IBP HAND IN COPY

Laser Optical Engineering Ltd JT3 – Final Report

Modular Diffractive Optic Mount

LOUGHBOROUGH UNIVERSITY

Teaching Contract

Laser Optical Engineering Ltd – JT3

Usman Tanveer

Samuel Skingsley

Peter Hamilton

Ahmad Mohammad

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TABLE OF CONTENTS.

1.1 SUMMARY............................................................................................................4

2.1 INTRODUCTION...................................................................................................5

2.2 BACKGROUND....................................................................................................6

2.3 PRODUCT DESIGN SPECIFICATION.................................................................8

3.1 PROPOSAL AND ANALYSIS............................................................................10

3.1.1 OPTICAL ARRANGEMENT.................................................................................10

3.1.2 CAROUSEL DEVELOPMENT..............................................................................11

3.1.2.1 Series 012 Dual Passage Threaded Shaft Union...............................22

3.1.2.2 Faulhaber DC Micromotor....................................................................22

3.1.2.3 Drive gears............................................................................................23

3.1.2.4 Solenoid................................................................................................23

3.1.2.5 Optic mounting plates..........................................................................24

3.1.2.6 Control gear and Servo........................................................................24

3.1.2.7 Bracket..................................................................................................26

3.1.2.8 Pipe attachments..................................................................................26

3.1.3 MIRROR TILTING MECHANISM..........................................................................27

3.1.4 ANALYSIS OF CURRENT MIRROR HOUSING.......................................................29

3.1.5 DIFFRACTIVE OPTIC AXIAL ALIGNMENT............................................................30

3.1.6 FUME EXTRACTION SYSTEM............................................................................31

3.1.7 CASING DEVELOPMENT...................................................................................35

4.1 DISCUSSION AND CONCLUSIONS..................................................................42

5.1 POSTSCRIPT.....................................................................................................43

6.1 APPENDIX..........................................................................................................44

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TABLE OF FIGURES.

Figure 1 - Current optical arrangement.................................................................................................6Figure 2 - Proposed mirror arrangement 1..........................................................................................10Figure 3 - Effect of rotating entire module..........................................................................................11Figure 4 - Basic 90 deg single passage rotary union.............................................................................12Figure 5- CAD model of initial concept................................................................................................13Figure 6 - Cooling block core...............................................................................................................13Figure 7 - First revision of carousel concept........................................................................................14Figure 8 - Series 013 dual passage rotary union..................................................................................15Figure 9 - Coolant flow direction.............................................................Error! Bookmark not defined.Figure 10..............................................................................................................................................16Figure 11 - Carousel chassis.................................................................................................................16Figure 12..............................................................................................................................................18Figure 13 – Series 003 90 degree single passage rotary union............................................................19Figure 14 - Cooling block core.............................................................................................................20Figure 15 - Diffractive optics assembly................................................................................................20Figure 16 - Final carousel assembly.....................................................................................................21Figure 17 - Series 012 Dual Passage Threaded Shaft Union.................................................................22Figure 18 - DC Micromotor..................................................................................................................22Figure 19 - CAD models of drive gears.................................................................................................23Figure 20 - Linear pull-type solenoid...................................................................................................24Figure 21 - Optic mounting plates.......................................................................................................24Figure 22 - Parallax continuous rotation servo motor.........................................................................25Figure 23 - Control gear.......................................................................................................................25Figure 24 - Bracket...............................................................................................................................26Figure 25 - Tilting plate........................................................................................................................27Figure 26A - Tilting plate reverse view.................................................................................................27Figure 27B............................................................................................................................................27Figure 28 - Analysis test rig.............................................................................................................29Figure 29 - Axial alignment diagram....................................................................................................30Figure 30 – Vernier Caliper..................................................................................................................30Figure 31 - Current Fume extraction system.......................................................................................31Figure 32 - Air flow through fume capture system..............................................................................31Figure 33 - Revised fume extraction system 1.....................................................................................32Figure 34 - Revised fume extraction system 2.....................................................................................33Figure 35 - O-ring sizes........................................................................................................................34Figure 36 - Perspex tubing sizes...........................................................................................................34Figure 37 - Final optical arrangement..................................................................................................36Figure 38 - Positive pressure................................................................................................................37Figure 39 - Module assembly...............................................................................................................38Figure 40 - Basic dimensions of module assembly...............................................................................39Figure 41 - Draw latch..........................................................................................................................40

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1.1 SummaryThis project is set by Laser Optical Engineering Ltd (LOE) who are pioneering laser

material processing technology. LOE produce holographic diffractive optical

elements for a variety of applications including the optimisation of laser welding and

glazing.

The product currently being developed is a standalone module that enables the

optimisation of laser welding through the use of holographic diffractive optics.

This report analyses the current diffractive optic module, identifying its weaknesses

and details ways to improve each aspect of its design. The final product is expected

to be fit for commercial retail.

The report includes a detailed proposal complete with engineering drawings to allow

LOE to further develop and/or manufacture a prototype of the product.

