Field of the Invention

The present invention relates to layered object manufacture (LOM) systems providing rapid prototyping capacity. In a preferred arrangement the invention relates to an adhesive dispensing device and in particular an adhesive dispensing device for use in applying adhesive in a Layered Object Manufacture (LOM) system for rapid prototyping (RP). Background

Rapid prototyping is defined as computer-controlled additive fabrication, in that an object can be fabricated by the addition of material rather than conventional machining methods that rely on removal or the subtraction of material. The term "rapid" is, it will be appreciated, a relative term but one that has specific meaning within the art, in that construction of a finished three dimensional articles can take from several hours to several days, depending on the method used and the size and complexity of the model. There are many known methodologies that are employed within the general field of rapid prototyping Layered Object Manufacture (LOM) is one form of Rapid prototyping (RP) which relates to the successive layering of adhesive-coated paper, plastic or metal laminates which are then successively glued together and cut to shape with a knife or laser cutter.

In existing LOM systems that employ paper based raw materials, the paper is provided in the form of a roll. The roll of paper may be provided with adhesive already present on the underside. In this case, the adhesive may be activated by heat and/or pressure to form a bond onto the previous layer. In an alternative approach, adhesive may be applied to the underside of the material as it is drawn from a roll. However, there are a number of disadvantages associated with the use of roll material. For example, a machine is often operable only with specifically manufactured rolls of material, which may be expensive to obtain and/or difficult to replace. There are also disadvantages associated with the day to day use of rolls of raw material. For example, the rolls may become stuck or jammed in the feeding mechanism due to the pre-applied adhesive thereon. With the above, removal of the waste material can be very difficult because it is adhered together with the same adhesive force as the part being made. This can lead to the part being damaged during waste removal "weeding", as chisels and other sharp implements are often needed to prise the object free.

There are further limitations in the types of paper that are suitable for use in conventional LOM systems. As paper is composed of a randomly felted layer of fibre, it follows that the structure may have varying degrees of porosity. Paper is a highly porous material and contains as much as 70% air. Porosity of a sheet or layer is an indication of the moisture absorption of the paper, or the ability of a particular sheet or layer of paper to accept ink, water or in this case adhesive. When selecting a particular type of paper for LOM, it is important to consider the porosity of the paper.

The properties of the paper are clearly closely related to, and place limits on the types of adhesive that may be used. There are further issues and concerns relating to the application of adhesive to paper. In known printer like dispensing systems which rely on computer controlled electro-mechanical devices such as piezoelectric dispensing heads, the heads are often of a delicate nature and over long periods of inactivity these devices can become clogged and may need to be serviced, maintained and replaced frequently. Thus such arrangements may have high overheads for maintenance and repair.

Other methods of applying adhesive between paper layers include:

1 . Coating the entire working area of the substrate or layer, which as noted above produces significant difficulties when removing waste material during post processing the finished part;

2. Using a substance which when placed in certain locations on the layer or sheet prevents adhesion at these locations. This technique has the disadvantage of effectively wasting adhesive by initially coating the entire layer or sheet and then rendering portions of the adhesive "non-sticky" with the use of an "anti-glue" substance; or,

3. Using an electrostatic system to xerographically deposit adhesive toner onto the sheet surface like a conventional printer prints ink. This method can have the disadvantage of being technically complicated and requiring specially manufactured adhesive toner.

It is further noted that current LOM systems use adhesives that are solvent based and which are not water soluble and thus present environmental issues for example, for the purposes of disposal. However, such solvent based adhesive have to date been used in LOM as the use of water based adhesives having a high wet content presents further problems such as warping and distortion of the paper which has prejudiced their application in LOM systems.

Reference is made to applicant's earlier PCT application WO 2009/068672. The arrangement of that application provides an adhesive dispensing device which allows for controlled application of adhesive for building a 3-D object. The systems are methods therein support the use of water based adhesives as binding agent for the layering process. By controlling the volume and/or location of the dispensed adhesive such a LOM system allows for the use of water based adhesives while minimising the warping or distortion of the cellulose based paper material that is used in the layering. The wheel of the present specification may be used with the arrangements of the earlier PCT application WO 2009/068672 the contents of which are herein incorporated by reference. The wheel of the present specification may also be used with other suitable arrangements and SDL or LOM systems.

