1. introduction

© 2008-2015 Young-Woo Park
PrecisionEngineering
Department of Mechatronics Engineering
CHUNGNAM NATIONAL UNIVERSITY
 In an industrialized nation,
manufacturing is the main wealth creating activity.
 About 1/3 of the value of all goods & services produced in a nation
 Manufacturing
Definition

Definition

Definition
Ref.: OECD(2004), ( )는 국가별 수위도시 인구비중

 Various Concepts of National Income
 Gross National Product (GNP)
 Gross Domestic Product (GDP)
 Net National Product (NNP)/National Income
 Personal Income
Definition

 GNP (국민 총 생산)
 The total money value of all final goods & services produced
by the residents of a country in one year period
 GNP = C + I + G + (X – M)
 C = Consumption Expenditure
 I = Investment
 G = Government Expenditures
 X – M = Net Exports
Definition

 GDP (국내 총 생산)
 The total market value at current prices of all final goods &
services produced within a year by the factors of production
located within a country
 Distinction between GDP and GNP
 GDP = GNP – Net Foreign Income from Abroad
Definition

 Main thrusts in manufacturing engineering
 Automation
 CAD/CAM/CAE/…
 Manufacture with higher precision
 precision engineering
 Sustainable Manufacture
 green growth, green economy, …
Definition

 Various Definitions
 Precision engineering may be broadly defined as work
at the forefont of current technology, implicitly in the field of
metrology and manufacturing technology [McKeown].
 The achievement of dimensions & tolerances in the order of
0.01 mm and surface roughness of 0.001 mm (1 nm)
 Any technology related to features of nanometer scale: thin film,
fine particles, chemical synthesis, advanced microlithography,
and so forth [Drexler].
 The technology of manufacture to dimensions or tolerances
in the range of 0.1 – 100 nm (from the size of the atom to the
wavelength of light) [Franks].
Definition

 Accuracy
 the degree of closeness of
a measured OR calculated quantity
to its actual (true) value
 Precision
 the degree of reproducibility
Precision, Accuracy, & Smoothness

High precision, but low accuracyHigh accuracy, but low precision

 Suppose you machine a certain dimension of a part to length L.
machine with a machine tool
measure the machined parts with a sufficiently accurate instrument
plot the results as the frequency distribution

_
y
_
y

 Bias
 the difference between the mean value & specified dimension
 Mathematical expression
 dm = L –
where, L = specified (or nominal) dimension, = sample mean
_
x
_
x

 Probability Distribution
 The probability distribution of a discrete random variable (r.v.)
 a list of probabilities associated with each of its possible values
 The probability density function of a continuous r.v.
 a function which can be integrated to obtain the probability that
the r.v. takes a value in a given interval.

 Probability Distribution
 A random variable is a function that associates a unique
numerical value with every outcome of an experiment.
 A coin is tossed ten times. The r.v. X is the number of tails that are
noted. X can only take the values 0,1,....,10, so X is a discrete r.v.
 A light bulb is burned until it burns out. The r.v. Y is its lifetime in
hours. Y can take any positive real value, so Y is a continuous r.v.

 Population mean, m
 the mean of a probability distribution (=population)
 Mathematically y continuous
y discrete
 m = E(y), where, E = expected value operator.
 Sample mean,
 A point estimator of a population mean (=the mean of a sample)

n
x
x i
_








m





n
1i
ii )y(Py
)y(yf
_
x

 Accuracy,

 = t-distribution value when the degree of freedom is
f = n-1 and the probability is (1-a).
 n = the sample size (i.e. number of data points used)
 a = the significance level
 n = the unbiased variance
 a non-negative number which gives an idea of how widely spread
the values of the random variable are likely to be.
n
x)
2
,(t
na
fd 
d
)
2
,(t
a
f




n
1i
2
i )xx(
1n
1
n

 Unbiased
 The long-run average or expected value of the point estimator
should be the parameter that is being estimated.
 E( ) = = = = = m
∴ is an unbiased estimator of m.
y













n
y
E
n
1i
i







n
1i
iyE
n
1
 
n
1i
iyE
n
1

n
1in
1
m
y

 Example
 If we take n = 21 and n = 4 mm2 with a = 0.05 = 95% reliability,
= ?
∴ = 0.192 mm.
 The accuracy of the machining process is evaluated as 0.192
mm with a probability of 0.95 (or 95% reliability).
)
2
,(t
a
f
n
x)
2
,(t
na
fd 

 Precision, e
 measured by how small the dispersion e is from the mean value
 Mathematically
 Example
= 4.18 mm.
 this machining process has a precision of 4.18 mm with a
probability of 0.95.
n
a
fe x)
2
,(t
n
a
fe x)
2
,(t

_
y
_
y
 Why high precision?

 State of Current Technology
 PE is the science underlying the manufacture of high precision
machinery.
 Traditional precision machines: watches and cameras
 Computers and their peripheral equipments
 Video equipments
 Aerospace equipments, measuring equipments (including
astronomical telescopes, etc.)
 High precision machine tools
 Telecommunication devices

 Hard disk drive
 Aluminum alloy disk + magnetic head
 Rotational speed = 5,200 ~ 7,200 RPM

 Hard disk drive
 RPM is getting higher.
 ball bearing  air bearing
 aluminum alloy disk  ceramic disk

 Boeing B747-200

a = 0.3~1.0 mm ± 0.02 mm
q = 5°
 Plane-reflection type diffraction grating
 The critical component of spectroscope
 A spectroscope is a device that lets us find out what things
are made of. It works by taking light and splitting it up into its
component colors.

 Shaper-type ruling engine
 engraves grooves spaced at 600 to 1200 lines per mm.
= 83 grooves onto the width of a hair, about 100 mm.
 accumulated pitch error must not exceed 0.2 mm for 1200 grooves.

1. introduction

Recomendados

Recomendados

Más contenido relacionado

Similar a 1. introduction

Similar a 1. introduction (20)

Último

Último (20)

1. introduction