CMM’s Styli Length Effect On Error Propagation.
CMM’S STYLI LENGTH EFFECT ON ERROR
PROPAGATION
SHAHIRUL AINI BINTI KAMARUL KHISHAM
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
a
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
CMM’S STYLI LENGTH EFFECT ON ERROR PROPAGATION
This report submitted in accordance with requirement of the Universiti Teknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Manufacturing Process) with Honours.
By
SHAHIRUL AINI BINTI KAMARUL KHISHAM
FACULTY OF MANUFACTURING ENGINEERING
2009
a
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS LAPORAN PSM
TAJUK: CMM’s Styli Length Effect on Error Propagation
SESI PENGAJIAN: 2008/2009 Semester 2
Saya
SHAHIRUL AINI BINTI KAMARUL KHISHAM
mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti
Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:
1.
2.
3.
4.
Tesis adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis.
Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan
untuk tujuan pengajian sahaja dengan izin penulis.
Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran
antara institusi pengajian tinggi.
*Sila tandakan (√)
SULIT
(Mengandungi maklumat yang berdarjah keselamatan
atau kepentingan Malaysia yang termaktub di dalam
AKTA RAHSIA RASMI 1972)
TERHAD
(Mengandungi maklumat TERHAD yang telah ditentukan
oleh organisasi/badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh:
Alamat Tetap:
19-0-5, TMN BKT ANGKASA,
PANTAI DALAM,
59200 KUALA LUMPUR.
Cop Rasmi:
Tarikh: _______________________
Tarikh: _______________________
* Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan
dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.
a
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Karung Berkunci 1200, Ayer Keroh, 75450 Melaka
Tel : 06-233 2421, Faks : 06 233 2414
Email : [email protected]
FAKULTI KEJURUTERAAN PEMBUATAN
20 Mei 2009
Rujukan Kami (Our Ref) :
Rujukan Tuan (Your Ref):
Pustakawan
Perpustakawan UTeM
Universiti Teknikal Malaysia Melaka
Hang Tuah Jaya,
75450, Melaka
Saudara,
PENGKELASAN LAPORAN PSM SEBAGAI SULIT/TERHAD LAPORAN PROJEK
SARJANA MUDA KEJURUTERAAN PEMBUATAN (MANUFACTURING PROCESS):
SHAHIRUL AINI BINTI KAMARUL KHISHAM
Sukacita dimaklumkan bahawa laporan PSM yang tersebut di atas bertajuk
“CMM’s Styli Length Effect on Error Propagation” mohon dikelaskan
sebagai SULIT/TERHAD untuk tempoh LIMA tahun dari tarikh surat ini.
Sekian dimaklumkan. Terima kasih.
Yang benar,
……………………………………………………..
Dr. Mohd Rizal B. Salleh
Dekan ,
Fakulti Kejuruteraan Pembuatan .
b
DECLARATION
I hereby, declared this reported entitled “CMM‟s Styli Length Effect on Error
Propagation” is the results of my own research expect as cited in references.
Signature
:
………………………………………
Author‟s Name
:
Shahirul Aini Binti Kamarul Khisham
Date
:
23 Mei 2009
i
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a
partial fulfillment of the requirements for the degree of Bachelor of Manufacturing
Engineering (Manufacturing process) with Honours. The member of supervisory
committee is as follow:
………………………………….
Dr. Mohd Rizal B. Salleh
(Supervisor)
ii
ABSTRACT
Coordinate Measuring Machine (CMM) are fast in operation and has high accuracy
too. However, accuracy has their limitation. To get the accuracy of CMM, a method
of correcting error in the coordinate measurement is proposed. This research
describes an investigation of the CMM‟s styli length effect on error propagation. The
result from the experiment will be shown that the shorter stylus used the better
accuracy of measurement. The experiment will be done by comparing data from the
lobbing model that had been given by supplier and pre-travel measurement from the
experiment.
iii
ABSTRAK
Mesin Pengukur Koordinat (MPK) boleh menyelesaikan pengukuran dalam masa
yang singkat dan mempunyai ketepatan yang tinggi. Tetapi, ketepatan juga
mempunyai hadnya sendiri. Bagi mendapatkan ketepatan, satu cara akan
dicadangkan untuk mengatasi ralat yang berlaku. Kajian ini akan menganalisa
tentang kesan panjang jejari MPK terhadap penyebaran ralat. Hasil daripada
eksperimen yang akan dijalankan akan menunjukkan bahawa semakin pendek jejari
MPK semakin tepat ukuran yang akan diambil. Kajian dijalankan dengan
membezakan antara bacaan daripada ukuran sebenar artifak yang telah diberi oleh
pembekal dan ukuran yang diambil daripada eksperimen yang yang dijalan.
iv
DEDICATION
To my beloved parents, my lovely sisters, friends and colleagues, not forgeting
UTeM‟s lecturers.
v
ACKNOWLEDGEMENT
Alhamdullilah, with the bless from Allah the Almighty, finally I have completed the
final year project and research writing on time. Firstly, I would like to express my
appreciation to my supervisor and co-supervisor, Dr. Mohd Rizal Salleh and Mr.