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2.1 IntroductionLaser beam welding is a relatively new innovation in the welding industry. The laser

welding process typically involves using a high intensity laser beam as a

concentrated source of heat to fuse materials together. The process is commonly

used in automotive, aerospace and defence/military industries where high volume

production is needed.

In conventional laser processing, the distribution of heat energy throughout a laser

beam’s cross-section is highly uneven. Most of the energy is distributed towards the

centre point of the beam. The impact of this is that as the spot of the beam moves

across the surface of a material, the centre line gets an excess of energy applied,

whilst the outer edges are not supplied with enough energy. This causes the welded

area to cool at an uneven rate, resulting in uneven grain sizes across the weld. As

these grain sizes do not match those of the parent material, the weld becomes a

weak point in the structure.

Laser Optical Engineering specialise in the manufacture of diffractive optical

elements that have the capability of altering the heat pattern of high power laser

beams. By reflecting a beam off a special holographic element whose characteristics

are unique to the process material, they are able to control the lasers heat

distribution pattern. This creates a weld structure more similar to the parent material

giving the bond a greater strength, and instead of the curved weld lines that we are

familiar with, this causes straight line welds between the two materials. These

straight line welds are revolutionary in welding industry and are a breakthrough in

laser welding technology.

Apart from laser beam shaping, LOE also offer other services including Non-

Destructive Testing (NDT), Light Emitting Diode (LED) and laser safety testing.

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2.2 BackgroundCurrently in development by LOE is a diffractive optic module that attaches on to the

conventional CO2 laser, and with integrated holographic optical elements, is

designed to reshape the beam. The typical laser product the module is designed for

is a Class 1 1kW CO2 laser welder, with a beam diameter of 35mm.

With a beam of such high intensity, the mirrors used reflect it must be capable of

withstanding the high energies involved. The mirrors used in the module are made

from Zinc Silicon.

The diffractive optic elements are Silicon blanks imprinted with a hologram specific to

the material and process being performed. These are then coated with a layer of

gold.

The current diffractive mount was created for experimental and testing purposes.

The casing of the mount is made from 3mm thick aluminium. The input beam is at a

right angle to the output beam, with the mirror arrangement shown in Figure 1 -

Current optical arrangement

Figure 1 - Current optical arrangement

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The critical working angle of the beam coming off the holographic diffractive optic is

110, with a focal length of 451mm from the centre of the optic to the material being

processed.

Within the current system, only the diffractive optic element is set in place, the other

2 mirrors are used to steer the beam onto the diffractive optic. Every time a mirror or

optic is replaced, the steering mirrors have to be adjusted to re-align the laser beam

onto the correct path, this is both time consuming and tedious for the operators.

Each time the laser beam is deflected off a mirror, losses to the beams power occur,

therefore it is desirable that the module includes minimal numbers of mirrors before

the diffractive optic. The diffractive optical element is the last contact the laser beam

should have before making contact with the working surface, other than passing

through a ZnSe window. Otherwise the heat distribution pattern caused by the

holographic diffractive optic can become distorted and skewed rendering it useless.

A summary of problems facing the current diffractive optic mount are listed below:

It does not have the capability to weld in more than one plane/direction

The outside of the housing is subject to violent corrosion when in use due to

highly corrosive weld spatter

The module is only capable of operating with one holographic optic at a time –

interchanging optics takes a lot of time and effort

Front of housing is not easily removable, and is often not used. As a result the

optics inside the housing are exposed to dust and dirt, risking failure

2.3 Product Design Specification7


1. Function

Input and output beam must be coaxial

A system must be in place to allow the leading edge of the laser beam

print to rotate, at least in 900 increments

System to allow the user to easily change between multiple diffractive

optical elements. At least 2 diffractive optical elements

Integral cooling within mount

Integral mirror and diffractive mount alignment-2 axis

A means of preventing ingress of dust/fumes

Cutting nozzle with gas jet

Welding gas shroud

Annular fume capture system

Removable face to allow access to inner components, for initial setup

and maintenance only

2. Constraints

26 weeks development time

3. Competition

Two other companies competing to develop a solution to the same

problem

4. Customer

Laser Optical Engineering Ltd is the primary customer, who will then go

on to distribute the product commercially

5. Deliverables

Engineering drawings, parts list

CAD model of assembly

Feasibility study

6. Environment

Dust and dirt will be present in its working environment

7. Installation

Laser Optical Engineering Ltd will perform the installation

8. Maintenance

Maintenance to be performed by Laser Optical Engineering

9. Manufacture

Manufacture in-house

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Specialist components bought separately

10.Materials

High quality materials must be used to maximize end product’s

performance and durability

11.Quantities

Produce sufficient technical drawings to allow LOE to take product for

further development, and/or fabrication

12.Standards and specifications

All specifications must adhere to British Standards

13.Storage/Shelf life

Does not need to be stored, once mounted can be left on Laser

Components that are subject to corrosion during operation should be

replaceable

3.1 Proposal and Analysis

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3.1.1 Optical ArrangementIn accordance with the PDS it was important to change the mirror arrangement so as

to allow for co-axial input and output beams. The introduction of co-axial input and

output beams means that the module can universally mount to most laser systems.

This cannot be achieved with the current arrangement as the laser input and output

beams are perpendicular.

