GB2582181A

GB2582181A - Additive manufacturing apparatus and method

Info

Publication number: GB2582181A
Application number: GB1903565.8A
Authority: GB
Inventors: Marsden Philip; Dowton Kevin; Platten Robert; Brown Pauline
Original assignee: Unitive Design And Analysis
Current assignee: Unitive Design And Analysis
Priority date: 2019-03-15
Filing date: 2019-03-15
Publication date: 2020-09-16
Also published as: GB201903565D0; WO2020188253A1

Abstract

An additive manufacturing apparatus and a method of manufacturing fused fibre arrays of optically structured material comprises a print bed , a feed system 40, 50 to receive raw material 20 and deposit the raw material on the print bed (60, fig 4), a heating member to fuse the raw material to the print bed, a cleaving member (80, fig 4) to cleave the raw material and a heat source to provide heat to the raw material and/or deposited material and/or print bed, the raw material includes optically structured material. The feed system may include active and passive guide means 40, 50, the active guide means is driven by a motor, the second passive guide means may be spring loaded, the guide means may each comprise a rotatable puck. The method may include providing an optical fibre having a core and a cladding layer.

Description

Additive manufacturing apparatus and method

Field of the Invention

The present invention relates to additive manufacturing systems, in particular to additive manufacturing systems for optics and optical devices.

Background to the Invention

Glass waveguides with cylindrical symmetry (more commonly called optical fibres) have potential uses in a countless number of applications, but their use in said applications is often hindered due to the impracticality of manufacturing optical fibre solutions tailored to the needs of the application. Current suboptimal manufacturing capabilities mean that tailored optical fibre solutions for a number of applications are either impossible, impractical, or are prohibitively expensive, time-consuming or manually intensive.

Optical fibres are typically created by drawing a thin structure from a larger structure (called a preform) by applying heat and tension to the larger structure. Imaging or spatially coherent structures can currently be formed by either assembling arrays of optical fibres and gluing them together or by drawing preforms assembled from single or multiple fibre preforms, and then fusing these together.

Fused arrays of fibres can then be machined and manipulated (with a very limited range of operations) into other shapes. This process is manual and very labour intensive.

Coherent optical fibre structures today fall into a number of limited categories. These can include: Leached fibre bundles -used commonly in endoscopes and other imaging systems where flexibility is required; Fibre optic faceplates -commonly used to transfer images from a displaced image plane to an image sensor. These can also be used to project an image from a light emitter such as an OLED display or backlit LCD. These are also commonly used where an imaging component needs to be protected from ionising radiation, such as in an X-ray detector; Solid fibre rod -commonly used to transfer illumination and images from one place to another. These work in a similar way to fibre optic faceplates, but can be carefully bent into shape with the aid of a heat. They are typically used with other free-space optical imaging components; Coherent fibre optic tapers -these are typically constructed from thicker fibre optic faceplates which are heated in the middle and drawn out into a dual taper, similar to the way that a fibre taper is drawn. The dual taper can then be sawn in half, ground and polished, producing, two fibre optic tapers. Coherent fibre optic tapers are typically used for magnification or demagnification from compact imaging systems such as scintillation detection in electron microscopes; and Coherent fibre optic inverters -these are typically used in night sights in firearms. It is interesting to note that these are difficult to source and are subject to International Traffic In Arms Regulations (ITAR).

These currently available structures carry a number of disadvantages which will now be discussed. All of these applications involve quite simple shapes. All of their shapes are limited in some way by the basic building blocks of the structure. These building blocks are invariably basic wound and leached fibre bundles and they are drawn and stacked on a faceplate block. They all have a limited bend radius. They typically have additional material in place for mechanical robustness and handling when processing. The fibre packing structure is not well controlled and is typically not aligned to the application. Bifurcations are not typically possible. The selection of materials is extremely limited due to large batch fabrication. This last limitation is especially important in environments where material properties are critical for requirements such as biocompatibility and ability to be effectively sterilised.

It is therefore desirable to provide an apparatus enabling the manufacturing of optical fibre solutions tailored according to the dimensional or property requirements of a variety of applications, in a quick, precise and cost-effective manner which may be more attractive to potential manufacturers and customers alike.

Summary of the Invention

In accordance with a first aspect of the present invention, there is provided an additive manufacturing apparatus arranged to provide fused fibre optic arrays from a raw material to be deposited, the apparatus comprising, a print bed having a print bed surface arranged to support a raw material; a feed system arranged to receive the raw material from a raw material supply and deposit the raw material onto the print bed surface; a fusion member arranged to fuse the deposited raw material to the print bed surface; a cleaving member arranged to cleave the raw material; a heat source having an adjustable temperature, and arranged to provide heat to the raw material and/or the deposited material and/or the print bed; wherein the raw material comprises optically structured material.

