WO2015133969A1

WO2015133969A1 - Stereolithographic apparatus, handheld computing device and methods of use thereof

Info

Publication number: WO2015133969A1
Application number: PCT/SG2014/000106
Authority: WO
Inventors: Kok Boon FANG; Tze Sian Pui
Original assignee: Blacksmith Group Pte. Ltd.
Priority date: 2014-03-04
Filing date: 2014-03-04
Publication date: 2015-09-11

Abstract

A stereolithographic apparatus (100) is arranged to form an object (102) using a digital model of the object. Apparatus (100) comprises a reservoir (106) for containing photoactive liquid (114), the photoactive liquid being curable when exposed to light (120) in a range of wavelengths. The reservoir has a window (116) transparent to light in the range of wavelengths and a curing volume (118). A handheld computing device (108) has a display (112) for emitting, through the window of the reservoir and into the curing volume, light in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object.

Description

STEREOLITHOGRAPHIC APPARATUS, HANDHELD COMPUTING DEVICE AND METHODS

OF USE THEREOF

The invention relates to stereolithographic apparatus arranged to form an object using a digital model of the object. The invention also relates to a handheld computing device for use with a stereolithographic apparatus arranged to form an object using a digital model of the object. The invention also relates to a computer program product comprising instructions for a handheld computing device, the handheld computing device being for use with a stereolithographic apparatus arranged to form an object using a digital model of the object. The invention also relates to a computer program comprising instructions for a handheld computing device, the handheld computing device being for use with a stereolithographic apparatus arranged to form an object using a digital model of the object. The invention also relates to a method of operating a stereolithographic apparatus to form an object, using a digital model of the object.

Three-dimensional (3-D) printing has and continues to attract a significant amount of attention. In many ways it is considered revolutionary technology. A so-called stereolithographic apparatus was first proposed in United States Patent No.

4,575,330. This document discloses a system for generating three-dimensional objects by creating a cross-sectional pattern of the object to be formed at a selected surface of a fluid medium. Successive adjacent laminae, representing corresponding successive adjacent cross-sections of the object, are automatically formed and integrated together to provide a step-wise laminar buildup of the desired object, whereby a three-dimensional object is formed and drawn from a substantially planar surface of the fluid medium during the forming process.

Numerous other techniques have been proposed. For instance, International Patent Publication No. WO 2013/015518 relates to a visible light-applied high-speed moulding apparatus using an LCD mask, and a movable source of visible light. P T/SG2014/000106

Operation of the movable source of visible light and the LCD mask is controlled to form a set pattern for the mould.

The invention is defined in the independent claims. Some optional features of the invention are defined in the dependent claims.

Implementation of the techniques disclosed herein may provide significant benefits. These may include decreased cost of operation and enhanced flexibility for a user, all whilst maintaining acceptable (or better-than-acceptable, perhaps significantly better-than-acceptable) print quality. For instance, the computing device may be, say, a smart phone or a tablet which the user of the apparatus already possesses.

Implementing the techniques disclosed herein, the handheld computing device, having appropriate executable instructions (software) loaded therein, can use predefined or even create 3-D models of objects to be formed using the

stereolithographic apparatus. These models may then be "sliced" into shapes that represent one or more layers of the object to be printed. If a slice is sufficiently thin in one - say, the vertical - direction, the slice can be considered, for all intents and purposes, to be a 2-D slice perhaps of the order of microns. The model, including one or more layers thereof, can be displayed, in whole or in part, on a display of the handheld computing device, and the user can customise a model - and, thereby, the printed object - to his or her satisfaction. This manipulation can include scaling the model to the desired dimensions of the object, specifying the print resolution, the thickness of the layers of the model and the shape of the model.

