Development of the Mechanical Design of a Video Magnifier: A Comparative FEM and Cost Analysis

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Degree Project

Development of the

Mechanical Design of a Video Magnifier

A Comparative FEM and Cost Analysis

Author: Nora Esho Faris Supervisor: Martin Kroon Examiner: Martin Kroon

Supervisor, company: Fredrik Permo, Henric Stodell

Date: 21-06-08

Course code: 5MT35E,15 hp Subject: Mechanical Engineering Level: Master

Department of Mechanical Engineering Faculty of Technology

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Abstract

LVI develops, manufactures, and sells products for people with impaired vision. These products include different types of video magnifiers and reading machines. The MagniLink ZIP is a foldable and portable video magnifier with an HD monitor which comes in two sizes: 13” and 17”. The video magnifiers have several types of materials produced using different manufacturing methods such as casting, injection molding, 3D printing, etc. The stand holding up the monitor and camera, and the plate module in MagniLink ZIP are cast magnesium alloys. LVI is interested in using composite materials in their products to possibly reduce weight. Composite materials can offer good mechanical properties while maintaining a low density. In order to replace

magnesium alloy, it is important to find a fiber-reinforced plastic with Young’s modulus in the same range as magnesium alloy. PEEK is a high-performance polymer that has excellent mechanical properties among polymers, however it is relatively expensive as well. By reinforcing PEEK with glass and carbon fibers, the Young’s modulus can be increased to the same range as the magnesium alloy in this study with 41 GPa.

The video magnifier is today made up of different types of materials including plastics.

Choice of material influences the design as one should consider the manufacturing method and mechanical properties of the material.

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Sammanfattning

LVI utvecklar, producerar och säljer produkter för personer med nedsatt syn. Dessa produkter inkluderar läskameror och läsmaskiner. MagniLink ZIP är en hopfällbar och portabel läskamera med en HD skärm i storlekarna 13” och 17”. Dessa produkter är uppbyggda av flera typer material som produceras med olika tillverkningsmetoder som gjutning, formsprutning, 3D-printing mm. Stativet som håller upp skärmen och

kameran, och plattan i MagniLink ZIP är delar av gjuten magnesiumlegering. LVI är intresserade av att börja använda kompositmaterial i sina produkter för att eventuellt reducera vikten. Kompositmaterial kan erbjuda bra mekaniska egenskaper och samtidigt bibehålla en låg densitet. För att kunna ersätta magnesiumlegering är det viktigt att hitta fiberförstärkta plaster med elasticitetsmodul som är ungefär lika hög som

magnesiumlegering. PEEK är en polymer med väldigt goda mekaniska egenskaper, den är däremot också dyr. Genom att förstärka PEEK med glas-eller kolfibrer, kan

elasticitetsmodulen höjas till ungefär samma nivå som magnesiumlegeringen i den här studien som var 41GPa. PEEK och PEEK-kompositer är dyra. Olika typer av polymerer utgör redan en del av delarna i läskamerorna. För att kunna ersätta legeringar med plaster måste delarna omkonstrueras eftersom de har olika mekaniska egenskaper men de måste också anpassas för olika tillverkningsmetoder så som formsprutning.

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Acknowledgements

I would like to thank supervisors and design engineers at LVI, Henric Stodell and Fredrik Permo for the opportunity of being part of this project. I would also like to thank my supervisor Martin Kroon, professor in material mechanics at Linnaeus University for his help and guidance in this project.

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1. Introduction

LVI Low Vision International produces, develops and sells products for visually impaired people. The products include different types of magnifiers and a reading machine. A video magnifier is to be developed to better meet customers’ needs.

1.1. Background

A video magnifier is a device that, through a camera and a screen, magnifies text and images. This type of devices is used by vision-impaired people.

Video magnifiers come in many sizes, some being portable while others are stationary. LVI (Low Vision International) manufactures different types of video magnifiers of which one is the MagniLink ZIP. MagniLink ZIP is a foldable and portable video magnifier. It has an HD camera with either 13”

or 17” screen. It is best suited as a stationary device to have at home, work, or school. MagniLink ZIP has cast magnesium alloy stand and plate module.

