Final Design Review of Light Measurement System

8/3/2019 Final Design Review of Light Measurement System

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The Optical Revolver: Final Design Review

Team Orange

Griffin Beemiller

Mate 340.360

Dr. Savage & Dr. London

12/3/10



1

Introduction

The cones in the human eye are sensitive to color which is measured in chromaticity values corresponding

to a two dimensional color scheme. Cathode Ray Tube TVs (CRTs) emit a spectrum of wavelengths of light that are

most recognizable to the human eye[1]

. A client has asked Team Orange to create a system that will filter the light

transmitted from a tungsten halogen light bulb with absorbance and dichroic filters; both with red, green and blue

separate color values. Team Orange has since researched, fabricated, and tested a Light Measurement System

(LMS) with an easy to use Revolver design. The LMS is a tool used in industry to measure quantitative color values

of light filters in order to ensure that the filtered light spectrum reflects the true color value of red, green, and blue

(RGB). These true colors are necessary to produce the multi colored screens in many LCD screens and countless

other applications in which these three basic colors produce a vast spectrum of colors.

User Needs

The need of the client was determined to be a holder for RGB plastic filters as well as three dichotic filters.

This holder needed to be a sturdy base that will be stable enough for long term reproducibility of.1% and also

simple enough to use for quick and easy repeatability of.04% in less than 5 seconds. The base must be easy

enough to use efficiently on an assembly line. The measured chromaticity values from the LMS must be comparable

to the chromaticity values produced by LCD pixels designed with back-lighted filters[2]

. This base must have a fiber

optic connection that will connect to a quartz halogen lamp, filter the light, and send the light to a spectrometer. The

base must therefore have fiber optic connections before and after the light filtration. The LMS base must be under

$500 and had to be designed and fabricated in less than 10 weeks.

Design of Base

The prototyped base was made out of A356 cast aluminum alloy, which will be discussed later in the

metallurgical analysis of the casting, and the wheel was rapid prototyped made of acrylonitrile butadiene styrene

(ABS)[3]

. Lenses and lens columns were purchased and positioned at the fiber optic connections in order to columnize

the incoming light and refocus the filtered light back into the second fiber optic cable. A system block diagram of this

process can be seen in Figure 1. Alignment of the light beams through the base is critical. The fiber optic cables must

transmit as much light as possible with minimal light loss on the surface of the end of the cable. For this reason

extensive polishing was done on the surface of each end of the cables. Upon connecting the fiber optic to the base,

the columnizer lens is perfectly aligned in order to parallelize the light rays and later refocus the rays back into the

fiber optic cable on the other side of the base. This process can be seen in Figure 2.



2

Figure 1: This system level block diagram above displays the principle components of the LMS and was used to

schematically determine the best design based on functional requirements

Figure 2: This figure expresses how crucial the alignment of the lenses is in order to focus the light rays accurately into the optic

cable on the right side of the figure. For this reason the light exit column must be adjustable in order to put the cable connection

precisely at the focal length of the lens.



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Our decision came down to choosing between two simple bases. One design shown in Figure 3 is the Drop-

In design where different the different filters would be simply dropped in through the top of the base. The slot would

be just big enough for the holder with a tolerance of 0.1 under the assumption that any extra space would run the risk

of light loss. Our other design shown in Figure 4 involves a rotating wheel that holds the three plastic filters so that the

change in color filtration can be done simply and easily. The original design involved the wheel spinning freely with 3

notches on the edge of the wheel to catch a small piece of spring steel and hold it in place. Upon fabrication of the

components it was realized that the friction between the A356 base and the ABS wheel is high enough for the wheel

to be stuck in place without spin. This friction fit increases stability of the design allowing for minimal movement when

obtaining color values.

(Hand drawn sketch)

Figure 3: The sketch above shows the top view of the basic

design for the Drop-In Filter Holder. They cylindrical filter

holder would be simply dropped into place from the top of

the base.

(Hand drawn sketch)

Figure 4: The sketch above shows the top view of the

Revolver Filter Holder. This design requires only the spin of

a wheel to change to a different colored filter, and the

replacement of the wheel to filter with dichroic filters.



4

Design Solution – Choosing Revolver

Given the functional requirements of the LMS and the components of the system, the decision

matrix between the two designs was determined using weighting factors[4]

for each attribute which can be

seen in Table I. The table shows the different attributes considered in the design of the LMS base and

their respective weighting factors and the collaborative score that each design received from Team

Orange. The respective values were added up and totaled at the bottom of the table. Note that the Drop-

In Design won by a value of only 0.4

A sensitivity analysis was conducted by changing the weighting factors yet the Drop-In base still

won indicating insensitive results. Although the drop in design scored higher in the decision matrix, the

decision was made to fabricate the revolver design for the following reasons.

