IPAD Weight Scale Mechanism Design

A MECHANISM FOR
IPAD WEIGHT SCALE
ME492 Engineering Project Presentation
DORUK ANGUN
Dept. Of Mechanical Engineering
Yeditepe University, ISTANBUL
Adviser: Asst. Prof. Namık Cıblak

Outline
 The Need and the Statement of the Problem
 The Objective & The Scope
 Literature Survey
 Preliminary Design Alternatives
 Detailed Design
 Conclusion
 References
02/06/15YEDITEPE UNI./ ISTANBUL
2

The Need and the Statement of the Problem
 People want IPAD to
do multiple tasks.
 Weighing an object
is a common thing
to do.
 There is a demand
for IPAD weight
scale.
 Weighing by using
the position change
of the slider.
Definition of the Need Statement of the Problem
3

The Objectives & The Scopes
 Low cost
 Accurate
 Precise
 Compact size
 Ease of installation
 Esthetic look
 Jewel bearing
 Registering a touch
 Harmless to IPAD
 Using the screen as
much as possible.
Objectives Scopes
4

Literature Survey
Parallelogram Linkage
 Consists of two identical
cranks fixed with a
distance between.
 Four straight sides.
 Opposing sides, parallel
and same length.
5

Literature Survey
Slider-Crank
Mechanism
 Converts rotational
motion in to translational
motion.
 Consists of a rotating
driving beam, a
connection rod and a
sliding body.
6

Literature Survey
Capacitive
Touchscreen
 IPAD 2 has a capacitive
touchscreen.
 In capacitive
touchscreens, there is
an insulator such as
glass coated with
indium tin oxide as
conductor.
 Touching, distortion in
the electrostatic field,
determining where the
body is touching. 02/06/15YEDITEPE UNI./ ISTANBUL
7

Preliminary Design Alternatives
Involute Mechanism
Slider-crank
mechanism
with guided stylus
Parallelogram with
Slider-crank
mechanism
8
Mechanism Ideas

Battery-Powered Stylus Jointed Stylus Stylus with Wheel
9
Stylus Ideas

0
10
20
30
40
50
60
Involute
mechanism
Slider-crank
mechanism
with guided
stylus
Parallelogram
with slider-
crank
mechanism
%
Mechanism
Series1
0
10
20
30
40
50
60
Battery
powered
stylus
Jointed stylus Stylus with
wheel
%
Stylus (slider)
Series1
10

Detailed Design
Parallelogram with Slider Crank Mechanism + Stylus With Wheel
+Weight Top part goes downExtension spring extends Slider goes forward
-WeightExtension spring relaxesTop part goes upSlider goes back
11

Detailed Design
Analysis
FBD of Crank FBD of Slider FBD of Top
12

Detailed Design
Numerical Implementation
13

Detailed Design
MATLAB Calculations
Inputs
“1” represents the weight holder, “2” represents the crank and “3”
represents the slider.
 Masses (kg)
m1=0.137, m2=0.172 , m3=0.086
 Link Lengths (m)
r1=0.11, r2=0.15, r3=0.15
 Connection points (m)
Length of the spring holder a=0.25*r2,
Distance between spring holder and the top of the link c=0.9*r2
 Target mass range (kg)
W∈ [0; 0.427,5]
 Target θ range (degrees)
θ∈ [75; 15]
14

Detailed Design
MATLAB Calculations
Outputs
 k = 664.2478 N/m
 L0 = 0.0752 m
15

Detailed Design
Mass vs. Theta Slider Position vs. Mass
16

Detailed Design
3D Modelling of the Design
7 parts
 Jewel (pivot hole)
 Pin
 Link
 Spring holders
 Base
 Top (weight holder)
17

Detailed Design
3D Modelling of the Design
Jewel Bearing
Torus shape hole
(bigger diameter)
+
Shaft
(smaller diameter)
Minimum fricition, better
than other bearings.
18

Detailed Design
Manufacturing Process
19

Detailed Design
Manufacturing Process
20

Detailed Design
 k=664.2478 N/m (MATLAB)
 L0=0.0752 m (MATLAB)
 d= 1 mm (design criteria)
 D=5.85 mm ( )
 C= 5.8499 ( )
NOT APPLICABLE
(ADJUSTING IS DIFFICULT)
 k=35.5 N/m (easy to adjust)
 Adjustable hook (adjustable
L0)
02/06/15
21
YEDITEPE UNI./ ISTANBUL
Extension Spring Rubber Band
Spring Design

