| JP2002132317 | CONTROLLER |
| JP63206197 | CONTROL MECHANISM OF MOTOR FOR CONTROLLING ARM MOVEMENT |
| JP53016988 | GRIND STONE COMPENSATING APPARATUS |
| 1. | A method of shaping a material using a shaping machine that has a shaping member, the method comprising determining a convex hull that is a minimum closed convex curve that encloses a plurality of input paths that define a surface that is to be cut; determining span portions of the convex hull that do not coincide with any of the input paths; replacing the span portions of the convex hull with visible portions of the input path, thereby to determine an output path curve, and controlling the shaping member so that it follows the desired output path and is maintained perpendicular to the convex hull in regions away from the span portions and at a substantially constant angle relative to each span portion when in span portion regions. |
| 2. | A method as claimed in claim 1, wherein the substantially constant angle is different for different spans. |
| 3. | A method as claimed in claim 1 or 2, further involving determining the plurality of input path curves that define the surface that is to be cut. |
| 4. | A method as claimed in any one of claims 1 to 3, comprising determining the visible portions of the of input path curves. |
| 5. | A method as claimed in claim 4, comprising determining the visible portions of the input paths by projecting the span portions onto the input paths along a plurality of parallel lines. |
| 6. | A method as claimed in claim 5, wherein the plurality of parallel lines are perpendicular to the span. |
| 7. | A method as claimed in claim 5 or claim 6, wherein the substantially constant angle is defined by the angle between the plurality of parallel lines and the span portion. |
| 8. | A shaping machine comprising: a machine head for carrying a shaping member, means for determining a convex hull that is a minimum closed curve that encloses a plurality of input path curves that define the surface shape that is to be formed; means for determining portions of the convex hull that do not coincide with any of the input curves; means for replacing the portions of the convex hull with visible portions of the path, thereby to form an output curve, and means for controlling the machine head so that when a shaping member is carried thereon it shapes the output curve whilst being maintained perpendicular to the convex hull in the regions of the span portions and at a substantially constant angle relative to each span portion in the span portion regions. |
| 9. | A machine as claimed in claim 8, wherein the substantially constant angle is different for different spans. |
| 10. | A shaping machine as claimed in claim 8 or claim 9, wherein the machine head has at least four degrees of freedom, preferably five. |
| 11. | A machine as claimed in claim 9 or claim 10 comprising means for determining the plurality of input path curves that define the surface that is to be cut. |
| 12. | A machine as claimed in any one of claims 8 to 11, comprising means for determining the visible portions of the of input path curves. |
| 13. | A machine as claimed in any one of claims 8 to 12, wherein the means for determining the visible portions of the input paths include means for projecting the span portions onto the input paths, along a plurality of parallel lines. |
| 14. | A machine as claimed in claim 13, wherein the plurality of parallel lines is perpendicular to the span. |
| 15. | A machine as claimed in any one of claims 8 to 14, wherein the substantially constant angle is defined by the angle between the plurality of parallel lines and the span portion. |
| 16. | A computer program for controlling a shaping machine that has a shaping member, the computer program comprising means for determining a convex hull that is a minimum closed curve that encloses a plurality of the input paths that define a surface that is to be cut; means for determining portions of the convex hull that do not coincide with any of the input paths; means for replacing the portions of the convex hull with visible portions of the input path, thereby to form an output path, and means for controlling the shaping member to follow out the output path whilst being maintained perpendicular to the convex hull in regions away from the span portions and at a constant angle relative to the span portions in the span portion regions. |
| 17. | A computer program as claimed in claim 16, wherein the substantially constant angle is different for different spans. |
| 18. | A computer program as claimed in claim 16 or claim 17, comprising means for determining the plurality of input path curves that define the surface that is to be cut. |
| 19. | A computer program as claimed in any one of claims 16 to 18, comprising means for determining the visible portions of the of input path curves. |
| 20. | A computer program as claimed in claim 19, wherein the means for determining the visible portions of the input paths include means for projecting the span portions onto the input paths, along a plurality of parallel lines. |
| 21. | A computer program as claimed in claim 20, wherein the plurality of parallel lines is perpendicular to the span. |
| 22. | A computer program as claimed in any one of claims 16 to 21, wherein the substantially constant angle is defined by the angle between the plurality of parallel lines and the span portion. |
