WO2004077185A2

WO2004077185A2 - Method and system for producing an article

Info

Publication number: WO2004077185A2
Application number: PCT/DK2004/000105
Authority: WO
Inventors: Bo Thoning Kristiansen; Kasper Fedde Krogh; Ulrik Solberg Lund
Original assignee: Lego A/S; Interlego Ag
Priority date: 2003-02-27
Filing date: 2004-02-17
Publication date: 2004-09-10
Also published as: WO2004077185A3

Abstract

A method of producing an article based on a physical model comprising the steps of scanning the physical model to obtain a set of scan data; converting the scan data into surface data representing surface characteristics of the model; generating instruction data from the surface data suitable for causing a computer-controlled machine tool to produce an article having surface characteristics corresponding to the surface characteristics of the model; simulating executing the generated instructions on a data processing system resulting in a set of simulated surface data representing a simulated as-machined article; and generating a representation of the updated surface data suitable for producing the article.

Description

Method and system for producing an article

This invention relates to a method of and a system for producing an article based on a physical model.

In many production areas, the generation of articles from a physical model is an important step in the production process.

Computer Aided Design / Computer Aided Manufacturing (CAD/CAM) tools are widely used for the design of articles and the generation of machine instructions for numerically controlled (NC) tools to produce articles according to the computer-aided design. However, there are a number of situations where this procedure is not feasible or at least undesired. For example, when articles are to be designed that represent intricate details, complex free-form shapes, living features, or the like, it is cumbersome to design such articles on the computer. In particular, when producing articles which resemble humans, animals, plants or other organic material, it is difficult to capture the organic or living features of the model with a CAD program or other drawing program.

Another possibility is to design the article as a physical model, e.g. a clay model, or a model made from another material. In fact, many designers prefer the preparation of physical models in order to create high-quality articles, in particular when modelling complex free forms. However, it is a difficult process to translate a physical model into machine instructions for an NC tool or into another data format suitable for production of articles resembling the physical model.

US patent no. 5,552,992 discloses a method and system of reproducing an article from a physical model. This prior art method comprises laser scanning of a clay model. From the resulting scan data, mathematical formulas representing the surface of the model are generated and, subsequently, the mathematical formulas are translated into instructions for a numerically- controlled machine tool to cut a representation of the article. Finally, the article is produced by an NC tool based on the generated instructions.

It is a problem of the above method that it is difficult to produce the desired article in a reproducibly high quality, in particular when the physical model comprises a high level of fine details.

The above and other problems are solved when a method of producing an article based on a physical model, the method comprising the steps of

(a) scanning the physical model to obtain a set of scan data;

(b) converting the scan data into surface data representing surface characteristics of the model; (c) generating instruction data from the surface data suitable for causing a computer-controlled machine tool to produce an article having surface characteristics corresponding to the surface characteristics of the model

is characterised in that the method further comprises the steps of

(d) simulating executing the generated instructions on a data processing system resulting in a set of simulated surface data representing a simulated as-machined article;

(e) generating a representation of the updated surface data suitable for producing the article.

It has been realised by the inventors that by simulating the generated instructions and, on the basis of the simulation results, generating surface data representing the simulated as-machined article, the quality of the produced article may be considerably improved.

In particular, as the resulting machine instructions not only reflect the features of the physical model but also the limitations of the simulated NC tool, the articles may subsequently be produced with a high level of reproducibility and a high quality without undesired artefacts.

It is a further advantage of the invention that it provides a data format of the model design which may directly be used in the further production without further processing, tuning, or the like. Hence the results may directly be introduced into the subsequent production process.

The scan data may be generated in any suitable data format. Examples of such data formats include point data representing the geometric locations of a plurality of surface points, polygon data representing a plurality a polygons, grid data, etc. Preferably, the data format is a standard data format facilitating import in a variety of commercial software packages.

The term surface data comprises any suitable representation of the surface of the scanned model. For example, such a representation may comprise a set of mathematical formulae defining respective patches of the surface, e.g. Non-Uniform Rational B-spline (NURBS) patches. The surface data may be stored in any suitable data format, preferably a data format suitable for input in standard CAD/CAM software packages.

The simulation of the machining tool operations may directly create simulated surface data. In another embodiment, the simulation step may create simulation data representing the surface characteristics of the simulated as- machined article. In a subsequent step, the simulation data is used as an input for the generation of the surface data.