Detailed Design
Final Design
22

Detailed Design
Experimental Results
23
Location Location Location Location Location Location Location Location
77,5 g 127,5 g 177,5 g 227,5 g 277,5 g 327,5 g 377,5 g 427,5 g
6 43 52 101 125 182 247 388
6 42 55 101 122 182 256 391
6 42 55 101 125 182 259 387
4 41 54 102 129 188 260 411
4 41 57 104 125 183 265 437
4 42 58 97 125 186 266 417
4 42 57 96 125 193 276 413
4 42 57 100 126 184 282 413
4 40 57 103 129 191 267 408
4 42 57 100 127 183 271 418
Mass(g) Location
77,5 4,6
127,5 41,7
177,5 55,9
227,5 100,5
277,5 125,8
327,5 185,4
377,5 264,9
427,5 408,3

Detailed Design
24
y = 3E-06x3 - 0.0044x2 + 2.1309x + 62.128
R² = 0.99474
0
50
100
150
200
250
300
350
400
450
0 100 200 300 400 500
Mass(g)
Slider Position (pixels)
Series1
Poly. (Series1)

Detailed Design
25
Position Weight (g) Average (g) Accuracy (%) Accuracy (AVG %) Precision (g)
101 235,555403 234,868503 3,540836484 3,238902549 10,727584
101 235,555403 234,868503 3,540836484
101 235,555403 234,868503 3,540836484
102 236,885824 234,868503 4,125636923
104 239,525792 234,868503 5,286062418
97 230,163719 234,868503 1,170865495
96 228,798208 234,868503 0,570640879
100 234,218 234,868503 2,952967033
103 238,209281 234,868503 4,707376264
100 234,218 234,868503 2,952967033

Conclusion
In this project
A working mechanism for IPAD weight scale is created by
 Selecting its design among preliminary design ideas.
 Applying a load analysis by using MATLAB.
 3D Modeling and assembling its parts on SOLIDWORKS.
 Manufacturing its parts.
 Calibrating it by conducting experiments.
Total Weight =823.71 grams
Dimensions=200mm*150mm*25mm
Capacity= 427,5 grams
Accuracy=+-3.25 grams
Precision= 10.73 grams
Total Cost= 450 TL
26

References
 [1] Tian, Y., Yao, Y.-A., Wei, X., Joneja, A. “Sliding-crawling
parallelogram mechanism” (2014)
 [2] H. Jiguang, Z. Chuanyan, Z. Weiyang, “Slider Crank
Mechanism Design with Time Ratio and Minimum
Transmission Angle” (2014)
 [3] G. E. Burnett, D. R. Large, G. Lawson, S. De-Kremer, L.
Skrypchuk “A comparison of resistive and capacitive
touchscreens for use within vehicles” (2013)
 [4] UBC. (n.d.). Stretching of Rubber Bands. Retrieved
from
http://c21.phas.ubc.ca/sites/default/files/rubber_band_write_u
p.pdf
27

