliding of the bearing due to damage. Thus, a proposal has been made to extract the level of the frequency spectrum of the actually measured data, compare it with the threshold value set for each frequency spectrum, and diagnose the presence or absence of abnormality and the abnormal part. In Patent Document 2, a proposal has been made to detect an abnormality from a detected value using an abnormality determining means by means for detecting vibration of a return tube due to the above-mentioned deterioration in a ball screw by a physical quantity signal.

JP 2009-20090 A JP 2001-349407 A

  However, the feed axis abnormality detection method according to Patent Document 1 and Patent Document 2 requires the cost of providing an additional sensor for each axis of the machine, and the cost of the entire machine is increased in a machine tool having multiple axes. End up.

  The present invention has been made in view of the above proposal, and provides a feed axis abnormality determination method capable of determining a feed axis abnormality of a machine tool without adding a sensor.

In order to achieve the above object, the invention according to claim 1 of the present invention is characterized in that, in a feed axis of a machine tool controlled by NC, a reference value of a frequency characteristic in which the feed axis is in a normal state and a frequency at the time of measurement. The characteristics are compared and checked, and abnormality of the feed axis is determined.
In order to achieve the above object, the invention according to claim 2 of the present invention is characterized in that, in the feed axis of the NC-controlled machine tool, the reference value of the frequency characteristic in which the feed axis is in a normal state and the measurement time It is characterized in that the abnormality of the feed axis is determined based on the difference in gain of the frequency characteristics.
In order to achieve the above object, the invention according to claim 3 of the present invention relates to the responsiveness to a specific frequency and the axis position of the feed shaft in the feed shaft of the NC controlled machine tool. And a method for obtaining an abnormality of the feed shaft based on a difference between a reference value for normality of responsiveness related to the axis position and a gain of responsiveness at the time of measurement.

  According to the present invention, since it is not necessary to add a sensor, it is possible to determine whether the feed axis is abnormal at low cost.

It is a block diagram of a feed shaft and a position control device. FIG. 6 is a relationship diagram between an amount of wear and a gain characteristic. It is the procedure of the abnormality determination method in 1st Embodiment. It is the procedure of the abnormality determination method in 2nd Embodiment. It is an example of a frequency characteristic. It is an example of the wear determination of a ball screw and a bearing in a specific position. It is an example of the wear determination of a ball screw and a bearing by the responsiveness regarding a feed shaft position.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is an example of a block diagram of a position control device for a feed axis of a machine tool to which the present invention is applied. The position command 7 and the current position from the position detector 15 are input to the adder 8, and the calculated position deviation is input to the position controller 9. The position controller 9 generates a speed command value corresponding to the position deviation. The speed controller 12 inputs the speed command value and the speed detection value obtained by calculating the current position by the differentiator 13 to the adder 11 and generates a torque command value according to the calculated speed deviation. The current controller 14 controls the current based on the input torque command. The current controller 14 outputs a current corresponding to the torque command value to the motor 16, and the motor 16 outputs torque. Torque output from the motor 16 is transmitted to the ball screw 20 through the joint 17 and the nut of the ball screw 20 moves. The position detector 15 is synchronized with the rotation of the motor 16, and closed control for controlling the position to a predetermined position by feeding back the detected position is performed. The screw shaft of the ball screw 20 is supported by a support bearing 19 assembled to the bracket 18, and the ball screw 20 is pretensioned.

  When measuring the frequency characteristic, the sweep signal generated from the sweep signal generating means 2 is added to the speed command value by the adder 10. The host controller 1 can record and display information used in the process under control, including the current position detected by the position detector 15.

  Next, a method for determining the wear state of the ball screw / support bearing based on the frequency characteristics of the feed shaft will be described. A difference as shown in FIG. 2 is produced in the frequency characteristics of the feed shaft due to wear of the ball screw and the support bearing. Since this relationship differs depending on the machine, it is necessary to experimentally obtain the relationship between the wear amount and the frequency characteristic for each machine in advance.

  In the example of the block diagram, an open loop frequency characteristic with the input as the speed command value and a response as a speed detection value and a closed loop frequency characteristic with a response as the speed command value can be acquired. In the present invention, the frequency characteristic in the former open loop control is described as an example, but the present invention is not limited to this.

The abnormality determination method of the first embodiment will be described. FIG. 3 shows a procedure for performing abnormality determination. Frequency characteristic of G ₁ in the predetermined position is calculated from the speed command value and the speed deviation that has been transmitted from the control unit 3 at a frequency characteristic calculation means 5. The gain characteristic of the frequency characteristic with the frequency series at a specific axis position as an axis is as shown in FIG. Compared with the frequency characteristic G ₀ in the initial state 25 in which an appropriate preload is applied, the frequency characteristic G ₁ in the state 26 in which the rolling force of the support bearing is worn and the preload is reduced is a gain characteristic value at 10 to 20 Hz. Will increase. Therefore, the gain characteristic change for calculating the difference between the measurement data G ₀ sent from the initial state storage unit 22 storing the frequency characteristics (measurement data) at the initial state of the component in advance and the acquired measurement data G _1. When the gain characteristic change amount G is calculated by the amount calculation unit 21, it is as shown in FIG. By comparing and comparing with the threshold value _Gth set in the abnormality determination unit 23, the worn state of the bearing can be determined as abnormal. The result is sent to the determination result storage unit 24 and stored and displayed on the host controller.

