This application claims the benefit of Japanese Patent Application Number 2019-202550 filed on Nov. 7, 2019, the entirety of which is incorporated by reference.

BACKGROUND

1. Technical Field

The disclosure relates to a method and a device that diagnose an abnormality of a feed axis device, in mechanical equipment such as a machine tool including the feed axis device by a ball screw.

2. Related Art

For example, among feed axis devices of machine tools, a system that transmits rotational motion of a motor to a ball screw to drive the ball screw is often used. However, in a machine that has been operated for several years, a preload loss by abrasion and a damage due to an entrance of foreign matter, a lubrication failure, or the like cause an accuracy failure, an abnormal noise, and the like possibly to occur. In the above-described state, a trouble of a shape defect, a failure in a pick feed direction, and the like of a workpiece occurs. Accordingly, it is preferred that machine components of the feed axis device such as the ball screw, a support bearing, and a guide be replaced before a deterioration or a damage occurs to cause the trouble.

Therefore, to know a state of the machine component of the feed axis device, it has been proposed various diagnostic methods such as a method that internally disposes a displacement sensor to measure a positioning accuracy, and a method that detects and diagnoses vibration of the ball screw, the support bearing, and a linear guide by a vibration sensor. In particular, Japanese unexamined patent application publication No. 2007-219689 (JP-A-2007-219689) discloses a method that calculates a deflection amount as a difference between a position detection value of a driven body and a position detection value of a motor and displays a warning for an abnormality of a machine when the magnitude of the deflection amount exceeds a threshold. Further, Japanese unexamined patent application publication No. 2013-164386 (JP-A-2013-164386) discloses a method that identifies which component that constitutes a ball screw has an abnormality by detecting a vibration and a rotational speed of the ball screw to perform a frequency analysis, and an order ratio analysis based on the rotational speed or a Campbell analysis based on the rotational speed, on a vibration signal.

A common machine tool often employs a semi-closed loop method where only a rotary encoder is used. However, since the machine in JP-A-2007-219689 employs a full-closed loop method, it cannot be applied to a machine that employs the semi-closed loop method. Further, in JP-A-2007-219689, a deflection amount detector is employed, and in JP-A-2013-164386, a sensor for diagnosis is added. In the methods, since there are more components than those in the minimum configuration used for controlling the feed axis device, there is a problem of causing a cost increase, and the increased parts that possibly break down causes a problem of an increased failure risk.

Therefore, the disclosure has been made in view of the above-described problems. It is an object of the disclosure to provide an abnormality diagnostic method and an abnormality diagnostic device that can perform an abnormality diagnosis for a feed axis device at low cost and low risk using a minimum configuration used for controlling the feed axis device in a machine tool.

SUMMARY

In order to achieve the above-described object, there is provided an abnormality diagnostic method for a feed axis device according to a first aspect of the disclosure. The abnormality diagnostic method diagnoses an abnormality of the feed axis device including a screw shaft and a nut. The feed axis device is incorporated in mechanical equipment. The abnormality diagnostic method includes the following three steps, operation control step, detecting step and abnormality diagnosis step. The operation control step is controlling an operation of the feed axis device such that the screw shaft operates in a predetermined operating pattern. The detecting step is detecting a physical quantity signal generated from the feed axis device. The abnormality diagnosis step is performing an abnormality diagnosis for the feed axis device based on the physical quantity signal detected by the detecting in accordance with a predetermined abnormality diagnosis algorithm. The abnormality diagnosis step includes performing a frequency analysis on the physical quantity signal to extract respective frequencies corresponding to a plurality of operating positions in the operating pattern and performing the abnormality diagnosis based on change of the frequencies corresponding to the respective operating positions.

In the disclosure of a second aspect in the above-described configuration, the abnormality diagnosis step includes comparing the change of the frequencies corresponding to the respective operating positions with bending vibration modes in the respective operating positions of the feed axis device to perform the abnormality diagnosis.

In the disclosure of a third aspect in the above-described configuration, the abnormality diagnosis compares proportions of the frequencies that are included within a predetermined region formed based on the bending vibration mode with a predetermined threshold, the frequencies corresponding to the respective operating positions.

In order to achieve the above-described object, there is provided an abnormality diagnostic device for a feed axis device according to a fourth aspect of the disclosure. The abnormality diagnostic device diagnoses an abnormality of the feed axis device including a screw shaft and a nut. The feed axis device is incorporated in mechanical equipment. The abnormality diagnostic device includes an operational control unit, a detecting unit, and an abnormality diagnosis unit. The operational control unit controls an operation of the feed axis device such that the screw shaft operates in a predetermined operating pattern. The detecting unit detects a physical quantity signal generated from the feed axis device. The abnormality diagnosis unit performs an abnormality diagnosis for the feed axis device based on the physical quantity signal detected by the detecting unit in accordance with a predetermined abnormality diagnosis algorithm. The abnormality diagnosis unit performs a frequency analysis on the physical quantity signal to extract respective frequencies corresponding to a plurality of operating positions in the operating pattern and performs the abnormality diagnosis based on change of the frequencies corresponding to the respective operating positions.

In the disclosure of a fifth aspect in the above-described configuration, the abnormality diagnosis unit compares change of the frequencies corresponding to the respective operating positions with bending vibration modes in the respective operating positions of the feed axis device to perform the abnormality diagnosis.

In the disclosure of a sixth aspect in the above-described configuration, the abnormality diagnosis compares proportions of the frequencies that are included within a predetermined region formed based on the bending vibration mode with a predetermined threshold, the frequencies corresponding to the respective operating positions.

With the disclosure, the abnormality diagnosis can be performed without adding another component such as a sensor to the minimum configuration used for the control of the feed axis device. As a result, the increase of a failure risk due to the addition of, for example, the sensor do not occur. Therefore, the abnormality diagnosis for the feed axis device can be performed at low cost and low risk.

