Accuracy diagnostic device and accuracy diagnostic method for machine tool

An accuracy diagnostic method for a machine tool that diagnoses an accuracy of the machine tool, wherein the machine tool includes a change amount detection unit that measures a temperature change amount and a change-amount-reference value recording unit that records and updates the temperature as a reference value of the change amount in response to a reference-value recording command, which is commanded by any one of (1) an operating panel and/or a screen, (2) executing a program, and (3) in conjunction with a specific operation of the machine tool, the change quantity changing due to an installation environment and an operational motion, wherein the accuracy diagnostic method comprises:

• obtaining the change amount from the change amount detection unit;
• diagnosing a change of the accuracy of the machine tool based on a first change index and a second change index;
• and
• deriving a first diagnostic result by diagnosing the change of the accuracy based on the first change index, and deriving a second diagnostic result by diagnosing the change of the accuracy based on the second change index,
• wherein the first change index and the second change index are each derived from the temperature change amount,
• wherein the first change index is derived from a magnitude of a change of the change amount per a predetermined period, and the second change index is calculated from a difference between the current change amount and the reference value, which is recorded in the change-amount-reference-value recording unit,
• wherein a value of the second change index is changed when the reference-value recording command is commanded,
• wherein the first diagnostic result is represented as good or poor depending on whether the measured change of accuracy is above or below a predetermined threshold, and the second diagnostic result is represented as good or poor depending on whether the measured change of accuracy is above or below a predetermined threshold, and
• wherein when the first diagnostic result is good and the second diagnostic result is poor, as an accuracy countermeasure for ensuring the accuracy of the machine tool, using a combination of the first diagnostic result and the second diagnostic result, an on-machine-measurement with the machine tool is started and a reset of a correction value of a coordinate of the machine tool is performed, and a current change amount recorded as the reference value.