JP6726646B2 - Bearing screw diagnostic method in lead screw device - Google Patents

Description

The present invention relates to a diagnostic method for diagnosing a state of a bearing that axially supports a feed screw in a feed screw device that moves a movable body by rotating the feed screw.

2. Description of the Related Art Conventionally, some machine tools include a feed screw device that moves a moving body such as a table by rotating a feed screw to position the moving body at a specific position. In the feed screw of such a feed screw device, for example, due to elastic deformation of the feed screw due to frictional resistance, backlash of the meshing portion of the feed screw, and the like, a position error occurs between the position in the forward direction command and the position in the reverse direction command. (So-called lost motion) occurs. This lost motion increases due to, for example, wear and looseness of the bearing supporting the feed screw due to deterioration over time. When the lost motion increases, the positioning accuracy of the feed screw device is lowered, and the processing accuracy cannot be ensured. In addition, if the machine is continuously used in a state where the so-called backlash with increased lost motion is large, it causes a major failure of the machine body, so that it is necessary for an operator or the like to regularly inspect. However, if the inspection is performed only by the operator, the burden on the operator becomes large. Therefore, as described below, techniques and methods have been devised for assisting or substituting inspection work by machine tools.

For example, in Patent Document 1, the lost motion amount is calculated using a touch sensor. Further, in Patent Document 2, a stopper is provided at the stroke end of the feed shaft, and the amount of play (lost motion) is calculated from the difference between the position of the moving body (machine coordinate) abutted against the stopper and the machine coordinate stopped by the torque limiting function. The amount) is calculated. Furthermore, in Patent Document 3, the first position detector that detects the position of the moving body and the second position detector that detects the rotational position of the motor are used, and the error in the detection results of both position detectors is the moving body. It is said that the lost motion amount is calculated based on the amount of change before and after the reversal of the moving direction of.

JP-A-8-1405 JP, 2002-132310, A JP, 2014-235587, A

The methods described in Patent Documents 1 to 3 are methods for calculating the lost motion amount of the entire feed shaft mechanism. Here, considering a typical friction element that causes a lost motion in the feed screw device, there are a feed screw, a guide, and a bearing that supports the feed screw. However, the wear of the bearing also affects the pretension of the feed screw, and if the pretension of the feed screw decreases, the amount of thermal displacement of the feed screw increases. Due to this, the dimensional accuracy may deteriorate. Further, depending on the balance of the rigidity of the elements constituting the feed shaft mechanism, the influence of the wear of the bearing on the lost motion may be small. Therefore, in order to more accurately diagnose the state of the feed screw device and effectively prevent machining defects, not only the wear state of the entire feed shaft mechanism as in the conventional case is diagnosed, but also the wear state of the bearing is checked. It is required to make a diagnosis separately from wear of the feed screw.

Therefore, the present invention has been made in view of the above requirements, and an object of the present invention is to provide a method for diagnosing a bearing in a feed screw device, which can diagnose the wear state of the bearing that supports the feed screw in the feed screw device. Is.

In order to achieve the above object, the present invention relates to a motor, a feed screw with a pretension that rotates according to the driving of the motor, a bearing that axially supports the feed screw, and a rotation of the feed screw. A position detector for detecting the position of the moving body in the screw feeding direction as position information, and a predetermined position calculated from the input position command value and the position information. A method of diagnosing a bearing in a feed screw device, the method comprising: diagnosing a wear state of the bearing by using a characteristic amount of One step, a second step of calculating the characteristic amount during acceleration at both stroke ends during the stroke operation, and a characteristic amount during deceleration at both stroke ends, respectively, and a second step during the calculated acceleration at one stroke end The difference between the change amount of the feature amount from the predetermined first reference value and the change amount of the calculated feature amount during acceleration at the other end of the stroke from the predetermined second reference value, and the calculated amount at one end of the stroke. The difference between the change amount of the characteristic amount during deceleration from the predetermined third reference value and the change amount of the calculated characteristic amount during deceleration at the other end of the stroke from the predetermined fourth reference value is a predetermined threshold value. If it exceeds, a third step of diagnosing that the bearing is in a worn state is executed.

