BACKGROUND

Glass is the optimal choice for mobile device makers worldwide. Through glass the

clarity of pictures and graphics are sharper, the touch screen response is more sensi-

tive, colour change of the glass is not a worry when it is exposed to sunlight for an ex-

cessive amount of time, and glass is more resistant to scratches than other transparent

mediums.

Companies are interested in testing glass to differentiate several types of glasses from

various manufacturers. Poor quality glass can lead to countless recalls, repair costs at

expense of company and unsatisfied customers. Testing glass for mobile devices al-

ready exists in the industry, but these methods are inconsistent, lack instrumentation

providing immediate test results and limited in terms of the variety of tests that can

be done.

GOALS & SCOPE

Goal

To create an instrumented localized impact tester to evaluate the resistance to crack

initiation and growth in glass. We must ensure that the impact tester can control the

following variables:

1. Speed and energy of the glass into the impactor; and

2. Type of impact into the glass

Scope

There are 3 important aspects to the impact tester:

Linear Motorized Guide Rail – must be able to reach a velocity high enough and

within a reasonable distance to replicate a 1.5m drop for different device weights

Modular Fixture – mount the test specimen for impact, low weight (200g), and

METHODOLOGY

1. Client Needs Assessment: Define voice of customer

2. Define: Create goal and scope for the design

3. Brainstorming and Selection Process: Generate designs and select based on feasi-

bility

4. Design: Take selected design and create a computer aided model

5. Refine Design: Meet with client and redesign based on client concerns

6. Quality Assurance: Test design using Finite Element Analysis (FEA) and classical

methods

CONCLUSIONS

The instrumented local contact impact tester is consistent, compact and can pro-

vide a variety of tests. The method of impact chosen is kinetic energy through the

use of the linear motion of a towing cart attached to a belt driven motor. A latch

connecting the towing cart to the test cart disengages when approaching the impac-

tor, leading to consistent results regardless of velocity. Included in the tester is a dy-

namic impact load cell located behind the impactor measuring results on the test

apparatus without the need for multiple load cells or large test areas. Various por-

tions of the glass can be tested by moving the impactor in the vertical or in the hori-

zontal direction, giving the ability to perform various tests.

Graph A -Displays the forces seen on the test cart and impactor @ 1ms impact time

and travelling mass of 198 grams

Linear Motorized Guide Rail

Interchangeable Impactor

Modular Fixture

Test Cart 1

Test Cart 2

Release Mechanism

Specimen Clamp

DESIGN

Test carts: Test Cart 1 drives Test Cart 2 to the desired velocity for impact on the

glass specimen

Interchangeable Impactor: Can be changed to evaluate different types of impact and

measure the force of impact through the connected load cell

Modular Fixture: Keeps the glass specimen upright during impact and meets the low

weight requirement of 200g to resemble the weight of an actual mobile device

Specimen Clamp: Able to clamp glass specimen in specific orientations

Release Mechanism: Is activated upon impact with the release post; used to release

Test Cart 2 from Test Cart 1 creating a free impact and reduce damage on Linear

Motorize Guide Rail

Linear Motor: Belt driven Tol-O-Matic Motor capable of achieving 0 - 10 m/s in

0.1 m/s increments.

ANALYSIS

Figure C — Stress Analysis of the Modular Fixture and of the Impactor Grid Using 4000N

PCB Piezotronics

Load Cell

Capstone Design Course

Instrumented Local Impact Tester for Research In Motion Brandon Ramsundar Jaimin Patel Prabhdyal Ravi Suri Syed Shaheer Aziz

Professor: Lidan You ECP: Aaron Persad

Figure A — Overview of Instrumented Local Impact Tester

Figure B — Close-up View of Modular Fixture & Release Mechanism

The Impulse equation (Impulse=Mass*∆Velocity) was used to determine the

force of impact, which was later inputted into ANSYS to design modular fixture

and the impactor grid.

ANSYS was used to:

Evaluate the critical parts during impact to ensure the part does not fail

Iterative testing to reduce weight of the modular fixture

Analysis showed that the maximum stress was concentrated around the clamp lo-

cations

0

500

1000

1500

2000

2500

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11

Velocity (m/s)

Impact vs. Velocity

Imp

ac

t Fo

rce

(N)

Release Post

5.4 m/s velocity replicates

1.5m drop