waters corp. variable aperture slit system (final)

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WATERS CORPORATION VARIABLE APERTURE SLIT MEIE 701-702 Capstone 2 Technical Design Report December 4th, 2012 Department of Mechanical and Industrial Engineering College of Engineering, Northeastern University Waters Corp Variable Aperture Slit Capstone 2 Design Report Design Advisor: Prof. Mohammad Taslim Design Team Aaron Gill, Kevin McMorrow Paul Ventola, Hanshen Zhang

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Page 1: Waters Corp. Variable Aperture Slit System (Final)

WATERS CORPORATION VARIABLE APERTURE SLIT

MEIE 701-702

Capstone 2 Technical Design Report

December 4th, 2012

Department of Mechanical and Industrial Engineering

College of Engineering, Northeastern University

Boston, MA 02115

Waters Corp Variable Aperture Slit

Capstone 2 Design Report

Design Advisor: Prof. Mohammad Taslim

Design TeamAaron Gill, Kevin McMorrowPaul Ventola, Hanshen Zhang

Page 2: Waters Corp. Variable Aperture Slit System (Final)

WATERS CORP VARIABLE APERTURE SLIT

Design Team

Aaron Gill, Kevin McMorrowPaul Ventola, Hanshen Zhang

Design AdvisorProf. Mohammad Taslim

Sponsor ContactsSenthil Bala and Colin Fredette

Abstract

The goal of this project is to design a Variable Aperture Slit (VAS) system used for providing different resolutions of light to be projected into a photodiode array (PDA) for examining the composition of a fluid sample. The VAS will consist of different slit sizes that will be used to limit or refine the light from an ultraviolet (UV) or deuterium light source. The VAS will attach to a holder aligned between a reflected and refracting mirror to permit a certain amount of light with a specific resolution that is unique to each slit size through from the light source to the PDA. Prior to passing through the slit, the UV light will pass through a sample fluid, prepared via liquid chromatography separating the components of a substance, which will absorb various wavelengths of light corresponding to the absorption pattern of the substance. Based on the remaining wavelengths of the light which are passed through the slit and then refracted into an optical detector, the composition of the sample fluid can be determined. In the detector, each slit width will provide a different signal-to-noise ratio and resolution.

Based on the need for a VAS system, an accurate and repeatable design is required to ensure the quality of the system. A simple design focused on movable holders for interchangeable slits provides repeatability for the process and manufacturing. Current designs display the benefits of a movable holder system. Physical models will be created based on the final design and tested to verify the system maintains accurate and repeatable with a rotating motor. The device will be able to be calibrated based on repeatable testing results for use in implementation for full scale manufacturing.

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Table of Contents

1 Acknowledgements................................................................................................................................8

2 Project Statement...................................................................................................................................9

3 Background Technologies and Components.........................................................................................9

3.1 Liquid Chromatography.................................................................................................................9

3.2 Optical Bench...............................................................................................................................11

3.2.1 Deuterium Lamp Light Source............................................................................................12

3.2.2 Concave Mirror Set..............................................................................................................12

3.2.3 Aperture Slit.........................................................................................................................13

3.2.4 Diffraction Grating...............................................................................................................14

3.2.5 Photodiode Array (PDA) Detector.......................................................................................15

4 Design and Sponsor Constraints..........................................................................................................16

4.1 Patented VAS Systems................................................................................................................19

5 Initial Designs......................................................................................................................................22

5.1 Rotating Pin Wheel Design..........................................................................................................22

5.2 Vertical Actuation Design............................................................................................................23

5.3 Horizontally Sliding Slit Aperture...............................................................................................24

5.4 Rotational Holder System............................................................................................................24

5.5 Control System Requirements.....................................................................................................26

6 Analysis and Testing............................................................................................................................26

6.1 Light Path Analysis......................................................................................................................26

6.1.1 Benefits of different slit widths............................................................................................26

6.1.2 Diffraction error from tilt in the “Z” direction.....................................................................27

6.2 Light Path Calibration and Verification Test Method.................................................................29

6.3 Motion Control Analysis.............................................................................................................30

6.3.1 Motor Systems.....................................................................................................................30

6.3.2 Control Path Design.............................................................................................................32

6.3.3 Control System Hardware....................................................................................................32

7 Final Prototype.....................................................................................................................................34

7.1 Optical Slit Aperture Holder........................................................................................................34

7.2 Rotational Control System...........................................................................................................35

7.3 Combined Prototype....................................................................................................................37

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7.4 System Operation.........................................................................................................................38

7.5 Testing and Analysis....................................................................................................................38

7.5.1 Optical Analysis and Testing...............................................................................................38

8 Project Management Overview............................................................................................................41

8.1 Design/Model/Construction Phases.............................................................................................41

8.1.1 Initial Design Phase.............................................................................................................41

8.1.2 Modeling Phase....................................................................................................................42

8.1.3 Ordering Phase.....................................................................................................................42

8.1.4 Initial Construction Phase....................................................................................................42

8.1.5 Final Production Phase........................................................................................................42

8.2 Report and Presentation Phases...................................................................................................43

9 Future Work.........................................................................................................................................43

10 Summary..........................................................................................................................................43

11 Intellectual Property.........................................................................................................................44

11.1 Description of Problem................................................................................................................44

11.2 Proof of Concept..........................................................................................................................44

11.3 Progress to Date...........................................................................................................................44

11.4 Individual Contributions..............................................................................................................44

11.5 Future Work.................................................................................................................................44

.....................................................................................................................................................References

......................................................................................................................................................................45

12..................................................................................................................................................................45

13 Appendices.......................................................................................................................................47

13.1 Appendix A: System Part Drawings............................................................................................47

13.2 Appendix B: Arduino Control Code............................................................................................63

13.2.1 Code to define the Arduino in MATLAB:...........................................................................63

13.2.2 Code to install arduino to work with MATLAB:.................................................................63

13.2.3 Code to run Control Program:..............................................................................................64

13.3 Appendix C: Driver Shield Schematic.........................................................................................65

13.4 Appendix D: Motor Wire Diagram..............................................................................................66

13.5 Appendix E: Stepper Motor Specifications.................................................................................67

13.6 Appendix F: Uno Schematic........................................................................................................68

13.7 Appendix G: H Bridge Circuit Schematic..................................................................................70

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13.8 Appendix H: Microcontroller Schematic.....................................................................................72

13.9 Appendix I: Microcontroller Block Diagram..............................................................................73

