Source document: https://docs-lawep.s3.us-east-2.amazonaws.com/1698057700469.pdf (Liberia)
Available online at www.sciencedirect.com ScienceDirect Procedia CIRP 34 ( 2015 ) 156 – 161 9th International Conference on Axiomatic Design — ICAD 2015 Low-cost spectrometer for Icelandic chemistry education Gunnar Óli Sölvasona, Joseph Timothy Foleya,* aDepartment of Science and Engineering, Reykjavík University, Menntavegur 1, Reykjavík 101, Iceland ∗ Corresponding author.

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: +354–599–6569; fax: +354–599–6201 E-mail address: foley@ru.is Abstract Spectrometers are common analytical instruments in Chemistry.

Ultraviolet-visible (UV-Vis) spectroscopy is the most commonly applied instru- mental analysis technique being used at universities in the United States for the last three decades.

Due to the popularity of spectroscopy and reduced budgets for undergraduate laboratories, there is great interest in low-cost, Do-It-Yourself spectrophotometers.
This paper presents an implementation devised with axiomatic design principles for an aﬀordable (sub $1000) spectrometer.

This design can be fabricated in a local Fab Lab using common oﬀ the shelf components and material to serve as a rigorous, analytical and teaching tool with a lifespan of at least 5 years.

Due to a ﬂaw in the concept of the optical path of the device, consistent measurements on absorption spectra could not be made comparable to a commercial equivalent.
Even with this limitation, the device is still capable of serving its original purpose by measuring light source spectra and absorption of a selected wavelength to demonstrate Beer’s law.

© 2015 The Authors.

Published by Elsevier B.V. © 2015 The Authors.

Published by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review statement: Peer-review under responsibility of the organizing committee of 9th International Conference on Axiomatic Design.

Peer-review under responsibility of the organizing committee of 9th International Conference on Axiomatic Design Keywords: fab lab, spectrometer, chemistry education 1.

Introduction Spectrometers are instruments commonly used for instru- mental analysis in Chemistry.
They come in a variety of types and conﬁgurations, depending on their application, ranging dra- matically in price based on their complexity.

Prices range from a few hundred dollars up to tens of thousands.

Ultraviolet- visible (UV-Vis) spectroscopy is the most commonly applied instrumental analysis technique being used at collage and un- dergraduate level in the United States, and has been for at least the last three decades [1,2].

2.
2.

Background A visible spectrometer is a simple unit in terms of its fun- damental principle.

White light is broken into its components (spectra) using diﬀraction grating.

The intensity of a speciﬁc wavelength of the spectra is then converted to a value directly proportional to the intensity of the light reaching a sensor.
Fundamentally, the idea behind the design of this device was to design an aﬀordable spectrometer with the performance of a 5000 USD commercial unit, have the design be capable of being manufactured in a local Fab Lab and a basic workshop from easily obtainable materials and oﬀ the shelf components, while avoiding a black box feel for the end user.

Fab Labs are semi-standardized and exist internationally, making them a rea- sonable basic level for manufacturing capabilities [3].
The de- vice described will be referred to as the AFL-Spectrometer or AFLS: “Aﬀordable Fab Lab Spectrometer”.

In 2011 a group of students in the course “T-865-MADE Precision Machine De- sign” developed a low-cost spectrometer hereafter referred to as the MADE-Spectrometer [4].

Shortcomings in the design of the optical arm assembly limited its performance.
While not a direct redesign of the MADE-Spectrometer, the AFL- Spectrometer can be considered a second iteration in the pro- cess of producing an aﬀordable instrument for laboratory ex- periments in chemistry at Reykjavík University.

In the design of the AFL-Spectrometer, the systematical ap- proach of axiomatic design was chosen to reach the highest quality design solution satisfying needs while minimizing re- sources utilized via iteration [5,6].
Results from the systematic process is what the inventor, Nam P. Suh, calls axiomatic de- sign.

This result is a structured description of how customer needs are systematically satisﬁed to end up with a design (be it a system, an artifact, or a computer program) that fulﬁlls all the needs of the customer (that the designer has turned into Func- tional Requirements (FRs)), with the least amount of trial and error.
In Suh’s own words, “Axiomatic Design deﬁnes design as the mapping process from the functional domain to the physical domain, with the aim of satisfying the functional requirements speciﬁed by the designer” [7, page 26].

2212-8271 © 2015 The Authors.