Hence, according to one embodiment of the invention, the step of simulating executing the generated instructions further comprises - simulating executing the generated instructions on a data processing system resulting in a set of simulation data representing a simulated as- machined article; - generating modified surface data from the simulation data, the modified surface data representing the surface characteristics of the simulated as- machined article.

The simulation data may comprise any data format suitable as an input to a software package performing the generation of the surface data. For example, the same data format as the above scan data may be used, i.e. point cloud data, grid data, polygon data, or the like. Examples of suitable data formats comprise ASCC1I data formats, STL, etc. It is an advantage of this embodiment that standard file formats may be used allowing the utilisation of standard software packages for generating surface data from point cloud data, polygons, or the I ike, and CAD/CAM software packages for processing the generated surface data.

The instruction data may be generated in any data format suitable for being interpreted by a numerically controlled machine, e.g. data defining tools paths. Examples of such data formats comprise G-Code, DIN/ISO, Heidenhain, or the like.

In a preferred embodiment of the invention, the step of generating instruction data further comprises selecting a predetermined minimum radius determining a maximum curvature of the surface of the article to be produced.

Hence, by defining a maximum curvature of the model surface, the subsequent production process is greatly facilitated. In this step a curvature may be selected which is suitable for both the features of the model as desired by the model designer as well as the limitations of the tools used for production.

In a further preferred embodiment, the step of simulating executing the generated instructions comprises simulating the generated instructions with a tool of a predetermined tool size corresponding to the selected minimum radius.

The maximum curvature is defined by defining a minimum radius corresponding to the size of the tool to be used for producing the article. The determined tool size is further used in the subsequent simulation step, resulting in simulation data corresponding to an article produced with the corresponding tool. Hence, by subsequently modifying the surface data based on the simulation data, the resulting modified surface data corresponds to an article produced with the selected tool size, thereby ensuring a consistently reproducible production process of the article with a predetermined tool and, at the same time, preserving the complex structures of the model design.

In another preferred embodiment, the article is a mould having one or more parting lines and the step of generating instruction data further comprises selecting respective positions of the one or more parting lines.

Many items are produced by a forming process using a mould. In order to be able to remove the formed item from the mould, the mould is equipped with a number of parting lines. In order to ensure that the position of the parting lines is substantially not visible on the final article, a careful positioning of the parting lines and a careful design of the machining instructions is important. According to the invention this is achieved by defining the parting lines prior to the simulation process, thereby ensuring that the simulated as-machined surfaces have a suitable design around the parting lines. In one embodiment, the parting lines are defined by a CAD program in response to corresponding user commands.

It is an advantage of the invention that the simulated machining process ensures that the formed item can be removed from the mould without damaging the item. In one embodiment, the step of generating instruction data comprises generating instruction data suitable for causing a computer-controlled machine tool to produce an article having a negative surface with respect to the surface of the physical model. Depending on the subsequent production process, a positive and/or negative form model is required as a basis. It is an advantage of the invention that both negative and positive form models may be generated with consistently high quality. Here, the term positive form model refers to an item having an outer surface defined by the scanned surface; the corresponding surface will also be referred to as positive surface. A negative form model refers to a form model defining a cavity with a surface corresponding to the scanned surface, e.g. a mould for producing an article having a surface corresponding to the scanned surface. The cavity surface will also be referred to as a negative surface.

In yet another embodiment of the invention, steps (c) and (d) are repeated at least once with the modified surface data as an input and resulting in further modified surface data. By repeating the process of surface data generation, generating a CAM program, simulating the CAM program, the quality of the as-machined model may iteratively be improved, e.g. by optimising the combination of parting line positions and tool size, or the like.

In a further preferred embodiment, step (d) is performed at least once to generate a set of simulated surface data representing a simulated as- machined positive form model and at least once to generate a set of simulated surface data representing a simulated as-machined negative form model. By simulating a machining of the surface of the item as a positive and as a negative surface, a smooth design of the article, in particular around parting lines, is achieved while avoiding undercuts, i.e. complexities in the design of a mould which prevents the removal of the article from the compression mould.

When the step of scanning the physical model comprises video scanning the physical model, a simple scanning method is achieved which uses visible light and generates high quality scan data. However, alternatively or additionally other scanning techniques may be employed, for example laser scanning or other 3D scanning techniques suitable for capturing the surface characteristics of a physical model, e.g. scanning techniques using electromagnetic radiation within and/or outside the visible part of the electromagnetic spectrum.