A model defines the general structure of an object to be printed, and the basic properties thereof. For instance, and subject to user manipulation, a model will define, say, overall dimensions (length, breadth and height) of the object to be formed. If the object is not to be completely solid, the model will define a thickness of a wall of the object (enclosing a hollow centre of the object). The structure of a wall or surface of the object may also be defined. For example, a wall may be solid, or a "honeycomb" structure, or other types of structure infills, including lines, rectangles, circles and the like. The model may define the general shape of the object, for example, whether the object is spherical, cuboidal and the like. The user may customise the model to his or her satisfaction, perhaps scaling the model to desired dimensions, perhaps varying the shape - e.g. elongating a spherical object so that it becomes ovoid - or a part of the shape.

The executable instructions for controlling the handheld computing device - the app - and the models may be retrieved over the Internet, for example, from an online repository, retrieved from a cloud storage service or, say, received by other means, including e-mail or other electronic messaging and communications protocols, whether wired or wireless. For example, in instances where the handheld computing device is a device supplied by Apple, Inc™, the model may be retrieved from the iTunes™ store. Where the handheld computing device is a device utilising the

Android™ operating system, the model may be retrieved from the Play store from Google™.

Of course, the techniques disclosed herein may be implemented using other operating systems, with the models being retrieved as required and/or permitted by the operating system.

Thus, users have the advantage of increased flexibility, and ease of operation. No specialised programming skills are required. Users may be able to retrieve and define the models using commonplace skills that anyone can develop through ordinary operation in day-to-day use of a tablet or smartphone, and then put the

stereolithographic apparatus into use with the same. It may be possible for the users to use any one of a number of different types of, say, tablets or smart phones. In fact, where the users already possess a suitable handheld computing device of their own, the users may benefit from a significant cost reduction in the capital cost of the stereolithographic apparatus. Traditionally, the light source of the stereolithographic apparatus has accounted for a significant part of the cost of the apparatus.

Furthermore, currently available handheld computing devices are typically provided with high quality displays, exhibiting very high screen resolutions. For example, AMOLED and "Retina" displays are commonplace. Thus, the print resolution is limited only by the pixel resolution of the display of the handheld computing device.

The models can be easily retrieved (and, if appropriate, paid for) via the online app stores. And by making use of the high processing capacity of the typical handheld computing device, this eliminates the need for the use of a separate personal computer to control the printing process and a separate light source.

For instance, implementation of the techniques disclosed herein in comparison to: - projector types (eg. DLP technology using either UV or visible light) the current techniques do not require special glasses and optics, expensive Mercury lamps or UV fluorescent tubes (heat generated by such sources require ventilation mechanism eg. fan etc). - laser scanning types require the laser 'dot' beam to trace the 2D cross section of the part pattern for each height; our tablet/smartphone can be configured to display the 2D at once, so no tracing would be required.

- In comparison to all conventional stereolithography printers the current tablet/smartphone app will integrate 3D modelling. For instance, everything required to define the model, and then generate the requisite light patterns are contained within a single device - the handheld computing device - and the display is a static display, not having any moving parts. - The online 3D object store, and printing together in a single software application allows system integration, which is easy to control and upgrade and monetise.

The apps control the operation of the display of the handheld computing device to emit light in patterns to cure photoactive liquid, described in more detail below. And the sequencing of this light emission in patterns may be synchronised with the movement of the print "platform" (also discussed in further detail below) to produce the appropriate screen patterns at the appropriate print resolution. Further, in addition to avoiding the use of expensive traditional light sources, such as lasers, the requirement for a large vat of photoactive liquid (e.g. photopolymer) may also be obviated. It is possible to implement the techniques disclosed herein using only a shallow reservoir which means that photoactive liquid can be sourced as and when it is required. A large vat of photoactive liquid as in conventional

stereolithography can cost several thousands of dollars, and result in undesirable waste material. Moreover, using large reservoirs of photoactive liquid increases the chance of the liquid being spoiled through contamination and degradation.

The invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 is a schematic block diagram illustrating a first stereolithographic apparatus; Figure 2 is a series of schematic block diagrams illustrating steps in a sequence of operation of the stereolithographic apparatus of Figure 1;

Figure 3 is a schematic block diagram illustrating a second stereolithographic apparatus; and

Figure 4 is an algorithm for diagram illustrating operation of the stereolithographic apparatus of Figure 1 or Figure 3. Turning first to Figure 1, this schematically illustrates a first stereolithographic apparatus 100 for forming an object 102. Stereolithographic apparatus 100 comprises, principally, printing platform 104, reservoir/vat 106 and handheld computing device 108 although, as mentioned above, handheld computing device 108 may be provided separately. Handheld computing device 108 is supported by support 110, described in more detail below. Handheld computing device also has a display 112.

Reservoir 106 is provided to contain photoactive liquid 114, such as a photopolymer. Of course, the photoactive liquid 114 may be provided separately. Reservoir 106 also has a section 116 which acts as a "window" to light in a range of wavelengths. Note that the window need not be transparent to light in the visible spectrum, it needs only to allow light in the range of wavelengths to pass therethrough. Further, it need not be completely transparent to light in that range of wavelengths; it need only not attenuate completely light in that range of wavelengths. Yet further, a dedicated window section may not be necessary; the entire vat structure may be transparent to light in the range of wavelengths, but careful control may be exercised to ensure light is emitted to form the object as desired. Any suitable photopolymer may be used. For instance, any photopolymer synthesised based on the following ingredients: photo initiator; monomer (e.g. Bis- GMA), which will cross-link to form a polymer because of the photo initiator/light; viscosity modifiers; fillers (assisting, for example, transparency); and (optionally) a catalyst.

An example of a suitable photoactive resin may be found at:

http://3dprinter.wikidot.com/photoactive-resins.

Further, and as may be found at http://en.wikipedia.org/wiki/Dental_composite: Composite resins are most commonly composed of Bis-GMA and other

dimethacrylate monomers (TEGMA, UD A, HDDMA), a filler material such as silica and in most current applications, a photoinitiator. Dimethylglyoxime are also commonly added to achieve certain physical properties such as flow ability. Further tailoring of physical properties is achieved by formulating unique concentrations of each constituent. Polymerization is accomplished typically with a curing light that emits specific wavelengths keyed to the initiator and catalyst packages involved.

Another example may be any dental liquid which will cure upon being exposed to "blue" light.

In the reservoir 106 there is a "curing volume" 118, a volume of space within the reservoir 106 where photoactive liquid is cured in response to light 120 being projected therein. In this example, light 120 in the range of wavelengths is emitted from display 112 of handheld computing device 108, and at least some of the light intensity from the projected light is transmitted through window 116 of reservoir 106 into the curing volume 118, for the object 102 to be formed from the cured photoactive liquid. This process is described in more detail with reference to Figure 2.

Thus, it will be appreciated that Figure 1 illustrates a stereolithographic apparatus 100 arranged to form an object 102 using a digital model of the object. The stereolithographic apparatus comprises: a reservoir 106 for containing photoactive liquid 114, the photoactive liquid being curable when exposed to light 120 in a range of wavelengths. The reservoir has: a window 116 transparent to light 120 in the range of wavelengths; and a curing volume 118. A handheld computing device 108 has a display 112 for emitting, through the window 116 of the reservoir 106 and into the curing volume 118, light 120 in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object. Further, it will be appreciated that there has been described a method of operating a stereolithographic apparatus 100 to form an object 102, using a digital model of the object, the stereolithographic apparatus 100 comprising: a reservoir 106 containing photoactive liquid 114, the reservoir having: a window 116 transparent to light 120 in the range of wavelengths; and a curing volume 118. The method comprises controlling a handheld computing device 108 to emit, from a display 112, through the window 116 of the reservoir 106 and into the curing volume 118, light 120 in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object 102 thereby to cure photoactive liquid 114 to form a layer of the object 102.

Where appropriate, the light to be transmitted to the reservoir can also have light waves with wavelengths outside of the range of wavelengths (that the photoactive liquid is sensitive to). If necessary, a filter can be applied so that only light waves in the (desired) range of wavelengths are transmitted to the reservoir.

