MPhil-2006-Singh.pdf (65.6 MB)
Accuracy testing of coordinate measuring machines
thesis
posted on 2013-02-25, 14:02 authored by Jagpal SinghThe proliferation of the bridge type Coordinate Measuring Machine (CMM) within
the manufacturing environment has resulted in it being a core and important tool in
the manufacturing cycle. In many circumstances, CMM's provide excellent
measurement services, but when manufacturing tolerances are small, then detailed
understanding of CMM error sources is ideally required, to maximise the confidence
in the measurement data
Multi-axis measurement arms (MMAs) are a unique subset of Coordinate Measuring
Machines (CMMs). They incorporate a large number of degrees of freedom and
compact design based on multi-element arm construction, which provides tremendous
versatility of movement and access around an object being measured. The
consequences of the flexibility of MMAs is that the volumetric accuracy and
repeatability specifications can be substantially inferior to those of more traditionally
designed CMMs.
Various CMM error sources have been previously identified, evaluated and
quantified, on a machine by machine basis. Many of these sources (parametric errors
for instance) are systematic and considered to be minimised from the measurement
system via verification procedures and the generation of software based error maps
(applying compensations). However a number of error elements still occur which
need to be considered.
The research reported here has considered variation between manual and automatic
probe tip qualification and the influence on the confidence of the measurement data
for a bridge type CMM. A range of probe orientation angles were examined, and the
results presented focused on the orientations most readily used. For the MMA the
manufacturers four probe tip calibration techniques recommended were executed and
the repeatability tested with the arm in different resolves. The investigation was
extended further to test the volumetric performance of a multi-axis measurement arm,
with repeated systematic measurements of a calibrated reference sphere.
The research has examined the influence of various styli on the confidence of the
measurement data on a bridge type CMM. Taking into account a number of existing
texts which consider different styli length, this work has extended the analysis to
consider the influence of stylus design and stylus material. Specifically, styli from two
different manufacturers were tested under the same conditions. Varying lengths of
stylus were examined, manufactured from stainless steel, tungsten carbide, ceramic
and carbon fibre. Further effects as a function of solid or hollow cross sectional
geometry and styli made up of extension joints were considered and are presented
here.
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© J. SinghPublication date
2006Notes
A Master's Thesis. Submitted in partial fulfilment of the requirements for the award of Master of Philosophy of Loughborough University.Language
- en