The present invention can be implemented in different ways including the methods described above and in the following, a system, and further product means, each yielding one or more of the benefits and advantages described in connection with the first-mentioned method, and each having one or more preferred embodiments corresponding to the preferred embodiments described in connection with the first-mentioned method and disclosed in the dependant claims.

The invention further relates to a system for producing an article based on a physical model, the system comprises

a scanning system for scanning the physical model to obtain a set of scan data;

a data processing system adapted to convert the scan data into surface data representing surface characteristics of the model; and to generate instruction data from the surface data suitable for causing a computer-controlled machine tool to produce an article having surface characteristics corresponding to the surface characteristics of the model.

The data processing system is further adapted

- to simulate executing the generated instructions resulting in a set of simulated surface data representing a simulated as-machined article; and

- to generate a representation of the updated surface data suitable for producing the article. The invention further relates to a method of facilitating producing an article based on a physical model, the method comprising the steps of

(a) receiving a set of scan data representing a scanning of the physical model;

(b) converting the scan data into surface data representing surface characteristics of the model;

(c) generating instruction data from the surface data suitable for causing a computer-controlled machine tool to produce an article having surface characteristics corresponding to the surface characteristics of the model;

It is noted that the features of the method described above and in the following may be implemented in software and carried out in a data processing system or other processing means caused by the execution of computer-executable instructions. The instructions may be program code means loaded in a memory, such as a RAM, from a storage medium or from another computer via a computer network. Alternatively, the described features may be implemented by hardwired circuitry instead of software or in combination with software.

The invention further relates to a data processing system adapted to perform the method described above and in the following.

The invention further relates to a computer program comprising program code means for performing all the steps of the method described above and in the following when said program is run on a computer.

The invention further relates to a computer program product comprising program code means stored on a computer readable medium for performing the method described above and in the following when said computer program product is run on a computer.

The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawing, in which:

fig. 1 schematically shows a system for producing an article based on a physical model according to an embodiment of the invention; and

figs. 2a-c show flow diagrams of examples of a method of producing an article based on a physical model according to an embodiment of the invention.

Fig. 1 schematically shows a system for producing an article based on a physical model according to an embodiment of the invention. The system comprises a scanning station 101 , a data processing system 102 and a numerically controlled machine 103.

The scanning station 101 comprises a support table 105 for placing the model 106. The scanning station further comprises a light source 108 and two video cameras 104a and 104b. The cameras and the light source are mounted on a common support arrangement 107 which, preferably, is further connected to the support table 105. This ensures a stable relative positioning of the cameras, the light source and the support table. Preferably, the support arrangement 107 is made of a material which is insensitive to vibrations and temperature variations. The cameras 104a-b and the light source are controlled by a controller 109 which further comprises an interface for connecting the scanning station to the data processing system 102, e.g. via a serial or parallel port. The scanning station is arranged to allow a positioning of the model 106 in different relative orientations relative to the light source and the cameras such that the surface of the model may be scanned from different sides and different angles. For example, this may be achieved by providing a support table which may be rotated and tilted and, for example, by mounting the model 105 in a frame (not shown) which may be rotated along different axes.

The light source 108 may be any suitable light source illuminating the model. For example, the light source may comprise a halogen lamp and an optical system for collimating and/or focussing the emitted light onto the model. The light source may further be adapted to emit light with a varying spatial intensity distribution, e.g. by providing a light pattern comprising alternating dark and light stripes.

The light reflected from the model 106 is detected by the video cameras 104a-b. By providing two cameras 104a-b in a predetermined spatial relationship, stereo vision is achieved.

It is noted that other scanning devices may be utilised, e.g. a scanning station using a different number of cameras and/or a different number and/or type of light sources, etc.

The controller 109 receives the video signals form the cameras 104a-b and forwards the signals to the data processing system. In some embodiments, the cameras and/or the controller perform some signal processing, such as A/D conversion, combining the respective video signals from cameras 104a and 104b into a combined signal, or the like. Alternatively or additionally, some or all of the signal processing is performed by the data processing system 102, e.g. by means of a special data acquisition board.

The scanning station may be any suitable known scanning station, for example the GOM Atos II 3D digitizer from GOM mbH, Braunschweig, Germany.