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List of FiguresFigure 1: Features of a Variable Aperture Slit [1].........................................................................................9Figure 2: Liquid Chromatography Sample Pathway [2]..............................................................................10Figure 3: Full HPLC system including column and detector modules. [3].................................................11Figure 4: How the detector displays sample peaks [3]................................................................................11Figure 5: Optical Bench Assembly, © Waters Corp. [3].............................................................................11Figure 6: Deuterium Light Spectrum...........................................................................................................12Figure 7: Diffraction pattern from a slit of width four wavelengths with an incident plane wave..............13Figure 8: Diffraction Grating Spectrograph of Visible Light......................................................................14Figure 9: Responsivity of silicon photodiode vs. wavelength of incident light..........................................15Figure 10: AutoCAD drawing of current aperture slit used in the PDA. All dimensions in millimeters....16Figure 11: View of the PDA casting from the bottom side. Note the location of the current aperture holder...........................................................................................................................................................17Figure 12: View of the PDA casting from the top displaying modifiable section.......................................17Figure 13: View of the PDA casting from the top displaying the optical mirror area.................................17Figure 14: Section view displaying the location of the aperture (displayed in red) within the casting.......17Figure 15: View of the PDA casting from the side, displaying bottom and top clearance values..............18Figure 16: Approximate path of light travel with the PDA.........................................................................18Figure 17: Thermo Scientific Variable Slit Detector Layout [1].................................................................19Figure 18: Fixed Position Aperture Slit Detector © Thermo Scientific Co. [1]..........................................20Figure 19: Mechanism for US Patent 7170595 [10]....................................................................................21Figure 20: Slit mechanism for U.S. Patent 4612440 [11]............................................................................21Figure 21: Mechanism for U.S. patent 2852684 [12]..................................................................................21Figure 22: Mechanism for U.S. patent 5451780 [13]..................................................................................21Figure 23: Initial design emulating a rotating pin wheel.............................................................................22Figure 24: Initial design displaying vertical actuation between two slits....................................................23Figure 25: Initial design with two moving surface plates with an internal gap as an optical slit................24Figure 26: Initial design of hexagonal slit aperture array............................................................................25Figure 27: Top-down view of hexagonal slit aperture array........................................................................25Figure 28: Initial design of holder with the attached aperture slits on a rotational base.............................25Figure 29: Experimental Set-up of a laser through an optical slit displaying a coordinate system [14].....27Figure 30: Diffraction pattern in the plane x'o, y'o of a single slit inclined at an angle θ=45° to the direction of propagation z’: lx = 0.02mm; D = 1m [14]..............................................................................28Figure 31: Light Path Calibration Set-up.....................................................................................................29Figure 32: Slit image and intensity detecting tool.......................................................................................30Figure 33: Linear Stage System...................................................................................................................31Figure 34: Brushless Servo Motor...............................................................................................................31Figure 35: DC Stepper Motor with Offset Rotation Point...........................................................................32Figure 36: Motion Control Diagram............................................................................................................32Figure 37: Front view of Arduino Uno........................................................................................................33Figure 38: Adafruit motor shield stacked on Arduino Uno.........................................................................34Figure 39: Current VAS design, with the aperture slits secured to a rotational base..................................35Figure 40: NEMA 11 Bipolar Stepper Motor..............................................................................................36Figure 41: Assembled Control System and Prompts...................................................................................36

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Figure 42: VAS assembly attached to rotary motor.....................................................................................37Figure 43: Model of PDA casting displaying the new bore hole required for integration of the VAS system..........................................................................................................................................................38Figure 44: Reference image for comparing test data to determine accuracy and repeatability...................39Figure 45: Raw test analysis data.................................................................................................................40Figure 46: Refined Data Table.....................................................................................................................41Figure 47: AutoCAD drawing for holder base............................................................................................49Figure 48: AutoCAD drawing for 50m aperture slit..................................................................................52Figure 49: AutoCAD drawing for 100m aperture slit................................................................................55Figure 50: AutoCAD drawing for 200m aperture slit................................................................................58Figure 51: Drawing of Stepper Motor.........................................................................................................59Figure 53: AutoCAD drawing of new bore hole required for PDA casting (page 1 of 2)...........................61Figure 54: AutoCAD drawing of new bore hole required for PDA casting (page 2 of 2)...........................62Figure 56: Schematic of Driver Shield........................................................................................................65Figure 57: Motor Wire Diagram..................................................................................................................66Figure 58: Stepper Motor Specifications.....................................................................................................67Figure 59: Arduino Uno Schematic.............................................................................................................70Figure 60: H Bridge Circuit Schematic.......................................................................................................70Figure 61: Microcontroller Schematic.........................................................................................................72Figure 62: Microcontroller Block Diagram.................................................................................................73

List of Equations

Equation 1: Beers Law.................................................................................Error! Bookmark not defined.Equation 2: Foci Location Determination Equation....................................Error! Bookmark not defined.Equation 3: Fraunhofer Diffraction Equation..............................................Error! Bookmark not defined.Equation 4: Diffraction Equation.................................................................Error! Bookmark not defined.Equation 5: Angle of Irradiance from Fraunhofer's Diffraction Equation...Error! Bookmark not defined.Equation 6: Angular Spectrum from the Fourier Transform of a wave field transmitted on an aperture......................................................................................................................Error! Bookmark not defined.Equation 7: Electric field at the aperture of a single unit-amplitude monochromatic plane wave......Error! Bookmark not defined.Equation 8: Integration of the Angular Spectrum from a Fourier Transform...........Error! Bookmark not defined.Equation 9: Direction condition for diffracted waves..................................Error! Bookmark not defined.Equation 10: Shift of a Slit Image................................................................Error! Bookmark not defined.Equation 11: Angle of tilt of a slit................................................................Error! Bookmark not defined.Equation 12: Intensity Drop/Gain................................................................Error! Bookmark not defined.

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1 Acknowledgements

Special thanks and acknowledgements to Colin Fredette for his assistance in providing materials and information regarding the desired designs for the current Waters Corporation Optical Bench System, as well as Professor Charles Dimarzio for use of the Northeastern University Optics lab and assistance with explaining the fundamentals of optics.

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2 Project Statement

For optical detector systems, the amount of light permitted into a system affects the signal to noise ratio, adjusting the resolution or accuracy of the composition of a test sample. Waters Corporation’s current systems allow for only a single aperture, containing a precise slit that allows light through and into the detector system by means of a reflecting mirror paired with a refraction mirror. To increase the capabilities of current Waters’ products, a new system is required to allow various intensities of light to enter the detector in order to examine a test sample. This system must be able to be integrated in a manner that does not drastically alter the current configuration of Waters’ optical detectors and must not interfere with the path of light outside of the intended use of the aperture.

Figure 1 displays a sample of the wavelengths and the change in a read-out for different slit widths. Note that the wider slit contains less noise, but does not necessarily contain the most accurate peaks in the system.

Figure 1: Features of a Variable Aperture Slit [1]

3 Background Technologies and Components

3.1 Liquid Chromatography

Liquid Chromatography (LC) is the science of separating a sample into a liquid. Samples are organized and prepared according to their natural properties before they enter the detector. Figure 2 displays a system pathway where solvents are pumped from containers to be mixed with a sample to break the sample down into elements, which can be analyzed. This is called preparatory chromatography. Rigorous study of analytical chemistry has allowed engineers to match historical data to new LC test data from the output of a detector such as a photo-diode array. Incident light is

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then passed through a flow cell and the remaining wave lengths which gets diffracted into a detector detail the composition of a sample in a graph called a chromatogram. In particular a substance is defined by the absorbance of the incident light according to Beer’s Law:

A = log (Io/I) = bc (1)

where A is the absorbance, Io is the incident light intensity, I is the intensity transmitted, is the molar

extinction coefficient, b is the path length of the cell in centimeters, and c is the molar sample

concentration. Changes to slit widths, mentioned in Section 2, will impact the incident light intensity

signified by Io in Beer’s Law.

High Pressure Liquid Chromatography (HPLC) uses high pressure pumps in order to enhance the

breakdown of the sample in the fluid and solvents. The sample mixture is then passed through filters in a

column stack releasing the waste byproducts into the filter. The Waters Corporation system uses an

HPLC column to break down samples for analysis. The specific pathway for Waters Corporation from

solvent to chromatogram analysis is displayed in Figure 3. Note that solvents are prepared and moved

through a pump system prior to the inclusion of the sample. Each individual sample is mixed with certain

mix of solvents to create the appropriate breakdown of the samples. In the final output for the sample the chromatograph plots the sample data with intensity on the Y-axis and wavelength on the X-axis as shown in Figure 4.

.

Figure 2: Liquid Chromatography Sample Pathway [2]

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Figure 3: Full HPLC system including column and detector modules. [3]

Figure 4: How the detector displays sample peaks [3]

3.2 Optical Bench

Figure 5 displays an optical bench consisting components used for optical analysis of a fluid sample. This particular optics system uses light from a deuterium lamp light source, reflected off a concave mirror to pass through a filter and fluid sample to a paired concave mirror. From the second concave mirror the light is reflected through an aperture slit, represented as being 50µm wide in Figure 5. Light passed through the slit will then refract off of a diffraction grating and into a detector system. [3] [4]

Figure 5: Optical Bench Assembly, © Waters Corp. [3]

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3.2.1 Deuterium Lamp Light Source

A deuterium lamp, composed of a low-pressure gas-discharge, emits a continuous spectrum in the ultraviolet (UV) region, traditionally used in spectroscopy. An electric arc is created from the tungsten filament to an anode inside the lamp. The arc will excite the deuterium gas contained in the bulb to a higher energy state. When molecules transit back to their initial states, the deuterium gas emits light. This continuous cycle provides continuous UV radiation. A fused quartz envelope is used for a casing to prevent blocking the UV lights.

