Patent Publication Number: US-2018043633-A1

Title: System for printing an object and a method for printing an object

Description:
TECHNICAL FIELD 
     The present invention relates to a system for printing an object and a method for printing an object, and particularly, although not exclusively, to a system for printing an object matched with an inserted physical object and a method for printing an object matched with an inserted physical object. 
     BACKGROUND 
     Typical optical devices such as projectors are deployed for projecting an image onto a surface. The projectors create an image by shining a light from an incandescent light bulb through a small transparent lens to a display, or alternatively directing the light to a human retina. The brightness of the image presented on the display depends on the ambient light level and luminous power of the light bulb. 
     In an optical arrangement, the projector and the display are spaced from each other for a minimum projection distance. For example, the projector may be disposed in a direction away from the display i.e. increasing the projection distance to serve as an enlarger, thereby magnifying the image to be displayed. The same amount of light is spread over a larger screen, resulting in a dimmer image throughout the illumination. The projector may thereby provide visual information of an object viewing from one of the views within the three-dimensional space. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, there is provided a method for printing an object comprising the steps of: displaying a two-dimensional representation within a two-dimensional space, wherein the two-dimensional representation is arranged to represent a two-dimensional view of a three-dimensional object within the two-dimensional space; transforming the two-dimensional representation into a plurality of two-dimensional expressions arranged to individually represent a portion of the three-dimensional object; forming the three-dimensional object from a fluid medium arranged to transform its physical state in response to a manipulated illumination exposed thereto, wherein the manipulated illumination exposed to the fluid medium is associated with the plurality of two-dimensional expressions disposed therebetween, and with the inner surface of the printed three-dimensional object being arranged to match the outer surface of a real-world object inserted therein. 
     In an embodiment of the first aspect, each of the represented portions of the three-dimensional object are evenly spaced along at least one of the X, Y and Z axis of the three-dimensional object. 
     In an embodiment of the first aspect, the two-dimensional representation includes a sketch displayed on a design interface. 
     In an embodiment of the first aspect, the sketch includes at least one sketched line. 
     In an embodiment of the first aspect, the sketch further includes at least one additional sketched line associated with the inserting location of the real-world object. 
     In an embodiment of the first aspect, the plurality of two-dimensional expressions includes a plurality of slides. 
     In an embodiment of the first aspect, the method further comprises the step of transforming the sketch into a plurality of slides. 
     In an embodiment of the first aspect, the method further comprises the step of shining the plurality of slides to cure a photo-reactive resin thereby forming the three-dimensional object layer by layer. 
     In an embodiment of the first aspect, the plurality of slides are shined in sequence by a light source to cure the photo-reactive resin gradually. 
     In an embodiment of the first aspect, the thickness of the three-dimensional object layer is manipulated by the light intensity of the light source, the length of exposure under the light source and/or the colour of the slides. 
     In an embodiment of the first aspect, an additional slide is shined by a projector to pause the curing of the photo-reactive resin. 
     In an embodiment of the first aspect, the method further comprises the step of inserting the real-world object or a mold of the real-world object into the photo-reactive resin during the step of printing. 
     In an embodiment of the first aspect, the real-world object or the mold of the real-world object is inserted into the photo-reactive resin when the curing is paused. 
     In an embodiment of the first aspect, the photo-reactive resin includes flexible silicon arranged to facilitate the removal of the printed three-dimensional object. 
     In an embodiment of the first aspect, the method further comprises the step of post-processing the printed three-dimensional object. 
     In an embodiment of the first aspect, the printed three-dimensional object is arranged to undergo a surface treatment. 
     In an embodiment of the first aspect, the surface treatment includes UV exposure and/or sanding. 
     In an embodiment of the first aspect, the method further comprises the step of mixing the photo-reactive resin with conductive gel prior to the shining step such that the formed three-dimensional object is conductive. 
     In an embodiment of the first aspect, the conductivity and touch sensitivity of the conductive three-dimensional object is associated with the ratio of conductive gel to photo-reactive resin, and/or the shape of the object. 
     In an embodiment of the first aspect, the real-world object includes a complex geometric structure. 
