Altered Images -

Thermal Distortion of an Overhead Projector

Ray Ellender

Elite Consulting Ltd.

Company

• Engineering Consultancy in UK• Office in Northampton• Long-Time Mechanica Users• CEP’s, Structure & Motion• Specialise in Mechanica-based FE and Dynamics Consultancy• General Engineering Problem Solving

Design and Project Management• PTC Functional Simulation Resellers• Pro/Mechanica and Pro/E Training

The Problem

• New Design of Reflective OHP• Thermal Distortion

of Base• Distortion of Image

The Method

• Make Simplified Model• Correlate with Test• Understand the Mechanism• Brain Storm a Solution

– Short-Term

– Long-Term

The Model

• Simple Mechanica Model• Deflection Measures

Thermal Analysis

• Set Up Temp Loads• (Load as a Function

of Coordinates)• Correlate with

Measurements• Take Results into

Structure

Structural Analysis

• Set Up Baseline Analysis• Correlate with

Measurements• Review Results

Understand the Problem

• Hotter at Top than Bottom• Platten Expands more

than ‘Ground’ Level• Therefore Get Bowing

of the Base• Takes Arm Support

with it

Potential Solutions - 1

• Reduce Temperature– Reduce Heat Input Tried - works

– Insulate Base Not very good

– Conduct Heat Away Not tried

• Change Material – Lower CTE Tried - works

• Stiffen Base Didn’t work

• Cut out most of Platten Didn’t work

Potential Solutions - 2

• Isolate Arm Base from Platten

(Hinge) Didn’t work

• Mount Arm to Ali Plate &

Control Plate Movement Not good enough

• Modify Geometry

(Lower Platten) Worked well

• Make Lower Plate High CTE Worked

• Bond Low CTE to Platten

(Bimetallic Strip) Worked too well

SolutionsReduce Temperature

• Reduce Temp

from 60o to 45o

• Improvement

As expected

SolutionsReduce CTE

• CTE reduced

from 10 x 105 (ABS)

to 7.3 x 105 (PC/ABS)• Works as expected

Solutions ?‘Hinge’

• Hinge to Isolate

Arm Mtg Area• Didn’t Work

Solutions ?Stiffer base - Ali Plate Underneath

• 3mm Ali Plate• Deflection Worse• Note Ali :

CTE = 2.3 x 105

SolutionsHigh CTE Plate Underneath

• PE Plate underneath• CTE = 15 x 105

• Deflection improved,

if high enough temp.

Solutions‘Bimetallic Strip’

• 1mm Ali Plate

attached to Platten

(2.3 x 105 CTE)• Works too well

Solutions ‘Bimetallic Strip’

• Smaller Ali Plate• Bonded to ABS• Not so severe• Next step to Optimise

SolutionsLower Platten Surface

• Lower by 15mm• Much Improved• Long Term Solution• To be Optimised

SolutionsLower Platten Surface

• Global Sensitivity• 12-17mm Depression

Is best• Virtually any amount

of depression is good

Angular Deflection v. Platten Depression

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0 5 10 15 20 25

Platten Depression (mm)

Ang

ular

Def

n (d

eg)

SolutionsLower Platten Surface

• Leave middle of platten undepressed to mount Fresnel lens

• Details require further development

Summary

• 24 Runs in 3 days• Wide Range of Different

Solutions• Thermal Solution often

Counter-intuitive• Concept Model enabled

Solutions to be found quickly

• Short & Long Term Solutions found