It has been selected to be further developed in order to better fit customers’

needs among many reasons. The joint connecting the stand and base is unstable to many customers, this can create vibrations during use which should be avoided as much as possible especially when working with magnified text and images. Furthermore, LVI is interested in reducing the weight of MagniLink ZIP by replacing the cast stand by a composite material. When developing this product, there are some aspects of

MagniLink ZIP that are unique to it and should not be changed in order to keep the product uniqueness. Composite materials can offer similar

mechanical properties to metals but with a lower weight. It is also of interest to see whether composite materials will lead to lower production cost

including material costs and production costs.

Figure 1. MagniLink ZIP video magnifier [1]

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1.2. Purpose and objectives

The portable video magnifier would benefit from having a lower weight to enable easier transportation to e.g., school, university, work etc. The MagniLink ZIP is in need of an upgrade in order to better meet customers’

wishes when it comes to stability, which is to reduce the vibration, caused by the joint connecting the stand to the plate module, when using the product. The goal of this project is to find a composite material to replace the magnesium alloy, as well as to redesign the MagniLink ZIP. The new design is going to be simulated to withstand typical loads. The results of this project shall include a design concept inspired by the design of MagniLink TAB which is another portable video magnifier manufactured by LVI.

Figure 2. MagniLink TAB video magnifier by LVI [1]

This project will also include a cost estimation of such material change and in the end a material should be recommended.

1.3. Delimitations

This project will be solely focused on MagniLink ZIP. However, if the material change is successful in the way that it has similar mechanical properties as the original material, and leads to lower manufacturing and material costs, then the composite material will be considered for

MagniLink TAB as well. MagniLink TAB has a milled aluminum alloy stand. The video magnifier would benefit from a low weight material since it was designed to be portable. However, a new design change for MagniLink TAB will not be suggested. A design concept will be generated for

MagniLink ZIP, however no mechanical solutions will be suggested, i.e.

how the joints will be designed and improved. The design should serve as merely a concept to further develop. The main aim is to create a design for simulation purposes which can aid in material selection.

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2. Literature survey

Composite materials are a combination of at least two different materials.

The composite material has superior properties than if the materials would be used separately on their own. Composites take a variety of forms, however the most common is fibers or particles of a particular material embedded in a matrix of another material. Composite materials having a sandwich form is also common, here the surfaces are made of a high- performance material while the core is a lower grade material [2].

Figure 3. Polymer pyramid [3]

Figure 3 is a polymer pyramid of thermoplastics. The plastics in the bottom are so called commodity thermoplastics which are used in non-critical applications where remarkable material properties are not needed and are produced in high volumes. In the middle are the engineering thermoplastics such as PC and PA which have better physical properties than commodity thermoplastics. At top of the pyramid, high-performance thermoplastics which are used in demanding applications. These polymers have stronger inter- and intramolecular bonds. They have superior mechanical properties, relatively high stiffness and strength as well as resistance to wear, creep, and fatigue. These plastics are used in the aerospace and defense industries to name a few [3].

Injection molding is a common manufacturing method for producing plastic components. This method is suitable for mass produced items as well as small volume production and is used to mold thermoplastics and thermosets.

There are many different types of materials available for injection molding.

Thermoplastics need to be able to deform, withstand heat during the manufacturing process while keeping the desired properties, and lastly be able to solidify when formed. With injection molding, there are factors to think about such as the setup and programming. Molding requires a design that is suitable for such manufacturing method [4].

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Composite materials can in some cases replace metals, offering a

lightweight alternative. Composite materials are, however, often associated with high material costs which limits profitability. It is therefore important to choose lower-cost production processes with high productivity. Organo sheet injection process (OSI), developed by FRIMO, has relatively short cycle times for components of thermoplastic materials. The Organo sheets are materials with carbon, glass or aramid fibers fabrics embedded in a thermoplastic matrix. The Organo sheets are preheated then formed in a tool and back injected, see appendix 1. The back injection can be combined with mounting of ribs, reinforcements and perfecting of edges [5].