The handheld computing device is, as noted, loaded with executable instructions, most likely in the form of a computer program product such as an app downloaded from an online store. The app could also be a web-based app that is run within an internet browser such as Firefox, Chrome, Safari, etc. That is, the handheld computing device is configured to obtain the digital model from an online repository.

The user has the opportunity to amend, manipulate and/or customise the model to the user's satisfaction. For instance, the app, when loaded onto the handheld computing device, may allow the user to scale the model, so that the object, when printed, is of a size defined by the user. That is, the handheld computing devices configured to modify a scale of the digital model responsive to user input. This user input can be the user using finger gestures on the touchscreen display 112 of the handheld computing device 108, including the likes of pinching, panning and/or zooming. The shape of the model may also be manipulated. The handheld computing device, running the app, may also allow the user to define the print resolution of the object. For instance, and as described in more detail with reference to the example of Figure 2, the user defines, for example, a thickness of a layer of the digital model. That is, the handheld computing device is configured to define layers of the digital model of the object responsive to user input. The thickness of a layer of the digital model may correspond with a movement of the print platform 104, described with reference to Figure 2, and, thus, the handheld computing device is configured to define a resolution step thickness of a layer of the digital model.

In forming a layer of the object 102, display 112 of handheld computing device 108 emits a pattern of light 120 corresponding to a complete layer of the model. It may be that the display 112 illuminates simultaneously all of the pixels necessary to form a complete layer of the digital model, for the entire layer of the object to be cured in the curing volume simultaneously or substantially simultaneously. The precise time required for full curing will depend on a number of factors, including the precise properties of the photoactive liquid, the photoinitiator (the light and/or the light pattern) and the geometrical arrangement of the apparatus. But it is contemplated that the time should be of the order of seconds, perhaps just a few seconds. Thus, the handheld computing device is configured to emit from the display,

simultaneously or substantially simultaneously, light from multiple pixels of the display in a pattern corresponding to a complete layer of the digital model. However, other arrangements are possible. For instance, pixels may be lit in a sequence to form a complete layer if the intensity of the light and the nature of the photoactive liquid permit this. There may be some time delay between the initiation of illumination of a first pixel and illumination of another pixel, even if this amounts to a time delay of fractions of a second, such as hundreds of thousandths of a second.

Emission of light 120 through window 116 into the curing volume 118 of the reservoir 106 causes curing of the photoactive liquid 114 in the curing volume. T 2014/000106

Note that the curing volume 118 is shown in dashed lines to denote that this may not have a fixed boundary. For instance, the precise boundary of a curing volume 118 will depend on the properties of the photoactive liquid, and the properties of the light 120 being emitted from the handheld computing device 108. For instance, if light is of a lesser intensity the depth of "penetration" into the reservoir 106 may be less than if the light is of a greater intensity. Moreover, it may be that the effects of the light on curing the photoactive liquid decreases across a "soft boundary", where the effects reduce the farther away from the light source, rather than cross a well- defined boundary indicated by the dashed lines in Figure 1.

Regardless of the depth of the curing volume 118, or the precise pattern of light 120 emitted thereto, curing of the photoactive liquid in the curing volume 118 occurs. The photoactive liquid is sensitive to the properties of the light 120, for example the wavelength, or range of wavelengths in the light. The precise position of the print platform 104 is shown in Figure 1 to assist clarity, and forming of a first layer of object 102 is described in more detail with reference to Figure 2. However, it will be appreciated that, in one example, print surface 122 is arranged to facilitate

formation of the first layer of object 102 thereon. In this example, the area of print surface 122 shown between arrows 124 has been roughened, or made at least partially porous to the cured photoactive liquid, to facilitate adhesion of cured photoactive liquid thereto.

On occasion, it may be desirable to avoid the possibility of ambient light curing the photoactive liquid in a way not corresponding to the digital model of the object.

