WO1997018533A1

WO1997018533A1 - Computer aided design system

Info

Publication number: WO1997018533A1
Application number: PCT/GB1996/002724
Authority: WO
Inventors: Brendan Kieran Hinds; David Creyke Reedman; William Samuel Hamilton; James Mccartney
Original assignee: British United Shoe Machinery Co. Ltd.; Usm Espana, S.L.
Priority date: 1995-11-15
Filing date: 1996-11-07
Publication date: 1997-05-22

Abstract

For use in designing irregular objects such as shoes, an element such as a shoe last (1) whose surface geometry has been digitised and stored and which can be thus displayed on a display screen (7) is provided with means (2) for generating an electromagnetic field which can be sensed by a tracking station (3) so that in response to variations in the position and orientation of the last (1) the displayed image (8) can be correspondingly varied. In addition a drawing tool (pen) (4) also has such field generating means (5) which again can be tracked by the tracking station (3) and an image (9) of which also can be displayed on the screen (7). By moving the pen (4) over the surface of the last (1) design lines (12) can be created on the image (8) displayed on the screen (7) and thus a shoe design can be created on the screen. If desired, components designed using the last (1) and pen (4) may alternatively or in addition be displayed as 'flattened' two-dimensional images. In addition, selected areas may show colour, surface texture, thickness and other features.

Description

COMPUTER AIDED DESIGN SYSTEM

The present invention relates to three-dimensional design and more particularly but not exclusively to a design system suitable for use in irregularly shaped articles such as three-dimensional design of footwear.

It will be appreciated that in a wide range of situations it would be advantageous to be able to create designs in three dimensions using computer-aided design (CAD) techniques. Instances that readily spring to mind are with regard to footwear, ceramics and automobiles. Of particular interest with regard to the present invention would be the situation in footwear where a shoe last could be used as a surface upon which a shoe design including stitching, surface contouring and colour could be applied.

Current three-dimensional CAD systems are controlled using a two-dimensional input device such as a tablet or mouse. This requires a two-dimensional - three-dimensional mapping to be performed, which often causes ambiguity between the user's movement and the visual feedback from the computer display. This leads to two problems:

(1) For designs based on irregular shapes, such as shoes, it becomes increasingly difficult for the user to position and orientate the object in order to achieve a view which allows the shape to be judged.

(2) Inputting points and creating three-dimensional curves is difficult in areas where the curvature of the shape changes rapidly. A method for painting on scanned three-dimensional surfaces is known. In this method a six degree of freedom input device was used as a virtual paintbrush which the user could manipulate and position at various locations on the scanned surface. This method does not allow for movement of the scanned object and hence the user has not the ability to easily select a satisfactory viewing position or a comfortable painting position. Furthermore, it is possible to provide an interface for designing complex object in three dimensions using two six degree of freedom sensors. One sensor corresponds to the pen and the other corresponds to the object. In this case the user does not have a physical representation of the object which acts as a drawing aid. The physical object offers tactile feedback on shape which helps the user to identify points in three dimensions on or near the object surface.

Previously in footwear design the approach has been to design footwear components in two dimensions and then to project those components using appropriate computer processing into three dimensions to view the eventual design. This obviously has inherent problems in so far as the designer is unable to see the consequences of design changes until the processing projection from two dimensions to three dimensions has been achieved. Designers would ideally wish to see the results of their design changes immediately.

There are commercially available various positional tracking devices which could be useful in computer-aided design. One such tracking device is provided by Polhemus, Inc., Vermont, U.S.A., and another by Ascension Technology Corp., Vermont, U.S.A. These systems use electromagnetic fields generated by sensor elements mounted in respective pallet and stylus elements. The electromagnetic fields are picked up by a tracker device such that their relative positions can be determined and appropriately manipulated/ plotted to determine position and orientation. A report in IEEE Computer Graphics & Applications, pages 18 to 26, November 1991, illustrates such an arrangement of pallet and stylus for three-dimensional design. Typically, the pallet is a base reference and the stylus is used for relative movement. Thus if the pallet, which is usually in the form of a flat sheet, is held by the designer in one hand and the stylus in the other hand, it is possible, by effecting relative movement between the pallet and stylus, to create a plotted design on a visual display unit in a relatively short period of time. Such design techniques, however, have proved not to be ideal.

It is an object of the present invention to provide a three-dimensional design tool which is more convenient for designers particularly with regard to creating designs on surfaces of three-dimensional physical objects.

The present invention thus provides, in one of its several aspects, a design system suitable for use in designing irregularly shaped articles such as footwear, comprising a base element in the form of a shoe last or as appropriate, a drawing tool, a tracking station, sensing means operatively connected to both the base element and the drawing tool and also to the tracking station, said means being effective to determine the position and orientation of the base element and drawing tool relative to one another and also to the tracking station, processor means for storing a digital map of the surface of the base element, or part thereof, and for receiving signals from the sensing means in accordance with the position and orientation of the base element, visual display means for receiving signals from the processor means in response to which a visual representation of the base element can be displayed thereby in accordance with the stored digital map and in accordance with the position and orientation of the base element as sensed, and also a visual representation of an operative portion of the drawing tool in relation to the base element, and tack point generating means whereby a succession of so- called tack points, indicative of a succession of positions of the drawing tool relative to the base element, can be generated and supplied to the processor means to be stored thereby, wherein in response to such supply further signals are supplied by the processor means to the visual display means whereby to create design lines on the representation of the base element displayed thereby, said design lines passing through and their location thus being determined in accordance with the tack points.