Ammar Abd Rahman for thier guidance, advice and continuous encouragement in
the process of completing my project successfully. Yours kindness in giving me
continuous knowledge will be remembered always. I would also want to express my
thankfulness to my beloved parent and my lovely siblings for thier never ending
support, advice and encouragement since childhood until now. May your love and
support will never be gone until the end of my life. For UTeM‟s lecturers who have
taught me, thank you for giving me precious and valuable knowledge. For my friends
and my classmates, thanks for your cooperation, support and help throughout these 4
years in UTeM. Thank you so much.
vi
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
iii
Acknowledgement
iv
Table of Content
v
List of Figures
viii
List of Tables
x
List Abbreviations and Nomenclature
xi
1.0
1
INTRODUCTION
Background of Study
1
Problem Statement
4
Objective of the study
4
Scope of the study
5
2.0
LITERATURE REVIEW
6
2.1
Coordinate Measuring Machine (CMM)
6
2.1.1 How to Select CMM
7
2.1.2 Type of CMM
9
2.2
11
Probe
2.2.1 Type of Probe Head
11
2.2.2 Touch Trigger Probe TP2-5W
14
2.2.3 Principles of Probe Operation
15
2.3
Probe Stylus
16
2.3.1 Type of Stylus Tip
16
2.3.2 Stylus Selection
19
2.3.3 Ruby Ball Tip
22
2.4
22
The Artifact
vii
2.4.1 Reference Sphere
22
2.4.2 Method for Calibration of a Probe
24
2.4.3 Other Type of Artifact
28
2.5
29
Error
2.5.1 Type of error occurred
29
2.6
The Statistical Data Analysis
30
2.6.1 Statistical Analysis of the T-test
31
2.7
The Used of Latest Technology
31
3.0
METHODOLOGY
33
3.1
Methodology Description
35
3.1.1 Define Experiment
35
3.1.2 Plan Measurement Parameter
37
3.1.3 Define Changes on Variable
38
3.1.4 Measure the Artifact
40
3.1.5 Data Recorded
42
3.1.6 Data Analysis
42
3.1.7 Conclude the Experiment
43
3.2.8 Suggestion for Improvement
43
4.0
RESULTS
44
4.1
Result for 10mm stylus length
45
4.2
Result for 20mm stylus length
47
4.1
Result for 30mm stylus length
49
4.2
Result for 40mm stylus length
51
4.1
Result for 50mm stylus length
53
4.2
Overall Results
55
viii
5.0
DISCUSSION
57
5.1
The Effect of Stylus Length on Propagation Error
57
5.2
The Range of Error Distribution
59
The Stylus Length Effect on Actual Value of Calibrated
60
5.3
Artifact
5.4
Comparison between Previous Studies
62
5.5
Average Error Distribution between Previous Studies
63
5.6
Statistical Analysis between Current Experiments with
65
Previous Study
5.7
Suggestion for Improvement
67
5.7.1 Suggested Precaution
67
6.0
CONCLUSION
68
6.1
Summary
68
REFERENCES
70
APPENDCES
73
A
Gantt Chart PSM I
73
B
Gantt Chart PSM II
74
C
Data of 10mm Stylus Length Reading
75
D
Data of 20mm Stylus Length Reading
77
E
Data of 30mm Stylus Length Reading
79
F
Data of 40mm Stylus Length Reading
81
G
Data of 50mm Stylus Length Reading
83
H
Data on T-test for Each Styli Length
85
ix
LIST OF FIGURE
1.1
Coordinate Measuring Machine
2
2.1
Moving Bridge CMM
9
2.2
Fixed Bridge
9
2.3
Cantilever CMM
10
2.4
Gantry CMM
10
2.5
Column CMM
11
2.6
Motorized probe
12
2.7
Manual Probe
12
2.8
Touch Trigger Probes
13
2.9
Scanning Probe
13
2.10
TP 2 -5-way Touch Trigger Probe
14
2.11
Kinematic Location
15
2.12a One-stage Type with an Electromechanical Switching
16
transducer
2.12b Two-stage Type Based on a Piezoelectric Transducer
16
2.13
Star Styli
17
2.14
Disc Stylus
17
2.15
Cylinder Styli Probing a Thread and a Thin Sheet
18
2.16
Ceramic Hollow Ball Styli
18
2.17
Pointer Styli
18
2.18
Five Way Stylus Centre
19
2.19
Effective Working Length (EWL)
20
2.20
Ruby Ball Tip
22
2.21
Reference Sphere
23
2.22
Ball Bar
29
2.23
Formula for the t-test
31
2.24
LK Metrology's Ultra CMM
32
2.25
Brown & Sharpe's Global
32
x
3.1
Research Flow Chart
33
3.2
Methodology Flow Chart
34
3.3
CMM Bridge Type
35
3.4
Touch Trigger Probe TP2-5W
35
3.5
Touch Trigger Probe TP2-5W
36
3.6
Variations of Styli
36
3.7
Ceramic Reference Sphere
36
3.8
Comparison between the Simulated and
40
Measured Pre-travel
3.9
Forces Directions
41
3.10
Region a and b
41
4.1
Error Distribution on 10mm stylus length
46
4.2
Error Distribution on 20mm stylus length
48
4.3
Error Distribution on 30mm stylus length
50
4.4
Error Distribution on 40mm stylus length
52
4.5
Error Distribution on 50mm stylus length
54
4.6
Error Distribution on each styli lengths
56
5.1
Graph of stylus length versus error
57
5.2
Graph of error distribution range
59
5.3
Graph of stylus length versus actual value
61
5.4
Graph of different experiment and previous studies
62
5.5
Graph of error distribution range
63
5.6
Normal Distribution for comparison between current
66
experiments with previous study
5.7
Variation of normal distribution for each styli length
xi
66
LIST OF TABLES
2.1
Typical Stiffness Properties of Materials
21
2.2
Number of Contact Points Required
27
3.1
Technical Product Specification
37
3.2
Styli Length Variation
39
3.3
Sample of Resulting Table
42
3.4
Sample of Data Analysis Table
42
3.5
Sample of Data Comparison Between Previous Studies
43
4.1
Data Analysis for 10mm stylus length
45
4.2
Data Analysis for 20mm stylus length
47
4.3
Data Analysis for 30mm stylus length
49
4.4
Data Analysis for 40mm stylus length
51
4.5
Data Analysis for 50mm stylus length
53
4.6
Data Average for each styli length
55
5.1
Mean, max and min value of error distribution
58
5.2
Data analysis for error distribution
60
5.3
Data of different between actual values with artifact
61
5.4