Published by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of 9th International Conference on Axiomatic Design doi: 10.1016/j.procir.2015.07.072 Gunnar Óli Sölvason and Joseph Timothy Foley / Procedia CIRP 34 ( 2015 ) 156 – 161 157 3.

Development of requirements When working inside the axiomatic design framework, the ﬁrst task at hand is acquiring and describing the Customer At- tributes (CAs).

In the case of the AFL-Spectrometer, the cus- tomer is the faculty and the students that will use the device.
Upon verbal communication with staﬀ of the biochemistry and physics courses of the Reykjavík University, their desires be- came clear.

What the customers wanted is an aﬀordable, ac- curate, durable spectrometer working on the visible spectrum.

Going deeper into examining those conversations, it became clear that the motivation is improving teaching capabilities, and the instrument is the means.
Therefore, the CA is deﬁned as: CA0 Teach students about Beer’s law and diﬀraction of electro- magnetic waves on the UV-Visible spectra.

Table 1.

Top level FRs and corresponding DPs.
FR DP 1 Supply power to components 2 Generate electromagnetic radiation on visible spectrum 3 Collimate light from 4 5 source Pass light through constant sample material thickness Split light into measurable ordered spectra Electronic circuit assembly Light source Collimating lens assembly Sample holding assembly Diﬀraction grating assembly Leading to a top level FR and Design Parameters (DPs): 6 Measure light intensity 7 Present data Light sensing assembly Display assembly FR0 Measure intensity of electromagnetic radiation for a se- lected wavelength.
DP0 Low-cost measuring device for light intensities on the UV- Vis spectra.

We proceed to ﬁnding lower level FRs and corresponding DPs.

This is done by decomposing and zig-zagging down the domains [8].

Not all of the information about the design is ﬁt to become functional requirements.

This information is, however, still rel- evant and needs to be kept track of.

This information is pre- served as Constraints (Cs), and presented in corresponding con- straint tables.
Other information includes optimization crite- ria presented in Table 4.

More detail can be stored inside an expanded classical axiomatic design framework, e.g.

require- ments that are not functional in their nature, or Non-Functional Requirements (NFRs) [9].

NFRs were not used in this particu- lar project and are therefore not discussed in detail.

Top level FRs along with their corresponding DPs are de- scribed in Table 1.

Top level constraints can be seen in Table 2.


Equation 1 is the top level design equation.

Table 2.

Top level constraints, not mapped to FRs Constraints 1 Maximum price 1000 USD.

2 Manufacture in a Fab Lab (Laser cutter, 3D Printer).

3 Setup time less than 15 minutes.

4 Lifespan of a minimum 5 years.

5 Usable with outside light source.

data is presented on an LCD display without electricity.
The only other non-diagonal element in the top level design matrix is the element corresponding to the eﬀect the collimating lens assembly has on FR5.

Without the collimating lens assembly the light can not be split into spectra, and therefore DP3 aﬀects FR5.
⎡ ⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎣ = ⎫ ⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎬ ⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎭ ⎧ ⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨ ⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎩ FR1 FR2 FR3 FR4 FR5 FR6 FR7 ⎤ ⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎦ · ⎧ ⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨ ⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎩ DP1 DP2 DP3 DP4 DP5 DP6 DP7 ⎫ ⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎬ ⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎭ (1) The second level design matrices can be found in Equa- tions 2–3.

For brevity any matrices that are purely diagonal are omitted.
All the matrices can be represented in a combined, total design matrix represented as Figure 1.

FR-DP mappings can be found in Tables 5–12.

Second level constraints can be found in Table 3.

⎧ ⎪⎪⎪⎨ ⎪⎪⎪⎩ ⎫ ⎪⎪⎪⎬ ⎪⎪⎪⎭ ⎫ ⎪⎪⎪⎬ ⎪⎪⎪⎭ (2) ⎥⎥⎥⎥⎥⎥⎥⎥⎦ ⎢⎢⎢⎢⎢⎢⎢⎢⎣ = ⎤ ⎡ · X 0 0 X X 0 0 X 0 ⎧ ⎪⎪⎪⎨ DP5.1 ⎪⎪⎪⎩ DP5.2 DP5.3 FR5.1 FR5.2 FR5.3 The top level design matrix is a triangular one and therefore de- coupled.
From the ﬁrst column of the matrix it is evident that the electronic circuit assembly (DP1) must have an impact on more of the FRs than just FR1.