As 3D printing systems and 3D printing develops, they systems are being used to make increasing complex objects and in increasing volumes. There is a need for an improved adhesive dispensing device taking account of the possible complexity of builds and the need to reduce durations of builds and the overall size and complexity of the systems.

Summary

According to a first aspect, there is provided an adhesive dispensing device, for use in layered object manufacturing (LOM) systems for rapid prototyping of a 3- dimensional (3D) object, for the application of adhesive to a target substrate S defining a layer of a 3D object, the device comprising an adhesive applicator wheel having a plurality of circumferentially spaced apart recesses for receiving adhesive, the adhesive dispensing device being movable relative to the target substrate to deposit adhesive at selected locations thereon, wherein the adhesive dispensing device is mounted for translation relative to the target substrate via a pivot mount configured such that the wheel aligns with its direction of translation relative to the target substrate to deposit adhesive at the selected locations.

In one arrangement the adhesive dispensing device including the wheel is mounted such that the center of gravity thereof is directly in line with the pivot point. In one arrangement, the adhesive dispensing device is mounted to pivot about a pivot axis passing through the pivot point. In one arrangement, the adhesive dispensing device is mounted for pivoting through 360 degrees relative to the pivot point.

In one arrangement the wheel is mounted at an offset relative to the pivot axis. In one arrangement, the wheel is mounted such that it aligns with the direction of translation of the wheel relative to the substrate. The wheel is mounted to pivot due to tangential forces when moved over the substrate to align with the direction of travel. In one arrangement the adhesive dispensing device is translated according to the form of the 3D object to deposit adhesive according to the form of the 3D object.

The arrangement of the adhesive dispensing device of the present specification advantageously provides a device and wheel which aligns with its direction of translation. This advantageously provides that the wheel is effectively translated in the forward direction continuously to deposit adhesive. The wheel has a leading edge and a trailing edge, and if effect as the wheel is arranged to align with the direction of travel, the adhesive device and wheel can be translated in a substantially continuous forward path for the adhesive deposition run for a particular layer. This is in contrast to prior art device where it may have been necessary to lift the wheel and move the wheel to a start position for laying down each adhesive line.

In one arrangement the wheel is configured to deposit adhesive in linear, circular or other irregular paths as it is translated relative to the substrate. The self-aligning adhesive dispensing device allows for a variety of glue patterns. The arrangement of the device advantageously provides for the adhesive dispensing device to be translated in a path following the form of the perimeter of the object layer and for the form to be filled, for example, in a meander pattern.

The wheel being rotatable to convey adhesive filled in one or more recesses to a target substrate and to deposit controlled amounts of adhesive at discrete points thereon, and in one arrangement the wheel is configured to be rotated by the friction between the wheel and the target substrate.

In one arrangement, the wheel further comprises a friction wheel or sprocket wheel to assist wheel rotation. The friction wheel may be coupled to the glue wheel. In one arrangement there is provided an adhesive wipe which together with the wheel defines an adhesive filling chamber for filling adhesive into one or more recesses as the wheel rotates relative to the wipe. In one arrangement the device further comprises a flow control means for control of adhesive flow to the adhesive filler and to the recesses of the wheel. In one arrangement the device is configured to prevent leakage of adhesive by the arrangement of the adhesive filling chamber and the flow control. In one arrangement, the flow control means is arranged such that when to wheel stops rotating, the adhesive is switched off too. In one arrangement, the control means comprises a valve for example a solenoid valve. In one arrangement, the device further comprises a downward force control means for controlling and varying the downward force exerted by the wheel on the substrate S as it is translated relative to the substrate. The control means provides for variation of the force applied allows control of the amount of adhesive deposited per glue dot.