The deuterium lamp has a spectra range from 112nm to 900nm with a continuous spectrum from 180nm to 370nm as shown in Figure 6. Its continuous spectrum covers about 49% of UV light range. The intensity between 250nm to 300nm does not actually decrease as shown in the plot. The decrease is due to reduced efficiency at low wavelengths of the photo detector. [5]

Figure 6: Deuterium Light Spectrum

3.2.2 Concave Mirror Set

A concave parabolic mirror, in this case an elliptical reflector, has a reflecting surface that bulges inward to reflect incident light emitted from the deuterium lamp inward to its focal point at where the fluid cell locates. If the major and minor radiuses are known for an ellipse, the location of the foci can be found by using the formula in Equation 2:

2 2F j n (2)

where F is the distance from each focus to the center of ellipse, j is the semi-major radius, and n is the semi-minor radius. [6] Adjustments can be made to the values for j and n to focus the light to reflect

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property. Note that the two concave mirrors should have identical foci locations as represented by Equation 2 to focus the light through the path in the optical bench.

3.2.3 Aperture Slit

The aperture slit used in the Waters Corporation system is an etched piece of molybdenum, which is used due to its lack of reflective properties. After passing through the slit, light travels in a circular wave as shown in Figure 7. Each circular wave is uniform with the other waves in intensity at a given angle as the waves travel from the slit itself so long as the slit width is smaller than the initial entering beam of light. Using smaller slit sizes creates a more intense or refined beam of light passing through the slit. With a smaller width of a slit there is a greater possibility for reflection between the edges of the slit, depending on the thickness of the slit material, which can create additional interference or noise.

Figure 7: Diffraction pattern from a slit of width four wavelengths with an incident plane wave.

Based on the size of a wavelength being emitted from a fluid sample different diffraction patterns can occur. A slit with a width less than or equal to one wavelength will produce a spectrum with very high intensity at the center and almost zero intensities on the sides; a slit with a width wider than one wavelength will produce a spectrum with less intensity at the center but some intensity on the sides. Due to each sample emitting a variety of wavelengths of light, various resolutions and signal-to-noise ratios can occur for each specific sample. To calculate the intensity of a specific wavelength for a given angle, Fraunhofer diffraction equation (Equation 3) can be used:

20 sin ( sin )dI c

(3)

where is the intensity at any given angle, I0 is the original intensity, d is the width of the slit, and is the wavelength of the light. Fraunhofer diffraction allows for a user to determine the error or noise that could be expected for a specific composition of a sample. Allowing for a sample to be examined by

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multiple slit widths permits an accurate examination of various wavelengths in a single analysis of a sample or analysis of a greater range of sample types. [7]

3.2.4 Diffraction Grating

A diffraction grating has a periodic structure which split and diffracts light into several beams in different directions. The directions of the beams are related to the spacing of the grating and the wavelength of incident lights. In this device, the grating is reflective.

The equation guiding the relationship between the grating spacing, the angles of the incident and diffracted beams is known as the grating equation (Equation 4). An idealized reflective grating is made up of a set of slits of spacing d. After the light with wavelength λ interacts with the grating, the diffracted light is composed of the sum of interfering waves passing through each slit of the grating. Since the path length to each slit in the grating varies, so will the phases of the waves at particular points from each slit. The end phenomenon will be either constructive interference as peaks, or destructive interference as valleys. When the path difference between two waves is equal to half of the wavelength, the waves will cancel each other and create a point of minimum intensity; this is called out of phase. On the other hand, when the path difference is one wavelength, the phase will add up and a maximum intensity will occur as in phase. [8]

Figure 8 shows the end results when an incident visible light beam is reflected by diffraction grating. The

light is separated and the locations where maximum intensities occur are arranged into a nice order

according to their wavelengths. This principle works the same for UV radiation diffraction.

Figure 8: Diffraction Grating Spectrograph of Visible Light

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The reflecting angle θm where the maximum intensities occur satisfy this relationship

(4)

where θi is any arbitrary angle for an incident plane wave, d is the distance from the center of one slit to the center of the adjacent slit, and m is an integer representing the propagation-mode of interest. Since the angles of diffracted in phase light will be different for different wavelengths, the PDA detector will be able to detect the intensity of a specific wavelength at a specific location. [8]

3.2.5 Photodiode Array (PDA) Detector

A photodiode is a photo detector which can convert light into either current or voltage. It is similar to a semiconductor diode, but it focuses on detecting UV radiations and X-rays. When a photon with sufficient energy strikes the diode, it transfers the energy to an electron and therefore creates an excited free electron. In the junctions, holes with positive charge move toward the anode, and free electrons move towards the cathode, resulting in the production of a photocurrent. Since the photocurrent is the sum of both the dark current and light current, the dark current must be minimized to increase the sensitivity of the detector. [9]

There are three critical performance parameters of a PDA detector, responsivity, dark current, and noise-equivalent power (NEP). Responsivity is the ratio of generated photocurrent to incident light power with unit (A/W). Depending on the material used to build the photodiodes, the responsivities are different for different wavelengths. As an example, Waters’ 2998 PDA detector has a detective range from 190nm to 900nm which should be made from silicon with an electromagnetic spectrum wavelength from 190nm to 1100nm. The responsivity vs. wavelength graph is displayed in Figure. 9.

Figure 9: Responsivity of silicon photodiode vs. wavelength of incident light.

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The dark current is what is generated in the absence of light. It includes photocurrent generated by both background radiation and saturation current of the semiconductor junction. It is an important source of noise when a photodiode is operated in UV light detection. NEP is the minimum input light power in order to generate photocurrent. It is basically the minimum detectable power. A signal light with power lower than NEP will not be detected.

When hundreds or thousands of photodiodes are arranged into a one-dimensional array (PDA), they can be used as an angle sensor or position sensor. In this case, the angles to be detected are reflecting angles θm of diffracted lights. With the information about reflecting angles, computers can measure the wavelengths of lights which interact with photodiodes by using Equation 3. Thus, the absorption spectrum of the deuterium lamp can be determined. [4]

4 Design and Sponsor Constraints

Waters Corporation has requested a design with a minimum of a 2 position automated aperture slit for a model 2998 PDA detector. The current aperture slit, shown in Figure 10, is placed on a solid stand or holder that is fixed into a casting. The aperture has a single slit with a width of 100±10µm which can vary by what is requested by customers as far as the targeted inspection light spectrum. The aperture is 50±10µm thick and made of molybdenum with a black oxide finish.

Figure 10: AutoCAD drawing of current aperture slit used in the PDA. All dimensions in millimeters.

The variable aperture to be developed is required to have slit widths of 50±10µm and 200±10µm. If possible, intermittent slit widths can be included as well. The height of the slit is not as critical, but should be no less than approximately ¾”. The slit thickness, parallelism of the slit, and tolerances of the variable aperture should reflect the current aperture.

The mechanisms to be developed for the variable aperture must fit into the existing PDA, therefore presenting space constraints. Waters has asked that minimal alterations be made to the existing casting in order to prevent interference with any of the current mechanisms of the PDA. However, there are a few areas where material on the casting can possibly be trimmed down to provide more space, as displayed in

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Figures 11 through 14. Looking from the top side, the casting can be modified in a cylindrical area around the aperture up to some of the intersecting walls.

Figure 11: View of the PDA casting from the bottom side. Note the location of the current

aperture holder.

Figure 12: View of the PDA casting from the top displaying modifiable section.

Figure 13: View of the PDA casting from the top displaying the optical mirror area.

Figure 14: Section view displaying the location of the aperture (displayed in red) within the casting.