It will thus be appreciated that, using the design system in accordance with the present invention the designer can hold the base element, which in normal practice for footwear would be a shoe last, in one hand and the drawing tool in the other and create on the last such design lines as he desires, to which end he will probably utilise the visual representation of the three-dimensional shape displayed on the visual display means. Moreover, by the provision of the facility for re-orienting the last, the designer will readily be able to appreciate the overall appearance of the shoe which he is designing in this manner.

To facilitate this design function, preferably the design system in accordance with the present invention further comprises selecting means for selecting a characteristic (e.g. colour, texture, thickness) of an area, which may be defined by design lines, of the representation of the base element displayed as aforesaid. In this way, the designer will be able to create as a visual representation the complete appearance of the shoe, which may be made up of several parts, e.g. vamp, quarters, eyelet facings, etc., with the overlaps displayed, and also the surface textures and the colours of the various parts may similarly be displayed.

Any of the known techniques available for determining the spatial position and orientation of one element relative to another may be incorporated into the design system in accordance with the invention; for example, in one convenient construction the sensing means comprises means for creating an electromagnetic field and sensors responsive to such field. In one preferred embodiment the means for creating an electromagnetic field is associated with each of the base element and the drawing tool and the sensors with the tracking station.

It will of course be appreciated that shoes are generally made up of a number of flat components which are secured together to form a complete shoe upper, some three- dimensional shaping being effected by the securement itself, but the conforming of the shoe upper to the shoe last being completed by tensioning the upper over the last and securing it in its tensioned condition and also, optionally, by a moulding process involving heat and pressure. When a designer designs a shoe, therefore, it is necessary for him not only to determine the overall appearance of the shoe, but also to create flat pieces of the correct shape for incorporation into the shoe upper of the desired overall shape. In addition, where e.g. style lines are created on the surface of the upper by stitching or the like, these must be so arranged on the flat components that in the finished shoe they are located in the desired position for achieving the overall appearance of the shoe as designed by the designer. Over the years, therefore, so-called "flattening" rules have been established, empirically, for determining the shape of the flat components and the arrangement of style lines and the like thereon necessary for the production of the finished shoe. When a designer is designing a shoe, therefore, he may begin by designing the overall appearance and then wish to ensure that the individual components are correctly shaped and the style lines and the like correctly positioned in the flat. On the other hand, the designer may in some instances wish to start from the flattened components and then wish to see the finished product when made up. To facilitate either of these approaches, in the design system in accordance with the invention preferably the processor means comprises conversion means whereby signals supplied to the processor means by the sensing means in respect of the base element, or an area thereof, can be processed to convert the three- dimensional shape of the base element, or such area thereof, into a two-dimensional flat shape, such conversion being determined by stored "flattening" rules. Moreover, preferably, the processor means supplies to the visual display means signals in response to which selectively a visual representation of at least one of such three- dimensional and such flat, two-dimensional, shape is displayed side-by-side and simultaneously. In such case, furthermore, the further signals previously referred to are also processed by the conversion means whereby design lines created as aforesaid are displayed on the selected visual representations) . Moreover, to facilitate the use of such a design system, conveniently selector means is provided whereby either or both of the visual representations can be selected for display.

It will thus be appreciated that using the design system in accordance with the invention the operator may, while holding the shoe last in one hand and the drawing tool in the other, by viewing the visual display design a shoe on the three-dimensional shape which he has selected for display on the visual display. On the other hand, if he so requires he may create, again using the shoe last and the drawing tool, a particular component which he then selects to display on the visual display in a two-dimensional flattened form. Moreover, while viewing such flattened form, he may amend the shape, still using the drawing tool on the surface of the shoe last, but still viewing the visual display.

It will thus be appreciated that the design system in accordance with the invention is a powerful but versatile tool for facilitating the design of shoes. Moreover, by the facility of displaying the finished shoe in a three- dimensional representation on the visual display, the designer and also potential buyers may view the finished product without the need for actually creating it as a real object, so that the production of samples, and indeed large numbers of samples, is facilitated without the accompanying expense which is usually involved.