Therefore, it is possible to provide a mask 128 to shield the reservoir 106 - or at least the curing volume 118 thereof - from light 130 emitted or generated by light sources (which may include light in the range of wavelengths) not emitted from handheld computing device 108, including ambient light 130. So, in one example, the apparatus comprises a mask 128 for shielding the reservoir 106 from ambient light 130 in the range of wavelengths. In one arrangement, the mask may take the form of a housing for surrounding the reservoir 106. But it will be appreciated that other arrangements, such as a housing not enclosing the reservoir completely, are also contemplated. As noted above, the handheld computing device may be provided separately. So, the remainder of the stereolithographic apparatus, including the reservoir 106 and the print platform 104 and other ancillary components may be purchased separately from the handheld computing device and installed in, for example, a user's home for use with an existing handheld computing device owned by the user.

In these instances, there is provided a stereolithographic apparatus 100 arranged to form an object 102 using a digital model of the object, the stereolithographic apparatus 100 comprising: a reservoir 106 for containing photoactive liquid 114, the photoactive liquid 114 being curable when exposed to light 120 in a range of wavelengths, the reservoir 106 having: a window 116 transparent to light 120 in the range of wavelengths; and a curing volume 118. The apparatus 100 further comprises a support 110 for supporting a handheld computing device 108 having a display 112 for emitting, through the window 116 of the reservoir 106 and into the curing volume 118, light 120 in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object 102.

In such a situation, there is also provided a handheld computing device 108 for use with a stereolithographic apparatus 100 arranged to form an object 102, the stereolithographic apparatus 100 comprising: a reservoir 106 for containing photoactive liquid 114, the photoactive liquid 114 being curable when exposed to light 120 in a range of wavelengths. The reservoir 106 has a window 116 transparent to light 120 in the range of wavelengths and a curing volume 118. The handheld computing device 108 is configured to emit from a display 112, through the window 116 of the reservoir 106 and into the curing volume 118, light 120 in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object. The support 110 may comprise a harness disposed beneath the reservoir 106, and arranged to receive the handheld computing device 108 therein. The harness may be of an arrangement such that the user can simply slot or otherwise insert the handheld computing device therein. In one exemplary arrangement, the support 110 is suspended from the reservoir 106.

The optimum distance between the display of the handheld device and the reservoir is variable dependent on the precise properties of the object to be formed, the properties of the photoactive liquid, the properties of the handheld computing device, and instructions in the app for the intensity of light to be emitted from the display. Therefore, it is contemplated that the support 110 may be adjustable so that its optimal position may be determined by the user, whether through the user's own judgement or in response to instructions, which might be included in, for example, the app itself for viewing on the handheld computing device.

The app, retrievable from, for example, the online repository, may be considered a computer program product, covering also the above-mentioned web-based app, that may be run within an Internet browser. Therefore, there is provided computer program product comprising instructions for a handheld computing device, the handheld computing device being for use with a stereolithographic apparatus arranged to form an object, the stereolithographic apparatus comprising: a reservoir for containing photoactive liquid, the photoactive liquid being curable when exposed to light in a range of wavelengths, the reservoir having: a window transparent to light in the range of wavelengths; and a curing volume; the instructions being for causing the handheld computing device to emit from a display, through the window of the reservoir and into the curing volume, light in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object. 00106

Of course, other forms of computer program products are also envisaged, including storage media such as "thumb drives", DVDs etc, having stored thereon, executable instructions for loading onto the handheld computing device. The executable instructions may be considered a computer program, then there is provided a computer program comprising instructions for a handheld computing device, the handheld computing device being for use with a stereolithographic apparatus arranged to form an object, the stereolithographic apparatus comprising: a reservoir for containing photoactive liquid, the photoactive liquid being curable when exposed to light in a range of wavelengths, the reservoir having: a window transparent to light in the range of wavelengths; and a curing volume; the

instructions being for causing the handheld computing device to emit from a display, through the window of the reservoir and into the curing volume, light in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object.