Figure 15 depicts available clearance space in the casting. From the top edge there is 2.118in of clearance, and from the bottom edge there is 1.187in of clearance. Figures 13 and 11 respectively display the portion of the casting the clearance measurements are taken from. The overall inside height of the casting is 7.020 in.

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Figure 15: View of the PDA casting from the side, displaying bottom and top clearance values.

Figure 16 shows the approximate paths that light travels within the PDA. It is important that nothing interferes with the path of the light.

Figure 16: Approximate path of light travel with the PDA.

Waters has recommended a simple adjustment mechanism for securing the aperture to the optical bench. With respect to the optical bench, the position tolerance of the slit location will be on the order of a few microns (~10µm). The bench has a reference datum that can be used to position the smallest slit width during assembly. This will help provide a tight position tolerance (~10µm) between the slits when the width is adjusted. The focus should be on the repeatability between the different positions. The variable aperture slit must have a position repeatability of less than 25µm in the horizontal direction (sensitive direction) and ±150µm along the vertical direction (less sensitive direction). The straightness of travel should be in the order of < 10µm. The intensity a slit’s image cannot drop more than 27% of the original intensity after switching to the other aperture with same slit width.

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The command to switch between slit sizes can be accomplished by either a software or hardware mechanism for moving the system. Any developed software can be a standalone system and will not have to be integrated into the Waters Corporation operating software. Any hardware used must fit into the space constraints for the casting and optical bench body of the Waters Corporation system.

4.1 Patented VAS Systems

Based on similarities in analyzing light, systems used for mass spectrometry provide a good comparison for analyzing HPLC systems. Figures 17 and 18 display light pathways for two Thermo Scientific systems used for mass spectrometry. Similarities between mass spectrometry systems, such as the one in Figure 17 and the Waters Corporation HPLC system allow for items designed for either system to be used for the other style of system.

Figure 17: Thermo Scientific Variable Slit Detector Layout [1]

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Figure 18: Fixed Position Aperture Slit Detector © Thermo Scientific Co. [1]

A patent search revealed the designs for VAS systems usable in either mass spectrometry or HPLC. Figure 19 displays a dual piston mechanism that would apply pressure to a plate in order to vary the slit widths. This design proves to be a bulky design with several moving parts and possibilities for error with uneven pressure from either piston. Figure 20 displays a slit system with motion on either side of a plate, caused by a screw system in front of a hole. The screw based system again would allow for additional error in the system because the screws if not turned evenly the system could be off centered and one side would have a greater distance from the center point than the other. Figure 21 displays a mechanism being held up by tensioned wires to create the various slit widths. A wired system could possibly have increased error over time, and once more if not tightened properly could have a greater distance from the center point than the opposing side. In Figure 22 is an additional screw based system, very similar to that in Figure 20, with the difference that only one side moves. With only one side moving, it is possible that the system could be off-centered and cause additional optical errors.

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Figure 19: Mechanism for US Patent 7170595 [10] Figure 20: Slit mechanism for U.S. Patent 4612440[11]

Figure 21: Mechanism for U.S. patent 2852684[12]

Figure 22: Mechanism for U.S. patent 5451780[13]

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5 Initial Designs

5.1 Rotating Pin Wheel Design

A rotary pin slit (shown in Figure 23) has a disc with multiple built-in slits. The incident light will pass through the slit at the top of the disc. When a bandwidth needs to be adjusted, a motor will rotate the disc until the next adjacent slit is vertically aligned at the top.

Figure 23: Initial design emulating a rotating pin wheel.

The intent behind this design is to overcome the limitation of having only a single slit in the vertical direction. However, it is easier to control a precise vertical motion than a rotational motion. An imprecise rotation can cause misalignment of the slit, which will affect the diffraction pattern of incident light. The design and manufacturing of such a precise rotary wheel is considered to be a challenge that could be overcome, but a rotary wheel system mathematically would not fit into the casting, needing an additional 0.25 inches in depth and height to be able to be removed from the optics wall.

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5.2 Vertical Actuation Design

The thought behind a vertical actuation slit (shown in Figure 24) is to maximize the use of the vertical space within the casting. The original Waters design has a slit holder bolted directly onto the casting. However, the vertical space under the slit holder is more than enough to contain a pressure pump or a power screw system as a motion feature, as well as two vertically aligned slits.

Figure 24: Initial design displaying vertical actuation between two slits.

The benefit of this design is that the tolerance of position repeatability along the direction of motion (the less sensitive direction) is 150µm, which is sufficiently larger than in the sensitive direction. If the length of the slit increases, this tolerance will also increase. The major disadvantage of this design is being limited to 2 to 3 slits to switch between, with limited opportunity for expanding the system. Additionally custom made multi-slit apertures would have to be used for each customer, eliminating interchangeability.

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5.3 Horizontally Sliding Slit Aperture

Instead of a rectangular slice or disc, the design in Figure 25 is formed by placing two planes very close to one another. Therefore, it is an open slit with the slices’ edges as its flanks. In order to vary the slit’s width, the two planes will slide horizontally about a fixed center point. This is feasible because the vertical length of the slit does not affect the diffraction pattern.

Figure 25: Initial design with two moving surface plates with an internal gap as an optical slit.

The benefit of this design is that it can incorporate a continuous variable aperture slit. Theoretically, the slit can be adjusted to serve any bandwidth, which the PDA can detect, but it is extremely difficult to adjust the planes 25µm. With this plate design, the system would have to be maintained perfectly parallel as well to ensure accuracy, and system wear would have to be examined to determine the accuracy of the system over its lifetime. In order to fit into the casting space available, this plate design would have to be smaller than a 2” by 0.5” rectangular enclosure. Combining the size and accuracy constraints, and examining preliminary cost estimates, this design proved to be too expensive to prototype as a system to be integrated into all manufactured detectors.

5.4 Rotational Holder System

In the early stages of the design process, the team selected a semi-hexagonal array of apertures to contain the various slit sizes for the current design by Waters (note: aperture dimensions are consistent with those described in Figure 10). The proposed hexagonal array, displayed in Figures 26 and 27, allows for 3 different slit sizes to be used during the operation of the detector stack. The proposed widths of 50µm, 100µm, and 200µm allow for a great range of resolutions based on the light projected onto the detector after passing through the slit and refracting mirror. Using the semi-hexagonal design, the 3 apertures can be cycled or rotated through with a rotary motor, shifting the aperture 60° for each change to the next available slit, which uses the center of a base holder as the datum for adjustment.

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Figure 26: Initial design of hexagonal slit aperture array.

Figure 27: Top-down view of hexagonal slit aperture array.

Figure 28 displays the initial model with a semi-hexagonal aperture holder (shown in blue) secured to a rotational base (shown in red). Due to space constraints, the rotational base has a smaller diameter than the circular base of the aperture holder currently utilized in the Waters PDA detector. Each aperture slit is affixed to the holder by means of press fit pins (shown in gold), which are forced into press fit holes to secure the apertures. The center of rotation is located in the geometric center of the rotational base and is equidistant from each of the slits, allowing for an even rotation distance from the center of one slit to another. With this semi-hexagonal design, the 3 apertures can be rotated through with a rotary motor, shifting the apertures 60° to change to an adjacent slit option.

Figure 28: Initial design of holder with the attached aperture slits on a rotational base

This rotational base system had such thin walls (0.5mm) that the assembly could not be machined accurately without the risk of failure in the walls due to the machining forces and stresses. This system provided the greatest opportunities for interchangeability and motion, and further modifications were necessary to conceptualize a more feasible design, described in detail in Section 7.

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5.5 Control System Requirements

The controller must fit within the cavity in between the center datum and the optical bench. It needs to operate within the tolerances and have a high repeatability. It should also be rugged and outlast the majority of the other components of the system before repair or replacement is required. The final design will dictate the specifications of the control system focusing on both micro-controllers and actuators with either rotational or linear capabilities.