In one arrangement, the dispenser operably provides for the selective dispensing of adhesive of predetermined volumes at specific locations on the paper substrate

In one arrangement, the down force control means comprises a solenoid or a voice coil. According to another aspect there is provided a layered object manufacturing (LOM) or SDL system for rapid prototyping incorporating an adhesive dispensing device as claimed in any preceding claim.

According to another aspect there is provided a layered object manufacturing (LOM) system for rapid prototyping, the system providing for the application of adhesive onto multiple layers of a paper substrate to effect generation of a three dimensional object, the system comprising:

a) a reservoir for the adhesive;

b) an adhesive dispenser device in fluid communication with the reservoir for dispensing the adhesive from the reservoir onto the substrate;

c) control means operable on the dispenser for directing the dispenser to specific locations of the substrate for subsequent dispensing of adhesive onto the paper substrate, and

wherein the dispenser is mounted for translation relative to a target substrate and comprises a pivotably mounted self-aligning dispenser configured to dispense adhesive as it is translated relative to the layer of the 3D object. In one arrangement the dispenser comprises a force control means which operably provides for the selective dispensing of adhesive of predetermined volumes at specific locations on the paper substrate. In one arrangement the device comprises control means operable on the dispenser for directing the dispenser to specific locations of the substrate for subsequent dispensing of adhesive onto the paper substrate. In one arrangement, the system comprising dispenser drive means and control means operable to control the direction and velocity of translation of the adhesive dispensing device and wheel relative to the substrate. In one arrangement, the angular movement of the wheel relative to the wipe and substrate is controlled by the translation of the dispenser relative to the substrate, the wheel being configured to rotate due to friction between wheel and substrate.

In one arrangement the adhesive comprises a water based adhesive, for example a PVA adhesive. In one arrangement, the adhesive is operably deposited from a filled recess to the target substrate by means of capillary action. In one arrangement, the adhesive dispenser device being configured for operable mounting to a head on a x-y frame of the system and configured for movement on the x-y frame relative to the target substrate. The head may be a multifunctional head configured to transport various components operable to form the object layer relative to the object layer.

According to a further aspect, there is provided a method of applying adhesive for the manufacture of a 3D object using the device of the specification, the method including:

- applying adhesive to individual layers of multiple layers of a 3D object;

- applying adhesive according to a glue pattern as defined by a digital print file for that layer;

wherein the glue pattern is firstly applied in a path according to the form of the periphery of the object at that layer and secondly applied to fill the form of the object at the layer.

In one arrangement the path comprises a continuous path. In one arrangement the adhesive is deposited in the form of a line of dots of adhesive. In one arrangement wherein the line is a continuous line. In one arrangement the volume of individual dots may be varied by varying the downward force exerted by the wheel on the layer of the object at the point of contact.

These and other features will be better understood with reference to the drawings which follow.

Brief Description Of The Drawings

The present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a perspective view of an adhesive dispensing device in accordance with an arrangement of the specification; Figure 2 is a perspective view of the device of Fig. 1 from the side showing the pivot axis;

Figure 3 is a front view of the device of Figs. 1 and 2 showing a wipe and dimpled adhesive dispensing wheel;

Fig. 4 is a perspective view from the side of the device of Fig. 4;

Fig. 5 is a drawing showing a perspective view of the components of Fig. 4.

Fig. 6 is block diagram of an exemplary SDL or LOM system including an adhesive dispensing device of the present specification;

Fig. 7a shows a prior art glue pattern and Fig. 7B shows a glue pattern as provided by the systems and method according to an arrangement of the present specification.

Detailed Description Of The Drawings

Referring to the drawings and initially in particular to Fig. 6 specific components of a layered object (LOM) manufacturing system or Selective Deposition Lamination (SDL) system 1000 for the manufacture of 3D objects are described. The system includes a build module 500. The build module 500 includes an adhesive dispensing device 100, a build plate 510, cutting means 520, bonding means 530, substrate or paper feed means 540. The specification in particular focuses on the adhesive dispensing device 100.