     In accordance with a second aspect of the present invention, there is provided a system for printing an object, comprising: a display module arranged to display a two-dimensional representation within a two-dimensional space, wherein the two-dimensional representation is arranged to represent a two-dimensional view of a three-dimensional object within the two-dimensional space; a processing module arranged to transform the two-dimensional representation into a plurality of two-dimensional expressions arranged to individually represent a portion of the three-dimensional object; a printing module arranged to form the three-dimensional object from a fluid medium arranged to transform its physical state in response to a manipulated illumination exposed thereto, wherein the manipulated illumination exposed to the fluid medium is associated with the plurality of two-dimensional expressions disposed therebetween, and with the inner surface of the printed three-dimensional object being arranged to match the outer surface of a real-world object inserted therein. 
     In an embodiment of the second aspect, each of the represented portions of the three-dimensional object are evenly spaced along at least one of the X, Y and Z axis of the three-dimensional object. 
     In an embodiment of the second aspect, the two-dimensional representation includes a sketch displayed on a design interface of the display module. 
     In an embodiment of the second aspect, the sketch includes at least one sketched line. 
     In an embodiment of the second aspect, the sketch further includes at least one additional sketched line associated with the inserting location of the real-world object. 
     In an embodiment of the second aspect, the plurality of two-dimensional expressions includes a plurality of slides. 
     In an embodiment of the second aspect, the processing module transforms the sketch into a plurality of slides. 
     In an embodiment of the second aspect, the plurality of slides are shined to cure a photo-reactive resin thereby forming the three-dimensional object layer by layer. 
     In an embodiment of the second aspect, the plurality of slides are shined in sequence by a light source to cure the photo-reactive resin gradually. 
     In an embodiment of the second aspect, the thickness of the three-dimensional object layer is manipulated by the light intensity of the light source, the length of exposure under the light source and/or the colour of the slides. 
     In an embodiment of the second aspect, an additional slide is shined by a projector to pause the curing of the photo-reactive resin. 
     In an embodiment of the second aspect, the real-world object or a mold of the real-world object is inserted into the photo-reactive resin during the printing. 
     In an embodiment of the second aspect, the real-world object or the mold of the real-world object is inserted into the photo-reactive resin when the curing is paused. 
     In an embodiment of the second aspect, the photo-reactive resin includes flexible silicon arranged to facilitate the removal of the printed three-dimensional object. 
     In an embodiment of the second aspect, the printed three-dimensional object is further post-processed. 
     In an embodiment of the second aspect, the printed three-dimensional object is arranged to undergo a surface treatment. 
     In an embodiment of the second aspect, the surface treatment includes UV exposure and/or sanding. 
     In an embodiment of the second aspect, the photo-reactive resin is mixed with conductive gel prior to shining such that the formed three-dimensional object is conductive. 
     In an embodiment of the second aspect, the conductivity and touch sensitivity of the conductive three-dimensional object is associated with the ratio of conductive gel to photo-reactive resin, and/or the shape of the object. 
     In an embodiment of the second aspect, the real-world object includes a complex geometric structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: 
         FIG. 1  is an illustration showing the display module in accordance with one embodiment of the present invention; 
         FIG. 2  is an illustration showing the printing module in accordance with one embodiment of the present invention; 
         FIGS. 3(A), 3(B), 3(C), 3(D), 3(E), 3(F) , and  3 (H) are illustrations showing the steps for designing an object within the sketch interface in accordance with one embodiment of the present invention; 
         FIG. 4  is an illustration showing the steps of printing an object in accordance with one embodiment of the present invention; 
         FIG. 5  is an illustration showing the physical object placed in the resin during the printing operation in accordance with one embodiment of the present invention; 
         FIG. 6(A)  is an illustration showing the pen inserted to the printed penholder in accordance with one embodiment of the present invention; 
         FIG. 6(B)  is an illustration showing the bottom surface of the pen inserted to the printed penholder in accordance with one embodiment of the present invention; 
         FIG. 6(C)  is an illustration showing the detailed patterns on the bottom surface of the pen are engraved within the inner surface of the printed penholder in accordance with one embodiment of the present invention; 