When calculating the manufacturing cost, the cost drivers to consider are material cost, production cost and mold cost. The material cost depends on the material and on the weight of the material. The production cost depends on the hourly rate, which includes manufacturing the part and tooling or performing a secondary operation, as well as cycle time. The hourly rate is proportional to the size of the injection molding machine. It is common to refer to injection molding machines based on the clamping force they provide, that is, the force that is applied to a mold by the molding machine to keep it closed while the material is injected. The clamping force depends on the projected area of the part, the pressure the material is injected with, and the type of material [6,7].

Figure 4. Projected area of a part [6]

Thus, a larger part requires a larger clamping force which results in a more expensive machine.

The cycle time includes injection, cooling and resetting time. The production cost depends on the cycle time, meaning by a lower cycle time, the

production cost can be reduced. A way to reduce the cycle time, and subsequently the production cost, is to minimize the wall thickness of the part as it will require less time to cool the part [7,8].

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3. Methodology and Implementation

In order to determine whether a composite material can replace magnesium alloy, simulations must be done of the components and the results compared.

MagniLink ZIP has two components made of magnesium alloy, the stand, and the plate module. These components are to be simulated in Solidworks using both magnesium alloy and a fiber-reinforced polymer. The important property for the FRP to have is a same magnitude of E modulus. These simulations will give information of whether the current material can be replaced. The stand will be subjected to a force of 17 N which corresponds to the mass of the screen and the displacement of the stand will be

compared.

A new design for the video camera will be proposed. The design will be created in Solidworks. The new stand will be simulated and be subjected to a force of 17 N and as former simulation, different materials will be

simulated. The new design should adhere to requirements as specified by the manufacturer.

3.1. Theory

In figure 3, there are different types of thermoplastics arranged according to cost and performance. When replacing magnesium alloy with a polymer, the important property to look at is the elastic modulus. Magnesium alloy has an elastic modulus of around 40 GPa. It is important to find a fiber-reinforced composite with the elastic modulus being in the same range, that is at least 40 GPa. Material databases can filter out materials depending on the desired properties. Suitable injection molding grades can be selected from the filtered results. In this case a PEEK composite with 10% carbon fiber and 30% glass fiber was selected since it is an injection molding grade. Other materials in the same range are composites consisting of a unidirectional tape which are suitable for reinforcement purposes [9].

Table 1. Young's modlues and density of magnesium alloy, PEEK composite and PA6 composite

Material Young’s modulus [GPa] Density [g/cm³]

Magnesium Alloy 45 1.7

PEEK composite 41 1.57

PA6 composite 5.1 1.3

PEEK (polyetheretherketone) is high-performance thermoplastic that in many cases can replace metals. The PEEK molecule is stiff due to the aryl groups which result in good mechanical properties such as high abrasion wear and impact toughness [10].

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Figure 5. PEEK molecule [11]

Figure 6. Polyamide 6 molecule [11]

PA6 along with PA66 are the most used engineering thermoplastics. They are used in automotive industry. Polyamides can be reinforced with fibers to increase Young’s modulus as well as lower cost with glass fibers [11].

When estimating the cost of switching to a new material one must take certain factors into consideration such as material cost, part volume, annual quantity, and mold cost to name a few [7].

3.2. CAD modelling

One part of the project is to develop a design concept. This will be achieved using Solidworks software. The CAD model will serve as a design concept for it to be further developed in the future. Simulations will also be

conducted on Solidworks. The simulations are static analyses of the stand.

The whole model is divided into elements and has boundary conditions such as the plate module being fixed at the bottom while a load is applied on top of the frame. The finite element method is a method of numerically solving differential equations to understand structural behavior. The problem domain is divided into small finite elements and differential equations are solved in an approximate manner over each element. These approximations determine the behavior of each element, the elements can then be patched together which allows for approximation of the behavior of the entire body [12].

