Diagnostic method and diagnostic device for feed screw device

Abstract

To provide a diagnostic method and a diagnostic device in a feed screw device capable of respectively and separately diagnosing wear of a feed screw and wear of guidance even in a such case that wear is complexly generated in both a feed crew and guidance.SOLUTION: A diagnostic method calculates an elastic deformation amount from first position information and second position information, uses the elastic deformation amount and shaft rigidity of a feed screw device to separate a torque command value relating to control of the position of a drive object into a linear component torque and a rotational component torque, uses the rotational component torque to calculate a preload degradation ratio of the feed screw, uses the preload degradation ratio to calculate the shaft rigidity of the feed screw, determines whether the shaft rigidity of the feed screw converges from currently calculated shaft rigidity of the feed screw and the precedingly calculated shaft rigidity of the feed screw, and repeats the above steps until convergence to respectively diagnose a wear state of the guidance from the linear component torque and a wear state of the feed screw from the rotational component torque when the shaft rigidity of the feed screw device converges.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a diagnostic method and diagnostic device for diagnosing the condition of a feed screw device that moves a driven object along a guide by the rotation of a feed screw. [Background technology]

[0002] Some machine tools are equipped with a feed screw device that moves a moving body such as a table along a guide arranged in a predetermined direction by the rotation of a feed screw. In such a feed screw device, problems such as reduced operating accuracy and abnormal noise during operation can occur due to wear of the feed screw due to aging or damage due to the inclusion of foreign matter. Therefore, in order to prevent such problems from occurring, it is desirable to replace the mechanical elements before the problems occur. Therefore, various diagnostic methods have been devised in the past for diagnosing the condition of the mechanical elements in the feed screw device.

[0003] For example, the diagnostic method described in Patent Document 1 estimates the driving force of the driven object based on the torque command value of the motor for rotating the feed screw, estimates the elastic deformation amount of the feed screw from that driving force, calculates a position deviation from the rotational position information of the motor and the position information of the table, and diagnoses the damage condition of the driven object by comparing the elastic deformation amount with the position deviation.Also, the diagnostic method described in Patent Document 2 calculates a lost motion value from the rotational position information of the motor and the position information of the table, and diagnoses the gib tightening state of the sliding guide using the lost motion value and the current value supplied to the motor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-154274 A [Patent Document 2] JP 2013-69192 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the diagnostic methods described in Patent Documents 1 and 2 do not separate the load components of the feed screw and the guide for the motor torque command value and the current value supplied to the motor, and do not take into account the impact of reduced feed screw rigidity due to wear of the feed screw. Therefore, there is a problem that when multiple abnormalities occur, such as when wear occurs in both the feed screw and the guide, phenomena that are not taken into account can become error factors and lead to incorrect diagnosis.

