Patent ID: 11921004
Assignee: NSK LTD.
Field: Measurement (Instruments)
Classification: CPC G  F | IPC F  G

Claim 0:
1. A method for detecting decreased preload in a ball screw, which is a method for detecting a decrease in a preload applied to the ball screw, the method comprising:
a vibration measurement step of measuring vibration during operation of the ball screw;
a calculation processing step of acquiring a vibration value of a vibration signal in a specific frequency band among vibration signals obtained at the vibration measurement step; and
an abnormality detection step of determining that a decrease in the preload has occurred in the ball screw when the vibration value is less than a threshold determined based on a vibration value in an initial stage of the operation of the ball screw or during a normal operation of the ball screw,
wherein the specific frequency band is less than 10 kHz and is set based on and includes a natural frequency of the ball screw,
wherein the ball screw comprises a ball screw shaft which is rotatably supported by rolling bodies of support bearings at axial ends of the ball screw shaft,
wherein the ball screw further comprises:
at least one of a nut and a linear motion table; and
an acceleration sensor attached to the at least one of the nut and linear motion table, and

wherein the vibration measurement step of measuring the vibration during the operation of the ball screw comprises measuring the vibration by the acceleration sensor.