| 23. | A data carrier that includes a computer program for controlling a shaping machine that has a shaping member, the computer program comprising means for determining a convex hull that is a minimum closed curve that encloses a plurality of the input paths that define a surface that is to be cut; means for determining portions of the convex hull that do not coincide with any of the input paths; means for replacing the portions of the convex hull with visible portions of the input path, thereby to form an output path, and means for controlling the shaping member to follow out the output path whilst being maintained perpendicular to the convex hull in regions away from the span portions and at a substantially constant angle relative to each span portions in the span portion regions. |
| 24. | A data carrier as claimed in claim 23, wherein the substantially constant angle is different for different spans. |
| 25. | A data carrier as claimed in claim 23 or claim 24, comprising means for determining the plurality of input path curves that define the surface that is to be cut. |
| 26. | A data carrier as claimed in any one of claims 23 to 25, comprising means for determining the visible portions of the of input path curves. |
| 27. | A data carrier as claimed in claim 26, wherein the means for determining the visible portions of the input paths include means for projecting the span portions onto the input paths, along a plurality of parallel lines. |
| 28. | A data carrier as claimed in claim 27, wherein the plurality of parallel lines is perpendicular to the span. |
| 29. | A data carrier as claimed in any one of claims 23 to 28, wherein the substantially constant angle is defined by the angle between the plurality of parallel lines and the span portion. |
| 30. | A computer readable medium or a computer program for controlling a shaping machine that has a shaping member comprising instructions for: determining a convex hull that is a minimum closed curve that encloses a plurality of the input paths that define a surface that is to be cut; determining portions of the convex hull that do not coincide with any of the input paths; replacing the portions of the convex hull with visible portions of the input path, thereby to form an output path, and controlling the shaping member to follow out the output path whilst being maintained perpendicular to the convex hull in regions away from the span portions and at a constant angle relative to the span portions in the span portion regions. |
| 31. | A computer readable medium or program as claimed in claim 30, wherein the substantially constant angle is different for different spans. |
| 32. | A computer readable medium or program as claimed in claim 30 or claim 31, comprising instructions for determining the plurality of input path curves that define the surface that is to be cut. |
| 33. | A computer readable medium or program as claimed in any one of claims 30 to 32, comprising instructions for determining the visible portions of the of input path curves. |
| 34. | A computer readable medium or program as claimed in claim 33, wherein the means for determining the visible portions of the input paths include means for projecting the span portions onto the input paths, along a plurality of parallel lines. |
| 35. | A computer readable medium or program as claimed in claim 34, wherein the plurality of parallel lines is perpendicular to the span. |
| 36. | A computer readable medium or program as claimed in any one of claims 30 to 35, wherein the substantially constant angle is defined by the angle between the plurality of parallel lines and the span portion. |
| 37. | A method of controlling a shaping member to follow a desired output path, the output path being determined by determining a convex hull that is a minimum closed convex curve that encloses a plurality of input paths that define a design that is to be shaped; determining span portions of the convex hull that do not coincide with any of the input paths; replacing the span portions of the convex hull with visible portions of the input path, thereby to determine an output path curve, the method of controlling comprising controlling the shaping member so that it follows the desired output path and is maintained perpendicular to the convex hull in regions away from the span portions and at a substantially constant angle relative to each span portion when in the region of the span portions. |
| 38. | A method substantially as described hereinbefore with reference to the accompanying drawings. |
| 39. | A machine substantially as described hereinbefore with reference to the accompanying drawings. |
| 40. | A computer program substantially as described hereinbefore with reference to the accompanying drawings. |
| 41. | A data carrier substantially as described hereinbefore with reference to the accompanying drawings. |
Figure 1 shows a known apparatus 9 for shaping a design from a material blank 10 such as, for example, clay. This apparatus comprises a tool head 11 that carries a cutting tool 12 for cutting the blank 10 and a control system 14, typically a pc, for controlling movement of the head 11. The pc 14 includes a tool-head control program that is adapted to control the head 11 to move in such a way that the cutting tool 12 is driven across the external surface of the blank 10, thereby to cut out a desired shape.