[0006] Therefore, the present invention has been made in consideration of the above problems, and aims to provide a diagnostic method and diagnostic device for a feed screw device that is capable of diagnosing wear of the feed screw and the guide individually, even when wear has occurred in both the feed screw and the guide in combination. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a feed screw device comprising a motor, a feed screw that rotates in response to the drive of the motor, a driven object that is screw-fed in response to the rotation of the feed screw, and a guide that guides the movement of the driven object, and further comprising a first position detector that detects a rotational position of the motor as first position information, and a second position detector that detects a position of the driven object in a screw feed direction as second position information, and the feed screw device controls a position of the driven object based on an input position command value, the first position information, and the second position information. The feed screw device further comprises a first step of calculating an elastic deformation amount from the first position information and the second position information, and a second step of detecting a wear state of the feed screw and the guide. Previously calculated A second step of separating a torque command value relating to control of a position of the driven object into a linear component torque and a rotational component torque using the axial stiffness of the feed screw device; a third step of calculating a preload reduction rate of the feed screw using the rotational component torque; and a fourth step of calculating the axial stiffness of the feed screw device using the preload reduction rate. Newthe fourth step of calculating the axial stiffness of the feed screw device; the fifth step of determining whether the axial stiffness of the feed screw device has converged based on the axial stiffness of the feed screw device calculated this time and the axial stiffness of the feed screw device calculated last time, and repeating the first step to the fourth step until the axial stiffness of the feed screw device has converged; and the sixth step of diagnosing the wear state of the guide from the linear component torque and the wear state of the feed screw from the rotational component torque when the axial stiffness of the feed screw device has converged. In order to achieve the above object, the present invention provides a feed screw device comprising a motor, a feed screw which rotates in response to the drive of the motor, a driven object which is screw-fed in response to the rotation of the feed screw, and a guide which guides the movement of the driven object, and further comprising a first position detector which detects a rotational position of the motor as first position information, and a second position detector which detects a position of the driven object in a screw feed direction as second position information, and which controls a position of the driven object based on an input position command value, the first position information, and the second position information. The feed screw device further comprises an elastic deformation amount calculation unit which calculates an elastic deformation amount from the first position information and the second position information, and a guide which guides the movement of the driven object. Previously calculated a torque command value separating unit that separates a torque command value relating to control of the position of the driven object into a linear component torque and a rotational component torque using the axial stiffness of the feed screw device; a preload reduction rate calculating unit that calculates a preload reduction rate of the feed screw using the rotational component torque; New a axial stiffness calculation unit that calculates the axial stiffness of the feed screw device, and ... Calculations in the elastic deformation amount calculation unit, the torque command value separation unit, the preload reduction rate calculation unit, and the shaft stiffness calculation unit Repeat and execute The feed screw device is characterized by comprising a convergence determination unit and a diagnosis unit that diagnoses the wear state of the guide from the linear component torque when the axial stiffness of the feed screw device converges, and the wear state of the feed screw from the rotational component torque. Furthermore, in order to achieve the above object, the present invention provides a feed screw device comprising a motor, a feed screw that rotates in response to the drive of the motor, a driven object that is screw-fed in response to the rotation of the feed screw, and a guide that guides the movement of the driven object, and also comprising a first position detector that detects a rotational position of the motor as first position information, and a second position detector that detects a position of the driven object in a screw feed direction as second position information, and the feed screw device controls a position of the driven object based on an input position command value, the first position information, and the second position information. The feed screw device further comprises a first step of calculating an elastic deformation amount from the first position information and the second position information, and a second step of detecting a wear state of the feed screw and the guide. Previously calculated A second step of separating a torque command value relating to control of a position of the driven object into a linear component torque and a rotational component torque using the axial stiffness of the feed screw device; a third step of calculating a preload reduction rate of the feed screw using the rotational component torque; and a fourth step of calculating the axial stiffness of the feed screw device using the preload reduction rate. New the fifth step of determining whether the axial stiffness of the feed screw device has converged based on the currently calculated axial stiffness of the feed screw device and the previously calculated axial stiffness of the feed screw device, and repeating the first step to the fourth step until the axial stiffness of the feed screw device has converged; and the sixth step of diagnosing the wear state of the guide from the linear component torque when the axial stiffness of the feed screw device has converged, and the wear state of the feed screw from the preload reduction rate. In addition, in order to achieve the above object, the invention according to claim 4 of the present invention provides a feed screw device comprising a motor, a feed screw which rotates in response to the drive of the motor, a driven object which is screw-fed in response to the rotation of the feed screw, and a guide which guides the movement of the driven object, and which also comprises a first position detector which detects a rotational position of the motor as first position information, and a second position detector which detects a position of the driven object in a screw feed direction as second position information, and which controls a position of the driven object based on an input position command value, the first position information, and the second position information. The feed screw device further comprises an elastic deformation amount calculation unit which calculates an elastic deformation amount from the first position information and the second position information, and a guide which guides the movement of the driven object. Previously calculated a torque command value separating unit that separates a torque command value relating to control of the position of the driven object into a linear component torque and a rotational component torque using the axial stiffness of the feed screw device; a preload reduction rate calculating unit that calculates a preload reduction rate of the feed screw using the rotational component torque; New a axial stiffness calculation unit that calculates the axial stiffness of the feed screw device, and ... Calculations in the elastic deformation amount calculation unit, the torque command value separation unit, the preload reduction rate calculation unit, and the shaft stiffness calculation unit Repeat and execute The feed screw device is characterized by comprising a convergence determination unit and a diagnosis unit that diagnoses the wear state of the guide from the linear component torque when the axial stiffness of the feed screw device converges, and the wear state of the feed screw from the preload reduction rate. Effect of the Invention