Data comparison between previous studies
62
5.5
Data analysis between experiment and previous studies
64
5.6
t-Tests for Two-Sample Assuming Unequal Variance
65
xii
LIST OF ABBREVIATION & NOMENCLATURE
ASME
American Standard Measuring Equipment
BS
British Standard
CMM
Coordinate Measuring Machine
CNC
Computer Numerical Control
DCC
Direct Computer Control
EWL
Effective Working Length
ISO
International Standard Organization
N
Newton (Force unit)
NC
Numerical Control
PH
Probe Head
PTV
Pre-Travel Variation
TP
Touch Probe
xiii
CHAPTER 1
INTRODUCTION
Coordinate measuring machines (CMMs) have become very widely used in recent years
because of their ability to measure most or all of the individual geometrical features on
complex engineering components. Compared with traditional methods, which normally
employ a variety of separate instruments, CMMs are fast in operation and are adequately
accurate for many applications. However, accuracy limitations often inhibit their use for
high precision metrology. Accuracy is limited by such factors as straightness and
orthogonality of the CMM movements (Renishaw, 2003).
.
In many cases, the errors introduced by the probes are very significant and often exceed the
errors from other sources. This report describes an investigation into the nature of probe
errors, the factors that influence their performance and proposes a method to verifying the
probe performance. Results from a number of probes used in different modes are presented
(Renishaw, 2003).
Background of Study
International Standard ISO 10360-1 defines CMM as a measuring system with the means
to move a probing system and capability to determine spatial coordinates on a work piece
surface. Over the years standards and guidelines have been developed to harmonize the
performance specifications of a CMM to enable a user to make meaningful performance
comparisons when purchasing a machine and, once purchased, to provide a well-defined
way in which the specified performance can be verified (Flack, 2001).
1
Figure 1.1: Coordinate Measuring Machine (Source: Renishaw, 2003).
CMM is essentially a very precise Cartesian robot equipped with a tactile probe, and used
as a 3-D digitizer. The probe, under computer control, touches a sequence of points in the
surface of a physical object to be measured, and the CMM produces a stream of x, y, z
coordinates of the contact points. The coordinate stream is interpreted by algorithms that
support applications such as reverse engineering, quality control, and process control. In
quality and process control, the goal is to decide if a manufactured object meets its design
specifications. This task is called dimensional inspection, and amounts to comparing the
measurements obtained by a CMM with a solid model of the object (Spitz, 1999).
Friction due to the trigger touches the surface profile. The touch probe provides the
connection between the probe head and the stylus and contains the necessary trigger
capability to record a data point, or scan data when in contact with the artifact. The stylus
length is measured from the centre of the ball to the point at which the stem will foul
against the feature when measuring 'normal' to the part. Generally, the larger the ball
diameter, the longer the stylus length and the greater the effective working length (EWL)
(Renishaw, 2003).
2
There are so many kind of touch probe system used today, such as Two Piece System,
Three Piece System - M8 Thread Mount, Three Piece System - TP20, Integral Kinematics
Mount, Four Piece System- M8 Thread Mount, Stylus Change Module, and OPT6M
Optical Trigger Probe. But for this study, the Three Piece System - M8 Thread Mount
which is separate touch probe screws into the probe head via a M8 thread will be used.
This style allows the use of M8 - 13mm diameter probe extensions between the probe and
the head to reach into deep parts. With this system the touch probes can be easily
exchanged if damaged or worn. The M8 thread mount is compatible with the standard TP2
and TP6 touch probes (Helmel, 2008).
Nevertheless, if this CMM‟s is precision dimension measuring equipment, it also has some
dynamic measurement error. The dynamic measurement error happens when the measuring
process needs short cycle‟s time. So the requirement for faster CMM operation is
increased. Then, because of that, the CMM system had been influenced by the dynamic
errors. The probe configuration, motion related factors, measured object, operating
environment and mode of the operation are the factors that influencing the dynamic
measurement errors (Johnson et.al, 1998).
It is well known that most touch trigger probes suffer from lobbing effects. These are
propagation errors and normally depend upon a number of factors including probe
orientation, stylus length, diameter, measuring speed, trigger force and etc. With most
touch trigger probes, lobbing errors have much larger sizes than their repeatability
uncertainty, resulting in difficulties in many applications (Johnson et.al, 1998).
In order to minimize the lobbing effects, careful consideration of probe selection, stylus
configuration, data collecting procedure and measuring techniques is required. Current
practices have relied largely on choosing probes of better performance, selecting stylus
configurations of shorter length and higher stiffness, using smaller probing forces, and a
careful sampling strategy (Johnson et.al, 1998).