Referring now to Figure 2, a sequence of operation of the apparatus of 100 of Figure 1 will be described. In the example of Figure 2, two steps in the process for printing or forming object 102 are shown by illustrating forming of the first two layers 200, 204 of object 102. Referring first to Figure 2a, this illustrates print surface 122 of print platform 104 in a first position disposed within the curing volume 118, and close to the bottom of the interior of the reservoir 106. Light from the handheld computing device (both of which are omitted from Figure 2 for clarity) is transmitted through window 116 to cure some of the photoactive liquid 114 to form first layer 200 of object 102 on print surface 122. The light pattern corresponds with the shape of the first layer 200 of object 102.

After forming of first layer 200, it is desired to form a second layer (and, most likely, subsequent layers, although these are not explicitly described herein). In this respect, and under control of the handheld computing device, print platform 104 is moved in direction 126 a resolution step distance 202. Print platform 104 - or, rather, print surface 122 - is now in the correct position for the forming of the second layer 204 of object 102 onto first layer 200, as depicted in Figure 2b.

The manner of controlling the movement of print platform 104 may be effected in a number of ways. For instance, the stereolithographic apparatus 100 may be provided with a separate machine controller (not illustrated) controlling, for example, the driver motor of the print platform. This separate machine controller may be in wireless communication with the handheld communications device over, for example, one of known wireless communications protocols, such as Wi-Fi or Bluetooth™. Further, the handheld computing device may be configured to emit another signal, whether a visible or audible signal to signal to the controller that the print platform is to be moved.

Although the entire print surface 122 is shown as being disposed within during volume 118 it will be appreciated that only a part of the surface may be required to be within the curing volume.

Thus, Figure 2 illustrates that the stereolithographic apparatus 100 is configured to form multiple layers 200, 204 of the object 102, the apparatus 100 comprising a print surface 122, at least a part of the print surface 122 being for disposal within the curing volume 118, for a first layer 200 to be formed thereon from cured photoactive liquid 114. Apparatus 100 is also configured, under control of the handheld computing device 108, to move the print surface 122 a resolution step distance 202 for a second layer 204 of the object to be formed from cured photoactive liquid 114.

In the example of Figure 2, second layer 204 is formed directly on first layer 200, but other arrangements are also contemplated. For instance, it may be desired for the second layer also to be formed directly onto print surface 122. In such an example, referring to layer 204 as the "second" layer made denote simply that the second layer is formed after the first layer. Subsequent layers (not shown) of object 102 may be formed may be formed in a similar manner.

Referring now to Figure 3, this illustrates a stereolithographic apparatus 100 which makes use of a collimator 300. In this example, collimator 300 is provided to mitigate any degradation in print quality which might arise from divergence of the light pattern emitted from display 112. In the example of Figure 3, collimator 300 is disposed between the display 112 of the handheld computing device 108 and the window 116 of reservoir 106.

Other devices to control the manner in which the emitted light is "routed" to the curing volume, such as other lightguides may also be used. For example, this may be desirable where the display of the handheld computing device is relatively small in comparison to the dimensions of the object to be formed. Thus, divergence of the emitted light pattern is actually desirable in the circumstances, subject to the divergence being controllable.

Figure 4 is a flow diagram illustrating process flow 400 of steps in forming of a 3-D printed object using the techniques disclosed herein. At 402, 3-D models are created and made available to users as described above through, for example, online stores. At step 404, a user selects a model to download from the online repository, or selects a model at the handheld communication device previously downloaded thereto. For instance, this may utilise drag and drop functionality for the user to select, drag and then drop into, say, a shopping basket one or more models to be downloaded.