[0008] According to the present invention, the elastic deformation amount is calculated from the first position information and the second position information, and the elastic deformation amount is Previously calculated A torque command value relating to control of the position of a driven object is separated into a linear component torque and a rotational component torque using the axial stiffness of the feed screw device, a preload reduction rate of the feed screw is calculated using the rotational component torque, and the axial stiffness of the feed screw device is calculated using the preload reduction rate. NewThe axial stiffness of the feed screw device is calculated, and it is determined whether the axial stiffness of the feed screw device has converged or not from the currently calculated axial stiffness of the feed screw device and the previously calculated axial stiffness of the feed screw device, and the above process is repeated until convergence occurs, and when the axial stiffness of the feed screw device has converged, the wear state of the guide is diagnosed from the linear component torque, and the wear state of the feed screw is diagnosed from the rotational component torque (preload reduction rate in claims 3 and 4). Therefore, even when wear has occurred in both the feed screw and the guide in a compound manner, the wear of the feed screw and the wear of the guide can be diagnosed individually. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a block diagram of a feed screw device. [Diagram 2] 4 is a flowchart showing a diagnostic method in the diagnostic device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A diagnostic method and diagnostic device for diagnosing the state of a feed screw device according to an embodiment of the present invention will be described in detail below with reference to the drawings.

[0011] FIG. 1 is a block diagram of a feed screw device. The feed screw device includes a servo motor 7, a feed screw 8 rotated by the drive of the servo motor 7, a table 9 screw-fed by the rotation of the feed screw 8, and a guide 15 for guiding the movement of the table 9 (of the elements constituting the guide 15, only the guide on the table 9 side is shown in FIG. 1). A first position detector 6 for detecting the rotational position of the servo motor 7 (hereinafter referred to as first position information) is attached to the servo motor 7. A scale 10 is disposed in parallel to the feed screw 8, and a second position detector 11 for detecting the position of the table 9 in the screw feed direction (hereinafter referred to as second position information) is attached to the scale 10 so as to be slidable along the scale 10 in conjunction with the movement of the table 9.

[0012] In the feed screw device, a subtractor 1 subtracts second position information fed back from a second position detector 11 from a position command value input from an NC device (not shown) to calculate a position deviation. A position control unit 2 calculates a speed command value based on the position deviation. A speed control unit 3 calculates a motor torque command value based on the speed command value and the rotation speed of a servo motor 7 obtained by differentiating the first position information fed back from a first position detector 6 by a differentiator 5. Then, the motor torque command value is amplified in a current control unit 4 and output to the servo motor 7, thereby executing full closed loop position control.

[0013] Here, the condition diagnosis of the feed screw device, which is an essential part of the present invention, and in particular the diagnosis of wear of the feed screw 8 and the guide 15 will be described. The feed screw device is provided with a diagnostic unit 13 for diagnosing wear of the feed screw 8 and the guide 15. A position command value from the NC device and a torque command value calculated by the current control unit 4 are input to the diagnostic unit 13. The difference between the first position information and the second position information calculated by the subtractor 12 is also input to the diagnostic unit 13 as an elastic deformation amount ε. The diagnostic unit 13 then diagnoses wear of the feed screw 8 and the guide 15 based on the torque command value and the elastic deformation amount ε.