In order to allow co-axial input and output beams the addition of an extra mirror was

required. Although this slightly reduces the laser beams power, the advantages of

having a co-axial input and output beam outweighs this minor setback (Figure 2).

3.1.2 Carousel DevelopmentCurrently, the diffractive module features one holographic optical element housed in

the same mount used to house the mirrors. Due to the fact it cannot rotate, the

leading edge of the beam print always faces the same direction. This limits the

module to only processing materials in a single direction.

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Figure 2 - Proposed mirror arrangement 1


To enable the module to process materials in more than one direction, the diffractive

optical element must have a means to rotate.

Another way of accomplishing this same task is to enable the whole mount to rotate.

However this provokes the danger of translational movement of the beam print

(Figure 3) as well as rotational if the mount is not completely aligned in the vertical

direction. A high moment of inertia of the module will also induce the same effect.

The moment of inertia of the mount will increase if more weight is added outside the

axis of rotation.

Slight misalignment in the vertical direction is always highly likely to occur, and would

be a highly undesirable effect. This concept was therefore eliminated as a viable

solution.

Taking further the concept of rotating the diffractive optic, the cube carousel design

was drawn up.

This is a simple solution that fulfils all major requirements. Four faces of the ‘cube’

would house a mirror, and all four mirrors would share a common liquid cooled core.

The carousel would rotate on a bearing, and its rotation controlled by an electronic

control system. To ensure the diffractives all stop in the same place, a mechanical

locking mechanism would be implemented similar to that of the barrel of a revolver

pistol.

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Figure 3 - Effect of rotating entire module


Research was carried out into mechanisms that could be used to provide cooling to

each optic whilst allowing it to rotate in at least one direction. After looking through

many different systems, it was decided that a single passage rotary union was the

ideal solution. Not only would it allow coolant to flow through the carousel, but it

would also allow it to rotate freely.

Rotary Systems Inc and Talco Rotary Unions are two manufacturers of mechanical

seals, rotary union systems, hydrostatic seals and integrated electrical slip rings.

Figure 4 shows a basic 90 degree rotary union offered by Talco Inc.

With the initial mirror arrangement, it was important to minimise dimension E (Figure

4), as the larger this dimension, the wider the carousel component would be. The

effect this would have is the length of the box would have to increase. The smallest

union available was model BB-2300-01, which had a dimension E of 1 7/8”. The first

CAD model of the carousel was created using this union (Figure 5).

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Figure 4 - Basic 90 deg single passage rotary union

Figure 5- CAD model of initial concept


This was a very basic conceptual CAD drawing of how carousel could be assembled.

The coolant could flow through one rotary union, and would be directed around the

system along a milled flow path and out of the other. Figure 6 shows the internal

core of the cooling block which would be housed within the outer chassis. The

approximated rotating profile of the component assembly was 133mm.

Coolant would be channelled around each face of the cooling block along one

continuous path until it reached the other side. It would then exit through the second

rotary union. As only one optic will be in operation at any one time, there is no need

for multiple coolant channels. This enables a single coolant feed to be sufficient in

cooling any of the four optics in use.

This concept provoked major problems with regards to sealing, and that the rotary

unions were widening the overall width of the carousel, meaning the length of the

module would have to increase dramatically.

Above all of these problems was the issue of the pipes twisting when the carousel

rotates over 360 degrees. A very desirable but not compulsory feature would be if

the carousel could be designed to rotate without this limitation.

Improvements were made to tackle these problems. To counteract the problem of

increasing the compactness of the carousel, the rotary unions were indented into the

cooling block by boring material out of the sides.

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Figure 6 - Cooling block core


The result would mean that it was now possible to use slightly higher quality rotary

union units and still decrease the rotating profile of the carousel by 14mm. Figure 7

shows a visualisation of this design.

This concept again involves screwing two rotary unions into a core around which a

chassis houses the holographic optical elements.

Rotary Systems Inc is a US based company specialising in high quality, high

precision rotary union systems. They have an extensive catalogue of different types

of rotary unions with many different applications. The union systems they offer are

made from high quality materials and feature precision ball bearing units. These

pose a much more reliable solution in comparison to the product supplied by Talco

Inc, and so it was decided that they were a more suitable supplier. Amongst the

company’s catalogue is the Series 013 multiple passage union (Figure 8).

Series 013 2-Passage Flange Mount

Rotary Union (part number 003-10210).

The operating specifications are listed

below:

Max. Hydraulic: 7,000 PSI

Max. Air: 250 PSI

Max. Vacuum: 28 Hg

Max. Temperature: 300 Degree F

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Figure 7 - First revision of carousel concept

To prevent leakage, small grooves would be cut into the block to house o-rings.


This dual passage rotary union is mounted to the assembly to channel the coolant to

and from the cooling block and allow the whole system to rotate freely without any

issues with twisting pipes.

The component has many industrial applications and its capabilities far exceed its

proposed use in this design. CAD models and detailed specifications were provided

by Rotary Systems Inc.

The cooling block also incurred many changes to improve its simplicity and

practicality. Instead of having a milled path for the coolant to flow through, it would

now flow through an open reservoir around the cooling block and exit through the

other rotary union (Figure 9).