3
1.2 Problem Statement
CMM are widely used throughout manufacturing industries, such as aerospace and
automotive, to meet the increasing need for high quality standards and dimensional
accuracy. However, in many applications, CMM measurement is not as efficient as it could
be (Smith, 2002). So new measuring methodology and techniques needs to be developed
that can be improve flexibility, reduce inspection time and achieve consistency.
Repeatability and reproducibility values for these probes are published in the
manufacturers' catalogues and each new probe should have a certificate of performance
provided with it. However, a customer may not be fully aware of how his mode of use
affects the accuracy of measurements made with the probe (Aston et. al, 1997).
Usually the users are advised that when calibrating a stylus they should keep the stylus as
short as possible to get the less error in measurement (Aston et. al, 1997). However, it is
often necessary to use a stylus that is much longer than the ideal minimum or effective
working length (EWL) , even though there will be a reduction in performance. So, how the
CMM‟s styli length effect on error propagation?
Objective of the study
To make sure this project is successfully achieved, certain objectives were outlined as
follows:
To identify the impact of styli length on the error distribution of CMM.
To propose the appropriate methods or technique of measurement to minimize the
measurement error.
4
Scope of the study
This study describes the CMM‟s styli length effects on propagation error. The
investigation of the stylus length effect is find base on the experiment that will be done at
Metrology Laboratory of Universiti Teknikal Malaysia Melaka (UTeM). The investigation
are not covering the effect on stylus approach direction, probing force, diameter and
measuring speed.
This study will focus on the CMM performance. The effect of styli length on the
propagation error will be discussed in details later in this report. Where the longer of styli
length used, the more the stylus bends or deflects, the lower the accuracy. Probing with the
minimum stylus length for application is recommended and where possible the use of one
piece styli is suggested. Probing with excessive styli or extension combinations should
therefore be avoided to achieve measurement efficiency (Renishaw, 2003).
In contact measurement, CMM data collection starts at the stylus tip, the part of the
measuring system that makes contact with the work piece. Most CMM users have a single
sensor and stylus configuration, and although they might not realize it, in most cases this is
limiting. Unless measuring a simple component, the stylus configuration needs to be
changed to suit different measurement tasks. Traditionally this has been done manually,
using a threaded connection. However, probe systems are now available with a repeatable
stylus interchange, greatly increasing system flexibility by allowing quick changes to long
or complex styli configurations, as well as different tips such as sphere, disc or cylinder
(Smith, 2002).
In this study the TP2 touch probe will be used on the one artifact and same touch point to
act as the independent variable during an experiment. TP2 is the traditional slim line
switching probe for most applications. The error during the measurement taking technique
must be reduced by finding the right way to get the high accuracy result. In order to find
the best method or technique of measuring by using CMM, the scope of study must include
the suggestion and improvement of measuring technique by using different and various
measuring technique.
5
CHAPTER 2
LITERATURE REVIEW
2.1 Coordinate Measuring Machine (CMM)
A coordinate measuring machine (CMM) is a measuring system with the means to move a
probing system and capability to determine spatial coordinates on a work piece surface.
The Co-ordinate Measuring Machine has its origins in manually operated simple layout
inspection equipment. With the development of numerical controlled (NC) machines in the
1950s for the production of complex components required in the United States aerospace
programmed and the subsequent introduction of computer numerical control (CNC)
machines in the 1970s, production techniques were often more accurate than inspection
equipment in general use (Flack, 2001).
A major factor in the evolution of the CMM was the invention in 1972 of the touch trigger
probe by David McMurtry of Rolls-Royce (Renishaw, 2003).The touch-trigger probe is a
3D sensor capable of rapid, accurate inspection with low trigger force. When incorporated
with precision linear measuring systems developed for CNC machines plus cheap and
powerful computer hardware and software, this paved the way for highly accurate,
automated inspection centers. CMMs are widely used in manufacturing industries for
accurate, fast and reliable dimensional measurement of components. They are generally
expensive to buy and maintain but their results are crucial to the manufacturing process
(Flack , 2001).
Two forms of CMMs are available; manual and Direct Computer Control (DCC). Manual
CMMs are generally used for first-article inspection work. If the primary manufacturing
environment is production orientated a DCC machine is the usual choice. DCC machines
6
generally are the tools of choice for manufacturers who need to gather and analyze large
amounts of data for maintaining control of the manufacturing process. The CMM is
normally completely under DCC operation thereby eliminating any user influence on the
quality of the recorded data (Flack , 2001).
2.1.1 How to Select CMM
The right chosen CMM will makes the measuring operations becomes more effective.
Therefore, there are some criteria needs to be considered when choosing the right CMM.
i.
The determination of minimum required measuring range
The first important selection criterion is the determination of the minimum required
measuring range of the CMM. This range usually depends on the dimensions of the part to
be measured, but is often more complex than that. For example, if the configuration of the
part and the inspection routine require the use of probe extensions and fixtures, the actual
minimum required measuring range could be considerably larger than work piece
dimensions (Flack, 2001).
ii.
Comparison with machine specification
However, in order to compare CMMs from different manufacturers, the comparison with
machine specifications must be done first. Most CMM manufacturers already offer their
specifications in a variety of formats to support their international customer base. In
addition, if you're an international manufacturer, it may be prudent to request the CMM's
specifications in the ISO 10360-2 format since it's becoming a world standard. This will
allow you to not only compare between competitors, but to compare the new machine to
your existing machines installed throughout the world (Flack, 2001).
iii.
Specify the temperature range
The uncertainty of every CMM depends to a great extent on environmental conditions.