6 Analysis and Testing

6.1 Light Path Analysis

Background research and analysis to determine the effects of errors and inaccurate motions in a slit system were examined. Each discrepancy from the desired slit position has a different effect on the results and these were tested to determine the accuracy of the system.

6.1.1 Benefits of different slit widths

According to the Fraunhofer diffraction equation, the first dark fringe or the minimum irradiance occurring for an angle θ is given by:

sinw

(5)

where λ is the wavelength of incident light and w is the width of the slit.

The system currently has a 50µm slit, and the variable slit width options range from 50µm to 200µm, with 50µm or 100µm increments. Comparing the 100µm slit and the 400µm slit diffraction with 180nm incident light; they output a 0.103o and 0.0258o angle respectively. This means the first dark fringe on each side will be 0.206o apart for the 100µm slit and 0.0516o apart for the 400µm slit.

The intensity of the diffraction light depends on the angle θ, wavelength and slit width. In the case described above, slit width and wavelength remained the same. With a larger diffraction angle, light with the same wavelength and similar intensity will cover a larger area when hitting the diffraction grating. On the other hand, a smaller diffraction angle will bring a concentrated light beam on to the diffraction grating, covering less area and the intensity contrast will be sharper.

The diffraction grating will reflect the light with the same wavelength and the same reflection angle no matter where it hits. However, the PDA only measures the intensity of the light, but not the wavelength of it. Each photodiode will receive whatever wavelength of light is preloaded in the system. If the diffraction beams from the slit spread far apart, it is more likely that light with a wavelength different from the preload setup of a particular photodiode will be reflected on to it. These intake intensities from other wavelengths are considered to be noise. [14]

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With a small slit, the system can have a higher resolution, but lower signal-to-noise ratio. This is why it is necessary to design a variable aperture slit. It is also the reason why there cannot be a V-shaped slit, since the diffraction angle for each wavelength needs to remain constant.

6.1.2 Diffraction error from tilt in the “Z” direction

Figure 29 comes from a technical report and displays an experimental set-up used to examine the phenomenon of light propagation through a tilted slit.

Figure 29: Experimental Set-up of a laser through an optical slit displaying a coordinate system [14]

In Figure 29, when the light wave E(x,y) at the points of an aperture t(x,y) in the plane of x and y are known, the angular spectrum A(fx,fy) is the Fourier transform of wave field on the aperture. This is represented by Equation 6:

[ 2 ( ]( , ) ( , ) ( , ) x yi f x f yx yA f f E x y t x y e dxdy

(6)

where the approximation evaluates the light wave E(x,y) at the points of the plane x0 and y0 are parallel to the plane x, y.

For a special case of a single, unit-amplitude wave illuminating the aperture normally, Equation 6 shows the angular spectrum of the Fourier transform of the aperture. The problem can be extended to the case of inclined incidence in the particular case of a single slit. When a single, unit-amplitude monochromatic plane wave is incident along the z’ axis, the electric field at the aperture is given by Equation 7.

2[ ( cos ]( , ) ( , )

i yE x y e t x y

(7)

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According to Equation 6, the angular spectrum becomes the Fourier transform shown in Equation 7. After integration, the result turns to be:

0sin( )( , ) ( )x x

x y x yx

l fA f f I f f

f

(8)

where 0 cos /f . Referring to Figure 29, the angle d is the angle between the y-axis and the diffracted ray r.

Considering only the angular dependence of the diffracted rays, it shows the typical distribution of the field diffracted by a single slit through normal incidence. The directions of the diffracted waves must satisfy the following condition:

cos / cos /d d (9)

where the index d refers to the diffracted ray. If the space in regions A and B in Figure 29 have the same

refractive index, then d so that Equation 9 gives (a) d , (b) d where (a) represents transmission and (b) represents reflection. In both cases the direction of the propagation of the diffracted rays lies on a conical surface with apex at zero and half-opening θ, because of the invariance of the angle between the y-axis and the diffracted rays. This means the propagation will have an even distribution and alignment. [14]

Figure 30 displays one of the diffraction patterns on a screen with a slit that is tilted at a 45º angle. If the slit is installed at a tilted orientation, Figure 30 can be used as a reference to adjust it back to its normal position.

Figure 30: Diffraction pattern in the plane x'o, y'o of a single slit inclined at an angle θ=45° to the direction of propagation z’: lx = 0.02mm; D = 1m [14]

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6.2 Light Path Calibration and Verification Test Method

A simplified optical system in the Northeastern University Optics Lab has been created to perform calibrations similar to those done in the full system of the Waters Corporation optical detector stack. The simplified version consisted of a light source, a variable aperture slit, a concave lens, and a camera, which detects light set-up in a straight line path. Having the light propagated in a straight path instead of a reflected path eliminates possible errors from misaligned mirrors. The straight system also eliminates a breakdown of the initial beam of light since visible light will be used instead of ultraviolet from a deuterium for safety and to simplify the experiment. Figure 31 displays the instruments used for the repeatability and calibration experiments.

Figure 31: Light Path Calibration Set-up

In the set-up the light source emits light through an adjustable focusing aperture onto the aperture slit. The light then passes through the aperture slit and onto the magnification lens, creating a larger image for the camera to read. Using the larger scale image the accuracy and position can be adjusted in a more precise manner. Since the light passed through the slit is normal ambient light, the experiment is run in a dark room to eliminate saturation and noise. The image captured by the software provides two benefits. The first such benefit is the overall images can be compared to examine repeatability and tilt or error in the system in a general manner. The image also can be converted into a bmp file and examined using MATLAB to find a mathematical comparison of the accuracies of the system.

Initial testing performed on the original aperture holder and slit (provided as a sample from Waters) revealed the image in Figure 32 with a display of the peaks in the light intensity.

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Light Detecting Camera

20x Magnification Lens

Aperture Slit

Light Focusing Aperture

Light Source and Holder

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Figure 32: Slit image and intensity detecting tool

The thin horizontal line seen in Figure 32 is the location at which the measurements for intensity were taken from. This location was selected because it is close in proximity to the center point of the slit, and because this location is in focus. From the intensity pattern of the slit, one can see the peaks in intensity on the edges and then a drop to an average value of more uniform intensity in the center.

An intensity drop would be the result of the image going out of focus. Using a base with a micrometer attached to either the aperture slit or the camera, the distance that a slit is off by can be determined and then divided by the square of the magnification to determine the “actual” error in distance (or discrepancy from the desired location) because the focused image is magnified. Using the error information, the accuracy of the system can be confirmed and then converted to the number of steps taken by the stepper motor. Adjustments can be made accordingly to account for any errors that may arise.

6.3 Motion Control Analysis

To properly rotate the system between various locations, a precise motor system is required for accuracy. Using the design factors outlined in Sections 4 and 6.3.1, different motors were evaluated to determine the optimal configuration as well as software and hardware systems required to accurately control them.

6.3.1 Motor Systems

Through research, three potential motor systems with rotational capabilities were compared and evaluated based on feasibility of implementation with the VAS design selected by the team. The first option, a linear actuator with a rotary stage (shown in Figure 33), would take the linear motion of the actuator and translate the motion through the stage into a rotational motion on a scaled stage. The system is accurate

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Point measurement is taken from

Intensity Pattern

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and responsive, but based on the size constraints in the casting, placing an actuator and a stage in the right location for the appropriate motion would be limited in location. Additionally, attaching a rotational holder to the stage would require sufficient material to bore and tap holes in to screw lock the holder to the stage as well as attaching the system to the base. Based on these stipulations, the stage system would necessitate significant alterations to the casting, which could prove to be ineffective in terms of cost.

Figure 33: Linear Stage System

A brushless servo motor system would provide the desired rotation for the system in a small vertical cavity. The system would be able to be scaled to require simple bracket attachments to the casting of the optical bench and a small servo motor would be able to fit into the available casting space. The servo motor in Figure 34 displays a compact gearing system, which would minimize the size impact on the system. The servo motor would constantly be moving to be controlled to the right angle during a control system. Due to the constant motion, vibrations in the system could throw off readings for the optical detectors, making the system unreliable and inaccurate.