In accordance with an alternative embodiment of the present invention there is provided a design system arrangement suitable for design of footwear, the system comprising a base, physical element such as a shoe last, and a drawing stylus, both the element and the stylus including position sensors which allow determination of the position and orientation of said element and stylus relative to a tracking station coupled to a processor means, a digital map of said element being stored in said processor means and represented upon a visual display means and the representation so displayed manipulated dependent upon said position and orientation determined by its positional sensor relative to the tracking station, said stylus being represented in the display means relative to said representation of said element, said stylus being moved about said element and tack points made upon said element represented in the visual display means by appropriate stimulation to said processor means, said tack points being processed to present design lines joining said tack points in said representation of said element in said visual display means. One embodiment of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is a schematic illustration of the elements of the present invention with a three-dimensional representation of the article and any design;

Figure 2 is a schematic illustration of the elements of the present invention with a three-dimensional and two- dimensional representation of the article and any design;

Figure 3 is a set of representations of the transformations considered to achieve manipulation of the article and the representations;

Figure 4 is a flow diagram illustrating the transformation procedure to ensure appropriate presentation of the representation; Figure 5 is a schematic illustration of the relationship between the real article or last and the virtual representation of the article or last;

Figure 6 is a graphic illustration used to show the relationship between the two different co-ordinates systems of the stylus and the article/last;

Figure 7 illustrates a series of translations and rotations required to achieve complete transformation;

Figure 8 illustrates the reference co-ordinate systems in both the real user's worktable and as represented; Figure 9 is a flow diagram of the method taken to ensure dynamic surface adherence despite inherent sensor inaccuracy;

Figure 10 is a schematic illustration to show that irrespective of angle of presentation the stylus is always represented in the representation normal to the surface; and

Figure 11 is a schematic perspective of the design system. A three-dimensional input device is used to define the geometry of the design. The device takes the form of a stylus 2 with a three-dimensional tracking sensor 4 attached. The position and orientation of the stylus 2 is recorded and this information passed to a computer which displays an image of the stylus 5 on the screen. The stylus co-ordinate system is transformed to the screen co-ordinate system so that the image changes to match the user's hand movements.

The second part of the invention includes a physical last or article, which has a positional tracking device 3 attached to it. The surface geometry of the last has been scanned and a three-dimensional representation or digital map is displayed on the screen. The last is registered so that the software model data is transformed directly to the co-ordinate system of the tracking device. This, in turn, is transformed to the screen co-ordinate system, so that if the last is moved, the image is updated in a corresponding manner.

An additional aspect of the invention is the ability to operate in the dual mode of two dimensions and three dimensions simultaneously. In many CAD applications, and particularly in shoe design, the user may wish to visualise designs in both two dimensions and three dimensions. In this case the dual mode allows the user to sketch lines on the actual flattened forms 9 or on the physical last 10 and visualise the style on both the three-dimensional last model 12 and two-dimensional forme screen representations 11, which can be displayed simultaneously on screen.

The switch from three-dimensional to two-dimensional mode is made when the stylus enters a region of space

(designed by the co-ordinates (x_lf y_1; z^ and (x₂, y₂, ^₂ ) allocated for two-dimensional operations only. When the arrangement is operating in two-dimensional mode it is analogous to a digitising tablet. Since the user may have been accustomed to operating the CAD package in two- dimensional mode, he may feel more comfortable performing some tasks in this manner. However, he has the immediate option of interacting fully in three dimensions for tasks where this is appropriate. The swift and easy interaction between three dimensions and two dimensions is an advantage of the invention which is not offered by previous systems.

Figure 1 consists of a physical element or last and o stylus 2, a tracking system 3, 4, 7 and a computer graphics workstation 8. The workstation must be powerful enough, in terms of capacity and speed, to update a three-dimensional image of a last and design entities in real time.

The tracking system should be capable of determining 5 six degree of freedom positional information for two sensors. The latency for retrieving all necessary data should be no more than a maximum of 25 msec, for real time display. There are a number of tracking technologies available but because unrestricted movement is required an 0 electromagnetic tracking device was used. Other devices suffer from "line of sight" problems (e.g. acoustic or optical systems) or physical hindrances to movement (e.g. mechanical arm systems) .

In this case a Polhemus Fastrak system was used. This 5 consists of a transmitter 7, which defines the reference axes and two receivers 3, 4 whose position and orientation are known relative to the reference axes. For each of the receivers the position is given by translation vectors and the orientation by 3 angles representing azimuth, elevation 0 and roll rotations.

The three-dimensional interface of the invention is based on the principle that the visual feedback from the screen image corresponds naturally to the input movements of the hands, i.e. the response is appropriate and expected for 5 the stimulus given. This requires a series of three- dimensional transformations to be performed on the geometrical data so that the image of the last and stylus are translated and rotated into the correct viewing positions.

A series of individual three-dimensional transformations, given ^bY ^TR, TL, T_Sf T_E are described, where: T_R is the transformation of scanned last data co-ordinate system to last tracking sensor co¬ ordinate system (Figure 3a). This is known as registration. T_L is the transformation of last tracking sensor 3 co-ordinates to the reference co-ordinate system of input device 7 (Figure 3b). T_s is the transformation of the stylus tracking sensor 4 to the reference co-ordinate system 7 (Figure 3c) . T_E is the transformation of co-ordinate system 7 to eye co-ordinates (Figure 3d) . Each of the above transformations includes three- dimensional rotations and translations which can be represented by a 4 x 4 matrix These matrices are denoted by: l^τ _R. * l^τ _L. > l^τs. , {T_E} respectively.