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Figure 8 - Series 013 dual passage rotary union

Figure 9 Carousel Design - Core

Figure 10 - Carousel chassis


Figure 10 shows the outer chassis which houses a holographic optical element in

each face. Four optical elements can be used at any one time in accordance with the

PDS. The thickness of the wall behind each optic is minimised to 2.5mm. It is

important to minimise this dimension to allow the coolant in contact with the back

surface to absorb as much heat energy as possible.

The chassis is designed so that it can be machined out of an 80x80mm aluminium

box-section with a wall thickness of 12.5mm; aluminium being the material of choice

due to its desirably high coefficient of thermal conductivity (250 W·m−1·K−1) compared

to that of low carbon steel (50 W·m−1·K−1). Source: Engineering Toolbox

(http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)

The edges are chamfered to reduce its rotational profile to 100mm. Grub screws are

used to hold each optic in place.

Reviewing this concept, the following problems were highlighted:

The use of o-rings or silicon gels to prevent water leaking around the

corners of the cooling block would be impractical

The cooling block and chassis components would need to be

manufactured to a very high dimensional accuracy, and currently

contain complex geometry that would make it highly difficult to

manufacture; too high to be considered practical

Compacting the carousel causes difficulties to be incurred

Assembling the parts is currently impossible

These problems meant a rather drastic design change was needed to alter the

parameters currently constraining the development of the carousel. Since the

carousel assembly was one of the most integral features of the design, it was

important to design the other features of the mount around it. This meant reviewing

the arrangement of the steering mirrors.

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It was decided that by changing the angle of the second steering mirror and by

moving it further away from mirror 1, more space could be created for the carousel

thus eliminating the need to compact it. See Figure 11.

The previous proposal for the mirror arrangement was restrictive in that it did not

allow for any space for a carrousel assembly to be housed. The calculated length of

the mount casing was 660mm x 186mm. It is clear from the diagram how increasing

the distance between mirror blocks 1 and 2 would mean having to lengthen the box

significantly.

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Figure 11 Mirror Arrangement

1

2

3


If the carousel concept was incorporated into this arrangement, the overall length of

the mount would exceed one meter. If this was to occur, the focal point would be

within the perimeter of the box. making it impossible to machine anything. The new

adjusted mirror arrangement would allow enough space for the carousel assembly to

sit. The only compromise would be an increase in overall length by 45mm, and width

to 370mm. With no restrictions on the width of the mount, it was decided that this

would be the adopted arrangement.

With the restriction of having to compact the carousel eliminated, it was no longer

necessary to minimise the length of the rotary unions. This allowed the integration of

single passage 90° ball bearing rotary unions, manufactured by Rotary Systems Inc

(Figure 12).

Operating Specifications:

Max. Hydraulic: 7,000 PSI

Max. Air: 250 PSI

Max. Vacuum: 28 Hg

Max. Temperature: 300 Degree F

The cooling block is also changed in the final revision of the carousel. It is simplified

even further to a design that is practical and easily machinable. The core of the block

is machined from one solid 60x60 block of aluminium. A series of holes that intersect

internally are drilled into the block, allowing coolant to flow through to reservoirs on

each face (Figure 13).

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Figure 12 – Series 003 90 degree single passage rotary union


Mounting plates are screwed onto each face, each holding an optical element. O-

rings are used around the edges of the reservoirs to seal them completely. Tapped

holes are drilled into the other sides of the block to allow the rotary unions to be

screwed on.. Figure 14 shows the diffractive optics assembly from various angles.

Into this design, a mechanism for rotating the block 90° also had to be incorporated

to allow the user to switch between each of the four optical elements. This meant

introducing electronic motors / solenoids onto the assembly.

A system to control the axial rotation of the whole assembly also had to be

implemented. This coupled with wires from the electrical components on the

assembly led to the complication of wires twisting, which was quickly overcome via

the introduction of slip-rings. Alternatively, a 3.5mm standard headphone jack could

have been used, but slip-rings were selected as the most reliable option.

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Figure 13 - Cooling block core

Figure 14 - Diffractive optics assembly


The final carousel assembly is shown from two different angles in Figure 15. A

detailed breakdown of each component follows.

3.1.2.1 Series 012 Dual Passage Threaded Shaft UnionThis union features the same specification of Series 013 Flange Mounted Union but

has inlets and outlets at the sides of the union.

The advantage of this is that the pipes

connecting the 90° single passage unions

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Figure 15 - Final carousel assembly


to the dual passage union cannot interfere with the rotation of the block. The union

also features a hollow tube through its central axis that wires can be fed down. The

option of an integrated electrical slip-ring is available as an added extra. The wires

from the solenoid and electric motor will be connected to terminals on the 6-circuit

slip-ring to prevent them from twisting as the assembly rotates. The component is

pictured in Figure 16.

3.1.2.2 Faulhaber DC MicromotorThis small electric motor is ideal for the rotation of the carousel. Small and

lightweight, the Faulhaber Series 1024 S (Figure 17) provides relatively good torque

and will drive the carousel via two gears on the side of the cooling block. A full data

sheet including dimensions can be found in Appendix 1.