When a blank 10 is to be shaped into a desired configuration, input tool path curves that define the desired design are devised and entered into the pc tool head-control program. These input tool path curves can be calculated in various ways using a mathematical description of the desired surface, for example a polyhedral description. Methods for calculating the input tool paths are well known to the skilled person.
Once the input tool paths are determined, there are several methods of controlling the cutting tool 12 to cut out the desired shape. Three axis machines are controlled so that the orientation of the cutter is kept constant, typically vertical, as shown in Figure 2. A disadvantage of this is that undercut or recessed portions of the design cannot be machined. Additionally, near vertical
and deep draw areas can cause the cutter and/or machine to clash with the material that is being cut. This is typically because of access problems due to the bulk of the tool head 11 that carries the cutting tool 12.
In order to overcome some of the problems associated with three axis machines, when machining a complex shape several tool paths with different orientations are typically combined to machine undercut and recessed areas of the design.
Figure 3 shows a blank that has been machined in this way, using a horizontal cutter angle in the sections marked A and B and a vertical cutter angle in the section marked C. Each of sections A, B and C is separately machined. A disadvantage of this is, however, that several machine operations are required to finish the job. In addition, operator skill is essential in order to ensure a sensible division of the job. Furthermore, lines can appear where the different sections meet.
In five axis machines, the tool head 11 is typically controlled so the cutting tool is always presented at a normal to the surface that is to be cut. This is shown in Figure 4. A disadvantage of this method is that for all but the simplest shapes, the cutter and machine head are likely to clash with the material that is being shaped. In addition, the machine can go through large angular swings and double back on itself as it follows the normal to the surface. This slows machining through increased length of movement. Furthermore, machine speed has to be reduced in order to avoid acceleration stresses. Consequently, it is not possible using this method to cut out complex shapes in a single pass of the tool head over the clay. Instead, a coarse cut of the clay must be done in a first pass of the tool head 11, which then has to be re-set before cutting is re-commenced in order to produce finer features.
In another known method the tool head 11 is positioned so that it always points to a specific reference point in space, as shown in Figure 5. In this method, the tool is always directed towards or away from a single point that is selected and entered by the operator. This method has the advantage that greater access can generally be achieved and large cutter swings can be avoided. However, a disadvantage is that the results of the cutting depend on the skill of the operator in selecting the initial reference point. In addition, in practice it is often impossible to place the point in a position where all of the problems of three- axis machine are removed.
Figure 6 shows yet another method for positioning the tool head. In this the reference point of Figure 5 is replaced with, for example, a line (other alternatives include curves, planes and surfaces). This achieves better results than using a reference point, but requires more time and effort. In addition, in practice it is still often impossible to place the reference line so that all problems are avoided. Furthermore, because the line is more complicated than using a point, the advantages of minimal cutter swings can be lost.
An object of the invention is to provide an improved method, apparatus and computer program for shaping materials.
According to the present invention there is provided a method of shaping material using a shaping machine that has a shaping member, the method comprising determining a convex hull that is a minimum closed convex curve that encloses a plurality of input paths that define a design that is to be shaped;
determining span portions of the convex hull that do not coincide with any of the input paths; replacing the span portions of the convex hull with visible portions of the input path, thereby to determine an output path curve, and controlling the shaping member so that it follows the desired output path and is maintained perpendicular to the convex hull in regions away from the span portions and at a substantially constant angle relative to each span portion when in the span portion regions.