A composite matrix can be created which represents the complete transformation of software models of last and stylus eye co-ordinates. Figure 4 shows the overall transformation procedure. This procedure schematically comprises transformations and translations for both the article and sensor. These transformations and translations can be performed either simultaneously or at appropriate slots in a time division multiplexed arrangement provided the effect is that the image is displayed in effective real¬ time.

For the article i.e. shoe last, initially the last geometry is created or acquired 4A, this geometry is then registered in the system spacial architecture 4B and transformed to reference co-ordinates 4C. For the stylus, the stylus geometry is created or acquired 4D and then a comparison is made with the last surface 4E. If the stylus is close to the last surface then this stylus geometry is transformed to reference co-ordinates i.e. free space 4F. If the stylus is near the last surface then the stylus geometry is transformed to reference co-ordinates on the last surface 4G. The stylus reference co-ordinates and last (physical element) reference co-ordinates are then transformed to eye co-ordinates 4H and displayed on a screen 41.

The above procedure is repeated for each refreshment of the image displayed.

The composite matrix for transforming the last to eye or as seen co-ordinates is given by:

[τ_E] - lτ_L] . [τ_Λ]

The composite matrix for transforming the stylus to eye or representation co-ordinates is given by:

[T_E] - [T_s]

A more detailed description of the individual transformations is given in the following sections:

Last Tracking Sensor Transformation - T_L

Co-ordinates specified in the last tracking sensor axis system are transformed to the reference co-ordinate system using three rotations and a translation. The rotational transformation matrices are formed using the orientation information given by the tracking sensor. This information will be system dependent but will generally be in the form of angular twist about the local x, y or z axis say θ_j-,θ_y,θ_z The rotational transformations will therefore be given by

If the translation is given by some vector V then the composite transformation T_L will be of the form:

Stylus Tracking Sensor Transformation - T_s

This transformation is determined in a similar manner to that described above with relation to T_L. However, there is a special case when the stylus tip is close to the surface of the last. In this instance, the stylus software model is forced to lie on the surface of the last model. This feature of the system will be discussed at greater length below. For now it will suffice to note that the translation component of the overall composite transformation will change depending on the proximity of the stylus to the last. Given that the opposite transformation is of the form: T_s = V.R_Q .R_Θ .R_Θ .

The translation vector V will be one of two options (1) V_F - the translation vector given by the tracking system for the case when the stylus is far from the last (2) V_N - the vector computed as described previously when the stylus is near to the last. The two composite transformations can therefore be described as:

T_s = V_F. R_Q^ .R_Θ^ .R_Q^ . T_s = V_N . R_Q^ .R_Q^ . R_Q^ .

Registration ^•Transformation - T_R

Registration is the process of matching the co¬ ordinates of a software model of an object to the actual object. The software model is usually constructed from surface geometry obtained by scanning the object and has its own co-ordinate system. This system must correspond directly to the specified co-ordinate system of the input device so that three-dimensional information can be inputted in a sensible manner. If this is achieved then a digitised point on the surface of the actual object will be represented by a point at the same location on the surface of the software model.

For the case of shoe design the physical element is a shoe last. The scanned surface geometry and the actual ⁰ last will subsequently be known as the virtual last and real last respectively.

It is possible to transform the virtual last to the location of the real last if the co-ordinates of three pairs of registration points are known. Each pair of points ^$ should represent the same position on each last i.e. real 51 and virtual 52 as shown in Figure 5.

The registration points are denoted by A_r, B_r, C_r, and Ay, B_v C_v for the real and virtual lasts respectively. Point A is located at the most forward position on the featherline and point B is located at the most rear position on the featherline. Point C is located at a known distance from point B on the heel centre-line. These points can be determined easily for the virtual last. However, the procedure is slightly more complicated for finding the same points on the real last.

Problems arise when locating registration points on the real last because two different co-ordinate systems are involved. The points are digitised using the stylus and are given in the reference co-ordinates system 7. However, the last is free to move within the system and hence the digitised points should be determined relative to the last tracking sensor 3 co-ordinates. Figure 6 illustrates the situation. Some point D on the last surface is digitised using the stylus. This point is given in reference co-ordinates and must be transformed to local tracker co-ordinates. As described above, the tracker system is transformed relative to the reference system. This inverse transformation T_L ^-1 can be applied to unit vectors in the X, Y and Z directions of the reference system to yield unit vectors which describe the local tracker axes. These vectors are denoted by u__j-, ju„ and u_z. The translation vector t is known and hence the origin o of the local system can be found, d represented the vector OD in the reference system. However, it is possible to describe d in local tracker co-ordinates by finding its component in each of the local x y z directions. This is done by finding the scalar product of d with u_χ Uy, u_z in turn. Hence a digitised point D_local, in last tracker co¬ ordinates, can be given as: D_x = d.u-_r

D_y = d. Uy

D_z = d. u_z The registration points A, B and C can now be located on both the virtual and real lasts. The next step is to determine the transformation which superimposes the virtual points on the real points. Figure 7 illustrates the series of translations and rotations required to achieve the complete transformation.

The first stage involves a translation so that A-, is coincident with A_r(A) . The virtual points then undergo a rotation so that the lines

and A_J-B_J. are co-linear (B) .