The data processing system 102 comprises a computer 115, a display 117, a keyboard 118 and a computer mouse 116 and/or other input devices, e.g. other pointing devices. For example, the computer may be a standard PC or workstation. The data processing system 102 receives the scan data from the scanning station, e.g. via a serial or parallel connection, via a local area network, or the like. In one embodiment, the computer is equipped with a data acquisition board for receiving and processing the scan signals. The data processing system further performs the generation of surface data, the generation and simulation of CAM programs, and the modification of surface data based on the simulation results. As will be described in greater detail below, this may be achieved via one or more software packages which, preferably, communicate via standard file formats. For example, the received scan data may be saved as a file on the hard disk of the computer, on a file server or on any other suitable storage medium. The software packages used to perform the subsequent processing steps may be executed on the computer one by one, each reading a data file as an input and generating a corresponding output file which may be read by the subsequent software package. Alternatively, one or more of the software packages may be executed simultaneously and dynamically exchange data. Alternatively, the data processing system may comprise a number of computers, e.g. connected via a computer network, each of which adapted to perform one or more steps of the process. Preferred embodiments of the process performed by the data processing system according to the invention will be described in greater detail in connection with figs. 2a-c.

The data processing system 102 generates instructions for controlling the tool path of a computer numerically controlled (CNC) machine 103. The instructions are forwarded to the CNC machine 103, e.g. via a direct communications link, such as a serial or parallel port, a computer network, by storing it on a storage medium, such as a diskette, or the like. The CNC machine 103 comprises a controller 111 which receives the instructions and translates them into control signals for controlling the actual machine 112. The machine 112 comprises a predetermined tool 114 for modifying a work piece 113. According to the instructions generated by the data processing system, the machine is controlled to produce an article 114 resembling the original physical model 106, but possibly in a different size.

Figs. 2a-c show flow diagrams of examples of a method of producing an article based on a physical model according to an embodiment of the invention. In the examples of figs. 2a-c it is assumed that the article is a mould for production of plastic items, such as plastic toy models, building blocks of a toy construction set, etc.

In the example of fig. 2a, the initial step 201 comprises the creation of a physical model by a designer, e.g. a clay model or a model made of another material. As the model is optically scanned, the model may be made of a formable material, such as clay. The model may be made in the same or in a different size as the intended article to be produced. In particular, when the final article is small, e.g. a few centimetres or even less than a centimetre, and/or comprises a high level of details, the model is preferably larger than the final article, e.g. 2-3 times the size of the article or even larger.

In the subsequent step 202, the model is scanned on a scanning station, e.g. a scanning station as described in connection with fig.1. Depending on the scanning equipment, a plurality of scans from different angles is performed providing scans of all parts of the surface and providing sufficiently detailed geometrical information. With a scanning station as described in connection with fig. 1 , good results have been achieved with 20-25 scans per model. However, depending on the requirements of spatial resolution and precision, a different number of scans may be used.

It is understood, that the scanning process may further comprise an initial calibration process. In the example of the scanning station of fig. 1 , the cameras may require calibration, e.g. by initially scanning one or more reference items. Furthermore, the model may need to be prepared for the scanning process. In one embodiment, the model is sprayed with a white powder to increase the quality of the scan result. Furthermore, a number of markers, e.g. in the form of white circles, dots, or the like, may be placed at certain locations of the model, thereby providing reference points for the subsequent data processing, such as the combination of different scans into a combined data set.

Furthermore, depending on the requirements on the precision of the scanning, the scanning is preferably performed in a controlled environment providing constant temperature, humidity, and light conditions, in order to avoid introduction of scan errors due to variations in temperature, external light, etc.

Using the above method, the inventors have achieved precisions of approximately 5μm.

In the subsequent step 203, a first software package is used to process the raw scan data. The point cloud data of the individual scans are combined to a combined set of point cloud data representing the model. Furthermore, noise reduction algorithms and/or other corrections may be performed on the point data in order to further reduce errors introduced by minor misalignments, missing data points, errors introduced by the scanning process, etc. The resulting point cloud data is stored, preferably as a standard file format, e.g. in XYZ / ASCII format, or the like.

In the subsequent step 204, a second software package is used to read the generated point cloud data and to generate surface data from the point data. This step includes representing the surface of the model by a set of mathematical formulas representing the surface of the object. In one embodiment, the point cloud data is transformed into polygons and, subsequently, the polygons are transformed into a network of NURBS patches, thereby representing the surfaces in a format suitable as an input for a CAD software package. In one embodiment, the second software package is the Geomagic software from Raindrop Geomagic, Inc., Research Triangle Park, NC, USA. The resulting surface data may be provided as a data file, preferably in standard file format suitable for importing the data into a CAD/CAM software package, e.g. IGES, 3DS, etc.