The term "structured material", in the context of the present invention, would be understood by the skilled addressee as being a material having a structure to be maintained before, during and after the additive manufacturing process.

Preferably the structured material is pliable and comprises a flexible solid. The term "optically structured material" in the context of the present invention will comprise optically structured material such as an optical fibre having a core and a cladding layer. The structured material can comprise physical structures, filament structures and filaments having a chemical gradient structure.

The invention comprises a new additive manufacturing based apparatus for the printing of fibre optic glass structures.

Overcoming limitations to the existing technology mean that structures beyond the typical end products of for example, image-transfer faceplates, tapers or leached fibre bundles should become available, and available beyond the finite number of standard dimension categories and limited range of properties currently available.

There are a number of applications for which the use of more tailored optical fibre solutions would pose a vast improvement in reliability, accuracy and efficiency of processes. The incorporation of optical fibres into such applications has, however, been previously hampered, or considered impractical, given the dearth of available solutions, or the unsuitability of standard size and property ranges.

The raw material optically structured material preferably comprises core characteristics and cladding characteristics appropriate to an end user requirement. The core characteristics may be understood by the skilled addressee to refer to: the core composition, which may include any suitable material and may further include any number of optical fibre dopants; the core diameter; the core refractive index; the core mode, which may be single mode or multimode; the core refractive index profile; the core numerical aperture; the core viscosity; the core tensile strength. The cladding characteristics may be understood by the skilled addressee to refer to: the cladding composition, which may include any suitable material and may further include any number of optical fibre dopants; the cladding diameter; the cladding refractive index; the cladding mode, which may be single mode or multimode; the cladding refractive index profile; the cladding numerical aperture; the cladding viscosity; the cladding tensile strength.

The apparatus preferably permits the precise laying down of optical fibres, preferably at speed, and preferably with the intention of producing optical fibre array shapes and/or sizes capable of high quality image transfer, which are preferably not possible to create using technology available prior to the present invention.

The apparatus preferably enables the design and development of fibre optic arrays tailored to end-user requirements i.e. products to fit the application and not as is possible currently, the other way around.

Preferably the apparatus of the present invention permits new design possibilities, which may preferably include new forms, including bends, splits, curves -preferably to enable images to be projected from below or the side.

The present apparatus preferably enables the production of structures having one or more of the following improvements over and above currently available technology: * inclusion of arbitrary bends and curves in a monolithic structure; * creation of monolithic structures where the input plane and output plane are not parallel; creation of 'many to one' and 'one to many' structures; robustness (leeched fibre bundles typically degrade and break/catastrophically fail over time so are not robust); * configurability to any type of glass (core-cladding combination); * configurability of choosing raw materials for the application -e.g. sterilisability and biocompatibility; * monolithic -no glue, no glue failure, avoiding limitations of free space optics.

Complex/interfaces/avoiding * configurability of re-arranging the input and output geometry and dimensionality. The obvious example being to turn a 2D image into a 10 projection for spectroscopic analysis. (Currently only possible by manual configuration.); * configurability of alignment to specific pixel pitches. (Current systems use spatial oversampling, but this introduces loss.); and/or * suitable for just-in -time manufacturing (versus an 8 week lead time for existing structures).

First and foremost, the core idea is in the additive manufacture of structured invention glass, specifically optical fibre. Preferably the apparatus of the present invention permits the printing of 1-dimensional structured raw materials. The structures comprise optical fibres or optically structured material with a chemical gradient structure and/or chemically structured filament.

Preferably the feed system comprises a first active guide means, a second passive guide means, and a guide nozzle.

Preferably the first active guide member is driven by a motor.

Preferably the second passive guide means is spring loaded.

Preferably the first and second guide means each comprise a rotatable puck.

Preferably the heat source is arranged to heat the raw material to a raw material temperature, the raw material temperature being 0 -1500 °C, preferably 650 -800 °C, more preferably 500 -550 °C.

Preferably the heat source is arranged to heat the print bed surface to a print bed surface temperature, the print bed surface temperature being 0 -1500 °C, preferably 650 -800 °C, more preferably 500 -550 °C. More preferably in an embodiment the raw material temperature and the print bed surface temperature are substantially the same.

Preferably the heat source comprises a heating element. Preferably the heating element comprises a wire arranged to transmit heat caused by electrical resistivity of the wire.