The axis and angle of rotation can be determined by finding the cross product of the vectors A_rB_r and A-,B_V. The transformation matrix in accordance with known principles can then be constructed which defines the rotation about this axis (C) .

The final element of the transformation (D) involves a similar rotation about an axis defined by the line A_rB_r so that the points C_v and C_r should become coincident.

The eye co-ordinate system defines the viewing volume for the graphics scene. Eye co-ordinates can then be transformed to screen co-ordinates using standard graphics procedures. It is necessary therefore, to transform the model of last and stylus into the eye co-ordinate system. The transformations which convert the models to the reference co-ordinate system of the tracking device have been described previously. Hence, it only remains to outline the transformation of reference co-ordinates to eye co-ordinates.

The reference co-ordinate system is defined by the input device. In this case it is aligned with the electromagnetic transmitter 7 which is rigidly fixed to the user's work table 13 (Figure 8). The real last will be manipulated within a certain work volume. The viewing volume should be defined so that the image of the last is always on screen when the real last is within the work volume 14. This can be managed if the reference co¬ ordinates are transformed so that the working volume and viewing volume 15 are aligned. This transformation is similar to the registration process described above where three pairs of points define the transformation. In this instance the set of points A_rβf, B_ref and C_ref are transformed to match the points A_eye, B_eye and C_eye. This transformation is denoted by T_E and describes the conversation from reference co-ordinates to eye co¬ ordinates.

It is accepted that any tracking system will suffer from inaccuracies which will cause problems when the user wishes to input points on the surface of the last. As the real stylus is brought to the surface of the real last the user may see the virtual stylus disappearing below the virtual last surface which contradicts the human-factors principle of stimulus-response compatibility. It is important that the computer image or representation behaves exactly like the real object when the user is performing fundamental operations such as drawing lines on the surface. Any deviation from reality will cause ambiguity and frustration. To overcome such problems this data input device employs dynamic surface adherence so that the virtual stylus appears to be continually touching the virtual last when the real stylus comes near the real last surface. This is accomplished by constantly checking the distance between the stylus tip and the last. If this distance falls below a specified threshold limit the stylus model will be force to adhere to the last model.

The method used is outlined in Figure 9. There are two levels of search procedures to identify the adherence point on the surface. An approximate surface determines which point on the surface mesh of the last image 6 is closest to the stylus tip 5 and calculates the distance between them. If the stylus is considered close to the last an accurate search routine is invoked to find the location on the surface to which the stylus model is forced to move. The schematic steps 9A - 9H illustrated in Figure 9 show the identification of the adherence point on the surface of the article. In steps 9A and 9B the spacial position of the sensor stylus and last are respectively determined. The processor in step 9C uses an approximation search routine to determine the distance between the stylus tip and the closest point on the last surface. Then, if the stylus is close to the surface of the article (9D), an accurate search routine is performed to find the adherence point on the surface (9F) and this point is transformed (9E) in accordance with a Transformation g2 derived from calibration/registration between the real and virtual last. However, if the stylus is not near the last surface then the transformation Tgi is applied (9E) as a general registration between the real and virtual image. Whichever transformation gi or Tg2 is applied the image is displayed (9H) in the visual display unit. Figure 10 shows how the stylus is moved from a point P in space and attached to the surface at P'. The translation path of PP' is determined to that the vector PP' is always normal to the surface.

It will be appreciated that as described points upon the real last and upon the representation of that last can be equated. A series of these points are determined as tack points in the design and the arrangement includes processor means in order to couple those tack points to create design lines. The processor means is designed to ensure that various design tools are available including different edge types

(saw tooth, straight etc.) or surface texture fill-in between design lines. Furthermore, the processor is designed to smooth design lines from raw tack point data and to ensure there is no foreshortening between tack points i.e. the design line adheres to the surface of the last representation rather than the shortest distance between tack points. The real last is not marked by the application of tack points. Tack points can be determined by manual operation of the stylus or through automatic polling.

Referring to Figure 11 the drawing a base element 101, in the form of a shoe last, has secured thereto a sensor 102 which provides positional and orientational details of the location of the base element 101 in relation to a tracking station 103. Similarly, a drawing tool in the form of a pen 104 has secured thereto a drawing sensor 105 which provides positional and orientational details of the location of the pen 104 in relation to the tracking station 103. In use the base element will be held by the designer in one hand and the pen 104 in the other. Thus, the pen 104 can be moved about the surface of the base element 101 as required.

The surface of the base element 101 is digitised to create an accurate map thereof in appropriate coded form, this digital map of the base element 101, being stored within a processor unit 106. Moreover, based upon and in response to the positional and orientational details received from the sensor 102 secured to the base element 101, the processor unit 106 supplies signals to a display unit 107 , e.g. a visual display unit (VDU) , whereby a visual representation or image 108 of the three-dimensional shape of the base element 101 can be displayed thereon. It will be understood that, since the base element in terms of its digital map is constant, transforms are required within the processor unit 106 whereby as the orientation of the base element 101 is altered by manipulation thereof in the hand of the designer the image 108 represented by the display unit 107 is both quickly and efficiently transformed accordingly. Transforms and algorithms to perform such functions are known. It will thus be understood that the base element 101 can be readily manipulated and represented as an image 108 by the display unit 107 in almost all orientations.