Without the electronic circuit assembly FR2, FR6 and FR7 would be aﬀected.

Without the electronic circuit no electromagnetic radiation would be cre- ated since the light source would not be powered up, so FR2 is aﬀected.

FR6 is the measurement of light intensity.


Without an electric circuit the sensor and micro-controller will not oper- ate, therefore FR6 cannot be fulﬁlled by its corresponding DP6 without the electronic circuit assembly.

In the same manner, no Table 3.

Second level constraints, mapped to FRs Constraints Sample contained in a standard disposable cuvette.

4.1 6.1 Wavelength selection in 1 and 10 nm steps.

6.2 Must handle micro-stepping.

6.3 Must handle 2 A of current draw.


158 Gunnar Óli Sölvason and Joseph Timothy Foley / Procedia CIRP 34 ( 2015 ) 156 – 161 Table 4.

Optimization criteria 2.1 Minimize drift 2.2 Minimize heat 2.3 Minimize energy use 4.1 Maximize repeatability 6.1 Minimize stray light reaching intensity measurement Table 5.

FR-DP mapping for power/electronics (FR1) FR DP 1.1 1.2 1.3 Supply power to lights Supply power to CPU Supply power to motor Light power circuit Light source Collimating lens assembly Table 6.
FR-DP mapping for light source (FR2) FR DP 2.1 Provide white light 2.2 Provide calibration peaks at three known wavelengths of the spectra Super-bright, ultra-white LED Three color (RGB) LED 2.3 Allow light from an external light source in Hole opening to the outside of structure Table 7.

FR-DP mapping for light collimation (FR3) FR DP 3.1 Collimate light 3.2 Align collimator with light path axially Set distance between collimator and light source 3.3 Biconvex lens Lens bracket Movement mechanism Table 8.
FR-DP mapping for sample (FR4) FR DP Table 9.

FR-DP mapping for splitting light (FR5) FR DP 5.1 Diﬀract collimated light Diﬀraction grating sheet 5.2 5.3 at an angle Focus ﬁrst order spectra onto a plane at a distance Set distance between focusing assembly and sensor Focusing lens assembly Movement mechanism Table 10.
FR-DP mapping for (FR6) FR DP 6.1 Select wavelength 6.2 Narrow light reaching sensor from spectra to band Process data 6.3 Wavelength selector assembly Narrow slit in front of sensor Arduino Uno ⎧ ⎪⎪⎪⎨ ⎪⎪⎪⎩ FR6.1 FR6.2 FR6.3 ⎫ ⎪⎪⎪⎬ ⎪⎪⎪⎭ ⎡ ⎢⎢⎢⎢⎢⎢⎢⎢⎣ = 0 X 0 X X 0 X 0 X ⎤ ⎥⎥⎥⎥⎥⎥⎥⎥⎦ · ⎧ ⎪⎪⎪⎨ DP6.1 ⎪⎪⎪⎩ DP6.2 DP6.3 ⎫ ⎪⎪⎪⎬ ⎪⎪⎪⎭ ⎧ ⎪⎪⎪⎪⎪⎪⎨ ⎪⎪⎪⎪⎪⎪⎩ FR6.1.1 FR6.1.2 FR6.1.3 FR6.1.4 ⎫ ⎪⎪⎪⎪⎪⎪⎬ ⎪⎪⎪⎪⎪⎪⎭ ⎡ ⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎣ = 0 0 X 0 0 X 0 0 0 X X 0 0 X 0 0 ⎤ ⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎦ · ⎧ ⎪⎪⎪⎪⎪⎪⎨ ⎪⎪⎪⎪⎪⎪⎩ DP6.1.1 DP6.1.2 DP6.1.3 DP6.1.4 (3) (4) ⎫ ⎪⎪⎪⎪⎪⎪⎬ ⎪⎪⎪⎪⎪⎪⎭ 4.
Implementation With completion of the initial design process described in Chapter 3, the next step was to create a prototype spectrometer.

The ﬁnished DSS SolidWorks™ CAD model can be seen in Figure 2.

Turning individual FRs into DPs requires designing physical parts that fulﬁll the purpose or function described by the FR.

Table 11.