According to the present invention, a first step of moving a moving body in a predetermined manner over a predetermined stroke distance, a characteristic amount during acceleration at both ends of the stroke during the stroke operation, and a characteristic during deceleration at both ends of the stroke. a second step of the amount calculated respectively, and the amount of change from the first reference value of the feature amount of a predetermined accelerating calculated at the stroke end, the predetermined feature quantity during acceleration calculated in the stroke other end second The difference from the reference value, the change amount of the calculated feature amount during deceleration at one end of the stroke from a predetermined third reference value, and the predetermined amount of the calculated feature amount during deceleration at the other end of the stroke. If the difference from the change amount from the four reference values exceeds a predetermined threshold value, the third step of diagnosing that the bearing is in a worn state is executed. In this way, the wear state of the feed screw bearing is diagnosed separately from the wear of the feed screw, so that the state of the feed screw device can be diagnosed more accurately, and thus machining defects can be effectively prevented. You can

It is a block block diagram of a feed screw device. It is explanatory drawing which showed the initial state, the state where the feed screw was worn, and the state where the bearing was worn regarding the rigidity of the whole shaft containing a feed screw and a bearing at the time of performing a predetermined stroke operation. It is a flowchart figure which concerns on the diagnostic operation of the wear state of a bearing. It is explanatory drawing which showed the result of having calculated the wear state of the feed screw and the bearing by the method shown in the modification of this invention, respectively.

Hereinafter, a method of diagnosing a bearing in a feed screw device according to an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of the feed screw device.
The feed screw device includes a servo motor 7, a feed screw 8 that is rotated by driving the servo motor 7, and a moving body (for example, a table) 9 that is screw-fed by the rotation of the feed screw 8. Further, the servo motor 7 is provided with a first position detector 6 for detecting a rotational position of the servo motor 7 (hereinafter referred to as first position information). Further, a scale 10 is arranged in parallel with the feed screw 8, and the scale 10 has a position in the screw feed direction of the moving body 9 (position information specified in the claims, hereinafter referred to as a second position). A second position detector 11 for detecting (referred to as information) is slidably attached along the scale 10 in association with the movement of the moving body 9.

In the feed screw device, the position deviation is calculated by subtracting the second position information fed back from the second position detector 11 from the position command value input from the NC device (not shown) by the subtracter 1. Further, the position control unit 2 calculates the speed command value based on the position deviation. Further, based on the speed command value and the rotation 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 speed control unit 3 outputs a motor torque command. Calculate the value. Then, the motor torque command value is amplified by the current control unit 4 and then output to the servo motor 7.

Here, the state diagnosis of the bearing that pivotally supports the feed screw 8 in the feed screw device, which is a main part of the present invention, will be described.
The feed screw device is provided with a diagnosis unit 13 for diagnosing the state of the feed screw 8 (in particular, the worn state of the bearing that supports the feed screw 8). The position command value from the NC device is input to the diagnosis unit 13, and the position deviation calculated by the subtractor 1 is input. Then, the diagnosis unit 13 diagnoses the wear state of the bearing based on the position command value and the position deviation.

Further, as a premise of diagnosis, in the lead screw device according to the present invention, regarding the rigidity of the entire shaft including the feed screw and the bearing when a predetermined stroke operation is performed, the initial state, the state where the feed screw is worn, and the bearing are FIG. 2 shows the worn states. As is clear from FIG. 2, when the feed screw is worn, the rigidity of the entire shaft is reduced substantially uniformly regardless of the stroke position of the moving body, while when the bearing is worn, the moving body is moved. There is a difference in the reduction of the rigidity of the entire shaft depending on the stroke position. Therefore, the present invention utilizes this characteristic to diagnose the wear state of the bearing.

Then, by utilizing the characteristics as described above, in the present invention, starting from the diagnostic operation in the initial state, the similar diagnostic operation is periodically executed to calculate a predetermined characteristic amount, and the characteristic amount is in the initial state. The state of the bearing is diagnosed according to how much it has changed from the characteristic amount during the diagnostic operation.
More specifically, referring to the flow chart shown in FIG. 3, for example, as a diagnostic operation, the moving body can be realized at a predetermined constant speed (a feed screw device can be realized so that the screw feeding direction of the moving body is reversed at both ends of the stroke. Full stroke operation (stroke operation with stroke distance from the maximum position on the plus side to the minimum position on the minus side) is performed for one stroke at the maximum speed is desirable. In addition, as the characteristic amount, the maximum absolute value of the position deviation during acceleration and deceleration at both ends of the full stroke operation is calculated. That is, first, the diagnosis operation is performed in the initial state (S1), and the first feature amount Epa_n during acceleration on the stroke plus end side, the second feature amount Emd_n during deceleration on the stroke minus end side, the stroke minus end side The third feature amount Ema_n during acceleration in step S4 and the fourth feature amount Epd_n during deceleration at the stroke plus end side are calculated (S2). Then, since this time is the diagnostic operation in the initial state (determined as YES in S3), the first to fourth feature quantities are stored as reference data with n=0 (S7). After that, the diagnostic operation is periodically executed at a desired timing (S1), and at the time of the diagnostic operation, the same first to fourth characteristic amounts as described above are calculated (S2). Since this is not the initial state this time (NO in S3), how much these feature quantities have changed from the first to fourth feature quantities calculated this time and the already stored reference data. Is calculated (S4), and if the change exceeds a predetermined threshold value L (YES in S4), it is determined that the bearing is likely to be worn (S5). On the other hand, if the threshold value L is not exceeded (NO in S4), it is determined that the bearing is not so worn (S6). With respect to the change in the above-mentioned characteristic amount at both ends of the stroke from the initial state, the change amount contributed by the wear of the feed screw is small, and therefore the wear of the bearing can be accurately diagnosed by the determination in S4. However, if the weight of the moving body at the time of diagnosis is significantly different because the moving body is a table or the like and the object placed on the table is different, etc. Also, the change of will greatly change due to the difference in the weight. Therefore, in order to accurately diagnose the wear state of the bearing, the weight state of the moving body in each diagnosis operation must be the same.