1. Team Orange would become more familiar with the ABS rapid prototyper

2. The revolver better meets the loading and measuring time requirements

3. The design is more user friendly and ergonomic

4. Reduces possible operator errors that may occur

5. Reduces the chance of damaging the lens from mishandling

The revolver design solution meets and exceeds the expectations of the client in that the light

sources gets filtered with any of the six filters with a high ease of use. The revolving filter mechanism

allows only fractions of a second to change the filter color between single chromatic filters and less than

30 seconds to switch in the dichroic filter wheel. A disadvantage of the revolver is that it requires more

ABS parts which cost more money, but it was later realized that the ABS parts were not of too high cost.

Table I: Conceptual Design Decision Matrix

Drop-In LMS Revolver LMS

Attribute/Criteria Measureable Objectives Score Weight Value Score Weight Value

Operation No light loss; maintain calibration; easy loading 8.7 0.15 1.31 9.2 0.15 1.38

Stability Rpt. .4; Repro. ±0.1 against RGB filters 9 0.3 2.7 8.7 0.3 2.61

Ergonomics Compact as Possible 8.2 0.05 0.41 9.3 0.05 0.47

Safety Shielded power supply; non toxic materials 10 0.05 0.5 9.7 0.05 0.49

Manufacturability Prototypability; must be cast 9.5 0.1 0.95 8.3 0.1 0.83

Cost $500 9 0.15 1.35 7.7 0.15 1.16

Schedule 10 weeks 9.8 0.2 1.96 9.3 0.2 1.86

9.2 8.8



5

Problems and Solutions

The original design concept involved one wheel, and the removal of the three plastic filters and

their holders to place the dichroic filters holders in the wheel with a friction fit. When a problem arose with

a CAD dimensioning mistake for the rapid prototyped wheel, the decision was made to friction fit the

filters in the wheel without the filter holders, shown in Figure 5, (saving us money at $17 dollars each

filter) and make another ABS wheel with larger diameter holes to hold the diachronic filter holders. What

was at first design problem turned out to lower our overall cost of the prototype and make our device

more user friendly by having two separate wheels for plastic and for dichroic filters.

Another problem that was determined was crucial alignment of the lens columns. This problem

was solved with 5 set screws for one column with low stability, and 2 for the other, slightly more stable

column. The set screws worked perfectly with low cost and high effectiveness. The final design can be

seen in Figure 6 A and B and the drawings for these parts can be seen at the end of the report.

Figure 5: The picture on the left shows the single wavelength filter

wheel and the red green and blue plastic filters that are placed in the wheel

flush with the flat surface with a friction fit. The revolver is made of ABS

(acrylonitrile butadiene styrene) and will be placed in the aluminum base and

held in place by its cylindrical spokes. The second ABS wheel for the

dichroic filters will have larger diameter holes for the dichroic lens holders.



6

Figure 6A: This computer generated picture depics the

LMS base in an exploded view. Positioning of the filter

holder and lens columns are evident in this picture

Figure 6B: This picture shows a view of the completed LMS

base. A set screw can be seen on top of the base holding

one of the lens columns in position.

Detailed Design Specs

- Light Source

o Spectrum: 360 to 1100 nm

Visual spectrum: 380-680 nm

o SMA 905 fiber optic connector

o 1 mW/cm2

@ 550 nm

- Filter Holder

o Utilize ThorLabs SM05 holders

o Hold 0.5’’ (12 mm diameter) lens

Edmund Optics NT43-936/930/942

ThorLabs FD1A

o 4 x 4 x 4 max. dimensions



7

- Wavelength Sorting/Light Detection

o CCD imaging detector 100 photons/count @ 550 nm

o 600 g/mm grating

o 350-1000 nm spectral range

o 25 µm entrance slit

o Resolution: 1.5 nm FWHM

- Spectral Analysis

o Utilize SpectraSuite

Plots “Counts vs. Wavelength” & “% Transmission vs. Wavelength”

Integration time of 4 ms

Export data to Excel Spreadsheet

Testing Prototype

The standard operating procedures of Team Orange’s LMS require the system to be assembled

carefully following the SOPs. Once the system is set up properly, it’s then calibrated with 100%

transmission and with 0% transmission[5]

. The color values of each filter were then obtained with a

software program called SpectraSuite used with a calibrated spectrometer. When collecting data, Team

Orange took five measurements over a period of one hour to obtain specs on the LMS’s repeatability as

well as five measurements per day over a period of 5 days to test the reproducibility of the system.

