Inaccuracy of machine tools due to verification conditions

Abstract

Machine tool accuracy has become an area of competition in several industries. To improve accuracy, machine tools are periodically verified and compensated. Verification must be performed at a certain time under specific conditions. However, machine tools operate in an uncontrolled environment with changing conditions. Along with the measurement noise of verification systems, these are the main differences between working and verification conditions. This paper proposes a simplified linear model based on real tests to estimate the influence of temperature on the position of the tool centre point of a machine with the XFYZ configuration after verification. To achieve this, the equation of movement obtained from the kinematic model of the machine was modified to include the thermal influence. The influence of the measurement noise of a laser tracker, as the verification system, was also modelled. Using both models, the effectiveness of using compensation functions outside the verification conditions was studied, considering the temperature variations and measurement noise. The test results showed that, despite the use of a simplified model, the measurement noise reduced the compensation efficacy by approximately 25%. Moreover, the use of compensation functions obtained with a temperature different from that of working conditions can worsen the accuracy of the machine.