Performance evaluation of a new taut wire system for straightness measurement of machine tools

Oleg Borisov,Andrew Longstaff,Simon Fletcher,Alan Myers

doi:10.1016/j.precisioneng.2014.01.003

Oleg Borisov, Andrew Longstaff + Show 2 more

Open Access

https://doi.org/10.1016/j.precisioneng.2014.01.003

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Journal: Precision Engineering	Publication Date: Jan 30, 2014
Citations: 12	License type: cc-by

Affiliation: University of Huddersfield

Abstract

This paper describes evaluation of a method of measuring the straightness of motion of machine tool axes using a taut wire and an optical sensor head mounted at the tool point location. In contrast to commonly used taut wire instruments, straightedges or laser-based methods, this solution combines low cost, simplicity of setup and automated data capture while achieving state of the art accuracy suitable for application on precision machine tools. A series of tests are discussed which examine the performance of the new sensing head and different wires which highlight the suitability of the taut wire properties as a straightness reference. Experimental results obtained on a production machine tool are provided with respect to the accuracy and repeatability of both the proposed taut wire system and a laser interferometer operated under the same conditions. The reference errors of wires made of different materials are compared and the wire catenary is separated from the measurement results. The uncertainty budget for taut wire and laser systems is presented and expanded uncertainty of 4 μm obtained for both. During the experiment, the method showed excellent repeatability with two standard deviations of 1.5 μm over a measuring range of 1.5 m; this performance matches that of a commercial laser interferometer-based straightness reference to within 0.1 μm.

Highlights

Straightness errors, along with positioning and angular errors, are present in every linear motion system [1]
This paper describes evaluation of a method of measuring the straightness of motion of machine tool axes using a taut wire and an optical sensor head mounted at the tool point location
A series of tests are discussed which examine the performance of the new sensing head and different wires which highlight the suitability of the taut wire properties as a straightness reference

Summary

Introduction

Straightness errors, along with positioning and angular errors, are present in every linear motion system [1]. In order to do this, a straightness reference and a displacement indicator are required This gives rise to a variety of straightness methods utilizing straightedges, taut wires or laser interferometers. The reason for such a dependency is the physical contradiction between different requirements of the straightness reference: it must be long, stable and straight, ideally two-dimensional and, which is important, capable of being placed at any area of the machine’s workspace to represent the desired tool point path Finding such an artefact presents a significant challenge that leads to a compromise between the factors. Partial overlapping introduced by Pahk et al [3] extends the potential measuring range but the speed of process, accuracy and uncertainty of measurement can be compromised by the size and quantity of overlaps Another approach utilizes laser-based techniques relying on a highly coherent light beam, having long axial ranges suitable for most machine tools and a high quoted level of accuracy. Despite being a well-known reference for measuring straightness [1,4,11], a detailed analysis of the taut wire measurement for longrange measurement has not been the subject of published research

Method

Test setup

Test conditions

Performance evaluation

Uncertainty analysis

Findings

Conclusions