Consequently, CMM manufacturers usually specify the temperature range, temperature
7
PROPAGATION
SHAHIRUL AINI BINTI KAMARUL KHISHAM
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
a
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
CMM’S STYLI LENGTH EFFECT ON ERROR PROPAGATION
This report submitted in accordance with requirement of the Universiti Teknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Manufacturing Process) with Honours.
By
SHAHIRUL AINI BINTI KAMARUL KHISHAM
FACULTY OF MANUFACTURING ENGINEERING
2009
a
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS LAPORAN PSM
TAJUK: CMM’s Styli Length Effect on Error Propagation
SESI PENGAJIAN: 2008/2009 Semester 2
Saya
SHAHIRUL AINI BINTI KAMARUL KHISHAM
mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti
Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:
1.
2.
3.
4.
Tesis adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis.
Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan
untuk tujuan pengajian sahaja dengan izin penulis.
Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran
antara institusi pengajian tinggi.
*Sila tandakan (√)
SULIT
(Mengandungi maklumat yang berdarjah keselamatan
atau kepentingan Malaysia yang termaktub di dalam
AKTA RAHSIA RASMI 1972)
TERHAD
(Mengandungi maklumat TERHAD yang telah ditentukan
oleh organisasi/badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh:
Alamat Tetap:
19-0-5, TMN BKT ANGKASA,
PANTAI DALAM,
59200 KUALA LUMPUR.
Cop Rasmi:
Tarikh: _______________________
Tarikh: _______________________
* Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan
dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.
a
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Karung Berkunci 1200, Ayer Keroh, 75450 Melaka
Tel : 06-233 2421, Faks : 06 233 2414
Email : [email protected]
FAKULTI KEJURUTERAAN PEMBUATAN
20 Mei 2009
Rujukan Kami (Our Ref) :
Rujukan Tuan (Your Ref):
Pustakawan
Perpustakawan UTeM
Universiti Teknikal Malaysia Melaka
Hang Tuah Jaya,
75450, Melaka
Saudara,
PENGKELASAN LAPORAN PSM SEBAGAI SULIT/TERHAD LAPORAN PROJEK
SARJANA MUDA KEJURUTERAAN PEMBUATAN (MANUFACTURING PROCESS):
SHAHIRUL AINI BINTI KAMARUL KHISHAM
Sukacita dimaklumkan bahawa laporan PSM yang tersebut di atas bertajuk
“CMM’s Styli Length Effect on Error Propagation” mohon dikelaskan
sebagai SULIT/TERHAD untuk tempoh LIMA tahun dari tarikh surat ini.
Sekian dimaklumkan. Terima kasih.
Yang benar,
……………………………………………………..
Dr. Mohd Rizal B. Salleh
Dekan ,
Fakulti Kejuruteraan Pembuatan .
b
DECLARATION
I hereby, declared this reported entitled “CMM‟s Styli Length Effect on Error
Propagation” is the results of my own research expect as cited in references.
Signature
:
………………………………………
Author‟s Name
:
Shahirul Aini Binti Kamarul Khisham
Date
:
23 Mei 2009
i
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a
partial fulfillment of the requirements for the degree of Bachelor of Manufacturing
Engineering (Manufacturing process) with Honours. The member of supervisory
committee is as follow:
………………………………….
Dr. Mohd Rizal B. Salleh
(Supervisor)
ii
ABSTRACT
Coordinate Measuring Machine (CMM) are fast in operation and has high accuracy
too. However, accuracy has their limitation. To get the accuracy of CMM, a method
of correcting error in the coordinate measurement is proposed. This research
describes an investigation of the CMM‟s styli length effect on error propagation. The
result from the experiment will be shown that the shorter stylus used the better
accuracy of measurement. The experiment will be done by comparing data from the
lobbing model that had been given by supplier and pre-travel measurement from the
experiment.
iii
ABSTRAK
Mesin Pengukur Koordinat (MPK) boleh menyelesaikan pengukuran dalam masa
yang singkat dan mempunyai ketepatan yang tinggi. Tetapi, ketepatan juga
mempunyai hadnya sendiri. Bagi mendapatkan ketepatan, satu cara akan
dicadangkan untuk mengatasi ralat yang berlaku. Kajian ini akan menganalisa
tentang kesan panjang jejari MPK terhadap penyebaran ralat. Hasil daripada
eksperimen yang akan dijalankan akan menunjukkan bahawa semakin pendek jejari
MPK semakin tepat ukuran yang akan diambil. Kajian dijalankan dengan
membezakan antara bacaan daripada ukuran sebenar artifak yang telah diberi oleh
pembekal dan ukuran yang diambil daripada eksperimen yang yang dijalan.
iv
DEDICATION
To my beloved parents, my lovely sisters, friends and colleagues, not forgeting
UTeM‟s lecturers.
v
ACKNOWLEDGEMENT
Alhamdullilah, with the bless from Allah the Almighty, finally I have completed the
final year project and research writing on time. Firstly, I would like to express my
appreciation to my supervisor and co-supervisor, Dr. Mohd Rizal Salleh and Mr.