         FIG. 7  is an illustration showing the post-processing module in accordance with one embodiment of the present invention; 
         FIG. 8  is a schematic diagram showing the overall process of the system in accordance with one embodiment of the present invention; 
         FIG. 9(A)  is an illustration showing a mold wrapped around a finger in accordance with one embodiment of the present invention; 
         FIG. 9(B)  is an illustration showing a mold placed in the resin in accordance with one embodiment of the present invention; 
         FIG. 9(C)  is an illustration showing a printed ring in accordance with one embodiment of the present invention; 
         FIG. 9(D)  is an illustration showing the printed ring fitted with the finger in accordance with one embodiment of the present invention; 
         FIG. 10(A)  is an illustration showing a screw placed in the resin in accordance with one embodiment of the present invention; 
         FIG. 10(B)  is an illustration showing a printed object with internal threads fitted with the outer surface of the screw in accordance with one embodiment of the present invention; 
         FIG. 11(A)  is an illustration showing an assembly structure with a printed part in accordance with one embodiment of the present invention; 
         FIG. 11(B)  is an illustration showing an assembly structure with a printed part mounted to a wall in accordance with one embodiment of the present invention; 
         FIG. 11(C)  is an illustration showing an assembly structure with a printed part for hanging clothes in accordance with one embodiment of the present invention; 
         FIG. 12(A)  is an illustration showing the toy placed in the resin in accordance with one embodiment of the present invention; 
         FIG. 12(B)  is an illustration showing the toy with printed part in accordance with one embodiment of the present invention; 
         FIG. 12(C)  is an illustration showing another toy with printed part in accordance with one embodiment of the present invention; 
         FIG. 12(D)  is an illustration showing printed part swapped between two toys in accordance with one embodiment of the present invention; 
         FIG. 13(A)  is an illustration showing the plastic bottle placed in the resin in accordance with one embodiment of the present invention; 
         FIG. 13(B)  is an illustration showing the printed plastic cap with internal threads fitted with the outer surface of the bottle opening in accordance with one embodiment of the present invention; 
         FIG. 14(A)  is an illustration showing the sketch of a stand with the aiding of the smart phone in accordance with one embodiment of the present invention; 
         FIG. 14(B)  is an illustration showing the perspective view of a stand with the smart phone inserted in accordance with one embodiment of the present invention; 
         FIG. 15(A)  is an illustration showing the steps of printing a solid sphere in accordance with one embodiment of the present invention; 
         FIG. 15(B)  is an illustration showing the printed solid sphere in accordance with one embodiment of the present invention; 
         FIG. 16  is an illustration showing a printed touch sensor in accordance with one embodiment of the present invention; 
         FIG. 17  is an illustration showing a plurality of printed touch sensors in different shapes in accordance with one embodiment of the present invention; 
         FIG. 18(A)  is an illustration showing a printed touch sensor attached to a pair of glasses in accordance with one embodiment of the present invention; 
         FIG. 18(B)  is an illustration showing a pair of glasses with a printed touch sensor attached worn by a user in accordance with one embodiment of the present invention; 
         FIG. 19  is a graph showing the thickness of the printed object against the colour of projected pattern with different cure duration in accordance with one embodiment of the present invention; and 
         FIG. 20  is a graph showing the electric resistance against the ratio of conductive gel and resin of printed object with different shapes in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The inventors have, through their own research, trials and experiments, devised that a low cost stereolithography-based rapid prototyping printing technique allows high-precision fabrication without high-end modelling tools. Advantageously, by mixing everyday physical artifacts with photo-reactive resin and preferably with the addition of liquid conductive gels during the printing process, this advanced technique facilitates the creation of objects that perfectly fit the existing physical objects without any accurate scanning or modelling tools or tolerance adjustment in the hardware. 
     In one example embodiment of the present invention, there is provided a design interface allowing users to design the printed shapes using physical objects as references, a processing module to generate projection patterns from the sketches, and a printing module notifies the user when to place the physical objects in the resin during the printing process. Optionally, the present invention further provides a post-processing unit for surface treating the printed object to enhance the product finishing. 
     Advantageously, the user may be highly engaged with the overall fabrication process. The present invention allows the user to get involved not only the design stage but from the design stage to the printing stage, thereby allows a rapid prototyping of any innovative concepts. 