Referring to the drawings in particular, Figs. 1 -5, a component is of the overall SDL (or LOM) system 1000 is the adhesive dispensing device 100. The adhesive dispensing device 100 comprises an adhesive applicator wheel 150 also referred to as glue wheel 150. The adhesive dispensing device 100 is configured for connection to an adhesive reservoir 1 10. The adhesive dispensing device comprises an adhesive filler 120, 130 which couples the reservoir 1 10 and which conveys the adhesive applicator wheel 150. The adhesive applicator wheel 150 has a plurality of circumferentially spaced apart recesses for receiving adhesive, the adhesive dispensing device 100 and wheel 150 is movable relative to the target substrate S to deposit adhesive at selected locations thereon. Adhesive is applied as recesses 152 of the wheel are moved as the wheel rotates into contact with the target substrate S. Adhesive is applied by capillary action.

In the specification, the terms glue wheel, adhesive dispensing wheel, applicator wheel have been used to describe the wheel arrangement reflecting the language of the field of technology.

The adhesive dispensing device 100 comprises a movable portion 140 or movable body portion 140. The movable components include filler 120, support 125, wipe 130 and wheel 150. The filler 120 is connected to an adhesive feed from an adhesive reservoir 1 10 at an inlet portion 122. The connection comprises a pivot connection 155. The adhesive filler 120 and wipe 130 convey adhesive A from the inlet portion 122 to an adhesive outlet portion 135 at the wheel 150. . The adhesive filler 120 may convey the adhesive for example via one or more channels to an adhesive outlet portion 135 at wipe 130. The wipe 130 together with the adhesive applicator wheel 150 define an adhesive filling chamber 136 for filling adhesive to the recesses 152 of the wheel. The wipe 130 depends or extends downwardly from the adhesive filler 120 and has lateral side walls 140, 141 connected by front and back longitudinal side walls 142 and 143 defining an opening and configured to be coupled to and to contact the wheel 150.

The adhesive dispensing device 100 may further comprise a controller 1 15 for controlling parameters of operation of the device including movement: location and translation, adhesive flow and downward force exerted by the wheel 150 on a substrate.

The adhesive dispensing device 100 is mounted for translation relative to the target substrate. The adhesive dispensing device 100 comprises a pivot mount 155 and is configured such that the body portion 140 (filler, support, wipe) and adhesive dispensing wheel 150, which is the portion of the device which contacts the target substrate, pivot as the device is translated relative to the substrate, such that the adhesive dispensing wheel operably aligns with its direction of translation relative to the target substrate S to deposit adhesive at the selected locations according to the form of the 3D object.

The pivot mount 155 provides that the adhesive dispensing device 100, comprising body portion 140 and the wheel 150 can pivot through 360 degrees. In the exemplary arrangement of the drawings the adhesive dispensing device including filler 120, 130 support 125, and wheel 150 are arranged to pivot.

Referring to Fig. 2, an exemplary rotatable or pivotable mounting arrangement according to the present specification is shown the axis of rotation is illustrated. Referring to Fig. 3 the axis of rotation of an exemplary arrangement of the present specification is shown in a front side view.

The adhesive dispensing device 100 is configured to swivel or pivot as it is moved over the substrate S to align the wheel 150 with the direction of travel. The swivel arrangement of the adhesive dispensing device is provided by virtue of the pivot mounting. The adhesive dispensing device can swivel due to tangential forces when moved over the target substrate or layer to align with the direction of travel.

It is noted that movable body portion 140 of the adhesive dispensing device 100 is mounted to pivot about the pivot axis P-P. Referring to Fig. 3 the adhesive dispensing device 100 is mounted such that the center of gravity of the rotating or pivoting mass thereof is directly in line with the pivot point. Referring to fig. 2 the mass of the rotating components is arranged in line with the pivot axis P-P. The point of contact of the wheel 150 with the substrate is offset (by an offset d- see Fig. 2) from the pivot axis P-P. In particular, the glue wheel is mounted to swivel or rotate relative to the pivot axis by virtue of the mounting of the wheel at an offset relative to the mounting see- figure 2 illustrating axis and mounting.

The glue wheel 150 (similarly to the overall adhesive dispensing device) is mounted via a swivel or pivot mounting 155 to rotate through 360 degrees. The components which are mounted to pivot include the support 125 and filler 120 and wipe 130 and wheel.