[0014] 2, the above diagnosis will be specifically explained. First, the subtractor 12 calculates the difference between the first position information detected by the first position detector 6 and the second position information detected by the second position detector 11, and inputs the difference as the elastic deformation amount ε to the diagnosis unit 13 (S1). When detecting the first position information and the second position information related to the calculation of the elastic deformation amount ε, it is preferable to detect the information during feeding at a constant speed, since it is often difficult to estimate the machine state when the table 9 is accelerating / decelerating, moving at high speed, or reversing the driving direction, because the effects of inertial forces, etc. become large or corrections are made.

[0015] Next, the diagnosis unit 13 separates the torque command value T into a linear component torque Tg(n) and a rotational component torque Tr(n) by the following formulas 1 and 2 using the elastic deformation amount ε calculated in S1 and the axial stiffness K(n-1) of the feed screw device (S2). Note that the axial stiffness of the feed screw device at the first calculation uses an initial set value that has been set in advance.

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[0016] Furthermore, the diagnosis unit 13 calculates the preload reduction rate ΔF(n) of the feed screw 8 by comparing the rotation component torque Tr(n) with a preset initial preload torque Tp(0) (S3). As shown in the following formula 3, the rotation component torque Tr(n) can be separated into a preload torque Tp(n) that is constant regardless of the speed, and a speed proportional component Tv that changes depending on the speed due to the viscous resistance of the lubricant, etc. Therefore, if a coefficient of the speed proportional component Tv is set in advance and the speed proportional component Tv is calculated from the feed speed at the time of detection of the first position information and the second position information, the current preload torque Tp(n) can be calculated. The preload reduction rate ΔF(n) of the feed screw 8 is calculated by the following formula 4.

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[0017] Furthermore, the diagnosis unit 13 calculates the axial stiffness K(n) of the entire feed screw device using the preload reduction rate ΔF(n) calculated in S3 (S4). a0 The initial axial stiffness of the nut when nut0 is calculated using the following formula 5, and the axial stiffness of the nut at preload Fa, K nut is the initial axial stiffness of the nut, K nut0 and the preload reduction rate ΔF, it is expressed by the following formula 6. Therefore, the axial stiffness K(n) of the entire feed screw device is calculated by the following formula 7. Note that the axial stiffness of each part that is not related to the stiffness of the feed screw is set in advance.

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[0018] In addition, the diagnosis unit 13 compares the currently calculated shaft stiffness K(n) with the previously calculated shaft stiffness K(n-1) to determine whether the value of the shaft stiffness K(n) has converged (S5), and repeats the processes of S2 to S5 until the shaft stiffness K(n) has converged. The determination of whether or not the shaft stiffness K(n) has converged is performed based on whether or not the convergence determination value calculated using |1-K(n-1) / K(n)| or |K(n)-K(n-1)| falls below a certain value, and it is determined that convergence has occurred when it falls below the certain value (YES is determined in S5). For example, in the convergence determination using |1-K(n-1) / K(n)|, it is determined that convergence has occurred when the convergence determination value calculated using this calculation is 0.01 or less (error 1% or less).

[0019] Finally, the diagnosing unit 13 determines whether the linear component torque Tg(n) after the convergence determination is below a predetermined linear component threshold value (S6), and if the linear component torque Tg(n) is below the linear component threshold value (YES in S6), it diagnoses that wear of the guide 15 is progressing (S7). In addition, it determines whether the rotational component torque Tr(n) after the convergence determination is below a predetermined rotational component threshold value (S8), and if the rotational component torque Tr(n) is below the rotational component threshold value (YES in S8), it diagnoses that wear of the feed screw 8 is progressing (S9).