The pen 104 is also represented by the display unit 107, in this case in the form of an image 109 of a drawing implement. The most important feature of the pen 104 is its tip 110 which is the point of engagement of the pen 104 with the base element 101. Thus, the relationship between the drawing sensor 105 and the tip 110 is most important, and generally the tip 110 and sensor 105 will be in simple alignment along an axis to reduce transform and process time and problems. In the drawing this axis is represented by the line A-A in respect of both the pen 104 itself and also the image 109. Although in the present case the image 109 is of a pen, it will be appreciated that the point of intersection of the axis A-A with the surface of the base element 101 is the important feature and thus a simple dot at the site of this intersection could be used.

The sensors 102 and 105 and the tracking station 103 are conveniently arranged to co-operate through electromagnetic fields which are generated by the sensors 102, 105 and detected and thus tracked by the tracking station 103. An example of a suitable system is that produced and manufactured by Polhemus, Inc. of Vermont, U.S.A. In this system electromagnetic coils located within the sensors 102, 105 are designed to create directional electromagnetic fields using alternating current of different frequencies in all three dimensions i.e. X, Y and Z. In fact the sensors 102, 105 are arranged to have six dimensions of electromagnetic field, namely X, Y, Z, -X, -Y and -Z. Thus, the tracking station 103 is designed to distinguish between the electromagnetic fields created by the sensors 102, 105 in these respective dimensions in order to determine through their relative strength and orientation the respective position and orientation of the sensors 102, 105. It will therefore be appreciated that since the sensors 102, 105 are secured to the base element 101 and pen 104 respectively it is possible accurately to determine the orientation of these respective components in relation to each other via the reference position of the tracking station 103.

For calibrating the present design system, the base element 101 may simply be placed on a table in a particular orientation and information concerning that orientation is then passed to the processor 106. In response the processor

106 will supply signals to the display unit appropriate to the digital map of the base element 101 and to the orientation thereof so that the image 108 will be displayed in a corresponding orientation also. Subsequent movement of the base element 101 away from such orientation will also move the sensor 102 with respect to the tracking station 103 and thus through transformation within the processor unit

106 the image 108 shown by the display unit will also change orientation correspondingly. Similarly, the pen 104 may be placed in a holster (not shown) which has a known orientation with respect to the X, Y, Z co-ordinate system and a similar calibration exercise can then be effected, the orientation of the pen 104 in the holster thus providing a basis for future transforms of the A-A axis by the processor unit 106 as the pen 104 is moved, whereby the orientation of the image 109 shown by the display unit 107 is correspondingly altered. It will be appreciated that, bearing in mind the range of sensors 102, 105 and tracking station 103, the base element 101 and pen 104 should remain within 0.5 and 1 metre of the tracking station 103. Furthermore, it is important that other sources of electromagnetic radiation are removed from the design area so as to avoid any distortion problems. In addition, since metal bodies may provide electromagnetic distortion effects, the base element 101 is typically made from a plastics material or wood. The pen 104 is simply a convenient tool which the designer can move about the base element 101 and thus will typically take the form of a pencil-type probe similarly made of plastic or wood to avoid electromagnetic field distortion effects.

In use the pen 104 is moved over the surface of the base element 101 in order to create design lines (one only shown in the drawing and designated 112). Such design lines are shown on the image 108 but obviously cannot be seen on the surface of the base element 1. In order to create the design line 112 successive tack points, representing points of intersection between the axis A-A and the surface of the base element 101 as the pen 104 is moved across said surface, are generated e.g. by the designer actuating a button or the like on the pen 104. Alternatively, tack points could be generated automatically at timed intervals, e.g. every l/50th second; in such case the designer would use a free-hand sketching technique and the processor unit 106 would as a subsequent operation fit the best curve to the lines thus drawn. It will be appreciated that in areas of the base element 101 which are highly curved it is necessary to have more tack points than in relatively flat straight areas thereof. The tack points are joined together by the processor unit 106 to create the design line 112 or image 108. It is important that the processor unit 106 includes sufficiently sophisticated plotting and transform (interpolation) algorithms to ensure that the design line 112 represented on the image 108 is properly shaped and lies on the surface of the image 108.

It will be appreciated than an area of the base element 101 could be enclosed by design lines 112. This enclosed area could then be designated either in terms of colour, texture or other design feature, e.g. thickness, by the designer using the processor unit and possibly some other input means, e.g. a keyboard. Particularly advantageous is the designation of an enclosed area to indicate thickness, namely by displacing the design line 12 from the surface of the base element 101 as portrayed by the image, thus" to show the thickness of e.g. a shoe upper component (vamp, quarter, etc.) placed on the surface of the base element 101. t will be appreciated that using the design system in accordance with the present invention the designer is now able to design in three dimensions directly on the base element 101 rather than design in two dimensions as was previously the case. In comparison with previous approaches involving a transformation from two-dimensional to three- dimensional design less real time transformation of data is required and thus a quicker response is achieved. On the other hand, in some instances the designer may prefer to create his design using a two-dimensional representation, but to be aware of the effect of that design when transformed into three dimensions. With this in mind, therefore, the processor unit of the design system in accordance with the present invention preferably also comprises conversion data by which the data constituting the digital map of the base element 101 and also the data on which the design lines 112 are based can be converted. Traditionally, the three-dimensional shape of a shoe last would be transformed into two dimensions by creating a so- called shell e.g. of a suitable mouldable plastics material, and then be "flattened". More recently such flattening has been able to be achieved by digitising the shape of the last and then subjecting it to certain "flattening" rules. These rules are of course in the present case stored in the processor unit 106 for use as part of the conversion program.