At step 406, the user defines the properties of the object to be formed, such as the print resolution, and whether the dimensions of the object are to be scaled, or the shape manipulated as described above. Autodetection of the particular model of the tablet/smart phone may also take place at this step. If a platform independent app, where the app is not customised specifically for a particular handheld

communications device, is made available for download, it may be beneficial to derive or detect automatically the precise model of handheld computing device in use with the stereolithographic apparatus. This will provide an understanding about, for example, properties of the display screen, such as the size and pixel density on the display. For example, a 1 cm x 1 cm square area of the display may mean that there are 10,000 pixels in a high-resolution screen, or 5000 pixels in a lower- resolution screen. In step 404, the user has the option of selecting, say, a model for printing which is a cuboid of 1 cm x 1 cm x 1 cm. The dimensions defined in centimetres are scaled to the number of pixels to be illuminated on the display for each layer of the cuboid in the printing process. Thus, the handheld computing device is configured to determine a pixel display pattern by correlating information about the technical specification of the handheld communications device - in this instance, information relating to the display - with the physical dimension of the object to be formed.

This auto-detection may take place in a "handshake" or the like when the handheld computing device establishes wireless communication with the separate controller of the stereolithographic apparatus, mentioned above. When the stereolithographic apparatus receives this information it can transmit information to the handheld computing device.

Thus, the stereolithographic apparatus is configured to determine an operating parameter of the handheld communications device. This may be done when wireless communication is established between the machine controller of the

stereolithographic apparatus and the handheld communications device.

In other instances, a user will select a particular version of the app customised for use with a particular handheld communications device, where the app will perform "slicing" according to its prior knowledge of the technical specifications of that particular device.

At step 408, the handheld computing device defines the individual layers of the object to be formed. That is, the handheld computing device "slices" the object - or, rather, the digital model thereof - into layers. The shape of the layers corresponds to the shape of the object to be formed, and the thickness of the layers corresponds to the print resolution, the step resolution distance 202 illustrated in Figure 2. The remaining parameters necessary to form the object are also defined at this stage, including, for example, the structure such as the inner structure which may be in the form of a honeycomb structure.

At step 410, a two dimensional shape is calculated for display on the display of the handheld computing device corresponding to the shape of a layer of the digital model of the object, and, of course, the object to be formed. The exposure time - the time which the light pattern is maintained for - also calculated at step 408 is also determined here. The exposure time may be calculated according to the parameters of the photoactive liquid, for example, and the pixel correlation as described above, correlating the dimensions of the object to be formed, to the number of pixels to be eliminated on the display of the handheld computing device.

Some operating systems - such as the Android operating system - provide for auto scaling, whether up-scaling or down-scaling, in an effort to provide the best possible display experience. For instance, Android coding uses "Density Independent Pixels; see http://developer.android.com/guide/practices/screens support.html#dips-pels. It is beneficial to reverse this auto scaling based on the pixel density information obtained from knowledge of the precise model of the handheld computing device in use. At step 412, a light pattern corresponding to a layer of the object is displayed at the appropriate light intensity, with the print platform in the correct position. Then, at step 414 the print platform is moved the step resolution distance, for another layer to be formed, with the algorithm looking around steps 412, 414 until the printing/forming process is completed.

It will be appreciated by those skilled in the art that the invention has been described by way of example only, and that a variety of alternative approaches may be adopted without departing from the scope of the invention, as defined by the appended claims.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings; all of these different combinations constitute various alternative aspects of the invention.

Claims

1. A stereolithographic apparatus arranged to form an object using a digital model of the object, the stereolithographic apparatus comprising:

a reservoir for containing photoactive liquid, the photoactive liquid being curable when exposed to light in a range of wavelengths, the reservoir having:

a window transparent to light in the range of wavelengths; and

a curing volume; and

a handheld computing device having a display for emitting, through the window of the reservoir and into the curing volume, light in the range of

wavelengths in a pattern corresponding to a layer of the digital model of the object.

2. The stereolithographic apparatus of claim 1, wherein the handheld computing device is configured to emit from the display, substantially

simultaneously, light from multiple pixels of the display in a pattern corresponding to a complete layer of the digital model.