3.1.2.3 Drive gearsThe gears are ordered standard parts custom built to specification by Rush Gears

Ltd (Gears), and then machined to allow them to integrate into the assembly. The

large wheel will be screwed into the cooling block using four M4 screws. It has a

PCD of 63.5mm and an outer diameter of 66.7mm, with 40 teeth. The pinion has an

outer diameter of 20.7mm and a PCD of 17.5mm, with 11 teeth. It is directly

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Figure 16 - Series 012 Dual Passage Threaded Shaft Union

Figure 17 - DC Micromotor


connected to the motor. Both gears are aluminium to minimise weight whilst

maintaining high strength. This lessens the load on the motor.

3.1.2.4 SolenoidThis component is a miniature linear

pull-type solenoid manufactured by The Solenoid Company, (part number MM05F24,

pictured in Figure 19). It is attached to one rotary union and locks into one of four

locating holes on the side of the cooling block. This will allow the carousel to lock to

four different positions, stopping each optic at exactly 90° to the other. A full data

sheet for the solenoid can be found in Appendix 2.

The surface of the rotary union the

solenoid attaches to cannot be machined or drilled into, as it will damage it. As a

result, for the purpose of the prototype, the solenoid will be bonded to the casing of

the union with two part epoxy resin.

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Figure 18 - CAD models of drive gears

Figure 19 - Linear pull-type solenoid


3.1.2.5 Optic mounting platesFour counterbore M4 holes on each of the mounting plates will allow them to be

screwed onto the central cooling block. The optical element will sit flush in the mount

and a small groove is milled into the edge of the rim to allow for easy removal.

The finish of the surface behind the optical element must be of very fine surface

roughness. More importantly, it needs to be perfectly parallel to the surface behind it.

The inside edge is to be undercut on a four-jaw lathe, ensuring no dirt or debris in

the corners causes the optic to misalign.

3.1.2.6 Control gear and ServoThe control gear is driven by a Parallax Continuous Rotation Servo. This allows the

whole assembly to rotate, in turn rotating the leading edge of the beam print. It is this

that will allow the mount to steer the beam around corners – one requirement

outlined in the PDS.

The gear is cut from aluminium and features 120 teeth and a PCD of 128.5 (pictured

in Figure 22). The large number of teeth and high gearing allow precise control of the

rotation of the assembly.

Six small holes are drilled around the central hole to allow the gear to be bolted in

between the bracket and dual passage rotary union. Two 10mm holes 180° apart

allow the pipes to be fed through to the rotary union inlet and outlet.

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Figure 20 - Optic mounting plates


The Parallax Continuous Rotation Servo (Figure 21) features a special type of servo

mechanism that allows full bidirectional continuous rotation. The user can precisely

and accurately control the angular displacement and acceleration of the motor, in

this case by PBASIC's or SX/B's PULSOUT commands. A full data sheet of

specifications can be found in Appendix 3.

The advantage of using a servo like this is the user is not restricted to a specific

angular displacement range. The impact this has is it provides the user with a whole

new level of freedom.

It would now be possible to weld in circles, or any shape no matter how complex its

geometry. This goes beyond the requirements LOE have outlined, and means the

technology can be applied to a new range of applications.

3.1.2.7 BracketThe bracket is the backbone of the assembly and holds all components together. It is

designed to be machined from flat 2mm sheet steel. This thickness should be easily

foldable and provide sufficient rigidity in holding all components together. Six small

holes on the top allow the gear and rotary union to be bolted to the bracket.

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Figure 22 - Control gearFigure 21 - Parallax continuous rotation servo motor


Sufficient clearance is provided below the bracket to ensure the carousel does not

interfere with nuts used to bolt it to the control gear and union.

It acts as a housing for the DC Micromotor, which is press fitted and bonded in place.

3.1.2.8 Pipe attachmentsThese are standard parts used to attach piping to rotary union inlet and outlets. The

pipes will carry coolant around the system.

The pipes are 8mm flexible silicon vacuum tubes, and will transport relatively low

pressure, low temperature coolant.

3.1.3 Mirror Tilting MechanismThe basic principle of this mechanism is to

provide precise adjustment of the position of

the mirrors. When the mirror is fixed to its

mounting point, accurate adjustments can

25

Figure 23 - Bracket


be made to ensure the laser beam is on target on successive mirrors. A CAD model

of the tilting plate currently being used (Figure 25)

The tilting mechanism adjusts the mirror

in two axes around the centre of the plate

(Figure 24 and 26), which allows the up

and down movement of the reflected

beam.

The current mechanism fulfils all requirements and is reliable and will therefore be

used in the final product. It is also an advantage that this mechanism is readily

available off the shelf.

Only improvement that needs to be made is to modify the spring in the mechanism to

provide more pressure to prevent movement of the plate.