3.3. Implementation

In order to find out if a fiber-reinforced polymer could replace magnesium alloy, a simple simulation of the stand if performed. A force of 17 N is applied on top of the stand, this corresponds to the weight of the screen and camera. This simple simulation allows the comparison of the current material with a potential material. The simulations are performed in Solidworks.

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Calculating the manufacturing cost requires information about the material and manufacturing method. The manufacturing costs are estimated using a cost estimator website. The estimation is based on the volume of the part which is used to calculate the part mass and then material cost per part. The production cost is assumed to be fixed regardless of the chosen material for the produced part. The production cost is therefore based on cycle time, mold cost, which has been estimated according to molds currently used by LVI to manufacture other plastic parts.

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4. Results

The results include the simulations, the manufacturing costs, and the new design concept.

4.1. Simulation of Current Design

To compare the current material, magnesium alloy, with fiber-reinforced polymers, simulations were done on the current design of MagniLink ZIP.

Figure 7. Displacement chart using magnesium alloy for stand and plate module

The figure above shows the displacement of the stand and plate module both in magnesium alloy. The E modulus of the magnesium alloy is 45 GPa.

Figure 8. Displacement chart using PA6 composite stand and plate module

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Figure 9 – Displacement chart using PEEK composite stand and plate module

The simulation figure above shows the displacement graph for the stand and plate module. The chosen material is a fiber-reinforced polymer with 30%

glass fibers and 10% carbon fibers. The E modulus of the material is 41090 MPa.

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4.2. Cost Calculation

Cost calculation of the manufacturing includes the material price which is based on the volume of the parts, on the machine rate which is approximated to 300 kr/h, as well as mold cost which is estimated based on the mold cost of injection molding molds currently owned by the LVI. The machine rate is merely an approximation to show that cycle time affects the production cost. The higher the cycle time, the higher the production cost.

The material in table 2 is a magnesium alloy with an estimated cost of 50 kr/kg.

Table 2. Part cost, magnesium alloy

Material Cost

Material Mg Alloy

Material Price (kr/kg) 50

Density (g/cm3) 1,7

Part Volume (cm3) 238,4

Mass (kg) 0,405

Material Cost per Part (kr) 20,26

Total Material Cost, annual (kr) 18238

Production Cost

Cycle Time (s) 25

Mold Cost (kr) 60 000

Mold Cost per Part (kr) 66,67

Machine rate (kr/h) 300

Total Production Cost, annual (kr) 1875

Production Cost per Part (kr) 2,08

Mold Cost 60000

Mold Cost per Part 66,67

Total Cost Per Part (kr) 89,01

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The material in table 3 is a PEEK composite with 30% glass fibers and 10% carbon fibers. An approximate material price of 860 kr/kg is assumed which is in the range of what PEEK polymer usually costs.

Table 3. Part cost, PEEK composite

Material Cost

Material PEEK-CF10-GF30

Density (g/cm3) 1,57

Mass (kg) 0,374

Production Cost

Cycle Time (s) 25

Mold Cost (kr) 60000

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Table 4 is a part cost estimation of PA6 composite with 25% glass fibers.

The cost of the material was estimated to about 18 kr/kg. This was the most affordable of the selected materials in this study.

Table 4. Part cost, PA6 composite with 25% glass fibers

4.3. Design Concept

The new design concept proposed is inspired by MagniLink TAB, having a similar stand. The position of the camera and screen are kept in the same position as the MagniLink ZIP, being attached to the stand. The new proposed design does not offer any mechanical solutions but serves as a concept to be further developed. The following figures will show the concept in different positions, open use position where the camera lens is directed down on the plate module and in closed position for transportation and storage.

Material Cost

Material PA6-GF25

Density (g/cm3) 1,33

Mass (kg) 0,317

Production Cost

Cycle Time (s) 25

Mold Cost 60000

Mold Cost per Part 66,67

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Figure 10 - video magnifier in open, reading position, right side and front view

The figures above display the video magnifier in reading mode where the camera lens is pointed down at the plate module.