     With reference to  FIGS. 1 to 2 , there is provided an example embodiment of a system  1  for printing an object, comprising: a display module  100  arranged to display a two-dimensional representation within a two-dimensional space, wherein the two-dimensional representation is arranged to represent a two-dimensional view of a three-dimensional object within the two-dimensional space; a processing module  150  (not shown) arranged to transform the two-dimensional representation into a plurality of two-dimensional expressions arranged to individually represent a portion of the three-dimensional object; a printing module  200  arranged to form the three-dimensional object from a fluid medium  30  arranged to transform its physical state in response to a manipulated illumination exposed thereto, wherein the manipulated illumination exposed to the fluid medium  30  is associated with the plurality of two-dimensional expressions disposed therebetween, and with the inner surface of the printed three-dimensional object being arranged to match the outer surface of a real-world object  80  inserted therein. 
     In this embodiment, the display module  100  comprises a display  10  or a mobile tablet with a design interface  10  for shape designing, and a processing module  150  for transforming a two dimensional representation into a plurality two-dimensional expressions for representing a three-dimensional object. A two-dimensional representation is designed in the form of sketch for displaying within a two-dimensional space. The sketch may be formed by at least one sketched line, or a plurality of sketched lines drawn by a user, for example using a stylus  5 . It will be appreciated by persons skilled in the art that the line may be sketched on a touch screen  10  with user&#39;s fingers or any other drawing tools. 
     With reference to  FIGS. 3(A), 3(B), 3(C), 3(D), 3(E), 3(F) , and  3 (H), there is shown an example embodiment showing the steps for designing a print object  80  e.g. a penholder  80 , and transforming the design into a plurality of slides  17  (as shown in  FIG. 3(G) ) for printing. These slides  17  each present a portion of the object and are evenly spaced along at least one of the X, Y and Z axis of the printed object  80 . 
     In this example embodiment, the user first draw the bottom shape of an object, such as basic shape drawings and freehand drawings in the canvas of the design interface  10  as shown in the sketch  11  of  FIG. 3(A) . The user activates the canvas in the top view where the processing module  150  automatically creates two cloned sketches  12   a  and  12   b  of the sketch  11  in the bottom view, one for editing and the other for reference. For example, the user may resize the top shape sketch  12   a  with reference to the bottom shape sketch  12   b.    
     Advantageously, a physical object  13  e.g. a pen  13 , may be placed on top of the sketch interface  10  to assist the user to adjust the shapes represented by the sketches  12   a  and  12   b , thereby ensuring the three-dimensional object designed may accommodate the physical object  13  as shown in  FIG. 3(B) . For example, the user may employ two marker pens to assist him in resizing the shape of the penholder sketch, to ensure the printed penholder  80  have enough space for receiving the stationaries  13 . 
     With reference now to  FIG. 3(D) , the design interface  10  may now switch to the side view where the user may design the height of the penholder  80 . For example, the user may draw two strokes  14   a  and  14   b  to indicate the bottom and the top of the penholder  80  as shown in  FIG. 3(D) , and the processing module  150  may generates two straight lines  14   c  and  14   d  based on the size of the shapes in bottom and top views represented by sketches  12   a - 12   b  and the positions of the two strokes  14   a - 14   b  drawn by the user as shown in  FIG. 3(E) . The vertical distance between the two straight lines  14   c  and  14   d  indicates the height h 1  of the penholder  80 . Advantageously, the user may design the height of the penholder  80  with the aiding of the pen  13 . 
     Preferably, the sketch may further include at least one additional sketched line  15  associated with the inserting location of the pen  13 . With reference to  FIG. 3(E) , the display interface  10  may further allow the user to draw an additional sketch line  15  between the two strokes  14   c  and  14   d , thereby indicating the location of the pen  13  to be inserted. For example, the pen  13  may be placed on top of the sketch interface  10  again to assist the user to draw the sketch line  15 , in order to determine the height of the object to be placed h 2  with reference to the bottom of the penholder  80 , as shown in  FIG. 3(E) . 
     Optionally, the sketch line  15  may be presented in other colours, e.g. red to contrast from the other sketches in the sketch interface  10 . It will be appreciated by persons skilled in the art that multiple sketch lines may be used to indicate the insertion of a plurality of physical objects  13 . 