The design system also includes selector means (not shown) whereby the designer can select to have displayed on the display unit 107 either the image 108 or an image (not shown) of a selected area of the surface of the base element 101, but converted into a flat two-dimensional shape, or indeed both. Thus, the designer now has the facility of having the image 108 displayed and creating design lines by moving the pen 104 over the surface of the base element 101 in the manner described above, or, by moving the pen 104 over the surface of the base element 101 creating on the display unit 107 an image of a shoe upper component in two- dimensional form. Moreover, in the latter case any style lines created by the designer, again by moving the pen over the surface of the base element, will also be shown on the shoe upper component, their position of course being converted by the conversion means according to the flattening rules stored in the processor unit 106. Again, the designer may choose to have both the image 108 and also the image of the shoe upper component displayed at the same time on the display unit 107, in order that he can simultaneously monitor the particular design of shoe he is creating and also the shape of the various shoe upper components which will ultimately go to make up the finished shoe upper.

It will also be appreciated that the converted data whereby two-dimensional shapes may be portrayed on the display unit 107 may also be used subsequently in order that the various components may be cut out or otherwise produced from sheet material as part of the shoe production process.

It is envisaged within the scope of the present invention that in addition to the digital map or surface geometry of the particular base element 101 being stored in the processor unit there may be provided within the processor unit 106 further basic or skeleton design patterns which may be displayed as images 108 by the display unit 107. These may be used as basic design forms which can be adapted as necessary by the designer rather than initiating a design each time from a blank image 108.

The design lines 112 may be used to define the shoe upper for component parts thereof; in addition they may indicate e.g. stitching or cutting lines e.g. feather cuts or decorative stitching. Furthermore, the processor unit may maintain a store of surface finishes and/or colours and also a store of decorative elements, e.g. buttons, beads, sequins or buckles which the designer may require and which he may cause to be displayed at locations on the image 108 or image 109 by appropriate application of the pen 104 to the surface of the base element 101.

It will be appreciated that an inherent problem with all positional and orientational devices is the relative tolerance of the sensors 102, 105 and the tracking station

103. It has been found with the Polhemus system that inaccuracy in the order of 2-3 millimetres is common. Thus when the pen 104 is brought within 2 or 3 millimetres of the surface of the base element 1, the point of intersection of the axis A-A may penetrate the surface of the image 108 and create spurious results. One approach to avoid this problem is to establish an in-built calibration between the base element 101 and the pen 104 by establishing a common calibration point within the base element 101. Conveniently, in the case of a shoe last, this calibration point could be the tip or toe end of the last. With such internal calibration between the base element 101 and the pen 104 the inaccuracies arising from electromagnetic field variation may be mitigated. An alternative calibration approach is outlined below.

It is also envisaged that designs previously created may be stored in the processor unit 106 and displayed next to the present design for comparison purposes. The processor unit 106 may include necessary transform projection means to allow size grading of designs. For example, in the case of footwear the designer may design a shoe of a particular size and this shoe design could then be graded over a range of sizes. Thus, a designer could see the applicability of his design to the full range of sizes of footwear. In addition, the two-dimensional transform process described earlier could be used to create press knife patterns for components to make up those three- dimensional designs in each size.

The above summary of the present invention will now be supplemented by further details.

As indicated above, an important factor in ensuring good accurate design is that the real and the virtual base element i.e. shoe last are correctly registered. The principal problem is that there are inherent inaccuracies in positional location detection using sensors such as the electromagnetic devices described above. The simplest approach to registration is to have a fixed point upon the base element to which the components i.e. base element, sensor pen and virtual image are calibrated. Unfortunately, irregular articles may have varying accuracy dependent upon shape. Thus, a preferred option is to acquire three principal points upon the article i.e. for a shoe last on the toe, heel and cone, and then obtain reasonable well spaced random points about the article surfaces. It has been found that at least eight points should be taken for statistical purpose and registration within an acceptable time of a few minutes. With these principal and random points a rough virtual skin is provided and therefore known article shape data stored in the processor can be "shaken" within this skin i.e. by an iterative re-try process, until the real last and virtual last are in correlation. Thus, there will be in effect a whole range of correction factors i.e. one for each part to ensure correct projection about the article surface. Alternatively, the article could be placed in a holster type receptacle with a multitude of displaceable transducers which contact the article and so give accurate information of the shape again to allow shake correlation between the real and virtual article. However, with a holster approach the sensor pen must also be registered in some way, possibly, in its own holster. Generally, the article surface and/or the sensor pen contact tip will be arranged such that the contact between them is not too slippy. For example, rubber pads could be used for the sensor. It will be understood if the contact between the article and sensor is too slippy there may be abrupt terminations in mutual contact with potential spurious results.