Figure 34: Brushless Servo Motor

DC stepper motors rotate between set locations or steps and are able to end rotation and “hold” a position at a certain step. Figure 35 displays a stepper motor that runs the system at an offset. The capabilities of the motor system to be offset would permit the system to fit into the casting in numerous configurations. A straight vertical stepper motor (similar to the servo motor shown in Figure 34) would be able to fit into

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the casting space. As a stepper rotates or steps, it moves between its set points to the next location typically in a rotational motion of 1.8º, or 200 steps per 360º rotation. Using gearboxes, the rotation can be adjusted to various desired rotational angles. The stepper motor system has the best capabilities for the motor system.

Figure 35: DC Stepper Motor with Offset Rotation Point

6.3.2 Control Path Design

To control the motor motion, a hardware and software control system is necessary to maintain accuracy. A simple position control system prompting a user input and relaying it into the hardware to move to a set-point similar to the path in Figure 36 is a simple and straightforward control method.

Figure 36: Motion Control Diagram

6.3.3 Control System Hardware

Hardware to control a rotational system must be able to handle an input voltage and then translate the voltage into motion in a system. Based on the possible motor systems, a basic open sourced hardware system, such as an Arduino, is capable of controlling the VAS. Due to being open source, commonly used, and advanced control requirements not being necessary an Arduino is a suitable hardware system

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for running the VAS. The Arduino Uno (shown in Figure 37) has USB capabilities to run off the voltage of a computer system integration and is stackable with a motor driver shield to control a motor system.

Figure 37: Front view of Arduino Uno

To connect the motor system to the control system a standard open source motor shield from Adafruit, shown in Figure 38, can operate the motor system for direction and rotation speed using the input leads shown.

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Sits under the Adafruit driver product (stackable)

USB 2.0 Connectivity Via Atmega8U2 (USB to serial)

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Figure 38: Adafruit motor shield stacked on Arduino Uno

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Stepper motor inputs for the four lead

wires

L293 H-Bridge

Power Header

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7 Final Prototype

The final prototype of the system is broken down into the optical holder components and the rotational control system. The two components are match machined to ensure fit and then combined together for the final prototype.

7.1 Optical Slit Aperture Holder

The team has selected a semi-hexagonal array of apertures which incorporates the various slit sizes desired by Waters. The proposed hexagonal array, displayed in Figure 39, gives the user the option of selecting from 3 different slit sizes to be used during the operation of the detector stack. Standard size widths of 50µm, 100µm, and 200µm will typically provide great range of resolutions, depending on the specific application of the system. Compared to Waters’ original aperture slit design (as shown in Figure 10), the only difference with these new apertures is that 1mm has been removed from both the left and right sides. This modification is necessary to ensure that space constraints within the casting were met. With this semi-hexagonal design, a rotary motor is used to switch between the 3 different positions. When switching between adjacent positions, the control system specifies for the motor to rotate 60°. This angle of rotation is measured from a center datum located at the center of the holder base.

Using the rotation of the semi-hexagonal design, the prototype avoids interfering with the light paths inside of the PDA. The two outer apertures will provide the greatest change of location, but will not interfere with the light pattern due to the slits being perpendicular on their respective plane.

Figure 39 displays the model of the variable aperture slit system placed on a rotational holder base. Each slit is affixed to the holder base by means of press fit pins (shown in gold), which are forced into press fit holes to secure the apertures. The center of rotation is located in the geometric center of the rotational base and is equidistant from each of the slits, allowing for an even angle of rotation from the center of one slit to another.

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Figure 39: Current VAS design, with the aperture slits secured to a rotational base.

The aperture slits are made from molybdenum with a black oxide finish. The press fit pins are made of aluminum. The holder is made of aluminum and is black anodized. It is necessary to anodize the aluminum holder to ensure that the light beam passing through the VAS is not reflected and cause undesired noise. Instead, the black anodized finish allows light to be absorbed, reducing noise. The machining of all parts was performed by the machine shop at the Waters facility. Refer to Appendix A for AutoCAD drawings of the parts in the VAS assembly, which were used for machining.

7.2 Rotational Control System

Using the Arduino control system (refer to Section 6.3.3) with a bipolar stepper motor for the prototype control system, the holder is able to be rotated 60º in either direction from a centered position, measured as 0. The bipolar motor system is able to make forward and backward movements by receiving a voltage input for both direction and rotation speed using a four wire design, as shown by the motor in Figure 40.

Figure 40: NEMA 11 Bipolar Stepper Motor

Using a National Electrical Manufacturers Association (NEMA) size 11 body style (11 representing the size of the diagonal in millimeters) the motor will fit inside of the casting system. Using a standard body

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BB AA

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style such as the NEMA 11 permits the use of a standard production size for mass production, as well as for adding similar components to the system.

Integrating the motor system with the control hardware as shown in Figure 41, the system relies on a user prompt to determine the translation command and then perform the movement action.

Figure 41: Assembled Control System and Prompts

The stepper motor performs steps in increments of 1.8º for moving. Based on the desired ±60º angle, the entire system would have to be rotated around the base multiple times in order to reach the desired location. To limit the motion, a gearbox was added to the system. Based on the standard sizes of gearboxes available from various companies, the step angle, including backlash, was determined to select a system that could create the rotation of 1.8º. A planetary gearbox small than 1.5” in height with a gear ratio of 27:1 or 26.85 including the testing backlash was selected to create the 60º rotation in a manner of 895 geared steps. From this calculation the number of steps the control system will communicate to the motor is determined.

7.3 Combined Prototype

Figure 42 shows the VAS assembly attached to a rotary motor, which is used to switch between the 3 different positions. When switching between adjacent positions, the control system specifies for the motor to rotate 60°. Using the rotation of the semi-hexagonal design, this VAS system avoids interfering with the light paths inside of the PDA. The two outer apertures will provide the greatest change of location, but will not interfere with the light pattern due to the slits being perpendicular on their respective planes.

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User is prompted

Commands translate to signals

Action is completed

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Figure 42: VAS assembly attached to rotary motor.

In order to incorporate the semi-hexagonal VAS assembly and motor, it is necessary to remove some material from the existing PDA casting. Figure 43 displays the new bore holes made in the casting. The team verified that this modification to the casting abided by the design constraints specified by Waters. Refer to Appendix A for AutoCAD drawings detailing the machining of these new bore holes.

Figure 43: Model of PDA casting displaying the new bore hole required for integration of the VAS system.

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To secure the motor to the casting and stabilize the VAS system, brackets were used to attach the motor to the casting. This fixed positioning ensures accuracy and repeatability of the VAS system.

7.4 System Operation

To operate the rotational system with the control system, the code for the motor driver is loaded onto the Arduino Uno. The code will then accept commands from the computer interface and send them to the motor. For MATLAB to communicate with the Arduino and motor shield, the COM channel is updated with a driver to operate the Arduino. Once the COM channel is updated, the Arduino definition file is run in MATLAB to define the Hardware components into bit formats for MATLAB to understand. Once the system is defined, the Arduino is installed to receive direct communications from MATLAB for operation. Once the installation is complete, the “M File” designed to operate the rotational system can be run to move the system between the designed set points based on the 895 step motion.

7.5 Testing and Analysis

To verify the accuracy and repeatability of the system a series of tests to compare the optics control systems is performed.

7.5.1 Optical Analysis and Testing

Using a tolerance of 25µm in the “X” direction, (or 27% intensity drop) as the acceptable criteria the system is tested using the calibration and analysis set-up discussed in Section 6.2. Using Figure 44 as a reference image, each position is compared to test the accuracy and repeatability between each position. The detailed intensity for each image shown at the top of Figure 44 is also compared between the reference image and the testing results.