An advantage of the method is that the input paths that define the desired shape do not have to be closed. In addition because the convex hull encloses all of the input paths, these paths are automatically ordered and orientated along the convex hull despite their being randomly arranged. Furthermore, the shaping member's angular position in the output path surface increases, or decreases, monotonically thereby avoiding large angular swings that can be associated with five axis machining. This reduces machining time. In addition, the method in which the present invention is embodied allows sharp concave tool- path intersections to be machined.
The substantially constant angle may be different for different spans.
Preferably, the method further involves determining the plurality of input path curves that define the design that is to be shaped.
Preferably, the method further involves determining the visible portions of the of input path curves. This involves determining the portions of the input path that can be seen from the span portion, i. e. the portions of the input path from
which a straight line can be drawn directly to the span without crossing any other input path. This may involve projecting the span portions onto the input path, along a plurality of parallel lines that are preferably perpendicular to the span.
Preferably the shaping member is a cutting tool. Alternatively the shaping member may comprise means for depositing material into a particular shape.
Preferably, the material is clay or polyurethane foam or polystyrene or foam or wood.
According to the present invention there is provided a method of controlling a shaping member to follow a desired output path, the output path being determined by determining a convex hull that is a minimum closed convex curve that encloses a plurality of input paths that define a design that is to be shaped; determining span portions of the convex hull that do not coincide with any of the input paths; replacing the span portions of the convex hull with visible portions of the input path, thereby to determine an output path curve, the method of controlling comprising controlling the shaping member so that it follows the desired output path and is maintained perpendicular to the convex hull in regions away from the span portions and at a substantially constant angle relative to each span portion when in the region of the span portions.
The substantially constant angle may be different for different spans. The substantially constant angle may be 90 degrees. Preferably the shaping member is a cutting tool. Alternatively, the shaping member may comprise means for depositing material into a particular shape.
Preferably, the material is clay or polyurethane foam or polystyrene or foam or wood.
According to another aspect of the present invention, there is provided a shaping machine system comprising: a machine head for carrying a shaping member, means for determining a convex hull that is a minimum closed curve that encloses a plurality of input paths that define the design that is to be shaped; means for determining span portions of the convex hull that do not coincide with any of the input curves; means for replacing the span portions of the convex hull with visible portions of the input paths, thereby to form an output curve, and a controller for controlling the machine head so that when a shaping member is carried thereon it follows the output curve whilst being maintained perpendicular to the convex hull in regions away from the span portions and at a substantially constant angle relative to each span portion when in the span portion regions.
The substantially constant angle may be different for different spans.
Preferably, the substantially constant angle at which the shaping member is moved relative to each span portion is ninety degrees so that the shaping member is maintained perpendicular to the convex hull in all regions.
Preferably, the machine has at least four degrees of freedom, typically five. In this way, this axis of the shaping member can be oriented substantially in any direction.
Preferably the shaping member is a cutting tool. Alternatively the shaping member may comprise means for depositing material into a particular shape.
Preferably, the machine further comprises means for determining the plurality of input path curves that define the design that is to be shaped.
Preferably, the machine includes means for determining the visible portions of the of input paths, which means are operable to determine the portions of the input path that can be seen from the span portion, i. e. the portions of the input path from which a series of straight parallel lines can be drawn directly to the span without crossing any other input path. The means for determining the visible portions of the input paths may include means for projecting the span portions onto the input paths, along a plurality of parallel lines. Preferably, the plurality of parallel lines are perpendicular to the span.
Preferably, the material is clay or polyurethane foam or polystyrene or foam or wood.