In the subsequent step 205, the minimum radius for the surface curvature of the article to be produced is determined. The minimum radius is determined such that the details of the model are still sufficiently reproduced and a reproducible production with sufficiently high quality is possible with a tool of a corresponding size, such as a milling tool corresponding to the minimum radius, e.g. a milling tool having a radius between 0.3 mm and 3 mm, e.g. 1 mm. This step further ensures that the generated CAD file and the actual produced article correspond to each other as closely as possible.

In step 206, a third software package, e.g. a CAD/CAM package, is used to define the parting lines of the article and the CAD representation is adjusted to ensure that formed items may be removed from the mould without damaging the item. For example, the third software package may be a standard CAD/CAM package, e.g. software packages such as Unigraphics, Tebis, Powermill, or the like .

In step 207, the resulting CAD model is used as an input for generating a CAM program for a numerically controlled machine. The determined minimum radius is a further input to the CAM program. Preferably, the above third software package is directly used for the generation of the CAM program.

In step 208, a simulation software package is used to simulate the generated CAM program, i.e. to generate a digital representation of an article as it would be machined based on the generated CAM program and with the tool size determined in step 205. The simulated as-machined article may be represented as polygons or in any other suitable format, such as a set of point cloud data similar to the point data originally generated by the scanning process. However, the simulated data incorporates the features introduced by the simulated production process. In one embodiment, the simulation software package is the Vericut software package from CGTech, Irvine, California.

In step 209, the second software package is used to generate the surface data corresponding to the simulated data. In one embodiment, this is achieved by generating new surface data based on the simulated data. In an alternative embodiment, the NURBS surface data from step 204 is used as a starting point for an incremental adjustment of the surfaces.

In step 210, an updated CAM program is generated based on the updated surface data, resulting in a CAM program for producing an article which reproducibly yields an article having the surface characteristics of the digital model.

Finally, in step 211 , the resulting CAM program is exported in a suitable file format for transfer to a CNC machine which produces the actual article.

Alternative or additionally, the result of the process may be stored in a different data format. For example, the NURBS surfaces may be stored for future use. Similarly, the polygon data may be stored, e.g. as a STL file suitably for rapid prototyping or the like.

It is further noted that, alternatively, the above process may be performed using different software packages. Furthermore, some of the above steps may be combined in a smaller number of software packages.

Fig. 2b shows another example of a method of producing an article based on a physical model according to an embodiment of the invention. The steps of the process depicted in fig. 2b correspond to the respective steps of the process of fig. 2a, where same numbers identify corresponding steps. In contrast to fig. 2a, the method of fig. 2b comprises a further iteration: After creating a physical model (step 201), scanning the model (step 202), postprocessing the obtained scan data (step 203), and generating surface data (step 204), the minimum radius of the surface of the article to be produced is defined (step 205), as was described in connection with fig. 2a. Subsequently, a CAM program is generated (step 207) and the execution of the CAM program is simulated resulting in a set of simulation data (step 208). Based on the simulated data, the surface data is updated (step 209) as described above. Subsequently, the parting lines are selected (step 206) and the steps of programming, simulating, and surface updating are repeated. The resulting surface data is used as a basis of the final CAM programming step 210, and the generated CAM program is exported in a suitable format (step 211).

Fig. 2c shows yet another example of a method of producing an article based on a physical model according to an embodiment of the invention. The steps of the process depicted in fig. 2c correspond to the respective steps of the process of fig. 2a, where same numbers identify corresponding steps.

According to this embodiment, an initial set of surface data is created starting from a clay model, as described in connection with fig. 2a: After creating a physical model (step 201), scanning the model (step 202), and postprocessing the obtained scan data (step 203), the scan data is transformed into surface data (step 204) and loaded into a CAD/CAM software package, a minimum radius of the surface of the article to be produced is defined (step 205), and the parting lines are defined (step 206), as was described in connection with fig. 2a. The subsequent steps of generating a CAM program, simulating the CAM program, and updating the surface data based on the simulation results are iterated twice: In a first iteration the generation of a positive form model having the desired surface is simulated and in a second iteration the generation of a negative form model is simulated. Correspondingly, in step 207a, a CAM program is generated for controlling a CNC tool to produce a positive form model having the specified surface. The tool size of the CNC tool is determined by the determined minimum radius. In step 208a, the execution of the CAM program is simulated resulting in a set of simulation data. In step 209a, modified surface data is generated from the simulation data, and the modified surface data is re-imported in the CAD/CAM software package, and. Hence steps 207a, 208a, and 209a correspond to steps 207, 208, and 209, respectively, of fig. 2a. Subsequently, in step 207b, an updated CAM program is generated based on the modified surface data. The updated CAM! program is loaded into the simulation software package and the execution of the updated program is simulated (step 208b) to produce a simulated negative form model having the specified surface. The resulting updated simulation data is again transformed into further modified surface data (step 209b). The resulting further modified surface data is used as a basis of the final CAM programming step 210 in the CAD/CAM software package, and the generated CAM program is exported in a suitable format (step 211).