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Figure 25 - Tilting plate Figure 24 - Tilting plate reverse view

Figure 26


3.1.4 Analysis of Current Mirror HousingThe reason for conducting analysis of the current mirror housing was due to its vital

role in the accuracy of the beam direction. When replacing a mirror or diffractive into

the mount, if it did not relocate correctly within the mount, for example the back

surface of the mirror sitting flat against the mount, then the direction of the beam

would have changed. If this was the case every time the mirror was replaced, then

all the mirror mounts would need to be adjusted in order for the laser to be able to

operate. If however the mirror consistently relocated accurately then in the new

design only the top 2 mounts would have the need to be adjustable.

To test the housing a standard mirror was placed within it and secured using the

grub screw. A visual laser beam was then directed at the centre of the mirror at 45 0

27


and a piece of paper was placed 45cm away from the mirror (working distance) and

the location of the laser beam was recorded. The mirror was then removed from the

housing. This process was repeated 15 times for accuracy. A diagram of the

experiment is shown below (

Figure 27 - Analysis test rig

Figure 27 - Analysis test rig

See Appendix 4 for a copy of the target sheet.

The results showed that relocation of the mirror in the housing produced an

insignificant change in the direction of the beam, and therefore the dimensions of the

mirror housing and the manufacturing process of the mirror will not need to be

changed from the current design.

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3.1.5 Diffractive Optic Axial AlignmentThe holographic diffractive optic’s specific design only allows it to be used in one

plane. The calibration of the optics directional plane is of vital importance to the

installation process. This can be done using the same system as is on a set of

manual vernier callipers (Figure 29 and Figure 28).

If the markings can be accurately machined onto the side of the holographic

diffractive optic that is the leading edge and the optic housing, then direction in which

the laser needs to operate is known. This combined with the module’s revolving

carousel diffractive optics holder allows the end user of the module to be able to

laser process in any direction with the confidence that it is functioning correctly.

3.1.6 Fume Extraction SystemThe fume extractor system is currently being used g during laser processing is

shown below (Figure 30). The current design consists of a large, heavy and bulky,

section of aluminium, and 3 different length Perspex rings. This design can be easily

changed to save money on materials, and to make it more aesthetically pleasing for

customers.

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Figure 28 – Vernier Caliper Figure 29 - Axial alignment diagram


Figure 30 - Current Fume extraction system

The air is pumped into the central tube, sucked out of the middle ring, and pumped

into the third ring. Alternatively, when welding it is possible to pump gas through the

centre ring to provide a welding gas shroud. Having 3 rings is more effective than a

2 ring fume extractor, as the outer most ring pumps more air in and prevents harmful

gas/splatter from escaping, as shown (Figure 31).

Figure 31 - Air flow through fume capture system

The new design would have to be lighter, use less material, have the same critical

dimensions, and be more aesthetically pleasing. These factors would both save

Laser Optical Engineering Ltd money in manufacturing the product, and also make it

a more desirable accessory to the main diffractive optic housing to potential

customers. As this is a product that would be sold to customers enabling them to

view the processes occurring, it would also be possible to incorporate a HD camera

into the extraction system for companies to view in more detail what they are doing.

In doing this, Laser Optical Engineering could increase the asking price, and make

more profit from this accessory.

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The first new design is similar to the current extraction system in that it consists of an

aluminium block for the air flow channels, and 3 Perspex rings below so that

customers can view the laser processes whilst still having the safety of fume

extraction. The air flow to each of the three sections would be delivered via 3 holes,

internally drilled as in the current system however as there is no tiers in the

modification, the holes will on be at the same level. This allows even flow throughout

the rings, and maximises the amount of fumes/splatter removed from the working

surface. The attachments for the air hoses are the same as the current ones so there

would not need to be a change in the connections. See modification 1 below in

Figure 32.

Figure 32 - Revised fume extraction system 1

This design was then taken further in the hope of being able to reduce the amount of

aluminium used, and making the area where the processes take place more visible

to the users. This design involved having a thin layer of aluminium at the top, to

which the Perspex rings would be attached. See modification 2 below (Figure 33).

Error: Reference source not found

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Figure 33 - Revised fume extraction system 2

This caused a problem in that, there would not be a sufficient air seal around the

pipes, and that if the Perspex got damaged during laser processing then it would be

hard to replace the rings. In this idea there is also a secondary chamber in the outer

2 rings, this was to reduce the number of pipe fittings needed.

From these 3 designs, the current one and the 2 modifications, the design we are

going to use as our final fume extraction system is modification 1. The aluminium

section of the fume extractor will be made from 132mm diameter aluminium rod. The

centre hole will then be drilled out on a lathe, and the rod cut into sections just over

that of the design. Once this is done, each part will have the other parts cut out via a

CNC machine, before having the top surface cut away until the overall depth is at the

correct value. The Perspex rings will be bought as longer sections and then cut down

to the required length. The pipe connectors will be bought in, as will the o-rings that

hold the Perspex rings in place.

Bought PartsThe o-rings can be purchased from www.simplybearings.co.uk, and the sizes

needed are as follows in Figure 34.

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Figure 34 - O-ring sizes

The Perspex rings can be bought in from www.theplasticshop.co.uk, and the sizes

needed are as follows in Figure 35.

