JP7612486B2 - Diagnostic method and diagnostic device for feed screw device - Google Patents

Description

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 rotating a feed screw.

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 specific direction by rotating a feed screw. In such feed screw devices, wear of the feed screw due to aging or damage due to the inclusion of foreign matter can cause problems such as reduced operating accuracy and abnormal noise during operation. Therefore, in order to prevent such problems from occurring, it is desirable to replace the mechanical elements before a problem occurs. Therefore, various diagnostic methods have been devised in the past to diagnose the condition of the mechanical elements in a feed screw device.

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, and estimates the elastic deformation of the feed screw from that driving force, while calculating a position deviation from the rotational position information of the motor and the position information of the table, and diagnosing the damage condition of the driven object by comparing the elastic deformation amount with the position deviation. In addition, 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 that lost motion value and the current value supplied to the motor.

JP 2009-154274 A JP 2013-69192 A

However, the diagnostic methods described in Patent Documents 1 and 2 do not separate the load components for 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 stiffness due to wear on 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.

The present invention has been made in consideration of the above problems, and aims to provide a diagnostic method and device for a feed screw device that can diagnose the wear of the feed screw and the wear of the guide separately, even when wear occurs in both the feed screw and the guide in a complex manner.

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 driving 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 a first step of calculating an elastic deformation amount from the first position information and the second position information, and a second step of calculating a wear state of the feed screw and the guide, the first step comprising : a second step of separating 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; a third step of calculating a preload reduction rate of the feed screw using the rotational component torque; a fourth step of newly calculating the 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 to fourth steps until the axial stiffness of the feed screw device has converged; and a 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 driving 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 based on the input position command value, the first position information, and the second position information. The elastic deformation amount calculation unit 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 based on the elastic deformation amount and a previously calculated axial stiffness of the feed screw device. a torque command value separating unit which separates a torque command value relating to control of the feed screw device into a linear component torque and a rotational component torque; a preload reduction rate calculating unit which calculates a preload reduction rate of the feed screw using the rotational component torque; a axial stiffness calculating unit which newly calculates an axial stiffness of the feed screw device using the preload reduction rate; a convergence determining unit which determines whether or not the axial stiffness of the feed screw device has converged based on a currently calculated axial stiffness of the feed screw device and a previously calculated axial stiffness of the feed screw device, and causes the elastic deformation amount calculating unit, the torque command value separating unit, the preload reduction rate calculating unit, and the axial stiffness calculating unit to repeatedly execute calculations until convergence is achieved; and a diagnosing unit which diagnoses a wear state of the guide from the linear component torque and a wear state of the feed screw from the rotational component torque when the axial stiffness of the feed screw device has converged.
Furthermore, 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 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 a first step of calculating an elastic deformation amount from the first position information and the second position information, and a second step of calculating a wear state of the feed screw and the guide, the first step including: a second step of separating 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 third step of calculating a preload reduction rate of the feed screw using the rotational component torque; a fourth step of newly calculating the axial stiffness of the feed screw device using the preload reduction rate; a 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 to fourth steps until the axial stiffness of the feed screw device has converged; and a sixth step of diagnosing a wear state of the guide from the linear component torque and a wear state of the feed screw from the preload reduction rate when the axial stiffness of the feed screw device has converged.
In addition, 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 driving 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 based on the input position command value, the first position information, and the second position information. the torque command value separating unit separating a torque command value related to position control into a linear component torque and a rotational component torque; a preload reduction rate calculating unit calculating a preload reduction rate of the feed screw using the rotational component torque; a axial stiffness calculating unit calculating a new axial stiffness of the feed screw device using the preload reduction rate; a convergence determining unit determining whether or not the axial stiffness of the feed screw device has converged based on a currently calculated axial stiffness of the feed screw device and a previously calculated axial stiffness of the feed screw device, and causing the elastic deformation amount calculating unit, the torque command value separating unit, the preload reduction rate calculating unit, and the axial stiffness calculating unit to repeatedly execute calculations until convergence is achieved; and a diagnosing unit diagnosing a wear state of the guide from the linear component torque and a wear state of the feed screw from the preload reduction rate when the axial stiffness of the feed screw device has converged.

According to the present invention, the elastic deformation amount is calculated from the first position information and the second position information, the elastic deformation amount and the previously calculated axial stiffness of the feed screw device are used to separate the torque command value related to the control of the position of the driven object into a linear component torque and a rotational component torque, the rotational component torque is used to calculate the preload reduction rate of the feed screw, the preload reduction rate is used to newly calculate the axial stiffness of the feed screw device, 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 the wear state of the guide is diagnosed from the linear component torque when the axial stiffness of the feed screw device has converged, 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 occurs in both the feed screw and the guide in a complex manner, the wear of the feed screw and the wear of the guide can be diagnosed individually.

FIG. 2 is a block diagram of a feed screw device. 4 is a flowchart showing a diagnostic method in the diagnostic device.

The following is a detailed explanation of a diagnostic method and diagnostic device for diagnosing the condition of a feed screw device, which is one embodiment of the present invention, with reference to the drawings.

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 (in FIG. 1, only the guide on the table 9 side among the elements constituting the guide 15 is shown). 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. Furthermore, 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.

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

Here, the diagnosis of the condition 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, and 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.

To explain the above diagnosis in detail with reference to the flowchart shown in Figure 2, 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 this difference as the elastic deformation amount ε to the diagnosis unit 13 (S1). When detecting the first position information and second position information related to the calculation of this elastic deformation amount ε, it is preferable to detect when the table 9 is being fed at a constant speed, since it is often difficult to estimate the machine state when the table 9 is accelerating or decelerating, moving at high speed, or reversing the driving direction, due to the large influence of inertial forces and other factors or corrections being made.

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 time of the first calculation is an initial set value that is set in advance.

In addition, 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. Then, the preload reduction rate ΔF(n) of the feed screw 8 is calculated by the following formula 4.

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). In calculating this axial stiffness K(n), the initial axial stiffness K _nut0 of the nut when it is not yet worn and an initial preload load F _a0 is applied is calculated by the following formula 5, and the axial stiffness K _nut of the nut under the preload Fa is expressed by the following formula 6 using the initial axial stiffness K _nut0 of the nut and the preload reduction rate ΔF. Therefore, the axial stiffness K(n) of the entire feed screw device is calculated by the following formula 7. The axial stiffness of each part that is not involved in the stiffness of the feed screw is set in advance.

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 shaft stiffness K(n) has converged (S5), and repeats the processes of S2 to S5 until the shaft stiffness K(n) has converged. This convergence determination is made based on whether 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).

Finally, the diagnostic unit 13 determines whether the linear component torque Tg(n) after the convergence determination is below a predetermined linear component threshold (S6), and if the linear component torque Tg(n) is below the linear component threshold (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 (S8), and if the rotational component torque Tr(n) is below the rotational component threshold (YES in S8), it diagnoses that wear of the feed screw 8 is progressing (S9).

According to the above-described diagnostic method and diagnostic device for a 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 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. When the axial stiffness K(n) of the feed screw device converges, the wear state of the guide 15 is diagnosed from the linear component torque, 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.

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 the specific control related to the diagnosis can be modified as necessary without departing from the spirit of the present invention.

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 is 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.

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 section), 13: Diagnosis section (torque command value separation section, preload reduction rate calculation section, shaft stiffness calculation section, convergence determination section, diagnosis section).

Claims (4)

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;
and a 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 rotational component torque. 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 ;
and a diagnostic unit that diagnoses 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. 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;
and a 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. 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 diagnostic unit that diagnoses 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.

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