According to the method of diagnosing the bearing in the feed screw device as described above, the first step of causing the moving body 9 to perform a full stroke operation and the absolute position deviation during acceleration and deceleration at both ends in the full stroke operation. The maximum value is calculated as the feature amount, that is, the first feature amount Epa_n during acceleration on the stroke plus end side, the second feature amount Emd_n during deceleration on the stroke minus end side, and the acceleration on the stroke minus end side Of the third feature amount Ema_n and the fourth feature amount Epd_n during deceleration on the stroke plus end side, the first to fourth feature amounts calculated this time, and the first to first calculated in the initial state. From the reference data, which is the fourth characteristic amount, how much the characteristic amounts are changing is calculated, and when the change exceeds a predetermined threshold value L, it is diagnosed that the bearing is in a worn state. Perform the process and. In this way, the wear state of the feed screw bearing is diagnosed separately from the wear of the feed screw, so that the state of the feed screw device can be diagnosed more accurately, and thus machining defects can be effectively prevented. You can

The method for diagnosing the feed screw in the feed screw device according to the present invention is not limited to the mode of the above-described embodiment, and the specific configuration relating to the diagnosis, as well as the overall configuration of the feed screw device, can be obtained. The above can also be appropriately changed as necessary without departing from the spirit of the present invention.

For example, in the above-described embodiment, the full stroke operation is performed in connection with the diagnosis operation, but the full stroke distance is not divided, but the full stroke distance is divided into a plurality of blocks, and the stroke operation is performed for each division to acquire the feature amount. You may do it. The results showing the wear state of the bearing thus obtained are shown in FIG. By performing the diagnosis divided into a plurality of blocks in this way, not only the amount of change at both ends of the stroke but also the tendency of the entire feed shaft mechanism can be grasped, so that more accurate diagnosis can be performed.
In addition, the history of the amount of change in the characteristic amount is stored each time the diagnosis is performed, and the wear state of the bearing is diagnosed not only from the comparison result with the reference value but also from the change tendency of the amount of change based on the history. May be.

1... Subtractor, 7... Servo motor, 8... Feed screw, 9... Moving body, 11... Second position detector (position detector), 13... Diagnostic unit

Claims (1)

A motor, a feed screw to which a pre-tension is applied that rotates according to the drive of the motor, a bearing that axially supports the feed screw, and a moving body that is screw-fed according to the rotation of the feed screw. Along with the position detector that detects the position of the moving body in the screw feed direction as position information, the wear state of the bearing is determined using a predetermined feature amount calculated from the input position command value and the position information. A method of diagnosing a bearing in a feed screw device including a diagnostic unit for diagnosing,
A first step of stroke-moving the moving body in a predetermined manner over a predetermined stroke distance;
A second step of calculating the characteristic amount during acceleration at both ends of the stroke during the stroke operation and the characteristic amount during deceleration at both ends of the stroke, respectively;
The difference between the amount of change from the first reference value predetermined characteristic quantity during acceleration that the calculated at the stroke end, the amount of change from the second reference value of the feature amount of a predetermined accelerating with the calculated at the stroke other end , And a change amount of the calculated feature amount during deceleration at one end of the stroke from a predetermined third reference value, and a change amount of the calculated feature amount during deceleration at the other end of the stroke from a predetermined fourth reference value. And a third step of diagnosing that the bearing is in a worn state when the respective differences exceed a predetermined threshold value, the method of diagnosing the bearing in the feed screw device.

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