Figure 35 - Perspex tubing sizes

3.1.7 Casing DevelopmentIt was important to build the mount around the carousel assembly to ensure there

was enough clearance to allow the carousel to rotate freely. The material selected

for the mount is Carbon Fibre, as stated in the Feasibility Report.

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The Diffractive Optic Mount may be subject to high internal temperatures when in

operation. With such a high energy beam, the estimated temperature inside the

mount is likely to rise to over 50oC. Because precision, accuracy and alignment play

such an important role in the operation of the mount, it is vital to take into account

factors such as thermal expansion when selecting materials to fabricate the mount.

The current mount has been made from steel which would have a typical coefficient

of linear thermal expansion of around 11.0 ~ 13.0. That of Aluminium is around

double, at 23.0, making it less suitable. However, carbon fibre has an almost

negligible coefficient of thermal expansion.

The mount can be fabricated in complex and diverse shapes, allowing it to be

fabricated out of a single piece. The optics can then be attached at mounting points

built in to the design. It is also much more resistant to decomposition from the highly

corrosive particles given off during the laser welding process, allowing it to lengthen

the life of a mount.

This in turn will be an attractive prospect to potential clients and will allow LOE to

increase profit margins by charging a higher price for the product.

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Figure 36 - Final optical arrangement


Figure 36 shows the basic dimensions around which the mount is built.

The current mount is fabricated from plates of aluminium bolted together to form a

box shape. The aluminium has a thickness of 3mm.

The Young’s Modulus of aluminium is ~69GPa, compared to that of carbon fibre

reinforced plastic, which has a Young’s Modulus of ~150GPa. Source: Engineering

Toolbox (http://www.engineeringtoolbox.com/young-modulus-d_417.html)

This shows the ratio of stress over strain of carbon fibre is over twice that of

aluminium, allowing the mount casing to be half as thick. Taking into consideration a

suitable safety factor, the chosen thickness of the carbon fibre mount casing is 2mm.

To ensure the internal components of the mount are protected from the ingress of

dust and dirt, the whole mount will be completely sealed. ZnSe windows will be

located at the points where the high energy laser beam enters and exits the mount.

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Figure 37 - Positive pressure

http://www.engineeringtoolbox.com/young-modulus-d_417.html


It was previously decided that a continuous feed of process gasses was the best

solution to this, as depicted in Figure 37. However, this meant that when the mount

was not in operation, it was not completely sealed and therefore not protected from

the ingress of dust and dirt.

The lid will be sealed using a large o-ring and is designed not to be removable. This

will ensure the internal workings of the mount are not exposed to tampering by its

users, and thus if necessary, only LOE engineers are able to open it and carry out

maintenance.

If LOE opt to allow the client full access to the internal workings of the mount after

set-up, the option is still available.

A problem with the current mount is that putting the lid on and off took time, and as a

result it was often left off. It was important to ensure the lid of the designed mount

was easy to take on and off if necessary and did not require extensive tightening of

screws.

Another feature that has been considered is making the internals of the mount visible

to the user. This will allow the user to see the inner workings of the mount and

identify problems if they arise. It will also increase the attractiveness of the design to

potential clients.

Taking into consideration all of the above, a CAD model of the assembly was

created. Figure 38 shows the final model. All engineering drawings are detailed in

Appendix 5.

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37

Figure 38 - Module assembly


Figure 39 - Basic dimensions of module assembly

As seen in Figure 39, the first 2 mirrors the beam comes into contact with are

mounted on tilting mirror plates that allow precise control of beam direction. The

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Cooling channel 1 pipe inlet/outlet

Cooling channel 2 pipe inlet/outlet


beam is directed off mirror 3, which is fixed into position and cannot be adjusted. As

the beam is reflected off of the holographic optical element held in the carousel, the

heat pattern of the beam is altered and goes on to hit the target 451mm away.

The mirrors and plates all fit to mounting points built into the carbon fibre casing.

This is to reduce the number of parameters that can potentially cause the beam to

misalign.

The optic encased in the carousel can rotate continuously in both directions, as

explained in section 3.1.2. The input and output beams remain co-axial, a

fundamental requirement LOE have issued.

The beam exits the mount through a window at the end, with an o-ring preventing

exposure to the outside atmosphere. A large o-ring also fits around the lip of the box.

The Perspex lid is then fixed on to the mount with draw latches that provide a

constant pull force. To ensure the latch keepers can attach properly to the edge of

the lid, the Perspex has to be a minimum of 16mm thick. The thickness of the lid

chosen is 20mm, and is supplied by (www.theplasticshop.co.uk). 10 draw latches are

placed fairly evenly around the mount to ensure the seal is not broken at any point.

These draw latches, shown in Figure 40, are supplied

by (www.southco.com), an international distributor of various locking and latching

mechanisms. The latch chosen (part number V7-10-115-50) features a lock that can

allow LOE to ensure its clients cannot access the internals of the mount unless they

wished. A CAD model of the latch system was provided by (www.southco.com).

The profile of the mount has been changed to reduce material wastage.

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Figure 40 - Draw latch

http://www.southco.com/products/v7-over-center-series-latches/v7-10-115-50.html


Holes are drilled on the right side of the mount to feed wires/ cables and pipes

through to the internal components. A silicon based sealant will be used to seal gaps

around the entry points of pipes and wiring.