The pivot mount 155 allows for the deposition of adhesive in a continuous adhesive dispensing run. The adhesive may be deposited in any direction, this is in contrast to prior art system where the adhesive may be deposited in linear rows or columns by the linear line-wise translation of the adhesive dispenser relative to a surface. The wheel 150 always aligns such that it is running forwardly in the direction of translation.

The arrangement of the adhesive dispensing device 100 provides for a new approach to laying down a glue pattern. Whereas in the prior art glue might often have been deposited in unidirectional lines or backward and forward lines, necessitating that the glue wheel be lifted and located in preparation for each line run. See Figs 7a.

The system of the present specification provides for deposition of glue to a substrate or layer in one or more continuous runs not limited to straight line runs. See Fig. 7B. For example, taking the case of a build object of cube form, adhesive may be deposited to layer of the object of square form by translating the adhesive dispensing device around the perimeter of the square form of a layer, and then translating the adhesive dispensing device to deposit adhesive to fill the square form. The glue is deposited to the perimeter and then in a meander pattern to fill. The wheel of the device 100 aligns with the direction of translation and therefore the wheel pivots through each right angle corner of the square form to align for the application of adhesive to each of the side.

The new glue pattern achievable with the system 100 allow increased control and efficiency in depositing glue to a layer. In comparison with the prior art a deposition run for application of glue to a layer may be a single continuous run. In comparison with the prior art the need to lift, locate and prime the wheel is addressed.

Referring to Fig 1 and Fig. 6 control of various components and operations of the adhesive dispensing device 150 include controller 1 15 which is configured to receive the digital print file, transport means 180 for translating the adhesive dispensing device, force application means 170 for controlling the downward force exerted by the wheel on the substrate and flow control 1 60 for controlling the flow of adhesive as stopped.

The example above refers to an object of regular form. However, it will be appreciated that the adhesive dispensing device and glue wheel 150 thereof may be used to deposit adhesive also to irregular form layers also in a series of one or more continuous runs, e.g. following the perimeter form and then filling in the meander.

As noted above the device 100 provides control of the amount of adhesive or glue deposited at a particular point by control of the downward force exerted at the contact point of the wheel on the substrate. The downward force exerted can be varied from point to point along the glue pattern.

The self-aligning pivot mount of the adhesive dispensing device of the present specification allows for the dispensing of adhesive in a continuous a path including a path of irregular form on a target substrate defining a layer of the 3D object according to the form at that layer. For example the adhesive may be dispensed according to the form of an edge of the object, including in a substantially circular path or in a spiral path or in a series of concentric circles corresponding to a generally circular object. The path may also be irregular. See Fig. 7B.

The glue wheel 150 is rotated by the friction between the wheel and the layer or target substrate S.

In one arrangement the glue wheel 150 may further comprise a friction wheel 155. The friction wheel 155 aids the glue wheel 150 rotation as the glue wheel 150 is moved across a target substrate S. The friction wheel 155 is in one arrangement according to Fig, 4 provided separate from the glue wheel 150 and arranged for coupling thereto. The friction wheel 155 may be provided integrated with the glue wheel 150. The friction wheel 155 may comprise a sprocket arrangement, however, it will be appreciated that other suitable arrangements which aid rotation of the glue wheel as it is moved across the target substrate S may also be provided. In particular the friction wheel 155 assists with wheel rotation in use when there is glue between the wheel and the target substrate or layer S.

The arrangement of the wheel for swivelling and rotating through 360 degrees and for alignment relative to the direction of movement provides a wheel which allows the deposition of adhesive according to the form and shape required. For example, the wheel can be used to apply adhesive in a circular path, the wheel can be used to apply adhesive according to the edge form of each layer of an irregularly shaped 3D object

Advantageously, the arrangement is therefore not limited to straight lines any more. This enables the placement of adhesive in a more complex pattern and therefore more complex waste cuts which will enable the building of more complex objects from the 3D printer. For illustration comparison, reference is made Fig. 7A which shows the printing of a layer of circular form with a prior art system in which the adhesive is dispensed to the circular form in a series of parallel and/or unidirectional straight lines, and Fig. 7B which shows a glue pattern provided with the system of the present application. Clearly, the glue pattern of the new system requires less glue and less time is required to dispense adhesive to the form/object layer.