3. The stereolithographic apparatus of claim 1 or claim 2 configured to form multiple layers of the object and wherein the stereolithographic apparatus:

comprises a print surface, at least a part of the print surface being for disposal within the curing volume, for a first layer of the object to be formed thereon from cured photoactive liquid; and

is configured, under control of the handheld computing device, to move the print surface a resolution step distance for a second layer of the object to be formed, from cured photoactive liquid.

4. The stereolithographic apparatus of claim 1 or claim 2, wherein the handheld computing device is configured to define layers of the digital model of the object responsive to user input.

5. The stereolithographic apparatus of claim 4, wherein the handheld computing device is configured to define a resolution step thickness of a layer of the digital model.

6. The stereolithographic apparatus of claim 3, wherein the print surface comprises at least a portion thereof which is arranged to facilitate adhesion of cured photoactive liquid thereto.

7. The stereolithographic apparatus of claim 1 or claim 2, wherein the apparatus comprises a mask for shielding the reservoir from ambient light in the range of wavelengths.

8. The stereolithographic apparatus of claim 1 or claim 2, wherein the apparatus comprises a collimator disposed between the display of the handheld computing device and the window of the reservoir.

9. The stereolithographic apparatus of claim 1 or claim 2, wherein the handheld computing device is configured to modify a scale of the digital model responsive to user input.

10. The stereolithographic apparatus of claim 1 or claim 2, wherein the handheld computing device is configured to obtain the digital model from an online repository.

11. A stereolithographic apparatus arranged to form an object using a digital model of the object, the stereolithographic apparatus comprising:

a window transparent to light in the range of wavelengths; and

a curing volume; and a support for supporting a handheld computing device having a display for emitting, through the window of the reservoir and into the curing volume, light in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object.

12. The stereolithographic apparatus of claim 11, wherein the support comprises a harness disposed beneath the reservoir, and configured to receive the handheld computing device.

13. The stereolithographic apparatus of claim 11 or claim 12, wherein the support is suspended from the reservoir.

14. The stereolithographic apparatus of claim 1 or claim 2, configured to determine an operating parameter of the handheld communications device.

15. The stereolithographic apparatus of claim 14, configured to determine the operating parameter when wireless communication is established between a machine controller of the stereolithographic apparatus and the handheld communications device.

16. The stereolithographic apparatus of claim 1 or claim 2, wherein the handheld computing device is configured to determine a pixel display pattern by correlating information about a technical specification of handheld communications device with a physical dimension of the object to be formed.

17. A handheld computing device for use with a stereolithographic apparatus arranged to form an object using a digital model of the object, the stereolithographic apparatus comprising:

a reservoir for containing photoactive liquid, the photoactive liquid being curable when exposed to light in a range of wavelengths, the reservoir having: a window transparent to light in the range of wavelengths; and

a curing volume; wherein

the handheld computing device is configured to emit from a display, through the window of the reservoir and into the curing volume, light in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object.

18. A computer program product comprising instructions for a handheld computing device, the handheld computing device being for use with a

stereolithographic apparatus arranged to form an object, the stereolithographic apparatus comprising:

a window transparent to light in the range of wavelengths; and

a curing volume;

the instructions being for causing the handheld computing device to emit from a display, through the window of the reservoir and into the curing volume, light in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object.

19. A computer program comprising instructions for a handheld computing device, the handheld computing device being for use with a stereolithographic apparatus arranged to form an object, the stereolithographic apparatus comprising: a reservoir for containing photoactive liquid, the photoactive liquid being curable when exposed to light in a range of wavelengths, the reservoir having:

a window transparent to light in the range of wavelengths; and

a curing volume;

20. A method of operating a stereolithographic apparatus to form an object, using a digital model of the object, the stereolithographic apparatus comprising: a reservoir containing photoactive liquid, the reservoir having:

a window transparent to light in the range of wavelengths; and a curing volume;

the method comprising:

controlling a handheld computing device to emit, from a display, through the window of the reservoir and into the curing volume, light in the range of wavelengths in a pattern corresponding to a layer of the digital model of the object thereby to cure photoactive liquid to form a layer of the object.