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Figure 44: Reference image for comparing test data to determine accuracy and repeatability

The horizontal X-axis coordinates of the edges of the slit image were recorded using the camera’s pixel position. Figure 44 has an origin located at the bottom left pixel of the image. Comparing between pixel positions, the shift of each position is numerically compared to determine the amount of shift in each coordinate direction (X, Y, and Z). Using the intensity breakdown of each slit image, the intensity peaks and average intensity were also compared to the reference image to determine the percent difference with the original reference to determine the amount of intensity drop.

The team performed 3 sets of testing to the system. Each set contained two 60o counterclockwise rotations from the left slit to the center slit and to the right slit and two 60o clockwise rotations back starting at the leftmost slit. The data set included information from 5 groups of X, Y, and Z position data sets and 5 images. Figure 45 displays a table of the information collected as raw data from the tests.

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Figure 45: Raw test analysis data

Knowing that each pixel of the camera had a length of 7.4µm and that the magnification on the system is at a ratio of 20:1, each pixel value in Figure 44 is representative of 0.37µm for the actual slit dimension. The shifts of the slits’ X positions were calculated by using Equation 10:

the larger one of ' 0.37 ' 0.37shift left left right rightX X X X X (10)

where X’left, X’right were the X-coordinates of tested positions’ left and right edges, Xleft, Xright were the X coordinates of the referenced slit’s left and right edges.

Using the values for the “Y” and “Z” direction, the angle of tilt in the Z direction of a slit is calculated using Equation 11,

1 ( ' ) ( ' )tan top top bot bot

ztop bot

Z Z Z ZY Y

(11)

where Z’top, Z’bot were the Z coordinates of the tested positions’ top and bottom edges, Ztop, Zbot are the Z-coordinates of the referenced slit’s top and bottom edges, and Ytop, Ybot were the Y-coordinates of the referenced slit’s top and bottom edges.

Using the intensity graph for each image, a drop or gain in light intensity from the original image is calculated using Equation 12:

'I III

(12)

where I is the referenced intensity and I’ is the measured intensity of each testing position. Using Equations 10, 11, and 12, the data is refined as shown in Figure 46 to display comparisons between the reference dimensions.

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Rotation between slits Average Intensity Change

Z-direction shift (µm) X-direction shift (µm)

Nominal - Left -0.71% ± 8.25 ± 3.4Nominal - Right -0.78% ± 6.45 ± 3.4Left – Nominal -0.904% ± 5.0 ± 3.4

Left - Right -2.74% ± 8.5 ± 3.4Right – Nominal -2.74% ± 10.8 ± 3.4

Right - left -3.84% ± 4.5 ± 3.4Figure 46: Refined Data Table

From Figure 46, the rotational device error values were below the specification and tolerance values. The greatest shift in sensitive direction is 3.4µm, in light path direction is less than 10.8µm, and the greatest intensity drop is 3.84%. Repetition of the motion of the system displayed that the system never varied greater than the tolerance limits from the desired location for each position and does not have an intensity drop implying inaccuracies.

8 Project Management Overview

The management of the project is divided into 5 design and construction phases for the development of the prototype itself. In addition to these phases the project is broken into various sections for the development of report and presentation deliverables.

8.1 Design/Model/Construction Phases

The Design/Model/Construction Phases are physical and digital deliverables related to the physical prototype being developed. Each section of the phases are broken down below with additional details related the work to be completed and current status.

8.1.1 Initial Design Phase

The initial design includes all preliminary design steps, including but not limited to design research, patent research, competitor analysis, and other research items that provide background information for the prototype. Each aspect of the research correlates to various aspects of the modeling phase of the project, and will be completed prior to the beginning of the modeling phase. Many items included in the research and documentation portion of the initial design phase provide information, which will be presented in the initial design presentation phase later discussed.

Responsibilities for the initial design phase were broken up into 4 main categories, analysis of Waters and key technologies that will be involved in the products associated with the project’s prototype completed by Aaron Gill, an evaluation of the Waters “Stack System” performed by Kevin McMorrow, detailed analysis the Waters optical detector, done by Hanshen Zhang, and a review of current design models and design constraints completed by Paul Ventola.

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8.1.2 Modeling Phase

The modeling phase included all modeling, virtual design and development of the prototype and early design iterations. During the modeling phase much of the mathematical analysis and design of the prototype occurred. Each modeled component is ordered after the modeling phase is completed. Evaluations of machinability for the holder system and gear ratios were determined as part of the modeling phase. Final approval for the purchase and construction of these parts was verified with Waters Corporation to ensure the items fit their intentions for the project.

Responsibilities for the modeling phase were separated between Aaron Gill and Paul Ventola performing SolidWorks modeling and analysis to determine the appropriate motor systems to use, and Hanshen Zhang evaluating how to calibrate the light path with integrated models.

8.1.3 Ordering Phase

The ordering phase includes a majority of the lead times associated with the purchasing, ordering, and external vendor work necessary for the prototypes. This phase comprised a significant portion of the 6 month time period, as vendor timelines are outside of the control of the team and are planned to exceed normal lead times.

The ordering phase relies heavily on the machinist at Waters Corporation responsible for the machining of the modeled parts. Each part is tightly toleranced due to the nature of the optical systems and required extra time in case items were made outside of tolerance and specifications and needed to be remade.

8.1.4 Initial Construction Phase

The initial construction phase is inclusive of all initial physical builds, a combination of initial components and testing inside of the optical bench itself. This phase is also inclusive of several debugging, modification, and fine-tuning phases to optimize the set-up, and determine the needs of any changes or additional components that need to be purchased. The initial construction phase will require a majority of the teams’ physical involvement and time. The project will not move into a final production phase, including placing the components into the optical bench casting until the design has been fully evaluated.

The initial construction phase involved the testing of the full motor control system performed and verification of the aperture holder dimensions by Aaron Gill.

8.1.5 Final Production Phase

The final production phase is comprised of the final development of the prototype for the Waters VAS system. The final production involves the placement into the final casting model for aperture system as well as methods for integration into the various models and castings used by Waters. The final production phase will additionally include some analysis of the design, debugging, and problem solving as necessary for the proper integration into Waters designs.

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The final production phase involved attaching the system onto the mounting brackets and placing it into the cavity and rotating the system through a series of step locations to ensure there is no interference with the casting performed by Aaron Gill, Paul Ventola and Hanshen Zhang.

8.2 Report and Presentation Phases

The report and presentation phases are divided into sections based on the reports to be given by the team over the development and production of the VAS prototype. The report and presentation will be developed as needed for each individual report and presentation throughout the scope of the project.

9 Future Work

Based on the final designs, adding an additional vertical actuation into the semi-hexagon design permits the addition of 3 additional slits as a second tier or level to the system. With a 6 aperture set-up a greater variety of resolutions could be used for the optical detector. Based on customer needs and the availability of time future efforts may include the introduction of the vertical actuation into the current design.

10 Summary

From the developed designs, a semi-hexagon formation of apertures placed on a rotating base or holder will allow for a variety of slit sizes permitting light through to the optical detector. The design will not interfere with the light patterns existing in the Waters optical detector. Using this design will also allow for some interchangeability based on individual customer needs, placing a customer’s 3 preferred slit sizes into the system they choose, without modifications to the system. Additionally this model permits the possibility of upgrading the system to include a vertical motion, adding an additional row of possible apertures possibilities.

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11 Intellectual Property

11.1 Description of Problem

The design of a Variable Aperture Slit (VAS) system used for providing different resolutions of light to be projected into a photodiode array (PDA) for examining the composition of a fluid sample. The VAS will consist of an aperture holder with attached aperture slits of various sizes that will be used to limit or refine the light from an ultraviolet (UV) or deuterium light source. The VAS will be mounted onto a rotational motor aligned between a reflected and refracting mirror to permit a certain amount of light with a specific resolution that is unique to each slit size through from the light source to the PDA. Prior to passing through the slit, the UV light will pass through a sample fluid, prepared via liquid chromatography separating the components of a substance, which will absorb various wavelengths of light corresponding to the absorption pattern of the substance. Based on the remaining wavelengths of the light which are passed through the slit and then refracted into an optical detector, the composition of the sample fluid can be determined. In the detector, each slit width will provide a different signal-to-noise ratio and resolution.