THANK YOU FOR
LISTENING
28

Appendix
150
200
A1
A2
B1
B2
B3
B4
A3
A4
X
Y
0
0
ETİKET X KONUMU Y KONUMU BOYUT
A1 5 -105
2,50 4
M3 - 6H 6
A2 5 -5
2,50 4
M3 - 6H 6
A3 145 -105 2,50 4
M3 - 6H 6
A4 145 -5
2,50 4
M3 - 6H 6
B1 37 -105 3 X 9
B2 37 -5 3 X 9
B3 113 -105 3 X 9
B4 113 -5 3 X 9
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
ÇİZEN
DENET.
ONAY.
ÜRET.
KALİTE
AKSİ BELİRTİLMEDİĞİ SÜRECE:
BOYUTLAR MİLİMETREDİR
YÜZEY CİLASI:
TOLERANSLAR:
DOĞRUSAL:
AÇISAL:
BİTİRME: KESKİN KENARLARI
PAHLAYIN VE
KIRIN
İSİM İMZA TARİH
MALZEME:
TEKNİK RESMİ ÖLÇEKLENDİRMEYİN REVİZYON
BAŞLIK:
RESİM NO.
ÖLÇEK:1:2 SAYFA 1 / 1
A3
ALUMINIUM
AĞIRLIK:
ANGUN
CIBLAK
CIBLAK
1
BASE
150
110
A1
A2
B1
B2
B3 B4 B5
B6
A3
A4
X
Y
0
0
ETİKET X KONUMU Y KONUMU BOYUT
A1 5 -105
2,50 4
M3 - 6H 6
A2 5 -5
2,50 4
M3 - 6H 6
A3 145 -105
2,50 4
M3 - 6H 6
A4 145 -5 2,50 4
M3 - 6H 6
B1 37 -105 3 X 9
B2 37 -5 3 X 9
B3 59 -105 3 X 9
B4 91 -105 3 X 9
B5 113 -105 3 X 9
B6 113 -5 3 X 9
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
ÇİZEN
DENET.
ONAY.
ÜRET.
KALİTE
YÜZEY CİLASI:
TOLERANSLAR:
DOĞRUSAL:
AÇISAL:
PAHLAYIN VE
KIRIN
İSİM İMZA TARİH
MALZEME:
BAŞLIK:
RESİM NO.
A3
21.05.2015
AĞIRLIK:
ANGUN
CIBLAK
2
TOP
40
20
14
6
10
2,50
3
C
D
E
B
F
A
23 14
C
F
E
A
B
D
2 14 3
ÇİZEN
DENET.
ONAY.
ÜRET.
KALİTE
YÜZEY CİLASI:
TOLERANSLAR:
DOĞRUSAL:
AÇISAL:
PAHLAYIN VE
KIRIN
İSİM İMZA TARİH
MALZEME:
BAŞLIK:
RESİM NO.
A3
AĞIRLIK:
SPRING HOLDER NEW
29

Appendix
1.1.1 Angle function
function y=angle(x)
y=- 2.1*e-19*x^(10) + 2.5*e-16*x^(9) - 1.3*e-13*x^(8) + 3.6*e-
11*x^(7) - 6.1*e-09*x^(6) +6.5*e-07*x^(5) - 4.2*e-05*x^(4) +
0.0015*x^(3) - 0.029*x^(2) + 0.0048*x + 75;
1.1.2 Function of theta function
function [fth,rsA,alp]=fOfTheta(th,W)
global a b c w1 w2 w3 r1 r2
th=pi/180*th;
rsvec=(r2-c)*[cos(th);sin(th)]+a*[-sin(th);cos(th)];
rsAvec=[r1;0]+rsvec;
rsA=norm(rsAvec);
alp=atan2(rsAvec(2),rsAvec(1));
fth=(r2*(w1+w2+W)+1/2*w3*(r2-b))*cos(th)/((r2-c)*sin(th-
alp)+a*cos(th-alp));
end
30

Appendix
1.1.1 Forces function
function [th,W,s,Fs,alp]=iPadFun(k,L0,thmax,thmin,nth)
global a b c w1 w2 w3 r1 r2 r3
thmax=thmax*pi/180;
thmin=thmin*pi/180;
th=linspace(thmin,thmax,nth);
W=zeros(size(th));
Fs=zeros(size(th));
alp=zeros(size(th));
s=zeros(size(th));
for ii=1:nth
rsvec=(r2-c)*[cos(th(ii));sin(th(ii))]+a*[-
sin(th(ii));cos(th(ii))];
rsAvec=[r1;0]+rsvec;
rsA=norm(rsAvec);
alp(ii)=atan2(rsAvec(2),rsAvec(1));
Fs(ii)=k*(rsA-L0);
W(ii)=Fs(ii)*((r2-c)*sin(th(ii)-
alp(ii))+a*cos(th(ii)-alp(ii)))/cos(th(ii))/r2-
(w1+w2+1/2*w3*(1-b/r2));
sPoly=[1,-2*(r2-b)*cos(th(ii)),(r2-b)^2-r3^2];
s(ii)=max(roots(sPoly));
end
th=th*180/pi;
alp=alp*180/pi;
end
1.1.2 Output function
function [k,L0]=iPadKL0(Wmax,thmax,thmin)
[fthmax,rsAmax]=fOfTheta(thmin,Wmax);
[fthmin,rsAmin]=fOfTheta(thmax,0);
k=(fthmax-fthmin)/(rsAmax-rsAmin);
L0=rsAmax-fthmax/k;
end
31

IPAD Weight Scale Mechanism Design

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