Figure 11. video magnifier in reading mode, top and dimetric view

Figure 12. side view when closed

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Figure 13. Top view when closed

Figures 13 and 12 show the video magnifier when closed with a 13” monitor.

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4.4. Static Analysis

Figure 14 - PEEK composite

Figure 15 - Magnesium alloy

The figures above show the static analyses of the design concept. The stand is positioned in reading mode where the camera lens would be facing downwards.

The plate module s fixed at the bottom. A load of 17 N corresponding to the screen and camera are applied at the top of the stand where the camera is fixed along with the screen. The maximum displacement is seen in the part where the camera is fixed. For PEEK composite the maximum displacement is

approximately 3.3 mm while it is about 3.1 mm for magnesium alloy.

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5. Discussion

5.1 Methods discussion

Performing simulations on the current design (chapter 4.1) is a good method to understand material behavior. It would have been beneficial to simulate the entire assembly in order to understand the design and how it can be improved or even experiment with different wall thicknesses.

The basic aspects of a cost calculation are included when estimating the cost of materials and production in chapter 4.2. However, there are more aspects to think about which influence the estimation. These aspects include for instance runner volume, material markup and post-processing time to name a few. The cost estimation should therefore serve as a rough estimation and including other aspects would provide a more realistic estimation. The design volume affects costs related to material, it is therefore important to base these estimations on final designs to get a realistic number.

5.2 Results discussion

The simulations of the current design of the stand of the video magnifier allows to understand how different materials withstand the same load and is a good method to compare materials with each other. Comparing the

simulation results of figure 7, 8 and 9, one can see the different materials produce different results. The insignificant difference in displacement between the magnesium alloy (fig.3) and the PEEK composite (fig.5) suggests that a fiber-reinforced polymer could replace magnesium alloy as the elastic modulus is in the same range. Figure 8 (PA6 composite) shows larger deformation as compared to the magnesium alloy due to differences in mechanical properties. The PA6 composite has a Young’s modulus of 5.1 GPa as compared to the magnesium alloy which has a Young’s modulus of 45 GPa. The largest deformations can be seen in the joint of the stand where the camera and screen would be attached (where the load was applied in simulation). As magnesium had higher Young’s modulus than both the PEEK composite and the PA6 composite, it showed, as expected, smaller deformations than both composites. However, the maximum displacement of the PEEK composite did not deviate much from the magnesium, thus the Mg alloy can be replaced by PEEK composite. In this simulation, the PA6 composite had a maximum displacement which was 3.3 larger than Mg alloy while the maximum displacement of the PEEK composite was 1.03 larger than the maximum displacement of Mg alloy. This suggests that PEEK composite is a suitable replacement in terms of performance.

The high cost of PEEK results in relatively high cost per part compared to the other materials in this study. As PEEK is a high-performance material (see fig. 2), it is one of the most expensive polymers on the market.

However, it is used in applications where weight reduction is essential. In

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this case, since the current material used (magnesium alloy) is a relatively light-weight metal alloy, there is no need for it to be replaced by another material for weight-reduction purposes. The density of the magnesium alloy in this study is 1,7 g/cm³,and 1,57 g/cm³ for the PEEK composite. The weight reduction of replacing magnesium alloy with PEEK composite would amount to about 8%. Changing to PA6 composte which has a density of 1.3 g/cm³ would result in a weight reduction of approximately 24%.

Considering the price difference of the two materials (magnesium on average costing approximately 4$/kg while PEEK (not composite) costing 50-100$/kg), it is not advised to change material for such small

improvement.