According to yet another aspect of the present invention, there is provided a computer program for controlling a shaping machine that has a shaping member, the computer program comprising means for determining a convex hull that is a minimum closed curve that encloses a plurality of input paths that define a surface that is to be cut;
means for determining span portions of the convex hull that do not coincide with any of the input paths; means for replacing the span portions of the convex hull with visible portions of the input path, thereby to form an output path, and means for controlling the shaping member to follow out the output path whilst moving perpendicular to the convex hull in regions away from the span portions and at a substantially constant angle relative to each span portion when in the span portion regions.
According to yet further aspect of the present invention, there is provided a data carrier that includes a computer program for controlling a shaping machine that has a shaping member, the computer program comprising means for determining a convex hull that is a minimum closed curve that encloses a plurality of input paths that define a surface that is to be cut; means for determining span portions of the convex hull that do not coincide with any of the input paths; means for replacing the span portions of the convex hull with visible portions of the input path, thereby to form an output path, and means for controlling the shaping member to follow out the output path whilst being maintained perpendicular to the convex hull in regions away from the span portions and at a substantially constant angle relative to each span portion when in the span portion regions.
Preferably, the substantially constant angle is different for different spans.
Preferably, the substantially constant angle at which the shaping member is moved relative to the span portions is ninety degrees so that the shaping member is maintained perpendicular to the convex hull in all regions.
Preferably, the computer program further includes means for determining the plurality of input path curves that define the design that is to be shaped.
Preferably, the computer program has means for determining the visible portions of the of input paths, which means are operable to determine the portions of the input path that can be seen from the span portion, i. e. the portions of the input path from which a series of straight parallel lines can be drawn directly to the span without crossing any other input path. The means for determining the visible portions of the input paths may include means for projecting the span portions onto the input paths, along a plurality of parallel lines. Preferably, the plurality of parallel lines are perpendicular to the span.
According to a still further aspect of the invention, there is provided a computer readable medium or a computer program for controlling a shaping machine that has a shaping member comprising instructions for: determining a convex hull that is a minimum closed curve that encloses a plurality of the input paths that define a surface that is to be cut; determining portions of the convex hull that do not coincide with any of the input paths; replacing the portions of the convex hull with visible portions of the input path, thereby to form an output path, and controlling the shaping member to follow out the output path whilst being maintained perpendicular to the convex hull in regions away from the span portions and at a constant angle relative to the span portions in the span portion regions.
The substantially constant angle may be different for different spans.
Preferably, instructions for determining the plurality of input path curves that define the surface that is to be cut are provided. Instructions for determining the visible portions of the input path curves may be provided. These instructions may include means for projecting the span portions onto the input paths, along a plurality of parallel lines, preferably, wherein the plurality of parallel lines is perpendicular to the span.
The substantially constant angle may be defined by the angle between the plurality of parallel lines and the span portion.
A system, apparatus, method and computer program in which the invention is embodied will now be described by way of example only with reference to the following drawings, of which: Figure 7 is a representation of input tool paths in a tool path surface in three-dimensional space; Figure 8 is a representation of input tool paths of the tool path surface in two-dimensional space; Figure 9 is a representation of the input tool paths of Figure 8 enclosed by a minimum closed convex curve; Figure 10 is similar to Figure 9 except visible portions of the input curves are indicated;
Figure 11 is a representation of the output tool path of Figure 10 in which spans in the convex hull are replaced with visible portions of the input tool path curves, and Figure 12 is a representation of the output tool path in three-dimensional space.
The machine of Figure 1 can be used in order to carry out the present invention.
It is preferred, however, that the machine has five degrees of freedom. In this way, the axis of the cutting tool can be oriented substantially in any direction.
In order to cut a particular surface, details of the surface profile are used to calculate a collection of tool paths 16 that define the design that is to be shaped.
The input tool paths 16 are usually generated as the intersection of design definition surfaces and the tool path surface or as the intersection of an offset design definition surface and the tool path surface. These paths 16 are typically three-dimensional and generally open polygons, ie strings of points. In addition, they can be smooth or composed of ordered line segments and can run in either direction, as shown in Figure 7. The paths 16 can also be spaced apart from each other or overlap. Methods of determining the input tool paths 16 are well known in the art.