Preferably the wire is arranged into a coil. Preferably the wire is comprised of a metal alloy.

Preferably the metal alloy comprises at least one selected from the range: nickel; chromium; iron. Preferably the metal alloy is nichrome.

Preferably the apparatus further comprises a controller arranged to control at least one selected from the range: the print bed; the feed system; the fusion member; the cleaving member: the heat source.

Preferably the print bed surface comprises a print bed surface material, wherein the print bed surface material comprises one selected from the range: silica glass; soda lime; borosilicate. Other examples of glasses include oxides of silica, Aluminium, Barium, Boron, lead, sodium, potassium, boron, aluminium, calcium, magnesium, lithium, phosphorous, titanium, zirconium and glass families such as Flint glass, crown glass, borosilicate glass, aluminosilicate glass, aluminoborosilicate glasses, alkali lead silicate glasses, alkali alkaline earth silicate glasses, lithium-aluminium silicate glasses, and their families.

Preferably the cladding layer of the raw material comprises the print bed surface material.

Preferably the print bed is arranged to move on a horizontal plane and/or a vertical plane as provided for by an xyz platform and translational stage.

Preferably the raw material supply is one selected from: an optical fibre drum; an optical fibre draw tower.

Preferably the raw material supply is an optical fibre draw tower, and wherein the raw material is output from the optical fibre draw tower and provided directly to the apparatus.

Preferably there is a cutting or cleaving stage of the raw material supply. For a heated cleave, process a temperature in excess of 1000 degrees is desirable such that the glass raw material is heated to the fusion temperature (approximately at the Littleton Softening Point).

In accordance with a second aspect of the present invention, there is provided a method of manufacture of fused fibre arrays of optically structured material, the method comprising the steps of: a. providing an optical fibre having a core and a cladding layer; b. heating the optical fibre to an optical fibre temperature, wherein at the optical fibre temperature the optical fibre remains substantially solid; c. feeding the heated optical fibre onto a print bed surface having a print bed surface temperature that is substantially the same as the optical fibre temperature; d. fusing a portion of the heated optical fibre to the print bed surface, such that a portion of the optical fibre is merged and fused together with the print bed; e. cleaving the heated optical fibre; f. repeating steps c and d, and optionally step e, such that a layer or layer portion of optical fibre is deposited onto, and supported by, the print bed surface; g. heating the layer to the optical fibre temperature; h. feeding the heated optical fibre onto the layer; i. fusing a portion of the heated optical fibre to the layer, such that a portion of the optical fibre is merged and fused together with the layer; j. cleaving the heated optical fibre; k. repeating steps g to i, and optionally step j, such that a subsequent layer or layer portion of optical fibre is deposited onto, and supported by, the previous layer or layer portion; I. repeating step k, such that a fused fibre optic array is provided.

Preferably steps b to I are performed in an oven.

Preferably the optical fibre temperature remains constant throughout steps c to I. This printing technology preferably facilitates the creation of structures which were previously considered impossible. Bend radii are preferably limited only by the loss characteristics of the waveguide and not by the mechanical properties.

Structures can preferably be made directly arbitrarily small or large to fit into the required footprint. They can also preferably be shaped to fit in around other components, fit inside other components and/or provide a mounting substrate for other components such as image sensors. The fibre packing arrangement can preferably be aligned to pixelated structures such as image sensors and displays. The fibre core size can preferably be optimised to feed into the centre of image sensor pixels, avoiding the need for micro-lenses and avoiding the dead space where the pixel fill fraction is low to get high speed and high dynamic range performance. Printing parameters can preferably be adjusted on the fly to adapt to different raw materials (which may optionally be glass) rapidly, preferably allowing for the printing from small batches of raw materials, dramatically increasing the range of possible raw material parameters.

Detailed Description

Specific embodiments will now be described by way of example only, and with reference to the accompanying drawings, in which: FIG. 1 shows a viscosity vs temperature plot for four example raw materials suitable for use with the present invention; FIG. 2 provides a schematic view of an example feed system suitable for an apparatus according to the first aspect of the present invention; FIG. 3 provides a sectional view of an example feed system and print bed for use suitable for an apparatus according to the first aspect of the present invention; FIG. 4 provides an isometric view of an example print bed and cleaving member of an apparatus according to the first aspect of the present invention; FIG. 5 provides an isometric view of a fibre optic array suitable for manufacture using an apparatus according to the first aspect of the present invention; FIG. 6 illustrates the front view of the structure of Figure 5 fabricated according to the first aspect of the invention; and FIG. 7 illustrates an alternative structure fabricated according to a first aspect of the invention.