Finally, as a further enhancement of the presentation of the design i.e. shoe design prior to prototype production, it will be understood that images could be produced and presented on the VDU 108 in a stereo projection format. Thus, with so-called 3D spectacles e.g. CRYSTALEYES from Silicon Graphics, it is possible to view the design in 3 dimension. Such 3D spectacles can approximate a 3D view by alternatively obscuring and revealing views to a viewer's right and left eyes respectively. Without the spectacles the image looks blurred. There are known projection algorithmns that the processor can use to achieve these stereo projection overlaid images.

Claims

Claims :

1. A design system suitable for use in designing irregular articles, comprising a base element (1), (101) in the form of the article (8) , a drawing tool, (4), (104) a tracking station, (3), (103) sensing means (2), (5); (102), (105) operatively connected to both the base element (1) and the drawing tool (4), (104) and also to the tracking station (3), said means (2), (5); (102), (105) being effective to determine the position and orientation of the base element (1), (101) and drawing tool (4), (104) relative to one another and also to the tracking station (3), (103), processor means for storing a digital map of the surface of the base element (1), (101), or part thereof, and for receiving signals from the sensing means in accordance with the position and orientation of the base element (1), (101), visual display means for receiving signals from the processor means in response to which a visual representation of the base element (1), (101) can be displayed thereby in accordance with the stored digital map and in accordance with the position and orientation of the base element as sensed, and also a visual representation of an operative portion of the drawing tool 4, 104 in relation to the base element

tack point generating means whereby a succession of tack points, indicative of a succession of positions of the drawing tool relative to the base element (1),

(101), can be generated and supplied to the processor means to be stored thereby, wherein in response to such supply further signals are supplied by the processor means to the visual display means whereby to create design lines on the representation of the base element displayed thereby, said design lines passing through and their location thus being determined in accordance with these tack points.

2. A design system according to Claim 1 further comprising selecting means for selecting a characteristic (e.g. colour, texture, thickness) of an area, designed by design lines, of the representation of the base element displayed as aforesaid.

3. A design system according to either one of the preceding Claims wherein the sensing means (2), (5), (102), (105) comprises means for creating an electromagnetic field and sensing coils responsive to such field.

4. A design system according to any one of the preceding Claims wherein the processor means comprises conversion means whereby signals supplied to the processor means by the sensing means in respect of the base element

(1), (101), of an area thereof, can be processed to convert the three-dimensional shape of the base element, of such area thereof, into a two-dimensional flat shape, such conversion being determined by stored "flattening" rules, and wherein the processor means selectively supplies to the visual display means signals in response to which a visual representation of at least one of such three-dimensional and such flat, two-dimensional, shape is displayed and further wherein said further signals are also processed by the conversion means whereby design lines created as aforesaid are displayed on the displayed visual representation.

5. A design system according to Claim 4 wherein selector means is provided whereby either or both of the visual representations can be selected for display.

6. A design system arrangement suitable for design of footwear, the system comprising a base, physical element (1), (101), such as a shoe last, and a drawing stylus (4, 104), both the element (1), (101) and the stylus (4), (104) including position sensors (2), (5), (102), (105) which allow determination of the position and orientation of said element (1), (101) and stylus (4), (104) relative to a tracking station (3), (103) coupled to a processor means, a digital map of said element (1), (101) being stored in said processor means and represented upon a visual display means and the representation so displayed manipulated dependent upon said position and orientation determined by its positional sensor (2), (102) relative to the tracking station, said stylus (4), (104) being represented in the display means relative to said representation of said element (4), (104), said stylus being moved about said element (1), (101) and tack points made upon said element represented in the visual display means by appropriate stimulation to said processor means, said tack points being processed to present design lines joining said tack point in said representation of said element (1), (101) in said visual display means.

7. A system as claimed in any preceding Claim wherein the drawing tool or stylus (4), (104) and the base element (1), (101) have a limited slip coefficient to substantially reduce sudden slip disengagement between the tool and the element.

8. A system as claimed in any preceding Claim wherein the visual representation is in stereo in order to provide a perceived 3 dimensional view of the base element (1), (101).

9. A system as claimed in any preceding Claim wherein a statistically acceptable number of principal registration points and random registration points about the base element (1) are acquired by the processor means and the stored representation of said base element in the processor means is brought into registration with these principal registration and random registration points by the processor in order to define a set of correction factors respectively applicable to parts of the base elements, said correction factors being used to ameliorate any inherent inaccuracy with the positional sensors of said base element and/or said stylus/drawing tool.

10. A system as claimed in any preceding Claim wherein the stylus/drawing tool is replaced by a non-contact sensor, such as a computer mouse, which although not in contact with the element, allows by manipulation, a virtual stylus/ drawing tool to be moved about the virtual element (108) represented on the display means in order to define tack parts.