CMM’S STYLI LENGTH EFFECT ON ERROR...

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CMM’S STYLI LENGTH EFFECT ON ERROR

PROPAGATION

SHAHIRUL AINI BINTI KAMARUL KHISHAM

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

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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

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(Mengandungi maklumat TERHAD yang telah ditentukan

oleh organisasi/badan di mana penyelidikan dijalankan)


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. Tesis adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran

antara institusi pengajian tinggi. 4. *Sila tandakan (√)

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan

atau kepentingan Malaysia yang termaktub di dalam

AKTA RAHSIA RASMI 1972)

Alamat Tetap: 19-0-5, TMN BKT ANGKASA, PANTAI DALAM, 59200 KUALA LUMPUR.

Tarikh: _______________________

Disahkan oleh:

Cop Rasmi:

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.

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FAKULTI KEJURUTERAAN PEMBUATAN

Rujukan Kami (Our Ref) : 20 Mei 2009 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 .

UNIVERSITI TEKNIKAL MALAYSIA MELAKA Karung Berkunci 1200, Ayer Keroh, 75450 Melaka

Tel : 06-233 2421, Faks : 06 233 2414 Email : [email protected]

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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

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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)

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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.

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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.

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DEDICATION

To my beloved parents, my lovely sisters, friends and colleagues, not forgeting

UTeM‟s lecturers.

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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.

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TABLE OF CONTENT

Abstract

Abstrak

Dedication

Acknowledgement

Table of Content

List of Figures

List of Tables

List Abbreviations and Nomenclature

1.0 INTRODUCTION

Background of Study

Problem Statement

Objective of the study

Scope of the study

2.0 LITERATURE REVIEW

2.1 Coordinate Measuring Machine (CMM)

2.1.1 How to Select CMM

2.1.2 Type of CMM

2.2 Probe

2.2.1 Type of Probe Head

2.2.2 Touch Trigger Probe TP2-5W

2.2.3 Principles of Probe Operation

2.3 Probe Stylus

2.3.1 Type of Stylus Tip

2.3.2 Stylus Selection

2.3.3 Ruby Ball Tip

2.4 The Artifact

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2.4.1 Reference Sphere

2.4.2 Method for Calibration of a Probe

2.4.3 Other Type of Artifact

2.5 Error

2.5.1 Type of error occurred

2.6 The Statistical Data Analysis

2.6.1 Statistical Analysis of the T-test

2.7 The Used of Latest Technology

3.0 METHODOLOGY

3.1 Methodology Description

3.1.1 Define Experiment

3.1.2 Plan Measurement Parameter

3.1.3 Define Changes on Variable

3.1.4 Measure the Artifact

3.1.5 Data Recorded

3.1.6 Data Analysis

3.1.7 Conclude the Experiment

3.2.8 Suggestion for Improvement

4.0 RESULTS

4.1 Result for 10mm stylus length





4.2 Overall Results

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5.0 DISCUSSION

5.1 The Effect of Stylus Length on Propagation Error

5.2 The Range of Error Distribution

5.3 The Stylus Length Effect on Actual Value of Calibrated

Artifact

5.4 Comparison between Previous Studies

5.5 Average Error Distribution between Previous Studies

5.6 Statistical Analysis between Current Experiments with

Previous Study

5.7 Suggestion for Improvement

5.7.1 Suggested Precaution

6.0 CONCLUSION

6.1 Summary

REFERENCES

APPENDCES

A Gantt Chart PSM I

B Gantt Chart PSM II

C Data of 10mm Stylus Length Reading

D Data of 20mm Stylus Length Reading

E Data of 30mm Stylus Length Reading

F Data of 40mm Stylus Length Reading

G Data of 50mm Stylus Length Reading

H Data on T-test for Each Styli Length

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LIST OF FIGURE

1.1 Coordinate Measuring Machine

2.1 Moving Bridge CMM

2.2 Fixed Bridge

2.3 Cantilever CMM

2.4 Gantry CMM

2.5 Column CMM

2.6 Motorized probe

2.7 Manual Probe

2.8 Touch Trigger Probes

2.9 Scanning Probe

2.10 TP 2 -5-way Touch Trigger Probe

2.11 Kinematic Location

2.12a One-stage Type with an Electromechanical Switching

transducer

2.12b Two-stage Type Based on a Piezoelectric Transducer

2.13 Star Styli

2.14 Disc Stylus

2.15 Cylinder Styli Probing a Thread and a Thin Sheet

2.16 Ceramic Hollow Ball Styli

2.17 Pointer Styli

2.18 Five Way Stylus Centre

2.19 Effective Working Length (EWL)

2.20 Ruby Ball Tip

2.21 Reference Sphere

2.22 Ball Bar

2.23 Formula for the t-test

2.24 LK Metrology's Ultra CMM

2.25 Brown & Sharpe's Global

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3.1 Research Flow Chart

3.2 Methodology Flow Chart

3.3 CMM Bridge Type

3.4 Touch Trigger Probe TP2-5W

3.5 Touch Trigger Probe TP2-5W

3.6 Variations of Styli

3.7 Ceramic Reference Sphere

3.8 Comparison between the Simulated and

Measured Pre-travel

3.9 Forces Directions

3.10 Region a and b

4.1 Error Distribution on 10mm stylus length





4.6 Error Distribution on each styli lengths

5.1 Graph of stylus length versus error

5.2 Graph of error distribution range

5.3 Graph of stylus length versus actual value

5.4 Graph of different experiment and previous studies

5.5 Graph of error distribution range

5.6 Normal Distribution for comparison between current

experiments with previous study

5.7 Variation of normal distribution for each styli length

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LIST OF TABLES

2.1 Typical Stiffness Properties of Materials

2.2 Number of Contact Points Required

3.1 Technical Product Specification

3.2 Styli Length Variation

3.3 Sample of Resulting Table

3.4 Sample of Data Analysis Table

3.5 Sample of Data Comparison Between Previous Studies

4.1 Data Analysis for 10mm stylus length





4.6 Data Average for each styli length

5.1 Mean, max and min value of error distribution

5.2 Data analysis for error distribution

5.3 Data of different between actual values with artifact

5.4 Data comparison between previous studies

5.5 Data analysis between experiment and previous studies

5.6 t-Tests for Two-Sample Assuming Unequal Variance

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ASME

BS

CMM

CNC

DCC

EWL

ISO

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NC

PH

PTV

TP

LIST OF ABBREVIATION & NOMENCLATURE

American Standard Measuring Equipment

British Standard

Coordinate Measuring Machine

Computer Numerical Control

Direct Computer Control

Effective Working Length

International Standard Organization

Newton (Force unit)

Numerical Control

Probe Head

Pre-Travel Variation

Touch Probe

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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).

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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).

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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).

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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).

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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.

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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.

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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

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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

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