The adhesive applicator wheel 150 comprises a contact surface 151 having a plurality of recesses 152 for receiving adhesive A at the outlet 126. Adhesive is filled into the recesses 152 at the wipe 135 and is conveyed in the recesses from the wipe to a target substrate S as the wheel is rotated so that the recesses contact the target substrate S.

The applicator wheel 150 contact surface 151 is that portion of the wheel 150 configured to contact both the wipe 135 of the filler 120 and a target substrate S, for example a sheet or layer of paper. The contact surface 151 and/or the recesses 152 may be comprised of or formed from a low friction material, for example Delrin and/or may comprise a low friction finish.

The adhesive dispensing device 150 comprises a flow control means 160 for control of adhesive flow to the adhesive filler 120 and to the recesses 152 of the wheel 150. The control means is arranged such that when to wheel 150 stops rotating, the adhesive is switched off too. In an exemplary arrangement of the present specification, the control means comprises value for example a solenoid valve 1 61 . While in the exemplary arrangement the valve is a solenoid valve it will be appreciated that other suitable valves may be provided.

The wheel further comprises force control means 170 for controlling and varying the downward force exerted by the wheel 150 on the substrate S. The force control means by providing for variation of the force applied allows control of the amount of adhesive deposited per glue dot. This is advantageous and allows for application of different volumes of adhesive to different portions of the target substrate, for example lower volumes are areas to be weeded that at areas of the build, or for example higher volumes at a particular extremity of the build. The adhesive is deposited to the substrate or layer or sheet S by capillary action. The capillary action due to the inherent porosity or water absorption of the substrate S. The substrate S may in particular be a paper substrate.

It will also be appreciated that the form of the recesses may be varied as required for the application needed for example to vary

The system and glue wheel of the present specification by virtue of the combination of features therein provides for control of the form and location of glue lines and also for control of the concentration of glue lines. The system further provides for the control of the glue weight per dot by varying the downward pressure.

The wipe 130 and applicator wheel 150 are designed to correspond and co-operate to define the chamber 136 having side walls defined by the wipe 130 and a base defined by the wheel 150 thereof. The dimensions and form of the wipe 130 correspond to the wheel 150 such that when the wipe 130 is coupled to the wheel. The contact side or open outlet 135 of the wipe 130 may comprise or be provided in an arc form corresponding substantially to the form of the wheel 150. The adhesive filler 120 and wipe 130 comprises or may be in contact with a biasing means, for example, spring means to maintain the wipe 130 in contact with the wheel 150. The wipe 130 is configured to enable filling of the recesses 152 passing there through with adhesive A In an exemplary arrangement, for the purposes of filling, the wipe 130 or sealed chamber 136 incorporates a vent means which facilitates replacement of air from a recess 152 with adhesive by allowing air to be displaced from the recess by the adhesive and providing means to remove or drive the air from the wipe/sealed chamber. The vent means is provided by relative dimensions of the lateral side walls 142 and 143 of the wipe 130 and the recesses 152 and the manner of driven interaction of these components. Thus the plurality of recesses 152 of the applicator wheel 150 are filled with adhesive A as they enter the wipe as the wheel 150 rotates. Filling is by gas or in this case air to adhesive exchange as the wheel moves relative to the wipe. Venting of a recess is by movement of the wheel which facilitates the air to adhesive exchange. Venting occurs at the point where a recess interacts with a leading or trailing edge 144 and 145 of the wipe 130.

The system provides for prevention of leak of adhesive. Firstly by the value control which stops the flow of adhesive when the rotation is stopped. Secondly by the form of the wipe 130, adhesive filling chamber 136 and wheel 150.