[0020] According to the above-mentioned diagnostic method and diagnostic device for the feed screw device, the elastic deformation amount ε is calculated from the first position information and the second position information, the elastic deformation amount ε and the axial stiffness k(n-1) of the feed screw device are used to separate the torque command value into a linear component torque and a rotational component torque, the preload reduction rate of the feed screw 8 is calculated using the rotational component torque, the axial stiffness K(n) of the feed screw device is recalculated using the preload reduction rate, and it is determined whether the axial stiffness K(n) of the feed screw device has converged or not from the axial stiffness K(n) of the feed screw device calculated this time and the axial stiffness K(n-1) of the feed screw device calculated last time, and the above process is repeated until convergence occurs, and the wear state of the guide 15 is diagnosed from the linear component torque when the axial stiffness K(n) of the feed screw device converges, and the wear state of the feed screw 8 is diagnosed from the rotational component torque. Therefore, even when wear occurs in both the feed screw 8 and the guide 15 in a composite manner, the wear of the feed screw 8 and the wear of the guide 15 can be diagnosed individually.

[0021] The diagnostic method and diagnostic device for the feed screw device according to the present invention are not limited to the above-described embodiment, and the overall configuration of the feed screw device as well as specific control related to the diagnosis can be appropriately modified as necessary without departing from the spirit of the present invention.

[0022] For example, in the above embodiment, the wear state of the feed screw 8 is diagnosed from the rotational component torque when the axial stiffness K(n) of the feed screw device converges. However, instead of the rotational component torque, it is also possible to adopt a preload reduction rate ΔF(n) when the axial stiffness K(n) of the feed screw device converges, and if the preload reduction rate ΔF(n) falls below a predetermined threshold value that has been set in advance, it is possible to diagnose that wear of the feed screw 8 is progressing. Furthermore, in the above embodiment, the driven object is a table, but there is no problem if the driven object is something other than a table as long as it moves along a guide by a feed screw. Furthermore, in the diagnostic device of the above embodiment, it is possible to provide a display device that displays various information calculated in relation to the diagnosis, values ​​to be used, diagnostic results, etc., and it may be configured to display and store various information calculated in relation to the diagnosis, values ​​to be used, diagnostic results, etc., by utilizing the display unit and memory unit of the NC device. [Explanation of symbols]

[0023] 6··first position detector, 7··servo motor (motor), 8··feed screw, 9··table (driven object), 11··second position detector, 12··subtractor (elastic deformation amount calculation unit), 13··diagnosis unit (torque command value separation unit, preload reduction rate calculation unit, shaft stiffness calculation unit, convergence determination unit, diagnosis unit).

Claims

1. A feed screw device includes a motor, a feed screw that rotates in response to driving of the motor, a driven object that is screw-fed in response to rotation of the feed screw, and a guide that guides movement of the driven object, and also includes a first position detector that detects a rotational position of the motor as first position information and a second position detector that detects a position of the driven object in a screw feed direction as second position information, and the feed screw device controls a position of the driven object based on an input position command value, the first position information, and the second position information, comprising: a first step of calculating an elastic deformation amount from the first position information and the second position information; a second step of separating a torque command value related to control of a position of the driven object into a linear component torque and a rotational component torque using the elastic deformation amount and a previously calculated axial stiffness of the feed screw device; a third step of calculating a preload reduction rate of the feed screw by using the rotational component torque; a fourth step of calculating a new axial stiffness of the feed screw device using the preload reduction rate; a fifth step of determining whether or not the axial stiffness of the feed screw device has converged based on the currently calculated axial stiffness of the feed screw device and the previously calculated axial stiffness of the feed screw device, and repeating the first step to the fourth step until the axial stiffness of the feed screw device has converged; a sixth step of diagnosing a wear state of the guide from the linear component torque when the axial stiffness of the feed screw device has converged, and a wear state of the feed screw from the rotational component torque, respectively; A diagnostic method for a feed screw device, comprising:

2. A diagnostic device for diagnosing wear conditions of the feed screw and the guide in a feed screw device comprising a motor, a feed screw that rotates in response to driving of the motor, a driven object that is screw-fed in response to rotation of the feed screw, and a guide that guides movement of the driven object, and further comprising a first position detector that detects a rotational position of the motor as first position information, and a second position detector that detects a position of the driven object in a screw feed direction as second position information, the feed screw device controlling a position of the driven object based on an input position command value, the first position information, and the second position information, the diagnostic device comprising: an elastic deformation amount calculation unit that calculates an elastic deformation amount from the first position information and the second position information; a torque command value separation unit that separates a torque command value related to control of a position of the driven object into a linear component torque and a rotational component torque by using the elastic deformation amount and a previously calculated axial stiffness of the feed screw device; a preload reduction rate calculation unit that calculates a preload reduction rate of the feed screw by using the rotational component torque; a shank stiffness calculation unit that calculates a new shank stiffness of the feed screw device using the preload reduction rate; a convergence determination unit that determines whether or not the axial stiffness of the feed screw device has converged based on the axial stiffness of the feed screw device calculated currently and the axial stiffness of the feed screw device calculated previously, and repeatedly executes calculations in the elastic deformation amount calculation unit, the torque command value separation unit, the preload reduction rate calculation unit, and the axial stiffness calculation unit until the axial stiffness of the feed screw device has converged; a diagnosis unit that diagnoses a wear state of the guide from the linear component torque when the axial stiffness of the feed screw device converges, and a wear state of the feed screw from the rotational component torque, respectively; A diagnostic device for a feed screw device, comprising:

3. A feed screw device includes a motor, a feed screw that rotates in response to driving of the motor, a driven object that is screw-fed in response to rotation of the feed screw, and a guide that guides movement of the driven object, and also includes a first position detector that detects a rotational position of the motor as first position information and a second position detector that detects a position of the driven object in a screw feed direction as second position information, and the feed screw device controls a position of the driven object based on an input position command value, the first position information, and the second position information, comprising: a first step of calculating an elastic deformation amount from the first position information and the second position information; a second step of separating a torque command value related to control of a position of the driven object into a linear component torque and a rotational component torque using the elastic deformation amount and a previously calculated axial stiffness of the feed screw device; a third step of calculating a preload reduction rate of the feed screw by using the rotational component torque; a fourth step of calculating a new axial stiffness of the feed screw device using the preload reduction rate; a fifth step of determining whether or not the axial stiffness of the feed screw device has converged based on the currently calculated axial stiffness of the feed screw device and the previously calculated axial stiffness of the feed screw device, and repeating the first step to the fourth step until the axial stiffness of the feed screw device has converged; a sixth step of diagnosing a wear state of the guide from the linear component torque when the axial stiffness of the feed screw device has converged, and a wear state of the feed screw from the preload reduction rate; A diagnostic method for a feed screw device, comprising:

4. A diagnostic device for diagnosing wear conditions of the feed screw and the guide in a feed screw device comprising a motor, a feed screw that rotates in response to driving of the motor, a driven object that is screw-fed in response to rotation of the feed screw, and a guide that guides movement of the driven object, and further comprising a first position detector that detects a rotational position of the motor as first position information, and a second position detector that detects a position of the driven object in a screw feed direction as second position information, the feed screw device controlling a position of the driven object based on an input position command value, the first position information, and the second position information, the diagnostic device comprising: an elastic deformation amount calculation unit that calculates an elastic deformation amount from the first position information and the second position information; a torque command value separation unit that separates a torque command value related to control of a position of the driven object into a linear component torque and a rotational component torque by using the elastic deformation amount and a previously calculated axial stiffness of the feed screw device; a preload reduction rate calculation unit that calculates a preload reduction rate of the feed screw by using the rotational component torque; a shank stiffness calculation unit that calculates a new shank stiffness of the feed screw device using the preload reduction rate; a convergence determination unit that determines whether or not the axial stiffness of the feed screw device has converged based on the axial stiffness of the feed screw device calculated currently and the axial stiffness of the feed screw device calculated previously, and repeatedly executes calculations in the elastic deformation amount calculation unit, the torque command value separation unit, the preload reduction rate calculation unit, and the axial stiffness calculation unit until the axial stiffness of the feed screw device has converged; a diagnosis unit that diagnoses a wear state of the guide from the linear component torque when the axial stiffness of the feed screw device converges, and a wear state of the feed screw from the preload reduction rate; A diagnostic device for a feed screw device, comprising:

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