Thermal error compensation of a 5-axis machine tool using indigenous temperature sensors and CNC integrated Python code validated with a machined test piece

• Published in: Precision engineering Vol. 66; pp. 21 - 30
• Main Authors: Mareš, Martin, Horejš, Otakar, Havlík, Lukáš
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.11.2020
• Subjects: Accuracy; Compensation; Implementation; Machine tool; Thermal error; Thermal error; Accuracy; Machine tool; Compensation; Implementation
• ISSN: 0141-6359; 1873-2372
• DOI: 10.1016/j.precisioneng.2020.06.010

Achieving high workpiece accuracy is the long-term goal of machine tool designers. There are many causes for workpiece inaccuracy, with thermal errors being the most common. Indirect compensation (using prediction models for thermal errors) is a promising strategy to reduce thermal errors without increasing machine tool costs. The modelling approach uses transfer functions to deal with this issue; it is an established dynamic method with a physical basis, and its modelling and calculation speed are suitable for real-time applications. This research presents compensation for the main internal and external heat sources affecting the 5-axis machine tool structure including spindle rotation, three linear axes movements, rotary C axis and time-varying environmental temperature influence, save for the cutting process. A mathematical model using transfer functions is implemented directly into the control system of a milling centre to compensate for thermal errors in real time using Python programming language. The inputs of the compensation algorithm are indigenous temperature sensors used primarily for diagnostic purposes in the machine. Therefore, no additional temperature sensors are necessary. This achieved a significant reduction in thermal errors in three machine directions X, Y and Z during verification testing lasting over 60 h. Moreover, a thermal test piece was machined to verify the industrial applicability of the introduced approach. The results of the transfer function model compared with the machine tool's multiple linear regression compensation model are discussed. •A model using transfer functions is capable of partial linearisation of thethermomechanical issue of the machine tool (MT).•Spindle speed and all linear axis movement and table rotation impact on MT accuracy are considered in the model structure.•The model is implemented directly into a MT control system without any additional devices.•Only internal temperature signals are used as model inputs.•Model efficiency is verified by thermal test piece machining and results are compared with indigenous software compensation.