If when the wheel stops rotating it happens that a single recess lies bridging an edge of the wipe any leakage would be very limited due to the small size and volume of the recess 152 and to the operation of the valve, If, when the wheel stops rotating there is no recess bridging an edge of the wipe then the wipe and wheel form a substantially sealed adhesive filling chamber 136. Further the valve will stop the filling of adhesive.

The spacing apart of the recesses 152 is selected taking account of the required concentration of glue dots to be laid down in a glue pattern. The spacing may be selected and varied as required.

Advantageously, in comparison with previous arrangements, the device and wheel do not require a motor, belt, pulleys etc because the glue wheel is rotated by the friction between the wheel and the layer or target substrate. In exemplary arrangement described the adhesive dispensing device is mounted to a translatable head and the wheel is rotated by friction as the wheel contacts the substrate surface. The arrangement is therefore simplified in comparison with the prior art and is easier to install and maintain.

Advantageously in comparison with previous systems, the glue wheel can swivel due to tangential forces when moved over the layer or target substrate to align with the direction of travel - therefore not limited to straight lines any more. This enables placement adhesive in a more complex pattern and therefore more complex waste cuts which will enable the building of more complex objects from the 3D printer.

As noted above the adhesive dispensing device and wheel 150 may be mounted within an overall system 1000 to effect movement of the wheel relative to the surface via transport means 180. The transport means 180 provides for the movement of the adhesive dispensing device and the wheel 150 relative to the target substrate to particular locations and for the rotation of the wheel relative to the target substrate, the wheel is rotated by friction relative to the substrate. In use, in an exemplary arrangement the adhesive dispensing device 100 may be mounted for translational movement relative to a substrate S, for example via an X-Y frame 1010 to enable movement of the head relative to the substrate.

The adhesive dispensing device 100 of the present specification is suitable for use with a water based PVA adhesive.

Due to the nature of such adhesive the open time between laying down the adhesive and drying/setting of the adhesive is long, thereby enabling sufficient time to place a subsequent substrate layers or sheets. The adhesive dispensing device provides for a very accurate control of the amounts of adhesive applied to a substrate. This is achieved in part by virtue of the form and dimensions of the recesses of the applicator wheel and by the spacing of the recesses on that wheel. In particular, the adhesive dispensing device 100 may be configured and used to dispense adhesive nanodots i.e. dots of adhesive having a volume of the order of 10-50 nanolitres, preferably in the order of 20-30 nanolitres. In this way the device may be used to deposit controlled amounts of a water based adhesive and such control obviates the problem of saturation of the substrate. Referring to the drawings and in particular Fig. 6, a Layered Object Manufacturing (LOM) system 1000 for rapid prototyping incorporating an adhesive dispensing device 100 is shown.

The adhesive dispensing device may in an exemplary arrangement be mounted directly to an adhesive dispensing device head 1005 or as part of a multifunctional head 1006 on an X-Y frame 1010, which enables the head 1005, 1006 to be positioned and moved as required over a substrate S on a build object O. Movement in the z direction is controlled by solenoid or voice call.

Paper is feed into the system. The system 1000 further comprises bonding means 530 for example a roller which passed over the build object to ensure a positive bond of subsequent layers. The system 1000 may further comprise a hot plate 1007 for applying pressure and curing the adhesive. The hot plate 1007 may be movable or fixedly mounted. Many of the features of the X-Y frame 1010 and the paper feed and placement are conventional and as such would be known to the skilled person in the field and are not described in detail here.

A method of use of the LOM system 1000 for rapid prototyping is also provided and may be considered as follows:

Using a three dimensional (3D) computer aided design (CAD) of an object / part to be manufactured; for example, a stereolithography (STL) file is generated within the CAD package and saved. This STL file is provided to a software package which controls operation of the system 1000.

The software operates in accordance with the system 1000 to generate a series of cross sections of the part and at any particular height each one a simple two dimensional (2D) profile. A user operates the system/controller to output a control signal to the system 1000 to commence building the build object O in 3D.

The system 1000 then operates to lay down the layers of paper (substrate layers) of the build object and to cut each layer to the required profile. Individual layers are layered one upon the other to effect fabrication of a final structure.