The diagram in Figure 1 shows the viscosity vs temperature plot for four different glasses. The essential elements of additive manufacturing of structured glass fibres are captured in this plot. To maintain the structure of the glass, it is important to stay well below the melting point temperature and, in preferable versions, below the working point temperature. To achieve fusion, it is important to ensure that the raw material is above the raw material temperature. In particular for fusion it is the aim to heat the glass to the fusion temperature (approximately at the Littleton Softening Point).

The glass enters the oven below To arriving at the print bed some fraction above Tg. As the fibre starts to lie on the print bed it is thermally cycled. The exact temperature of the cladding is likely to approach the working point temperature. At this point adjacent cladding structures and/or substrate materials fuse together holding the glass fibre in place.

Referring to Figure 2, the fibre feed system can be described. The feed system 10 takes the fibre 20 from a drum or draw tower (not shown) and drives it into the oven and fabrication space. The feed system 10 is driven by a stepper motor 30 to provide fine control and rubber pucks 40 and 50 are provided downstream of the stepper motor. Pucks 40, 50, provide mechanical control, the pucks comprise one driver; one idler and the pucks grip the fibre sufficiently to draw and feed the fibre into the oven. Damage to the surface of the fibre must be kept to a minimum to eliminate scatter losses and poor fusion. The pucks 40, 50 comprise soft rubber so that damage is kept to a minimum.

The feed system has provision for sourcing the optical fibre from a drum or optionally from a draw tower. Optical fibre is typically coated in a polymer when taken from the draw tower. This prevents surface damage when it is wound onto a drum. For pristine glass delivery with the best surface quality, the machine can be linked to a small fibre draw tower which runs quasi-synchronously with the print feed ensuring the best material quality.

The fibre 20 cannot be simply squeezed onto the print bed 60 bed like in other additive manufacturing processes. The angle of attack, the tackiness of the print bed surface 70 and the speed of attack are all controlled carefully to ensure rapid adhesion and minimal feedback back up through the nozzle 80 to the feed pucks 40, 50. The print bed surface arrangement is shown in Figure 3.

With reference to Figure 3 it can be seen that the design of the fibre lay up can be controlled and managed. Indeed the fibre lay up is the key to getting robust structures. Glass fusion requires close-packed stacking. Hermetic sealing introduces an additional critical laying up requirement. The other driving requirements are then the entry and exit facets of the final monolithic light guiding structure. The fibres lay up design may have one or more entry facets and one or more exit facets.

Fibre cleaving is illustrated in Figure 4. The fibre 20 needs to be cleaved at the end of print run so that the print bed 60 can move to the next start position for the subsequent fibre run.

The cleave needs to be clean, rapid, not send a shockwave up the feed nozzle and not leave any debris on the print bed 60. This is achieved by dropping the end of the fibre onto a heated wire 80, around 1000 ° C. The heated wire melts the fibre at the point of contact forcing it to both cleave and droop and drop out of the current print scope.

The first layer of fibre is fused to the print bed with the aid of nichrome coil heaters which are located above the print bed. The temperature of this additional heat source is static and carefully controlled. These heaters also ensure that subsequent layers are fused to the first layer.

The print bed 60 itself is chosen to be a planar glass material to which the print material can be adhered. This is matched to have a similar temperature-viscosity characteristic as the material being deposited. The temperature of the print bed is controlled by the heat elements on the oven wall.

Since the material is structured, standard gcode and Additive Manufacturing file formats do not contain sufficient information to describe how to produce the structures. A new file format for 1D raw material printing such as a print description (or an addition to the AMF standard) adds the core / cladding ratio and fibre diameter along with a set of 3D point trajectories through which the fibres need to pass.

An annealing step is described here as the structure, when formed, contains both the stress of the original fibre and the stress built into the new structure. In fact, the act of fusion can change the in-built stress characteristic. The fibre structure requires a careful cooling temporal profile to prevent it from cracking or shattering.

Examples of structures fabricated according to the invention include fused fibre optic arrays, degree bends, interlocked, spatially coherent Y junctions and the optical/image interleave of Figures 5 and 6 and the 90 ° bend or image corner shown in Figure 7.

It will be appreciated that the above described embodiments are given by way of example only and that various modifications thereto may be made without departing from the scope of the invention as defined in the appended claims. For example, one or more optical fibre layers can be envisaged arranged in layers in a packed arrangement. Alternatively strands of optical fibres may be arranged and fused together in part or portions of layers. Overlaid optical fibres may be created, although not necessarily forming strict planes, the overlaid fibres or filaments will still comprise depth and array characteristics.