11.2 Proof of Concept

A rotational system on a NEMA 11 stepper motor and gearbox configuration, rotating 895 steps between 60º set points maintains accuracy within 4µm. Repeatability examined images of optical slits, detailing consistent intensities and focus of light supports the repeatability of the mechanism. Additional validation of optical results from standard fluid samples supports the accuracy of the system.

11.3 Progress to Date

A functional rotational motor system connected to control software and an aperture holder containing three slits has been built and tested. Initial testing on the accuracy of the system has been performed to confirm overall repeatability.

11.4 Individual Contributions

The design and system layout has been created by Aaron Gill. 3D models of all components and parts have been created by Aaron Gill and Paul Ventola. Accuracy and repeatability validation and verification has been performed by Hanshen Zhang with the assistance of Aaron Gill and Paul Ventola. Control software coding and interface creation has been completed by Kevin McMorrow.

11.5 Future Work

Integration of a vertical actuation system increases the number of slits capable of examining a single fluid sample without disassembling the system. The system can also be integrated into other optical analysis devices such as mass spectrometers.

.

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12 References

[1] ThermoScientific, "Thermo Scientific Dionex UltiMate 3000 Diode Array and Multiple-Wavelength," Dionex, [Online]. Available: http://www.dionex.com/en-us/webdocs/69566-DS-DAD-3000-12Apr2012-. [Accessed July 2012].

[2] Wikipedia, "Chromotography," Wikipedia, [Online]. Available: http://en.wikipedia.org/wiki/Chromatography. [Accessed 15 September 2012].

[3] Waters Corporation, "HPLC - High Performance Liquid Chromatography Waters Inc. Primer," Waters Corporation, 2010. [Online]. Available: http://www.waters.com/waters/nav.htm?cid=10048919. [Accessed 2012].

[4] Waters Corporation, "2998 Photodiode Array (PDA) Detector specifications," [Online]. Available: http://www.waters.com/waters/nav.htm?cid=1001362. [Accessed 1 August 2012].

[5] Wikipedia, "Deuterium Arc Lamp," [Online]. Available: http://en.wikipedia.org/wiki/Deuterium_arc_lamp. [Accessed 12 August 2012].

[6] Math Open References, "Optical Properties of Elliptical Mirrors," [Online]. Available: http://www.mathopenref.com/ellipseoptics.html. [Accessed 12 August 2012].

[7] Wikipedia, "Diffraction," [Online]. Available: http://en.wikipedia.org/wiki/Diffraction. [Accessed 12 August 2012].

[8] Wikipedia, "Diffraction Grating," [Online]. Available: http://en.wikipedia.org/wiki/Diffraction_grating. [Accessed 12 August 2012].

[9] Wikipedia, "Photodiode," [Online]. Available: http://en.wikipedia.org/wiki/Photodiode. [Accessed 12 August 2012].

[10] B. J. E. Smith and A. M. Woolfrey, "Optical Slit". United States Patent 7170595, 30 January 2007.

[11] C. Brunnee, P. Dobberstein and G. Kappus, "Device for adjusting slit widths in spectrometers". United States of America Patent 4612440, 16 September 1986.

[12] J. H. Payne, "ADJUSTABLE SLIT MECHANISM". United States of America Patent 2852684, 16 September 1958.

[13] B. Laser, "Device for setting slit widths in the beam path of spectrometers". United States of America Patent 5451780, 19 September 1995.

[14] C. V. Fel'De and P. V. Polyanskii, "Peculiarities of light diffraction by an inclined slit," Optics for the quality of life; 19th Congress of the International Commission for Optics, no. 1, pp. 319-320, 2003.

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[15] S. Ganci, "Fourier Diffraction through a tilted slit," European Journal of Physics, vol. 2, no. 3, pp. 158-160, 1981.

[16] American Journal of Physics, "Journal of liquid Chromatography & Related Technologies 2010," American Journal of Physics, 2010.

[17] K.-L. Shu and P. R. Silverglate, "Spectrometer with planar reflective slit to minimize thermal background". United States of America Patent 6310347, 30 October 2001.

[18] L. Dong, A. K. Agarwal, D. J. Beebe and H. Jiang, "Variable-Focus Liquid Microlenses and Microlens Arrays Actuated by Thermoresponsive Hydrogels," Advanced Materials, pp. 1-5, 2007.

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13 Appendices

13.1 Appendix A: System Part Drawings

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Figure 47: AutoCAD drawing for holder base.

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Figure 48: AutoCAD drawing for 50m aperture slit.

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Figure 49: AutoCAD drawing for 100m aperture slit.

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Figure 50: AutoCAD drawing for 200m aperture slit.

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Figure 51: Drawing of Stepper Motor

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Figure 52: AutoCAD drawing of new bore hole required for PDA casting (page 1 of 2).

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Figure 53: AutoCAD

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drawing of new bore hole required for PDA casting (page 2 of 2).

13.2 Appendix B: Arduino Control Code

13.2.1 Code to define the Arduino in MATLAB:

This code will be provided as part of the transferred material to Waters Corporation. Defining the Arduino is required for the first run of the MATLAB system to properly detail the Arduino’s hardware capabilities for the software.

13.2.2 Code to install Arduino to work with MATLAB:

This code will be provided as part of the transferred material to Waters Corporation. The Arduino must be installed inside of the MATLAB software to correctly align the paths from the COM ports for the voltage transmission.

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13.2.3 Code to run Control Program:

The coded text for running the MATLAB control Program. The ‘COM’ port is adjusted based on what is selected when installed into the computer system, but the remaining items remain constant for rotating the system.

%a=arduino(‘COM6’)a.stepperSpeed(2,20);state=10; state=input('Wide:1 Narrow:2 Nominal:3 Quit:4'); % user input while(state~=4) %Start While Loop{if(state==1)%Code to move to the slit designated as “Wide” in position 1 a.stepperStep(2,'forward','single',255) a.stepperStep(2,'forward','single',255) a.stepperStep(2,'forward','single',255) a.stepperStep(2,'forward','single',130) state=input('ENTER Wide:1 Narrow:2 Nominal:3 Quit:4.......?'); a.stepperStep(2,'backward','single',255) a.stepperStep(2,'backward','single',255) a.stepperStep(2,'backward','single',255) a.stepperStep(2,'backward','single',130)end%close State #1 if(state==2)%Code to move to the slit designated as “Narrow” in position 2 a.stepperStep(2,'backward','single',255) a.stepperStep(2,'backward','single',255) a.stepperStep(2,'backward','single',255) a.stepperStep(2,'backward','single',130) state=input('Wide:1 Narrow:2 Nominal:3 Quit:4'); a.stepperStep(2,'forward','single',255) a.stepperStep(2,'forward','interleave',255) a.stepperStep(2,'forward','single',255) a.stepperStep(2,'forward','single',130)end %close state #2if(state==3)%Code to move to the slit designated as “Nominal” in position 3 a.stepperStep(2,'forward','single',0) state=input('Wide:1 Narrow:2 Nominal:3 Quit:4'); end%close state #3 end

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13.3 Appendix C: Driver Shield Schematic

Figure 54: Schematic of Driver Shield

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13.4 Appendix D: Motor Wire Diagram

Figure 55: Motor Wire Diagram

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13.5 Appendix E: Stepper Motor Specifications

Figure 56: Stepper Motor Specifications

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13.6 Appendix F: Uno Schematic

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Figure 57: Arduino Uno Schematic

13.7 Appendix G: H Bridge Circuit Schematic

Figure 58: H Bridge Circuit Schematic

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13.8 Appendix H: Microcontroller Schematic

Figure 59: Microcontroller Schematic

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13.9 Appendix I: Microcontroller Block Diagram

Figure 60: Microcontroller Block Diagram

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