The system provides for the variation of density and volume of adhesive dots applied to the substrate. This discriminatory application of the adhesive is facilitated through the use of a control system 1 15 that can accurately direct the adhesive dispensing system to specific target areas, and also by employing of an adhesive dispensing system 100 that does not effect a leaking or other inadvertent dispensing of the adhesive between desired dispensing positions.

The system may comprise a multifunctional head 1006 to which the adhesive dispensing device 150, the cutter head 520 are mounted. The multifunctional head 1006 may further comprise a printhead 550. In an alternative arrangement, the adhesive dispensing device and/or cutter and/or printhead may be supported or mounted on different heads.

The X-Y positioning means 1010 as controlled by controller 1 15 translates and locates the active components (cutter, printer, adhesive dispensing device etc.) as required.

While in the description above, the method is focussed on the arrangement and operation of the adhesive dispensing device 150, it is noted as background that the overall method includes the following: feeding the substrate to the build location 510 or build object, bonding the layer to the build object, cutting the profile of the layer, applying adhesive to the layer. The method may further include printing the layer before the application of adhesive.

This method continues until the entire 3D model has been built up layer by layer. It will be understood therefore, that the system 1000 incorporating the adhesive dispensing device 100 of the invention is thus suitable for use in the application of nanodots of adhesive for example in an LOM system for rapid prototyping. The recesses 152, of the exemplary arrangement described have a substantially hemispherical form which has the advantage of providing substantially the greatest volume for any given surface area. This form has the further advantage of facilitating the easy interchange of air and adhesive as the recesses pass under the wipe 130. In an exemplary arrangement, wheel 150 having a diameter of 15mm is used. It will be appreciated that the diameter of the wheel may be varied as required. However, the wheel is preferably less that 20mm in diameter, and most preferably in the range of 15-20mm in diameter.

While in the embodiment described the wheel 150 of the adhesive dispenser device has a single row of recesses on the wheel, it will be appreciated that a wheel may comprise more than one row of rows of recesses. Similarly, while in the embodiment described, the adhesive dispenser includes one wheel, in an alternative arrangement a number of wheels could be provided, one or more which may be independently moveable relative to others. Such arrangement would be aimed at increasing the speed of the adhesive application process. Also, it will be understood that while in the embodiment described, the recesses are equally spaced apart, in an alternative arrangement, the recesses spacing could be varied and substantially unequal. Such an arrangement would enable the deposition of different dot patterns depending on which part of the wheel was in contact.

It will be appreciated and understood that what has been described herein are exemplary arrangements of a layered object manufacturing system. Use of such a system provides for the use of water based adhesives to bind successive layers of paper in generation of a three dimensional model.

The invention provides a system and method of applying adhesive to paper which ensures that the paper does not become saturated with adhesive thus minimising warping of the layer or sheet. The warping of the page is minimised by the fact that the quantity of adhesive deposited onto the substrate may be controlled as required. By providing precise control of the amounts of adhesive deposited on a substrate, it is possible to use water based adhesives for example, Polyvinyl Acetate (PVA). The system similarly facilitates the use of different and standard types of paper. The system thus uses conventional and readily available raw materials for example standard office paper and has the advantages of being user-friendly and easy to operate and supply. It will be understood that by providing a LOM process that uses water based adhesives and can be used with conventional paper supplies that recycling and waste issues are less problematic than with existing RP solutions. The paper supply that is used in the LOM process can be waste or discarded paper, and the waste paper from the LOM process can be easily recycled in the same manner as conventional recycling. The discard of water based adhesives is easier than discarding solvents or plastics such as are used in existing RP processes. The system of the invention further provides excellent control on the positioning of the adhesive on a substrate. The density of adhesive laid down may also be controlled as can the size or volume of the dots. These features help to eliminate waste of adhesive. While preferred embodiments have been described with reference to the figures modifications can be made without departing from the scope of the invention which is to be limited solely by the claims. Where integers or components are described with reference to one figure it will be understood that they can be interchanged with those of another Figure without departing from the context of the invention.

The words comprises/comprising when used in this specification are to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers , steps, components or groups thereof.