     With reference to  FIG. 3(F) , upon the heights of the object h 1  and location for the insertion of the pen h 2  have been defined, the user may then design the slopes of the penholder  80  by sketching two sketches  16   a  and  16   b  to connect between the bottom and top lines  14   c  and  14   d . The processing module  150  may then analyse the design and calculate the number of interval layers  17  that are needed to be printed based on the design of the slope  16   a  and  16   b  and the height h 1 , thereby generating a plurality of two dimensional expressions  17 , preferably in the form of slides  17  between the bottom and top lines  14   c - 14   d , as shown in  FIG. 3(G) . 
     In this example embodiment, the processing module  150  may generates one interval layer in a desirable thickness, e.g. every 2 mm between the bottom and top lines  14   c  and  14   d . Advantageously, an additional slide  18  is formed between the bottom and top lines  14   c - 14   d  as shown in  FIG. 3(G) , for representing a layer corresponding to the sketch line  15  shown on the side view in  FIG. 3(F)  and indicating the location of the pen  13  to be inserted. 
     The plurality of slides  17 , each individually represent a portion of the penholder  80  viewed from the top as shown in  FIG. 3(H) . The shape in each slide  17  is scaled according to its distance from the bottom line  14   d . The processing module  150  may further converts the modelled object into a sequence of slides  17 , and automatically set the duration in which each slide  17  will be projected under a light source  20  of the printing module  200 . 
     With reference to  FIG. 2 , the printing module  200  comprises a light source  20 , a fluid medium  30 , and a computer  40 . The light source  20  may be a projector  20 . Preferably, the fluid medium  30  is a photo-reactive resin  30  filled within a container  32 . Optionally, the light source  20  may be disposed within a transparent case  22 , e.g. an acrylic case  22 , and preferably projected upward to the container  32  disposed on the acrylic case  22  thereby providing a manipulated illumination to shine and cure the photo-reactive resin  30 . It will be appreciated by persons skilled in the art that the light source  20  may be projected in any directions to provide illumination to the resin  30  without the transparent cases  22 . Preferably, the maximum illumination is achieved by a minimum project distance d of the light source  20  from the resin container  32 . 
     Optionally, the base of the resin  30  may be made of flexible silicon  34  for facilitating the easy-removal of the printed object from the container  32  for post-processing. 
     In this embodiment, the plurality of slides  17  obtained from the processing module  150  are projected through the light source  20  to the resin  30  in a desired sequence for curing the resin  30  layer by layer, thereby forming the designed object in the design module  100  layer by layer. The thickness of each layer is manipulated by the illumination through the intensity of the light source  20  and the duration in which the resin  30  is cured under. 
     With reference to  FIG. 4 , there is shown an example embodiment showing the steps for printing a penholder  80  designed in the example embodiment illustrated in  FIGS. 3(A), 3(B), 3(C), 3(D), 3(E), 3(F) , and  3 (H). In this example embodiment, a plurality of slides  17  (ten slides in this example) are exported from the computer  40  and subsequently projected under the light source  20  towards the resin  30 . 
     Optionally, after the first five slides  17  have been projected to cure the first few layers of the printed object  80  (not shown), the sixth slide  18  which corresponds to the sketched line  18  as depicted in  FIG. 3(G)  is exported and turned red by the computer  40  before projecting to the resin  30  to pause the printing process. Advantageously, the resin  30  would not be cured in the red light spectrum. Therefore, the user may place the pen  13  in the resin  30  and resume the remaining printing operations. The resin  30  is illuminated by the rest of the slides  17  under the light source  20  to complete the printing, as shown in  FIG. 5 . The detailed patterns on the bottom surface and the outer surface of the pen  13  are engraved and matched within the inner surface of the penholder  80 , as shown in  FIGS. 6(A), 6(B) , and  6 (C). 
     Advantageously, the thickness of each printed object  80  layer may be manipulated by the length of light exposure and the colour of the projected pattern under the light source  20 , such that computer  40  may compute the colour of the object and the advance timing of the slides  17  based on the thickness specified by the user in the sketch interface  10 . 
     Without wishing to be bound by theory, the inventors have discovered that thickness of the printed object  80  has a positive correlation with the RGB value of the projected colour and the increment of the length of the light exposure, and further devised that the thickness of each printed object layer (h) may be predicted by a mathematical polynomial model based on a particular setting of grayness of the projected colour (c) i.e. the projected colour, and projected duration (t) as below: 
         h=− 0.00280 t   3 −0.00125 t   2   c+ 0.0000477 tc   2 +0.000167 c   3 +0.300 t   2 +0.0125 tc− 0.00941 c   2 −3.53 t+ 1.66 c− 90.6  (1)
         Residual Sum of Square: rss=9.91   h (mm): height of the printed model   t (minute): length of light exposure   c: grayness of the projected color (setting the RGB values equally)       