Results and Color Analysis

The results of the testing of the repeatability and reproducibility of the system were used in a one

sample t test comparing our measured color values against the standard[6]

CRT phosphors values. These

values failed the test indicating that the colors of the absorbance filters did not match those of the CRT

phosphors. Although the dichroic color values obtained did match those of the 2009 dichroic values, all

but one of Team Orange’s dichroic chromaticity values did not match the dichroic standard values. Table

II shows the standard deviation of the absorbance filter’s chromaticity values against their standard color

values. The table shows an extremely low standard deviation for both Team Orange’s repeatability and

reproducibility. This data depicts the good precision of Team Orange’s system, though the accuracy of



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the system is not as good as desired. This lack of accuracy can be attributed to one of many things

including calibration of the filter and spectrometer.

Table II: Standard Deviation of Measured Chromaticity Values

Repeatability

(1 Hr) Std

Dev

Reproducability

(5 day) Std Dev

Blue Avg 0.0016167 0.00145

Green Avg 0.001235 0.0017

Red Avg 0.0055 0.0034

Total Avg 0.00275 0.00215

Client requirement <.04 <.1

Project Plan and Cost Analysis

The tasks that have been completed can be seen in Table III. This table depicts the total number

of man hours that were required to complete each task. These hours are totaled at the bottom to 93

hours. These hours equate to $9,300 of labor required to complete the LMS. The tasks have approximate

start and finish dates and dependencies on other tasks. A Gantt chart of the tasks can be seen in Figure

7. As you can see from the chart, the production of the LMS was effectively completed in less than 10

weeks. The bill of materials can be seen in Table IV and it should be noted that Team Orange remained

well under the $500 budget

Table III: Total Man Hours for Completion

Task Description Man Hours Name Dependency

1 Finish all models in SolidWorks 7 Ian

2 Updated parts list 2 Charlie

3 Purchase parts 1 Charlie

4 RPT mold 1 Griffin FS 1

5 Pour metal into mold 6 All FS 4

6 Heat Treating 9 W,C,I FS 5

7 Check specifications on Al base 1 Will FS 5

8 ABS wheel 1 Griffin FS 1

9 Make fiber optic cables 12 M,W,C,J FS 3

10 Assemble system 18 All FS 6, 7, 8, 9

11 Testing 35 All FS 10

Total Man Hours 93



9

Figure 7: The Gantt Chart above depicts relative time for each task to be completed in days. Note that all tasks are complete within

the 10 week period

Table IV: Bill of Materials: Parts List

Part Price ($) Quantity Total ($)

ABS Rapid Prototyping 10 1.52 15.2

Al 356, Casting Alloy 4.1 0.635 2.6035

Zcast 501 Powder/Binder 0.15 968.8 145.32

Multimode AMP 905 Connector 9.95 4 39.8

Polishing Pads 1 1 1

Epoxy for Fiber Optic Connections 3.75 2 7.5

SMA Bulkhead Adapter 15 0 0

3 cc Epoxy Syringe 1.25 2 2.5

UV/VISmulti-mode optical fiber 7 2 14

Furcation tubing (orange) 1.5 2 3

Lenses (BK7) Plano-convex 22.5 2 45

SMA-ST Fiber Optic Cable 165 0 0

Lens Holder, .5" 15.3 2 30.6

Adjustable Lens Holder, ,5" 28.6 0 0

Retaining Ring, .5" 5.1 4 20.4

ST to SMO5 Adaptor 24 2 48

1" Filter Holder 12.16 0 0

Retaining Ring, 1" 5.3 0 0

$374.9235

13-Sep 23-Sep 3-Oct 13-Oct 23-Oct 2-Nov 12-Nov 22-Nov 2-Dec

Finish all models in SolidWorksUpdated parts list

Purchase partsRPT mold

Pour metal into moldHeat Treating

Check specifications on Al baseABS wheel

Make fiber optic cablesAssemble system

Testing



11

Eutectic

Comp.

Pro-

eutectic

(Al)

Eute

Si ph

Eut

Proeute

(Al)

the risers of our casting should have had a larger diameter to prevent quick solidification in the

risers. This resulted in the bottom of our casting, but the top of our LMS base, to have some

shrinkage. Luckily this shrinkage played no part in the mechanical performance of our LMS

base. The as cast microstructure of one riser can be seen in Figure 8 A and B at a magnification

of 100x and 500x respectively.