It is noted, that further variations of the method according to the invention may be used, e.g. by iterating the steps of programming, simulating, and surface updating a different number of times.

The invention may be applied in the production of a variety of articles, e.g. articles produced by a forming process from a mould. In particular, the invention is advantageous in the production of articles having detailed surface features, complex free-form shapes, etc., such as plastic toy articles, e.g. toy figures, elements of toy construction sets, etc.

Claims

CLAIMS:

1. A method of producing an article based on a physical model, the method comprising the steps of

a) scanning the physical model to obtain a set of scan data; b) converting the scan data into surface data representing surface characteristics of the model; c) generating instruction data from the surface data suitable for causing a computer-controlled machine tool to produce an article having surface characteristics corresponding to the surface characteristics of the model;

characterised in that the method further comprises the steps of

d) simulating executing the generated instructions on a data processing system resulting in a set of simulated surface data representing a simulated as-machined article; e) generating a representation of the updated surface data suitable for producing the article.

2. A method according to claim 1 , characterised in that the step of simulating executing the generated instructions further comprises

- simulating executing the generated instructions on a data processing system resulting in a set of simulation data representing a simulated as- machined article;

- generating modified surface data from the simulation data, the modified surface data representing the surface characteristics of the simulated as- machined article.

3. A method according to claim 1 or 2, characterised in that the step of generating instruction data further comprises selecting a predetermined minimum radius determining a maximum curvature of the surface of the article to be produced.

4. A method according to claim 3, characterised in that the step of simulating executing the generated instructions comprises simulating the generated instructions with a tool of a predetermined tool size corresponding to the selected minimum radius.

5. A method according to any one of claims 1 through 4, characterised in that the article is a mould having one or more parting lines and the step of generating instruction data further comprises selecting respective positions of the one or more parting lines.

6. A method according to any one of claims 1 through 5, characterised in that the step of generating instruction data comprises generating instruction data suitable for causing a computer-controlled machine tool to produce an article having a negative surface with respect to the surface of the physical model.

7. A method according to any one of claims 1 through 6, characterised in that steps c) and d) are repeated at least once with the modified surface data as an input and resulting in further modified surface data.

8. A method according to claim 7, characterised in that step d) is performed at least once to generate a set of simulated surface data representing a simulated as-machined positive form model and at least once to generate a set of simulated surface data representing a simulated as-machined negative form model.

9. A method according to any one of claims 1 through 8, characterised in that the step of scanning the physical model comprises video scanning the physical model.

10. A system for producing an article based on a physical model, the system comprises a scanning system for scanning the physical model to obtain a set of scan data;

a data processing system adapted to convert the scan data into surface data representing surface characteristics of the model; and to generate instruction data from the surface data suitable for causing a computer-controlled machine tool to produce an article having surface characteristics corresponding to the surface characteristics of the model;

characterised in that

the data processing system is further adapted

- to simulate executing the generated instructions resulting in a set of simulated surface data representing a simulated as-machined article; and - to generate a representation of the updated surface data suitable for producing the article.

11. A method of facilitating producing an article based on a physical model, the method comprising the steps of

a) receiving a set of scan data representing a scanning of the physical model; b) converting the scan data into surface data representing surface characteristics of the model; c) generating instruction data from the surface data suitable for causing a computer-controlled machine tool to produce an article having surface characteristics corresponding to the surface characteristics of the model;

characterised in that the method further comprises the steps of

12. A data processing system adapted to perform the steps of the method according to claim 11.

13. A computer program comprising program code means for performing all the steps of claim 11 when said program is run on a computer.

14. A computer program product comprising program code means stored on a computer readable medium for performing the method of claims 11 when said computer program product is run on a computer.