Ammar Abd Rahman for thier guidance, advice and continuous encouragement in
the process of completing my project successfully. Yours kindness in giving me
continuous knowledge will be remembered always. I would also want to express my
thankfulness to my beloved parent and my lovely siblings for thier never ending
support, advice and encouragement since childhood until now. May your love and
support will never be gone until the end of my life. For UTeM‟s lecturers who have
taught me, thank you for giving me precious and valuable knowledge. For my friends
and my classmates, thanks for your cooperation, support and help throughout these 4
years in UTeM. Thank you so much.
vi
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
iii
Acknowledgement
iv
Table of Content
v
List of Figures
viii
List of Tables
x
List Abbreviations and Nomenclature
xi
1.0
1
INTRODUCTION
Background of Study
1
Problem Statement
4
Objective of the study
4
Scope of the study
5
2.0
LITERATURE REVIEW
6
2.1
Coordinate Measuring Machine (CMM)
6
2.1.1 How to Select CMM
7
2.1.2 Type of CMM
9
2.2
11
Probe
2.2.1 Type of Probe Head
11
2.2.2 Touch Trigger Probe TP2-5W
14
2.2.3 Principles of Probe Operation
15
2.3
Probe Stylus
16
2.3.1 Type of Stylus Tip
16
2.3.2 Stylus Selection
19
2.3.3 Ruby Ball Tip
22
2.4
22
The Artifact
vii
2.4.1 Reference Sphere
22
2.4.2 Method for Calibration of a Probe
24
2.4.3 Other Type of Artifact
28
2.5
29
Error
2.5.1 Type of error occurred
29
2.6
The Statistical Data Analysis
30
2.6.1 Statistical Analysis of the T-test
31
2.7
The Used of Latest Technology
31
3.0
METHODOLOGY
33
3.1
Methodology Description
35
3.1.1 Define Experiment
35
3.1.2 Plan Measurement Parameter
37
3.1.3 Define Changes on Variable
38
3.1.4 Measure the Artifact
40
3.1.5 Data Recorded
42
3.1.6 Data Analysis
42
3.1.7 Conclude the Experiment
43
3.2.8 Suggestion for Improvement
43
4.0
RESULTS
44
4.1
Result for 10mm stylus length
45
4.2
Result for 20mm stylus length
47
4.1
Result for 30mm stylus length
49
4.2
Result for 40mm stylus length
51
4.1
Result for 50mm stylus length
53
4.2
Overall Results
55
viii
5.0
DISCUSSION
57
5.1
The Effect of Stylus Length on Propagation Error
57
5.2
The Range of Error Distribution
59
The Stylus Length Effect on Actual Value of Calibrated
60
5.3
Artifact
5.4
Comparison between Previous Studies
62
5.5
Average Error Distribution between Previous Studies
63
5.6
Statistical Analysis between Current Experiments with
65
Previous Study
5.7
Suggestion for Improvement
67
5.7.1 Suggested Precaution
67
6.0
CONCLUSION
68
6.1
Summary
68
REFERENCES
70
APPENDCES
73
A
Gantt Chart PSM I
73
B
Gantt Chart PSM II
74
C
Data of 10mm Stylus Length Reading
75
D
Data of 20mm Stylus Length Reading
77
E
Data of 30mm Stylus Length Reading
79
F
Data of 40mm Stylus Length Reading
81
G
Data of 50mm Stylus Length Reading
83
H
Data on T-test for Each Styli Length
85
ix
LIST OF FIGURE
1.1
Coordinate Measuring Machine
2
2.1
Moving Bridge CMM
9
2.2
Fixed Bridge
9
2.3
Cantilever CMM
10
2.4
Gantry CMM
10
2.5
Column CMM
11
2.6
Motorized probe
12
2.7
Manual Probe
12
2.8
Touch Trigger Probes
13
2.9
Scanning Probe
13
2.10
TP 2 -5-way Touch Trigger Probe
14
2.11
Kinematic Location
15
2.12a One-stage Type with an Electromechanical Switching
16
transducer
2.12b Two-stage Type Based on a Piezoelectric Transducer
16
2.13
Star Styli
17
2.14
Disc Stylus
17
2.15
Cylinder Styli Probing a Thread and a Thin Sheet
18
2.16
Ceramic Hollow Ball Styli
18
2.17
Pointer Styli
18
2.18
Five Way Stylus Centre
19
2.19
Effective Working Length (EWL)
20
2.20
Ruby Ball Tip
22
2.21
Reference Sphere
23
2.22
Ball Bar
29
2.23
Formula for the t-test
31
2.24
LK Metrology's Ultra CMM
32
2.25
Brown & Sharpe's Global
32
x
3.1
Research Flow Chart
33
3.2
Methodology Flow Chart
34
3.3
CMM Bridge Type
35
3.4
Touch Trigger Probe TP2-5W
35
3.5
Touch Trigger Probe TP2-5W
36
3.6
Variations of Styli
36
3.7
Ceramic Reference Sphere
36
3.8
Comparison between the Simulated and
40
Measured Pre-travel
3.9
Forces Directions
41
3.10
Region a and b
41
4.1
Error Distribution on 10mm stylus length
46
4.2
Error Distribution on 20mm stylus length
48
4.3
Error Distribution on 30mm stylus length
50
4.4
Error Distribution on 40mm stylus length
52
4.5
Error Distribution on 50mm stylus length
54
4.6
Error Distribution on each styli lengths
56
5.1
Graph of stylus length versus error
57
5.2
Graph of error distribution range
59
5.3
Graph of stylus length versus actual value
61
5.4
Graph of different experiment and previous studies
62
5.5
Graph of error distribution range
63
5.6
Normal Distribution for comparison between current
66
experiments with previous study
5.7
Variation of normal distribution for each styli length
xi
66
LIST OF TABLES
2.1
Typical Stiffness Properties of Materials
21
2.2
Number of Contact Points Required
27
3.1
Technical Product Specification
37
3.2
Styli Length Variation
39
3.3
Sample of Resulting Table
42
3.4
Sample of Data Analysis Table
42
3.5
Sample of Data Comparison Between Previous Studies
43
4.1
Data Analysis for 10mm stylus length
45
4.2
Data Analysis for 20mm stylus length
47
4.3
Data Analysis for 30mm stylus length
49
4.4
Data Analysis for 40mm stylus length
51
4.5
Data Analysis for 50mm stylus length
53
4.6
Data Average for each styli length
55
5.1
Mean, max and min value of error distribution
58
5.2
Data analysis for error distribution
60
5.3
Data of different between actual values with artifact
61
5.4