It might be possible to select a more affordable material by improving the design. Engineering thermoplastics are more affordable than high-

performance thermoplastics (figure 3) and an improved design might allow for such material change. One way to improve the design and have it withstand typical loads without deforming to an extent which is

unacceptable during use of the product, is to increase the wall thickness of the parts, however this would result in higher cycle time (injection, cooling and resetting time) which might subsequently result in higher production costs. Table 1-3 shows the material and manufacturing costs of the different materials. The cost is based on one part (stand) of the design concept in figures 10-13. The machine rate is a rather arbitrary number to show how the cycle time affects the production cost. The higher the cycle time, the higher the production cost. Therefore, one should focus on either reducing cycle time or having thicker wall thickness in case a material with lower Young’s modulus is used.

The design in figures 14-15 is used for simulation purposes to showcase how the different materials behave. Improved design certainly influences the results however the difference in results between these materials would not be affected. It is therefore sufficient to gather data from material datasheets and choose material based on the desired value of a certain mechanical property.

5.3 Relevance for the society

Video magnifiers serve a purpose for vision-impaired people. This product is necessity as it aids in everyday life for a lot of people. This project serves to improve a product that is vital for people with impaired vision. The goal is to make these types of product easier to carry around by reducing the weight and bulk as well as improve the quality by potentially using better materials and manufacturing methods. LVI products create a more inclusive world where an impairment is not an obstacle.

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6. Conclusions

The purpose of the project was to find a material that would serve as a good replacement for the currently used material. The aim was to reduce weight and find out how this material change affects the any related costs. The simulations revealed that PEEK would be a great option however the high material cost of PEEK and its composites is a drawback. It is therefore recommended to keep using the same material, magnesium alloy, for the stand and plate module as it is both lightweight and affordable. Engineering materials can be used if the design is such that it can carry the load of the camera, screen, and other components.

The design concept is inspired by MagniLink TAB, another product by LVI, and should be further developed in order to be functional. For future work, a prototype could be created to test the product during use. The concept should be further developed to fit all the essential components of the product, at the same time reduce bulk and make it foldable and easier to carry around. Other manufacturing methods other than injection molding should be considered in future work, such as Organo sheet molding presented in chapter 2.

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References

[1] ”LVI Low Vision Internationl,” [Online]. Available:

https://lvi.se/catalog/products/magnilink-tab. [Använd 25 May 2021].

[2] M. F. Ashby, H. Shercliff och D. Ce, Materials: Engineering, Science, Processing and Design, Butterworth-Heinemann, 2013.

[3] O. Jacobs, Common Plastics, lecture notes, Polymer Science, Technische Hochschule Lübeck, 7 December 2020.

[4] V. Goodship, B. Middleton och R. Cherrington, Design and manufacture of plastic components for multifunctionality : structural composites, injection molding, and 3D printing, Oxford: W.Andrew, 2016.

[5] ”FRIMO. High Tech and High Passion,” [Online]. Available:

https://www.frimo.com/en/organo-sheet-injection. [Använd 07 May 2021].

[6] ”CustomPartNet,” [Online]. Available:

https://www.custompartnet.com/estimate/injection-molding-std/. [Använd 22 April 2021].

[7] C. G. Turc, C. Cărăuşu och G. Belgiu, ”Part cost estimation in injection moulding,” OP conference series. Materials Science and Engineering, vol. 400, nr 4, p. 42058, 2018.

[8] ”CustomPartNet,” [Online]. Available:

https://www.custompartnet.com/wu/InjectionMolding. [Använd 22 April 2021].

[9] ”Campus Plastics,” [Online]. Available:

https://www.campusplastics.com/campus/en/datasheet/LNP%E2%84%A2 +THERMOCOMP%E2%84%A2+LCF62E+-

+Europe/SABIC/658/fce0df37/SI?pos=4. [Använd 1 April 2021].

[10] O. Jacobs, Amorphous Thermoplastics, Lübeck: Technische Hochschule Lübeck, 2020.

[11] J. R. Fried, Polymer Science and Technology, Westford: Prentice Hall, 2014.

[12] N. Ottosen och H. Petersson, Introduction to the Finite Element Method, New : Prentice-Hall, 1992.

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Appendices

Appendix 1: Directions for the front page

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Development of the Mechanical Design of a Video Magnifier: A Comparative FEM and Cost Analysis

Degree Project