The mirrors will be on a separate cooling channel to the diffractive optics. One pipe

will travel around the inside edge of the module, linking to mirror 1, 2 and 3 in series,

before being fed round to its exit point. Cooling channel 2 is exclusive to the four

diffractive optical elements. Its inlet and outlet point is depicted in Figure 39 - Basic

dimensions of module assembly.

This is to ensure the cooling process remains effective as the coolant will gain heat

energy and increase in temperature after passing through each mirror. To reduce the

risk of the coolant causing a layer of condensate to form on the surface of the optics,

the feed temperature will be controlled at room temperature. Due to the fact that the

cooling system was inefficient with a feed rate of 6 litres per minute in the current

module, this is increased to 10. This will ensure the coolant is absorbing more heat

energy from the optics at a higher rate, allowing the module to stay in operation for

extended periods of time.

The final proposed design is a comprehensive improvement on the current module.

For this reason the design process was focused on creating a product with quality in

mind.

The retail price of a holographic diffractive optic can be up to £25 000 depending on

its intended use. Therefore, within reason, the cost of materials and labour involved

in the production of a prototype can be considered insignificant.

A basic analysis of the cost to produce a prototype shows it is not likely to total more

than £2000. This is a justified price considering the potential return if the technology

hits the mainstream market.

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4.1 Discussion and ConclusionsThe functionality of the module outlined in PDS has been thoroughly addressed in

the design process.

The final module features coaxial input and output beams, a feature that was highly

desirable for LOE. The feature allows the module to integrate easily into

conventional laser systems. It is designed so it can be aligned quickly with little

difficulty and requires a minimal level of maintenance, all highly attractive features to

potential clients of the company.

A comprehensive system to allow the beam print to rotate has been designed. Not

only does the designed system fulfil the requirements outlined in the PDS, but it goes

further to allow potentially ground-breaking functionality. The prospect of being able

to weld circles and process complex geometrical shapes bears much appeal. This

coupled with the ability to quickly interchange between four different diffractives is a

vast improvement on the current design.

A way of improving the design further would be to have all coolant feed channels

around the carousel encased in a cast manifold, improving its overall look and

strength. It would reduce the number of parts in the carousel’s assembly and remove

the hindrance of having to ensure the bracket component’s folds are perfectly

accurate.

An effective integrated cooling system is outlined that is easy to implement.

A newly designed fume capture system minimises material usage and weight, whilst

allowing the user to see the process. It encompasses the ability to introduce a

welding gas shroud to the surface being processed.

With the introduction of a Perspex lid that can be removed easily, it is possible to see

into the module whilst it is in operation. The module itself is sealed with o-rings or

silicon based sealants around all possible areas where air can enter the system. This

prevents the possibility of dust and dirt entering the system and settling on the

optics.

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Detailed engineering drawings of all components, assemblies and sub-assemblies

are provided in the appendix. These are sufficient to allow LOE fabricate a prototype.

5.1 PostscriptThe team would like to thank LOE and all involved for allowing the team this fantastic

opportunity.

The project was thoroughly enjoyed and allowed the team to apply our engineering

knowledge to an interesting real-world problem. It provided a fascinating insight into

the world of cutting edge laser processing technology.

The project tested our ability to work as a team, carry out research and apply our

technical knowledge.

Amongst the many challenges faced, a few internal conflicts were encountered

throughout the project’s duration. Had all members of the team been fully committed,

the overall outcome may have been a significant improvement to the one detailed.

However, regardless of these issues, we are thoroughly satisfied with the quality of

the end product.

We were able to utilise each individual’s areas of expertise and expand our technical

knowledge through research and exposure to more experienced individuals such as

our mentor, project supervisor and LOE staff.

We originally intended to build a prototype for Laser Optical Engineering Ltd.

However, as the project progressed it was soon realised that this was an unrealistic

prospect. We therefore decided to shift our aim to provide a detailed enough report,

including all relevant drawings for LOE to build the prototype themselves, if the

design was deemed commendable.

We realise that there will be some areas that we may have overlooked slightly, and

acknowledge that aspects of the design will need to be scrutinised and finalised

before fabrication.

The group would very much like to see a working prototype of the design, as we all

feel that we have produced a very credible and reasonable solution to LOE’s

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problem. We would be extremely proud if our design was taken forward to become a

product that LOE sold on to other laser processing companies

6.1 Appendix

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Appendix 1

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Appendix 2

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Appendix 3

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Appendix 4

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Appendix 5

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BibliographyGears, R. (n.d.). www.rushgears.com.

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html. (n.d.).

www.southco.com. (n.d.).

www.theplasticshop.co.uk. (n.d.).

www.laseroptical.co.uk

www.rotarysystems.com

www.thesolenoidcompany.com

http://www.futaba-rc.com/servos/

http://www.parallax.com/

www.rotaryunions.net

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http://www.rotaryunions.net/

http://www.parallax.com/

http://www.futaba-rc.com/servos/

http://www.thesolenoidcompany.com/

http://www.rotarysystems.com/

http://www.laseroptical.co.uk/


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