Data comparison between previous studies
62
5.5
Data analysis between experiment and previous studies
64
5.6
t-Tests for Two-Sample Assuming Unequal Variance
65
xii
LIST OF ABBREVIATION & NOMENCLATURE
ASME
American Standard Measuring Equipment
BS
British Standard
CMM
Coordinate Measuring Machine
CNC
Computer Numerical Control
DCC
Direct Computer Control
EWL
Effective Working Length
ISO
International Standard Organization
N
Newton (Force unit)
NC
Numerical Control
PH
Probe Head
PTV
Pre-Travel Variation
TP
Touch Probe
xiii
CHAPTER 1
INTRODUCTION
Coordinate measuring machines (CMMs) have become very widely used in recent years
because of their ability to measure most or all of the individual geometrical features on
complex engineering components. Compared with traditional methods, which normally
employ a variety of separate instruments, CMMs are fast in operation and are adequately
accurate for many applications. However, accuracy limitations often inhibit their use for
high precision metrology. Accuracy is limited by such factors as straightness and
orthogonality of the CMM movements (Renishaw, 2003).
.
In many cases, the errors introduced by the probes are very significant and often exceed the
errors from other sources. This report describes an investigation into the nature of probe
errors, the factors that influence their performance and proposes a method to verifying the
probe performance. Results from a number of probes used in different modes are presented
(Renishaw, 2003).
Background of Study
International Standard ISO 10360-1 defines CMM as a measuring system with the means
to move a probing system and capability to determine spatial coordinates on a work piece
surface. Over the years standards and guidelines have been developed to harmonize the
performance specifications of a CMM to enable a user to make meaningful performance
comparisons when purchasing a machine and, once purchased, to provide a well-defined
way in which the specified performance can be verified (Flack, 2001).
1
Figure 1.1: Coordinate Measuring Machine (Source: Renishaw, 2003).
CMM is essentially a very precise Cartesian robot equipped with a tactile probe, and used
as a 3-D digitizer. The probe, under computer control, touches a sequence of points in the
surface of a physical object to be measured, and the CMM produces a stream of x, y, z
coordinates of the contact points. The coordinate stream is interpreted by algorithms that
support applications such as reverse engineering, quality control, and process control. In
quality and process control, the goal is to decide if a manufactured object meets its design
specifications. This task is called dimensional inspection, and amounts to comparing the
measurements obtained by a CMM with a solid model of the object (Spitz, 1999).
Friction due to the trigger touches the surface profile. The touch probe provides the
connection between the probe head and the stylus and contains the necessary trigger
capability to record a data point, or scan data when in contact with the artifact. The stylus
length is measured from the centre of the ball to the point at which the stem will foul
against the feature when measuring 'normal' to the part. Generally, the larger the ball
diameter, the longer the stylus length and the greater the effective working length (EWL)
(Renishaw, 2003).
2
There are so many kind of touch probe system used today, such as Two Piece System,
Three Piece System - M8 Thread Mount, Three Piece System - TP20, Integral Kinematics
Mount, Four Piece System- M8 Thread Mount, Stylus Change Module, and OPT6M
Optical Trigger Probe. But for this study, the Three Piece System - M8 Thread Mount
which is separate touch probe screws into the probe head via a M8 thread will be used.
This style allows the use of M8 - 13mm diameter probe extensions between the probe and
the head to reach into deep parts. With this system the touch probes can be easily
exchanged if damaged or worn. The M8 thread mount is compatible with the standard TP2
and TP6 touch probes (Helmel, 2008).
Nevertheless, if this CMM‟s is precision dimension measuring equipment, it also has some
dynamic measurement error. The dynamic measurement error happens when the measuring
process needs short cycle‟s time. So the requirement for faster CMM operation is
increased. Then, because of that, the CMM system had been influenced by the dynamic
errors. The probe configuration, motion related factors, measured object, operating
environment and mode of the operation are the factors that influencing the dynamic
measurement errors (Johnson et.al, 1998).
It is well known that most touch trigger probes suffer from lobbing effects. These are
propagation errors and normally depend upon a number of factors including probe
orientation, stylus length, diameter, measuring speed, trigger force and etc. With most
touch trigger probes, lobbing errors have much larger sizes than their repeatability
uncertainty, resulting in difficulties in many applications (Johnson et.al, 1998).
In order to minimize the lobbing effects, careful consideration of probe selection, stylus
configuration, data collecting procedure and measuring techniques is required. Current
practices have relied largely on choosing probes of better performance, selecting stylus
configurations of shorter length and higher stiffness, using smaller probing forces, and a
careful sampling strategy (Johnson et.al, 1998).