Claims

CLAIMS1. An additive manufacturing apparatus arranged to provide fused fibre arrays from a raw material to be deposited, the apparatus comprising, a print bed having a print bed surface arranged to support a raw material; a feed system arranged to receive the raw material from a raw material supply and deposit the raw material onto the print bed surface; a fusion heating member arranged to fuse the deposited raw material to the print bed surface, such that a portion of the deposited raw material is fused together with the print bed; a cleaving member arranged to cleave the raw material; a heat source having an adjustable temperature, and arranged to provide heat to the raw material and/or the deposited material and/or the print bed; wherein the raw material comprises optically structured material.
2. An additive manufacturing apparatus according to claim 1, wherein the feed system comprises a first active guide means, a second passive guide means, and a guide nozzle.
3. An additive manufacturing apparatus according to claim 2, wherein the first active guide member is driven by a motor.
4. An additive manufacturing apparatus according to claim 2 or claim 3, wherein the second passive guide means is spring loaded.
5. An additive manufacturing apparatus according to claim 2, claim 3 or claim 4, wherein the first and second guide means each comprise a rotatable puck.
6. An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the heat source is arranged to heat the raw material to a raw material temperature in the range from 0 -1500 °C, preferably 650 -800 °C, more preferably 500 -550 °C.
7. An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the heat source is arranged to heat the print bed surface to a print 8. 9. 10. 11. 12. 13. 14. 15.bed surface temperature, the print bed surface temperature being a temperature in the range from 0 -1500 °C, preferably 650 -800 °C, more preferably 500 -550 °C.
An additive manufacturing apparatus as claimed in claim 6 or claim 7, wherein the raw material temperature and the print bed surface temperature are substantially the same.
An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the print bed surface comprises a print bed surface material, wherein the print bed surface material comprises one selected from the range: silica glass; soda lime; borosilicate; oxides of silica, Aluminium, Barium, Boron, lead, sodium, potassium, boron, aluminium, calcium, magnesium, lithium, phosphorous, titanium, zirconium and glass families such as Flint glass, crown glass, borosilicate glass, aluminosilicate glass, aluminoborosilicate glasses, alkali lead silicate glasses, alkali alkaline earth silicate glasses, lithium-aluminium silicate glasses, and their families.
An additive manufacturing apparatus as claimed in claim 9, wherein the cladding layer of the raw material comprises the print bed surface material.
An additive manufacturing apparatus as claimed in any one of claims 8 to 10, wherein the print bed is arranged to move on a horizontal plane and/or a vertical plane.
An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the apparatus further comprises a controller arranged to control at least one selected from the range: the print bed; the feed system; the fusion member; the cleaving member; the heat source.
An additive manufacturing apparatus as claimed in any one of the preceding claims, wherein the raw material supply is one selected from: an optical fibre drum; an optical fibre draw tower.
An additive manufacturing apparatus as claimed in claim 13, wherein the raw material supply is an optical fibre draw tower, and wherein the raw material is output from the optical fibre draw tower and provided directly to the apparatus.
A method of manufacture of fused fibre arrays of optically structured material, the method comprising the steps of: a. providing an optical fibre having a core and a cladding layer; b.heating the optical fibre to an optical fibre temperature, wherein at the optical fibre temperature the optical fibre remains substantially solid; c. feeding the heated optical fibre onto a print bed surface having a print bed surface temperature that is substantially the same as the optical fibre temperature; d. fusing a portion of the heated optical fibre to the print bed surface, such that a portion of the optical fibre is merged and fused together with the print bed; e. cleaving the heated optical fibre; f. repeating steps c and d, and optionally step e, such that a layer or layer portion of optical fibre is deposited onto, and supported by, the print bed surface; g. heating the layer to the optical fibre temperature; h. feeding the heated optical fibre onto the layer; i. fusing a portion of the heated optical fibre to the layer, such that a portion of the optical fibre is merged and fused together with the layer; j. cleaving the heated optical fibre; k. repeating steps g to i, and optionally step j, such that a subsequent layer or layer portion of optical fibre is deposited onto, and supported by, the previous layer or layer portion; I. repeating step k, such that a fused fibre optic array is provided.
16. A method as claimed in claim 15, wherein steps b to I are performed in an oven.
17. A method as claimed in claim 16 or claim 17, wherein the optical fibre temperature remains constant throughout steps c to I.
18. A method as claimed in any one of claims 15 to 17, wherein the step of cleaving the heated optical fibre is arranged wherein the cleave temperature is 800 -1100 °C.