     The inventors have further validated the above mathematical model and the printing module  200  of system  1  by comparing the resulting thickness of a plurality of cured resin  30  formed by slides  17  projected through light source  20  as shown in  FIG. 19  with the designed thickness. Advantageously, the thickness of the printed object  80  achieved marginally low errors (rss=1.63) with reference to the desired thickness, and thus validated the polynomial model in equation 1 as shown in the result of Table 1 below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Validation of Equation 1 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Calculated 
                 Designed 
                 Printed 
                   
               
               
                 Time 
                 Color 
                 Height 
                 Height 
                 Error 
               
               
                 (minute) 
                 (R, G, B) 
                 (mm) 
                 (mm) 
                 (mm) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 10 
                 (152, 152, 152) 
                 6 
                 5.93 
                 0.07 
               
               
                 5 
                 (249, 249, 249) 
                 10 
                 9.35 
                 0.65 
               
               
                 15 
                 (212, 212, 212) 
                 15 
                 14.23 
                 0.77 
               
               
                 8 
                 (252, 252, 252) 
                 17 
                 17.66 
                 0.66 
               
               
                 12 
                 (255, 255, 255) 
                 24 
                 24.42 
                 0.42 
               
               
                   
               
            
           
         
       
     
     With reference to  FIGS. 7 to 8 , the system  1  may optionally comprise a post-possessing module  300  to post-process the obtained object  80  from printing module  200 . The post-possessing module  30  may comprise a washing container  50  e.g. filling with alcohol  50   a  or water  50   b , a UV light box  60  and a sand paper  70 . The user gently peels the model off the container base  30  facilitated by flexible silicon  34 , washes off the remaining liquid resin  30  on the printed object surface, applies UV exposure by putting the printed object in the UV light box  60 , for example a 30W UV light tube for 3 minutes, and finally sands the surface of the printed object with the sand paper  70  to provide a fine finishing. 
     It will be appreciated by persons skilled in the art that the physical object  13  may be placed within the resin  30  at any time i.e. different stages of the printing process. Alternatively, when the physical object  13  is placed at the beginning of the printing process, a printed object  80  with a through hole fitting the contour of the physical object  13  may be formed. 
     With reference to  FIGS. 9(A), 9(B), 9(C) , and  9 (D), the physical object  13  may be a mold  19  of the real-life object  13 . For example, a mold  19  of human finger  13  created with accessible materials such as paper, plastics or clay may be placed within the resin  30 , thereby creating a well-fitting ring  80 . For example, the user may make a ring  80  that matches his/her finger as shown in  FIGS. 9(A), 9(B), 9(C) , and  9 (D). The user first create the wrapping  19  that fit the finger as shown in  FIG. 9(A) , designing the shape of the ring through the sketch interface  10 , printing the ring with the wrapping  19  inserted into the resin  30  of the printing module  200  as shown in  FIG. 9(B) , and post-processing the printed ring  80  by the post-processing module  300 . 
     With reference to  FIGS. 10(A) to 10(B) , the physical object  13  may be an object with complex geometric structures or surfaces such as screw thread  13  or any other parts for industrial applications. The screw  13  is placed within the resin  30  as shown in  FIG. 10(A) , such that the resin  30  may be cured under the light source  20  around the screw  13  and thereby creating a printed object  80  with internal threads that fit the outer surface of the screw  13  as shown in  FIG. 10(B) . Advantageously, this embodiment is highly desirable, as the printed object  80  may fit the screw  13  without any measuring and modelling of the screw  13  or knowing the detailed specification of the screw  13 . 
     With reference to  FIG. 11(A) , the physical object  13  may be part of an assembled structure  90  comprising detailed original parts  13  such as screw threads, special screws, screw bolts and missing parts for fitting to these detailed parts. The user may print a tiny part  80  as a substitution of the missing parts for fitting to the original parts  13  of the assembled structure  90 . For example, the printed part  80  may accommodate the screw threads and thereby resemble the assembled structure  90  such as a wall mounted hook for hanging clothes as shown in  FIGS. 11(B) and 11(C) . 