Figure 8A: The 50 micron bar seen in the bottom

right of this unetched microstructure expresses the

low magnification of the picture. In this as cast

microstructure, the proeutectic (Al) phase can be

seen in the lighter areas, where the darker areas are

made up of eutectic composition of (Al) and an

unidentified Si phase.[8]

Figure 8B: In this higher magnification unetched

microstructure the proeutectic (Al) phase is much

more evident. The darker regions are a combination

of two eutectic phases. These eutectic phases do not

follow a lamellar structure since the casting was not

equilibrium cooled.[8]

Heat treatment (T6)

The aluminum base underwent a T6 heat treatment in which the aluminum alloy was

solutionized at a temperature of 540°C

for 12 hours. At this point of the heat treatment process the

aluminum phase becomes supersaturated with Silicon particles. The casting was then removed from

the furnace and quenched immediately into room temperature water. This quench trapped the

supersaturated solid solution at room temperature, keeping the composition of vacancies which isn’t



12

(Si)

(Al)

(Al)

(Si)

otherwise available at room temperature. After the quench the casting was artificially aged for 12

hours at a temperature of 155°C

and was then removed from the furnace and quenched again to room

temperature[8]

. During the artificial aging process, the silicon particles in the supersaturated solution

begin to diffuse out of Aluminum solvent and form precipitates. Although these precipitates are so

small that they cannot be seen without a Transmission Electron Microscope (TEM), the microstructure

of this heat treated alloy can be seen in Figure 9 A and B at 100x and 500x respectively.

Figure 9A: In this unetched low magnification

microstructure of the A356-T6 casting, the Aluminum

lattice can be seen in the light regions, which are rich in

precipitates that are too small to be seen. The darker

regions are the Si rich phase which has spherodized and

become equiaxed, which is indicative of a heat treatment.

Figure 9B: This unetched higher magnification picture

shows a close view of the spherodized silicon rich phase.

The Silicon particles have diffused through the Aluminum

lattice and combined into the equiaxed grains shown. As

previously stated the silicon precipitates cannot be seen in

the (Al) lattice at this magnification

The casting A356 has a composition of 7% Silicon and .3% Mg[8]

. As you can see in the

Aluminum Silicon phase diagram in Figure 10, even at elevated temperatures the maximum

solubility of Silicon in the (Al) phase is ~1.65%. This means that even when supersaturated there

is still at least 5.35 wt% Si in its own unidentified silicon phase that would require further

research to identify. Though this may seem like low solubility of Silicon in the (Al) phase, it is



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much more than that soluble at room temperature, since there is a decreasing solubility of Si in

(Al) with decreasing temperature. During the heat treatment, at high temperatures this silicon

phase becomes spherodized.

Figure 10: In the phase diagram to the

right, the red line is representative of 7

wt% Silicon, the composition of A356. The

.3 wt% Mg is negligible, therefore this

phase diagram can be considered. Notice

should be taken to the decreasing

solubility of Si in (Al) with decreasing

temperature. This is what allows

precipitation hardening to occur.

After the heat treatment process, the hardness of the as-cast riser and the heat treated

riser were compared in order to determine quantitatively if the heat treatment process

produced an increase in strength. The HRB scale was used when measuring the hardness of the

precipitation hardened alloy, but the average of these values was later converted to the HRE

scale, which was used for the as-cast sample; a scale for softer metals. The comparison of these

values can be seen in Table V. Though the heat treatment has a higher standard deviation, it is

evident by the average hardness value that the hardness of the casting doubled after the T6

heat treatment. Since hardness is the resistance to plastic deformation, it can be concluded

that through the heat treatment our casting had a large increase in strength.



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Table V: As-Cast Hardness vs T6 Heat Treatment

As Cast T6 Heat treatment

(HRE) (HRE) (HRB)

Average 43.85 88 51.9

Range 36.2-51.3 N/A 34.2-81.6

Std Dev 6.6 N/A 14.3

References

1. "Cathode Ray Tube." Wikipedia, the Free Encyclopedia. Web. 06 Dec. 2010.

<http://en.wikipedia.org/wiki/Cathode_ray_tube>.

2. Edmund Cast Plastic Color Filters, Blackboard

3. Uprint Specifications, Blackboard

4. Conceptual Design Decision Matrix (nps46E2.tmp)

5. Diffraction Gratings: Technical information, Blackboard

6. ASTM E308 “Standard Practice for Computing the Colors of Objects by Using the CIE System ”

(npsE8FB.tmp)

7. Z-cast 501 Direct Metal Casting. Design Guide, Blackboard

8. ASM Handbook. Cal Poly Library

<http://products.asminternational.org.ezproxy.lib.calpoly.edu/matinfo/index.jsp>

Final Design Review of Light Measurement System

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