FRs for level 6.1 along with corresponding DPs.
FR DP 6.1.1 Set desired wavelength value Rotary encoder 6.1.2 Control movement of Motor controller motor Sample holder geometry 6.1.3 Move center of light Stepper motor 4.1 Keep length of light path through sample constant 4.2 Keep sample at a ﬁxed Lens bracket distance from collimator lens 6.1.4 sensor to selected wavelength Prohibit movement of motor outside of desired range End stop sensor Gunnar Óli Sölvason and Joseph Timothy Foley / Procedia CIRP 34 ( 2015 ) 156 – 161 159 Table 12.
FR-DP mapping for data presentation (FR7) FR DP 7.1 Display data LCD Display Fig.
3.

CAD model of the lens holder assembly, designed to be 3D printed.

DPs should fulﬁll the FRs and nothing else.

When all the FRs have been met, the design is complete.

In the following sec- tion, particularly interesting DPs will be elaborated and their fulﬁllment of the FRs described.

4.1.

DP3.2 Lens bracket An important FR is described in (FR3.2, DP3.2): to align the collimator with the light path axially.
As can be seen in Table 7 DP3.2 is a lens bracket in the physical domain.

Its purpose is to keep a biconvex collimating lens aligned with the light path (Figure 3).

Fig.

1.

Total design matrix 4.2.

DP4 Sample holder The design matrix and examination of the light path make clear that it is critical how the sample will be held, due to its eﬀect on the spectra alignment on the sensor (high information).
Samples used in the AFL-Spectrometer will usually be liquid solutions in standard glass or plastic disposable cuvettes (12 × 12 × 45 mm) as described in C4.1 in Table 3.

It is clear that he sample holder needs to reliably and repeatably ﬁxture cuvettes.

For maximum repeatability, the center of mass of the cuvette was compared to the desired alignment translation axes (x, y,z) and rotational angles around those axes (θx, θy, θz).
For an align- ment reference, y is normal to gravity and z is the path of travel for the light.

Critical movement directions are θy, θx, y and x. θy and θx result in elongation of the light path through the sample, while the other movements move the cuvette out of the path of light inside the device.

Traditional holding mechanisms use spring loaded coil spring or ﬂexure “ﬁnger” mechanisms; a sample is inserted into an aperture to interface with the ﬂexures.
Some spectrome- ter models require the additional step of locking the sample in place to increase preload.

Commercial units commonly use a plastic cassette for the cuvette that slid into a chamber with a stamped-metal ﬂexure.

We used a similar design but reduced the ﬁxture to a minimum number of mechanical elements that would be easily manufactured in the Fab Lab.

Figure 4 shows the design concept of the sample holder.
One spring-loaded shaft and four static shafts align the cuvette along the optically-ﬂat sides.

These contact areas ensure repeatable positioning of the sample focusing on eliminating movement Fig.

2.

CAD model of the AFL-Spectrometer.

Most components are in the top enclosure.

LED light sources are attached on the left.

Possible light paths are represented as ﬂat wedges.

The stepper motor which moves the platform is visible on the right.
The top lid has been made transparent to allow observation of the internal mechanisms.

The rotating platform moves the light sensor.

The small box on the left contains the control electronics and user interface.

160 Gunnar Óli Sölvason and Joseph Timothy Foley / Procedia CIRP 34 ( 2015 ) 156 – 161 Fig.

4.
4.

Details of the cuvette holder design.

Fig.

5.

CAD model closeup of the AFLS sample holder with cuvette inserted.

in the samples critical movement directions.

Constraining only these four degrees of freedom only needs ﬁve shafts thus keep- ing the information content of the design to a minimum as per Axiom 2: adding more restraints would only add unnecessary complexity.

A CAD rendering of the physical implementation of the concept in Figure 4 can be seen in Figure 5.
The other directions are limited by laser-cut MDF features because they do not signiﬁcantly aﬀect the light path.
5.

Results This project should be considered from two viewpoints.
First oﬀ, a design is developed where the end goal is to have the design of a mechanically functioning device that fulﬁlls a set of physical requirements inside a boundary of constraints and optimization criteria.

On the other hand, the constructed system based upon this design must perform as a measuring de- vice.

The design is complete when all FRs have been met as set up by the designer but the system is not complete until it can give measurements in the quality range deﬁned in the require- ments.
5.1.

Physical mechanics From an axiomatic standpoint, each FR in the project has a DP that satisﬁes it.

Systematic evaluation was carried out for the FRs, their corresponding DPs, constraints and optimization criteria.

This evaluation is omitted in this paper for brevity but can be found in [10].