     With reference to  FIGS. 12(A), 12(B), 12(C) , and  12 (D), the physical object  13  may be a toy  13  or any other objects for personal entertainment. New part  80  for toy  13  may be designed in the sketch interface  10 . The existing toy  13  may be placed in the resin  30  of the printing module  200  during printing as shown in  FIG. 12(A) , such that the printed objects  80 , i.e. the new parts  80  may fit into the slots in the original toy  13  as shown in  FIGS. 12(B) and 12(C) . Advantageously, the inner surface of the printed parts  80   a  and  80   b  may be fitted to the outer surface of different toys  13   a  and  13   b  manufactured from the same company with the same standard as shown in  FIG. 12(D) . 
     With reference to  FIGS. 13(A) to 13(B) , the physical object  13  may be a plastic bottle  13  without a cap. Different bottle caps may be sketched in the sketch interface  10  and printed through the printing module  200 . In this example embodiment, the star-shaped printed cap  80  with internal threads that fit the outer surface of the bottle  13  opening is formed by placing the bottle  13  into the resin  30  during the printing process as shown in  FIG. 13(A) . The printed plastic bottle cap  80  may facilitates the reuse of plastic bottles, and also differentiate the bottle from other. In one example, the different caps may be used for creating different medicine bottles for vision-impaired person. 
     With reference to  FIGS. 14(A) to 14(B) , the physical object  13  may be a mobile phone  13 . The shape of a stand is sketched in the sketch interface  10  as shown in  FIG. 14(A) . With the aiding of the mobile phone  13 , the user may trace the edge of the phone  13  to ensure the slot of the printed stand  80  fit the size of the mobile phone  13  well as shown in  FIG. 14(B) . 
     It will be appreciated by persons skilled in the art that the printed object  80  may be a solid object without slots or opening for receiving any physical objects. For example, the slides  17  may be projected under the light source  20  to form a solid half sphere  80  as shown in  FIGS. 15(A) and 15(B) . 
     In one example embodiment, the photo-reactive resin  30  filled within the container  32  may be mixed with conductive gel  36 , thereby forming a mixture  38  for creating conductive printed object  80  that can be used as capacitance-based touch sensors as shown in  FIG. 16 . Selectively, the conductive gal  36  may be any gels widely used in cosmetic and medical treatments. 
     Without wishing to be bound by theory, the inventors have discovered that the electric resistance is significantly reduced with the increase in portion of the conductive gel in the mixture  38 , and also varies among the triangle, circle and rectangular shape as shown in  FIG. 20 . The ratio of conductive gel  36  to photo-reactive resin  30  may be 1:3, 1:2, 1:1 or 2:1 etc., and more preferably to be 1:2 as the surface roughness increases along with the increment of conductive gel  36  in the mixture  38  to provide stronger effect on light scattering. 
     In one example embodiment, the conductivity and the touching sensitivity may be manipulated by the shape of the printed object  80 , thereby assigning a unique touch ID to each of the printed objects  80 . Advantageously, the printed object  80  may detect the number of touch points, thereby facilitating the design of multi-touch interaction. 
     With reference to  FIG. 17 , the various electric resistances of the printed object  80  from the mixture  38  may provide interactivity, such that objects  80  with different resistances may be created in different shapes. Advantageously, the three conductive objects  80   a ,  80   b  and  80   c  in this embodiment, may be connected to the normal capacitive touch-sensing circuit to form different touch sensor circuits. 
     With reference to  FIGS. 18(A) and 18(B) , the user may create a tiny accessory for his glasses using the mixture  38  of photo-reactive resin  30  and conductive gel  36 , for turning his glasses into a pair of glasses with touch-sensitive capabilities. In this example embodiment, the user may use sketch the shape of the sensor in the sketch interface  10  with the aiding of the glasses  13 . A plastic sheet  19  is then wrapped around the earpiece of the glasses  13  and inserted into the mixture  38  for printing a touch sensor  80 . The formed touch sensor  80  may be fitted and attachable to the glasses  13 , thereby developing an interactive demo. Advantageously, the present invention may shorten the iteration of prototyping for designers by allowing the designers to create a nice proof of concept in the first iteration without any tedious modelling and printing processes. 
     It will be appreciated by person skilled in the art that the present invention may be applied in mechanical fabrication, toy design, wearable design, interactive system prototyping, bioengineering, biomechanics and healthcare etc. 
     It will be appreciated by persons skilled in the art that the present invention may also be applied in high-precision assembly mechanisms fabrication, including non-permanent assembly such as screw threads in valve structures, and permanent assembly such as shaft-hole sockets and pipes without requiring any high-end modelling tools. 
     It will be appreciated by persons skilled in the art that the present invention may be further applied to prosthesis for delivering a printed part that perfectly fit the bodies of disabled patients. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 
     Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.