3
1.2 Problem Statement
CMM are widely used throughout manufacturing industries, such as aerospace and
automotive, to meet the increasing need for high quality standards and dimensional
accuracy. However, in many applications, CMM measurement is not as efficient as it could
be (Smith, 2002). So new measuring methodology and techniques needs to be developed
that can be improve flexibility, reduce inspection time and achieve consistency.
Repeatability and reproducibility values for these probes are published in the
manufacturers' catalogues and each new probe should have a certificate of performance
provided with it. However, a customer may not be fully aware of how his mode of use
affects the accuracy of measurements made with the probe (Aston et. al, 1997).
Usually the users are advised that when calibrating a stylus they should keep the stylus as
short as possible to get the less error in measurement (Aston et. al, 1997). However, it is
often necessary to use a stylus that is much longer than the ideal minimum or effective
working length (EWL) , even though there will be a reduction in performance. So, how the
CMM‟s styli length effect on error propagation?
Objective of the study
To make sure this project is successfully achieved, certain objectives were outlined as
follows:
To identify the impact of styli length on the error distribution of CMM.
To propose the appropriate methods or technique of measurement to minimize the
measurement error.
4
Scope of the study
This study describes the CMM‟s styli length effects on propagation error. The
investigation of the stylus length effect is find base on the experiment that will be done at
Metrology Laboratory of Universiti Teknikal Malaysia Melaka (UTeM). The investigation
are not covering the effect on stylus approach direction, probing force, diameter and
measuring speed.
This study will focus on the CMM performance. The effect of styli length on the
propagation error will be discussed in details later in this report. Where the longer of styli
length used, the more the stylus bends or deflects, the lower the accuracy. Probing with the
minimum stylus length for application is recommended and where possible the use of one
piece styli is suggested. Probing with excessive styli or extension combinations should
therefore be avoided to achieve measurement efficiency (Renishaw, 2003).
In contact measurement, CMM data collection starts at the stylus tip, the part of the
measuring system that makes contact with the work piece. Most CMM users have a single
sensor and stylus configuration, and although they might not realize it, in most cases this is
limiting. Unless measuring a simple component, the stylus configuration needs to be
changed to suit different measurement tasks. Traditionally this has been done manually,
using a threaded connection. However, probe systems are now available with a repeatable
stylus interchange, greatly increasing system flexibility by allowing quick changes to long
or complex styli configurations, as well as different tips such as sphere, disc or cylinder
(Smith, 2002).
In this study the TP2 touch probe will be used on the one artifact and same touch point to
act as the independent variable during an experiment. TP2 is the traditional slim line
switching probe for most applications. The error during the measurement taking technique
must be reduced by finding the right way to get the high accuracy result. In order to find
the best method or technique of measuring by using CMM, the scope of study must include
the suggestion and improvement of measuring technique by using different and various
measuring technique.
5
CHAPTER 2
LITERATURE REVIEW
2.1 Coordinate Measuring Machine (CMM)
A coordinate measuring machine (CMM) is a measuring system with the means to move a
probing system and capability to determine spatial coordinates on a work piece surface.
The Co-ordinate Measuring Machine has its origins in manually operated simple layout
inspection equipment. With the development of numerical controlled (NC) machines in the
1950s for the production of complex components required in the United States aerospace
programmed and the subsequent introduction of computer numerical control (CNC)
machines in the 1970s, production techniques were often more accurate than inspection
equipment in general use (Flack, 2001).
A major factor in the evolution of the CMM was the invention in 1972 of the touch trigger
probe by David McMurtry of Rolls-Royce (Renishaw, 2003).The touch-trigger probe is a
3D sensor capable of rapid, accurate inspection with low trigger force. When incorporated
with precision linear measuring systems developed for CNC machines plus cheap and
powerful computer hardware and software, this paved the way for highly accurate,
automated inspection centers. CMMs are widely used in manufacturing industries for
accurate, fast and reliable dimensional measurement of components. They are generally
expensive to buy and maintain but their results are crucial to the manufacturing process
(Flack , 2001).
Two forms of CMMs are available; manual and Direct Computer Control (DCC). Manual
CMMs are generally used for first-article inspection work. If the primary manufacturing
environment is production orientated a DCC machine is the usual choice. DCC machines
6
generally are the tools of choice for manufacturers who need to gather and analyze large
amounts of data for maintaining control of the manufacturing process. The CMM is
normally completely under DCC operation thereby eliminating any user influence on the
quality of the recorded data (Flack , 2001).
2.1.1 How to Select CMM
The right chosen CMM will makes the measuring operations becomes more effective.
Therefore, there are some criteria needs to be considered when choosing the right CMM.
i.
The determination of minimum required measuring range
The first important selection criterion is the determination of the minimum required
measuring range of the CMM. This range usually depends on the dimensions of the part to
be measured, but is often more complex than that. For example, if the configuration of the
part and the inspection routine require the use of probe extensions and fixtures, the actual
minimum required measuring range could be considerably larger than work piece
dimensions (Flack, 2001).
ii.
Comparison with machine specification
However, in order to compare CMMs from different manufacturers, the comparison with
machine specifications must be done first. Most CMM manufacturers already offer their
specifications in a variety of formats to support their international customer base. In
addition, if you're an international manufacturer, it may be prudent to request the CMM's
specifications in the ISO 10360-2 format since it's becoming a world standard. This will
allow you to not only compare between competitors, but to compare the new machine to
your existing machines installed throughout the world (Flack, 2001).
iii.
Specify the temperature range
The uncertainty of every CMM depends to a great extent on environmental conditions.
Consequently, CMM manufacturers usually specify the temperature range, temperature
7