An abnormality determination method according to the second embodiment will be described. FIG. 4 shows a procedure for performing abnormality determination. In the frequency characteristic calculation means 5, the speed command value vibrated only at a specific frequency and the response obtained by the speed deviation are related to the position X of the feed shaft sent from the detector. The response G ₁ (X) related to the shaft position X is measured while moving the moving body of the feed shaft at a constant speed within a predetermined axis range, and the response G ₁ (X) within the range is calculated. . The responsiveness G ₀ (X) relating to the position X of the axis in the initial state of the component is sent from the initial state storage unit 22 in which the responsiveness G ₀ (X) is stored in advance to the gain characteristic change amount calculation unit 21 and measured responsiveness G ₁ (X ), The gain characteristic change amount G (X) at the axis position X is calculated. This is compared with the threshold value G _th (X) set by the abnormality determination unit 23, and if the comparison is larger, the abnormality is determined, and if the comparison is smaller, the determination is normal, and the result is stored as a determination result. Sent to the unit 24 and stored and displayed in the host controller.

The determination result recorded in the determination result recording unit 24 is not necessarily limited to displaying only the determination result on the host controller, and the initial calculation data G ₀ (X) and the gain characteristic change amount G (X) The threshold value G _th (X) may be displayed / warned with the determination result together with the frequency series or the axis position series data as necessary.

  Since the responsiveness G (X) relating to the position X of the feed axis is obtained for the feed axis moving at a constant speed, when calculating by the discrete Fourier transform, at least one cycle of the excited sweep waveform A time signal is needed. Therefore, the responsiveness of each axis position is calculated for each section divided by the movement amount for one period. However, it is not necessary to divide the movement amount in one cycle, and a measurement point may be provided for each movement amount in one cycle or more, and the averaging process or peak hold may be used. In addition, the responsiveness according to the movement amount for each cycle may be a response value obtained by averaging the responsiveness before and after the movement amount section as the responsiveness of the measurement point.

  This makes it possible to determine the abnormality of wear for each measurement section. FIG. 7A shows a case where the difference from the initial state in the responsiveness of a part of the shaft position range 21 is increased, and FIG. 7B shows a case where the responsiveness is increased in the entire axial position. Show. In the former case, wear is observed only in a certain range, so that only a partial range of the thread groove in the ball screw is worn 22. In the latter case, a state 23 in which the support bearing is worn or the thread groove of the nut in the ball screw is worn is feared.

  If an abnormality such as these appears, the machine tool administrator can determine that the ball screw or the support bearing has worn, and by operating outside the range of the axis where the abnormality has been determined, Defects can be reduced. In addition, by repeating these measurements periodically, it is possible to avoid long-term machine tool outages for parts replacement, such as by preparing the parts before they are judged as worn, and operating a stable production system. Can be realized.

  1 ··· Higher-level controller 2 · · Sweep signal generation means 3 · · Control unit · · · Actuator 5 · · Transfer function or frequency characteristic calculation means · 6 · · Abnormality determination means · 7 · · Position command 8 ..Adder, 9 ... Position controller, 10 ... Adder, 11 ... Adder, 12 ... Speed controller, 13 ... Differentiator, 14 ... Current controller, 15 ... Position detector , 16 ··· Motor, 17 ·· Joint, 18 · · Bracket, 19 · · Support bearing, 20 · · Ball screw, 21 · · Gain characteristic change amount calculation unit, 22 · · Initial state recording unit, 23 · · Abnormal Judgment unit 24 ・ ・ Judgment result recording unit 25 ・ ・ Initial state in which appropriate preload is applied, 26 ・ In a state where the support bearing is worn, 27 ・ ・ Determine abnormality of wear on the shaft of the feed shaft Range, 28 ・ ・ Partial range of the screw axis of the ball screw Wearing state, 29 .... Wearing of support bearings or wearing of ball screw nuts or balls.

Claims (3)

  In a feed axis of a machine tool controlled by NC, a feed axis characterized by comparing and collating a reference value of a frequency characteristic in a normal state of the feed axis with a frequency characteristic at the time of measurement, and determining an abnormality of the feed axis. Anomaly judgment method.   In the feed axis of a machine tool controlled by NC, the feed axis abnormality is determined based on a difference between a reference value of the frequency characteristic in which the feed axis is in a normal state and a gain of the frequency characteristic at the time of measurement. Axis abnormality judgment method.   In a feed axis of a machine tool controlled by NC, there is provided a method for acquiring a response to a specific frequency in association with a shaft position of the feed shaft, and a reference value and a measurement for making the response state related to the shaft position normal. An abnormality determination method for a feed shaft, wherein the abnormality of the feed shaft is determined based on a difference in response gain at the time.

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