5.2.
5.2.

Functioning system To test the performance of the AFL-Spectrometers, measure- ments on two types of widely available sports drinks with dis- tinct appearance were used, namely blue (berry & tropical ﬂa- vor) and red (cherry ﬂavor) Powerade™.
Measurements were Fig.

6.

Measurement without a sample compared to Powerade readings.
made using full volume disposable plastic cuvettes.

Measure- ments showed that the device was not distinguishing a notice- able diﬀerence between blank spectra (produced by the light source) and the solutions being measured.

This is shown in Figure 6.

The device could, however, replicate the spectra of the light-source very well.

This led to the discovery of a ﬂaw in the concept of the device.
The sample-holder was placed on the wrong side of the diﬀraction grating, and would therefore be unusable to produce the spectra of solutions.

This was proven by doing a measurement using food dye to see how concen- tration would aﬀect the sensor output, since it was known that measuring diﬀerent concentrations at the peak wavelength of a solution should result in a linear increase in absorption.

A set of reference solutions were created with food dyes water-ﬁlled cuvettes.
The dilutions are annotated Dn where n is the num- ber of drops of dye.

These solutions were then measured in the sample-holder of the device as it had been designed (before the diﬀraction grating), then manually placed in front of the sensor (after the diﬀraction grating).

Results from these measurements for the red food dye can be seen in Table 13.

Figure 7 repre- sents the results from Table 13 graphically.

Similar results were realized for the blue food dye, but omitted for brevity.
Gunnar Óli Sölvason and Joseph Timothy Foley / Procedia CIRP 34 ( 2015 ) 156 – 161 161 Table 13.

AFL-Spectrometer sensor raw readout for various concentrations of red food dye at 520 nm.

Notation: Dn where n is the number of drops into a water-ﬁlled cuvette.
Before grating After grating 191 140 85 52 11 7 Blank Water D1 D2 D3 D4 191 190 187 184 183 179 Fig.
7.

Absorbance plot (Beer’s graph) of red food dye data from Table 13.

As can be seen, no signiﬁcant increase in absorption was realized with the sample in the designed sample-holder, while placing the sample behind it resulted in a fairly linear increase in absorbance values.

6.

Conclusion Results from this project should be considered with two as- pects: reﬂecting on the success of the mechanical design and the system as a measuring device on the other.
It became clear that evaluation of the mechanical design would be very hard if no measurements had been made on the device.

Measurements were performed to test the performance of the device, which led to the discovery of a ﬂaw in the design concept.

Even though the capabilities were impacted by the location of the sample holder, the device fulﬁlled all the mechanical de- sign requirements set up in the axiomatic design framework.
Every FR had a DP satisfying it completely, the system was de-coupled, and therefore the design was completed in a sat- isfactory manner from an axiomatic standpoint.

A more de- tailed analysis of what FR-DP mapping is inaccurate will be performed to better understand this problem.

Even though full spectra of solutions cannot be measured by the device it its current state, it still is capable of its top- level educational purpose.

It can accurately measure the spectra of a light source.
It can also be used to conduct experiments on Beer’s law and thus serve students in both chemistry and physics.

The only desired measurement it cannot produce is the absorption spectra of a solution.

Pending another design iteration, this may be corrected by moving the sample-holder behind the diﬀraction grating.

It is expected that this would involve a redesign of the sample-holder and its position inside the device, since the sample would have to rotate to always be parallel to the sensor assembly.
The axiomatic design framework as a design foundation helped the designer discover many other ﬂaws in the stage of zigzagging down the domains, realizing errors in the early stages of the design when they were cheap and easy to ﬁx.

That being said, it did not help in discovering this ﬂaw in the con- cept, conﬁrming that a design can never be better than the un- derstanding of the designer: a design is only as good as the functional requirements.
What has been designed and realized can serve as a strong foundation for a accurate and aﬀordable measuring device for physics and chemistry experiments in the undergraduate labo- ratory setting.

Acknowledgments Many thanks to Andrei Manolescu and Markéta Foley for their motivation and guidance from the RU chemistry and physics courses.

We would also like to thank the class of T-865- MADE 2011 who developed the previous design [4].
We are very thankful to Svana Hafberg Stefánsdóttir who generously granted us access to spectrometers on behalf of the University of Iceland.

Finally, we would like to thank Baldur Þorgilsson for his general guidance and ideas on how to approach the prob- lem.

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