Once the three-dimensional tool paths 16 are determined, they are used to calculate the input tool paths in the two-dimensional space of the tool path surface 18, as shown in Figure 8. A minimum closed convex curve 20 that encloses all of the input tool paths in two-dimensional space 18 is then constructed, as shown in Figure 9. This closed convex curve 20 shall be referred to as the"convex hull"20. As can be seen from Figure 9, some
straight-line portions 22 of the convex hull 20 do not coincide with any of the input tool path curves 18-these portions 22 shall be referred to as"spans". As will be appreciated, the convex curve is typically constructed using computer software.
In the region of the spans 22, the visibility of the input tool paths 18 is determined. By this it is meant that those portions of the input tool paths 18 which can be observed from a span 22 of the convex hull 20 are calculated.
This involves determining the portions of the input paths 18 from which a series of straight substantially parallel lines can be drawn directly to the span, without crossing any other input path. This can be done by projecting each span portion 22 onto the adjacent input paths along a plurality of substantially parallel lines that extend at a pre-determined angle relative to the span 22. One specific way of doing this is to project each span 22 onto the input paths 18 along a plurality of parallel lines 24 that are perpendicular to the span 22, as shown in Figure 10.
The pre-determined angle of the parallel lines may be different for different spans.
Once the visibility is determined, a continuous two dimensional output tool path 26 is formed by replacing the spans 22 in the convex hull 20 with the visible portions 27 of the input tool paths 18, as shown in Figure 11. Segments 28 of the input tool paths 18 that are contained within the continuous output tool path 26 are then discarded. The two-dimensional output path 26 is then projected back into three-dimensional space in order to construct a continuous three- dimensional output tool path surface 29, as shown in Figure 12. As will be appreciated, in order to build up an entire design it is typically necessary to construct a plurality of output tool path surfaces 29.
In order to shape a material such as a clay blank to have the profile of the continuous output tool path surface 29, details of the output tool path surface 29, the convex hull 20 and the span portions 22 are input into the drive control software of the cutting machine 9. Additionally input are details of the pre- determined angle of the plurality of parallel lines relative to each span portion 22 that was used to determine the visibility of the input paths 18. The tool head 11 is then driven by the control program so as to follow the output tool path 29.
Additionally, the axis of the cutting tool 12 is set so that it is perpendicular to the convex hull 20 in regions away from the span portions 22. In the span portions 22 themselves, the cutting tool 12 is positioned at the pre-determined constant angle relative to each span 22, which may or may not be perpendicular to the span portions 22, and may or may not be different for different spans 22.
Hence, the cutting tool 12 is driven so that it follows the output tool path and is perpendicular to the output tool path 26 where the output tool path coincides with the convex hull 22 and at a substantially constant angle relative to the span portions 22 in the span regions. In this way a"slice"of the blank is cut or shaped to have the shape of the output tool path surface 29. In order to shape an entire surface typically a plurality of output tool path surfaces 29 are shaped.
Whilst the cutter direction is defined above, the orientation of the cutter during the cutting process can vary depending on the profile of the feature that is to be shaped. For example, if the tool path surface as shown in Figure 12 lies in the plane of the page, the cutter would also typically be moved in that plane. The cutter could, however, be moved to an orientation that extends out of the page as and when deemed necessary or preferable, provided the projection of the cutter back into the plane of the page is maintained perpendicular to the convex
hull away from the span 22 and at the pre-determined substantially constant angle relative to the spans 22 in the span regions.
The specific description relates to a machine that has a cutting head. The invention could, however, equally be applied to machines that are used to deposit material rather than remove it.
A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the invention. Accordingly, the above description of a specific embodiment is made by way of example and not for the purposes of limitation. It will be clear to the skilled person that minor modifications can be made without significant changes to the operation described above.
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